SECTION A: LIVING ORGANISMS IN
THE ENVIRONMENT
CSEC BIOLOGY
-​ Characteristics of Living Things:
●​ Movement – Plants move by growing, animals move from place to place.
●​ Excretion – living organisms get rid of waste produced in cells.
●​ Reproduction – Living organisms are able to produce new organisms like
themselves.
●​ Respiration – the cells in living organisms release energy from food. This often
involves oxygen.
●​ Irritability – living organisms interact with their surroundings and respond to
them.
●​ Nutrition – all living organisms feed. Plants make their own food while animals
eat other organisms for food.
●​ Growth – living organisms develop and increase in size.
-​ Classification is defined as the grouping of organisms according to their structural
similarities.
-​ Taxonomy: The hierarchical classification system is used to organize and classify the
diversity of living things into groups referred to as taxa(singular taxon).
-​ The Monera Kingdom(Prokaryotae) consists of unicellular organisms(made up of one
cell).
-​ Their cells are simple and often lack many parts, such as a nucleus, found in other cells.
-​ Bacteria are a type of monera.
-​ Protist(Proctotista) are unicellular organisms, similar to Monera.
-​ Protists are more complex because they have a nucleus.
-​ They have moving parts and can move around in their environment.
-​ Fungi belong to their own kingdom because they are unique.
-​ They were once thought to be plants but differ in a key way: fungi cannot make their own
food.
-​ Mushrooms are an example of fungi
-​ All plants belong to the Plant Kingdom(Plantae).
-​ Plants share the ability to make their own food using water and sunlight.
-​ Plants can grow almost anywhere due to their simple requirements.
-​ Organisms in the Animal Kingdom(Animalia)(largest kingdom) are multicellular.
-​ They rely on other organisms for food.
-​ They range in size from very tiny to extremely large.
The Animal Kingdom
-​ Porifera (Sponges)
●​ Stationary, multicellular organisms lacking tissues and organs.
●​ Body contains a single cavity with many pores in the body wall.
●​ Live in the sea.
●​ e.g. vase sponge
-​ Coelenterates
●​ Bag or umbrella-shaped body.
●​ Gut has a single opening- the mouth.
●​ Ring of tentacles around the mouth.
●​ Live in water.
●​ eg jellyfish, sea anemone, coral
-​ Platyhelminthes (flatworms)
●​ Fairly long, flat, unsegmented body.
●​ Some Live in freshwater
●​ Many are parasitic.
●​ eg, tapeworm, liver fluke
-​ Nematoda(roundworms)
●​ Elongated, round, unsegmented body with pointed ends.
●​ Most are parasitic.
●​ eg. hookworm
-​ Annelida (segmented worms)
●​ Elongated body divided into segments.
●​ Segments have chaetae (bristles).
●​ Most live in water, a few live in soil.
●​ e.g. earthworm
-​ Arthropoda
●​ Jointed legs.
●​ Hard, waterproof external skeleton made of chitin which sometimes contains
𝐶𝑎𝐶𝑂3
●​ Crustaceans
➢​ 5 or 7 pairs of legs.
➢​ Two pairs of antennae.
➢​ Exoskeleton contains 𝐶𝑎𝐶𝑂3
➢​ Body divided into three parts- head, thorax and abdomen.
➢​ Head and thorax are often covered by a shield (carapace).
➢​ e.g. crab, lobster, shrimp
●​ Insects
➢​ Three pairs of legs.
➢​ Two pairs of wings.
➢​ One pair of antennae.
➢​ One pair of compound eyes.
➢​ Body divided into three parts-head, thorax and abdomen.
➢​ e.g. cockroach, grasshopper, moth
●​ Arachnids
➢​ Four pairs of legs.
➢​ No antennae.
➢​ Body divided into two parts(cephalothorax & abdomen)
➢​ e.g. spider, scorpion, tick
●​ Myriapods
➢​ Many pairs of legs.
➢​ One pair of antennae.
➢​ Elongated body divided into many segments.
➢​ e.g. millipede, centipede
-​ Molluscs
●​ Soft, moist, unsegmented body divided into head, muscular foot and hump.
●​ Many have shells.
●​ e.g., snail, slug, octopus
-​ Echinoderms
●​ Body based on a pattern of five parts.
●​ Body wall contains CaCO plates with projecting spines.
●​ have tubed feet with with suction pads for movement
●​ e.g. starfish, sea urchin, sand dollar
-​ Craniates (vertebrates)
●​ Well developed head with brain enclosed in cranium.
●​ Backbone.
●​ Internal skeleton of bone and cartilage.
●​ Fish
➢​ Skin has scales.
➢​ Gills for breathing. Fins for swimming
➢​ Eggs laid and developed in water.
➢​ Live in water. e.g. barracuda, flying fish
●​ Amphibians
➢​ Soft, moist, non-waterproof skin without scales.
➢​ Eggs laid in water.
➢​ Larvae (tadpoles) live in water, adults live on land.
➢​ Larvae have gills for breathing, adults have lungs.
➢​ e.g. frog, toad
●​ Reptiles
➢​ Dry, waterproof skin with scales.
➢​ Lungs for breathing
➢​ Eggs have a leathery shell and are told on land. Most live on land.
➢​ e.g. Izard, snake, turtle
●​ Birds
➢​ Feathers.
➢​ Beak, no teeth.
➢​ Forelimbs modified as wings.
➢​ Eggs have a hard shell and arelaid in nests.
➢​ Warm blooded.
➢​ e.g. sparrow, cattle egret
●​ Mammals
➢​ Waterproof skin with hair and sweat glands.
➢​ Young feed on milk from mother. Different types of teeth.
➢​ Warm blooded.
➢​ e.g. Man, dog
-​ A dichotomous key uses contrasting characteristics to divide organisms into smaller
groups.
-​ Each choice eliminates a number of organisms.
-​ With enough contrasts, the identity of the unknown organism is narrowed down to one.
-​ Dichotomous keys are based on successive choices between only two statements.
-​ They are the preferred type of key for most biologists.
-​ The binomial system is used to name living things.
-​ It consists of a two-part Latin name.
-​ The first part represents the genus, and the second part represents the species. eg: Cannabis sativa
(King Philip Comes Over For Good Soup)
Ecological Studies
-​ Ecology is a branch of biology which studies organisms and how they interact with each
other and their surroundings/ environment.
-​ An ecosystem includes the community of organisms and all the factors that influence
them.
-​ A species is a group of organisms which have similar features and DNA make up and
that can breed together to produce fertile offspring.
-​ A population is a group of organisms belonging to the same species who live in a
particular habitat.
-​ A community is made up of all the different organisms living in a particular place or
habitat.
-​ A niche is the role a species fulfills in an ecosystem, including its trophic level and its
relationships with other species.
-​ Biodiversity refers to the variety of living organisms present in the world or specifically
a habitat or ecosystem.
-​ Habitat is a place where an organism lives.
-​ Sampling helps determine which organism lives where and their abundance in a
particular region.
-​ Ecology provides knowledge of the interdependence between people and nature, crucial
for: Food production, Maintaining clean air and water, Sustaining biodiversity and
Adapting to a changing climate.
Sampling Methods
-​ A quadrat is a frame made of wire or wood that encloses a known area
-​ such as 1m squared.
-​ A transect is a line(string or rope) across a habitat or part of a habitat used to observe
and record the number of organisms of each species at regular intervals along the line.
-​ A beating tray is a white sheet placed under a tree, where the tree is shaken to dislodge
animals onto the tray.
-​ A pooter is a tube used to suck small animals into a glass or plastic container.
-​ Sweep Nets are used to catch flying insects.
-​ Pond nets are used to lift water from ponds or rivers, trapping animals and plants as the
water drains out.
-​ Pitfall traps are cans or jars buried in the ground, covered to blend in, capturing
ground-dwelling or nocturnal organisms.
-​ Mark-Release-Recapture involves capturing animals, marking them with a non-toxic
substance, releasing them, and later recapturing a sample to estimate the total population
using the formula:
𝑁𝑢𝑚𝑏𝑒𝑟 𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 𝑎𝑛𝑑 𝑚𝑎𝑟𝑘𝑒𝑑×𝑁𝑢𝑚𝑏𝑒𝑟 𝑟𝑒𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑
𝑁𝑢𝑚𝑏𝑒𝑟 𝑟𝑒𝑐𝑎𝑝𝑡𝑢𝑟𝑒𝑑 𝑡ℎ𝑎𝑡 𝑤𝑒𝑟𝑒 𝑚𝑎𝑟𝑘𝑒𝑑
Factors Influencing Organisms
-​ Biotic factors are the influences that organisms in a community have on each other.
-​ Examples: Food; Water; Disease; Predation; Competition for food, living space;
Reproduction and Symbiotic Relationships
-​ Symbiotic Relationships(Symbiosis)
●​ Commensalism is an association between two organisms where one benefits and
the other is neither harmed nor benefited.
●​ Mutualism is an association between two organisms of different species where
both benefit.
●​ Parasitism is a symbiotic relationship where one organism (the parasite) lives on
or in another organism (the host), causing harm, and is structurally adapted to this
lifestyle.
-​ Abiotic factors are the non-living or physical features of an ecosystem that influence the
organisms in the community.
-​ Examples include elements such as salinity, wave action, humidity, depth of water, water
clarity, latitude, altitude, climate, temperature, water, oxygen concentration, carbon
dioxide concentration, light intensity, and soil pH and mineral content
-​ Soil is important in providing water as it absorbs and retains moisture, acting as a
reservoir for plants, and regulates the movement of water through its layers, ensuring a
steady supply for ecosystems.
Components of the Soil
-​ Mineral nutrients are essential for growth, development, and metabolism in living
organisms. They help in processes like energy production, bone formation, and enzyme
function. Without them, organisms may experience deficiencies that affect their health
and survival.
-​ Oxygen is crucial for respiration in most organisms, providing the energy needed for
various life processes. It is necessary for the production of ATP (adenosine triphosphate),
the energy currency of cells, and supports metabolic functions. Without oxygen, many
organisms, especially animals and plants, would not be able to survive.
-​ Air is important in providing essential raw materials for living organisms:
●​ Oxygen is crucial for respiration, enabling organisms to produce energy through
cellular respiration.
●​ Carbon dioxide is used by plants in photosynthesis to produce glucose, which is
the primary source of energy for most organisms.
●​ Nitrogen is vital for the synthesis of proteins and nucleic acids in plants and
animals, as it is a key component of amino acids and DNA.
-​ Light is essential for photosynthesis in plants, enabling them to produce food, which
supports the entire food chain. It also affects growth, behavior, and reproduction in
various organisms.
-​ Temperature influences the rate of metabolic processes in organisms. Each species has
an optimal temperature range for survival and functioning. Temperature affects enzyme
activity, reproduction, and overall health, and determines the types of organisms that can
thrive in specific environment
-​ A food chain shows the feeding relationships between some of the organisms in an
ecosystem.
-​ The arrows represent the flow of energy from one organism to another.
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
The trophic level of an organism is the position it occupies in a food web.
●​ The first trophic level – consists of autotrophs that make their own food. These
are called Primary Producers/Producers. E.g. plants, algae.
●​ The second trophic level – consists of heterotrophs that eat other organisms for
food. These are called Primary Consumers and are usually herbivores e.g. cows.
●​ The third trophic level - consists of heterotrophs. These are called Secondary
Consumers and are usually carnivores or sometimes omnivores. E.g. snakes.
●​ The fourth trophic level – consists of heterotrophs. These are called Tertiary
Consumers and are usually carnivores or sometimes omnivores. They are apex
predators. E.g. lions.
A pyramid of numbers shows the number of organisms at each trophic level.
It is typically upright because producers (plants) are always more numerous than
organisms at higher trophic levels.
The pyramid shape ensures there are enough plants to produce food at the base for the
entire ecosystem.
A pyramid of biomass represents the total biomass at each trophic level, typically shown
as a modified bar chart.
Biomass refers to living or recently dead tissues.
In a healthy ecosystem, the biomass decreases at each trophic level.
A pyramid of energy shows the flow of energy from one trophic level to the next in an
ecosystem.
It is a diagram that compares the energy used by organisms at each trophic level.
Energy in the pyramid is measured in kilocalories (kcal).
Energy pyramids are not inverted due to the 1/10th rule.
Only 10% of energy is passed on to the next level, as the rest is used by organisms at
each level.
-​ Food webs are a series of organisms connected by predator-prey and consumer-resource
interactions.
-​ They represent the entirety of interrelated food chains in an ecological community.
-​ Food webs consist of interconnecting food chains.
-​
-​
-​
-​
-​
-​
-​
Producers (Plants) use solar energy to make food through photosynthesis.
Not all sunlight is absorbed by plants (refer to diagram).
Plants use energy for photosynthesis, respiration, growth, reproduction, and maintenance.
The remaining energy (10%) is passed on to other organisms when plants are eaten.
Consumers receive only 10% of the energy from the previous trophic level.
Not all plant materials are digested by consumers.
Some of the energy from plants is used by primary and secondary consumers to stay
alive.
-​ When consumers die, their bodies contain stored energy, some of which is transferred to
decomposers.
-​ The energy flow through a herbivore can be summarized as:
Energy intake = energy used in respiration + energy used in production of body mass +
energy in urine + energy in faeces.
-​ Decomposition is the process of breaking down organic material into smaller parts,
primarily through the action of decomposers like fungi and bacteria.
-​ It involves the disintegration and rotting of substances.
-​ Decomposition is ecologically significant as it plays a key role in the nutrient cycle and is
essential for recycling matter in the biosphere.
-​ Dead organisms are decomposed by various decomposers.
-​ Decomposers ensure that energy stored in dead organisms is not wasted.
-​ Decomposers release carbon dioxide (CO₂) into the atmosphere during decomposition,
which plants use in photosynthesis.
-​ A nutrient cycle involves the movement and exchange of organic and inorganic matter
back into the production of living matter
-​ The process is regulated by food web pathways, which decompose organic matter into
inorganic nutrients.
-​ The nitrogen cycle involves processes such as nitrogen fixation, nitrification,
assimilation, ammonification, and denitrification.
-​ About 79% of the air is nitrogen gas, which is essential to life as it is a key component of
proteins and nucleic acids.
-​ Nitrogen exists in organic and inorganic forms, cycling among them through various
processes and bacteria.
-​ Symbiotic bacteria convert inert atmospheric nitrogen into usable forms like nitrites and
nitrates for plants.
-​ Organic nitrogen is found in living organisms and transferred through the food chain.
Stages of the Nitrogen Cycle
-​ Nitrogen fixation converts atmospheric nitrogen (N2) into ammonia (NH3) using
symbiotic bacteria like Diazotrophs, Azotobacter, and Rhizobium.
-​ Nitrification oxidizes ammonia into nitrites (by Nitrosomonas) and then into nitrates (by
Nitrobacter).
-​ Assimilation allows plants to absorb nitrates and ammonia through roots, incorporating
them into proteins and nucleic acids, which are passed to animals.
-​ Ammonification releases nitrogen from dead plants and animals back into the soil as
ammonium through decomposers like bacteria and fungi.
-​ Denitrification converts nitrates (NO3-) into atmospheric nitrogen (N2) in the absence of
oxygen, using bacteria like Clostridium and Pseudomonas.
-​ The carbon cycle describes how carbon is transferred between different reservoirs located on
Earth.
-​ This cycle is important for maintaining a stable climate and carbon balance on Earth.
-​ Carbon is essential for life and stored in various reservoirs, including plants, animals,
atmosphere, and oceans.
-​ Carbon is used by plants to build leaves and stems, which are then digested by animals and used
for cellular growth
-​ Some organisms, such as clams or coral, use the carbon to form shells and skeletons
-​ In the atmosphere, carbon is stored in the form of gases, such as carbon dioxide.
-​ The carbon cycle shows how carbon atoms are passed from one organism to another and their
-​ environment as they live, breathe, eat, die, and decay.
-​ The atmosphere contains approximately 0.03% carbon dioxide.
-​ Plants use carbon dioxide from the atmosphere during photosynthesis to produce carbohydrates,
proteins, and lipids, making plants the first source of carbon in living organisms.
-​ Animals obtain carbon by consuming plants or other animals that have eaten plants.
-​ Respiration by plants and animals releases carbon dioxide back into the atmosphere.
-​ Waste materials (e.g., urine and feces) and dead organisms are decomposed by bacteria and
fungi, which feed on organic matter, incorporating carbon atoms into their bodies.
-​ The respiration of decomposers releases carbon dioxide into the atmosphere.
-​ In oxygen-poor, waterlogged soils, decomposers are unable to fully break down plant and animal
tissues, which leads to the accumulation of organic remains. This process formed fossil fuels like
coal, oil, and natural gas.
-​ Fossil fuels, containing large amounts of carbon, release carbon dioxide into the atmosphere
when burned (combustion).
Human’s Contribution to Increasing Carbon in the ecosystem:
-​ Burning fossil fuels by using cars, trucks airplanes etc- releases large amounts of carbon
dioxide into the atmosphere
-​ Deforestation- reduces the number of trees available to absorb CO₂ through
photosynthesis.
-​ Rice paddies- Waterlogged fields produce methane due to anaerobic decomposition.
Practices to Reduce the Human Impact on the carbon cycle
-​ Transition to Renewable Energy Sources: to reduce reliance on carbon-intensive fuels.
-​ Practice Reforestation: to increase the absorption of CO₂ from the atmosphere
-​ Use organic fertilizers: to reduce nitrous oxide emissions
-​ The atmosphere acts like a blanket, keeping Earth warm by retaining heat.
-​ Greenhouse gases (carbon dioxide, water vapor, methane, nitrous oxide) prevent heat from
escaping into space.
-​ Solar energy passes to the Earth’s surface, but some is absorbed and re-radiated back by these
gases.
-​ Without the greenhouse effect, Earth’s average temperature would be about -17°C.
-​ Over the last 100 years, human activities have increased greenhouse gases.
-​ Burning of fossil fuels (coal, oil, gas) releases carbon dioxide into the atmosphere.
-​ Deforestation reduces trees that absorb carbon dioxide.
-​ Agriculture contributes methane from rice cultivation, cattle digestion, and decomposing organic
waste.
-​ Methane is also released from landfills, rubbish tips, and fossil fuel extraction
Largest increase in greenhouse gases is carbon dioxide (CO₂), with levels rising by 10%
in the last 35 years.
Methane and CFCs have a greater impact per molecule on the greenhouse effect than
CO₂.
Greenhouse gases trap heat, preventing it from escaping into space and causing the
atmosphere to warm.
Human activities increase the atmosphere's carbon dioxide and other greenhouse gases.
Climate Change
-​ Human activity is increasing greenhouse gas concentrations, leading to global warming.
-​ Earth has warmed by 0.7°C over the past century.
-​ Predicted temperature increases:
-​ Caribbean: 1.5-1.9°C (by 2040-2069), 0.9-4.8°C (by 2070-2099).
-​ Impacts of Arctic and Antarctic warming:
●​ Polar ice melt will raise sea levels and flood coastal areas.
●​ Impacts on Caribbean cities and farmland.
-​ Changes in rainfall patterns and weather distribution:
●​ Some areas become wetter, others drier.
●​ Agriculture in regions like the USA and Asia could be affected.
●​ Warm waters could intensify hurricanes, impacting the Caribbean and North
America
-​ Measures to Reduce Effects
●​ Strategies to mitigate effects:
●​ Use energy more efficiently.
●​ Transition to renewable energy sources (e.g., solar, wind).
●​ Increase ethanol-based fuel usage.
-​ Vulnerabilities of the Caribbean
●​ High risk of storm damage.
●​ Intense hurricanes caused devastation in:
●​ 2007 and 2010 (hurricanes traveling >5 km inland).
●​ 23 hurricanes from 2005-2007.
●​ Coastal protection by mangroves is crucial to prevent rapid erosion.
-​
-​ Natural resources are materials we obtain from the environment to meet various needs
including; Food, fuel, and fiber; Shelter and building materials; Coastal protection from
erosion; Soil fertility renewal; Revenue and employment from tourism; Medicine;
Natural purification of air and water; Nutrient cycling; Recreation and aesthetic benefits
-​ Renewable resources, such as sunlight, soil, plants, and water, can be naturally
replenished by the environment.
-​ Non-renewable or finite resources, including minerals like gold and bauxite, and energy
sources like oil, cannot be replaced once used.
-​ Population growth increases the demand for resources.
-​ More cars lead to more fuel consumption and higher GHG emissions.
-​ More appliances lead to increased electricity use and more GHG emissions.
-​ Carrying capacity is the maximum population size that an environment can support.
-​ Ecological footprint measures how quickly we consume resources and generate waste,
compared to the Earth's ability to absorb waste and regenerate resources.
-​ Sustainable use of resources is promoted to ensure resources remain available for future
generations.
Effects of Human Activities on Resources
Pollution
-​ Causes:
●​ Excessive use of pesticides and fertilizers in farming/fishing
●​ Solid and liquid waste from urban settlements
●​ Industrial pollutants from industries
●​ Toxic mining waste
●​ Airborne pollutants from burning fossil fuels
Climate Change
-​ Caused by burning fossil fuels, forest clearing, and industrial gases, leading to rising
levels of greenhouse gases and contributing to global warming.
Habitat Destruction
-​ Habitats are destroyed causing wildlife to struggle to survive, due to human activities:
●​ Deforestation
●​ Exploitation of resources for food, shelter, housing lands, etc.
●​ Pollution
Species Extinction
-​ Overuse or irresponsible exploitation of wild plants and animals for food, raw materials,
and medicine leads to faster depletion than reproduction, causing species loss
(extinction).
Invasive Species
-​ Movement of species (deliberate or accidental) can harm indigenous species by:
●​ Competing for food and space
●​ Predation or parasitizing
●​ Genetically Modified Organisms (GMOs) affecting native species.
-​ Biodegradable waste is organic matter that can be broken down by microorganisms and
other living things.
-​ It includes composting, aerobic digestion, anaerobic digestion, and similar methods.
-​ Examples: solid waste, food waste, paper waste, biodegradable plastics, human waste,
manure, sewage, sewage sludge and slaughterhouse waste.
-​ Non-biodegradable materials cannot be broken down by natural organisms and
contribute to pollution.
-​ These wastes cannot be decomposed or dissolved by natural agents.
-​ Examples: plastics, chemicals, rubber, paints, batteries and metals.
-​ Current resource usage leads to serious economic and environmental consequences.
-​ Reducing: Creating less waste to prevent pollution at the source, keeping the earth
cleaner.
-​ Reusing: Finding new uses for old items that would otherwise be discarded, especially
when reducing isn't possible.
-​ The impact of the continual re-use of materials in nature:
●​ Reducing pollution: Reusing materials reduces the need to extract new raw
materials, which prevents pollution from waste disposal.
●​ Conserving resources: Reusing materials reduces the demand for mining and
extracting virgin materials, such as timber, water, and minerals.
●​ Saving energy: Reusing materials reduces the amount of energy used to make new
products. For example, recycling 10 plastic bottles saves enough energy to power
a laptop for more than 25 hours.
●​ Reducing greenhouse gas emissions: Reusing materials reduces greenhouse gas
emissions that contribute to climate change.
●​ Limiting biodiversity loss: Reusing materials reduces landscape and habitat
disruption, which helps to limit biodiversity loss.
●​ Alleviating water and land stress: Reusing materials can help alleviate water and
land stress by preventing materials from being sent to landfills.
-​ Recycling: Converting waste materials into new materials and objects. Eg. Iron and steel
scrap, aluminum cans, glass bottles, paper, wood, plastics.
-​ Importance of Recycling Manufactured Materials:
●​ Environmental Protection: Reduces waste in landfills and conserves natural
resources.
●​ Energy Conservation: Recycling consumes less energy compared to
manufacturing new products.
●​ Pollution Reduction: Lessens air and water pollution from waste disposal.
●​ Economic Benefits: Creates jobs in recycling industries and reduces the need for
raw material extraction.
●​ Sustainability: Supports the transition to a circular economy by reducing reliance
on finite resources.
●​ Conservation of Biodiversity: Helps protect ecosystems by reducing the
environmental impact of waste.
-​ Conservation means saving natural resources for future use.
-​ Methods to conserve natural resources include:
●​ Passing laws to protect the environment.
●​ Signing international agreements.
●​ Declaring reserves and limiting human access (e.g., nature reserves).
●​ Controlling population from farming and industry.
●​ Restoring damage caused by human activity
Pollution
-​ Pollution is the unfavourable alteration of the environment by the release of harmful
substances or forms of energy into the environment.
-​ A pollutant is a harmful substance or form of energy that causes unfavourable changes to
the environment.
-​ Types of Pollutants:
●​ Domestic Pollutants: Released from homes. Includes sewage from the kitchen,
bathroom, and laundry room.
●​ Agricultural Pollutants: Associated with modern agricultural practices. Includes
pesticides and fertilizers.
●​ Industrial Pollutants: Released from industrial activities. Includes oxides of
carbon, oxides of nitrogen, smoke, dust and other particulate matter
Air Pollution
-​ Air pollution results from the release of harmful substances or forms of energy into the
atmosphere.
-​ Causes: energy production in power plants and processing of materials, motor vehicle
emissions and agricultural practices such as land clearance by slash and burn.
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
Greenhouse Effect
Greenhouse gases (e.g., carbon dioxide, water vapor, methane) trap heat in the
atmosphere.
Heat from the Sun passes through the gases, warming the Earth.
The gases reflect much of the heat back towards Earth, warming it further.
Global Warming
Human activities, like burning fossil fuels and deforestation, release more carbon dioxide.
These activities enhance the greenhouse effect.
Global warming leads to an increase in Earth's temperature over time.
Effects of Global Warming
Melting of polar ice caps and
-​ Extreme weather and severe natural
glaciers.
hazards.
Rising sea levels.
-​ Rising sea temperatures.
Flooding of low-lying coastal areas.
-​ Wider spread of some infectious
Changes in global weather patterns.
diseases.
Water pollution
-​ Water pollution results from the release of harmful substances or forms of energy into a
body of water
Eutrophication
-​ Excess nutrients (mainly nitrates and phosphates) in water cause overgrowth of aquatic
plants and algae.
-​ The water takes on a green appearance due to the algae and plant growth.
-​ When plants and algae die, decomposers (aerobic bacteria) break them down.
-​ The decomposers multiply quickly and use up the dissolved oxygen in the water.
-​ The lack of oxygen causes other aquatic organisms, like fish, to suffocate and die.
Methods of Controlling Pollution
-​ Controlling Air Pollution
●​ Reduce fossil fuel use by using alternative energy sources like solar and wind
energy.
●​ Pass laws (e.g., Clean Air Act) with strict penalties to limit air pollutants from
industry.
●​ Clean gaseous emissions from factories before releasing them into the
atmosphere.
●​ Equip motor vehicles with pollution control devices and improve engine fuel
efficiency.
●​ Ban or restrict smoking to specific locations.
●​ Public education programs to raise awareness about air pollution.
-​ Controlling Water Pollution
●​ Properly treat sewage before releasing it into bodies of water.
●​ Compost plant waste (e.g., vegetable peelings, crop residues).
●​ Produce biogas from farm waste and food industry waste.
●​ Use organic fertilizers instead of chemical ones.
●​ Use biodegradable detergents.
●​ Implement biological control or natural, biodegradable pesticides.
●​ Pass laws (e.g., Clean Water Act) with strict penalties to limit water pollutants
from industry.
●​ Public education programs to raise awareness about water pollution.
The water cycle
-​ The water cycle, also known as the hydrological cycle, shows how water moves on,
above and below the surface of the Earth.
-​ Water Cycle Processes
●​ Evaporation – Heat from the Sun causes liquid water in bodies of water (e.g.
oceans, lakes, ponds, rivers, and streams) and in the soil to change into water
vapour, which enters the atmosphere.
●​ Transpiration – Heat from the Sun causes water from plants to be lost to the
atmosphere as water vapour.
●​ Respiration – When organisms respire aerobically, water is produced as a
by-product and some of this is released into the atmosphere as water vapour when
the organisms exhale.
●​ Condensation – As water vapour rises, it cools and becomes water droplets that
form clouds.
●​ Precipitation – Water returns to the surface of the Earth in the form of rain, hail,
or snow.
●​ Surface runoff – Some water flows across the surface of the ground into bodies
of water.
●​ Infiltration – Some water moves downwards through the soil.
●​ Percolation – The water then moves through rocks into groundwater and may
eventually return to bodies of water.
Water Purification
-​ Potable water – Water that is safe to drink or use in food preparation.
-​ Aim of water purification:
●​ Ensure drinking water is safe for human consumption.
●​ Ensure drinking water is clear and not discoloured.
●​ Ensure drinking water has an acceptable taste.
●​ Ensure drinking water has an acceptable smell.
-​ Sources of water requiring purification: Rivers, streams, lakes, and rainwater collected
using gutters.
Small Scale water purification
-​ Filtration:
●​ Muslin cloth can filter suspended material from water.
●​ Not safe for drinking but useful for bathing and washing clothes.
●​ Domestic filters attached to taps can remove suspended material, including
bacteria and protozoa.
-​ Boiling:
●​ Oldest and effective method for small-scale water purification.
●​ Water must reach a 'rolling boil' for 10–20 minutes.
●​ Kills bacteria, spores, cysts, and ova of intestinal parasites.
●​ Removes water hardness, producing soft water.
-​ Chlorination:
●​ Chlorine tablets effectively disinfect small quantities of water.
●​ One 500 mg tablet disinfects 20 litres of water.
●​ Chlorine bleach is also effective: One teaspoon of bleach for 1 litre of water.
Large Scale Water Purification
-​ Screening:
●​ Water passes through grid screens to
remove large floating materials and
suspended solids.
-​ Sedimentation:
●​ Water is pumped to a settlement
tank where fine suspended particles
coagulate and settle.
-​ Filtration:
●​ Clear water from the settlement tank
passes through sand filters with microorganisms that remove organic matter by
feeding on it.
-​ Chlorination:
●​ Filtered water is treated with chlorine to kill harmful microorganisms.
●​ Fluoride may be added to reduce tooth decay.
●​ Water is then pumped to storage tanks for distribution.
-​ Testing water for bacteria
-​ The presence of pathogenic coliform bacteria in water can be determined using agar
plates.
-​ The agar is liquid when hot and forms a gel when cooled.
-​ It contains nutrients that allow bacteria to grow rapidly.
-​ Water that is safe for drinking will have no colonies of coliform bacteria.
-​ Steps involved in testing water for bacteria:
●​ Collect a sample of the water to be tested in a sterile container.
●​ Pour a small amount of the water onto an agar plate.
●​ Cover the plate and tape the lid to ensure it does not come off.
●​ Incubate the plate at 35°C for 24 hours.
●​ Count the number of colonies of bacteria.
-​ Humans negatively impact water supplies in several ways:
●​ Harvesting freshwater for agricultural, industrial, and domestic use.
●​ Increasing demands for freshwater due to population growth.
●​ Deforestation, reducing transpiration and precipitation.
●​ Releasing waste and harmful substances into bodies of water.
-​ Effects of these activities:
●​ Reduction of freshwater availability for various purposes.
●​ Contamination of water sources, leading to a loss of potable water.
●​ Increased cost of water treatment due to heavily contaminated water.
-​ Contaminated water is detrimental to human health because it may contain:
●​ Pathogens – Cause diseases like typhoid, cholera, and gastroenteritis.
●​ Pesticides – Harm the nervous and endocrine systems.
●​ Heavy metals (e.g. mercury, lead) – Damage body tissues, especially the nervous
system, leading to mental illness and brain damage.
●​ Nitrates – Reduce oxygen in the blood, posing risks to infants and pregnant
women (can cause blue baby syndrome).
●​ Radioactive waste – Can cause genetic defects and even death.
The Treatment and Disposal of Human Waste
Sewage Disposal
-​ Sewage consists of Human feces and urine, Household wastewater, Wastewater from
some industries and Rainwater
Improper Sewage Disposal
-​ Occurs when untreated sewage:
●​ Is released directly onto the land
●​ Is released directly into open water
●​ Leaks from cracked sewage pipes
Negative Effects of Improper Sewage Disposal
-​ Health Hazards – Spreads infectious diseases like cholera, typhoid, and dysentery.
-​ Breeding of Vectors – Attracts flies and rats, which spread diseases.
-​ Water Pollution – Floating sewage blocks light, reducing photosynthesis and affecting
aquatic food chains.
-​ Oxygen Depletion – Lowers dissolved oxygen levels, leading to aquatic organism deaths.
-​ Eutrophication – Nutrients in sewage contribute to excessive algae growth.
-​ Foul Odour – Contaminates the environment with bad smells.
Proper Sewage Disposal
-​ Sewage is removed through underground pipes or sewers.
-​ Transported to sewage treatment plants or areas far from homes and water sources.
-​ Flush toilets and pit latrines are commonly used in the Caribbean.
Flush Toilet
-​ Faeces and urine pass into the toilet bowl.
-​ Water from the tank flushes waste into the
sewers.
-​ A bend in the toilet retains water to prevent
odours and microorganisms from rising.
-​ Effective for sewage disposal but requires
large
amounts of water.
-​ Low-flow toilets use significantly less
water.
-​
-​
-​
-​
Pit Latrines
Used in areas with limited water supply or no sewage treatment system.
Must be properly sited to prevent water contamination and health hazards.
Guidelines for Siting Pit Latrines
●​ Depth: At least 3 meters deep to
reduce odours and ensure long-term
use.
●​ Soil Type: Should be placed in
sandy soil for proper drainage and
decomposition.
●​ Location: Should be downhill and
far from wells or drinking water
sources to prevent contamination.
Usage and Maintenance
●​ No disinfectants should be added,
as they kill bacteria needed for
decomposition.
●​ Once full, the pit should be covered and left for at least six months before reusing
the land.
-​ Advantages of Pit Latrines
●​ Require less water than flush toilets.
●​ Relatively cheap to construct.
-​ Disadvantages of Pit Latrines
●​ Risk of water and food contamination.
●​ Can contribute to the spread of infectious diseases.
●​ Limited land space makes it difficult to site new pit latrines due to population
growth.
Sewage Treatment
-​ Methods: Biological Filter Method and Activated Sludge Method
Initial Treatment Steps for Both Processes
-​ Screening – Large objects (plastic bottles, rags, paper, twigs) are removed using screens.
-​ Grit Settling – Sewage passes through a grit pit where grit and sand settle.
-​ Sedimentation – Sewage flows through sedimentation tanks where remaining solid
material settles to form sludge.
-​ Sludge is removed and used for methane production or as fertilizer.
-​ The liquid left (effluent) contains suspended organic matter and is treated further.
-​ Biological (Percolating) Filter Method
●​ The effluent is sprayed onto small
stones covered with a film of aerobic
bacteria and protozoa.
●​ Microorganisms feed on and break
down the organic matter in the
effluent.
●​ The effluent then moves to a final
settlement tank to allow remaining
solids to settle.
●​ After this, it is safe to release the
treated effluent into bodies of water
(e.g., rivers or the sea).
-​ Activated Sludge Method
●​ The effluent is passed into aeration
tanks where compressed air is forced
through it, and paddles mix the air
and effluent.
●​ This provides enough oxygen for aerobic bacteria to decompose the organic
matter.
●​ The effluent then flows to a final settlement tank to allow any remaining solids to
settle.
●​ After this, the treated effluent is safe to release into bodies of water.
Domestic Refuse Disposal
-​ Domestic refuse refers to unwanted solids that accumulate after use in the home,
including organic matter (e.g., waste food and garden waste) and other solid wastes (e.g.,
plastics, paper, glass).
-​ Importance of Proper Disposal: It is important to dispose of domestic refuse properly to
maintain cleanliness and prevent health hazards.
-​ Before collection refuse should be placed in bins with tight-fitting lids to prevent rats and
flies from entering.
-​ Refuse should be collected at least once per week.
-​ Bins should be inspected and cleaned regularly.
-​ Methods of Disposal:
●​ Landfills
●​ Composting
●​ Incineration
●​ Recycling
Method
How Method Works
Advantages
Disadvantages
Landfill
Refuse is buried in a
specially prepared site.
- Convenient and easy to use
once constructed.
- Can dispose of many types
of waste.
- Methane can be used as a
fuel to generate electricity.
- Site can be re-landscaped
after full.
- Requires continuous maintenance to
prevent leachate and toxic gases from
escaping.
- Can contribute to air pollution and
unpleasant odours.
- Leachate can contaminate soil and
water sources.
- Uses up valuable land.
- Unsightly when in operation.
Incineration
Solid combustible
waste is burned at very
high temperatures.
- Reduces the volume of
solid waste entering
landfills.
- High temperatures kill
harmful pathogens.
- Heat can be used for
electricity or heating.
- Does not take up a lot of
land.
- Expensive to build and operate.
- High energy requirements.
- Produces waste gases that can
contribute to air pollution and
respiratory issues.
Composting
Biodegradable waste is
broken down by
aerobic bacteria in
compost heaps or
composters.
- Reduces the volume of
solid waste entering
landfills.
- Produces organic fertilizer
beneficial to soil.
- Reduces demand for
synthetic fertilizers.
- Time-consuming to turn the
compost regularly.
- Can give off unpleasant odours.
- Can attract pests and disease
vectors.
The Impact of Solid Waste on the Environment
-​ If solid waste is not disposed of properly, it becomes a threat to the environment:
●​ Toxic chemicals in the waste can leach out and contaminate thecontributing soil, aquatic
environments, and water sources.
●​ Greenhouse gases like methane and carbon dioxide can be released into the atmosphere, to the
greenhouse effect.
●​ Hydrogen sulfide gas can be released into the air, which is extremely toxic. Even low
concentrations irritate the eyes and respiratory system.
●​ Plastics can enter waterways and oceans, harming aquatic organisms.
●​ Refuse attracts rodents, which can spread disease.
●​ Refuse creates an eyesore, negatively impacting tourism, especially eco-tourism.
-​
SECTION B: LIFE PROCESSES AND
DISEASE
CELLS
-​ Cells are the basic membrane-bound unit that contains the fundamental molecules of life
and of which all living things are composed.
-​ Unicellular- made of one cell, such as a bacterium or yeast.
-​ Multicellular- made of many cells, such as humans and other animals.
-​ Cell Theory states:
●​ All organisms are composed of one or more cells.
●​ Cells are the basic unit of structure and function in organisms.
●​ All cells come only from other cells.
-​ A light microscope and electron microscope can be used to see the different structures
of a cell.
Functions of the Structures of the Cells
-​ Cell Membrane:
●​ Forms the boundary between
the cell and its surroundings.
●​ Controls the movement of
substances in and out of the
cell.
-​ Nucleus (contains Chromosomes):
●​ Contains chromosomes with
genetic material (DNA).
●​ Information in the
chromosomes is used to
control the development and
function of the cell.
●​ Most cells die without a
nucleus.
-​ Cytoplasm:
Contains cell organelles.
●​ Site of cell activities.
-​ Mitochondria:
●​ Releases energy for the cell.
-​ Cell Wall(Plants Cell only):
●​ Provides protection and
shape to the cell.
●​ Helps the plant stay upright.
-​ Vacuole (Plant Cell only):
●​ Stores water and dissolved
substances.
●​ Facilitates the exchange of
various substances.
-​ Chloroplast(Plant Cell only):
●​ Contains chlorophyll (green
pigment).
●​ Site of food production
through photosynthesis.
-​ Endoplasmic
●​ reticulumTransports
substances throughout the
cell.
-​ Ribosome
●​ Where proteins are
synthesised (produced).
-​ Specialized cells are cells that are adapted to carry out specific functions.
-​ Tissues are formed when similar cells group together to perform the same function.
Animal Tissues
-​ Connective:
●​ Examples: Bones, cartilage, tendons, and
ligaments.
-​ Epithelial:
●​ Found on skin surfaces and lining mucous
membranes (e.g., nose, throat).
-​ Muscle:
●​ Found in legs, heart, and other internal
organs.
-​ Nervous:
●​ Found in the brain and spinal cord.
●​ Includes specialized cells called neurons.
-​
-​
-​
-​
-​
Plant Tissue
Epidermal:
●​ Lines and protects the plant.
Photosynthetic:
●​ Responsible for food production.
Packing (Parenchyma):
●​ Provides filling and support.
Transport:
●​ Transports food and water.
Supportive/Strengthening:
●​ Includes collenchyma and
sclerenchyma tissues.
●​ Provides structure and support.
-​ Microbes or microorganisms are bacteria, fungi and viruses.
-​ Bacteria and Fungi have cells similar to plant cells, but bacteria do not have nuclei and
fungi do not have chloroplasts.
-​ Bacteria are unicellular with cell walls and cytoplasm but without organelles, such as
nuclei.
-​ Fungal cells have cell walls, nuclei, large vacuoles and mitochondria, but no chloroplasts.
-​ Viruses do not have cells. They are made of genetic material enclosed in a protein coat.
-​ Some protists, such as Amoeba and Euglena, are unicellular; others, such as seaweeds,
are multicellular and can be very large.
​
Virus Structure.
Bacteria Cell Structure
Fungi Cell Structure
-​ Hypotonic or Dilute Solution is one that has fewer dissolved particles (eg. salts,
electrolytes) and more water particles.
-​ It has higher concentration of water molecules.
-​ Hypertonic or Concentrated Solution: is one that has more dissolved particles (eg.
salts, electrolytes and less water particles.
-​ It has a lower concentration of water molecules.
-​ An Isotonic Solution contains equal concentrations/amount of dissolved particles and
water particles. Both solutions are said to be in equilibrium.
-​ A "concentrated solution in water molecules" means there are plenty of water molecules
compared to dissolved solutes.
-​ A "concentrated solution" on its own means the solution has more dissolved substances
compared to water.
-​ Concentration Gradient refers to the movement of particles up or down a slope,
influenced by concentration differences.
-​ Down/Along the Gradient: Spontaneous movement from high to low concentration, no
energy required.
-​ Up/Against the Gradient: Movement from low to high concentration using energy.
Active Transport
-​ Active Transport is the movement of molecules from low to high concentration against
the gradient, requiring energy.
➢​ This process is facilitated by specific transport proteins.
➢​ Transport proteins require energy to function.
➢​ Energy is provided by the breakdown of ATP inside the cell.
Importance of Active Transport:
-​ Maintains Ion Balance – Cells rely on active transport to regulate ion concentrations,
which is critical for functions like nerve signaling and muscle contraction.
-​ Example: The sodium-potassium pump (Na+/K+ pump) in nerve cells actively
transports Na⁺ out and K⁺ into the cell to generate electrical signals.
-​ Nutrient Absorption – Active transport enables the uptake of essential nutrients, even
when their concentration outside the cell is lower than inside.
-​ Example: In the small intestine, glucose is absorbed from the gut into the
bloodstream through the sodium-glucose co-transport mechanism.
-​ Removes Waste and Toxins – Cells use active transport to expel harmful substances and
metabolic waste.
-​ Example: In the kidneys, active transport helps remove excess ions and waste
products into urine for excretion.
-​ Maintains Cell Turgor in Plants – Active transport helps plants absorb essential
minerals from the soil, which contributes to water uptake and structural support.
-​ Example: Root hair cells absorb mineral ions (e.g., potassium and nitrate) from
the soil through active transport to support growth and photosynthesis.
-​ Plasmolysis is the shrinkage of plant cells due to water loss via osmosis, occurring in
extreme conditions.
-​ Turgidity is the condition in plant cells where they are full of water due to turgor
pressure, preventing further water intake.
-​ The pressure exerted by water inside a plant cell against its cell wall when the cell is full
of water, making it turgid and unable to accept more water
-​ Cells cannot exist in isolation; they require substances from their surroundings and need
to expel waste.
-​ The cell membrane surrounds the cytoplasm and is partially permeable, allowing some
substances to enter while keeping others out.
Diffusion
-​ Diffusion is the movement of a substance from an area of high concentration to an area
of low concentration.
-​ Occurs along the concentration gradient
-​ It usually occurs in gases, solids in liquids, and liquids in liquids.
-​ Particles in gases and liquids move randomly and collide, causing them to change
direction.
-​ Diffusion occurs naturally without stirring, shaking, or wafting.
-​ Importance of Diffusion in Living Organisms
●​ Oxygen enters cells for aerobic respiration, and carbon dioxide exits by diffusion.
●​ Glucose and amino acids from digestion are absorbed into the blood via diffusion in the
ileum.
●​ In plants, carbon dioxide enters leaves for photosynthesis, and oxygen exits by diffusion.
-​ Examples of Diffusion:
●​ Carbon dioxide removal:
➢​ Respiration increases carbon dioxide concentration in cells.
➢​ Carbon dioxide diffuses from the cell (high concentration) into the
surrounding blood (low concentration) through the cell membrane.
●​ Water uptake in plants:
➢​ Water diffuses into root hair cells from the soil.
➢​ Movement occurs from high water concentration in the soil to a lower
concentration in the root hair cell.
➢​ Root hair cells are partially permeable.
Osmosis
-​ Osmosis is the diffusion of water molecules from a dilute solution (high concentration of
water) to a concentrated solution (low concentration of water) through a selectively
permeable membrane.
-​ Water moves down the concentration gradient.
-​ A selectively permeable membrane allows small substances to pass through but blocks
larger substances.
Effect of Osmosis on Plant and Animals Cells
Animal Cells
-​ Red blood cells placed in a solution with the same water concentration as their cytoplasm
(0.85% salt solution) will not experience an overall change in volume. No osmosis
occurs.
-​ Red blood cells placed in a solution with a higher water concentration compared to their
contents (e.g. pure water) will gain water by osmosis, swell up and burst.
➢​ Water will diffuse from a higher water concentration outside the cell to a lower
water concentration inside the cell.
-​ Red blood cells placed in a solution with a lower water concentration compared to their
contents (e.g. 1.7 percent salt solution) will lose water by osmosis and shrink.
➢​ Water will diffuse from a higher water concentration inside the cell to a lower
water concentration outside the cell.
Plant Cells
-​ Plant cells placed in a solution with an equal water concentration to the contents of their
cytoplasm and vacuole (dilute sugar solution) will not experience an overall change in
volume. No osmosis occurs.
-​ Plant cells placed in a solution with a high water concentration compared to their contents
(e.g., pure water) will gain water by osmosis and swell up until their cytoplasm and cell
membrane are pushing against their cell wall. They are said to be turgid.
➢​ Water will diffuse from a higher water concentration outside the cell to a lower
water concentration inside the cell. The presence of the plant cell wall prevents
plant cells from bursting.
-​ Plant cells placed in a solution with a low water concentration compared to their contents
(e.g., concentrated sugar solution) will lose water by osmosis. Their cell membranes will
peel away from their cell walls and they are said to be plasmolysed.
➢​ Water will diffuse from a higher water concentration inside the cell to a lower
water concentration outside the cell.
NUTRITION
-​ Producers, such as green plants and phytoplankton, are at the base of food chains and
webs.
-​ They convert light energy from the Sun into chemical energy.
-​ Producers absorb simple inorganic compounds (carbon dioxide and water) and use them
to make complex organic compounds.
-​ The type of nutrition used by producers is autotrophic nutrition.
-​ Organisms that use autotrophic nutrition are called autotrophs.
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
Consumers cannot use simple inorganic compounds or absorb light energy.
They feed on other organisms.
The type of nutrition used by consumers is heterotrophic nutrition.
Organisms that feed this way are called heterotrophs.
Autotrophic Nutrition
Autotrophic means "self-feeding."
Autotrophic organisms only need simple inorganic substances (carbon dioxide and water)
from their environment.
Carbon dioxide and water provide the elements carbon, hydrogen, and oxygen.
Autotrophs also require other elements to make various substances.
These elements, such as nitrogen, potassium, and phosphorus, are absorbed as ions.
Green plants require larger quantities of nitrogen, potassium, and phosphorus compared
to elements like magnesium, sulfur, iron, and calcium.
-​ Nitrogen (N) – Promotes leaf and stem growth by helping plants produce proteins and
chlorophyll.
-​ Essential for photosynthesis and overall plant vigor.
-​ Phosphorus (P) – Supports root development and energy transfer.
-​ Helps in flowering, fruiting, and seed formation.
-​ Potassium (K) – Improves overall plant health, disease resistance, and water regulation.
-​ Enhances stomatal function and enzyme activation.
-​ Magnesium (Mg) – A key component of chlorophyll, necessary for photosynthesis.
-​ Helps in enzyme activation and nutrient transport.
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
Heterotrophic Nutrition
Heterotrophs get their food in various ways:
Protists (e.g., Amoeba): Engulf food particles into food vacuoles through phagocytosis.
Multicellular Animals: Eat solid food by biting into it with jaws and teeth.
Fluid Feeders: Pierce the surface of the body and suck body fluids.
●​ Examples:
➢​ Aphids feed on plant phloem.
➢​ Mosquitoes feed on blood.
Fungi:
●​ Fungi, like mushrooms, have fruiting bodies supported by hyphae that spread
through dead wood.
●​ Hyphae release enzymes to digest food and absorb the products.
Parasites:
●​ Feed in different ways:
➢​ Some live on the surface of hosts (e.g., lice, ticks, fleas) using piercing
mouthparts to suck blood.Some live inside the host, feeding on digested
food or nutrients transported in the blood.
●​ Examples of parasitic fungi: Ringworm.
●​ Examples of parasitic bacteria: Cholera, typhoid, and tuberculosis (TB).
Saprophytic Nutrition
Many bacteria and fungi feed on dead and decaying matter.
These organisms are decomposers, breaking down dead remains and recycling elements
like carbon and nitrogen.
Saprophytic nutrition is a form of heterotrophic nutrition because these organisms secrete
enzymes into their food and absorb the soluble products.
Decomposers can digest cellulose, which is important for breaking down dead plant
material.
-​ Without decomposers, the world would be full of dead organisms that are not broken
down (e.g., trees would remain intact).
-​ Photosynthesis is the process used by plants, algae and certain bacteria to harness energy
from sunlight and turn it into chemical energy (food).
-​ Conditions necessary for photosynthesis: Presence of Sunlight & Presence of Chlorophyll
Two Stages of Photosynthesis:
-​ Light-Dependent Reactions (Light Stage):
●​ Occur in the chloroplasts and require continuous light energy.
●​ Chlorophyll absorbs light energy, which is converted into chemical energy.
●​ Water molecules are split, releasing oxygen gas.
-​ Light-Independent Reactions (Dark Stage):
●​ Do not require light directly.
●​ Use energy from the light-dependent reactions and carbon dioxide to form
glucose.
Plants use the glucose they produce to make:
-​ Sucrose:
●​ Transported around the plant via the phloem.
●​ Used in nectar and fleshy fruits to attract animals for pollination and seed
dispersal.
●​ Sucrose can be converted to:
➢​ Glucose: Used in respiration to release energy.
➢​ Starch:Stored in storage organs such as seeds, swollen roots (e.g., yams),
and swollen stems (e.g., Irish potatoes) as a long-term energy store. Also
stored in leaves for use in respiration at night.
➢​ Amino acids and proteins: Formed by adding nitrogen from nitrates and
sulfur from sulfates, used for growth. These amino acids are then used to
make proteins, such as enzymes and carrier proteins in cell membranes.
➢​ Lipids: Used to make cell membranes and for energy storage, e.g., in
seeds.
Structure of the Leaf
External Features and Adaptations for Photosynthesis:
-​ Thin: Provides a short distance for carbon dioxide to move by diffusion into the leaf
-​ Green Color: The green pigment, chlorophyll, absorbs light for photosynthesis.
-​ Stomata: Allows carbon dioxide to move by diffusion into the leaf
-​ Guard cells: To open and close the stomata depending on the conditions
-​ Veins: Transport water and ions throughout the leaf and carry sucrose out.
Internal Structure of the Leaf
-​ Cuticle: Waxy layer waterproofing upper leaves.
-​ Upper epidermis: Upper layer of cells. No chloroplasts. Protection.
-​ Palisade Mesophyll: Tightly packed upper layer of chloroplast containing cells. Light is
collected.
-​ Spongy Mesophyll: Lower layer of chloroplast containing cells. Air spaces around them.
Photosynthesis occurs here.
-​ Lower Epidermis: Lower external layer of cells in the leaf.
-​ Vascular Bundle: Bundle of many vessels (xylem and phloem) for transport.
-​ Xylem: Living vascular system carrying water & minerals throughout the plant.
-​ Phloem: Living vascular system carrying dissolved sugars and organic compounds
throughout the plant.
-​ Guard Cells: 2 cells surrounding stomata that control rate of gas & water exchange.
-​ Stomata: Opening between guard cells for gas & water exchange.
Factors Affecting Rate of Photosynthesis:
-​ Light- If we increase the amount of light available to the plant, the rate of p/sys will also
increase and vice versa until another factor becomes limited.
-​ Carbon Dioxide: If we increase the amount of carbon dioxide available to the plant, the
rate of p/sys will also increase and vice versa until another factor becomes limited.
-​ Temperature: If we increase the amount of warmth available to the plant, the rate of
p/sys will also increase and vice versa.
➢​ Passing the optimum temperature the rate declines due to the denatured enzymes.
-​
-​
-​
-​
-​
Testing for starch
Testing leaves for starch is a good way to show that a plant has been photosynthesising.
Iodine solution is used to detect the presence of starch which is converted from sugars
produced during photosynthesis
Procedure:
1.​ Boil the Leaf: Place the leaf in boiling water for one minute to destroy cell
membranes and extract chlorophyll.
2.​ Decolorize the leaf: Place the leaf in a test tube with ethanol. The chlorophyll
dissolves in the ethanol.
3.​ Heat the leaf: Stand the test tube in a beaker of hot water for about 10 minutes.
4.​ Wash the Leaf: Remove the leaf and wash it in cold water to remove ethanol and
rehydrate it. This softens the leaf.
5.​ Apply Iodine Solution: Spread the leaf flat on a white surface and apply iodine
solution
Blue-Black Color: Starch is present.
Yellow-Brown Color: No starch present.
Testing if light is needed for Photosynthesis
-​ Procedure:
1.​ Destarch the Plant: Use a destarched plant and cover part of the leaf with tin foil
or black paper to block light from reaching it. Secure the covering with tape or
paper clips.
2.​ Leave the Plant in Light: Place the plant in light for a few hours.
3.​ Test for Starch: Test the leaf for starch using the iodine solution as described.
-​ Blue-Black Color: The parts of the leaf exposed to light have starch.
-​ Yellow-Brown Color: The covered parts, which did not receive light, have no starch.
Testing if Chlorophyll is needed for Photosynthesis
-​ Procedure
1.​ Use a Destarched Variegated Plant: Choose a variegated plant (e.g., hibiscus)
with both green and white areas on its leaves. The white parts lack chlorophyll.
2.​ Expose to Light: Place the plant in the light for about six hours.
3.​ Examine the Leaf: Pick a leaf and observe the distribution of the green and white
parts. You can draw or photograph it.
4.​ Test for Starch: Test the leaf for starch using the iodine solution.
-​ The green parts of the leaf (where chlorophyll is present) will turn blue-black because
starch is produced there.
-​ The white parts (without chlorophyll) will not turn blue-black, showing no starch
production.
-​ Mineral nutrients (also called mineral salts, salts, mineral ions) are elements plants need
besides carbon, hydrogen, and oxygen.
-​ These nutrients are crucial for making complex compounds like amino acids, proteins,
chlorophyll, and DNA.
-​ Plants absorb mineral ions by active transport through root hair cells, which provide a
large surface area.
Key Nutrients:
-​ Nitrogen (Nitrate Ions):
●​ Essential for making amino acids and proteins.
●​ Although nitrogen gas is abundant in the air, most plants can't use it directly.
Legumes, like Pride of Barbados, have root nodules filled with bacteria that
convert nitrogen gas into usable amino acids.
●​ Non-legume plants must absorb nitrate ions from the soil.
-​ Magnesium:
●​ Vital for producing chlorophyll, the molecule responsible for trapping light energy
in photosynthesis.
●​ Magnesium is continuously needed because plants constantly break down and
rebuild chlorophyll in their leaves.
Role of Mineral Nutrients:
-​ Transport to Leaves: Nitrate and magnesium ions are carried to the leaves through the
xylem.
-​ Amino Acid Production: Leaves use nitrate ions and sugars (from photosynthesis) to
make amino acids, which are then transported via the phloem for protein synthesis in new
growth areas like leaves, flowers, roots, and seeds.
Investigating Mineral Deficiencies:
-​ Hydroponics is a method used to grow plants in water or sand while supplying the
necessary mineral nutrients in a solution.
-​ By preparing different solutions, we can study the effects of missing nutrients on plant
growth.
-​ Complete solution: Contains all required mineral nutrients.
-​ Control solution: Contains all nutrients but is varied to exclude one specific nutrient at a
time.
Effects of Mineral Deficiencies:
-​ Nitrogen (Nitrate) Deficiency:
●​ Plants grow slowly due to insufficient protein production.
●​ Roots and stems are short, with few leaves.
●​ Lower leaves turn yellow due to a lack of chlorophyll production.
-​ Magnesium Deficiency:
●​ Magnesium is redirected to new leaves, causing older leaves to have a mottled
yellow and green appearance due to insufficient chlorophyll.
Breaking Bonds (Hydrolysis)
●​ Boiling sucrose with hydrochloric acid breaks the bond between glucose and fructose.
●​ The breakage of this bond requires the use of water.
●​ Hydrochloric acid acts as a catalyst in this reaction.
●​ The process of breaking bonds using water is called hydrolysis.
Forming Bonds (Dehydration Synthesis)
●​ The synthesis of sucrose involves the reaction between glucose and fructose.
●​ A chemical bond is formed between them when water is removed.
●​ This reaction is known as a condensation or dehydration reaction.
●​ The formation of larger molecules, such as starch and protein, occurs through this
process, which is called dehydration synthesis.
Digestion
-​ Digestion is the process of breaking down large, insoluble food fragments into smaller,
water-soluble particles for absorption into the blood plasma.
-​ The Digestive System involves all body parts responsible for food uptake, digestion, and
elimination of undigested material.
The Digestive Process
-​ Mechanical Digestion:
●​ Large pieces of food are broken down into smaller pieces.
●​ Begins in the mouth where food is chewed by the teeth.
●​ Continues in the stomach where contractions churn the food.
-​ Chemical Digestion:
●​ Large, usually insoluble food molecules are broken down into small, soluble food
molecules by enzymes.
●​ Starts in the mouth and is completed in the ileum.
-​ The Alimentary Canal (Digestive Tract) is the pathway through which food enters the
body.
-​ It is a tube-like structure extending from the mouth to the large intestine that plays a key
role in the digestion process.
-​ Functions of the Digestive System:
●​ Breaks down food.
●​ Releases nutrients.
●​ Absorbs nutrients into the body.
The Digestive System
The Tooth
Types of Teeth
Internal Structure of the tooth
Functions of the main parts of a tooth
Tooth Decay (Dental Caries)
-​ Tooth decay occurs when bacteria, saliva, and food particles in the mouth combine to
form plaque on the teeth and gums.
-​ The bacteria in plaque feed on sugars from food and produce acid.
-​ The acid gradually erodes the enamel on the teeth, leading to tooth decay.
The process of tooth decay
-​ Causes of Tooth Decay:
●​ Eating foods with a high sugar or starch content, and drinking drinks with a high
sugar or acid content (e.g., fruit juices).
●​ Poor oral hygiene practices (e.g., not brushing properly, not brushing and flossing
regularly, not visiting the dentist regularly).
●​ Not getting enough fluoride.
●​ Grinding the teeth.
●​ Smoking.
-​ Guidelines for the Care of Teeth:
●​ Brush teeth and gums in the proper way, twice a day.
●​ Use a fluoride toothpaste and good quality toothbrush when brushing.
●​ Use dental floss and an interdental brush once a day.
●​ Use an antibacterial mouthwash after brushing and flossing.
●​ Avoid eating sugary and starchy foods and drinking sugary drinks, especially
between meals and before going to bed.
●​ Visit a dentist regularly for a checkup and cleaning.
-​
-​
-​
-​
-​
-​
-​
-​
Enzymes are organic chemicals that change the rate of chemical reactions.
They are secreted in solution in the living cells of plants and animals.
They Aid in metabolic processes necessary for life.
Properties of Enzymes:
➢​ They are proteins.
➢​ They are affected by temperature.
➢​ Each has a specific function
➢​ Not used up in reactions so they can be reused.
➢​ They are affected by pH.
➢​ They are required in small quantities.
Role of Enzymes in Digestion
They are essential for digestion and overall health.
Work with stomach acid and bile to break down food.
They convert food into absorbable molecules.
For example breaking down:
➢​ Carbohydrates to Provide energy.
➢​ Proteins to Build and repair muscle.
-​ Enzymes work best at a particular temperature known as the optimum temperature.
-​ This is about 37 °C for human enzymes
-​ High temperatures denature enzymes, i.e. the shape of the enzyme molecules changes so
that they are inactivated.
-​ Enzymes start to be denatured at about 40 °C to 45 °C.
-​ Enzymes work best at a particular pH
known as the optimum pH.
-​ This is about pH 7 for most enzymes.
-​ Extremes of acidity or alkalinity denature
most enzymes.
-​ The action of enzymes is helped by certain vitamins and minerals, e.g. vitamin B1 helps the
action of respiratory enzymes.
-​ The action of enzymes is inhibited by certain poisons, e.g. arsenic and cyanide
-​ Food is moved through the oesophagus and the rest of the alimentary canal by a process
known as peristalsis.
-​ Absorption is the movement of digested food molecules into the blood or lymph.
-​ Simple sugars, amino acids, fatty acids, and glycerol pass through epithelial cells of the
small intestine by diffusion or active transport
-​ Small intestine adaptations for efficient absorption:
●​ Long length (6m in adults).
●​ Large surface area (9m²).
●​ Thin epithelial lining (one cell thick) for easy diffusion into blood and lymph.
●​ Microvilli on epithelial cells (increase surface area).
●​ Cell membranes with many carrier proteins for active transport.
-​ The Large surface area is
due to folded inner lining
with millions of tiny
projections called villi
(singular: villus).
-​
-​
-​
-​
Absorption process:
Digested food enters
capillaries and lacteals
(lymph capillaries) in the
villi.
Capillaries transport
absorbed molecules
quickly to the liver via the
hepatic portal vein.
Lacteals transport fatty acids and glycerol more slowly in the lymph.
Villi contain muscle fibers
-​ Muscle contractions squeeze lacteals, pushing lymph into lymphatic vessels.
-​ Lymphatic vessels have Thin-walled, like veins.
-​ They Empty into blood vessels near the heart (ensuring fat enters the bloodstream
gradually).
-​ Undigested food from the small intestine moves into the colon.
-​ Water and mineral salts are absorbed in the colon.
-​ As waste moves through the colon to the rectum, it becomes more solid due to water
absorption.
-​ Assimilation is the process by which the body uses the soluble food molecules absorbed
after digestion
-​ A nutrient is a substance in food that provides benefits to the body.
-​ Macronutrients (Major Nutrients) are Organic compounds eaten in large quantities that
provide energy.
-​ They supply essential compounds for cell formation (amino acids, sugars, fatty acids).
-​ Include:
●​ Carbohydrates
●​ Fats
●​ Proteins
-​ Micronutrients (Minor Nutrients) do not provide energy and are needed in tiny
quantities.
-​ Include:
●​ Vitamins – Organic compounds (e.g. vitamins A and C).
●​ Minerals – Inorganic, often absorbed as ions (e.g. calcium and iron).
-​ A Diet is the food an animal eats.
-​ A Balanced diet is one that provides all energy and nutrients required for immediate
needs.
-​ It includes:
●​ Energy sources – Carbohydrates, lipids, and proteins.
●​ Essential amino acids – 8 to 10 types the body cannot synthesize.
●​ Essential fatty acids – 2 types the body cannot synthesize.
●​ Vitamins – e.g. vitamins A and C.
●​ Minerals – e.g. calcium and iron.
●​ Water – To replace daily water loss.
●​ Fibre – Essential for digestion.
-​ Vegetarians – Do not eat meat but may consume animal products like eggs and milk.
-​ Vegans – Do not consume any foods of animal origin.
-​ Many nutrients are obtained from animal products, so vegetarians and vegans must
ensure their diet includes nutrient-rich plant foods.
-​ A properly balanced vegetarian diet is healthy.
-​ They both have a risk of vitamin B₁₂ deficiency:
●​ Vitamin B₁₂ is only found in animal-based foods.
●​ Essential for red blood cell production.
●​ Vegetarians and vegans may need supplements or fortified foods.
Carbohydrates
-​ Composed of carbon, hydrogen, and oxygen atoms with a 2:1 ratio of hydrogen to
oxygen.
-​ Classified into three groups based on their chemical structure:
●​ Monosaccharides: Simplest carbohydrate molecules, formula C6H12O6. All are
reducing sugars.
●​ Disaccharides: Formed by joining two monosaccharide molecules, formula
C12H22O11. All are reducing sugars except sucrose (non-reducing sugar).
●​ Polysaccharides: Formed by joining many monosaccharide molecules into
straight or branched chains. Includes starch, cellulose, and glycogen (animal
starch).
Properties of Different Carbohydrates
Proteins
-​ Composed of carbon, hydrogen,
oxygen, nitrogen, and sometimes
sulfur and phosphorus atoms.
-​ Formed by joining 20 different
amino acids into long chains.
Properties of Proteins
-​ Can be denatured (their chemical
structure changes due to heat or
chemicals).
-​ Structure:
●​ Some are globular (soluble in
water), e.g., haemoglobin,
albumen.
●​ Some are fibrous (insoluble),
e.g., collagen, keratin.
-​ React with biuret reagent.
Lipids
-​ Composed of carbon, hydrogen, and
oxygen atoms.
-​ Have fewer oxygen atoms than
carbohydrate molecules (e.g., beef
fat: C57H110O6).
-​ Made up of three fatty acid
molecules and one glycerol
molecule.
-​ Properties of Lipids
●​ Feel greasy.
●​ Insoluble in water.
●​ Leave a grease spot on paper.
Sources and functions of carbohydrates, proteins and lipids
Testing for Food Substances
Precautions for Benedict’s Test
●​ Place test tubes in a water bath.
●​ Water should be at
approximately 80°C (not boiling).
●​ Always wear eye protection.
●​ Essential to neutralize the
reaction mixture in the
non-reducing sugar test (Benedict’s
test doesn’t work if acid is present).
General Precautions
●​ Wear gloves and lab coats
●​ Ensure you don’t reuse the
same test tubes or pipettes to
prevent cross-contamination
●​ Make sure test tubes are clean
Limitations of Chemical Tests
●​ Show presence of food
substances but not their quantity.
●​ Modified tests (e.g., iodine solution, Benedict’s solution, and Biuret solution) give color
ranges.
●​ Color intensity increases with substance concentration.
●​ Results are compared to color standards, and human judgment may vary.
Some important vitamins required by the human body
Vitamin
Sources
Functions
Results of Deficiency
A
Liver, cod liver oil,
yellow and orange
vegetables and fruits
(e.g., carrots, pumpkin),
green leafy vegetables
(e.g., spinach).
• Helps to keep the
skin, cornea, and
mucous membranes
healthy.
• Helps vision in dim
light (night vision).
• Strengthens the
immune system.
• Dry, unhealthy skin and cornea.
• Increased susceptibility to infection.
• Reduced vision at night or complete
night blindness.
• Xerophthalmia: eyes fail to
produce tears leading to a dry,
damaged cornea and sometimes
blindness.
B₁
Whole-grain cereals and
bread, brown rice, peas,
beans, nuts, yeast
extract, lean pork.
• Aids in respiration to
produce energy.
• Important for the
proper functioning of
the nervous system.
• Beri-beri: weakness and pain in the
limb muscles, difficulty walking,
nervous system disorders, paralysis.
B₂
Fish, lean meats,
whole-grain cereals,
yeast extract.
• Aids in respiration to
produce energy.
• Pellagra: skin, digestive system,
and nervous system disorders
resulting in dermatitis, diarrhoea, and
dementia.
C
West Indian cherries,
citrus fruits, raw green
vegetables.
• Keeps tissues
healthy, especially the
skin and connective
tissue.
• Strengthens the
immune system.
• Scurvy: swollen and bleeding gums,
loose teeth or loss of teeth, red-blue
spots on the skin, muscle and joint
pain, wounds do not heal.
• Increased susceptibility to infection.
D
Oily fish, eggs, cod liver
oil.
Made in the body by the
action of sunlight on the
skin.
• Promotes the
absorption of calcium
and phosphorus in the
ileum.
• Helps build and
maintain strong bones
and teeth.
• Strengthens the
immune system.
• Rickets in children: soft, weak,
painful, deformed bones, especially
limb bones, bow legs.
• Osteomalacia in adults: soft, weak,
painful bones that fracture easily,
weakness of limb muscles.
• Poor teeth.
-​ Solubility of Vitamins:
●​ Fat-soluble: Vitamins A and D
●​ Water-soluble: Vitamins B and C
-​ Results of Vitamin Surplus: Excessive consumption, especially through supplements,
can be harmful.
-​ Surplus of Vitamin A:
○​ Fatigue
○​ Liver damage
-​ Surplus of Vitamin D:
○​ Jaundice
○​ High calcium levels in the blood
○​ Itchy skin
○​ Excessive thirst and urination
○​ Cracked fingernails
○​ Loss of appetite
○​ Blurry vision
○​ Nausea and vomiting
○​ Nausea
○​ Calcification of soft tissues (e.g.,
kidneys, lungs, inside blood vessels)
○​ Headaches
○​ Development of kidney stones
Some Important Minerals Required by the Human Body
Element
Sources
Functions
Results of Deficiency
Calcium (Ca)
Dairy products
(milk, cheese,
yoghurt), green
vegetables (e.g.,
broccoli).
• To build and maintain
healthy bones and teeth.
• Helps blood to clot at
cuts.
• Rickets in children.
• Osteoporosis in adults:
brittle, fragile bones.
• Weak, brittle nails.
• Tooth decay.
Phosphorus
(P)
Protein-rich foods
(milk, cheese,
meat, poultry,
fish, nuts).
• To build and maintain
healthy bones and teeth.
• To make ATP, an
energy-rich compound.
• Weak bones and teeth.
• Tiredness, lack of energy.
Iron (Fe)
Red meat, liver,
eggs, beans, nuts,
dark green leafy
vegetables.
• To make
haemoglobin, the red
pigment in red blood
cells.
• Anaemia: reduced
number of red blood cells
in the blood, pale
complexion, tiredness, lack
of energy.
Iodine (I)
Seafood (fish,
shellfish,
seaweed), milk,
eggs.
• To make the hormone
thyroxine.
• Cretinism in children:
retarded physical and
mental development.
• Goitre in adults: swollen
thyroid gland in the neck.
• Reduced metabolic rate,
leading to fatigue in adults.
Sodium (Na),
Potassium
(K)
Sodium: table salt,
cheese, cured
meats.
Potassium: fruits,
vegetables.
• Needed for the
transmission of nerve
impulses and muscle
contraction.
• Helps maintain the
correct concentration of
body fluids.
• Muscular cramps.
Fluorine (F)
Fluoridated tap
water, fluoride
toothpaste.
• Strengthens tooth
enamel, making it more
resistant to decay.
• Teeth decay more rapidly
than normal.
-​ Results of Mineral Surplus: Minerals can become harmful when consumed in excess,
especially through supplements.
-​ Surplus of calcium:
●​ Can cause calcification of soft tissues, especially in the kidneys and blood vessels.
●​ May lead to the development of kidney stones.
-​ Surplus of sodium:
●​ Raises blood pressure, leading to hypertension.
●​ Causes the body to retain fluid, which may lead to kidney damage.
-​ Surplus of iron:
●​ Can lead to liver damage.
Water
-​ Water is an essential inorganic compound. The human body is about 65% water.
-​ Functions of water:
●​ Dissolves chemicals in cells for reactions to occur.
●​ Dissolves substances so they can be transported around the body (e.g., products of
digestion in blood plasma).
●​ Dissolves waste substances for excretion (e.g., urine).
●​ Acts as a reactant in hydrolysis during digestion.
●​ Acts as a coolant, removing heat through evaporation of sweat.
-​
-​
-​
-​
-​
-​
-​
-​
-​
-​
Roughage (Dietary Fibre)
Food that cannot be digested.
Mainly consists of cellulose from plant cell walls, lignin, husk of brown rice, and bran of
whole-grain cereals.
Adds bulk to food, stimulating peristalsis (movement of food through the digestive
system).
Helps prevent constipation.
Reduces the risk of colon cancer.
Energy Requirements
Daily energy requirements depend on age, occupation, and gender (sex).
Increase as age increases up to adulthood, then remain fairly constant before decreasing
in old age.
Increase with activity level, e.g., a manual labourer needs more energy than an office
worker.
Higher in males than females of the same age and occupation.
Increase in females during pregnancy or breastfeeding.
Malnutrition
-​ Malnutrition Occurs when a person’s diet lacks or has an excess of nutrients.
-​ It Can lead to serious conditions.
Obesity
-​ Excess accumulation of fat.
-​ Caused by consuming energy-rich foods high in sugar/fat and lack of physical activity.
-​ Increases the risk of hypertension, heart disease, stroke, diabetes, osteoarthritis, and
certain cancers.
Anorexia
-​ A mental health condition where a person keeps their body weight extremely low by
eating very little, vomiting, using laxatives, and excessive exercise.
-​ Primarily affects girls and young women and can lead to death.
Bulimia
-​ A cycle of binge eating followed by purging (vomiting or taking laxatives).
-​ Affects a person’s weight and health.
Protein-Energy Malnutrition (PEM)
-​ Caused by inadequate intake of protein and energy-rich foods.
-​ Includes:
-​ Kwashiorkor: Severe protein shortage. Symptoms: muscle loss, stunted growth, swollen
abdomen/legs, skin/hair changes, liver fat accumulation.
-​ Marasmus: Severe protein and energy shortage. Symptoms: extreme weight loss, visible
ribs/shoulders, thin arms/legs, dry skin, brittle hair.
Body Mass Index (BMI)
-​ BMI is an indicator of body fat.
-​ It compares a person’s mass (weight) to their height using the formula:
-​ BMI (kg/m²) = Body mass (in kilograms) ÷ Height (in meters)²
-​ It helps determine whether a person is underweight, normal weight, overweight, or obese.
RESPIRATION
-​ Respiration is the process by which energy is released from food by living cells
-​ Each reaction is catalyzed by a specific enzyme.
-​ Respiration releases energy from glucose and this energy is used to convert ADP
(adenosine diphosphate) into ATP (adenosine triphosphate).
-​ Some energy is also released as heat.
-​ ATP efficiently transfers energy from respiration to energy-consuming processes in cells.
-​ It diffuses easily through the cell.
-​ It readily breaks down to ADP, releasing energy for cellular activities.
-​ Aerobic Respiration is a chemical process that uses oxygen to convert glucose into
energy, carbon dioxide, and water.
-​ Occurs in the mitochondria of the cell
-​
-​
-​
-​
Anaerobic respiration is a process that produces energy without oxygen
Occurs in the cytoplasm of the cell
It's a backup process that cells use when they can't get enough oxygen.
For eg. During hard exercise, not enough oxygen may reach the muscles for aerobic
respiration to supply all the energy needed. Muscle tissue therefore respires anaerobically
so that there is enough energy released.
-​ Some glucose is broken down to lactic acid. The extra oxygen absorbed after exercise is
used to respire the lactic acid.
-​ Oxygen consumption does not return to resting levels immediately after the exercise
finishes. Oxygen is required to repay an oxygen debt.
-​
-​
-​
-​
Anaerobic Respiration In Muscles:
Produces much less energy than aerobic respiration.
Waste product: lactic acid, which builds up in muscles.
Causes pain, tiredness, and cramp.
Lactic acid is broken down only when aerobic respiration resumes.
Anaerobic Respiration In Microorganisms:
-​ Occurs in microorganisms like bacteria to release energy from glucose.
-​ Yeast (unicellular fungi) undergoes fermentation (a type of anaerobic respiration).
-​ Equation for fermentation:
Anaerobic respiration in bacteria:
-​ Some bacteria obtain energy by breaking down organic waste
-​ Manure and garden waster under anaerobic respiration produce biogas.
-​ Biogas is a mixture of app. 60% methane (𝐶𝐻4), 40% carbon dioxide and traces of other
contaminant gases such as hydrogen sulfide (𝐻2𝑆)
-​ Gaseous exchange is the process by which oxygen diffuses into an organism, and carbon
dioxide is diffused out of an organism, through a gaseous exchange surface.
-​ Breathing refers to the movements in animals that bring oxygen to a gaseous exchange
surface and removes carbon dioxide from the surface
-​ Breathing and gaseous exchange are essential to organisms that respire aerobically:
●​ To ensure they have a continual supply of oxygen to meet the demands of aerobic
respiration.
●​ To ensure that the carbon dioxide produced in respiration is continually removed
so that it does not build up and poison cells.
Gaseous Exchange in humans
-​ Gaseous exchange occurs in the lungs of humans.
-​ Lungs are composed of:
●​ Thousands of air passages called bronchioles.
●​ Millions of swollen air sacs called alveoli.
-​ Each lung is surrounded by:
●​ two pleural membranes which have pleural fluid present between them.
●​ a single bronchus leads into each lung from the trachea.
-​ Blood supply to and from the lungs:
●​ Pulmonary artery carries blood from the heart to the lungs.
●​ Pulmonary vein carries blood from the lungs back to the heart.
-​ The lungs are surrounded by ribs, forming the chest cavity (thorax).
-​ Intercostal muscles are located between the ribs.
-​ The diaphragm is a dome-shaped sheet of muscle that stretches across the floor of the
thorax.
-​ Movements(Contraction and relaxation) of the ribs and diaphragm allow breathing by
causing air to move in and out of the lungs.
Structure of the human respiratory system
Parts of
the
Respiratory System
-​ Nose & Mouth: Air can enter the body through either nose or mouth.
●​ It is better to breathe through the nose because the structure allows the air to
become warm, moist and filtered before it gets to the lungs.
-​ The respiratory tract is lined with a thin layer of cells.
●​ Some of these cells, called goblet cells, produce mucus.
●​ It also has cells that have tiny hair-like projections called cilia.
●​ The cilia move back and forth to trap dust and bacteria.
●​ The dust and bacteria gets trapped in the cilia and mucus, and is pushed towards
the throat so that it can be swallowed.
-​ Trachea: From the nose or mouth, the air passes into the windpipe.
●​ The trachea is reinforced by rings of C- shaped cartilage and conveys air to and
from the lungs.
●​ The trachea branches into two bronchi (one to each lungs).
-​ The bronchi splits into smaller and smaller tubes called bronchioles.
●​ At the end of each bronchiole, there are many air sacs or alveoli. This is where
gas exchange takes place.
Surface view of a cluster of alveoli showing the blood supply
-​ The walls of the alveoli from the gaseous exchange surface.
-​ Each alveolus:
●​ Has a wall that is one cell thick.
●​ Is lined with moisture.
●​ Is surrounded by a network of capillaries
-​ During inhalation, air is drawn into the body.
-​ In the nasal passages:
●​ Air is warm.
●​ Air is cleaned and moistened by mucus lining the nasal passages and trachea.
-​ Mucus movement:
●​ Cilia (microscopic hairs) line the nasal passages and trachea.
●​ Cilia moves the mucus to the throat.
●​ Mucus is then swallowed.
-​ Air pathway:
●​ Air passes through the bronchi.
●​ Air moves through the bronchioles.
●​ Air enters the alveoli.
-​ Gaseous exchange occurs in the alveoli: Exchange happens between the air in the alveoli
and the blood in the capillaries.
-​ Gaseous exchange in flowering plants occurs in Leaves, Stems and Roots
-​ Exchange happens by direct diffusion between intercellular air spaces and all cells in
the organs that are in contact with the air spaces.
-​ Gases diffuse between the atmosphere and air spaces through:
●​ Stomata in leaves
●​ Lenticels in bark-covered stems and roots
-​ Lenticels are small areas of loosely packed cells.
-​ Gaseous exchange surfaces include walls and membranes of all cells in leaves, stems,
and roots
-​ The direction of gas movement depends on whether the plant organ is carrying out
photosynthesis.
-​ Gaseous exchange in photosynthesising organs (mainly leaves) depends on the time of
day.
-​ Rate of respiration remains almost constant throughout the day and night.
-​ Rate of photosynthesis changes depending on light availability.
-​ At Night:
●​ Only respiration occurs.
●​ Oxygen diffuses in and Carbon dioxide diffuses out.
-​ At Dawn:
●​ Photosynthesis begins and gradually increases.
●​ The compensation point is reached when the rate of photosynthesis equals the rate
of respiration.
●​ Here no net movement of gases in or out of leaves.
-​ During the Day:
●​ Photosynthesis rate is greater than the respiration rate.
●​ Carbon dioxide diffuses in and Oxygen diffuses out.
-​ At Dusk:
●​ A second compensation point occurs.
●​ Rates of photosynthesis and respiration become equal once more.
-​ Gaseous exchange in non-photosynthesising organs (e.g., stems and roots):
●​ Only respiration occurs.
●​ Oxygen diffuses in and Carbon dioxide diffuses out at all times.
-​
-​
-​
-​
-​
Gaseous exchange in fish occurs in the gills.
A bony fish has four gills on each side of its head.
Each gill has two rows of long, thin, finger-like projections called gill lamellae.
The walls of the gill lamellae form the gaseous exchange surface
Each gill lamella:
●​ Has a wall that is one cell thick.
●​ Is moist due to water passing over it as the fish breathes.
●​ Contains a dense network of capillaries down the centre.
-​ Gaseous Exchange Surfaces form part of the respiratory system in many animals.
-​ Adaptations of Gaseous Exchange Surface for efficient gas exchange:
●​ Large surface area for exchanging large quantities of gases.
●​ Very thin for rapid diffusion of gases.
●​ Moist surface to allow gases to dissolve before diffusing.
●​ Rich blood supply (in organisms with blood) for quick transport of gases between
the surface and body cells.
Factors Affecting the Breathing Rate:
Normal Breathing Rate:
-​ For a healthy adult at rest: 12 to 16 breaths per minute.
-​ Controlled by the medulla of the brain, which detects carbon dioxide levels in the blood
and sends impulses to the intercostal muscles and diaphragm.
Factors that Increase Breathing Rate:
-​ Carrying out exercise.
-​ Taking stimulant drugs (e.g., caffeine, amphetamines, cocaine).
-​ Smoking cigarettes.
-​ Suffering from anxiety or fear.
-​ Being exposed to certain environmental factors (e.g., being in a confined space or
polluted air).
-​ Being at high altitude.
-​ Being overweight.
Factors that Decrease Breathing Rate:
-​ When resting or asleep.
-​ Taking depressant drugs (e.g., sedatives, sleeping pills, alcohol).
-​ Being exposed to certain environmental factors (e.g., being in fresh, unpolluted air).
Lung Capacities and Volumes
Vital Capacity
-​ Vital Capacity is the maximum volume of air that can be exhaled from the lungs after
inhaling as deeply as possible.
-​ Uses: Measuring vital capacity can help indicate lung function and identify lung diseases.
-​ Factors Affecting Vital Capacity: Age, Gender, Body size, Fitness
-​ Effects on Vital Capacity:
●​ Increased by: Regular exercise.
●​ Decreased by: Smoking, obesity, or respiratory disease.
-​ Total lung capacity- volume of air in the lungs after maximum inhalation
-​ Tidal volume- volume of air inhaled and exhaled in a single normal breath
-​ Residual volume- volume of air remaining in the lungs after forceful exhalation
Effects of smoking Cigarettes
-​ Cigarette smoke contains several thousand chemicals, including, Nicotine, Tar and
Carbon monoxide
Nicotine Addiction
-​ Nicotine is highly addictive, leading to Increased smoking and Difficulty in quitting.
-​ Toxic effects of nicotine:
●​ Decreased appetite.
●​ Increased heart rate and blood pressure hence a higher risk of stroke and
osteoporosis.
Reduced Oxygen Carrying Capacity of Blood
-​ Carbon monoxide binds more readily with haemoglobin than oxygen.
-​ This results in:
●​ Reduced oxygen supply to body cells.
●​ Decreased respiration and exercise ability.
●​ In pregnant women, oxygen deprivation of the fetus, affecting growth and
development.
Persistent Cough
-​ Cigarette smoke increases mucus production.
-​ This Causes cilia to stop beating and leads to persistent coughing to remove excess
mucus.
Chronic Bronchitis
-​ This is caused by:
●​ Irritation and inflammation of the bronchi and bronchioles by cigarette smoke.
●​ Increased mucus production.
-​ Which results in obstructed airways and difficulty in breathing.
Emphysema
-​ Effects of cigarette smoke:
●​ Reduced elasticity of alveolar walls.
●​ Breakdown of walls between alveoli, decreasing surface area.
-​ Results in:
●​ Reduced gaseous exchange.
●​ Difficulty exhaling, with trapped air in lungs.
●​ Bronchioles may collapse when exhaling, further obstructing airways.
-​ Chronic bronchitis and emphysema are two types of Chronic Obstructive Pulmonary
Disease (COPD).
Cancer (Mouth, Throat, Oesophagus, Lungs)
-​ Tar and about 60 other carcinogenic chemicals in cigarette smoke cause cancerous tumors
in the respiratory system.
-​ The tumors replace normal, healthy tissue.
Effects of Smoking Marijuana
-​ Marijuana is one of the most widely used illegal drugs worldwide.
-​ Usually smoked, leading to similar health risks as tobacco, including:
Persistent Cough
-​ Caused by irritation of the respiratory tract.
Bronchitis
-​ Inflammation of the bronchial tubes.
Frequent Acute Lung Infections
-​ Due to marijuana reducing the body’s ability to fight infection.
Lung Cancer
-​ Increased risk due to inhalation of carcinogenic substances.
Marijuana Addiction
-​ Long-term use can lead to dependency and addiction.
LIFE PROCESSES CONT'D
TRANSPORT SYSTEMS
Unicellular Organisms (e.g., Amoeba):
-​ It is very small with a large surface area to volume ratio.
-​ Diffusion through the body surface is adequate for Taking in requirements (e.g., oxygen)
and Removing waste (e.g., carbon dioxide).
-​ No part of the body is far from the surface hence substances can move short distances by
diffusion.
-​ No transport system needed to carry substances around the body.
Large Multicellular Organisms:
-​ Have a small surface area to volume ratio.
-​ Diffusion through their body surface is not adequate to supply body cells with
requirements and remove waste.
-​ In these organisms Transport systems are developed:
●​ To carry useful substances from specialized absorption organs to body cells:
➢​ e.g., Lungs (for oxygen)
➢​ e.g., Ileum (for nutrients)
●​ Carry waste substances from body cells to specialised excretory organs:
➢​ e.g., Kidneys (for waste removal)
The circulatory system in humans
-​ Components of the Circulatory System:
Blood: Serves as the medium to transport substances (e.g., oxygen, nutrients, waste)
around the body.
-​ Blood Vessels: Tubes through which blood flows to and from all parts of the body.
-​ Heart: Pumps the blood through the blood vessels, ensuring circulation throughout the
body.
The Heart
-​ The pumping action of the heart maintains constant circulation of blood around the body.
-​ The heart is composed of cardiac muscle, which has its own inherent rhythm and does not
get tired.
-​ The heart is divided into four chambers:
●​ Two right chambers contain deoxygenated blood.
●​ Two left chambers contain oxygenated blood.
-​ The right and left sides are separated by the septum.
-​ Atria (Top Chambers):
●​ Thin walls.
●​ Function: Collect blood entering the heart.
-​ Ventricles (Bottom Chambers):
●​ Thick walls.
●​ Function: Pump blood out of the heart.
-​ Valves:
●​ Valves are located between:
➢​ Each atrium and ventricle
➢​ The pulmonary artery and aorta as they leave the ventricles.
●​ Function of valves: Ensure that blood flows through the heart in one direction.
Cardiac Cycle
-​ The atria and ventricles on both sides of the heart contract and relax together in a
coordinated cycle.
-​ The cycle consists of the following phases:
-​ Diastole (Relaxation Phase):
-​ Atrial Systole (Atria Contraction):
●​ Duration: 0.4 seconds.
●​ Duration: 0.1 seconds.
●​ The atria and ventricles relax
●​ The atria contract, forcing
together.
any remaining blood into the
●​ Semilunar valves close.
ventricles.
●​ Blood fills the atria from the
-​ Ventricular Systole (Ventricles
anterior and posterior vena
Contraction):
cava and pulmonary vein.
●​ Duration: 0.3 seconds.
●​ Blood flows into the
●​ The ventricles contract.
ventricles.
●​ Tricuspid and bicuspid valves
close.
●​ Blood is forced into the
pulmonary artery and aorta
-​
The heartbeats on average 75 times per minute.
-​ This rate is maintained by a group of specialised cardiac muscle cells in the right atrium
called the pacemaker.
-​ The pacemaker can modify the heart rate in response to nerve impulses, e.g., the rate
increases during exercise.
-​ Humans have a double circulation, meaning blood flows through the heart twice during
one complete circulation around the body.
Pulmonary Circulation:
-​
-​
-​
Blood travels from the right ventricle through
the pulmonary artery to the lungs.
In the lungs, blood picks up oxygen and loses
carbon dioxide (blood becomes oxygenated).
The oxygenated blood then returns via the
pulmonary vein to the left atrium.
Systemic (Body) Circulation:
-​
-​
-​
Blood travels from the left ventricle through the
aorta to the body.
In the body, blood delivers oxygen to the body
cells and picks up carbon dioxide (blood
becomes deoxygenated).
The deoxygenated blood then returns via the
anterior or posterior vena cava to the right atrium.
-​ Why Double Circulation is Necessary:
-​ Blood pressure loss in the lungs: Blood loses pressure as it passes through the lungs, so
it returns to the heart to be pumped with enough pressure to reach the body organs.
-​ Blood pressure loss in body organs: As blood passes through body organs, it loses
pressure again. It returns to the heart to be pumped with enough pressure to reach the
lungs to remove waste carbon dioxide and pick up oxygen.
Blood Vessels
Arteries:
-​ Function: Carry blood away from the heart.
-​ Pathway:
●​ On entering an organ, an artery branches into smaller arteries called arterioles.
●​ Arterioles further branch into a network of capillaries that run throughout the
organ.
Capillaries:
-​ Function: Exchange of substances between blood and body cells.
-​ Pathway:
●​ Capillaries join into small veins called venules.
Veins:
-​ Function: Carry blood back towards the heart.
-​ Pathway:
●​ Venules join to form a single vein that leads back from the organ to the heart.
Blood
-​ Blood is composed of three types of cells:
●​ Red blood cells
●​ White blood cells
●​ Platelets. Hi percival-shane
-​ These cells are suspended in a fluid called plasma.
-​ Plasma is a yellowish fluid composed of about 90% water and 10% dissolved substances.
-​ The Dissolved Substances:
●​ Products of Digestion: e.g., glucose, amino acids, vitamins, and minerals.
●​ Waste Products: e.g., carbon dioxide as the hydrogen carbonate ion (HCO₃⁻) and
urea.
●​ Hormones: e.g., insulin, thyroxine.
●​ Plasma Proteins: e.g., fibrinogen, albumen, and antibodies.
Functions of Plasma:
-​ Transporting Products of Digestion: From the ileum to the liver and body cells.
-​ Transporting Carbon Dioxide (HCO₃⁻ ion): From body cells to the lungs.
-​ Transporting Urea: From the liver to the kidneys.
-​ Transporting Hormones: From the endocrine glands to target organs.
-​ Transporting Heat: From the liver and muscles to all parts of the body.
Blood Groups
-​ Blood can be classified into different groups based on antigens present on the surface of
red blood cells.
-​ There are two main grouping systems:
●​ The ABO system which divides blood into four groups: group A, group B, group
AB and group O.
●​ The rhesus system which divides blood into two groups: rhesus positive and
rhesus negative
Causes of Heart Attacks:
-​ Atherosclerosis: Fatty deposits (atheromas) containing cholesterol build up inside the
walls of coronary arteries, narrowing the arteries and making them less elastic.
-​ Coronary Thrombosis: A blood clot forms in a narrowed artery, partially or completely
blocking blood flow to the heart, causing heart muscle to die and leading to a heart attack.
Risk Factors for Heart Attack:
-​ Hypertension (high blood pressure)
-​ Being overweight or obese
-​ Smoking
-​ Excessive salt or fat in the diet
-​ Excessive alcohol consumption
-​ Lack of physical exercise
-​ Stress
Symptoms of a Heart Attack:
-​ Chest pain or discomfort (feeling like pressure or squeezing)
-​ Upper body pain (arms, shoulders, neck, jaw, or back)
-​ Shortness of breath
-​ Feeling weak, lightheaded, or dizzy
-​ Cardiac arrest: In some cases, the heart stops beating, which can lead to death.
Clot Formation:
-​ When the skin is cut, platelets are exposed to air.
-​ They become sticky and clump together to plug the wound.
-​ Platelets release an enzyme called thromboplastin.
-​ Thromboplastin, with the help of calcium ions and vitamin K in the blood, starts a series
of chemical reactions.
-​ These reactions convert the soluble plasma protein called fibrinogen into insoluble fibrin.
-​ Fibrin forms a meshwork of threads over the wound.
-​ As the blood flows out, erythrocytes & platelets are trapped in the fibrin fibers and a
blood clot forms.
-​ It dries to form a scab
-​ When the wound heals, new skin is formed & the scab peels off.
-​ Why is blood clotting necessary
●​ To prevent excessive blood loss from the body when there is damage of the blood
vessel
●​ Maintain blood pressure to ensure proper blood circulation
●​ Prevent the entry of microorganisms and foreign particles into the body through
the wound
●​ Promote wound healing
Consequences of an Impaired Blood Clotting Mechanism
Haemophilia
-​ A hereditary disease.
-​ Caused by the lack of a gene for producing certain clotting factors (e.g., Factor VIII).
-​ Results in an impaired clotting mechanism.
-​ Causes serious bleeding, especially in the joints.
-​ Even minor cuts and bruises can lead to excessive bleeding.
-​ Blood clotting cannot take place, which can be fatal.
Thrombosis
-​ A local blood clot (thrombus) forms on a damaged or rough inner artery wall (e.g.,
cholesterol deposition).
-​ This clot can block the artery, causing thrombosis.
-​ If the thrombus dislodges, it becomes an embolus.
-​ The embolus can travel through blood circulation.
-​ If trapped in a small artery, it blocks blood flow, causing embolism.
-​ If thrombosis occurs in a coronary artery, oxygen and nutrient supply to heart muscles is
cut off, leading to a heart attack.
External Defense System
Internal Defense System- Immunity
-​ Immunity is the body’s resistance to a specific condition or diseases
-​ Immunity may last for short periods or long term.
-​ The body’s immune response is its reaction to being invaded by specific foreign
materials, such as viruses, bacteria, toxins or other unrecognized proteins.
-​ Substances which can cause an immune response are called an antigen.
-​ When antigens come into contact with pathogens, they stimulate the lymphocytes to
produce antibodies which begin the process of destruction.
-​ The antibodies bind to the targeted antigens, cause the pathogens to clump together then
destroy them.
-​ The Phagocytes complete the job by engulfing the foreign substances, such as bacteria,
digesting and killing them.
Role of Phagocytes
-​ Phagocytes leave the blood by squeezing between capillary wall cells into tissues.
-​ If tissues are infected by many pathogens (e.g., in a cut, wound, or inside the body), the
inflammatory response is triggered.
-​ Blood vessels at the infection site dilate, increasing blood flow to the area.
-​ This response causes swelling and redness.
-​ More phagocytes are brought to the site of infection.
-​ Capillary wall permeability increases, allowing phagocytes to squeeze out into tissues
easily.
-​ Antigens are specific to the type of pathogen and are foreign to all other organisms.
-​ When a pathogen enters the body, lymphocytes make specific antibodies in response to
the pathogen’s specific antigen.
-​ Antibodies can:
●​ Cause the pathogens to clump together so that the phagocytes can engulf them
●​ Cause the pathogens to disintegrate, or
●​ Neutralize the toxins produced by the pathogens
-​ Antibodies that neutralize toxin are called antitoxins
Natural Immunity
-​ Natural immunity
results from a person
having been exposed to
a pathogenic disease
caused by a virus or
bacterium.
-​ Production of
antibodies takes time.
-​ Pathogens produce
symptoms before being
destroyed or having
their toxins neutralized.
-​ After recovery, antibodies gradually disappear from the blood.
-​ Some lymphocytes develop into lymphocyte memory cells that remember the specific
antigen.
-​ If the pathogen re-enters the body, memory lymphocytes recognize the antigen.
-​ They multiply and quickly produce large quantities of the specific antibody.
-​ The pathogen is destroyed or its toxins are neutralized before disease symptoms develop.
-​ The person becomes immune to the disease.
-​ Immunization is the process of protecting a person from a disease by giving them a
substance, by mouth or injection, that provides artificial immunity.
-​ Artificial immunity is acquired by vaccination and is used to control the spread of
communicable diseases, i.e. diseases that pass from person to person.
-​ A vaccine is a substance that is injected or swallowed stimulates the body’s immune
system
-​ Vaccines are made from:
●​ Dead microorganisms (e.g., whooping cough, cholera, influenza, and polio
vaccines).
●​ Weakened (attenuated) live pathogens that are harmless (e.g., tuberculosis,
measles, mumps, and rubella vaccines).
●​ Toxins from the pathogen that have been made harmless (e.g., diphtheria and
tetanus vaccines).
●​ Fragments of the pathogen (e.g., influenza vaccine).
●​ Specific antigens (proteins) from the pathogen's coat produced by genetic
engineering (e.g., hepatitis B vaccine).
●​ Ready-made antibodies produced by other organisms, injected into a sick
person.
Active Immunity
-​ Results from exposure to a disease organism, triggering the immune system to produce
antibodies.
-​ Occurs through:
●​ Natural immunity: Infection with the actual disease.
●​ Vaccine-induced immunity: Introduction of a killed or weakened form of the
disease organism through vaccination.
-​ If exposed to the disease in the future, the immune system recognizes it and quickly
produces antibodies.
-​ Long-lasting and sometimes life-long immunity.
-​ Occurs through direct infection or vaccination.
Passive Immunity
-​ Provided when a person is given antibodies rather than producing them through their own
immune system.
-​ Occurs through:
●​ Mother to baby via the placenta.
●​ Breast milk from the mother.
●​ Antibody-containing blood products (e.g., immune globulin) for immediate
protection.
-​ Immediate protection is provided, unlike active immunity which takes weeks to develop.
-​ Short-lived immunity, lasting only a few weeks or months.
-​ Occurs through breast milk, placenta, and vaccination.
The Lymphatic System
The lymphatic system consists of:
-​ Lymph, which serves as the transporting medium.
-​ Lymph vessels or lymphatic vessels, which are tubes through which lymph flows.
-​ Lymph vessels begin inside tissues.
-​ They have thin muscular walls, valves to prevent the backflow of low pressure lymph,
and oval-shaped swellings along their length called lymph nodes or lymph glands.
-​ Lymph nodes form clusters in various parts of the body, especially in the neck, armpits,
and groin.
-​ Lymphocytes and phagocytes are numerous in lymph nodes.
-​ Lymph is a colourless watery fluid that contains lymphocytes. It is formed in body tissues
from tissue fluid, which is constantly being formed from plasma.
-​ Lymph rejoins the plasma in the subclavian veins from the arms just before they join the
anterior vena cava.
-​ Lymph flows in one direction from tissues toward the heart, and its flow is helped by the
contraction of surrounding muscles, especially during exercise.
Functions of the lymphatic system:
-​ Functions of lymph:
●​ Lymph removes cellular waste and cell debris from around body cells.
●​ Lymph drains excess tissue fluid from tissues, which helps to prevent fluid from
building up in them.
●​ Lymph helps maintain normal blood volume and pressure.
●​ Lymphocytes in lymph defend the body against pathogens.
●​ Lymph in the lacteals (lymph capillaries) in the ileum absorbs fatty products of
digestion.
-​ Functions of lymph nodes:
●​ Lymphocytes and phagocytes in lymph nodes help destroy pathogens in lymph.
●​ Lymph nodes filter dead cells and cancerous cells out of lymph.
●​ Lymph nodes release lymphocytes into lymph during times of infection.
Transport systems in flowering plants
-​ Substances are transported around plants by vascular tissue composed of xylem and
phloem
The Xylem
-​ The xylem transports water and soluble mineral nutrients from the roots throughout the
plant.
-​ Made of dead tissue and is hallow:
●​ Thick, lignified walls
●​ No organelles
-​ Occupy center of vascular bundle.
-​ Water flows unidirectional (upwards) and is driven by transpiration.
-​
-​
-​
-​
-​
-​
-​
-​
Xylem vessels transport water from roots to leaves for photosynthesis.
They are long, narrow, hollow tubes that are non-living.
Formed from columns of elongated cells whose contents die.
Cross walls between adjacent cells break down, allowing continuous water flow.
Cellulose walls become thickened with lignin in rings, spirals, or a net-like pattern.
Lignin provides toughness and strength, helping to support the plant.
Being long, narrow, and hollow with no cross walls, they allow continuous water flow.
Wood is almost entirely composed of lignified xylem vessels
The Phloem:
-​ The phloem transports sugars, amino acids and other foods.
-​ Made of living cells and located on the outer edges of the vascular bundle.
-​ Contains sieve tubes, companion cells, and phloem parenchyma cells.
-​ Moves substances up and down the stem via active transport which requires energy.
-​ Water moves through a flowering plant by a combination of:
●​ root pressure
●​ transpiration
●​ capillarity
Transpiration
-​ Transpiration is the process of water movement through a plant and its evaporation from
leaves.
-​ Water is necessary for plants but only a small amount of water taken up by the roots is
used for growth and metabolism.
-​ The remaining 97–99.5% is lost by transpiration and guttation.
Transpiration Process
-​ Cohesion: Water molecules stick together.
-​ Evaporation of water from leaf cells creates a pull on the water between cells.
-​ Water moves from the xylem in leaf veins to replace the evaporated water.
-​ The pulling effect of evaporation is transmitted through the xylem in the stem down to
the roots, forming a transpiration stream.
-​ Transpiration pull moves columns of water under tension.
-​ On hot, dry, sunny days, water loss is faster than absorption from the soil.
➢​ This creates high tension, sometimes pulling the trunks of large trees inward.
-​ Root hair cells absorb water by osmosis from the soil.
➢​ Water passes through the fully permeable cell wall and differentially permeable
cell membrane into root hair cells and epidermal cells
➢​ Water then moves across the root tissue(cortex cells) into the xylem.
Mechanism of the movement of water through a flowering plant
Opening and closing of stomata
Factors Affecting Transpiration
Temperature
-​ Plants transpire more rapidly at higher temperatures because
water evaporates more rapidly as the temperature rises.
Light
-​ Plants transpire more rapidly in the light than in the dark.
-​ This is largely because light stimulates the opening of the
stomata.
-​ Light also speeds up transpiration by warming the leaf.
Wind
-​ In windy conditions, water vapour is carried away from the
surface of leaves so more can diffuse outand transpiration is
rapid.
-​ In still conditions, water vapour remains around the leaves and
very little more can diffuse out so transpiration is slow
Humidity
-​ In low humidity, the concentration gradient between the water
vapour in the air spaces in leaves and the air surrounding the
leaves is high, so water vapour diffuses out easily and
transpiration is rapid.
-​ In high humidity, the air surrounding the leaves is almost
saturated with water vapour so the concentration gradient is low
and very little more can diffuse out causing transpiration to be
slow
-​ Transpiration is important to plants for the following reasons:
●​ It draws water up to leaves for use in photosynthesis.
●​ It supplies plant cells with water to keep them turgid. This supports non-woody
stems and leaves
●​ Moving water carries dissolved mineral salts up to the leaves.
●​ Evaporation of water from the surface of leaves cools the plant.
Methods and Adaptations by which plants conserve water
-​ Deep roots that extend to great depths
-​ Extensive, shallow roots that cover a wide area
-​ Thick leaves and/or stems to store water
-​ Leaves have extra-thick waxy cuticles.
-​ Leaves have reduced numbers of stomata
-​ Stomata are grouped together in sunken pits that trap water vapour, e.g.oleander.
-​ Stomata almost close in the daytime if temperatures are very high and open at night.
-​ Leaves can roll with the stomata to the inside, e.g. marram grass
-​ Leaves have fine hairs on their surface that trap water vapour.
-​ The surface area of leaves is reduced, e.g. needle-shaped leaves of conifers,spines of cacti
and scales of casuarina.
-​ Leaves are shed in the dry season or winter months
Movement of organic food through a flowering plant
-​ Phloem Sieve Tubes transport organic food (mainly sucrose and some amino acids) from
leaves to all other parts of the plant.
-​ They consist of long, narrow tubes formed
from columns of elongated cells.
-​ Cross walls between adjacent cells become
perforated to form sieve plates.
-​ Each cell is called a sieve tube element and
contains living cytoplasm but no nucleus.
-​ Cytoplasm of adjacent sieve tube elements is
connected through the holes in the sieve
plates.
-​ Companion cells are located next to each
sieve tube element and contain a nucleus.
-​ The nucleus of the companion cell controls
the functioning of both the sieve tube element
and itself.
-​ Movement of organic food through phloem sieve tubes is called translocation.
Mechanism of Translocation
-​ The pressure flow hypothesis helps to explain how dissolved sugars move through the
phloem
-​ The hypothesis states that sugars flow from a sugar source to a sugar sink
-​ A pressure gradient is created between the source and the sink, causing the contents of
the phloem sieve tubes to move both upwards and downwards.
-​ Sugar Sources include parts of plants that produce sugars or release stored sugars:
●​ Photosynthesising leaves – produce sugars.
●​ Storage organs – release sugars at the beginning of the growing season.
●​ Cotyledons of seeds – release sugars at the beginning of germination (stored
starch is hydrolysed to sugars).
-​ Sugar Sinks include parts of plants that require sugars:
●​ Stems, roots, fruits, storage organs, and growing parts.
-​ Sugars in sugar sinks may be:
●​ Used in respiration.
●​ Stored as starch.
●​ Converted to other substances for growth, e.g. proteins.
Movement of Mineral Salts Through a Flowering Plant
-​ Mineral salts are absorbed by roots in the form of ions.
-​ Ions are dissolved in the water present in the soil.
-​ Absorption occurs through root hairs by active transport against a concentration
gradient.
-​ After absorption:
●​ Ions move through the cortex cells.
●​ They then enter the xylem vessels dissolved in the moving water.
●​ Ions are carried throughout the plant dissolved in the water within the xylem
vessels.
Storage of Food in Living Organisms
Importance of Food Storage
-​ Ensures Availability of Food for Future Use:
●​ Food that is not needed immediately is stored for future needs.
-​ Overcomes the Need for Continuous Food Intake or Manufacture:
●​ In heterotrophs – reduces the need for continuous food intake.
●​ In autotrophs – reduces the need for continuous food manufacture.
-​ Provides Food Reserves During Periods of Scarcity:
●​ In heterotrophs – essential during food scarcity periods, e.g., winter in temperate
climates.
●​ In autotrophs – useful when food manufacture is not possible, e.g., during drought
or low temperatures.
➢​ Enables hibernation in animals.
➢​ Supports survival of plants through dry seasons or winter months.
-​ Supports Special Functions:
●​ Required for the production of sexual or vegetative reproductive structures.
●​ Supports embryo development:
➢​ Seeds of plants and eggs of animals store food for the growing embryos.
➢​ New plants utilize stored food as they develop from vegetative organs.
Storage Forms and Benefits
-​ Soluble Food Substances (e.g., glucose, amino acids, fatty acids, glycerol) are condensed
into insoluble storage substances such as:
●​ Starch and glycogen (carbohydrates).
●​ Protein.
●​ Lipid.
-​ Advantages of Storing Insoluble Substances:
●​ Do not interfere with osmosis and other cellular processes.
●​ Can be hydrolysed back into soluble substances when needed.
Storage of Food in Animals
-​ Glycogen and fat are the primary storage forms of food in animals.
-​ Protein is not stored in animals.
-​ Storage in Adipose Tissue
●​ Excess fat is stored in fat cells within adipose tissue.
●​ Adipose tissue is located under the skin and around organs.
●​ Excess glucose can also be converted into fat and stored in adipose tissue.
-​ Storage in the Liver. The liver stores:
●​ Glycogen – Formed by the condensation of excess glucose in the blood.
●​ Vitamins – Specifically A, B12, and D.
●​ Iron – Obtained from the breakdown of haemoglobin in red blood cells.
-​ Storage in Skeletal Muscle
-​ Skeletal muscles store glycogen formed from the condensation of excess glucose in the
blood.
-​ Muscle cells can convert stored glycogen back to glucose for use in respiration, providing
energy when needed (e.g., during exercise).S
Storage of food in Plants
-​ Food can be stored in roots, stems, leaves, fruits and seeds
-​ Phloem sieve tubes transport sugars (from photosynthesis) to storage sites.
-​ Here Sugars are either stored directly or converted into starch, oils, or proteins for
storage.
Storage in Vegetative Organs
-​ Vegetative organs are underground structures swollen with food at the end of the growing
season.
-​ Functions:
●​ Allow plants to survive unfavourable seasons (e.g., dry season, winter).
●​ Enable rapid growth at the beginning of the favourable season (e.g., rainy season,
summer).
●​ Facilitate asexual reproduction as multiple new plants can grow from one organ.
-​ Types of Vegetative Organs:
●​ Stems: Stem tubers – e.g., yam, English potato. Rhizomes – e.g., ginger.
●​ Corms – e.g., eddo.
●​ Roots: Root tubers – e.g., sweet potato.
●​ Leaves or Leaf Bases: Form bulbs – e.g., onion.
-​ Main Food Stored is Starch.
Storage in Tap-Roots
-​ Tap-roots are single, vertical roots.
-​ Food Stored:
●​ Starch – e.g., turnip.
●​ Sugars – e.g., carrot, sugar
beet.
Storage in Succulent Fruits
-​ Succulent fruits store:
●​ Sugars – e.g., mango,
paw-paw.
●​ Starch – e.g., breadfruit.
●​ Oils – e.g., avocado, olive.
-​ Function is to Attract animals to eat
the fruits, aiding in seed dispersal.
Storage in Seeds
-​ Stored in the cotyledons and
endosperm of seeds.
-​ Food Stored:
●​ Starch – e.g., rice, wheat.
●​ Protein – e.g., peas, beans.
●​ Oil – e.g., nuts.
-​ Used during seed germination.
Storage in Stems
-​ Stems of Sugar Cane:
●​ Store sucrose in the vacuoles
of cells.
●​ Stems of Succulent Plants:
●​ Store water in their cells –
e.g., cacti.
Storage in Leaves
-​ Leaves of Succulent Plants store
water in their cells – e.g., aloe.
EXCRETION
-​ Excretion is the biological process of removal of harmful nitrogenous metabolic waste
from the body.
-​ Metabolism is all the chemical and physical changes that occur in bodies.
-​ Egestion is the removal of undigested dietary fibre and other materials as faeces.
-​ These materials are not produced by the body's metabolism, so their removal is not
excretion.
Importance of Excretion in Living Organisms
-​ It is Essential because it helps regulate internal conditions such as pH, temperature, and
the concentration of water and solutes, ensuring that cells can function optimally
-​ Excretion is essential because waste products can be harmful and, if accumulated, can
damage or kill cells.
Products Excreted by Plants
-​ Oxygen (O₂)
●​ Produced during photosynthesis.
●​ Excreted during the day when the rate of photosynthesis is higher than the rate of
respiration.
-​ Carbon Dioxide (CO₂)
●​ Produced during respiration.
●​ Excreted during the night when no photosynthesis is occurring.
-​ Water (H₂O)
●​ Produced during respiration.
●​ Excreted during the night when no photosynthesis is occurring.
-​ Organic Waste Products
●​ Examples include:
➢​ Tannins
➢​ Alkaloids
➢​ Anthocyanins
➢​ Salts of organic acids (e.g., calcium oxalate)
Mechanisms of Excretion in Plants
-​ Unlike animals, plants do not have specialized excretory organs.
Excretion of Gases and Water:
-​ Oxygen (O₂), carbon dioxide (CO₂), and water vapour diffuse out of the plant through:
●​ Stomata of the leaves.
●​ Lenticels in the bark-covered stems and roots.
Excretion of Organic Waste Products:
-​ Organic waste products can be Stored in dead, permanent tissue eg. heartwood
-​ Organic waste products can be Converted into insoluble substances eg. oils and insoluble
crystals.
●​ Example: Excess calcium ions combine with oxalic acid to form calcium oxalate
crystals.
●​ These insoluble waste products do not affect osmotic or metabolic processes in
cells.
●​ They can be stored in various plant parts such as leaves, bark, petals, fruits, and
seeds.
●​ The waste products are removed when the plant sheds these structures.
Products Excreted by Animals
-​ Carbon Dioxide (CO₂): Produced during respiration.
-​ Water (H₂O): Produced during respiration.
-​ Nitrogenous Compounds: Produced by the deamination of amino acids in the liver.
●​ Urea – Less toxic compared to ammonia.
●​ Ammonia – Highly toxic.
●​ Uric Acid – Least toxic.
-​ Bile Pigments: Bilirubin is produced during the breakdown of haemoglobin from red
blood cells in the liver.
-​ Heat: Produced during general metabolism.
Excretory organs in humans
-​ Humans have several organs that excrete waste productsL:
●​ The kidneys excrete water, nitrogenous waste (mainly urea) and salts asurine
●​ The lungs excrete carbon dioxide and water vapour during exhalation
●​ The skin excretes water, urea and salts as sweat. It also excretes heat (see page
111).
●​ The liver excretes bile pigments. It also makes nitrogenous waste.
The Kidney
-​ Humans have two kidneys, part of the urinary system.
-​ Each kidney is divided into three regions:
●​ Cortex (outer region)
●​ Medulla (inner region)
●​ Pelvis (central hollow region)
-​ Blood vessels associated with each
kidney:
●​ Renal artery – Carries blood to
the kidney.
●​ Renal vein – Carries blood away from the kidney.
-​ Each kidney is composed of thousands of nephrons (kidney tubules) packed in the renal
cortex that produce urine.
The Nephron
Structure of each nephron:
-​ The glomerulus is a network of intertwined capillaries mass.
-​ Bowman’s capsule (in the cortex) is A cup-shaped structure surrounding the glomerulus.
-​ After the Bowman’s capsule, the nephron is divided into:
●​ Proximal convoluted tubule: reabsorption of nutrients and substances that the
body needs
●​ Loop of Henle: thin-lobed structure that controls the concentration of the urine
●​ Distal convoluted tubule: regulates sodium, potassium and pH
●​ Collecting duct: regulates water and sodium reabsorption.
-​ Arteriole from the renal artery leads into each glomerulus.
-​ A network of blood capillaries surrounds the nephron and leads from the glomerulus into
a venule, which joins the renal vein.
-​ Nephrons join into collecting ducts in the cortex, which lead through the medulla and into
the pelvis.
Processes of Urine Formation
Ultra-filtration (or Pressure Filtration)
-​ Occurs in the glomeruli.
-​ The diameter of the capillary entering each glomerulus from an arteriole decreases, which
increases blood pressure.
-​ This pressure forces small molecules, such as glucose, amino acids, hormones, vitamins,
water, salts, and urea, from the blood into the Bowman’s capsule, forming the filtrate.
-​ Filtrate Contains Glucose, amino acids, hormones, vitamins, water, salts and urea.
-​ Blood cells and large molecules (e.g., plasma proteins) remain in the bloodstream.
Selective Reabsorption
-​ Occurs in the nephrons.
-​ Useful substances are reabsorbed from the filtrate back into the blood via capillaries
wrapped around each nephron
-​ Glucose, amino acids, hormones, vitamins, some water, and some salts are reabsorbed in
the first convoluted tubule.
-​ Some water is reabsorbed in the Loop of Henle.
-​ Some salts and some water are reabsorbed in the second convoluted tubule.
-​ Water is reabsorbed by osmosis, while other substances are reabsorbed by diffusion and
active transport.
Formation of Urine
-​ The remaining
filtrate, containing
urea, excess water,
and excess salts,
enters the collecting
ducts.
-​ In the collecting
ducts, some water is
reabsorbed by
osmosis.
-​ The filtrate, now
called urine, travels
down the collecting
duct, through the
ureter, and into the
bladder, where it is
stored.
Renal dialysis
-​ Kidney failure occurs when nephrons cannot properly remove waste or regulate blood
plasma and body fluids.
-​ Harmful waste, especially urea, builds up in the blood, reaching toxic levels and leading
to death.
-​ Kidney failure can be treated with a kidney transplant or renal dialysis.
-​ During dialysis, blood from a vein (usually in the arm) flows through a dialysis machine
and is returned to the body.
-​ The dialysis machine separates blood from dialysis fluid using a partially permeable
membrane.
-​ Waste products (mainly urea), excess water, and salts pass from the blood into the
dialysis fluid.
-​ Dialysis removes waste and regulates the volume/composition of blood plasma and body
fluids.
-​ Dialysis is done at regular intervals, typically three sessions per week, lasting four hours
each.
The Skin
-​ The skin is the largest organ in the human body and is made up of three layers:
-​ Epidermis (outermost layer)
-​ Dermis (below the epidermis)
-​ Subcutaneous layer (bottom layer made up mainly of fat cells)
Functions of the structures of the skin:
Structure
Function
Epidermis
Protects the body against pathogens, water loss, the Sun’s harmful
ultraviolet rays, and harmful chemicals in the environment.
Sebaceous glands
Secretes sebum, an oily substance, which helps to keep the skin soft,
supple and waterproof, and inhibits the growth of bacteria.
Nerve endings
Detect various stimuli, e.g., touch, pressure, pain, temperature, and hair
movement.
Hairs and hair erector
muscles
Muscles contract causing hairs to stand upright, creating "goose
bumps" and trapping a layer of air next to the skin for insulation.
Arterioles and capillary
networks
Help regulate body temperature.
Sweat glands
Produce sweat by absorbing water, urea, and salts from the blood,
which then evaporates to cool the body if it is too hot.
Subcutaneous layer
Protects the body against heat loss in low environmental temperatures
and against damage by acting as ‘padding’.
Osmoregulation in Humans
-​ Osmoregulation is the regulation of the concentration of blood plasma and body fluids,
which is essential to prevent water from moving into or out of body cells unnecessarily.
●​ Too dilute body fluids: Water enters body cells by osmosis, causing the cells to
swell and potentially burst.
●​ Too concentrated body fluids: Water leaves body cells by osmosis, causing cells
to shrink and leading to dehydration.
-​ If too much water leaves the cells, metabolic reactions cannot take place,
and cells may die.
The Kidneys and Osmoregulation
-​ The kidneys play a vital role in regulating the concentration of body fluids by controlling
how much water is reabsorbed into the blood during selective reabsorption.
If Body Fluids Become Too Concentrated
-​ Causes: Excessive sweating, drinking too little, or eating salty foods.
-​ The hypothalamus detects the increased concentration of blood plasma.
-​ It signals the pituitary gland to release antidiuretic hormone (ADH).
-​ ADH travels through the bloodstream to the kidneys, where it makes the walls of the
second convoluted tubules and collecting ducts more permeable to water.
-​ Most of the water is reabsorbed from the filtrate back into the blood, resulting in the
production of small quantities of concentrated urine.
If Body Fluids Become Too Dilute
-​ Causes: Drinking a lot of liquid.
-​ The hypothalamus detects the lower concentration of blood plasma.
-​ The pituitary gland stops secreting ADH.
-​ Without ADH, the walls of the second convoluted tubules and collecting ducts remain
impermeable to water, so very little water is reabsorbed.
-​ This leads to the production of large quantities of dilute urine.
-​ Osmoregulation is a crucial aspect of homeostasis, ensuring that the internal environment
of the body remains stable and optimal for metabolic processes.
Regulation of body temperature:
-​ Humans must maintain a constant internal body temperature of 37°C for enzymes to
function correctly.
-​ Most heat is gained from
metabolic processes, mainly
respiration, and the blood
carries this heat around the
body.
-​ Heat is lost mainly by:
Conduction, Convection
and Radiation through the
skin
-​ Evaporation of water during
exhaling and sweating.
-​ The hypothalamus of the
brain detects changes in the
blood temperature and
sends messages to
appropriate effectors,
mainly in the skin.
-​ Note:
●​ Heat is the total amount of energy an object contains, measured in joules (J).
●​ Temperature is a measure of how hot or cold an object is, measured in degrees
Celsius (°C).
Regulation of carbon dioxide levels:
-​ Carbon dioxide reacts with water in plasma, forming carbonic acid.
-​ As carbon dioxide levels increase, the blood becomes more acidic (its pH decreases).
-​ Carbon dioxide levels must be controlled to prevent the blood from becoming too acidic
or too alkaline.
-​ Receptors, mainly in the medulla of the brain, detect changes in pH and send messages to
the intercostal muscles and diaphragm to adjust the rate and depth of breathing.
Regulation of blood sugar (glucose) levels:
-​ The normal concentration of glucose is approximately 80 mg per 100 cm³ of blood.
-​ The pancreas constantly monitors the blood glucose level and secretes two hormones to
keep the level constant:
-​ If blood glucose level rises
(e.g., after a meal rich in
carbohydrates), the pancreas
secretes insulin.
-​ Insulin stimulates body cells to
absorb glucose for respiration
and liver cells to convert excess
glucose to glycogen for storage.
-​ If blood glucose level falls
(e.g., between meals, during
exercise or sleep), the pancreas
secretes glucagon.
-​ Glucagon stimulates liver cells
to convert stored glycogen to
glucose, which then enters the
blood.
MOVEMENT
-​ Movement is a change in the position of a whole organism or of parts of an organism.
Types of Movement
-​ Growth movement is a movement displayed by a plant due to the plant growing. Shoots
grow and bend towards light while roots grow and bend downwards with the pull of
gravity
-​ Part movement is a movement displayed by part of a plant or of a sedentary animal. Part
movements include the opening and closing of petals, the‘feeding’ movements of
insectivorous plants, the folding of leaves of the sensitive plant (Mimosa) when touched,
and the movement of the tentacles of coral polyps and limbs of barnacles
-​ Locomotion is the movement of the entire body from one place to another and occurs in
animals. Locomotion is brought about by muscles contracting against a skeleton in most
animals.
Skeletal System
-​ The human skeleton is made of 206 bones, which are held together at joints by ligaments.
-​ The skeleton is made from two types of connective tissue, bone and cartilage.
-​ Bone makes up the bulk of the skeleton. It is composed of living cells surrounded by the
non-living mineral, calcium phosphate, together with some collagen (protein) fibers.
-​ Bone is hard and has blood vessels running throughout.
-​ Cartilage is composed of living cells surrounded mainly by collagen fibers. It is more
elastic and flexible than bone and does not have blood vessels running through it.
-​ Cartilage is important because:
●​ It covers the ends of bones at joints where its slipperiness helps to reduce friction
and aids in shock absorption.
●​ It forms the skeleton of certain fleshy appendages, e.g., the nose and outer ear,
which maintains their shape.
●​ It makes up the intervertebral discs between the vertebrae, enabling the discs to
act as shock absorbers.
-​ The skeleton can be divided into the Axial skeleton and Appendicular skeleton
The axial skeleton
-​ Consists of the skull, vertebral column, ribs, and sternum.
●​ Skull: Made up of the cranium and upper jaw (fused), and the lower jaw
(articulates with the upper jaw). Encloses the brain and sense organs of the head.
●​ Vertebral column: Composed of 33 bones (vertebrae). Supports the body, protects
the spinal cord, provides attachment for girdles and muscles, and allows
movement.
●​ Ribs: Attached to the vertebral column dorsally and sternum ventrally. Forms the
rib cage around the heart and lungs. Essential for breathing.
The appendicular skeleton
-​ Composed of the pectoral girdle, pelvic girdle, arms (forelimbs), and legs (hindlimbs).
●​ Girdles: Connect the limbs to the axial skeleton. Have broad, flat surfaces for
muscle attachment.
●​ Pelvic girdle: Fused to the bottom of the vertebral column. Supports the lower
body and transmits thrust from the legs to the vertebral column.
●​ Limbs: Composed of long bones with joints for movement. Provide a large
surface area for muscle attachment and allow long strides.
●​ Pentadactyl limb: Basic pattern of both arms and legs.
Functions of the skeletal system
-​ Protection:
●​ Cranium protects the brain,
eyes, and ears.
●​ Ribcage protects the lungs and
heart.
●​ Vertebral column protects the
spinal cord.
●​ Pelvis protects internal urinary
and genital organs (e.g. uterus,
ovaries, bladder).
-​ Support:
●​ Provides a framework for the
body's systems (digestive,
excretory, nervous, endocrine,
muscular).
●​ Backbone supports the limbs
and head.
●​ Jawbones support the teeth.
-​ Breathing:
●​ Ribcage moves up and down
due to intercostal muscles,
changing thorax volume.
-​ Production of Red Blood Cells:
●​ Red bone marrow in short
bones and at the ends of long bones contains stem cells that divide by mitosis to
produce red blood cells.
-​ Muscle Attachment:
●​ Bones provide a firm structure for muscle attachment via tendons.
The Humerus
Skeletal muscles
-​ Skeletal muscles consist of bundles of multinucleate muscle fibres which are surrounded
by connective tissue. Tendons attach these muscles to the bones of the skeleton.
Joints
-​ Movement in humans is brought about by skeletal muscles working across joints
-​ Joints are formed where two bones meet. There are three main types:
-​ Immovable Joints (Fibrous Joints)
●​ Bones are firmly joined by fibers.
●​ No movement allowed.
●​ Example: The cranium, which consists of several bones joined by immovable
joints.
-​ Partially Movable Joints (Cartilaginous Joints)
●​ Bones are separated by cartilage pads.
●​ Allow slight movement.
●​ Example: The vertebrae, which are separated by intervertebral discs of cartilage.
-​ Movable Joints (Synovial Joints)
●​ Articulating surfaces of bones are covered with articular cartilage.
●​ Separated by synovial fluid, which lubricates movement.
●​ Bones are held together by ligaments, which are tough, elastic, and prevent
dislocation while allowing movement.
-​ Two types:
●​ Hinge Joints:
➢​ Formed when the ends of bones meet.
➢​ Allow movement in one plane.
➢​ Can bear heavy loads.
➢​ Examples: Elbow, knee, finger, and toe joints.
●​ Ball and Socket Joints:
➢​ Formed when a ball at the end of one bone fits
into a socket in another.
➢​ Allow movement in all planes.
➢​ Examples: Shoulder and hip joints.
Tendons & Ligaments
-​ Tendons:
●​ Fibrous connective tissue that
attaches muscle to bone or
structures (e.g. the eyeball).
●​ Transmits muscle force to
move bones or structures.
Cartilage
-​ Semi-rigid but flexible avascular
connective tissue.
-​ Composed primarily of water but
extremely tough.
-​ Ligaments:
●​ Fibrous connective tissue that
attaches bone to bone.
●​ Holds structures together and
keeps joints stable.
-​ Found in:
●​ Joints
●​ Nose
●​ Airway
●​ Intervertebral discs of the
●​ Ear
spine
Synovial Fluid
-​ Viscous, non-Newtonian fluid found in synovial joint cavities.
-​ Egg-white-like consistency.
-​ Function: Reduces friction between articular cartilage during movement.
-​ Part of the transcellular fluid component of extracellular fluid
Antagonistic Pairs of Muscles
-​ Muscles only pull; they cannot push.
-​ To move a joint in opposite directions, antagonistic muscle pairs are needed.
-​ Example: Elbow Joint
●​ Raising the forearm:
➢​ Biceps contracts
➢​ Triceps relaxes
●​ Lowering the forearm:
➢​ Triceps contracts
➢​ Biceps relaxes
The effect of exercise on the skeletal system
-​ Improves muscle tone (low-level contraction of muscles at rest), maintaining balance,
good posture, and readiness for coordinated action.
-​ Increases production of synovial fluid in joints, keeping joints healthy, reducing friction,
and increasing flexibility.
-​ Improves strength and elasticity of ligaments, increasing the range of movement at joints.
-​ Stimulates growth of muscle tissue, increasing muscle size and strength.
-​ Encourages bones to lay down more mineral matter, making them denser and stronger,
reducing the risk of fractures and osteoporosis.
Factors which adversely affect the skeletal system
Poor posture
-​ Strains muscles, causing more energy to keep the body upright, leading to fatigue and
backache.
-​ Changes curvature of the spine, causing back, neck, and shoulder pain.
-​ Puts stress on joints and wears down intervertebral discs, causing a decrease in height.
-​ Compresses major organs, affecting breathing, digestion, and circulation efficiency.
Poor footwear
-​ High heels shift body weight to the ball of the foot, leading to painful arches, bad posture,
and lower back pain.
-​ Shortens and bulges calf muscles, placing excess pressure on knee and hip joints.
-​ Can lead to corns, bunions, hammer toe, or ingrown toenails from badly fitting shoes.
Obesity
-​ Extra weight strains the skeleton, especially joints, causing cartilage to wear down and
leading to arthritis.
An unbalanced diet
-​ Vitamin D deficiency causes rickets in children and osteomalacia in adults.
-​ Calcium deficiency leads to rickets in children and osteoporosis in adults.
-​ Protein deficiency causes a decrease in bone density and muscle mass.
The importance of locomotion to humans
-​ Essential for work and recreation.
-​ Necessary for finding food and a
partner for reproduction.
-​ Allows humans to escape from
danger and avoid overcrowding.
Importance of Locomotion in Animals
-​ Searching for Food: Unlike plants,
which make food via photosynthesis,
animals must move to find food.
-​ Finding a Mate for Sexual
Reproduction: Animals move to
locate mates, whereas plants rely on
external agents like wind and insects
for pollination.
-​ Escaping Predators: Movement
allows animals to flee from
predators.
-​ Some plants use defenses like spines
or toxic substances to prevent being
eaten.
-​ Distributing Offspring: Movement
helps animals spread their young.
-​ Plants rely on wind, water, or
animals for seed dispersal.
-​ Other Reasons for Locomotion:
●​ Prevent overcrowding.
●​ Avoid danger.
-​ Important for exercise to maintain a
healthy body.
-​ Walking on two hindlimbs frees up
forelimbs and hands for other
activities like manipulating tools and
writing.
●​ Move away from waste
products.
●​ Escape harsh
environmental conditions.
●​ Colonize new habitats
LIFE PROCESSES CONT'D 2
IRRITABILITY
-​ Irritability: the ability of living organisms to respond to stimuli (changes) in their
environment which tends to disturb the steady state or homeostasis which all organisms
prefer for maintaining life.
-​ Stimulus: A change in the internal or external
environment of an organism that initiates a response.
-​ Response: A change is an organism or part of an organism
which is brought about by a stimulus.
-​ Receptor: the part of the organism that detects the
stimulus.
-​ Effector: the part of an organism that responds to the
stimulus.
Responses of green plants to stimuli
-​ Plants respond to stimuli by making part movements or growth movements, which aid in
survival.
-​ Changes in the turgidity of cells bring about many part movements:
●​ The leaves of some plants respond to touch or strong winds by folding, which
protects them from damage, e.g. Mimosa (the sensitive plant).
●​ The leaves of some plants respond to changing light intensities by folding at night
and opening in the morning to access light for photosynthesis, e.g. tamarind.
●​ The flowers of some plants respond to changing light intensities by opening in the
morning to expose the stamens and carpels for pollination, and closing at night,
e.g. hibiscus. Others open at night and close in the morning, e.g. night flowering
cactus.
●​ Parts of insectivorous plants move to trap prey, e.g. Venus fly trap snaps closed to
trap insect
Investigating Plant Responses
●​ Responses to Light
○​ If seedlings are kept in the dark, etiolation occurs whereby the seedlings continue
to grow upwards in search of light instead of producing chlorophyll for
photosynthesis.
○​ Features:
■​ Long, thin stems (rapid growth to search for light)
■​ Small or underdeveloped leaves (limited energy for leaf growth)
■​ Yellow or pale color (lack of chlorophyll due to no light exposure)
■​ Weak structure (elongated internodes, making the plant fragile)
○​ If seedlings are put in an environment with uniform light, the seedling develops
normally.
○​ Features:
■​ Balanced growth → Even exposure to light results in steady stem and
leaf development.
■​ Green leaves → Chlorophyll production occurs as photosynthesis is
active.
■​ Stronger stems → Internodes remain short, providing structural support.
○​ If seedlings are exposed to light from one side, phototropism occurs.
○​ Features:
■​ Stem bends towards the light → More elongation occurs on the shaded
side due to hormone distribution.
■​ Leaves orient towards light → Maximizes photosynthesis.
■​ Roots remain unaffected → No phototropic response in underground
roots.
●​ Responses to gravity
○​ Roots and shoots respond differently to gravity to ensure proper growth and
survival.
○​ Features:
■​ Roots grow downward (positive geotropism) → Ensures access to water
and anchorage.
■​ Shoots grow upward (negative geotropism) → Helps the plant reach
light for photosynthesis.
■​ Starch grains in root cells detect gravity → Direct hormone distribution
to regulate growth.
■​ Uneven growth occurs → More elongation on the upper side of the root
causes downward bending.
●​ Responses to touch
○​ Plants show two types of response to touch. Some, like the Mimosa (‘sensitive’
plant) and Venus flytrap, react suddenly, while others, like morning glory
tendrils, respond slowly based on stimulus position.
○​ Features:
■​ Sudden movements in sensitive plants → Independent of stimulus
direction.
■​ Tendrils curl around supports → Slower response dependent on
stimulus position.
■​ Roots change direction when touching obstacles → Prevents energy
loss and allows efficient growth through soil.
■​ Seedlings adjust root and shoot growth → Roots grow downward, and
shoots grow upward for optimal orientation.
■​ Etiolated growth in darkness → Stems grow rapidly, leaves stay yellow
and small until light is reached.
​
Responses of invertebrates
-​ Organisms involved: Millipedes, earthworms, and woodlice (all invertebrates).
-​ Movement response: These organisms move their whole bodies toward or away from
stimuli (e.g., moisture, light, temperature).
-​ Purpose of response: The movement responses help the organisms survive in their natural
environments.
-​ Investigative method: A choice chamber is used for investigation.
-​ Design of the chamber: The choice chamber has two adjacent environments with
different conditions (e.g., one side may be dry, the other moist).
-​ Procedure:
●​ The organisms are placed in the center of the choice chamber.
●​ The distribution of the organisms is recorded after a fixed time period.
-​ Measurement: The distribution (location of organisms in the chamber) is recorded to see
how they respond to different environmental conditions.
-​ This approach helps in studying how environmental factors influence the movement and
survival of these invertebrates.
-​
-​
-​
-​
Sensory receptors (Specialized cells) detect stimulus in the environment.
Thermoreceptors: Detects changes in temperature.
Photoreceptors: Detects changes in light intensity.
Hygroreceptors: Detects changes in moisture levels.
Human/Vertebrate Response to Stimuli
-​ Importance
●​ Detection of danger
●​ Hunting for food
●​ Escaping harsh conditions
●​ Finding their mates
-​ Humans use five sensory organs to respond to environmental changes:
●​ Nose: Responds to smell.
●​ Eyes: Respond to light.
●​ Ears: Respond to sound.
●​ Skin: Responds to touch, hotness, coldness, pressure, and pain.
●​ Tongue: Responds to taste.
Human Nervous System:
-​ Divided into two parts:
●​ Central Nervous System (CNS): Composed of the brain and the spinal cord.
●​ Peripheral Nervous System (PNS): Composed of cranial and spinal nerves, which
connect the CNS to all parts of the body.
The Human Brain
-​ The human brain has
different regions that are
responsible for different
functions:
●​ the cerebrum
which is
composed of
two cerebral
hemispheres
●​ the cerebellum
●​ the medulla.
The Cerebrum
-​ Functions
●​ Conscious thought.
●​ Coordination of voluntary
actions.
●​ Memory, learning, and
reasoning.
●​ Understanding language and
control of speech.
●​ Interpretation of sensory
information from sense
organs.
The Cerebellum
-​ The cortex is divided into four
lobes, corresponding to skull bones:
●​ Frontal Lobe: Controls
motor activity, personality,
and speech.
●​ Parietal Lobe: Interprets
language, temperature,
pressure, and touch.
●​ Temporal Lobe: Contains
centers for hearing, smell,
and language input.
●​ Occipital Lobe: Specializes
in vision.
-​ Second-largest part of the brain.
-​ Contains nerve fibers connecting it to all parts of the CNS.
-​ Functions:
●​ Coordinates voluntary and involuntary movement patterns.
●​ Coordination of balance, posture and movement.
The Brainstem
-​ Consists of three structures:
●​ Midbrain (Gray Matter): Controls visual reflexes and sense of hearing.
●​ Pons (White Matter): Plays a role in regulating visceral (internal organ) control.
●​ Medulla Oblongata:
➢​ Connects the brain to the spinal cord.
➢​ Regulates breathing, swallowing, coughing, sneezing, vomiting, heartbeat,
and blood pressure.
The Diencephalon
-​ Composed of the thalamus and hypothalamus.
Thalamus
-​ Acts as a relay center for all sensory impulses except olfactory (sense of smell).
-​ Also relays information to motor areas of the cortex.
Hypothalamus
-​ Regulates behavior and emotional expression.
-​ Controls body temperature and various metabolic activities.
-​ Attached to the pituitary gland, it controls hormonal secretions of this gland.
Neurons:
-​ Neurons (nerve cells) make up both the CNS and PNS and transmit messages called
nerve impulses.
-​ Structure of Neurons:
●​ Cell body: Main part of the neuron.
●​ Dendrites: Thin fibres that carry impulses toward the cell body.
●​ Axons: Thin fibres that carry impulses away from the cell body (each neuron has
only one axon).
Types of Neurons:
Sensory Neurons:
-​ Function: Transmit impulses from receptors to the CNS.
-​ Structure: Detect and respond to external signals.
-​ Reception: Receive information through receptors in the PNS and convert it into
electrical impulses.
-​ Example: In the skin, sensory neurons detect tactile stimuli (touch, pain, cold) and carry
this information to the cell body and axon.
Motor Neurons:
-​ Function: Transmit impulses from the CNS to effectors (muscles or glands).
-​ Role: Control movements, speech, swallowing, and breathing by sending commands
from the brain to muscles.
-​ Example: When you snap your fingers or wiggle your toes, motor neurons send
instructions to the muscles to carry out the action.
Relay (Intermediate) Neurons:
-​ Function: Transmit impulses throughout the CNS.
-​ Role: Link sensory and motor neurons within the CNS.
-​ Location: The brain and spinal cord are mainly composed of relay neurons and motor
neuron cell bodies.
The connection between a receptor and an effector
Nerves:
-​ Composition: Nerves are made up of bundles of nerve fibres (sensory and/or motor
neurons) surrounded by connective tissue.
-​ Nerves can be classified into three types based on what they are composed of:
●​ Sensory nerves (afferent nerves): Composed of nerve fibres of sensory neurones
only. They carry impulses from receptors to the CNS.
●​ Motor nerves (efferent nerves): Composed of nerve fibres of motor neurones only.
They carry impulses from the CNS to effectors.
●​ Mixed nerves: Composed of nerve fibres of both sensory and motor neurones.
They carry impulses in both directions: from receptors to the CNS and from the
CNS to effectors.
-​ Nerves can be classified into two types based on where they connect to the CNS:
●​ Cranial nerves: Connect to the brain.
●​ Spinal nerves: Connect to the spinal cord.
Synapse
-​ A synapse is the microscopic space between two nerve cells where electrical impulses
pass.
Structure of a Synapse:
-​ Presynaptic Neuron:
●​ Located at the end of the axon.
●​ Contains neurotransmitters within synaptic vesicles to send signals.
-​ Synaptic Cleft:
●​ The gap between the axon of one neuron and the dendrite of the next neuron.
-​ Postsynaptic Neuron:
●​ Located at the dendrite of the next neuron.
●​ Contains receptors to receive signals.
Functions of a Synapse:
-​ Transmit nerve impulses from one neuron to another across the synaptic cleft.
-​ The neurotransmitters released from the presynaptic neuron bind to receptors on the
postsynaptic neuron, allowing the signal to continue.
Central Nervous System (CNS)
-​ Composed of the brain and spinal cord.
Function of the Central Nervous System (CNS):
-​ Coordinates the activities of all parts of the body.
-​ Gather information from receptors via sensory neurons.
-​ Processes information to determine the most appropriate response.
-​ Sends messages to effectors (muscles or glands) via motor neurons.
-​ Relay neurons pass messages between the brain and spinal cord to facilitate communication.
Gray Matter (Midbrain):
-​ Found in the cortex (surface layer) of the brain and spinal
cord.
-​ Consists of unsheathed nerve fibers (lack myelin sheath).
-​ Cannot be regenerated if damaged.
White Matter (Pons):
-​ Forms the internal structure of the brain and spinal cord.
-​ Composed of myelinated nerve fibers (covered with myelin
sheath).
Voluntary Actions
-​ A voluntary action is an action that is consciously controlled by the brain. The cerebrum
initiates voluntary actions in two ways:
-​ It coordinates incoming sensory information and initiates an action.
-​ It spontaneously initiates an action without receiving sensory input.
Process of Voluntary Actions:
-​ The cerebrum sends impulses along relay neurones in the brain and spinal cord.
-​ Motor neurones carry impulses to skeletal muscles (effectors).
-​ The muscles respond, resulting in conscious movement (e.g. talking, writing, running).
-​ Characteristics of Voluntary Actions:
●​ Learned
●​ Relatively slow
●​ Complex (one stimulus can result in various responses)
Involuntary Actions
-​ An involuntary action occurs without conscious thought.
-​ Characteristics of Involuntary Actions:
●​ Not learned
●​ Rapid
●​ Simple (same stimulus always produces the same response)
-​ Types of Involuntary Actions:
●​ Actions controlled by the autonomic nervous system
●​ Reflex actions
Actions Controlled by the Autonomic Nervous System
-​ The autonomic nervous system consists of motor nerves only.
-​ It regulates internal organs, controlling functions such as:
●​ Breathing rate
●​ Heart rate
●​ Digestion
●​ Peristalsis
●​ Blood pressure
-​ Information from internal receptors is sent to the medulla of the brain.
-​ The medulla then sends impulses along motor neurones in cranial and spinal nerves to
effectors.
-​ The autonomic nervous system plays a crucial role in homeostasis.
Simple Reflex Actions
-​ A Reflex Action is a rapid, automatic, involuntary response to a stimulus by a muscle or
gland.
-​ Example: Withdrawing the hand when touching a hot object.
-​ Happens without conscious thought, is not learned, and aids in survival.
Reflex Arc (Pathway between receptor and effector):
-​ Receptor – Detects the stimulus.
-​ Sensory Neuron – Carries the impulse to the central nervous system (CNS).
-​ Relay Neuron – Located in the CNS, carries the impulse to a motor neuron.
-​ Motor Neuron – Carries the impulse away from the CNS.
-​ Effector – Responds to the stimulus (e.g., muscle contracts, gland secretes).
Types of Simple Reflexes:
Cranial Reflexes:
-​ Impulses pass through the brain.
-​ Examples:
●​ Pupil reflex – Adjusts pupil size in response to light.
●​ Blinking reflex – Protects the eyes from dust or bright light.
●​ Sneezing reflex – Clears irritants from the nasal passage.
●​ Coughing reflex – Clears the airway.
●​ Saliva production – Stimulated by the presence of food.
Spinal Reflexes:
-​ Impulses pass through the spinal cord.
-​ Examples:
●​ Knee jerk reflex –
A sudden leg
movement in
response to a tap
on the patellar
tendon.
●​ Withdrawal reflex
– Automatic
pulling away from
a painful stimulus
(e.g., touching
something hot).
Physiological Effects of Drug Abuse
-​ A Drug is any chemical substance that affects body functions.
-​ Medical use: Improves health when used correctly.
-​ Drug Abuse: Misuse of any drug, including prescription drugs, leading to addiction and
harm.
-​ Withdrawal symptoms: Occur when an addicted user stops taking the drug.
Abuse of Alcohol
-​ Alcohol is a depressant of the central nervous system.
-​ Alcoholism: Dependence on alcohol; classified as a disease.
-​ Severe alcoholism can lead to death.
-​ Short-term effects:
●​ Impaired muscular skills, coordination, and reflexes.
●​ Reduced mental functioning, concentration, and judgment.
●​ Blurred vision and slurred speech.
●​ Memory lapses and drowsiness.
●​ Increased urine production, leading to dehydration.
●​ Loss of consciousness.
-​ Long-term effects:
●​ Long-term memory loss.
●​ Increased blood pressure, leading to heart disease, heart attack, and stroke.
●​ Inflammation of the stomach walls, stomach ulcers, and intestinal disorders.
●​ Liver diseases: Fatty liver, alcoholic hepatitis, and cirrhosis (scarring).
●​ Nervous system damage: Brain damage as brain cells die.
●​ Cancer: Mouth, throat, and esophagus.
●​ Delirium tremens (DTs): Body tremors, anxiety, and hallucinations.
●​ Foetal Alcohol Syndrome (FAS): Babies of alcoholic mothers may suffer from
mental retardation.
Abuse of Cocaine
-​ Cocaine is a highly addictive stimulant of the central nervous system.
-​ Effects of cocaine abuse:
●​ Euphoria: Feelings of well-being, increased energy, alertness, confidence, and power.
●​ Psychological effects: Paranoia, anxiety, depression, hallucinations, and violent behavior.
●​ Physical effects: Increased breathing rate and heart rate.
●​ Reduced need for sleep.
●​ Damage to lungs and nasal passages.
●​ Loss of appetite, leading to nutritional deficiencies and weakened immune system.
●​ Constriction of blood vessels: Raises blood pressure, increasing the risk of heart attack or
stroke.
●​ Mental disorders: Can contribute to schizophrenia and other conditions.
Abuse of Prescription Drugs
-​ Commonly abused prescription drugs:
●​ Tranquilizers (e.g., Valium).
●​ Antibiotics.
●​ Diet pills.
●​ Painkillers (analgesics).
●​ Caffeine.
●​ Steroids.
-​ Effects of tranquilizer abuse:
●​ Slurred speech, poor coordination, dizziness, drowsiness.
●​ Reduced attention span, blurred vision, hallucinations, confusion.
●​ Low blood pressure, mental apathy.
-​ Effects of antibiotic misuse:
●​ Overuse or incomplete courses lead to antibiotic-resistant bacteria.
●​ Infections by resistant strains become untreatable.
●​ Allergic reactions (e.g., to penicillin), which can be fatal.
-​ Effects of diet pill abuse:
●​ Nervousness, dizziness, anxiety, insomnia.
●​ Diarrhea, stomach pain.
●​ High blood pressure, irregular heartbeat, heart palpitations.
●​ Heart failure
Social and Economic Effects of Drug Abuse
-​ Social Effects
●​ Strained relationships with family and friends.
●​ Personal neglect (poor hygiene, malnutrition, and lack of self-care).
●​ Increased crime (theft, violence, or prostitution to fund drug use).
●​ Higher risk of sexually transmitted infections (STIs) due to prostitution.
●​ Risk of AIDS and hepatitis A from intravenous drug use.
●​ Babies of drug abusers may suffer from birth defects or be born addicted.
-​ Economic Effects
●​ Job loss due to inability to work.
●​ Financial problems from spending on drugs.
●​ Increased demand on healthcare services for treatment and rehabilitation.
●​ High cost to society for:
➢​ Treating and rehabilitating drug addicts.
➢​ Combating drug-related crimes.
➢​ Arresting, convicting, and imprisoning drug traffickers and pushers.
●​ Reduced standard of living.
●​ Loss of human resources due to addiction-related deaths and disabilities.
The Human Eye
-​ The eye detects light reflected from objects and converts it into nerve impulses.
-​ These impulses are transmitted along the optic nerve to the brain, which translates them
into a precise picture of the object.
Anatomy and Protection
-​ Eyes are located in bony sockets of the skull, known as orbits.
-​ Muscles attached to the eyes allow movement.
-​ Orbits protect the back of the eyes from damage.
-​ Eyelids and eyelashes protect the front of the eyes from foreign particles.
Tears and Tear Glands
-​ Tears are produced by tear glands above each eye.
-​ Functions of tears:
●​ Keep the eyes moist.
●​ Wash away foreign particles.
●​ Contain an enzyme that destroys micro-organisms.
Structure and functions of the parts of the human eye as seen in longitudinal section
Image Formation
-​ Light rays from an object must be refracted (bent) as they enter the eye to form a clear
image on the receptor cells of the retina.
-​ The cornea and lens are both convex in shape, which helps to refract the light rays.
Detection of Light Intensity and Color by the Eye
-​ The retina contains two types of photoreceptors (light-sensitive cells):
-​ Rods
●​ Function in low light intensities.
●​ Responsible for detecting the brightness of light.
●​ Located around the sides of the retina.
●​ Images seen through rods are in black and white only.
-​ Cones
●​ Function in high light intensities.
●​ Responsible for detecting color and fine detail.
●​ Mainly located around the back of the retina.
●​ The fovea (center of the retina) is composed entirely of cones, packed closely
together.
●​ There are three types of cones, each sensitive to either red, green, or blue
wavelengths of light.
Focusing Light onto the Retina – Accommodation
-​ The lens changes its shape to fine-tune the focus of light rays onto the retina.
-​ Accommodation is the process of adjusting the lens to focus light from different
distances.
-​ Ciliary muscles and suspensory ligaments are responsible for bringing about
accommodation by changing the shape of the lens.
Control of Light Entering the Eye
-​ The size of the pupil controls the amount of light entering the eye.
-​ Muscles of the iris control the pupil size to regulate the amount of light that reaches the
retina.
Sight Defects and How They Are Corrected
Short-Sight (Myopia)
-​ A person with short-sight can see near objects clearly, but distant objects appear out of
focus.
-​ Cause: Light rays from distant objects focus in front of the retina. This occurs when the
eyeball is too long from front to back or the lens is too curved (thick).
-​ Myopia is corrected with diverging (concave) lenses in spectacles or contact lenses.
Long-Sight (Hypermetropia)
-​ A person with long-sight can see distant objects clearly, but near objects are out of focus.
-​ Cause: Light rays from near objects focus behind the retina. This occurs when the eyeball
is too short from front to back or the lens is too flat (thin).
-​ Hypermetropia is corrected with converging (convex) lenses in spectacles or contact
lenses.
Glaucoma
-​ Glaucoma is a condition resulting from increased pressure in the eyeball, obstructing the
blood vessels that supply the optic nerve, reducing the flow of oxygen and nutrients.
-​ Cause: The increased pressure is due to poor drainage of fluids in the eye. This causes the
death of neurons in the optic nerve, starting with those supplying the periphery of the
retina and later affecting those from the fovea.
-​ Symptoms:
●​ Slow deterioration of peripheral vision.
●​ People may be unaware of changes as it develops gradually.
●​ Children born with glaucoma may have cloudy eyes and watery eyes.
-​ Effect: If untreated, it can lead to vision loss, particularly in the peripheral areas
Old Sight (Presbyopia)
-​ Difficulty seeing near objects clearly.
-​ Caused by loss of lens elasticity and weakening of ciliary muscles with age.
-​ Corrected by wearing converging lenses for near vision.
Astigmatism
-​ Both near and distant objects appear blurry or distorted.
-​ Occurs when the cornea or lens is unevenly curved, causing unequal refraction of light
rays.
-​ Corrected by wearing unevenly curved lenses to counteract the eye's curvature.
Cataract
-​ Cloudy area forms in the lens, leading to:
●​ Blurred or cloudy vision
●​ Halos around lights
●​ Colours appearing faded
●​ Difficulty seeing in bright light and at night
-​ Usually caused by aging.
-​ Corrected by surgical removal of the cloudy lens and replacement with an artificial lens.
Pupil Reflex
Situation:
-​ Bright to Dark: When you move from a well-lit area to a dark place, you initially can't
see much because your pupils dilate (enlarge) to let more light in.
-​ Dark to Bright: When moving from a dark area to a very bright place, your pupils
initially appear to be blinded by the light as they constrict (shrink) to reduce the amount
of light entering the eye.
Control Mechanism:
-​ Circular muscles in the iris contract to decrease the diameter of the pupil in bright light.
-​ Radial muscles in the iris contract to increase the diameter of the pupil in low light.
Reflex Action:
-​ Sensory neurons transmit impulses from the retina to the brain along the optic nerve.
-​ Motor neurons transmit impulses from the brain to the iris muscles through another
cranial nerve, controlling the size of the pupil.
The Skin and Its Functions
-​ The skin is the largest organ in the human body and plays a vital role in interactions with
our environment.
-​ It has three main layers:
Epidermis:
●​ The outermost layer of skin, made up of squamous cells filled with keratin.
●​ These cells provide mechanical protection against injury and are gradually rubbed
away.
●​ Contains stem cells that divide by mitosis to replace cells lost from the surface.
●​ Melanocytes produce melanin, which absorbs ultraviolet light, protecting the
body from its harmful effects.
Dermis (below the epidermis):
●​ Contains hair follicles, sweat glands, arterioles, sensory nerve endings, and
sensory cells.
●​ Hair provides insulation on the head.
●​ Sweat glands secrete sweat, which travels up sweat ducts to sweat pores, where it
evaporates to cool the body.
●​ Arterioles control the flow of blood to capillaries, which lose heat to the
surroundings.
Subcutaneous Layer (bottom layer, made up mostly of fat cells):
●​ Fat acts as a store of energy and a thermal insulator.
-​ Other Key Functions of the Skin:
●​ Sensory nerve endings and sensory cells detect changes in temperature, pressure,
and pain.
●​ Sensory neurons transmit nerve impulses to the central nervous system (CNS).
●​ Motor neurons send impulses to instruct hair muscles to contract and raise the
hairs (goosebumps).
●​ Vasodilation (Heat Loss Mechanism)
●​ When the body overheats, the blood vessels in the skin widen (dilate).
●​ More blood flows to the surface, allowing heat to escape by radiation.
●​ Sweat glands become active, increasing evaporative cooling.
●​ Vasoconstriction (Heat Retention Mechanism)
●​ When the body is cold, the blood vessels narrow (constrict).
●​ Less blood flows to the skin, reducing heat loss.
●​ This helps maintain core body temperature in cold conditions.
The endocrine system
-​ The endocrine system is composed of endocrine glands or ductless glands which secrete
hormones directly into the blood
Hormones of the Main
Endocrine Glands and
Their Functions
Pituitary Gland
-​ Antidiuretic
Hormone (ADH) –
Controls water content of
blood plasma by
regulating water
reabsorption in the
kidneys.
-​ Growth Hormone (GH)
➢​ In children: Stimulates growth and protein synthesis in cells and bones.
➢​ In adults: Helps maintain healthy bone and muscle mass.
-​ Follicle-Stimulating Hormone (FSH)
➢​ In females: Stimulates follicle and ovum development in ovaries and oestrogen
production.
➢​ In males: Regulates sperm production in the testes.
-​ Luteinising Hormone (LH)
➢​ In females: Triggers ovulation and corpus luteum development.
➢​ In males: Stimulates testosterone production.
Thyroid Gland
-​ Thyroxine – Controls metabolism, energy production, physical growth, and mental
development, especially in children.
Adrenal Glands
-​ Adrenaline (Fight-or-Flight Hormone) – Released when frightened, excited, or
anxious. Increases blood sugar levels, heartbeat, breathing rate, and blood supply to
muscles.
Pancreas
-​ Insulin & Glucagon – Regulate blood glucose levels.
Ovaries
-​ Oestrogen (Produced by the Graafian Follicle)
➢​ Controls the development of female secondary sexual characteristics (breasts,
pubic & underarm hair, broad pelvis).
➢​ Stimulates thickening of the uterus lining after menstruation.
-​ Progesterone (Produced by the Corpus Luteum & Placenta during Pregnancy)
➢​ Maintains a thick uterus lining after ovulation and during pregnancy.
➢​ Stimulates milk-producing glands during pregnancy.
Testes
-​ Testosterone
➢​ Controls male reproductive organ development and secondary sexual
characteristics (deep voice, facial & body hair, muscle growth, broad shoulders).
➢​ Regulates sperm production.
GROWTH
-​ Growth is a permanent increase in the size of an organism.
-​ To grow, the cells of multicellular organisms undergo cell division by mitosis.
-​ The new cells grow to full size by manufacturing more protoplasm (the living part of
the cell; cytoplasm, nucleus, organelle).
-​ Plant cells increase in size further by absorbing water into their vacuoles.
-​ Most cells then differentiate (specialize) to carry out specific functions.
-​ Animals also grow by making more extracellular materials, eg. Minerals of bones, Fibres
of connective tissue
-​ If the parameter used to measure growth is plotted against time, a growth curve is
obtained which is described as being sigmoid or S-shaped.
Germination
-​ Germination is the process by which the embryonic plant in a seed grows into a seedling.
Structure of a Seed
-​ A seed contains the embryo of the plant.
-​ In dicotyledonous seeds, the embryo consists of:
●​ Radicle (embryonic root)
●​ Plumule (embryonic shoot)
●​ Two cotyledons (store food for the radicle and plumule during germination).
-​ The cotyledons contain stored food such as protein, starch, and lipids.
-​ The testa (seed coat) surrounds and protects the seed.
Conditions for Germination
-​ Water – Activates enzymes for chemical reactions.
-​ Oxygen – Needed for aerobic respiration to produce energy.
-​ Suitable Temperature (about 5°C – 40°C) – Activates enzymes.
Process of Germination
-​ Water is absorbed through the micropyle, causing the seed to swell and activating
enzymes.
-​ Enzymes break down stored food:
●​ Proteins → Amino acids
●​ Starch → Maltose → Glucose
●​ Lipids → Fatty acids + Glycerol
-​ These soluble substances are transported to the radicle and plumule.
Use of Stored Food
-​ Amino acids – Used to build new cells at the tips of the radicle and plumule.
-​ Glucose – Used in respiration for energy and in making cellulose for cell walls.
-​ Fatty acids & Glycerol – Used in respiration for energy.
Growth of the Seedling
-​ The radicle emerges first and grows downward.
-​ The plumule emerges and grows upward.
-​ The cotyledons may be carried above the soil or they may remain below the soil.
Stages in the germination of a green bean
Stages in the germination of a pigeon pea
Growth curve of a germinating seed
Meristems
-​ Plant cells have semi-rigid cell walls that restrict their ability to divide and grow.
-​ Meristems are groups of immature, undifferentiated cells with thin walls that actively
divide and grow through mitosis.
-​ They can develop into different types of plant cells.
-​ They are the only actively growing tissues in plants.
Primary Growth (Growth in Length of Roots and Shoots)
-​ Occurs at the tips of roots and shoots.
-​ Apical meristems at the tips divide constantly by mitosis.
-​ Newly formed cells elongate behind the apical meristems by absorbing water into their
vacuoles.
-​ Once elongated, cells differentiate into xylem and phloem.
Growth in length of a root
Secondary Growth (Growth in Width of Roots and Stems)
-​ Occurs in plants that live for multiple years (e.g., trees).
-​ Lateral meristems are responsible for secondary growth.
-​ Types of Lateral Meristems:
●​ Vascular cambium (between xylem and phloem):
➢​ Divides and differentiates into xylem towards the inside and phloem
towards the outside.
➢​ In stems, xylem is added in rings, each ring representing a season’s
growth.
●​ Cork cambium (below the bark):
➢​ Divides and produces cork (bark) to the outside.
Comparison of growth in plants and animals:
REPRODUCTION
-​ Reproduction is the process by which living organisms generate new individuals of the
same kind as themselves.
Types of reproduction:
Asexual Reproduction
-​ Involves only one parent.
-​ Offsprings are produced by mitosis.
-​ All offspring are genetically identical and collectively called a clone.
-​ Conserves the characteristics of the parent.
-​ Found in certain plants, fungi, and unicellular organisms (e.g., amoeba and bacteria).
Sexual Reproduction
-​ Involves two parents.
-​ Gametes (sex cells) are produced in reproductive organs by meiosis.
-​ A male and female gamete fuse during fertilization to form a zygote.
-​ The zygote divides by mitosis to form an embryo and later an adult.
-​ Offspring receive genes from both parents, leading to variation.
Comparison of Asexual and Sexual Reproduction
Feature
Asexual Reproduction
Sexual Reproduction
Variation
No variation; all offspring are
identical.
Produces variation; no two organisms
are identical.
Adaptation
Does not allow species to change and Enables species to change and adapt to
adapt to changing conditions
changing conditions (beneficial in an
(beneficial in a stable, unchanging
environment, or in an under-crowded unstable, changing environment, or in
environment)
an overcrowded environment)
Speed of
Process
Rapid; does not involve a mate,
gamete production, fertilization, or
embryo development
Slow; involves finding a mate, gamete
production, fertilization, and embryo
development
Population
Growth
Results in a rapid increase in
population size
Leads to a slower increase in
population size
Offspring
Location
Offspring usually remain close to the
parent, leading to overcrowding and
competition
Offspring are usually dispersed over a
wide area, reducing overcrowding and
competition
-​ Many plants use both methods, gaining the advantages of each.
-​ Example: Grass species reproduce asexually by runners and sexually by flowers and
seeds.
Human Reproduction
The Male Reproductive System
-​ Gonads are organs that produce sex cells. Male gonads are testes.
-​ Male gametes are called sperm or spermatozoa.
-​ The testes produce the sperm cells by meiosis.
-​ Sperm production occurs in the seminiferous tubules, which are lined with
sperm-producing cells.
-​ Unlike ovaries (inside the female body), testes are located outside the body in the
scrotum.
-​ The scrotum keeps sperm at a lower temperature than body temperature which is
essential for sperm production.
-​ Once produced, sperm is stored in the epididymis until ejaculation.
-​ If not released within 6 weeks, they are broken down and reabsorbed into the
bloodstream (resorption).
-​ Sperm duct (vas deferens) carries sperm to the urethra, which transports both sperm and
urine.
-​ Sperm cells are carried in a liquid called semen.
-​ Semen is produced by:
●​ Seminal vesicles
●​ Prostate gland
●​ Cowper’s glands
-​ Semen also contains nourishment for sperm cells.
-​ Ejaculation releases about 50-300 million sperm at once.
-​ Sperm cells are haploid containing 23 chromosomes.
-​ Production begins at puberty
The Penis
-​ The penis is adapted to transfer sperm into the female body.
-​ The tip of the penis is called the glans.
-​ Erection occurs when blood rushes into the penis.
-​ Male Hormones are produced by the pituitary gland during puberty.
●​ FSH (Follicle Stimulating Hormone) – Stimulates the production of sperm by
meiosis.
●​ LH (Luteinising Hormone) – Stimulates the testes to produce testosterone.
Testosterone
-​ During pregnancy testosterones cause the development of primary male sex
characteristics (penis and other male reproductive parts).
-​ During puberty testosterones:
●​ Causes the enlargement of reproductive parts.
●​ Leads to the development of secondary sexual characteristics.
➢​ Hair growth on the face, underarm, chest, and pubic region.
➢​ Enlarged larynx producing a deeper voice.
➢​ Wider shoulders.
➢​ Greater skeletal muscular development
➢​ Growth in height and weight
Male Infertility
-​ Most common cause: Low sperm production.
-​ Causes of low sperm production:
●​ Stress
●​ Alcohol and drug abuse
●​ High temperature of the testes
●​ Low testosterone production
The Female Reproductive System
-​ Ovaries
●​ Produce eggs and female hormones.
Production of Ova
●​ At puberty: About 40,000 diploid eggs are present.
●​ Each immature ovum(diploid eggs) is surrounded by a fluid-filled space, forming
a primary follicle.
●​ From puberty (11-13 years) to menopause (45-50 years) about 20 haploid eggs are
produced each month
●​ Maturation occurs through meiosis, producing four cells, but only one develops
into a mature ovum.
●​ The haploid egg cell (ovum) is surrounded by the Graafian follicle, which
produces oestrogen.
●​ Ovulation – Release of the egg from the follicle when it bursts.
Production of Ova in Ovary
Structure of the ova
-​ Fallopian Tubes
●​ About 12 cm long with funnel-shaped ends that collect the egg after ovulation.
●​ Cilia and peristalsis move the egg along the tube.
●​ If not fertilized, the egg dies in the tube.
-​ Uterus (Womb)
●​ Made of involuntary muscle.
●​ Lined with the endometrium, which thickens monthly with cells and blood to
nourish an embryo (if present).
●​ The cervix is the opening of the uterus.
-​ Vagina
●​ A muscular tube that allows sperm to enter and the baby to exit.
●​ Lined with mucous-secreting cells.
●​ The urethra opens near the vagina.
●​ Protected by folds of skin called the vulva.
●​ The hymen partially blocks the entrance and can be broken by sexual intercourse
or tampon use.
The Menstrual Cycle
-​ The menstrual cycle is a series of steps that prepares the uterus for the implantation of a
fertilised egg.
-​ Occurs every 28 days from puberty to menopause.
-​ Happens only if fertilization does not occur.
Typical Events of the Menstrual Cycle:
Day 1 to Day 5:
-​ Menstruation – The endometrium breaks down and is shed.
-​ Meiosis occurs in the ovary, producing a new egg surrounded by the Graafian follicle.
Day 6 to Day 13:
-​ Oestrogen is produced by the Graafian follicle.
-​ Oestrogen stimulates the endometrium to thicken.
-​ One Graafian follicle with one egg develops.
-​ Oestrogen stimulates the production of LH (Luteinising Hormone).
Day 14:
-​ A surge of LH stimulates ovulation.
-​ The egg enters the Fallopian tube and can be fertilized for 48 hours.
Day 15 to Day 26:
-​ The corpus luteum (yellow body) develops from the Graafian follicle and produces
progesterone and some oestrogen.
-​ Progesterone:
-​ Maintains the thickened endometrium.
-​ Prevents new eggs from forming.
-​ If the egg is not fertilized, it dies.
-​ If fertilization does not occur, the corpus luteum degenerates.
Day 26 to Day 28:
-​ Oestrogen and progesterone levels decline.
-​ The endometrium starts to break down.
-​ Day 1 of the cycle begins again.
Female Hormones
-​ Endometrium thickening:
●​ Days 1-14: Thickened by oestrogen.
●​ Days 15-28: Thickened by progesterone.
●​ Both hormones prevent egg development.
-​ Oestrogen at Puberty:
●​ Causes primary female sexual characteristics (growth of sex organs).
●​ Along with progesterone, causes secondary female characteristics:
➢​ Enlargement of the breasts.
➢​ Widening of the hips.
➢​ Increased body fat.
➢​ Growth of pubic and underarm hair.
➢​ General growth spurt in height.
Hormones and Their Functions
Hormone
Site of
Production
Time of
Production
Functions
FSH (Follicle
Stimulating
Hormone)
Pituitary
Gland
Days 1-5 of
menstrual
cycle
- Stimulates egg production in Graafian
follicles.
- Used in fertility treatments to
stimulate egg production.
- Graafian follicles secrete oestrogen.
Oestrogen
Graafian
Follicle
Days 5-14 of
menstrual
cycle
- Develops the endometrium.
- Inhibits FSH, preventing new egg
development.
- Stimulates the release of LH
(Luteinising Hormone).
LH
(Luteinising
Hormone)
Pituitary
Gland
Day 14 of
menstrual
cycle
- Causes ovulation.
- Causes the Graafian follicle to
develop into the corpus luteum,
which produces progesterone.
Progesterone
Corpus
Luteum
Days 14-28 of
menstrual
cycle
- Maintains the endometrium.
- Inhibits FSH, preventing new egg
development.
- Inhibits LH, preventing further
ovulation.
- Prevents uterine contractions.
Female Infertility
-​ Inability to conceive due to fertilization failure or implantation failure.
-​ Causes:
●​ Hormone imbalance – Prevents egg formation or ovulation.
●​ Blocked Fallopian tubes – Prevents egg from reaching the uterus.
-​ Treatment Options:
●​ Hormone therapy to regulate ovulation.
●​ In-vitro fertilization (IVF) – Fertilization outside the body followed by
implantation.
Fibroids
-​ Benign tumours of the uterus that grow slowly and vary in size.
-​ Symptoms:
●​ Small fibroids – No symptoms.
●​ Large fibroids – May cause:
➢​ Heavy and prolonged menstrual bleeding.
➢​ Pain.
➢​ Miscarriage.
➢​ Infertility.
-​ Possible Cause:
●​ Abnormal response to oestrogen.
-​ Treatment:
●​ Surgical removal of large fibroids.
●​ Hysterectomy (removal of the uterus) in severe cases.
Copulation
-​ Also called coitus or sexual intercourse.
-​ It is the process by which the penis enters the vagina to deposit semen containing sperm
cells.
-​ The process of depositing semen is called insemination.
Fertilization
Steps of Fertilization:
-​ After insemination, sperm move up the Fallopian tubes.
-​ If ovulation has occurred and an egg is present, the egg releases a chemical that attracts
sperm. This process is called chemotaxis.
-​ The sperm reaching the egg uses an enzyme in its acrosomes to create an opening in the
egg's membrane.
-​ Once one sperm enters the egg (only the head enters), the egg forms a membrane to
prevent other sperm from entering.
-​ The nucleus of the sperm fuses with the nucleus of the egg, forming a diploid zygote.
-​ Fertilization typically occurs between days 11-16 of the menstrual cycle.
Implantation
-​ About 6–9 days after fertilization, the fertilized egg (zygote) undergoes mitosis,
forming a hollow ball of cells called the blastocyst. The blastocyst moves down the
oviduct and implants into the lining of the uterus.
-​ During this stage:
-​ The zygote uses nutrients from the original ovum's yolk for nourishment.
-​ Implantation is the process where the blastocyst becomes embedded in the
uterine lining.
-​ Once implanted, nutrients and oxygen diffuse from the mother’s blood into the
embryo, while carbon dioxide and waste diffuse back into the mother's
bloodstream.
-​ A protective membrane called the amnion develops around the embryo.
-​ The amnion secretes amniotic fluid, which surrounds and protects the
embryo from mechanical shock and drying out.
Placenta Formation
-​ After implantation, the embryo forms another membrane called the chorion, which
encases the embryo.
-​ Projections from the chorion, known as villi, extend into the endometrium and join with
maternal blood vessels to form the placenta.
-​ The placenta becomes fully functional in about 3 months.
-​ The umbilical cord connects the embryo (at the navel) to the placenta, facilitating the
exchange of substances.
Functions of the Placenta:
-​ Protection:
●​ Hinders the entry of pathogens from the mother.
●​ Allows the passage of maternal antibodies, providing passive immunity.
●​ Keeps the embryo insulated from the mother's higher blood pressure.
●​ Prevents the exchange of red blood cells, reducing the risk of agglutination.
-​ Gas Exchange:
●​ Supplies oxygen (O₂) to the embryo.
●​ Removes carbon dioxide (CO₂) from the embryo to the mother's blood.
-​ Nutrient Supply:
●​ Transfers essential nutrients such as glucose, amino acids, lipids, vitamins, and
minerals from the mother's blood to the embryo.
-​ Endocrine Functions:
●​ Secretes hormones, including estrogen and progesterone, which help maintain the
pregnancy and prepare the mother's body for birth and lactation.
-​ Excretion:
●​ Facilitates the transfer of metabolic wastes, including CO₂ and urea, from the
embryo into the mother's blood.
The developing human embryo/foetus in the uterus
Development of the embryo
Time after
Fertilization
Developmental Milestones
4 weeks
1. Heart forms and starts to beat.
2. Brain develops.
3. Umbilical cord forms.
5 weeks
1. Internal organs start to form.
2. Limbs start to form.
(Embryo highly vulnerable to alcohol and drugs)
6 weeks
1. Eyes become visible.
2. Mouth, nose, and ears begin to form.
8 weeks
1. Tail is gone.
2. Face becomes human-looking.
3. Major organs are formed.
4. Ovaries or testes are seen.
5. Bone replaces cartilage.
6. The embryo is now called a foetus.
12 weeks
1. Bone growth continues to replace cartilage.
2. Nerves and muscles coordinate arm and leg movement.
3. Thumb sucking and kicking begin.
4. Milk (baby) teeth form.
5. Foetus takes amniotic fluid into the mouth and releases urine
and faeces into amniotic fluid.
6. External sex organs clearly seen. Gender can be determined
with a scan.
12-38 Weeks
The foetus continues to grow and the organs continue to develop
and mature.
-​ The Gestation period(pregnancy) is the length of time from fertilization to birth. In
humans it is generally 266 days (38 weeks/9months).
Birth Process
-​ The foetus turns to lie head down in preparation for birth.
-​ Progesterone secretion by the placenta is reduced.
-​ This reduction stimulates the pituitary gland to secrete oxytocin.
-​ Oxytocin triggers contractions of the uterine muscles (labour begins).
-​ The amnion bursts (release of amniotic fluid).
-​ Contractions cause the cervix to dilate.
-​ Once fully dilated, the baby is pushed head first through the cervix and vagina.
-​ The umbilical cord is cut after birth.
-​ The placenta is expelled as the afterbirth due to further uterine contractions.
Contraceptives
Method
How the Method
Works
Advantages
Disadvantages
Natural Contraception
Abstinence
Refraining from
sexual intercourse.
Completely effective.
Protects against
sexually transmitted
infections.
Relies on self-control
from both partners.
Withdrawal
Penis is withdrawn
before ejaculation.
No artificial device
needs to be used or pills
taken, making it
acceptable to all
religious groups.
Very unreliable since
some semen is released
before ejaculation.
Relies on self-control.
Rhythm
Method
Intercourse is
restricted to times
when ova should be
absent from the
oviducts.
No artificial device
needs to be used or pills
taken, making it
acceptable to all
religious groups.
Unreliable since the
time of ovulation can
vary.
Restricts the time when
intercourse can occur.
Unsuitable for women
with an irregular
menstrual cycle.
Very reliable if used
correctly.
Easy to use.
Readily available.
Protects against
sexually transmitted
infections.
May reduce sensitivity,
interfering with
enjoyment.
Condoms can tear,
allowing sperm to enter
the vagina.
Latex may cause an
allergic reaction.
Mechanical Contraception
Condom
A latex rubber or
polyurethane sheath
placed over the erect
penis or into the
female vagina before
intercourse.
Acts as a barrier to
prevent sperm from
entering the female
body.
Diaphragm
A dome-shaped latex
rubber disc inserted
over the cervix before
intercourse. Should
be used with a
spermicide.
Acts as a barrier to
prevent sperm from
entering the uterus.
Fairly reliable if used
correctly.
Not felt, so it does not
interfere with
enjoyment.
Easy to use once the
female is taught.
Must be left in place for
6 hours after
intercourse, but no
longer than 24 hours.
Latex may cause an
allergic reaction.
May slip out of place if
not fitted properly.
Intra-Uterine
Device
(IUD/Coil)
A T-shaped plastic
device, usually
containing copper or
progesterone, inserted
into the uterus by a
doctor.
Prevents sperm from
reaching the ova or
prevents
implantation.
Very reliable.
Once fitted, no further
action is required except
an annual check-up.
No need to think further
about contraception.
Few, if any, side effects.
Must be inserted by a
medical practitioner.
May cause
menstruation to be
heavier, longer, or more
painful.
Chemical Contraception
Spermicides
Creams, jellies, or
foams inserted into
the vagina before
intercourse.
Kill sperm.
Easy to use.
Readily available.
Not reliable if used
alone, should be used
with a condom or
diaphragm.
May cause irritation or
an allergic reaction.
Contraceptive
Pill
A hormone pill, taken
daily, containing
oestrogen and
progesterone, or
progesterone only.
Prevents ovulation.
Makes cervical
mucus thicker and
more difficult for
sperm to swim
through.
Almost totally reliable if
taken daily.
Menstruation is lighter,
shorter, and less painful.
Ceases to be effective if
one pill is missed.
May cause side effects
in some women,
especially those who
smoke.
Surgical Contraception
Surgical
Sterilisation
The sperm ducts or
oviducts are
surgically cut and tied
off.
Prevents sperm from
leaving the male body
or ova from passing
down the oviducts.
Totally reliable.
No need to think further
about contraception.
No artificial device
needs to be used or pills
taken.
Usually irreversible.
-​ One disadvantage of all methods except abstinence and condoms is that they do not
protect against sexually transmitted infections
Importance of Birth Control
-​ Prevents unintended pregnancies, allowing couples to plan when and how many children
they have.
Benefits
-​ Reduces health risks to women and maternal deaths caused by unintended pregnancies
and unsafe abortions.
-​ Decreases infant deaths and improves infant health by increasing the spacing between
births.
-​ Enables smaller family sizes, ensuring children receive better emotional, physical, and
educational support.
-​ Allows women to fully participate in society and advance in the workplace by planning
their future and careers.
Global Perspective
-​ The human population is rapidly growing, projected to increase from 7.3 billion in 2015
to over 9 billion by 2050.
-​ Rapid population growth may cause:
●​ Shortages of food, water, natural resources, and land for housing, crops, and
livestock.
●​ Increased pollution, environmental destruction, unemployment, and disease
spread.
●​ Lower living standards globally.
-​ Birth control helps manage population growth, promoting a healthy, productive
environment with fewer shortages and better living conditions.
Importance of Family Planning
-​ Family planning involves making decisions about the number of children in a family and
the time between their births. Contraception plays a major role in this process.
Benefits of Family Planning
-​ Better child care:
➢​ Smaller families allow parents to spend more time with each child, providing
greater emotional and physical care.
➢​ Ensures better education opportunities for children.
-​ Financial benefits: Raising fewer children is less expensive.
-​ Parental decision-making: Parents can choose when to start a family, whether at a
young age or later after career establishment.
-​ Health benefits: Reduces health risks to women and maternal deaths caused by
unintended pregnancies and unsafe abortions.
-​ Women’s empowerment:
➢​ Allows women to complete their education before having children.
➢​ Enables women to participate fully in society and advance in the workplace.
Global Perspective
-​ Population control: Slows down rapid human population growth.
-​ Prevents resource shortages: Helps prevent shortages of food, water, land, and other
natural resources.
-​ Environmental protection: Reduces pollution and environmental destruction.
-​ Economic and social improvements:
➢​ Decreases unemployment and the spread of diseases.
➢​ Helps improve overall living standards.
Issues Related to Abortion
-​ Abortion is the termination of a pregnancy.
-​ It can occur naturally (spontaneous abortion/miscarriage) or be induced.
Spontaneous Abortion (Miscarriage)
-​ Causes:
●​ Chromosomal abnormalities in the foetus.
●​ Uterine abnormalities preventing proper implantation or a weak cervix unable to
support the foetus.
●​ Medical conditions like diabetes or thyroid disease affecting the uterus.
●​ Immune system disorders causing the mother’s body to reject the foetus.
●​ Substance abuse (heavy smoking, excessive alcohol consumption, or illegal drug
use).
Induced Abortion
-​ Can be done through medication (abortion pill) or surgical procedures.
-​ A controversial topic; illegal in many parts of the world.
Arguments For Induced Abortion
-​ Health risks: If the mother’s or foetus’s health is at risk.
-​ Genetic abnormalities: Severe conditions that would impact the child’s quality of life
and strain the family.
-​ Pregnancy due to rape: Prevents the mother from enduring emotional trauma.
-​ Unwanted pregnancy:
-​ Parents are financially or emotionally unprepared.
-​ Prevents children from being born into difficult situations.
Arguments Against Induced Abortion
-​ Encourages irresponsibility: Could be misused as contraception.
-​ Medical risks: Possible infections, infertility, and complications, especially with illegal
procedures.
-​ Psychological effects: Can lead to depression and emotional distress.
-​ Moral and religious beliefs: Some view abortion as murder and consider life to begin at
conception.
Prenatal and Postnatal Care
Prenatal (Antenatal) Care
-​ Ensures the foetus grows and develops normally and the mother remains healthy.
-​ The mother must:
●​ Attend regular prenatal checkups to monitor her health and baby's development.
●​ Eat a balanced diet with adequate protein, carbohydrates, vitamins, minerals
(especially calcium and iron).
●​ Avoid drugs, alcohol, cigarettes, and illegal substances to prevent harm to the
foetus.
●​ Protect herself against infectious diseases.
●​ Exercise regularly to maintain fitness.
●​ Attend prenatal classes to learn proper exercises, breathing techniques, and baby
care.
Postnatal Care
-​ Ensures the baby grows and develops healthily, and the mother remains physically and
emotionally well.
-​ The newborn baby should be breastfed for at least six months because:
●​ Breast milk contains all necessary nutrients in the right proportions.
●​ It provides antibodies that protect against bacterial and viral infections.
●​ It is sterile, at the right temperature, and always available.
●​ It reduces the baby's risk of asthma, allergies, and other non-communicable
diseases.
●​ It strengthens the emotional bond between mother and baby.
-​ The newborn must be:
●​ Kept warm and clean.
●​ Given plenty of interaction with parents and surroundings.
●​ Taken for regular medical checkups.
●​ Vaccinated against infectious diseases.
●​ Weaned onto semi-solid and solid foods.
●​ Given continuous physical, emotional, and educational care.
-​ The mother must:
●​ Maintain a balanced diet.
●​ Avoid drugs of any kind.
●​ Exercise regularly.
●​ Receive physical and emotional support.
Sexually Transmitted Infections (STIs)
-​ Sexually transmitted infections (STIs) are infections passed on during sexual intercourse.
Common STIs include HIV/AIDS, gonorrhoea, syphilis, and genital herpes.
Implications of HIV/AIDS
Factors Making HIV/AIDS Difficult to Control:
-​ No vaccine or cure currently exists.
-​ Long incubation period – symptoms may take several years to appear, allowing
unknowingly infected individuals to spread the virus.
-​ Highly Active Antiretroviral Therapy (HAART) is:
●​ Expensive and requires a lifetime commitment.
●​ An ongoing financial burden for individuals and healthcare systems.
-​ Difficult to change sexual behavior, leading to continued transmission.
Consequences of HIV/AIDS:
-​ Shortened life expectancy.
-​ Job loss, resulting in loss of income.
-​ Increased medical costs and strain on healthcare services.
-​ Discrimination and stigma.
-​ Neglect by family and friends.
-​ Parentless children due to loss of parents.
-​ Decreased standards of living for individuals and affected families.
Prevention:
-​ Education can help reduce transmission and some of these consequences.
Cancers of the Reproductive Systems
-​ Cancer is a disease resulting from abnormal cells developing and dividing in an
uncontrolled way.
-​ These cells replace normal cells and usually produce a tumour (lump).
-​ Some of the cells can metastasise, i.e. spread to other parts of the body.
-​ Cancer can be treated by:
●​ Surgery to remove the tumour or the entire organ containing the tumour.
●​ Radiotherapy.
●​ Chemotherapy.
Plant Reproduction
-​ Plant reproduction is the production of new offspring in plants.
-​ It can occur through sexual or asexual reproduction.
Sexual Reproduction
-​ Involves the fusion of gametes, producing genetically different offspring.
-​ Two key processes:
●​ Meiosis – Rearranges genes and reduces chromosome number.
●​ Fertilization – Restores diploid chromosome number.
Alternation of generations:
-​ Two multicellular phases:
●​ Gametophyte (haploid): Produces gametes through mitosis.
●​ Sporophyte (diploid): Develops from zygote and produces spores through meiosis
(reduction division).
Gametophytes
-​ Is a haploid structure containing a single set of chromosomes per cell.
-​ Produces male or female gametes (or both) through mitosis.
-​ Types of gametophytes:
●​ Mega gametophyte (female): Produces large egg cells.
●​ Micro gametophyte (male): Produces small sperm cells.
Fertilization & Sporophyte Development
-​ Male and female gametes fuse to form a diploid zygote.
-​ The zygote undergoes mitotic cell division, developing into a multicellular sporophyte.
-​ The mature sporophyte produces spores via meiosis, restoring the haploid state.
-​ Mosses & Liverworts: Large gametophyte, small sporophyte (never separates from
gametophyte).
-​ Ferns, Gymnosperms, Angiosperms: Small gametophytes, large sporophyte.
-​ In Gymnosperms & Angiosperms:
●​ Mega gametophyte is contained in the ovule (may become seed).
●​ Micro gametophyte is contained in the pollen grain.
-​ Fertilization: The fusion of male and female gametes.
Asexual Reproduction
-​ No fusion of gametes.
-​ Offspring are genetically identical to the parent and each other, except for mutations.
Sexual Reproduction in Flowering Plants
-​ Flowering plants produce flowers for sexual reproduction.
-​ A flower consists of a receptacle that bears four whorls of modified leaves.
-​ The four whorls are sepals, petals, stamens, and one or more carpels.
-​ Most flowers contain both male and female reproductive parts.
-​ The female reproductive parts are the carpels.
-​ Carpels produce ovules containing female gametes.
-​ The male reproductive parts are the stamens.
-​ Stamens produce pollen grains containing male gametes.
Structure and Functions of the Parts of the flower:
Pollination
-​ Pollination is the transfer of pollen grains from anthers to stigmas.
-​ Pollination leads to fertilization.
-​ Types of pollination:
●​ Self-pollination: Pollen is transferred within the same flower or to another flower
on the same plant.
●​ Cross-pollination: Pollen is transferred between flowers of different plants of the
same species.
-​ Agents of pollination:
●​ Wind
●​ Insects
●​ Some birds (e.g., hummingbirds)
-​ Flowers are adapted for pollination by either wind or insects.
Comparison of Wind-Pollinated and Insect-Pollinated Flowers
Feature
Wind-Pollinated Flowers
Insect-Pollinated Flowers
Flower
Small and inconspicuous
Large and conspicuous
Petals
Often absent or small, green, and
dull-colored; no scent, nectar, or honey
guides
Large, brightly colored, scented, with
nectaries and honey guides
Pollen
Grains
Small, smooth, and light for wind
transport; produced in large quantities
Large, sticky, or spiky to attach to
insects; produced in smaller quantities
Stamens
Anthers loosely attached to long, thin
filaments and hang outside the flower;
large anthers to produce a lot of pollen
Anthers firmly attached to short, stiff
filaments; inside the flower for insect
contact
Stigmas
Long, branched, feathery, and hanging
outside to catch pollen
Flat, lobed, sticky, and inside the flower
for insect contact
Examples
Guinea grass, maize, sugar cane
Pride of Barbados, flamboyant,
allamanda
Fertilisation In Flowering Plants
-​ After pollination has occurred, the male gamete then has to reach the female gamete for
fertilisation to take place.
Fertilization Mechanism
Seed and Fruit Development
Seed Development
-​ After fertilization, each ovule develops into a seed.
-​ The zygote divides by mitosis to form the embryo.
-​ The embryo consists of:
●​ Plumule (embryonic shoot)
●​ Radicle (embryonic root)
●​ Cotyledon(s):
➢​ One in monocotyledons
➢​ Two in dicotyledons
-​ The Endosperm:
●​ Remains in endospermic seeds (e.g., maize, castor oil) and stores food.
●​ Is absorbed by cotyledons in non-endospermic seeds (e.g., green bean, pigeon
pea), where cotyledons store food.
Seed Coat Formation
-​ The integuments dry out and develop into the testa (seed coat).
-​ The micropyle remains in the testa.
-​ Water is withdrawn, and the seed becomes dormant.
Fruit Development
-​ After fertilization, the ovary wall develops into the fruit.
-​ A fruit contains one or more seeds, depending on how many ovules were fertilized.
-​ Many fruits resemble the original ovary in shape and structure.
-​ The stigma, style, stamens, and petals wither and drop off.
-​ Sepals may drop off or remain (e.g., in eggplant).
Fruits
-​ Fruits protect developing seeds and aid in seed dispersal.
-​ The fruit wall is called the pericarp and consists of three layers:
●​ Exocarp (epicarp): Outer layer
●​ Mesocarp: Middle layer
●​ Endocarp: Inner layer
Types of Fruits
-​ Succulent (fleshy) fruits:
●​ One or more layers of the pericarp are fleshy and juicy.
●​ Examples: Mango, guava, tomato, cucumber.
-​ Dry fruits:
●​ The pericarp is thin and dry.
●​ Examples: Pride of Barbados pod, pigeon pea pod, castor oil capsule.
Scars on Fruits and Seeds
-​ Fruits have two scars:
●​ One where it was attached to the parent plant.
●​ One where the style was attached.
-​ Seeds have one scar, the hilum, where they were attached to the fruit.
Seed Dispersal
-​ Fruits help in dispersing seeds.
-​ Importance of seed dispersal:
●​ Increases chances of survival.
●​ Prevents overcrowding and
competition for:
➢​ Light
➢​ Water
➢​ Carbon dioxide
➢​ Minerals
●​ Allows plants to colonize
new habitats.
-​ Fruits and seeds have adaptations for
dispersal
Dispersal by Animals
-​ Many succulent fruits contain stored food that attracts animals to eat them.
-​ seeds – pass through digestive systems unharmed when the fruit is eaten; the testa
provides protection against digestive enzymes
-​ Examples: Orange, mango, guava, tomato, golden apple.
-​ Certain small dry fruits develop hooks that attach to the fur of animals.
-​ Examples: Castor oil, duppy needle, sweethearts, burr grass.
Dispersal by Wind
-​ Some small dry fruits develop wing-like extensions to help wind carry them.
-​ Examples: Crow, Combretum.
-​ Some seeds contained in fruits develop wings for wind dispersal.
-​ Examples: Mahogany, Tecoma.
-​ Some small dry fruits develop hair-like extensions forming a "parachute" to help the wind
carry them.
-​ Examples: Tridax.
-​ Seeds in certain fruits develop a "parachute" of hairs for wind dispersal.
-​ Examples: Stephanotis, cotton, silk cotton.
Dispersal by Water
-​ Some succulent fruits have a waterproof exocarp and become buoyant, allowing them to
float on water.
-​ Examples: Coconut, manchineel.
Dispersal by Mechanical Means
-​ Some dry fruits split open along lines of weakness and eject their seeds.
-​ Examples: Pride of Barbados, pigeon pea, crotalaria.
DISEASE
-​ A disease is a condition that impairs the normal functioning of cells, tissues or organs
and it leads to the health of an organism being damaged.
-​ Symptoms of diseases are what individuals feel and can report to medical professionals.
-​ Signs are indicators that medical professionals look for to help identify the disease.
-​ Diseases can be divided into four main types:
●​ pathogenic diseases
●​ hereditary diseases
●​ deficiency diseases
●​ physiological disease
-​ Pathogenic Diseases can be classified in a variety of different ways. Two large categories
are:
●​ Communicable Diseases: These are caused by pathogens and often known as
infectious diseases.
●​ Non-Communicable Diseases: These are not caused by organisms and vary
based on the type.
-​
-​
-​
-​
A Vector is an organism that carries pathogens in or on its body.
It transmits pathogens from one person to another.
The vector is usually not harmed by the pathogen.
Examples of vectors and diseases they transmit:
●​ Houseflies → Gastroenteritis
●​ Rats → Leptospirosis
●​ Fleas → Bubonic plague
●​ Mosquitoes → Several diseases
Asthma
-​ Asthma is a condition where airways narrow, swell, and may produce extra mucus.
-​ Symptoms:
●​ Breathlessness
●​ Wheezing
●​ Tight chest
●​ Coughing
-​ Asthmatic Attack: Triggered episode where symptoms worsen.
-​ Triggers:
●​ Smoke
●​ Anxiety
●​ Allergens
●​ Exercise
●​ Fungi
-​ Treatment: Inhaler (steroid drugs that relax muscles).
Chronic Diseases
-​ Chronic Diseases are conditions lasting 1 year or more requiring ongoing medical
attention or limiting daily activities.
-​ Risk Factors: Overweight and obesity increase the risk of chronic diseases.
-​ Examples of Chronic Diseases
●​ Arthritis
●​ Diabetes Type II
●​ High blood pressure &
Coronary heart disease
●​ Cancers:
➢​ Colon
➢​ Rectum
The Life Cycle of a Mosquito
-​ A mosquito undergoes complete
metamorphosis, passing through four
distinct stages:
-​ Egg:
●​ Laid by the adult female in
protected areas that hold
water when it rains.
●​ Eggs float on the surface of
the water.
-​ Larva:
●​ Hatches from the egg.
●​ Feeding and growing stage –
feeds on microorganisms and
organic matter.
●​ Lives in water, hangs from
the surface, and breathes
through breathing tubes.
➢​ Prostate (men)
➢​ Uterus, cervix, breast
(women)
●​ Hernias
●​ Varicose veins
●​ Gallstones
-​ Pupa:
●​ Develops from the larva.
●​ Non-feeding stage – larval
tissue reorganizes into adult
tissue.
●​ Lives in water, hangs from
the surface, and breathes
through two breathing tubes.
-​ Adult (Imago):
●​ Emerges from the pupa.
●​ Flying and reproducing stage
– feeds on nectar and sugars
from plants.
●​ After mating, the female
requires a blood meal to
mature her eggs before laying
them.
●​ Adults live near human
residences, resting in cool,
dark places during the day
and flying/feeding in the
evenings
The Role of the Mosquito as a Vector
-​ Pathogens transmitted by mosquitoes have two hosts:
●​ Primary host: Humans – where the pathogens cause disease.
●​ Secondary host (intermediate host): Mosquitoes – where the pathogens reproduce
without harming the mosquito.
-​ How mosquitoes transmit pathogens:
●​ When a female mosquito feeds on infected blood, pathogens pass through her
intestinal walls and move into her salivary glands.
●​ The pathogens multiply in the salivary glands and remain there throughout her
life.
●​ Each time she bites to obtain blood for egg maturation, she injects saliva into the
host’s blood to prevent clotting.
●​ This saliva transmits the pathogens to humans, spreading disease.
-​ Mosquitoes as reservoirs:
●​ Mosquitoes remain unharmed by the pathogens.
●​ They continuously spread pathogens to humans, ensuring disease transmission
and pathogen survival.
Diseases Transmitted by Mosquitoes
Malaria
-​ Vector: Anopheles mosquito
-​ Pathogen: Plasmodium (a protozoan)
-​ Symptoms:
●​ Recurrent attacks of chills and shivering, followed by high fever and sweating
●​ Periodic high fever and weakness
●​ Can be fatal
Yellow Fever
-​ Vector: Aedes mosquito
-​ Pathogen: Virus
-​ Symptoms:
●​ Fever, headache, muscle aches (especially back muscles), nausea, vomiting
●​ Toxic phase (in some cases):
●​ Yellowing of skin and eyes (jaundice)
●​ Bleeding from the nose, mouth, eyes, and internally
●​ Liver and kidney failure
●​ Can be fatal
Dengue
-​ Vector: Aedes mosquito
-​ Pathogen: Virus
-​ Symptoms:
●​ High fever lasting several days
●​ Severe headaches and pain behind the eyes
●​ Severe joint and muscle pain
●​ Nausea, vomiting, and skin rash
●​ Hemorrhagic dengue: Can cause internal and external bleeding and can be fatal
Chikungunya
-​ Vector: Aedes mosquito
-​ Pathogen: Virus
-​ Symptoms:
●​ Similar to dengue
●​ Severe joint pain lasting for months, especially in wrists, hands, ankles, and feet
Control of Mosquitoes
-​ Controlling mosquitoes is essential to prevent the spread of mosquito-borne diseases.
-​ Understanding their life cycle helps determine the most effective control methods.
-​ Controlling Larvae and Pupae
●​ Eliminate breeding sites: Drain all areas of standing water.
●​ Use insecticides: Apply insecticides to breeding areas to kill larvae and pupae.
●​ Biological control: Introduce fish (e.g., Tilapia) to breeding areas to feed on
larvae and pupae.
●​ Surface treatment: Spray oil, kerosene, or non-toxic lecithins on still water to
prevent larvae and pupae from breathing.
-​ Controlling Adult Mosquitoes
●​ Reduce shelter areas: Remove dense vegetation to limit mosquito resting places.
●​ Use insecticides: Spray insecticides to kill adult mosquitoes.
Treatment and Control of Disease
-​ The aim of Treatment of Disease is to relieve symptoms and cure the disease if possible.
-​ The aim of Control of Disease is to prevent further spread and reduce incidence in the
population.
-​ The Ultimate Goal of treatment and control is disease eradication.
Methods Used to Treat the Four Types of Disease
Type of Disease
Treatment Methods
Pathogenic
Diseases
- Drugs to relieve symptoms (e.g., aspirin for fever, painkillers for
pain).
- Drugs, creams, and ointments to kill pathogens:
• Antibiotics for bacteria
• Antiviral agents for viruses
• Antifungal agents for fungi
- Injections of ready-made antibodies (e.g., tetanus antibodies for
‘tetanus-prone’ wounds).
Deficiency
Diseases
- A diet rich in the missing nutrient or fortified foods.
- Dietary supplements containing the missing nutrient.
Hereditary
Diseases
- Drugs to relieve symptoms as they develop.
- No cure currently exists.
Physiological
Diseases
- Drugs to relieve symptoms.
- Other disease-specific treatments (e.g., insulin for diabetes,
medication for hypertension).
Methods Used to Control the Four Types of Disease
Type of Disease
Control Methods
Pathogenic Diseases
- Quarantine and treat contagious individuals.
- Immunisation programs to vaccinate populations.
- Eradicate disease vectors.
- Improve sanitation and sewage treatment.
- Ensure safe drinking water.
- Public health education.
- Practice good hygiene and food preparation techniques.
- Use condoms to prevent STIs.
Deficiency Diseases
- Improve nutrition in populations.
- Public health education on nutrition.
Hereditary Diseases
- Avoid situations that worsen symptoms.
- Genetic counseling to predict risk in offspring.
Physiological Diseases
- Adopt a healthy lifestyle with reduced risk factors.
- Eat a balanced diet with fiber, fresh fruits, and vegetables.
- Reduce obesity.
- Engage in regular, moderate exercise.
- Attend regular medical check-ups.
Physiological Diseases
Diabetes
Diabetes Mellitus:
-​ Occurs when the body stops producing insulin or target cells stop responding.
-​ Results in inability to regulate blood glucose levels.
-​ Signs: Presence of glucose in urine (detected using test strips).
-​ Symptoms:
●​ Frequent urination (especially
●​ Itchiness around the
at night)
vagina/penis
●​ Excessive thirst
●​ Recurring thrush (due to
glucose in urine)
●​ Increased appetite
●​ Blurred vision (due to dry
●​ Extreme tiredness & weight
eye lenses)
loss with muscle loss
-​
-​
-​
-​
-​
-​
Type I Diabetes
Usually starts in childhood or
adolescence.
Cause: The cells producing insulin in
the pancreas are destroyed, leading
to no insulin production.
Treatment: Insulin injections.
Trigger: Can be triggered by viruses,
even a cold.
Type II Diabetes
Usually starts later in life.
Risk Factors:
●​ Genetic predisposition
●​ High-fat, refined sugar diet
with low fiber
●​ Obesity, high blood pressure,
and high cholesterol
-​ Treatment: Diet and exercise.
-​ Complications:
●​ Retinal damage → Blindness
●​ Nerve and kidney damage
●​ Possible amputations due to
complications.
Hypertension (High Blood Pressure)
-​ Hypertension is a condition where blood pressure in the arteries is persistently higher
than normal.
-​ Factors Contributing to Hypertension:
●​ Being overweight or obese
●​ Smoking
●​ Excessive salt or fat in the diet
●​ High alcohol consumption
●​ Lack of physical activity
●​ Stress
-​ Treatment: Medications to lower blood pressure
The Role of Diet in Controlling Physiological Diseases
-​ A healthy, balanced diet is essential in controlling:
●​ Diabetes: Helps regulate blood sugar levels and prevents obesity.
●​ Hypertension: Reduces salt and unhealthy fats, helping to maintain normal blood
pressure.
The Role of Exercise in Controlling Physiological Diseases
-​ For Diabetes:
●​ Regular aerobic exercise
●​
Lower blood glucose levels by
(e.g., swimming, walking,
increasing respiration in muscle cells
aerobics) helps:
●​
Reduce obesity
●​ Increase muscle activity
●​
Improve circulation and maintain
fitness
-​ For Hypertension:
●​ At least 30 minutes of moderate
●​ Lower stress levels
aerobic exercise daily helps:
●​
Improve circulation
●​ Reduce obesity
●​
Maintain overall fitness
Hygiene and defences against disease
Personal Hygiene
-​ Personal hygiene refers to practices that individuals carry out to maintain cleanliness and
good grooming of the body.
-​ Importance of Personal Hygiene
●​ Ensures good health.
●​ Prevents the spread of infections.
●​ Eliminates body odours.
●​ Prevents dental caries (tooth decay).
●​ Promotes social acceptance.
Skin and Hair Hygiene
-​ Sweating occurs when the body is active or in high temperatures.
-​ Sweat contains salts, urea, and dead skin cells.
-​ Bacteria feed on these substances, causing body odour (BO) and possibly infections.
-​ Measures to Reduce Body Odour and Infections
●​ Regular washing of the body, focusing on armpits, genitalia, and between the toes.
●​ Regular washing of hair.
●​ Dry skin and hair thoroughly after washing.
●​ Apply deodorant to clean, dry skin in the armpits.
●​ Change and wash clothing frequently.
Genital Hygiene
-​ Measures:
●​ Clean the genitalia thoroughly, especially during menstruation for females.
●​ Wipe female genitalia from front to back to prevent fecal contamination of the
vagina.
●​ Male circumcision (removal of the foreskin) or pull back the foreskin to wash
with soap and water.
Hand Hygiene
-​ Measures
●​ Wash hands before preparing and eating meals.
●​ Wash hands after using the toilet.
●​ Keep fingernails short and clean.
Controlling the Growth of Microorganisms
Sterilisation
-​ Sterilisation is the complete destruction of all microorganisms in a specified region.
Methods of sterilisation:
-​ Ultra-High Temperature Treatment (UHT)
●​ Used for sterilising liquid food items like milk, soups, sauces, and baby food.
●​ Food is heated above 135°C for 1 to 2 seconds, then rapidly cooled and packaged
in pre-sterilised containers.
●​ May affect the flavour.
-​ Pasteurisation
●​ Kills most microorganisms in food and drinks while maintaining the product's
quality.
●​ Commonly used for sterilising milk.
●​ Milk is heated to 72°C for 15 to 25 seconds, then cooled quickly.
-​ Canning
●​ Protects various foods from microorganisms.
●​ Food is placed in containers, sealed with lids, and heated in a boiling water bath
or steam bath to kill microorganisms.
●​ Lids are sealed after removal, preventing re-entry of microorganisms.
-​ Autoclaving (Steam Sterilisation)
●​ Uses pressurised steam to kill microorganisms on liquids, equipment, and
instruments (e.g., hospital and surgical tools).
●​ The autoclave maintains temperatures above 121°C under high pressure to
destroy microorganisms and their spores.
-​ Boiling
●​ Involves boiling materials (e.g., surgical instruments) in water at 100°C for 15 to
30 minutes.
●​ Used for purifying drinking water.
●​ Kills all bacteria and some spores.
Disinfection
-​ Disinfection involves using chemicals to reduce the number of microorganisms in a
specified region to a level that cannot cause infection. This can be done using:
Disinfectants
-​ Used to destroy microorganisms on non-living objects, such as water, countertops, and
floors.
-​ Examples: Chlorine, Ethanol.
-​ Disinfectants are stronger and more toxic than antiseptics and can be harmful to living
tissues.
Antiseptics
-​ Used to destroy microorganisms on living tissues, such as skin and in the mouth.
-​ Examples: Hydrogen Peroxide, Rubbing Alcohol, Iodine.
-​ Antiseptics are milder and cause little or no harm to living tissues.
Antibiotics and Antifungal Agents
Antibiotics
-​ Chemicals used to kill bacteria or slow their growth.
-​ Many antibiotics are produced by living organisms.
-​ The first antibiotic discovered was penicillin, produced by the Penicillium fungus.
-​ Synthetic antibiotics are now available for treating various bacterial infections.
Antifungal Agents (Fungicides)
-​ Chemicals used to treat fungal infections, such as athlete’s foot and ringworm.
Social, Environmental, and Economic Implications of Disease
Social Implications:
-​ Loss of earnings as sick individuals are unable to work.
-​ Reduced productivity in businesses due to fewer working hours.
-​ Increased demand on healthcare services as more people require treatment.
-​ Lower standards of living due to the burden of disease.
Environmental Implications:
-​ Disease in livestock and crops leads to reduced food production.
-​ Loss of agricultural yield affects biodiversity and ecosystem stability.
-​ Some disease control measures (e.g., pesticides, antibiotics) may have negative
environmental effects.
Economic Implications:
-​ Lower workforce productivity reduces overall economic growth.
-​ Farmers face financial losses due to reduced agricultural output.
-​ Higher food prices result from shortages in agricultural production.
-​ Countries reliant on exports of agricultural goods experience economic decline.
Drug Use and Misuse
-​ A drug is any chemical substance that affects the functioning of the body.
-​ Drug dependence occurs when a person takes a drug over a period of time and becomes
addicted to it, needing the drug to function.
-​ Drugs can affect the body in two main ways:
●​ Physiological Effects – Affecting the physical functioning of parts of the body.
●​ Psychological Effects – Affecting the brain, causing changes in mood and behavior.
-​ Drug dependence can be:
Physical Dependence
-​ Occurs when the body adapts to the drug and the cells can no longer function without it.
-​ Withdrawal symptoms can occur if the drug use stops suddenly, including tremors,
nausea, diarrhea, and body aches.
Psychological Dependence
-​ Occurs when the person feels a constant need for the drug.
-​ The drug becomes the central focus of their life, and they feel they cannot function
without it.
Drug Misuse
-​ Drug misuse refers to:
●​ Using a drug for purposes for which it was not intended.
●​ Using a drug in excessive quantities, beyond what is recommended.
Prescription Drugs
-​ A prescription drug is a drug that legally requires a prescription from a medical
practitioner to be dispensed.
Types of Prescription Drugs
Sedatives
-​ Used to treat anxiety and insomnia.
-​ Slow down body functions, causing the user to feel calm and inducing sleep.
-​ Examples: Sleeping pills, tranquillisers.
-​ Effects:
●​ Depressants of the central nervous system.
●​ Slow heart rate, breathing rate, and nerve signal transmission.
-​ Misuse consequences: Poor muscular coordination, slurred speech, blurred vision, and
mental confusion.
Painkillers
-​ Interfere with nerve signals and reduce the perception of pain.
-​ Examples: Paracetamol, aspirin, morphine.
-​ Effects:
●​ Reduce anxiety, promote muscle relaxation, and have similar effects to depressants.
-​ Misuse consequences: Nausea, vomiting, mental confusion, dizziness, and fluctuations in heart
rate.
Antibiotics
-​ Used to treat bacterial infections, either killing or inhibiting the growth of bacteria.
-​ Examples: Penicillin, streptomycin.
-​ Misuse consequences:
●​ Development of antibiotic-resistant strains of bacteria.
●​ Allergic reactions, which in some cases can be fatal.
Non-Prescription Drugs
-​ Non-prescription drugs are drugs that can be obtained over-the-counter at a pharmacy
without a prescription.
Types of Non-Prescription Drugs
Cocaine
-​ A highly addictive illegal drug, usually inhaled as a white powder.
-​ Effects:
●​ Stimulant of the central nervous system.
●​ Increases heart rate, blood pressure, and body temperature.
-​ Misuse consequences: Sudden death by heart attack or stroke, weight loss, nose damage,
paranoia, anxiety, depression, and potential mental illnesses such as schizophrenia.
LSD (Acid)
-​ A powerful hallucinogenic illegal drug.
-​ Taken as a pill or blotting paper.
-​ Effects:
●​ Alters perception of colors and lights.
●​ Body reactions: Dilated pupils, increased body temperature, increased blood pressure.
-​ Misuse consequences: Anxiety, disorientation, impaired judgment.
Heroin
-​ A highly addictive narcotic from the opium poppy.
-​ Taken by sniffing or injecting.
-​ Effects:
●​ Depressant of the central nervous system, reducing stress and anxiety.
-​ Misuse consequences: Withdrawal symptoms like diarrhea, vomiting, muscle pain, cold
flashes, and increased risk of HIV transmission from shared needles.
Ecstasy
-​ A hallucinogenic drug in tablet form.
-​ Effects:
●​ Heightened perception, sexual stimulation, and reduced appetite.
-​ Misuse consequences: Increased heart rate, blood pressure, and body temperature; risk of
heat exhaustion and death. Long-term use may result in heart issues, brain damage, and
kidney failure.
Marijuana (Cannabis)
-​ A hallucinogen that is commonly smoked.
-​ Effects:
●​ Creates a "high" followed by a "low."
●​ Short-term effects: Dilated pupils, red eyes, dizziness, increased appetite, and
hallucinations.
●​ Long-term effects: Lung and heart problems, mental disorders in vulnerable
individuals, and reduced male fertility.
Alcohol
-​ A legal depressant of the central nervous system.
-​ Alcoholism: Addiction to alcohol, leading to disease.
-​ Foetal Alcohol Syndrome (FAS): Caused when the fetus is exposed to alcohol, leading to
mental retardation.
-​ Short-Term Effects of Alcohol Use
●​ Slowed reflexes and reduced muscular coordination.
●​ Impaired concentration and judgment.
●​ Lack of self-control and increased aggression.
●​ Slurred speech, distorted vision, and hearing.
●​ Dehydration due to frequent urination.
●​ Memory lapses (blackouts).
●​ Vomiting.
●​ Drowsiness.
●​ Loss of consciousness.
-​ Long-Term Effects of Alcohol Use
●​ Fatty liver disease and cirrhosis (scarring) of the liver.
●​ Increased blood pressure, leading to a higher risk of heart attack and stroke.
●​ Cancer of the mouth, throat, and esophagus.
●​ Ulcers and other intestinal disorders.
●​ Permanent brain damage.
●​ Long-term memory loss.
●​ Alcohol poisoning.
●​ Malnutrition
SECTION C - CONTINUITY AND
VARIATION
SECTION C - CONTINUITY AND VARIATION
Chromosomes and Genes
Chromosomes
-​ Chromosomes are present in the nuclei of all living cells.
-​ They are composed of a single DNA molecule wrapped around histone proteins.
-​ DNA (deoxyribonucleic acid) as nucleic acid that contain all genetic information.
-​ In non-dividing cells, chromosomes exist as chromatin threads spread throughout the
nucleus.
-​ They Become shorter and thicker (visible) when a cell begins to divide.
-​ They are Passed from one generation to the next through gametes.
-​ Each species has a specific number of chromosomes in body cells.
●​ Humans have 46 chromosomes (23 pairs).
-​ The total number of chromosomes in a body cell is called the diploid number (2n).
-​ Chromosomes exist in homologous pairs: One chromosome from the mother, one from
the father.
-​ Except for sex chromosomes, members of each pair look alike.
Genes
-​ Genes are specific sections of DNA on chromosomes.
-​ They are the basic units of heredity.
-​ Each human body cell has over 30,000 genes.
-​ Each gene controls a specific characteristic.
-​ Genes work by controlling the production of proteins, especially enzymes.
-​ All cells in an organism contain the same genes, but different genes are active in different
cells:
●​ Nerve cell → genes controlling nerve activity active, muscle-related genes inactive.
●​ Muscle cell → genes controlling muscle activity active, nerve-related genes
inactive.
-​ Each individual has a unique combination of genes, except for Identical twins and
ssexually reproduced organisms from the same parent.
-​ Alleles are two or multiple forms of the same gene.
Cell Division
-​ When a cell divides, chromosomes with their genes are passed on to the newly produced
daughter cells.
-​ There are two types of cell division: mitosis and meiosis.
Mitosis
-​ Occurs in all body cells except for gamete
formation.
-​ Produces two genetically identical daughter
cells.
-​ Each daughter cell contains the same number of
chromosomes as the parent cell (diploid number,
2n).
Importance of Mitosis
-​ Ensures that each daughter cell contains the
diploid number of chromosomes, maintaining
the chromosome number of a species.
-​ Ensures that each daughter cell has an identical
combination of genes.
-​ Responsible for the formation of all cells in a
multicellular organism → essential for growth
and tissue repair.
-​ Enables asexual reproduction, producing
genetically identical offspring.
Mitosis and Asexual Reproduction in Plants
-​ Some plants reproduce asexually through
mitosis in specific structures of the parent plant.
-​ This process is called vegetative propagation.
-​ Since mitosis produces genetically identical cells, all offspring from one parent are
genetically identical and form a clone.
-​ Cloning is the process of creating genetically identical organisms without sexual
reproduction.
Examples of Natural Vegetative Propagation
-​ Growth from vegetative organs at the beginning of the growing season:
●​ Rhizomes
●​ Stem tubers
●​ Corms
●​ Bulbs
-​ Growth from outgrowths of the parent plant:
●​ Runners
●​ Leaf buds
●​ Suckers
Examples of Artificial Vegetative Propagation
Cuttings
-​ Farmers and gardeners artificially propagate plants by taking cuttings.
-​ Cuttings are plant parts that develop roots and shoots under suitable conditions.
-​ Examples:
●​ Sugar cane: A stem piece with two or three buds, when placed in soil, grows into new
plants.
●​ Hibiscus: A stem cutting with leaves grows roots from the cut end, forming a new
plant.
Tissue Culture
-​ Used to propagate plants like orchids, potatoes, and tomatoes.
-​ Process:
●​ Small pieces of tissue (explants) are taken from a parent plant.
●​ They are grown in a nutrient-rich culture under sterile conditions.
●​ The tissue forms cell masses called calluses.
●​ Plant hormones stimulate each callus to grow into a new plant.
-​ Advantages:
●​ Produces plants with desirable traits (e.g., high yield, disease resistance, fast
growth).
●​ Ensures all new plants are genetically identical to the parent plant.
Cloning in Animals
-​ Process of Animal Cloning:
●​ A nucleus is removed from an ovum (egg cell) of a female donor.
●​ A body cell (with its nucleus intact) is taken from the animal to be cloned.
●​ The nucleus from the body cell is fused with the enucleated ovum.
●​ The reconstructed ovum is placed into a surrogate mother.
●​ The surrogate mother carries the embryo and gives birth to a genetically identical
copy of the donor animal.
-​ Example: Dolly the sheep was the first mammal cloned using this method.
-​ Challenges and Risks of Cloning:
●​ Low success rate – very few cloned embryos survive to birth.
●​ Cloned animals often suffer from health problems or genetic abnormalities.
●​ Clones may have reduced life spans compared to naturally born animals.
●​
Meiosis (Reduction Division)
-​ Meiosis occurs in reproductive organs during gamete production.
-​ Produces four genetically
non-identical cells with half
the chromosome number of
the parent cell (haploid, n).
-​ It Ensures that:
●​ Each daughter cell has
the haploid number of
chromosomes.
●​ The diploid number is
restored during
fertilization.
●​ Each daughter cell has
a unique combination
of genes, leading to
genetic variation
among offspring.
-​ Variation
allows species
to adapt to
changing
environmental
conditions
Inheritance
-​ Genes exist in pairs, like chromosomes.
-​ One gene in each pair is maternal in origin, and the other is paternal.
-​ Genes occupy equivalent positions on homologous chromosomes.
-​ A gene controlling a characteristic can have different forms called alleles.
-​ Each gene usually has two different alleles.
-​ The genotype is the genetic composition of an organism.
-​ The phenotype refers to the observable characteristics of an organism.
-​
-​
-​
-​
-​
-​
-​
Example: Albinism in Humans
Albinism is caused by the lack of melanin production in the skin, eyes, and hair.
The gene controlling melanin production has two alleles:
●​ N – stimulates melanin production (dominant allele).
●​ n – fails to stimulate melanin production (recessive allele).
Dominant allele (N): Always expressed in the phenotype if present.
Recessive allele (n): Only expressed if both alleles are recessive (nn).
Possible genotypes:
●​ NN – Homozygous dominant (normal melanin production).
●​ Nn – Heterozygous (normal melanin production, but carries the albinism allele).
●​ nn – Homozygous recessive (person has albinism).
Homozygous – When both alleles are the same (NN or nn).
Heterozygous – When the alleles are different (Nn).
Possible combinations of the alleles controlling melanin production
Results of possible crosses:
-​ If one parent is homozygous dominant and one is homozygous recessive:
-​ If one parent is heterozygous and one is homozygous recessive, showing the use of a
Punnett square to predict the outcome of the cross:
-​ If both parents are heterozygous, i.e. carriers:
-​ Incomplete Dominance: Neither allele is completely dominant, resulting in a blended
phenotype
-​ Co-Dominance: Both alleles are fully expressed, and both traits appear together in the
phenotype.
Examples:
Example
Incomplete Dominance
Flower Color
Red (RR) × White (WW) →
Red (RR) × White (WW) → Red &
Pink (RW) (Blended phenotype) White patches (RW) (Both traits appear
together)
Animal Fur
Black (BB) × White (WW)
→ Gray (BW)
Codominance
Black (BB) × White (WW) → Black
and White speckled (BW)
-​ Other examples for codominance include:
●​ Sickle cell anaemia
●​ ABO blood groups.
-​
-​
-​
-​
-​
-​
-​
Sickle Cell Anaemia
Sickle Cell Anaemia is caused by an abnormal allele.
The blood of a person with sickle cell anaemia contains abnormal haemoglobin S instead
of normal haemoglobin A.
The normal allele (HbA) stimulates the production of normal haemoglobin A.
The abnormal allele (HbS) stimulates the production of abnormal haemoglobin S.
Co-dominance occurs, meaning both alleles (HbA and HbS) are expressed.
People with HbA/HbS genotype have sickle cell trait, which means they are carriers.
People with HbS/HbS genotype have sickle cell anaemia, experiencing health
complications due to sickle-shaped red blood cells.
ABO Blood Groups
-​ Controlled by three alleles: A, B, and O.
●​ A and B are dominant over O.
●​ A and B are co-dominant, meaning neither dominates the other.
-​ Each person inherits two alleles (one from each parent).
-​ Genotypes and Corresponding Blood Groups
Genotype
Phenotype
IA IA
Blood Group A
IA IO
Blood Group A
IB IB
Blood Group B
IB IO
Blood Group B
IA IB
Blood Group AB
IO IO
Blood Group O
Pedigree Charts
-​ A pedigree chart shows how a specific trait is inherited across generations in a family.
-​ Purpose:
●​ Determines genotypes and possible genotypes of individuals.
●​ Predicts possible genotypes and phenotypes of future offspring.
●​ Helps genetic counselors assess the risk of genetic disorders in future generations.
-​ Symbols Used in Pedigree Charts:
●​ Circle (○) – Represents a female.
●​ Square (□) – Represents a male.
●​ Shaded symbol – Indicates an affected individual.
●​ Unshaded symbol – Represents an unaffected individual.
●​ Half-shaded symbol – Denotes a carrier (for recessive traits).
●​ Horizontal line between a male and female represents a mating.
●​ Vertical line leading to offspring represents their children.
-​ Uses in Genetics:
●​ Identifies patterns of inheritance (dominant, recessive, sex-linked).
●​ Helps diagnose and manage genetic conditions.
●​ Aids in family planning and genetic counseling.
Sex Determination and Sex Chromosomes
-​ Each cell contains a pair of sex chromosomes that determine an individual's gender.
-​ There are two types of sex chromosomes: X and Y.
-​ Genotypes and Sex:
●​ XX → Female
●​ XY → Male
Sex Determination:
-​ Only males can pass on the Y chromosome.
-​ A male can pass either an X or a Y chromosome.
-​ Females can only pass an X chromosome.
-​ The father determines the gender of the offspring.
-​ If the father passes an X chromosome, the child is female (XX).
-​ If the father passes a Y chromosome, the child is male (XY).
Sex-Linked Characteristics
-​ Sex-Linked Characteristics are traits determined by genes located on the sex
chromosomes (X or Y) but not related to gender determination.
-​ These genes are called sex-linked genes.
-​ The X chromosome is larger than the Y chromosome and carries more genes.
-​ Males (XY) have only one X chromosome, so any allele on it (dominant or recessive) is
expressed in the phenotype.
-​
-​
-​
-​
-​
-​
-​
-​
Haemophilia (Example of a Sex-Linked Condition)
Haemophilia is a disorder where blood fails to clot properly.
The alleles for haemophilia are located only on the X chromosome.
●​ H (dominant allele) → Normal blood clotting.
●​ h (recessive allele) → Haemophilia.
Males (XY) Have only one X chromosome.
Males are much more likely to have haemophilia than females
If their X chromosome carries the h allele, they will have haemophilia (XʰY).
Females (XX) however need both X chromosomes to carry h (XʰXʰ) to have
haemophilia.
If they have only one recessive allele (XʰX), they are carriers but do not have the
condition.
Males are more likely to have haemophilia than females because they only need one
recessive allele (XʰY) to express the condition.
Colour Blindness (Example of Sex-Linked Condition)
-​ Colour Blindness is a condition where a person cannot distinguish between certain colours.
-​ Cause: It is caused by a recessive allele (n) on the X chromosome.
-​ Alleles:
●​ N (dominant allele) → Normal vision.
●​ n (recessive allele) → Colour blindness.
Inheritance Pattern (Same as Haemophilia)
-​
-​
-​
-​
-​
Males (XY) have only one X chromosome.
Males are more likely to be colour blind
If they inherit the n allele (XⁿY), they will have colour blindness.
Females are less likely to be colour blind
Females (XX) need both X chromosomes to carry the n allele (XⁿXⁿ) to have colour
blindness.
-​ If they inherit one recessive allele (XⁿX), they are carriers but have normal vision.
Variation
-​ No two living organisms are exactly alike, not even identical twins.
-​ Variation is caused by a combination of genetic factors and environmental factors.
-​ The phenotype of an organism is determined by both:
Phenotype = Genotype + Environmental Influences
Genetic Causes of Variation
Meiosis
-​ Each gamete produced by meiosis has a unique combination of genes due to:
●​ Crossing over: Chromatids of homologous chromosomes exchange genetic
material.
●​ Independent assortment: Chromosomes align randomly during meiosis, creating
genetic diversity.
Sexual Reproduction
-​ During fertilisation, male and female gametes fuse randomly, leading to different genetic
combinations in each zygote.
Mutations
-​ A mutation is a sudden change in a gene or part of a chromosome.
-​ Mutations in body cells → Not inherited.
-​ Mutations in gametes or zygotes → Can be inherited.
-​ Most mutations are harmful, but some may be beneficial, providing a selective
advantage.
-​ Example: The peppered moth evolved due to environmental changes.
Environmental Causes of Variation
-​ Living organisms are constantly affected by different factors in their environment.
-​ Factors affecting animals: Food, drugs, physical forces, temperature, and light can
influence animals.
-​ Factors affecting plants: Temperature, light intensity, availability of mineral salts, and
water affect plant growth and development.
-​ This variation is not caused by genes and cannot be passed onto offspring.
The Importance of Variation
-​ It enables species to adapt to changing environmental conditions, improving their chances
of survival.
-​ It provides the raw material for natural selection, allowing species to remain well adapted
to their environment or to gradually improve by becoming better suited to their
surroundings.
-​ It reduces the risk of extinction by ensuring that some organisms can survive adverse
environmental changes.
Types of Variation
Continuous Variation
-​ Continuous Variation is where Characteristics show a
gradual range from one extreme to another without a break.
-​ Characteristics show normal distribution: most individuals
fall in the middle of the range, with fewer at the two
extremes.
-​ Examples: Height, weight, foot size, hair color, leaf size in
plants.
-​ Controlled by:
●​ Multiple genes (polygenic inheritance).
●​ Environmental factors can influence these traits.
Discontinuous Variation
-​ Discontinuous Variation is where characteristics show distinct differences with no
intermediates.
-​ Individuals can be divided into clear categories.
-​ Examples: ABO blood groups, tongue rolling, presence or absence of horns in cattle.
-​ Controlled by:
●​ A single gene (monogenic inheritance).
●​ Environmental factors have little to no effect.
Species:
-​ A species is a group of organisms that share common ancestry, look alike, and can
interbreed to produce fertile offspring.
Interbreeding Between Species:
-​ Members of some closely related species are capable of interbreeding and producing
offspring.
-​ However, their offspring are usually either sterile or biologically weak, preventing further
reproduction.
-​ This keeps species as distinct groups.
Examples of Interbreeding Species:
-​ Birds:
●​ Certain species of owls, gulls, crows, and ducks.
-​ Plants:
●​ Shaddock + Jamaican sweet orange → Grapefruit
●​ Spearmint + Water mint → Peppermint
-​ Mammals:
●​ Donkey + Horse → Mule or Hinny
●​ Lion + Tiger → Liger or Tigon
The Formation of New Species – Speciation
-​ As long as organisms from different groups within a species can interbreed and genes can
flow between them, they remain the same species.
-​ If groups become separated or isolated, gene flow stops.
-​ Genetic differences develop over time.
-​ Eventually, they can no longer successfully interbreed.
-​ They become separate species, each with its own gene pool.
Speciation by Geographical Separation
-​ A physical barrier prevents two groups of the same species from meeting and
interbreeding.
-​ Examples of barriers:, Mountain ranges, Deserts, Oceans, Rivers, Streams
Speciation by Ecological and Behavioural Separation
-​ Occurs when two groups of the same species live in the same region but adapt to different
habitats, reducing gene flow.
-​ Also occurs when animals have elaborate courtship behaviours before mating.
-​ Courtship behaviours may involve: Colour, Markings, Calls, Actions of the opposite sex
-​ Small differences in these stimuli can prevent mating, stopping gene flow.
Extinction of Species
-​ Over time, species can become extinct, meaning they no longer exist.
-​ Causes of extinction:
●​ Habitat loss
●​ Disease
●​ Predation by introduced species
●​ Competition with introduced species
●​ Overexploitation by humans, e.g. overfishing or overhunting
-​ Example: The Caribbean monk seal became extinct due to overhunting for its fur, meat,
and oil.
The Role of Natural Selection in Biological Evolution
-​ Natural selection is the process by which populations change over time (evolve) to
remain well adapted to their environment.
-​ Charles Darwin proposed the idea of evolution by natural selection in 1859 in his book
On the Origin of Species.
Theory of Natural Selection
-​ Overproduction of Offspring:
●​ Most organisms produce more offspring than needed for replacement.
●​ Despite this, population sizes remain relatively constant.
●​ This means there is a constant struggle for survival in nature.
-​ Variation and Survival of the Fittest:
●​ All organisms show variation, and many variations are inherited.
●​ Organisms with variations that better adapt them to their environment are more
likely to survive.
●​ This is known as survival of the fittest.
-​ Passing on Advantageous Traits:
●​ Well-adapted organisms are more likely to survive and reproduce.
●​ They pass on their advantageous characteristics to their offspring.
●​ Over time, species remain well adapted or gradually improve by becoming even
better adapted.
-​ Natural selection preserves useful adaptations.
-​ Genes that produce advantageous traits are passed on more frequently than genes with
less advantageous traits.
-​ This helps populations retain the genes that keep them well adapted.
-​ Genetic variation, especially from beneficial mutations, is the raw material for natural
selection.
Evidence for Natural Selection
The Peppered Moth
-​ The peppered moth lives in Britain and is preyed on by birds.
-​ Before the Industrial Revolution the moths were black and white speckled, blending in
with pale lichen-covered tree trunks.
-​ This camouflage helped them avoid predators.
-​ During the Industrial Revolution a melanic (all black) variety appeared in industrial
areas around Manchester.
-​ This variety arose due to a dominant mutation.
-​ The tree trunks became blackened with soot, making the black moths better camouflaged
than the speckled ones.
-​ The melanic variety had a selective advantage in industrial areas.
-​ Over time, it became far more numerous than the speckled variety in those areas.
Antibiotic and Pesticide Resistance
-​ In natural populations of bacteria and various pests (e.g. insects, fungi, and weeds), some
individuals carry genes that make them resistant to antibiotics or pesticides (e.g.
insecticides, fungicides, and herbicides).
-​ These resistance genes arise due to mutations.
-​ When exposed to antibiotics or pesticides:
●​ Resistant organisms have a selective advantage.
●​ They are more likely to survive and reproduce than non-resistant organisms.
●​ They pass on their resistance genes to their offspring.
-​ Over time, this leads to an increase in the number of resistant organisms within
populations.
Galapagos Finches
-​ The Galapagos Islands in the Pacific Ocean have at least 13 different species of finches.
-​ These finches are likely descendants of a single South American species that colonized
the islands from the mainland.
-​ The main difference between the species is the shape and size of their beaks.
-​ Due to natural selection, their beaks have become highly adapted to the different types of
food available on the various islands.
-​ Examples of food sources: Seeds, Insects, Nectar, Fruits
Caribbean Lizards
-​ Anole lizards are believed to have colonized the Caribbean islands from Central and
South America.
-​ Through natural selection, lizards stranded on the four larger islands—Cuba, Hispaniola,
Jamaica, and Puerto Rico—independently evolved into different species.
-​ These species developed similar characteristics that helped them fit into similar
ecological niches on each island.
-​ Examples of adaptations:
●​ Twig anoles → Long, slender bodies and tails; short legs.
●​ Trunk-ground anoles → Long, muscular legs.
●​ Canopy anoles → Large toe pads.
-​ Today, each island has equivalent species with similar body types
Artificial Selection
-​ Artificial selection involves humans selecting and breeding organisms with desirable
characteristics.
-​ This process results in new breeds, strains, or varieties of plants and animals that suit
human needs.
-​ Undesirable characteristics are "bred out".
-​ Artificial selection produces new varieties faster than natural selection.
-​ However, it reduces variation in populations, making them more vulnerable if
environmental conditions change.
Inbreeding
-​ Involves breeding closely related individuals with desirable characteristics.
-​ It is usually done to improve one particular trait.
-​ Continued inbreeding reduces the gene pool, increasing the frequency of undesirable
genes and lowering the overall fitness of the organisms.
-​ After several generations of inbreeding, outbreeding is necessary to introduce new genes
into the population.
Outbreeding
-​ Involves breeding individuals from genetically distinct populations with desirable
characteristics.
-​ The offspring produced are called hybrids and typically show characteristics that are
superior to both parents.
-​ This is known as hybrid vigour.
Artificial Selection in Agriculture
-​ Artificial selection is used extensively in agriculture to produce crop plants and farm
animals with:
-​ Increased yields:
●​ Cattle that produce more milk or meat.
●​ Chickens that lay more or larger eggs.
●​ Sugar cane that produces more sucrose.
●​ Cereal crops that produce more grain.
-​ Increased quality of product:
●​ Meat with less fat.
●​ Cereals and ground provisions with higher protein content.
-​ Faster growth rates.
-​ Increased number of offspring.
-​ Shorter time to reach maturity, allowing for more generations per year.
-​ Increased resistance to pests and disease, reducing product loss and the need for
pesticides.
-​ Increased suitability to the environment.
Artificial Selection in Action in the Caribbean
-​ Jamaica Hope: A breed of dairy cattle developed in Jamaica by breeding Jersey, Zebu,
and Holstein cattle.
-​ This breed is:
●​ Heat tolerant
●​ Has high resistance to ticks and tick-borne diseases
●​ Produces a high yield of milk, even on the poor pasturelands of the Caribbean.
-​ Sugar Cane:
-​ Sugar cane has been bred to produce varieties with:
●​ High sucrose content
●​ Increased resistance to disease and insect pests
●​ Greater suitability to its environment
●​ Improved ratooning ability (ability to produce new shoots after harvesting).
Genetic Engineering
-​ Genetic engineering involves changing the traits of one organism by inserting genetic
material from a different organism into its DNA.
-​ The organism receiving the genetic material is called a transgenic organism or genetically
modified organism (GMO).
-​ Uses of Genetic Engineering
●​ Protect agricultural crops against environmental threats, such as pathogens, pests,
herbicides, and low temperatures.
●​ Modify the quality of a product, e.g. increasing nutritional value.
●​ Make organisms produce materials they do not usually produce, such as vaccines
and drugs.
●​ Improve yields, e.g. increasing size or growth rate, or making organisms more
hardy.
Genetic Engineering and Food Production
Golden Rice:
-​ Two genes, one from maize and one from a soil bacterium, are inserted into rice plants.
-​ This stimulates the endosperm of the rice grains to produce beta-carotene, which the body
converts to vitamin A.
-​ Golden rice is aimed at fighting vitamin A deficiency, which is a leading cause of
blindness and death in children in many underdeveloped countries.
Roundup Resistant Crops:
-​ A gene from a soil bacterium is inserted into certain crop plants like soya bean, corn, and
canola.
-​ These crops become resistant to the herbicide Roundup, which can be sprayed to destroy
weeds without harming the crops.
Bt Corn:
-​ A gene from a soil bacterium is inserted into corn plants, causing them to produce a toxic
chemical harmful to corn-boring caterpillars.
-​ This makes the corn plants resistant to these pests.
Bovine Somatotrophin (BST) Hormone:
-​ The gene controlling BST hormone production in cattle is transferred to bacteria.
-​ The bacteria produce the hormone, which is then injected into cattle to increase milk and
meat production.
Chymosin (Rennin):
-​ The gene for chymosin production, found in calf stomach cells, is transferred to bacteria
or fungi.
-​ These micro-organisms produce chymosin, which is used in cheese production,
significantly increasing cheese production worldwide.
Genetic Engineering and Medical Treatment
Insulin:
-​ The gene that controls insulin production in humans is transferred into bacteria, which
then produce insulin used to treat diabetes.
Human Growth Hormone (HGH):
-​ The gene controlling the production of HGH is transferred into bacteria, which then
produce the hormone used to treat growth disorders in children.
Hepatitis B Vaccine:
-​ The gene controlling the production of hepatitis B antigens in the hepatitis B virus is
transferred into yeast, which produces the antigens used as a vaccine.
-​ Other drugs produced by genetic engineering:
●​ Blood clotting drugs for people with haemophilia.
●​ Follicle stimulating hormone (FSH) to stimulate the ovaries to produce mature
ova in women who are infertile.
●​ Interferons to treat viral infections and certain cancers.
●​ Anticoagulants to prevent life-threatening blood clots in heart patients.
●​ Human papilloma virus (HPV) vaccine.
Advantages of Genetic Engineering
-​ Increased Yields:
●​ Genetic engineering can increase crop yields, potentially boosting the world food
supply and reducing food shortages.
-​ Improved Nutritional Value:
●​ The nutritional value of foods can be enhanced, helping to reduce deficiency diseases
globally.
-​ Reduced Need for Chemical Pesticides:
●​ Crops can be genetically engineered to be resistant to pests, reducing the need for
harmful chemical pesticides.
-​ Safer Vaccines:
●​ Vaccines produced through genetic engineering are generally safer than those
containing live, weakened, or dead pathogens.
-​ Larger Quantities of Safer Drugs:
●​ Drugs can be produced in larger quantities and in a safer and purer form
compared to those made from animal sources, providing more people worldwide
with access to life-saving drugs.
-​ Ethical Benefits:
●​ Genetic engineering overcomes ethical concerns about obtaining certain drugs
from animals, such as insulin from pigs and cows.
Disadvantages of Genetic Engineering
-​ Toxicity to Beneficial Organisms:
●​ Plants genetically engineered to be toxic to pests may also harm useful organisms
like pollinators, potentially affecting wild plants and reducing crop reproduction,
which could decrease food production.
-​ Unpredictable Environmental Issues:
●​ Plants genetically engineered to resist pests and herbicides could lead to problems
like the development of pesticide-resistant insects or the creation of
herbicide-resistant superweeds through interbreeding with wild plants.
●​ Once a genetically modified organism (GMO) is released into the environment, it
cannot be contained or recalled, and any negative effects may be irreversible.
-​ Increased Allergens:
●​ The transfer of genes causing allergic reactions between species could increase
the number of allergens in foods.
-​ Unknown Health Risks:
●​ There may be unknown health risks associated with eating genetically modified
plants and animals.
-​ Economic Disparities:
●​ Large companies with the funds and technology for genetic engineering could
make large profits at the expense of smaller companies and poorer nations.
-​ Ethical Concerns:
●​ Future genetic engineering advancements may allow us to alter the genetic
make-up of higher organisms, including humans (e.g., designer babies), raising
difficult moral and ethical issues.
●​ Questions arise about how far we should go in changing our genes and those of other
animals.
Other Applications of Genetic Technology
DNA Testing or DNA Fingerprinting
-​ Crime-solving: To determine if DNA samples are from the same person, helping to solve
crimes.
-​ Paternity and Maternity Testing: To determine the paternity or maternity of a child.
-​ Identification: To identify a body or detect genetic disorders or diseases before birth or early in
life, allowing early treatment.
-​ Genetic Counseling: To help predict the likelihood that a child will inherit a genetic disease
from carrier parents.
-​ Family Relationships: To identify family relationships and reunite families or determine
ancestral lines for family trees.
Gene Therapy
-​ Gene Replacement: Inserting a functional gene into cells to replace a defective one causing a
disease.
-​ Gene Inactivation: Turning off a defective gene that causes a disease.
-​ Immune System Enhancement: Introducing a gene to help the body’s immune system fight
diseases.
Captive Breeding Programs
-​ Conservation: Breeding and raising animals in controlled environments (e.g., zoos, aquaria,
wildlife reserves) to prevent extinction and reintroduce animals into the wild.
-​ Genetic Diversity Assessment: Using DNA profiling to assess genetic diversity to avoid
inbreeding and ensure healthier offspring in future generations.
-​ Biodiversity Preservation: To conserve species and preserve biodiversity.