Chapter 1
Characteristics & classification of living
organisms
Characteristics of living organisms
(MRS. H. GREN)
Movement: Action by an organism or part of an organism causing a change of position or place
Respiration: Chemical reactions in cells that break down nutrient molecules and release energy for metabolism
Sensitivity: Ability to detect and respond to changes in the internal or external environment
Homeostasis
Growth: Permanent increase in size and dry mass
Reproduction: Processes that make more of the same kind of organism
Excretion: Removal of the waste products of metabolism and substances more than requirements
Nutrition: The taking in of materials for energy, growth, and development
Concept and uses of classification systems
 Organisms can be classified into groups by
the features that they share.
Species: group of organisms that can reproduce to
produce fertile offspring
The binomial system of naming species
An internationally agreed system in which the
scientific name of an organism is made up of two
parts showing the genus and species
The sequence of classification is: Kingdom, Phylum,
Class, Order, Family, Genus, Species
Dichotomous keys
Used to identify organisms based on a series of questions about their features.
Dichotomous means “branching into two” (two descriptions at a time)
Example:
Classification systems
Aim to reflect evolutionary relationships.
In the past, scientists have encountered many difficulties when trying to determine the evolutionary relationships
of species based on this method. Using the physical features of species (such as color/shape/size) has many
limitations and can often lead to the wrong classification of species
DNA as means of classification.
Organisms share features because they originally descend from a common ancestor.
Example: all mammals have bodies covered in hair, feed young from mammary glands, and have external ears
Originally classified using morphology and anatomy
DNA sequences studies show that the more similar the base sequences in the DNA of two species, the more closely
related those two species are (and the more recent in time their common ancestor is)
Groups of organisms which share a more recent ancestor (are more closely related) have base sequences
in DNA that are more similar than those that share only a distant ancestor
Features
Main features are used to place organisms into groups within the animal kingdom.
 the main groups of vertebrates: mammals, birds, reptiles, amphibians, fish
 the main groups of arthropods: myriapods, insects, arachnids, crustaceans
Vertebrates
All have backbone.
Invertebrates
Main features of all fungi (e.g., moulds, mushrooms, yeast)
o
usually, multicellular
o
cells have nuclei and cell walls not made from
cellulose.
o
do not photosynthesize but feed by
saprophytic (on dead or decaying material) or
parasitic (on live material) nutrition.
Main features of all Protoctista (e.g., Amoeba, Paramecium, Plasmodium)
o
most are unicellular but some
are multicellular
o
all have a nucleus, some may
have cell walls and chloroplasts
o
meaning some Protoctista
photosynthesize and some feed
on organic substances made by
other living things.
Main features of all Prokaryotes (bacteria, bluegreen algae)
o
o
often unicellular
cells have cell walls (not made of cellulose)
and cytoplasm but no nucleus or mitochondria.
Ferns
Leaves called fronds, do not produce flowers but
instead reproduce by spores
Flowering Plants
Reproduce sexually by means of flowers and seeds
How do you distinguish between monocotyledons and dicotyledons?
Viruses
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Viruses are not part of any classification system as they are not
considered living things.
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They do not carry out the seven life processes for themselves,
instead they take over a host cell’s metabolic pathways in
order to make multiple copies of themselves.

Virus structure is simply genetic material (RNA or DNA) inside
a protein coat.
Chapter 2
Cells
The smallest units from which all organisms are made
Animal Cell
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Multicellular
Contain nucleus with a distinct membrane.
Do not have cellulose cell walls.
Do not contain chloroplasts.
Feed on organic substances
Store carbohydrates as glycogen
Nervous coordination
Able to move.
Plant Cell
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Multicellular
Contain nucleus with a distinct membrane.
Cell walls made from cellulose.
Cells contain chloroplasts.
They food y photosynthesis
Store carbohydrates as starch or sucrose
Do not have nervous coordination.
Cell Structure in both animal and plant cells
Structure
Nucleus
Cytoplasm
Cell
membrane
Ribosomes
Mitochondria
Function
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Contains genetic material (DNA) which controls the activities of the cell
A gel-like substance composed of water and dissolved solutes.
Supports internal cell structures.
Site of many chemical reactions (Anaerobic Respiration)
Holds the cell together separating the inside from the outside.
Controls what enters and leaves
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Found in the cytoplasm.
Site of protein synthesis
Most of reactions: Aerobic respiration where energy is released to fuel cellular
processes.
Cells with high rates of metabolism have higher number of mitochondria than
cells
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Cell structure only in plant cells
Cell wall
Chloroplasts
Permanent
Vacuole
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Made of cellulose
Gives the cell extra support, defines the shape
Contains green chlorophyll pigments to absorb light and energy, and the enzymes
needed for photosynthesis
Contains cell sap, solution of sugars and salts dissolved in water.
Used for storage of certain materials.
Helps support of the shape of the cell
Bacteria Cells
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They are microscopic single-celled
organisms.
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Possess a cell wall (made of peptidoglycan,
not cellulose), cell
membrane, cytoplasm, and ribosomes.
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Lack a nucleus but contain a circular
chromosome of DNA that floats in the
cytoplasm.
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Plasmids are sometimes present - these
are small rings of DNA (also floating in the
cytoplasm) that contain extra genes to those
found in the chromosomal DNA.
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They lack mitochondria, chloroplasts and
other membrane-bound organelles found in animal and plant cells.
Examples of bacteria: Lactobacillus (yoghurt for milk) Pneumococcal (pneumonia)
Production of New Cells
New cells are produced by division of existing cells so to help the body grow and repair itself
Specialized cells
Those which have developed certain characteristics
to perform specific functions. Differences controlled
by genes.
ciliated cells – movement of mucus in the trachea
and bronchi
root hair cells – absorption
palisade mesophyll cells – photosynthesis
nerve cells – conduction of electrical impulses
red blood cells – transport of oxygen
sperm and egg cells (gametes) – reproduction
Levels of Organization
cell: The smallest units from which all organisms
are made.
tissue: a group of similar cells that work together to
perform a particular function.
organ: a group of tissues that work together to
perform a particular function.
organ system: several organs that work together to
perform a particular function
organism: a living thing
Size of Specimens
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Magnification = image size / actual size
Actual size = image size / magnification
Image size = magnification x actual size
𝑚𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 =
MAGNIFICATION IS ALWAYS WRITTEN WITH AN “X” IN
FRONT OF IT
3 Convert measurements between millimeters and
micrometers.
0.1 CENTMETER
(cm)
1 MILIMETER
(mm)
1000
MICROMETER (μ)
𝐼𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒
𝐴𝑐𝑡𝑢𝑎𝑙 𝑠𝑖𝑧𝑒
Chapter 3
Movement into and out of cells
Diffusion
The net movement of particles from a region of their higher
concentration to a region of their lower concentration down a
concentration gradient, because of the kinetic energy of
random movement of molecules and ions.
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Substances move into and out of cells by
diffusion through the cell membrane.
Importance of diffusion of gases and solutes:
The diffusion of gases is what makes gas exchange possible as oxygen is obtained and carbon dioxide its
released. Diffusion of solutes is what gives plant cells their proper shape and enables plants to transpire.
Factors that influence diffusion:
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Limited to surface area: The bigger a cell or structure is, the smaller its surface area to volume ratio is,
slowing down the rate at which substances can move across its surface.
Temperature: The higher the temperature, the faster molecules move as they have more energy
Concentration gradients: The greater the difference in concentration either side of the membrane, the
faster movement across it will occur.
Distance: The smaller the distance molecules must travel the faster transport will occur
Osmosis
The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower
water potential (concentrated solution), through a partially permeable membrane (Very thin layer)
 Water moves in and out of cells by osmosis through the cell membrane.
Effects on plant tissues of immersing them in solutions of different concentrations.
Solution
Effects
Hypertonic solution (lower water potential
than that of the plant cells)
This causes the cytoplasm to shrink, and thus
the cell membrane gets ripped away from the
cell wall. This process is called plasmolysis.
Cells become weak and flaccid, as there isn’t
enough cytoplasm to support the cell and help
it maintain its shape.
Isotonic solution (Equal
water potential)
No net movement of
water
This means the volume or
shape of the plant cell is
unlikely to change.
Hypotonic solution (Higher
water potential)
Plant cells have
extraordinarily strong cell
walls. This holds the plant
cell intact, and as the
cytoplasm pushes outside,
the cell simply swells to its
full size and becomes rigid.
This cell is turgid.
State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall.
Turgor pressure: the pressure of the water pushing outwards on a plant cell wall.
Water potential is the potential of water to leave a system.
This is affected by:
1. water pressure
2. the volume of the water relative to the volume of the system (e.g., a lot of water in a small system
will force water out of the system)
3. the concentration of the water
Water is important as a solvent in the following situations within organisms:
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Dissolved substances can be easily transported around organisms.
Digested food molecules are in the alimentary canal but need to be moved to cells all over the body without water as a solvent this would not be able to happen.
Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water
which makes them easy to remove from the body in urine.
Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can
happen as necessary in cells.
Experimentation
If the plant tissue gains mass:
Water must have moved into the plant tissue from the
solution surrounding it by osmosis.
The solution surrounding the tissue is more dilute than
the plant tissue (which is more concentrated)
If plant tissue loses mass:
Water must have moved out of the plant tissue into the
solution surrounding it by osmosis.
The solution surrounding the tissue is more
concentrated than the plant tissue (which is more dilute)
If there is no overall change in mass:
There has been no net movement of water as the
concentration in both the plant tissue and the solution
surrounding it must be equal.
Active transport
The movement of particles through a cell membrane from a
region of lower concentration to a region of higher
concentration using energy from respiration.
Importance of Active Transport:
Energy is needed because particles are being moved against
a concentration gradient, in the opposite direction from
which they would naturally move (by diffusion)

Vital process for the movement of molecules or ions
across membranes: uptake of glucose and uptake of
ions from soil water by root hair cells in plants
Protein carriers: Active transport works by using carrier
proteins embedded in the cell membrane to pick up specific
molecules and take them through the cell membrane against their concentration gradient.
Chapter 4
Biological molecules
Molecules
Molecule
Carbohydrates
Fats (Lipid)
Proteins
Chemicals elements that make up
Carbon, oxygen, and hydrogen
Carbon, oxygen, hydrogen, and nitrogen (Some contain
small number of other elements)
Carbohydrates
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Long chains of simple sugars
Glucose is a simple sugar (a monosaccharide)
When two glucose molecules join together maltose is
formed (a disaccharide)
When lots of glucose molecules join together starch,
glycogen (Energy stores) or cellulose can form (a
polysaccharide)
Fats
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Most fats (lipids) in the body are made up of triglycerides
Their basic unit is 1 glycerol molecule chemically bonded to 3 fatty acid
chains
The fatty acids vary in size and structure.
Lipids are divided into fats (solids at room temperature) and oils (liquids
at room temperature)
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Proteins
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Long chains of amino acids
There are about twenty different amino acids.
They all contain the same basic structure, but the ‘R’ group is
different for each one.
When amino acids are joined together a protein is formed
The amino acids can be arranged in any order, resulting in
hundreds of thousands of different proteins.
Even a small difference in the order of the amino acids results in a
different protein being formed.
Food tests
Test for glucose (a reducing sugar)
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Add Benedict's solution into sample solution in test tube.
Heat at 60 - 70 °c in water bath for 5 minutes
Take test tube out of water bath and observe the color.
A positive test will show a color change from blue to orange or brick red.
Test for starch using iodine.
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We can use iodine to test for the presence or absence of starch in a food sample.
Add drops of iodine solution to the food sample
A positive test will show a color change from orange, brown to blue-black.
Test for protein
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Add drops of Biuret solution to the food sample
A positive test will show a color change from blue to violet / purple.
Test for lipids (fats)
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Food sample is mixed with 2cm3 of ethanol and shaken.
The ethanol is added to an equal volume of cold water.
A positive test will show a cloudy emulsion forming.
Test for vitamin C
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Add 1cm3 of DCPIP solution to a test tube.
Add a small amount of food sample (as a solution)
A positive test will show the blue color of the dye disappearing.
The structure of DNA
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DNA stands for deoxyribonucleic acid.
Material that makes up our genes and
chromosomes. The nucleus of every cell in
the body contains DNA.
Made up of smaller molecules called
nucleotides (molecules that are linked
together into long chains)
Each nucleotide contains a base: A, C, G
and T, the sequence determines the
proteins that are made in a cell.
Chapter 5
Enzymes
Catalyst: a substance that increases the rate of a chemical reaction and is not changed by the reaction
Enzymes: Proteins that function as biological catalysts
Importance of enzymes in all living organisms in terms of reaction speed necessary to sustain life:
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Enzymes are the catalysts that alter the rates of chemical/biochemical reactions thereby enabling the
sustenance of life.
Enzymes bind reversibly with the substrates forming enzyme-substrate complex. These complexes are then
converted to the product and the enzymes are regenerated.
Enzymes operate by lowering the activation energy of the reaction by providing alternate pathway for the
reaction. This saves the energy required to overcome the high activation energy levels and increases the
rates of the reactions.
Types of enzymes:
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Carbohydrase: Breaks down carbohydrates
Lipases: Break down lipids
Maltase: Enzyme that catalyzes the breakdown of maltose to glucose
Sucrase: breaks down sucrose.
Explain enzyme action with reference to the active site, enzyme-substrate complex,
substrate, and product.
An enzyme works by allowing a molecule of
its substrate to fit into the active site, where
the substrate and the enzyme bind together.
For this to happen, the fit must be perfect.
We say that the shape of the enzyme and the
shape of the substrate are complementary to
one another. When the substrate is in the
active site and bound to the enzyme, the
enzyme makes the substrate change into a new substance called the product. Then the product breaks away from
the enzyme. Now the enzyme is free, and ready to bind with another substrate molecule. The short-lived structure
that forms as the substrate slots into the enzyme’s active site is called the enzyme-substrate complex.
Explain the specificity of enzymes in terms of the complementary shape and fit of the active
site with the substrate.
Each enzyme can only catalyze reactions with one type of substrate, as the shape of the enzyme is
complementary to the one of the substrates in the active site. This is described as enzyme specificity.
Lock and key hypothesis
Factors that affect Enzymes
Explain the effect of changes in temperature on
enzyme activity in terms of kinetic energy, shape and
fit, frequency of effective collisions and denaturation.

This is extremely important around the active
site area as the specific shape is what ensures
the substrate will fit into the active site and
enable the reaction to proceed.
The optimum pH for most enzymes is 7 but
some that are produced in acidic conditions,
such as the stomach, have a lower optimum
pH (pH 2) and some that are produced in
alkaline conditions, such as the duodenum,
have a higher optimum pH (pH 8 or 9)
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Enzymes work fastest at their ‘optimum
temperature’ – in the human body, the
optimum temperature is 37⁰C.
If the pH is too high or too low, the bonds that
hold the amino acid chain together to make
up the protein can be destroyed.
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This will change the shape of the active site,
so the substrate can no longer fit into it,
reducing the rate of activity
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Moving too far away from the optimum pH
will cause the enzyme to denature and
activity will stop.
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Enzymes are proteins and have a specific
shape, held in place by bonds.
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Heating to high temperatures (beyond the
optimum) will break the bonds that hold the
enzyme together and it will lose its shape -this
is known as denaturation
Denaturation is irreversible - once enzymes
are denatured they cannot regain their proper
shape and activity will stop
Investigating the Effect of Temperature on Amylase
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Explain the effect of changes in pH on enzyme activity
in terms of shape and fit and denaturation
Starch solution is heated to a set
temperature.
Iodine is added to wells of a spotting tile.
Amylase is added to the starch solution and
mixed well.
Every minute, droplets of solution are added
to a new well of iodine solution.
This is continued until the iodine stops
turning blue-black (this means there is no
more starch left in the solution as the amylase
has broken it all down)
Time taken for the reaction to be completed
is recorded.
Experiment is repeated at different
temperatures.
The quicker the reaction is completed, the
faster the enzyme is working.
Investigating the Effect of pH on Amylase
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Place single drops of iodine solution in rows
on the tile.
Label a test tube with the pH to be tested.
Use the syringe to place 2cm3 of amylase in
the test tube.
Add 1cm3 of buffer solution to the test tube
using a syringe.
Use another test tube to add 2cm3 of starch
solution to the amylase and buffer solution,
start the stopwatch whilst mixing using a
pipette
After 10 seconds, use a pipette to place one
drop of mixture on the first drop of iodine,
which should turn blue-black.
Wait another 10 seconds and place another
drops of mixture on the second drop of iodine
Repeat every 10 seconds until iodine solution
remains orange, brown.
Repeat experiment at different pH values the less time the iodine solution takes to
remain orange brown, the quicker all the
starch has been digested and so the better
the enzyme works at that pH
Chapter 6
Plant Nutrition
Photosynthesis
The process by which plants manufacture
carbohydrates from raw materials using energy
from light.
Word
equation
Chemical
Equation
carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll
6CO2 + 6H2O light chlorophyll C6H12O6 + 6O2
Explain that chlorophyll transfers light energy into chemical energy in molecules, for the synthesis of
carbohydrates.
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Chlorophyll is a green pigment that is found in chloroplasts within plant cells.
It is this pigment which gives plants their characteristic green color.
Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
It is essential for photosynthesis to occur.
Subsequent use and storage of the carbohydrates made in photosynthesis.
Limiting factor: Something present in the
environment in such short supply that it
restricts life processes.
Identify and explain the limiting factors of
photosynthesis in different environmental
conditions
Light intensity: As light intensity increases,
the rate of photosynthesis increases
Carbon dioxide: The more carbon a plant is
given, the faster it can photosynthesize.
But once carbon dioxide concentration
reaches a certain level there is no further
increase in photosynthesis.
Temperature: Chemicals reactions of
photosynthesis can only take place at low
temperatures, so a plant photosynthesizes
faster on a warm day than on a cold.
Stomata: If stomata are closed,
photosynthesis cannot take place as the
plant lacks one of its raw materials.
Describe the use of carbon dioxide enrichment, optimum light and optimum temperatures in glasshouses in
temperate and tropical countries
Carbon Dioxide enrichment
Optimum light
Optimum temperatures
- Growers can pump CO2 into
glasshouses to increase conc.
- Can also burn BUTANE or
NATURAL GAS which: provide
CO2 and heat -> raise temp. in
cold weather
- Glass lets in sunlight
- ARTIFICAL LIGHTING for when light
intensity is too low
- BLINDS keep out very strong light
- SHADING lowers temp. in tropical
countries
- Sunlight heats up inside of glasshouse
- Glass stops heat escaping
- ELECTRIC HEATERS used in cold
weather
- VENTILATOR FLAPS are opened to cool
the glasshouse on hot days
Use hydrogen carbonate indicator solution to investigate the effect of gas exchange of an aquatic plant kept in the
light and in the dark
(Hydrogen carbonate indicator solution is RED)
1.
1st: Set up a test tube w/ 10 cm pondweed, TINFOIL (to prevent light passing) and hydrogen carbonate indicator
2nd: Set up a test tube with 10 cm pondweed and hydrogen carbonate indicator
3rd: CONTROL Set up a test tube with hydrogen carbonate indicator solution ONLY
2. Leave the test tubes near a light for 2-3 hours
*If carbon dioxide is added to the water by the plant the solution will turn YELLOW.
*If carbon dioxide is removed from the water by the plant the solution will turn PURPLE.
1st will turn yellow by carbon dioxide was ADDED by
PONDWEED by of RESPIRATION (since there was no
sunlight)
2nd will turn purple by carbon dioxide was TAKEN IN
by PONDWEED for PHOTOSYNTHESIS
3rd is red by CONTROL
Leaf structure
Mineral requirements
Carbohydrates contain the elements carbon, hydrogen, and oxygen but proteins, for example, contain nitrogen as
well (and certain amino acids contain other elements too)
Other chemicals in plants contain different elements as well, for example chlorophyll
contains magnesium and nitrogen.
This means that without a source of these elements, plants cannot photosynthesize or grow properly.
Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells
‘Mineral’ is a term used to describe any naturally occurring inorganic substance
Explain the effects of nitrate ion and magnesium iron deficiency on plant growth
Chapter 7
Human nutrition
Diet
Balanced diet for humans consists of all the food groups in the correct proportions.
Necessary food groups:
Vitamins and Minerals requirements:
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Carbohydrates: Source of energy
Proteins: Growth and repair
Lipids: Insulation and energy storage
Vitamins: Maintain health
Minerals: Maintain health
Dietary Fiber: Provides bulk for the intestine to
push food through.
Water: Chemical reactions in cells
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Vitamin C: Collagen protein, which makes up skin,
hair, gums, and bones (deficiency causes scurvy)
Vitamin D: Helps the body absorb calcium and
required for strong bones and teeth.
Calcium: Needed for strong bones and teeth, also
involved in the clotting of blood (deficiency can
lead to osteoporosis later in life)
Iron: Needed to make hemoglobin, the pigment in
red blood cells
Describe the effects of malnutrition in
relation to starvation, constipation,
coronary heart disease, obesity and
scurvy
Effects of scurvy:
 Anemia
 Exhaustion
 Spontaneous bleeding
 Pain in the limbs
 Swelling
 Gum ulcerations
 Tooth loss
Effects of Rickets:
 Bone pain
 Lack of bone growth
 Soft, weak bones
(Sometimes causing deformities)
Explain the causes and effects of protein-energy malnutrition, e.g., kwashiorkor and
marasmus.
Kwashiorkor is a severe form of malnutrition. It's most common in some developing
regions where babies and children do not get enough protein or other essential
nutrients in their diet.
Alimentary canal
Ingestion is the taking of substances, e.g. food and drink, into the body through the mouth
Mechanical digestion: the breakdown of food into
smaller pieces without chemical change to the food
molecules
Chemical digestion: the breakdown of large, insoluble
molecules into small, soluble molecules
Absorption: the movement of small food molecules
and ions through the wall of the intestine into the
blood
Assimilation: the movement of digested food
molecules into the cells of the body where they are
used, becoming part of the cells
Egestion: the passing out of food that has not been
digested or absorbed, as feces, through the anus
Diarrheal: the loss of watery feces (treatment of
diarrhoea: using oral rehydration therapy)
Cholera: disease caused by a bacterium
(The cholera bacterium produces a toxin that causes
secretion of chloride ions into the small intestine,
causing osmotic movement of water into the gut,
causing diarrhea, dehydration and loss of salts from
blood)
Identify the main regions of the alimentary canal and associated organs, limited to mouth, salivary glands,
esophagus, stomach, small intestine (duodenum and ileum), pancreas, liver, gall bladder and large intestine (colon,
rectum, anus)
Stages of food breakdown
Food taken into the body goes through five
different stages during its passage through the
alimentary canal (the gut):
Ingestion - the taking of substances, e.g., food
and drink, into the body through the mouth
Mechanical digestion - the breakdown of food
into smaller pieces without chemical change to
the food molecules
Chemical digestion - the breakdown of large,
insoluble molecules into small, soluble molecules
Absorption - the movement of small food
molecules and ions through the wall of the
intestine into the blood
Assimilation - the movement of digested food
molecules into the cells of the body where they
are used, becoming part of the cells.
Egestion - the passing out of food that has not
been digested or absorbed, as feces, through the
anus Mechanical digestion
Types of human teeth
 Incisors - chisel-shaped for biting and cutting
 Canines - pointed for tearing, holding, and biting.
 Premolars and molars - larger, flat surfaces with ridges at the
edges for chewing and grinding up food.
Structure of human teeth
State the causes of dental decay in terms of a
coating of bacteria and food on teeth, the bacteria
respiring sugars in the food, producing acid which
dissolves the enamel and dentine
Describe the proper care of teeth in terms of diet
and regular brushing
Chemical digestion
Producing small, soluble molecules that can be absorbed.
Describe the digestion of starch in the alimentary canal:
1. Amylase is secreted into the alimentary canal and breaks down starch to maltose.
2. Maltose is broken down by maltase to glucose on the membranes of the epithelium lining the small intestine
Amylases
Produced in the mouth and pancreas
(secreted into the duodenum)
Digest starch into smaller sugars
Proteases
Enzymes that break down
proteins into amino acids in
the stomach and small
intestine
The digestion of proteins
Protein digestion takes place in the stomach
and duodenum with two main enzymes
produced:
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
Pepsin is produced in the stomach and breaks
down protein in acidic conditions.
Trypsin is produced in the pancreas and
secreted into the duodenum where is breaks
down protein in alkaline conditions.
Hydrochloric Acid


The stomach produces several fluids which
together are known as gastric juice
One of the fluids produced is hydrochloric
acid.

Lipases
Produced in the pancreas and secreted
into the duodenum.
Digest lipids into fatty acids and glycerol
This kills bacteria in food and gives an acid pH
for enzymes to work in the stomach.
How is a low pH helpful in the stomach?
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
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The low pH kills bacteria in food that we have
ingested as it denatures the enzymes in their
cells, meaning they cannot carry out any cell
reactions to maintain life.
Pepsin, produced in the stomach, is an
example of an enzyme which has a very low
optimum pH.
The hydrochloric acid produced in the
stomach ensures that conditions in the
stomach remain within the optimum range
for pepsin to work at its fastest rate
Bile has two main roles:

It is alkaline to neutralize the hydrochloric acid which comes from the stomach.
The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach

It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area
allows lipase to chemically break down the lipid into glycerol and fatty acids faster.
Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper. This is an example of mechanical
digestion, not chemical digestion – breaking something into smaller pieces does not break bonds or change the chemical
structure of the molecules which make it up, which is the definition of chemical digestion.
Absorption
Absorption is the movement of digested food molecules from the digestive system into the blood (glucose and
amino acids) and lymph (fatty acids and glycerol)
Nutrients are absorbed in the small intestine.
Absorbing Water
Water is absorbed in both the small intestine and the colon, but most absorption of water (around 80%) happens in
the small intestine.
Adaptations of the Small Intestine


The ileum is adapted for absorption as it is very
long and has a highly folded surface with
millions of villi (tiny, finger like projections)
These adaptations massively increase the
surface area of the ileum, allowing absorption to
take place faster and more efficiently.
Microvilli on the surface of the villus further increase
surface area for faster absorption of nutrients
Wall of the villus is one cell thick meaning that there is
only a short distance for absorption to happen by
diffusion and active transport
Well supplied with a network of blood capillaries that
transport glucose and amino acids away from the small
intestine in the blood
Lacteal runs through the center of the villus to transport
fatty acids and glycerol away from the small intestine in
the lymph.
Chapter 8
Transport in plants
Xylem and phloem
Functions of xylem and phloem:
xylem – transport water and minerals from the roots to the stem and leaves
phloem – transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesizing
leaves to non-photosynthesising regions in the roots and stem.
These vessels are arranged in groups called vascular vessels.
Position of xylem and
phloem as seen in
sections of roots, stems
and leaves of nonwoody dicotyledonous
plants



Thick walls with lignin: Very strong and can support the great weight pf even a heavy tree (also waterproof)
No cell contents: Water can flow easily through the tube.
Cells joined end to end with no cross walls: form a long continuous tube for water to flow through, all the way
from the roots to the leaves
Water uptake
Root hair cells: single-celled extensions of epidermis cells in the root
They grow between soil particles and absorb
water and minerals from the soil
Water enters through osmosis (This happens
because soil water has a higher water
potential than the cytoplasm of the root hair
cell)


The root hair increases the surface area of
the cells significantly.
This large surface area is important as it
increases the rate of the absorption of
water by osmosis and mineral ions by
active transport
Pathway of water into and across a root
Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells
So the pathway is:
root hair cell → root cortex cells → xylem → leaf mesophyll cells
Investigating Water Movement in Plants



The pathway can be investigated by placing a plant into a beaker of water that has had a stain added to it
(food colouring will work well)
After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving
that water is being taken up by the celery
If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water,
showing that the water is being carried in specific vessels through the stem - these are the xylem vessels
Transpiration
Loss of water vapor from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by
diffusion of water vapor through the stomata.
Functions:




transporting mineral ions
providing water to keep cells turgid to support
the structure of the plant.
providing water to leaf cells for photosynthesis.
keeping the leaves cool
Investigate and describe the effects of variation of
temperature and wind speed on transpiration rate.













Cut a shoot underwater to prevent air entering the
xylem and place in tube.
Set up the apparatus as shown in the diagram and
make sure it is airtight, using Vaseline to seal any
gaps.
Dry the leaves of the shoot (wet leaves will affect the
results)
Remove the capillary tube from the beaker of water
to allow a single air bubble to form and place the
tube back into the water.
Set up the environmental factor you are
investigating.
Allow the plant to adapt to the new environment for
5 minutes.
Record the starting location of the air bubble.
Leave for a set period.
Record the end location of air bubble.
Change the wind speed or temperature (only one whichever factor is being investigated)
Reset the bubble by opening the tap below the
reservoir.
Repeat the experiment.
The further the bubble travels in the same time
period, the faster transpiration is occurring and vice
versa.
Water Vapor Loss (Extended)



Evaporation takes place from the surfaces of spongy mesophyll cells.
The many interconnecting air spaces between these cells and the stomata create a large surface area.
This means evaporation can happen rapidly when stomata are open.
Effects of Temperature, Wind Speed &
Humidity
A potometer can be used to investigate
the effect of environmental factors on
the rate of transpiration.
Wilting
If more water evaporates from the
leaves of a plant than is available in the
soil to move into the root by osmosis,
then wilting will occur.
This is when all the cells of the plant are
not full of water, so the strength of the
cell walls cannot support the plant and it
starts to collapse.
A wilted plant cannot support itself and starts to collapse.
Translocation
the movement of sucrose and amino acids in phloem from sources to sinks.
Sources: the parts of plants that release sucrose or amino acids
Sinks: the parts of plants that use or store sucrose or amino acids
Xylem and Phloem tissue comparison
Chapter 9
Transport in animals
Circulatory systems
Circulatory system definition:
System of blood vessels with a pump and valves to ensure one-way flow of blood Supplement.
Circulation of a fish


Fish have a two-chambered heart and a
single circulation.
This means that for every one circuit of the
body, the blood passes through the heart
once.
Circulation of a mammal




Mammals have a four-chambered heart and
a double circulation.
This means that for every one circuit of the
body, the blood passes through the heart
twice.
The right side of the heart
receives deoxygenated blood from the body
and pumps it to the lungs (the pulmonary
circulation)
The left side of the heart receives oxygenated
blood from the lungs and pumps it to the
body (the systemic circulation)
Advantages of a double circulation

Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it by the pumping of
the heart, meaning it cannot travel as fast.

By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to
the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster and more
frequently
Heart Structure
(Extended)
The Mammalian Heart





The heart is labelled as if it was in the
chest so what is your left on a
diagram is actually the right-hand side
and vice versa.
The right side of the heart
receives deoxygenated blood from
the body and pumps it to the lungs.
The left side of the heart
receives oxygenated blood from the
lungs and pumps it to the body
Blood is pumped towards the heart in
veins and away from the heart
in arteries
The two sides of the heart are
separated by a muscle wall called
the septum
 The heart is made of muscle
tissue which are supplied with blood
by the coronary arteries
The activity of the heart may be monitored by: ECG, pulse rate and listening to sounds of valves closing.
Heart and pulse rate is measured in bpm (beats per minute)



To investigate the effects of exercise on heart rate, record the pulse rate at rest for a minute.
Immediately after they do some exercise, record the pulse rate every minute until it returns to the
resting rate
This experiment will show that during exercise the heart rate increases and may take several minutes to
return to normal
Coronary heart disease
Partial blockage of the coronary
arteries creates a restricted blood flow
to the cardiac muscle cells and results
in severe chest pains called angina
Complete blockage means cells in that
area of the heart will not be able to
respire and can no longer contract,
leading to a heart attack
Diet, Exercise & Coronary Heart
Disease
Reducing the risks of developing
coronary heart disease
Quit smoking.
Diet - reduce animal fats and eat more
fruits and vegetables - this will reduce
cholesterol levels in the blood and help
with weight loss if overweight.
Exercise regularly - again, this will help with
weight loss, decrease blood pressure and
cholesterol levels and help reduce stress
Risk factors for CHD Table
Relative thickness of:
the muscle walls of the left and right ventricles: thicker muscle walls than atria as they are pumping blood out of the
heart and so need to generate a higher pressure.
the muscle walls of the atria compared to those of the ventricles: Thicker as it has to pump blood at high pressure
around the entire body.
The septum separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood
Functioning of the heart
In terms of the contraction of muscles of the atria and ventricles and the action of the valves

Deoxygenated blood coming from the body flows into the right atrium via the vena cava.

Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through
the tricuspid (atrioventricular) valve into the right ventricle

The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar
valve which prevents blood flowing backwards into the heart

The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes
place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries
which would burst under higher pressure)

Oxygen-rich blood returns to the left atrium via the pulmonary vein

It passes through the bicuspid (atrioventricular) valve into the left ventricle

The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all
the way around the body

The semilunar valve in the aorta prevents the blood flowing back down into the heart
Explain the effect of physical activity on the heart rate.






So that sufficient blood is taken to the working muscles to provide them with enough nutrients and
oxygen for increased respiration.
An increase in heart rate also allows for waste products to be removed at a faster rate.
Following exercise, the heart continues to beat faster for a while to ensure that all excess waste products
are removed from muscle cells.
It is also likely that muscle cells have been respiring anaerobically during exercise and so have built up
an oxygen debt
This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure that extra
oxygen is still being delivered to muscle cells
The extra oxygen is used to break down the lactic acid that has been built up in cells as a result of anaerobic
respiration.
Blood vessels
Blood vessel
Arteries
Function
Carry blood
away from the
heart
Structure of wall
Thick and
strong,
containing
muscle and
elastic tissue
Capillaries
Supply all cells
with their
requirements,
and take away
waste products
Return blood to
the heart
Very thin, only
one cell thick
Veins
Quite thin,
containing far
less muscle and
elastic tissue
than arteries
Width of lumen
Relatively
narrow; it varies
with heartbeat
because the
walls can stretch
and recoil
Very narrow,
just wide
enough for a red
blood cell to
pass through
Wide; contains
valves
Arterioles and venules




As arteries divide more as
they get further away from
the heart, they get
narrower
The narrow vessels that
connect arteries to
capillaries are called
arterioles
Veins also get narrower the
further away they are from
the heart
The narrow vessels that
connect capillaries to veins
are called venules
How structure fit’s function
Strength and elasticity needed to
withstand the high pressure and pulsing
of the blood as it is pumped through the
arteries by the heart
No need for strong walls, as most of the
blood pressure has been lost; thin walls
and narrow lumen bring blood into
close contact with body tissues
No need for strong walls, as most of the
blood pressure has been lost; wide
lumen offers less resistance to blood
flow; valves prevent backflow
Identify, in diagrams and images, the main blood vessels to and from the liver as: hepatic
artery, hepatic veins and hepatic portal vein.
The hepatic artery brings
oxygenated blood from the heart
to the liver
The hepatic vein brings
deoxygenated blood from the
liver back to the heart
The hepatic portal
vein transports deoxygenated
blood from the gut to the liver
Blood
Components of blood:
Components of Blood: Function

Plasma is important for the transport of carbon dioxide, digested food (nutrients), urea, mineral ions,
hormones, and heat energy.

Red blood cells transport oxygen around the body from the lungs to cells which require it for aerobic
respiration.
o
They carry the oxygen in the form of oxyhemoglobin.

White blood cells defend the body against infection by pathogens by carrying
out phagocytosis and antibody production

Platelets are involved in helping the blood to clot.
White Blood cells: Extended
Lymphocytes
Function: Anti-body production
Phagocytes
Function: Engulfing pathogens by phagocytosis
The process of clotting as the conversion
of fibrinogen to fibrin to form a mesh.
Chapter 10
Diseases and immunity
Pathogen: Disease-causing organism
Transmissible disease: disease in which the
pathogen can be passed from one host to
another.
A pathogen is transmitted:


direct contact, including through blood
and other body fluids.
indirectly, including from contaminated
surfaces, food, animals, and air
The Body Defenses
Mechanical barriers – structures that make it difficult
for pathogens to get past them and into the body.
a) Skin - covers almost all parts of your body
to prevent infection from pathogens. If it is cut or
grazed, it immediately begins to heal itself, often by
forming a scab.
b) Hairs in the nose - these make it difficult
for pathogens to get past them further up the nose,
so they are not inhaled into the lungs
Chemical barriers – substances produced by the body
cells that trap / kill pathogens before they can get
further into the body and cause disease
a) Mucus - made in various places in the body,
pathogens get trapped in the mucus and can then be
removed from the body (by coughing, blowing the
nose, swallowing etc.)
b) Stomach acid - contains hydrochloric acid
which is strong enough to kill any pathogens that have
been caught in mucus in the airways and then
swallowed or have been consumed in food or water
Cells - different types of white blood cell work to
prevent pathogens reaching areas of the body they
can replicate in
a) By phagocytosis - engulfing and digesting
pathogenic cells
b) By producing antibodies - which clump
pathogenic cells together so they cannot move as
easily (known as agglutination) and releasing
chemicals that signal to other cells that they must be
destroyed
Active immunity: defense against a pathogen by antibody production in the body
(Slow acting and provides long-lasting immunity)
Each pathogen has its own antigens, which have specific shapes.
Antibodies: Proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for
destruction by phagocytes
Active immunity is gained after an infection by a pathogen or by vaccination.
All cells have proteins and other substances
projecting from their cell membrane.
These are known as antigens and
are specific to that type of cell
Lymphocytes have the ability to ‘read’ the
antigens on the surfaces of cells and
recognize any that are foreign
They then make antibodies which are
a complementary shape to the
antigens on the surface of the pathogenic
cell
Vaccination
Vaccinations give protection against specific diseases and
boost the body’s defense against infection from pathogens
without the need to be exposed to dangerous diseases that
can lead to death.
Outline the process of vaccination:
1. weakened pathogens or their antigens are put into the
body.
2. the antigens stimulate an immune response by
lymphocytes which produce antibodies.
3. memory cells are produced that give long-term immunity.
The memory cells remain in the blood and will quickly respond
to the antigen if it is encountered again in an infection by a
‘live’ pathogen
As memory cells have been produced, this immunity is longlasting
Passive Immunity
Fast-acting, short-term defense against a pathogen by antibodies acquired from another individual.
Importance of breast-feeding:

Antibodies pass from mother to infant via breast milk - this is important as it helps the very young to fight
off infections until they are older and stronger, and their immune system is more responsive
The body does not make its own antibodies or memory cells in passive immunity, hence the name
Cholera
Disease caused by a bacterium which is transmitted in contaminated water.
Explain that the cholera bacterium produces a toxin that causes secretion of chloride ions into the small intestine,
causing osmotic movement of water into the gut, causing diarrhea, dehydration and loss of ions from the blood.
How cholera leads to diarrhea
Ingested via infected water or food, if it enters the small intestine it can cause illness in the following way:
1. Bacteria attach to the wall of the small
intestine.
2. They produce a toxin.
3. The toxin stimulates the cells lining the
intestine to release chloride ions from
inside the cells into the lumen of the
intestine.
4. The chloride ions accumulate in the lumen
of the small intestine and lower the water
potential there
5. Once the water potential is lower than that
of the cells lining the intestine, water starts
to move out of the cells into the intestine
(by osmosis)
6. Large quantities of water are lost from the
body in watery feces.
7. The blood contains too little chloride ions
and water.
Chapter 11
Gas exchange in humans
Features of gas exchange surfaces
Large surface area to allow faster diffusion of gases across
the surface.
Thin walls to ensure diffusion distances remain short.
Good ventilation with air so that diffusion gradients can be
maintained.
Good blood supply to maintain a high concentration
gradient so diffusion occurs faster.
The limewater tests.
Simple test to investigate the difference between inspired and
expired air.





When we breathe in, the air is drawn through boiling
tube A
When we breathe out, the air is blown into boiling
tube B.
Lime water is clear but becomes cloudy (or milky)
when carbon dioxide is bubbled through it
The lime water in boiling tube A will remain clear, but
the limewater in boiling tube B will become cloudy
This shows us that the percentage of carbon dioxide in
exhaled air is higher than in inhaled air
Differences in inspired & Expired Air
Investigating the Effects of Physical Activity on Breathing





Exercise increases the frequency and depth of breathing.
This can be investigated by counting the breaths taken during one minute at rest and measuring average chest
expansion over five breaths using a tape measure held around the chest.
Exercise for a set time (at least 3 minutes)
Immediately after exercising, count the breaths taken in one minute and measure the average chest expansion
over 5 breaths.
Following exercise, the number of breaths per minute will have increased and the chest expansion will also
have increased.
Internal and external intercostal muscles
Function of Cartilage in the Trachea: Extended
Rings of cartilage surround the trachea (and bronchi)
The function of the cartilage is to support the airways and keep them open during breathing.
(If they were not present then the sides could collapse inwards when the air pressure inside the tubes drops)
Volume and Pressure changes
Roles
The ribs: Forced exhalation (ribs down and in)
The internal and external intercostal muscles: work as antagonistic pairs (meaning they work in different directions
to each other) Pull the ribs up and out to increase the volume of the thorax.
Diaphragm: Control ventilation in the lungs (contracts = increase volume of the chest)
Explaining the Link Between Physical Activity & Breathing: Extended






Frequency and depth of breathing increase when exercising.
This is because muscles are working harder and aerobically respiring more and they need more
oxygen to be delivered to them (and carbon dioxide removed) to keep up with the energy demand.
If they cannot meet the energy demand they will also respire anaerobically, producing lactic acid.
After exercise has finished, the lactic acid that has built up in muscles needs to be removed as
it lowers the pH of cells and can denature enzymes catalyzing cell reactions
It can only be removed by combining it with oxygen - this is known as ‘repaying the oxygen debt’
This can be tested by seeing how long it takes after exercise for the breathing rate and depth to
return to normal - the longer it takes, the more lactic acid produced during exercise and the
greater the oxygen debt that needs to be repaid
Roles in protecting the breathing system from pathogens and other particles.
The passage down to the lungs are lined with ciliated epithelial cells, the tiny hairs at the end of them beat and push
mucus up the passages towards the nose and throat where is removed. Mucus is made of goblet cells and trap
particles, pathogens like bacteria or viruses, and dust and prevent from them reaching the lungs.
Respiration
(A chemical process that involves the breakdown of
nutrient molecules and is Enzyme-controlled)
Humans need the energy released during
respiration carry out many processes:







Muscle contraction
Protein synthesis
Cell division (to make new cells)
Growth
Active transport across cell membranes
Generation of nerve impulses
Maintaining a constant internal body
temperature
The effect of temperature on respiration







The Effect of Temperature on the Respiration of Yeast Cells
There are several different experimental methods that can be used to investigate the rate of respiration in
organisms.
Some methods, such as the experiment described below, involve the use of a colored indicator.
An indicator can be used to investigate the effect of temperature on the rate of aerobic respiration in yeast.
Methylene blue dye is a suitable indicator.
This dye can be added to a suspension of living yeast cells because it doesn't damage cells.
Yeast can respire both aerobically and anaerobically, though in this experiment it is their rate of aerobic
respiration that is being investigated.
The time taken for the methylene blue to discolor (lose its colour) is a measure of the rate of respiration of
the yeast cells in the suspension (The faster the dye changes from blue to colorless, the faster the rate of
respiration)
Apparatus

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

Yeast suspension
Glucose solution
Test tubes
Stopwatch
Methylene blue
Temperature-controlled water bath(s)
Methylene blue is added to a solution of aerobically
respiring yeast cells in a glucose suspension. The rate
at which the solution turns from blue to colorless
gives a measure of the rate of aerobic respiration.
Chapter 12
Coordination and response
The mammalian nervous system:
The human nervous system consists of the central nervous system
(CNS) and peripheral nervous system (PNS). The central nervous
system consists of the brain and the spinal cord and the peripheral
nervous system of all the nerves in the body.
Role of the nervous system
It allows us to make sense of our surroundings, respond to them
and coordinate and regulate body functions.
Information is sent through the nervous system as nerve impulses
which are electrical signals that pass along nerve cells known as
neurons. Bundle of neurons is known as a nerve.
Neurons
There are three main types of neurons: sensory, relay and motor.
Sensory neurons carry impulses from sense organs to the
CNS (brain or spinal cord)
Relay neurons are found inside the CNS and connect sensory and
motor neurons.
Motor neurones carry impulses from the CNS to effectors (muscles
or glands)
Neurones connect one with another and receive
impulses because of dendrites, extensions in
neurons. In this way they form a neuron network.
Simple reflex arc
A stimulus is detected by a sensory receptor in the
skin. The receptor starts off an electrical impulse,
which travels to the spinal cord along the axon from
the receptor cell. This cell is called a sensory
neurone. In the spinal cord, the neuron passes the
electrical impulse into several relay neurons as they
pass the impulse to the brain. Then it’s passed to a
motor neurone to pass to an effector.
Reflex Summary:
Stimulus -> Receptor -> Sensory Neurone -> Relay
Neurone -> Motor Neurone -> Effector ->
Response
Voluntary Responses
Where you make a conscious
decision to carry out a particular
action therefore it starts with your
brain
Reflex Responses
A reflex response does not involve the brain as the coordinator
of the reaction, and you are not aware you have completed it
until after you have carried it out. It is an automatic and rapid
response to a stimulus.
Synapses
A junction between two neurones, where nerve impulses can transmit across synapses and be directed along the
appropriate route.
Structure of a synapse
(a) an impulse stimulates the release of neurotransmitter
molecules from vesicles into the synaptic gap
(b) the neurotransmitter molecules diffuse across the gap
(c) neurotransmitter molecules bind with receptor proteins
on the next neurone
(d) an impulse is then stimulated in the next neurone
Synapses ensure that impulses travel in one direction only.
Sense Organs
(Groups of receptor cells responding to specific stimuli: light,
sound, touch, temperature, and chemicals)
*Detect a change in the environment and stimulate electrical
impulses in response
Eye Structure & Function:






Cornea: refracts light as it enters
the eye
Iris: controls how much light
enters the pupil
Pupil: Hole that allows light to
enter the eye
Lens: Change shape to focus
light onto the retina
Retina: Contains light receptor
cells, rods (light intensity) and
cones (colour)
optic nerve: Sensory Neurone
that carries impulses between
the eye and brain.
Blind spot: The point where the optic nerve joins the retina, there are no light-sensitive rod and cone cells on that part of the
retina, so no object is detected in out peripheral vision.
Pupil reflex: A reflex action carried out to protect the retina
from damage in bright light and protect us from not seeing
objects in dim light, as it dilates. In bright light the pupil
constricts so it prevents to much light entering the eye.
Pupil reflex in terms of the antagonistic action of circular
and radial muscles in the iris:
Accommodation:
The way to view near and distant objects in terms of the contraction and relaxation of the ciliary muscles, tension in
the suspensory ligaments, shape of the lens and refraction of light.
Near objects:
1.
2.
3.
4.
Ciliary muscle contracts
Lens becomes fatter.
Suspensory ligaments slacked.
Light is refracted more.
Distant objects:
1. Ciliary muscles relax.
2. This causes the suspensory ligaments to
tighten.
3. Lens becomes thinner.
4. Light is refracted less.
Distribution of rods and cones in the retina of a human
The fovea is an area on the retina where almost all the cone cells are found. Rod cells are found all over the retina,
other than the area where the optic nerve attaches to the retina - there are no light-sensitive cells at all in this area,
and so it is known as the blind spot.
Fovea´s is responsible for high acuity vision.
Function of rods and cones:
(a) greater sensitivity of rods for night vision
(b) There are 3 types of cone cells which are sensitive to different colours of light (red, blue and green)
Hormones
(Chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs)
The glands that produce hormones are known
collectively as the endocrine system.
Adrenaline:
The hormone secreted in ‘fight or flight’
situations and its effects, its produced in danger
situations and produces an increased breathing
rate and increased heart rate so glucose and
oxygen can be delivered to muscle cells and
ensure muscles are well for high activity in a
´flight or fight´, and increased pupil diameter so
that more information Is sent to the brain.
(Blood flow towards muscles and increase blood
glucose concentration)
Gland
Adrenal gland
Pancreas
Testis
Hormone that it secretes
adrenaline
Insulin
Glucagon
Testosterone
Ovary
Oestrogen
Function of hormone
Prepares the body for vigorous action
Reduces the concentration of glucose in the blood
Increases the concentration of glucose in the blood
Causes the development of male secondary sexual
characteristics
Causes the development of female secondary sexual
characteristics, and helps in the control of the menstrual
cycle
Nervous System
Endocrine System
Made up of neurones
Information transmitted in the form of electrical
impulses
Impulses transmitted along neurones
Impulses travel very quickly, so action is fast
Effect of a nerve impulse usually only lasts for a very
short time
Made up of glands
Information transmitted in the form of chemicals called
hormones
Chemicals carried in the blood plasma
Chemicals travel more slowly, so action is slower
Effect of a hormone may last longer
Homeostasis
(The maintenance of a constant internal environment)
Insulin: Secreted when decreases blood glucose
concentration (As kidneys only cope with a certain level
of glucose, when levels to high glucose is excreted and
lost in urine)
The glycogen is converted back to glucose several hours later
when blood glucose levels have dipped due to respiration in all
tissues.
Homeostatic control by negative feedback with
reference to a set point
Occurs when conditions change from the set point (ideal)
and returns to this set point.
Something rises, control systems are switched on to reduce
it again.
If something falls, control systems are switched on to raise it
again.
Control of blood glucose concentration by the liver and
the roles of insulin and glucagon
Insulin is produced when blood glucose rises and
stimulates liver and muscle cells to convert excess
glucose into glycogen to be stored. Glucagon is
produced when blood glucose falls and stimulates liver
so converted glucose can be released into blood.
Treatment of Type 1 diabetes
Condition where blood glucose levels are not able to
be regulated as the insulin secreting cells in the
pancreas are not working well. So, glucose levels very
high. It can be treated by injecting insulin, so the liver
converts glucose into glycogen, reducing the blood
glucose level. Also having a controlled diet.
Symptoms: extreme thirst, weakness or tiredness,
blurred vision, weight loss and loss of consciousness.
The Skin & Homeostasis
Maintenance of a constant internal body temperature
Regulation is controlled by the brain, where the receptors sensitive to blood temperature are located. The brain
responds to this information by sending nerve impulses to effectors in the skin to maintain the temperature within a
range of the optimum, 37 degrees Celsius.
Increase in temperature: thermoreceptors ->
sweating; vasodilation; hairs lie flat again skin ->
decrease in body temp.
Decrease in temperature: thermoreceptors ->
vasoconstriction; shivering; skin hairs erect -> increase
in body temp.
Maintenance of a constant internal body temperature:
vasodilation and vasoconstriction of arterioles supplying skin surface capillaries.
Coordination in Plants
Tropisms
Plants can respond to changes in environment (stimuli) for survival.
Factors:




Light
Water
Gravity
Others
Responses much slower than mammals
Stimulus Name of response
Gravity
Gravitropism
(Geotropism)
Light
Phototropism
Definition
a response in which parts of a
plant grow towards or away from
gravity.
A response in which parts of a
plant grow towards or away from
the direction of the light source
Positive response
Growth towards
gravity (roots)
Negative Response
Growth away from
gravity (shoots)
Growth towards
light (shoots)
Growth away from
light (roots)
Investigating gravitropism and phototropism in shoots and roots
To investigate phototropism in shoots, one can use a
simple experiment called the phototropism
experiment. In this experiment, a shoot is placed in a
container with a light source on one side. The shoot
will bend towards the light source, demonstrating
positive phototropism. By blocking certain parts of the
light source, the researcher can determine which
wavelengths of light are responsible for the
phototropic response.
To investigate phototropism in roots, one can use a
similar experiment called the phototropic response
assay. In this experiment, the root is grown in a gel or
agar medium with a light source shining on one side.
The growth of the root towards or away from the light
source can be measured over time, revealing the
root's phototropic response.
Role of auxin in controlling shoot growth, limited
to:
(b) auxin diffuses through the plant from the shoot tip
Auxin concentrates on the shady or lower side of a
shoot, making the cells in those areas elongate faster
than on the other side. This causes the shoot to bend
towards light or away from gravity as it grows.
(a) auxin is made in the shoot tip
(c) auxin is unequally distributed in response to light
and gravity
(d) auxin stimulates cell elongation
Chapter 13
Excretion and homeostasis
Excretion
(Removal of waste substances of metabolic reactions, toxic
materials, and substances more than requirements)


Carbon dioxide is excreted through the lungs. (During
Exhalation)
Kidneys excrete urea and excess water and ions
(Through urine production)
Kidney filters the blood, the ureter connects the kidney to the bladder, which stores urine produced by the kidney.
Finally, the urethra connects the bladder to the exterior, where urine is released.
Urea: waste product produced in the liver, from the breakdown of excess amino acids
Structure of the kidney
Located in the back of the abdomen and have two important functions:


Regulate water content in the blood.
Excrete the toxic waste products of metabolism.
The structure and function of a nephron and its
associated blood vessels
Function: 1. Filtration 2. Re-Absorption 3. Formation of
Urine
(a) the role of the glomerulus in the filtration
from the blood of water, glucose, urea, and ions
(b) the role of the nephron in the reabsorption
of all the glucose, some of the ions and most of the
water back into the blood
(c) the formation of urine containing urea,
excess water and excess ions (details of these processes
are not required)
Excretion by Deamination of Amino Acids: Extended
Many digested food molecules absorbed into the blood in
the small intestine are carried to the liver for assimilation.
These include Amnio acids (which are used to build
proteins as fibrinogen)
Excess amino acids absorbed in the blood cannot be
stored, so they are broken down in deamination.
The amino group of all amino acids – NH2 is
removed, hence the term de-amin(o)-action.
Enzymes in the liver split up amino acid molecules.
Urea is formed in the liver from excess amino acids.
Deamination: The removal of the nitrogen-containing part of amino acids to form urea
IMPORTANCE OF EXCRETION





Urea is a toxic substance, if it accumulates in the body, it can become toxic and cause damage to organs
such as the kidneys and liver.
Maintaining water balance, by removing urea, the body can maintain its water balance and prevent
dehydration.
The excretion of urea is important for the regulation of blood ph.
Excretion of urea and other metabolic waste products is essential to prevent the build-up of toxic
substances in the body that can interfere with normal cellular function and lead to disease.
Excretion of urea is the primary way that excess nitrogen is removed from the body.
Chapter 14
Reproduction in plants
Asexual Reproduction
Process resulting in the production of genetically identical
offspring from one parent.
Advantages
Population increased
rapidly
Can exploit suitable
environments quickly
More time and energy
efficient
Disadvantages
Limited genetic variation in
population (off-spring identical)
Population vulnerable to changes
in conditions and may only be
suited to one habitat
Disease is likely to affect the
whole population as there is no
genetic variation
Reproduction is
completed much faster
than sexual
reproduction
In crop plants, asexual reproduction can be advantageous as it
means that a plant that has good characteristics (high yield,
disease-resistant, hardy) can be made to reproduce asexually,
and the entire crop will show the same characteristics.
Sexual reproduction
Process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilized egg cell) and the
production of offspring that are genetically different
from each
other
Fertilization: as the fusion of the nuclei of gametes
Nuclei of gametes are haploid -> 23 chromosomes.
Nucleus of a zygote is diploid -> 23 pairs of chromosomes.
Most crop plants reproduce sexually, and this is an
advantage as it means variation is increased and
genetic
variant may produce which is better able to cope
with weather changes and produce higher yield.
Sexual reproduction in plants
(Flowers are the reproductive organ of the plant)
Sepal: Protects unopened flower
Petals: Pollinated flowers to attract insects
Anther: Produces and releases the male sex cell
(Pollen grain)
Stigma: Top of the female part of the flower,
collects pollen grains
Ovary: Produces the female sex cell (ovum)
Ovule: Contains the female sex cells
Pollination: The transfer of pollen grains from an anther to a stigma

Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule.
Germination
Factors:



Water – Allows seed to swell up and the enzymes in the embryo to start working so that growth can occur.
Oxygen – So that energy can be released for germination.
Warmth – Germination improves as temperature rises.
Investigating: The environmental conditions
that affect germination of seeds

Set up 4 boiling tubes each containing 10 cress
seeds on cotton wool.

Set each test tube as shown in diagram below.

Leave tubes in set environment for a period of
time: A, B and C incubated at 20°C; D placed in a fridge
at 4°C.

Compare results and see which tube has the greatest
number of germinated seeds
Self-Pollination
(the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on
the same plant)
Cross-pollination
(The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same
species)
Cross-Pollination


Much more variation because parents’
plants can be genetically different from
another.
(CHAPTER 17)
Self-Pollination



New combinations of genes can be formed. So, there is
some variation - though usually not very much.
Good in keeping variation to a minimum.
Useful if difficulty in finding another plant nearby to
exchange pollen without pollinators.
Growth of the pollen tube and its entry into the ovule followed by fertilisation
(Details of production of endosperm and development are not required)
Chapter 15
Reproduction in Humans
The male reproductive system:
Prostate Gland: Production of semen
(provide sperm cells with nutrients)
Sperm duct: Sperm passes through it to be
mixed with fluids produced by the glands
before being passed into the urethra for
ejaculation.
Urethra: Tube running down the penis that
carries out urine or semen, a ring of muscle
prevents semen and urine from mixing.
Testis: Contained in a bag of skin (scrotum)
and produces sperm (male gamete) and
testosterone (hormone)
Scrotum: Sac supporting the testes outside the body
to ensure sperm are kept at temperature slightly
lower than body temperature.
Penis: Passes urine out of the body from the bladder
and allows semen to pass into the vagina of a woman
during sexual intercourse
The female reproductive system:
Oviduct: connects the ovary to the uterus and is lined
with ciliated cells to push the released ovum down it.
(Fertilization occurs here)
Vagina: Muscular tube that leads to the inside of the
woman´s body, where the male´s penis will enter
during sexual intercourse and sperm are deposited.
Ovary: Contains OVA (Female gametes)
which will mature and develop when
hormones are released
Uterus: Muscular bag with a soft lining
where the fertilised egg (Zygote) will be
implanted to develop into a foetus.
Cervix: Ring of muscle at the lower end
of the uterus to keep the developing
foetus in place during pregnancy
Fertilization: The fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell)
Adaptive features of sperm and eggs
Pregnancy
In early development, the zygote forms an embryo which is a ball of cells that implants into the lining of the uterus.
Amniotic acid: Protects fetes during development
by cushioning it from bumps.
Umbilical cord: joins the foetus blood supply to
the placenta (exchange of nutrients and removal
of waste)
Uterus: The zygote travels towards the uterus
where implantation occurs and continues to grow
and develop
Fatus: The placenta has formed, and the embryo is
called a foetus.
Some pathogens and toxins can pass across the
placenta and affect the foetus.
Function of the placenta and umbilical cord




The foetus needs glucose, amino acids, fats, water, and
oxygen, these are provided from the mother through the
placenta.
Fetus and placenta connected by the umbilical cord.
Waste is also absorbed (Carbon Dioxide and Urea)
Movement of molecules across placenta occurs by
diffusion.
Testosterone and Oestrogen
Testosterone is a male sex hormone that is produced in the testes. It is responsible for the development of male
secondary sexual characteristics, such as facial and body hair, a deeper voice, and increased muscle mass.
Testosterone also stimulates the growth of the testes and the penis.
In females, testosterone is produced in small amounts in the ovaries. However, the primary female sex hormone is
oestrogen. Oestrogen is responsible for the development of female secondary sexual characteristics, such as breast
development, the widening of the hips, and the growth of pubic and underarm hair.
Both testosterone and oestrogen are involved in the regulation of the menstrual cycle in females. Oestrogen helps
to thicken the lining of the uterus in preparation for pregnancy, while testosterone stimulates the growth of the
follicles in the ovaries.
The menstrual cycle
The menstrual cycle is a complex physiological process that occurs in females of reproductive age, typically
between the ages of 11 and 50 years. The cycle is regulated by hormones and is characterized by a series of events
that occur over approximately 28 days, although this can vary from person to person.
Menstrual phase:
Ovulatory phase:
The menstrual phase is the first phase of the menstrual
cycle, and it begins with the shedding of the thickened
lining of the uterus that was built up during the previous
cycle. This is what is commonly known as a period or
menstruation. The menstrual phase usually lasts for 3 to 7
days.
The ovulatory phase is the third phase of the menstrual
cycle, and it typically occurs around day 14 of a 28-day
cycle. The surge in luteinizing hormone (LH) from the
pituitary gland triggers the release of a mature egg from
one of the follicles. This is known as ovulation.
Follicular phase:
The follicular phase is the second phase of the menstrual
cycle, and it begins on the first day of menstruation. During
this phase, the pituitary gland in the brain releases folliclestimulating hormone (FSH), which stimulates the growth
and development of a number of follicles (fluid-filled sacs)
in the ovaries. Each follicle contains an immature egg.
Where hormones involved in the
menstrual cycle are made and act:
Luteal phase:
The luteal phase is the final phase of the menstrual cycle,
and it begins after ovulation. The empty follicle that
released the egg transforms into a glandular structure
called the corpus luteum. The corpus luteum produces
progesterone, which helps to thicken the lining of the
uterus in preparation for a possible pregnancy. If the egg is
not fertilized, the corpus luteum breaks down,
progesterone levels drop, and the thickened lining of the
uterus is shed during the next menstrual phase.
The role of hormones in controlling the menstrual
cycle and pregnancy
(Limited to FSH, LH, progesterone, and oestrogen)
Sexually transmitted infections
(An infection that is transmitted through sexual contact)
Human immunodeficiency virus (HIV) is a pathogen that causes an STI.
HIV infection may lead to AIDS.
Methods of transmission of HIV



Unprotected sexual intercourse.
Shared via needles.
Blood transfusions


From mother to foetus
Breastfeeding
How the spread of STIs is controlled


Limiting the number of sexual partners an
individual has
Not having unprotected sex, but making sure
to always use a condom.


Getting tested if unprotected sex or sex with
multiple partners has occurred.
Raising awareness by education programmes
Chapter 16
Chromosomes, genes, and proteins
The nucleus of every cell contains several long
threads called chromosomes. Chromosomes are
made of DNA, which contains genetic
information in the form of genes.
Gene: Length of DNA that codes for a protein.
Alleles are alternative forms of a gene. These
give all organisms their characteristics.
The inheritance of sex in humans
(Reference to X and Y chromosomes)
Sex is determined by an entire chromosome pair.
Females: Chromosomes XX
Males: Chromosomes XY
Only a father can pass on a Y chromosome, he is
responsible for determining the sex of the child.
(Half of the sperm cells carry X chromosome and the
other half carry Y chromosome)
Genetic Diagram (Punnet Square)
*The sequence of bases in a gene determines the
sequence of amino acids used to make a specific protein
(knowledge of the details of nucleotide structure is not
required)
DNA Base sequence to Amino Acid Sequence
The DNA code is converted into proteins (series of amino acids)
1. Transcription (rewriting base code of DNA into bases of RNA)
2. Translation (using RNA base sequence to build amino acids into sequence in a protein)
The sequence of bases in a gene determines the sequence of amino acids that make a specific protein.
Transcription & Translation: Extended

Proteins are made by ribosomes with
sequences of amino acids controlled by
the sequence bases within DNA.

DNA cannot travel out of the nucleus
to the ribosomes, so the base code is
transcribed onto RNA molecule called
mRNA.

mRNA moves out of the nucleus and
attaches to a ribosome.

Ribosome reads the code on the
mRNA in groups of three.

Each triplet of bases codes for a
specific amino acid

The ribosome translates the
sequence of bases into a sequence of
amino acids that make up a protein.

Once the acid chain has been
assembled, it is released from the
ribosome so it can fold and form the final
structure of the protein.
DNA controls cell function
In this way DNA controls cell function by
controlling the production of proteins,
these may be enzymes, antibodies, or
receptors.
Many genes in a particular cell are not
expressed because the cell only makes
specific proteins it needs.
• the gene coding for the protein remains in the
nucleus
• messenger RNA (mRNA) is a copy of a gene
• mRNA molecules are made in the nucleus and
move to the cytoplasm
• the mRNA passes through ribosomes
• the ribosome assembles amino acids into protein
molecules
• the specific sequence of amino acids is determined
by the sequence of bases in the mRNA
All humans have 23 different chromosomes in each cell, in most body cells we have 2 copies of each chromosome.
Nuclei with two sets of chromosomes are known as diploid nuclei. (Pair of each type of chromosome and there are
23 pairs)
Nuclei with one set of unpaired chromosomes are known as haploid nuclei.
Mitosis (New cells)
(Nuclear division giving rise to genetically identical cells)
Importance and roles of mitosis:




Growth: mitosis produces new cells
Repair: to replace damaged or dead cells
Asexual reproduction: mitosis produces offspring that are genetically identical to the parent.
Mitosis of the zygote: as all cells in the body are produced by it.
The exact replication of chromosomes occurs before mitosis. (diploid)
During mitosis, the copies of chromosomes separate, maintaining the chromosome number in each daughter cell.
5 Describe stem cells as unspecialised cells that divide by mitosis to produce daughter cells that can become
specialised for specific functions
Many tissues in the human body contain a small number of unspecialised cells. These are called stem cells and their
function is to divide by mitosis and produce new daughter cells that can become specialised within the tissue and
be used for different functions. A zygote divides several times by mitosis to become a ball of unspecialised cells
(around 200-300 cells). These are embryonic stem cells. These cells are all the same and start differentiating as the
foetus develops with recognisable features
Meiosis (New cells genetically different)
(Involved in the production of gametes) Meiosis: reduction division in which the chromosome number is halved
from diploid to haploid resulting in genetically different cells (details of the stages of meiosis are not required)
Importance: Variation and forming new combinations of maternal and paternal chromosomes
Monohybrid inheritance
Inheritance: The transmission of genetic information from generation to generation
Genotype: The genetic make-up of an organism and in terms of the alleles present
Phenotype: The observable features of an organism
Homozygous: having two identical alleles of a particular gene
Gene: short length of DNA found on a chromosome that codes for a specific characteristic
Alleles: Variations of the same gene
Two identical homozygous individuals that breed together will be pure-breeding
If the, we describe the individual as being heterozygous (hetero = different)7 State that a heterozygous individual
will not be pure-breeding



Homozygous (Dominant): only needs
to be inherited from one parent in
order for the characteristic to show up
in the phenotype
Homozygous (Recessive): needs to be
inherited from both parents in order
for the characteristic to show up in the
phenotype.
Heterozygous: two alleles of a gene
are different, individual will not be
pure-breeding
A dominant allele is an allele that is expressed if it is present in the genotype.
Recessive allele: An allele that is only expressed when there is no dominant allele of the gene present in the
genotype
Genetic Diagrams
Standard way of showing all the steps in making predictions about the
probable genotypes and phenotypes of the offspring from two parents
Sex-Linked Characteristic
Feature in which the gene responsible is located on a sex chromosome
and that this makes the characteristic more common in one sex than
in the other.
In the cross above, there is a 25% chance of producing a male who is colorblind,
a 25% chance of producing a female carrier, a 25% chance of producing a
normal female and a 25% chance of producing a normal male
Example of sex linkage: red, green colour blindness
Interpret pedigree diagrams for the inheritance of a given characteristic.
The family pedigree above shows:




both males and females are affected
every generation has affected individuals.
That there is one family group that has no affected parents or children
the other two families have one affected parent and affected children as well.
 Use genetic diagrams to predict the results of monohybrid crosses and calculate phenotypic ratios,
limited to 1 : 1 and 3: 1 ratios
 Use Punnett squares in crosses which result in more than one genotype to work out and show the
possible different genotypes
Test cross to identify an unknown genotype.

Breeders can use a test cross to find out the genotype of an organism showing the dominant phenotype.

This involves crossing the unknown individual with an individual showing the recessive phenotype - if the
individual is showing the recessive phenotype, then its genotype must be homozygous recessive

By looking at the ratio of phenotypes in the offspring, we can tell whether the unknown individual is
homozygous dominant or heterozygous
Codominance
(Situation in which both alleles in heterozygous organisms contribute to the phenotype)
Example: blood group
Inheritance of ABO blood groups: There are three alleles of the gene governing this instead of the usual two
Alleles IA and IB are codominant, but both are dominant to IO




I represents the gene and the superscript A, B and O
represent the alleles
IA results in the production of antigen A in the blood
IB results in the production of antigen B in the blood.
IO results in no antigens being produced in the blood.
Chapter 17
Variation and Selection
Variation
(Differences between individuals of the same species)
Continuous variation




Results in a range of phenotypes between two extremes.
-Examples include body length and body mass
Results in a limited number of phenotypes with no intermediates; examples include ABO blood groups, seed
shape in peas and seed colour in peas
Caused by genes only and continuous variation is caused by both genes and the environment (Genetic
Variation)
Discontinuous variation


Distinct differences for a characteristic
Example: People are either blood group A, B, AB, or O, are either male or female
Height is an example of continuous variation which
gives rise to a smooth bell-shaped curve when plotted
as a graph
Blood group is an example of discontinuous variation
which gives rise to a step-shaped graph
Phenotypic Variation

Phenotypic variation can be caused in two main ways:
o
It can be genetic - controlled entirely by genes.
o
Or it can be environmental - caused entirely by the environment in which the organism lives
Genetic Variation

Examples of genetic variation in humans include:
o
blood group
o
eye colour
o
gender
o
ability to roll tongue.
o
whether ear lobes are free or fixed
Environmental Variation

Characteristics of all species can be affected by environmental factors such as climate, diet, accidents,
culture and lifestyle

In this instance ‘environmental’ simply means ‘outside of the organism’ and so can include factors like
climate, diet, culture, lifestyle and accidents during lifetime

Examples include:
o
An accident may lead to scarring on the body
o
Eating too much and not leading an active lifestyle will cause weight gain
o
Being raised in a certain country will cause you to speak a certain language with a certain accent
o
A plant in the shade of a big tree will grow taller to reach more light
Genetic and Environmental Causes

Discontinuous variation is usually caused by genetic variation alone

Continuous features often vary because of a combination of genetic and environmental causes, for example:

o
tall parents will pass genes to their children for height.
o
their children have the genetic potential to also be tall.
o
however, if their diet is poor then they will not grow very well
o
therefore, their environment also has an impact on their height.
Another way of looking at this is that although genes decide what characteristics we inherit, the surrounding
environment will affect how these inherited characteristics develop
Mutation
Genetic change
The way in which new alleles are formed (survival advantage or can lead to harmful changes)
Ionising radiation and some chemicals increase the rate of mutation.
gene mutation: Random change in the base sequence of DNA
Mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations.
Can happen: spontaneously and continuously (increased by exposure to gamma rays and/or certain types of
chemicals)
Mutations: New alleles form through random changes to DNA
Meiosis: New allele combinations form through segregation
Random mating: Which partnerships form for sexual reproduction.
Random fertilisation: Which sperm and egg combinations occur during sexual reproduction.
Adaptive features
Inherited feature that helps an organism to survive and reproduce in its environment
Fitness: probability of an organism surviving and reproducing in the environment in which it is found
A typical question here might be to explain how the leaf area and distribution and density of stomata help different
species of plant survive in their different habitats
Adaptive features of hydrophytes and xerophytes to their environments:
Hydrophytes:


Plants adapted to live in extremely wet
conditions.
Common adaptations: Large air spaces in
their leaves to keep them close to the surface
of the water where there is more light for
photosynthesis, Small roots as they can also
extract nutrients from suirroudning water and
the stomata open all the time and mainly
found on the upper epidermis.
Xerophytes:


Plants adapted to live in extremely dry
conditions
Thick waxy cuicle as it cuts down water,
Sunken stomata so moist air can be trapped
and reduce the evaporation rate, Leaf rolled
with stomata inside and inner surface
covered in hairs so prevent air movement
reducing transpiration, small leaves which
reduce the surface area and therefore the
evaporating surface, extensive shallow roots
which allow for the quick absorption of water
when it rains and Thickened leaves or stems
which contain cells that store water
Selection
Natural selection:
The genetic variation within populations related with the production of many offspring, which leads to competition and
struggle for survival, including competition for resources. A greater chance of reproduction by individuals that are
better adapted to the environment than others, therefore these individuals pass on their alleles to the next
generation.
Selective breeding:
Selection by humans of individuals with desirable features. Crossing these individuals to produce the next generation
entail selection of offspring showing the desirable features
Selective breeding by artificial selection is carried out over many generations to improve crop plants and
domesticated animals and apply this to given contexts
Adaptation: The process, resulting from natural selection, by which populations become more suited to their
environment over many generations
Development of strains of antibiotic resistant bacteria: example of natural selection
Differences between natural and artificial selection
Chapter 18
Organisms and their environment
Transfer of Energy: The Sun is the principal source of energy input to biological systems
Energy Flow
Plant gets energy from respiration, energy flows through the different trophic levels in a food web.
Food chains and food webs
Food chain: showing the transfer of energy from one organism to the next, beginning with a producer.
Food web: a network of interconnected food chains and interpret food webs.
Producer: an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
Consumer: an organism that gets its energy by feeding on other organisms (consumers may be classed as primary,
secondary, tertiary, and quaternary according to their position in a food chain)
Herbivore: an animal that gets its energy by eating plants
Carnivore: an animal that gets its energy by eating other animals
Decomposer: an organism that gets its energy from dead or waste organic material
Impact humans have through overharvesting of food species and through introducing foreign species to a habitat.




Food webs give us a lot more information about the transfer of energy in an ecosystem.
They also show interdependence - how the change in one population can affect others within the food web.
Most of the changes in populations of animals and plants happen as a result of human impact - either by
overharvesting of food species or by the introduction of foreign species to a habitat
Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or
web
Pyramids of numbers

Most of the changes in populations of animals and plants happen
as a result of human impact - either by overharvesting of food
species or by the introduction of foreign species to a habitat

Due to interdependence, these can have long-lasting knock-on
effects to organisms throughout a food chain or web.
Pyramids of biomass

A pyramid of biomass shows how much mass the creatures at
each level would have without including all the water that is in
the organisms (their ‘dry mass’)

Pyramids of biomass are ALWAYS pyramid-shaped, regardless
of what the pyramid of numbers for that food chain looks like
Discuss the advantages of using a pyramid of biomass rather than a pyramid of
numbers to represent a food chain
Trophic level: the position of an organism in a food chain, food web or ecological pyramid
Identify the following as the trophic levels in food webs, food chains and ecological pyramids: producers, primary
consumers, secondary consumers, tertiary consumers and quaternary consumers
Pyramids of Energy
In order for the energy to be passed on, it has to be
consumed (eaten)
However not all of the energy grass plants receive goes
into making new cells that can be eaten
Only the energy that is made into new cells remains with
the organisms to be passed on
Energy lost through: Making waste products, movement,
heat and/or undigested waste (food for decomposers)
Explain, in terms of energy loss, why food chains usually have fewer than five trophic levels
The majority of the energy an organism receives gets ‘lost’ (or ‘used’) through:




making waste products eg (urine) that get removed from the organism
as movement
as heat (in mammals and birds that maintain a constant body temperature)
as undigested waste (faeces) that is removed from the body and provides food for decomposers
This inefficient loss of energy at each trophic level explains why food chains are rarely more than 5 organisms long
Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed
on crop plants




Given what we know about energy transfer in food chains, it is clear that if humans eat the wheat there is much
more energy available to them than if they eat the cows that eat the wheat
This is because energy is lost from the cows, so there is less available to pass on to humans
Therefore, it is more energy efficient within a crop food chain for humans to be the herbivores rather than the
carnivores
In reality, we often feed animals on plants that we cannot eat (eg grass) or that are too widely distributed for us
to collect (eg algae in the ocean which form the food of fish we eat)
Nutrient Cycles
The Carbon Cycle
The carbon cycle is a natural process that involves the
transfer of carbon between living organisms and the
environment. It starts with photosynthesis, where
plants and algae use carbon dioxide and water to
produce glucose and oxygen. This glucose is used for
respiration, which releases carbon dioxide back into
the atmosphere, where it can be reused by plants.
Carbon is also transferred between organisms through
feeding and decomposition, where dead organisms
release carbon into the soil and atmosphere. Fossil
fuels, which contain large amounts of carbon, are
formed over millions of years through the
compression and heating of organic matter. When
these fuels are burned through combustion, carbon
dioxide is released back into the atmosphere,
contributing to climate change. Overall, the carbon
cycle is a vital process that sustains life on Earth, but
human activities have disrupted this natural balance,
leading to an increase in atmospheric carbon dioxide
and global warming.
The Nitrogen Cycle
The nitrogen cycle is the process by which nitrogen is
converted between different forms, facilitating its
availability to living organisms. It begins with the
decomposition of plant and animal protein, releasing
ammonium ions into the soil. Nitrifying bacteria then
convert ammonium ions into nitrite and then into
nitrate ions, which can be absorbed by plants.
Nitrogen fixation occurs through lightning and
bacteria, which convert atmospheric nitrogen into
ammonia, which can be used by plants. Nitrogen is
also acquired by organisms through the feeding and
digestion of proteins, which are broken down into
amino acids. These amino acids can be used to
produce new proteins. When organisms die the
nitrogen is released back into the soil through
decomposition, which can then be used by other
organisms. Denitrifying bacteria convert nitrates back
into nitrogen gas, completing the nitrogen cycle.
Roles of microorganisms in the nitrogen cycle




Decomposition
Nitrification
Nitrogen fixation
Denitrification
Populations
Population: a group of organisms of one
species, living in the same area, at the same
time
Community: all the populations of different
species in an ecosystem
Ecosystem: a unit containing the community of
organisms and their environment, interacting
together
Population growth:
Factors:



Food supply
Predation
Disease
Explain the factors that lead to each phase in the sigmoid curve of population growth, referring, where
appropriate, to the role of limiting factors
Organisms in a natural environment are unlikely to show population growth like a sigmoid growth curve because they
are affected by many other factors, including:
o
changing temperature or light
o
predators
o
disease
o
immigration (individuals moving into the area)
o
emigration (individuals moving out of the area)
Birth rate: the total number of live births over time. Balanced by death rates.
Death rates: the total number of deaths over time
When
Population
Factors affecting birth rate:

Birth rate = death
rate
Stays the same
Countries with high infant mortality have high birth rates.

In agrarian economies of many LEDCs more people are needed
for manual labor, so families tend to be bigger
Birth rate > death
rate
Grows

In MEDCs it is expensive to have children and pensions are
provided by the stare
Birth rate < declines
Declines

Social and political factors result in low use of birth control in LEDCs, whereas in MEDCs birth control is widely
used
Population or age pyramid describes how the
population is made up in terms of age and sex.
Looking at a pyramid, from bottom to top, it can
be divided into three groups:
the young (dependent), middle aged
(independent) and the old (dependent). The ≠ in
age structure presents different challenges for
governments of LEDC’s with youth populations
and MEDC’s with older populations.
Limiting factor: a factor that is in short supply, which stops and activity happening at a faster rate
Chapter 19
Human influences on ecosystems
Food supply
How humans have increased food production:
Agricultural machinery to use larger areas of land and improve efficiency.
Chemical fertilizers to improve yields.
Insecticides to improve quality and yield.
Herbicides to reduce competition with weeds.
Selective breeding to improve production by crop plants and livestock
Large-scale monocultures of crop plants
Advantages
Large scale growth
Lower biodiversity
Used for pests
Intensive livestock production
Disadvantages
Harmless insects killed as
well.
Pollution by pesticides
Pest may eventually become
resistant
Advantages
Help provide more
food for people.
Provide cheap
food.
Fewer people go
hungry.
Takes up less land
than extensive
farming
Disadvantages
Welfare issues for the livestock
Disease can spread easily among
them.
Waste from intensive farming
can pollute land.
Wasted energy (How we feed
animals)
Energy is used to transport
animals.
Large quantities of water
provided
Biodiversity: the number of different species that live in an area
Habitat destruction means a downward pressure on biodiversity
Habitat destruction
Reasons for habitat destruction:



increased area for housing, crop plant production and livestock production (increasing population and
demand for food)
extraction of natural resources (Wood, stone, and metal)
freshwater and marine pollution (Humana activities and eutrophication)
Through altering food webs and food chains, humans can have a negative impact on habitats
Deforestation
(The clearing of trees in large scales)
If trees are replanted It would be a sustainable practice
Undesirable effects of deforestation

(Habit destruction)





Consequences
reducing biodiversity
extinction
loss of soil
flooding
increase of carbon dioxide in the atmosphere



Pollution
Effects of untreated sewage and excess fertilizer on
aquatic ecosystems:


Human activities have led to the pollution of
land, water and air.
Pollution comes from a variety of sources,
including industry and manufacturing processes,
waste and discarded rubbish, chemicals from
farming practices, nuclear fall-out, and untreated
sewage
Forest habitats if destroyed causes the loss of
large numbers of plant and animal species
Without trees, nutrients and minerals will
remain unused in the soil so will be washed
away into rivers and lakes by rain (leaching)
Without trees topsoil will be loose and
unstable so will be easily washed away
(increased risk of flash flooding and
landslides)
The removal of significant number of trees
means less carbon dioxide being removed
from the atmosphere (an less O2 released)
Effects of non-biodegradable plastics, in both aquatic and terrestrial ecosystems:
Marine Habitats
Animals eat plastic or are caught in it (Injuries and/or
death)
As plastic breaks down toxins are released
Once it’s broken down into very small particles, ingested
by animals and enters food chain
Land habitats
Plastic is disposed of by burying in landfills
As it breaks down, it releases toxins into the
surrounding soil
Land no good for growing crops or grazing animals
Air Pollution
Acid Rain
Combustion of fossil fuels that contain sulfur
impurities creates sulfur dioxide.
This is released into the atmosphere where it
combines with oxygen to form sulfur trioxide
Sulfur trioxide dissolves in water droplets in
clouds and forms acid rain
Sources and effects of pollution of the air by
methane and carbon dioxide:
Both gases insulate the Earth and act as a 'blanket'
around the atmosphere
Higher levels of both have led to global warming and
climate change.
Human activity has increased levels of both gases in the
atmosphere
Burning fossil fuels increases carbon dioxide.
Keeping livestock generates methane gas.
Global warming melts the permafrost in sub- polar
regions, which results in even more trapped
methane being released into the atmosphere
The process of eutrophication of water:






increased availability of nitrate and
other ions
increased growth of producers
increased decomposition after death of
producers
increased aerobic respiration by
decomposers.
reduction in dissolved oxygen
death of organisms requiring dissolved
oxygen in water
The sequence of events causing eutrophication
in lakes and rivers
Conservation
Sustainable resource: one which is produced as rapidly as it is removed from the environment so that it does not run
out.
Some resources can be conserved and managed sustainably, limited to forests and fish stocks.
Why organisms become endangered or extinct:






Climate change
habitat destruction
hunting
overharvesting
pollution
introduced species.
How endangered species can be conserved:




monitoring and protecting species and habitats
education
captive breeding programs
seed banks
There are moral, cultural and scientific reasons for conservation programs, including:



reducing extinction rates of both plant and animal species
keeping damage to food chains and food webs to a minimum and protecting vulnerable ecosystems (egg
the rainforests)
protecting our future food supply and maintaining nutrient cycles and possible sources of future medical
drugs and fuels
How forests can be conserved using:
education, protected areas, quotas, and replanting.
 Forests are needed to produce paper
products and provide wood for timber.
 Much of the world’s paper is now produced
from forests which replant similar trees when
mature trees are cut, ensuring that there will be
adequate supply in the future
 Tropical hardwoods such as teak and
mahogany take many years to regrow but are
highly desirable for furniture
 Using these types of wood has now been
made more sustainable due to the introduction
of several schemes designed to monitor logging
companies and track the wood produced (e.g.
the Forestry Stewardship Council)
 Education helps to ensure logging companies
are aware of sustainable practices and consumers are aware of the importance of buying products made
from sustainable sources
How fish stocks can be conserved

Controlling the number of fish caught
each year (quotas)

Controlling the size of fish caught (to
ensure there are enough fish of a
suitable age for breeding remaining)

Controlling the time of year that certain
fish can be caught (to prevent large scale
depletion of stocks when fish come
together in large numbers in certain
areas to breed)

Restocking (breeding and keeping
offspring until they are large enough to
survive in their natural habitat then
releasing)

Educating fishermen as to local and international laws and consumers so they are aware of types of fish
which are not produced sustainably and can avoid them when buying fish.
Reasons for conservation programs:

There are numerous reasons why conservation programs are important.
o Maintaining or increasing biodiversity
 Which allows ecosystems to remain stable?
o Reducing extinction
 Helps to retain iconic species and maintain biodiversity.
o Protecting vulnerable ecosystems which would have been quickly lost to human
activity.
o Maintaining ecosystem functions
 Nutrient cycling e.g., carbon cycling to hold back climate change
 Resource provision, such as
 Food - making sure we have enough for the population.
 Drugs - having access to plants for plant-based remedies.
 Fuel - for important activities such as cooking.
 Genes - so the gene pool remains wide, and variety exists in all species
The use of artificial insemination (AI)
In captive breeding programs
This allows large numbers of offspring to be produced without the need for conventional sexual intercourse between
males and females
In Vitro fertilization (IVF)
In captive breeding programs
This allows gametes with known alleles to be used in ensuring the next generation remains biodiverse
Risks to a species if its population size decreases, reducing genetic variation.
(Knowledge of genetic drift is not required)

If its population size decreases, a species will experience reduced genetic variation.

This renders the species more susceptible to environmental change.

The species is less resilient and has a greater risk of extinction.
Chapter 20
Biotechnology and genetic modification
Bacteria are useful in biotechnology and genetic modification due to their rapid reproduction rate and their ability
to make complex molecules
Bacteria useful in biotechnology and genetic modification:


Few ethical concerns over their manipulation and growth
Presence of plasmids (ideal for transferring DNA from one cell to another)
Biotechnology
Role of anaerobic respiration in yeast during the
production of ethanol for biofuels:
Use of pectinase in fruit juice production
Yeast is a single celled fungus that uses sugar as its
food source. When it respires, ethanol and carbon
dioxide are produced.
Role of anaerobic respiration in yeast during breadmaking:
Yeast will respire anaerobically if it has access to
plenty of sugar, even if oxygen is available. Yeast is
mixed with flour and water and respires anaerobically
By adding an enzyme called pectinase to the chopped
up fruit, more juice is released. Pectinase works by
breaking down a chemical called pectin that is found
inside plant cell walls. Once pectin is broken down,
the cell walls break more easily and more juice can be
squeezed out of the fruit. Adding pectinase to fruits
also helps to produce a clearer juice as larger
polysaccharides like pectin can make the juice seem
cloudy - once they are broken down into smaller
molecules, the juice becomes clearer
Use of biological washing powders that contain enzymes.
Stains on clothes are organic molecules. Detergents that only contain soap can remove some
of these stains when mixed with hot water, but it can take a lot of time and effort. Biological
washing powders contain enzymes like digestive enzymes that help to break down large food
molecules.
Advantages:

Quickly breaking down large, insoluble molecules such as fats and proteins
into smaller, soluble ones that will dissolve in washing water.

They are effective at lower temperatures, meaning less energy (and money) has to be
used in order to wash clothes to get them clean as washing water does not need to be
heated to higher temperatures

They can be used to clean delicate fabrics that would not be suitable for washing at
high temperatures
Use of lactase to produce lactose-free milk.




Lactose is the sugar found in milk.
Humans have the ability to produce lactase.
Milk can be lactose free by adding the enzyme
lactase to it and leaving it to stand for a while to
allow the enzyme to break down lactose.
This is because of lactose intolerant people.
Fermenters
(used for the large-scale production
of useful products by bacteria and
fungi, including insulin, penicillin and
mycoprotein)
Fermenters are containers used
to grow (‘culture’)
microorganisms like bacteria and
fungi in large amounts. These can
then be used for many
biotechnological processes like
producing genetically modified
bacteria and the penicillium
mould that produces penicillin. The advantage of using a fermenter is that conditions can be
carefully controlled to produce large quantities of exactly the right type of microorganism.
Conditions that need to be controlled in a fermenter.
Aseptic Precautions
Nutrients
Optimum Temperature
Optimum pH
Oxygenation
Agitation
Cleaned by steam to kill microorganisms and prevent chemical
contamination
Added for use in respiration to release energy for growth and
reproduction
Monitored using probes and maintained using the water jacket
to ensure an optimum environment for enzymes
pH inside it is monitored using a probe to check it as to the
microorganisms being grown
Oxygen is needed for aerobic respiration
Stirring paddles ensure that microorganisms, nutrients, oxygen,
temperature, and pH are evenly distributed
Genetic modification
Changing the genetic material of an organism by
removing, changing, or inserting individual genes
Examples of genetic modification:




the insertion of human genes into bacteria
to produce human proteins.
the insertion of genes into crop plants to
confer resistance to herbicides.
the insertion of genes into crop plants to
confer resistance to insect pests.
the insertion of genes into crop plants to
improve nutritional qualities.
The process of genetic modification using bacterial
production of a human protein as an example:
(a) isolation of the DNA making up a human gene
using restriction enzymes, forming sticky ends
(b) cutting of bacterial plasmid DNA with the
same restriction enzymes, forming
complementary sticky ends
(c) insertion of human DNA into bacterial
plasmid DNA using DNA ligase to form a
recombinant plasmid
(d) insertion of recombinant plasmids into
bacteria (specific details are not required)
(e) multiplication of bacteria containing
recombinant plasmids
(f) expression in bacteria of the human gene to
make the human protein
Advantages and disadvantages of genetically modification
Paper 5: Practical assessment
Experiments:
(In order of appearance in the book)
1. Simple quantitative experiments, including the measurement of: –
volumes of gases and liquids – masses – temperatures – times –
lengths.
2. Diffusion & Osmosis Experiments
3. food tests
4. Rates of enzyme-catalyzed reactions, including judging endpoints,
e.g. color changes
5. pH and the use of hydrogen carbonate indicator, litmus, and
universal indicator
6. photosynthesis (rate and limiting factors) º.
7. Heart rate and breathing rate.
8. Transpiration, respiration, and tropic responses in plants
9. Dissection of seeds and flowers
10.Germination
11.Continuous and discontinuous variation





Use methods of sampling that are representative and avoid bias, e.g.,
consideration of sample size and simple random sampling.
observe, record and measure images of familiar and unfamiliar biological
specimens.
Make clear line drawings of biological specimens, calculating the magnification or
actual size and adding labels
as required.
Use simple apparatus in situations where the method may not be familiar to the
candidate.