Relationships of organisms with one another and with the environment.
(Chapter – 19 - Biology)
Food chains and food webs:
•
•
A food chain shows the transfer of energy from one organism to the next beginning with
a producer.
A food web is a network of interconnected food chains.
A decomposer:
•
•
•
It is an organism that gets its energy from dead or waste organic matter.
Bacteria and fungi are great decomposers that help cycling of nutrients in the
environment.
Decomposers are sometimes called saprotrophs.
Trophic levels (feeding levels):
A trophic level is the position of an organism in a food chain, food web or in an ecological
pyramid such as a number pyramid,
Planktons:
•
•
•
•
The microscopic organisms that live in the surface waters of the sea or fresh water are
called planktons.
Phytoplankton: Photosynthetic plankton.
Zooplankton:
They can’t do photosynthesis. They depend on phytoplankton for food.
Ecological pyramids:
•
•
Ecological pyramids show the relative number of various parameters across the trophic
levels.
Eg: Number of organisms, amount of energy, biomass etc.
Number pyramids:
The number of organisms in each trophic level along a food chain is counted and made into a
pyramid.
1
Number pyramids do not show the usual shape of the pyramid always.
Biomass pyramids are constructed to overcome the problem.
Biomass pyramids:
This type of pyramid represents the total living biomass or organic matter present at different
trophic levels in a food chain.
Biomass pyramids always show the normal shape of a pyramid.
2
Transfer of energy:
From the sun to a green plant:
➢ Sun light is converted to chemical energy and stored in green plants by the process
called photosynthesis.
➢ Grenn plants and other all organisms depend on this product of photosynthesis for food
and oxygen for respiration.
From green plants to an animal:
➢ There is a great energy lost from one trophic level to the next trophic level along a food
chain.
➢ Only 10% of energy passes from one trophic level to the next trophic level.
➢ It is very unusual for food chains to have more than trophic levels.
➢ This is because about 90% of the energy is lost at each energy trophic level.
➢ As a result, very little of the energy entering the chain through the producer is available
to the top consumer.
3
Nutrient cycles:
Carbon Cycle:
➢ Carbon is an element present in all the compounds that make up living organisms.
➢ Green plants get their carbon from the atmosphere.
➢ Animals get their carbon from green plants.
Removal of CO2 from the atmosphere:
➢ Photosynthesis
➢ Fossilisation:
• Any condition that stops fast decomposition may produce fossils.
• The carbon in the dead organisms becomes trapped and compressed to make
fossils.
• We use these fossils as fossil fuels such as coal, mineral oils and natural gas.
• When carbon is trapped as fossils it takes millions of years to add this carbon to
the carbon cycle.
Addition of CO2 to the atmosphere.
➢ Respiration
➢ Decomposition
➢ Combustion
4
Nitrogen cycle:
•
•
•
•
The atmosphere contains about 78% nitrogen gas.
But green plants can’t use this nitrogen gas to make their proteins.
Plants can absorb nitrogen as NO3- ions in the soil.
Therefor it is very important to have NO3- ions in the soil.
Processes that add nitrates to the soil:
(A) Nitrification is done by nitrifying bacteria.
Nitrification – The process of getting energy from ammonia.
A group of bacteria living in the use ammonia in the excretory matter and decaying
organic matter as a source of energy.
Nitrate ions are produced because of nitrification.
Eg: Nitrite bacteria oxidise ammonium compounds to nitrite.
Nitrate bacteria oxidise nitrites to nitrates.
(B) Nitrogen fixation done by Nitrogen fixing bacteria:
The process of building nitrogen gas into compounds of ammonia is called nitrogen
fixation.
This process is done by a special group of bacteria called nitrogen fixing bacteria.
Some nitrogen fixing bacteria are living in root nodules of leguminous plants. (eg.pea
.dhall,bean)
Some of them live freely in the soil.
(C) Lightning
The high amount of energy discharged in the lightning causes N2 and O2 in the
atmosphere to react and make oxides of nitrogen.
Itrogen gas
Then they make nitrates in the soil.
Processes that remove nitrates from the soil:
(i)Uptake by plants.
(ii)Denitrification –
Some bacteria obtain energy by braking down nitrates to nitrogen gas.
This process is called denitrification.
The group of bacteria involved in denitrification is called denitrifying bacteria.
5
Ecosystems and biodiversity:
Population:A group of organisms of one species living in the same area at the same time.
Eg. Human population in Sri Lanka in 2021 is 21,715,079 million
Community:All the populations of different species in an ecosystem.
Ecosystem: It is a unit containing community of organisms and their environment
interacting with each other.
Eg: A freshwater pond is an ecosystem. Biotic factors in the pond(community) fish ,frogs, water
beetles,Aquatic plants,birds which come for food and shelter.
Abiotic factors – water, oxygen ,CO2 dissolved in water, sunlight, soil and mud at the bottom
Biodiversity: The number of different species that live in an area.
Factors that affect population growth:
A population grows when the birth rate exceeds the death rate.
There are several factors that affect this condition.
Eg: Food supply
Competion
Predators pray relation ships
Disease
6
Human population:
•
•
The rate of growth of human population is very high compared to other organisms.
Low infant mortality rate, increase in life expectancy, improvements in agriculture,
Medicine,transport,sanitary facilities are the main reasons for increase in human
population.
As a community grows wealthier the birth rate goes down due to four main
reasons:
The demand for global resources:
➢ AS the population increases the demand for global resources too increases.
➢ This includes food, fuels, materials for constructions such as sand,gravel,limestones and
metals.
➢ Recycling and reuse are becoming more important to satisfy some of the increase in
demand for materials.
➢ As the demand for building, roads and agriculture increases natural habitats are being
removed.
Effects of humans on ecosystems:
Overharvesting of plant and animal species.
The species may be harvested for different reasons.
Eg: for food, body parts such as tusks (tuskers), hones (rhinos), bones and fur (tigers), for
selling as pets(reptiles,birds,fish)
Overharvesting causes loss of biodiversity, species become endangered and extinct.
7
Overfishing:
•
•
•
•
•
Overfishing can reduce the fish populations in the ocean and in rivers.
Therefore, it can reduce biodiversity.
It also causes damage to the environment.
The use of heavy nets dragged along the sea floor for fishing can damage the coral
reefs.
Coral reefs are the great habitats of many species.
Introducing non-native species:
•
•
•
Plants and animals living in areas where they don’t naturally exist are called non-native
species.
They are introduced to the new environment by humans for several reasons.
Sometimes these non-natives become invasive species in the new environment and
cause many problems.
Eg: (a) Cause extinction of native organisms.
(b) Reduce biodiversity.
© Compete with native organisms for limited resources.
Effects of deforestation:
➢
➢
➢
➢
➢
➢
Habitat destruction
Loss of biodiversity.
Extinction of species.
Loss of soil fertility.
Flooding.
Increase of CO2 level in the atmosphere.
At present tropical forests are destroyed by human for three main purposes.
(a) For timber
(b) For agriculture, roads, and shelters
(c) For firewood.
Eutrophication:
➢ Plants can grow faster if they have high amounts of nitrates, phosphates, and other
required ions from the soil.
➢ In recent past the amount of nitrates and phosphates including other ions in rivers and
lakes has been greatly increased.
➢ This leads to the process called eutrophication.
Main steps and effects of eutrophication:
▪
▪
▪
▪
▪
Addition of nitrates, phosphates, and other ions to the river/lake from human activities
Human activities – Use of chemical fertilizers in agriculture, detergents, pesticides,
weedicides.
Growth of algae is increased in the river.
Algae – microscopic green plants.
Large numbers of algae cause algae blooms on the surface of water.
8
▪
▪
▪
▪
▪
▪
▪
▪
▪
Algal blooms stop sun light entering the river/lake.
Submerged green plants can’t get light energy for photosynthesis.
Algae also start to die due to the competition.
Aerobic decomposers start their action on dead plants and algae.
Aerobic decomposers(bacteria) use dissolved oxygen in water.
Oxygen level decreases.
Fish die due to suffocation.
Anaerobic decomposers start to grow.
Water becomes dark, bad smell due to the toxic gases such as methane and hydrogen
sulfide produced by anaerobic bacteria.
Biological Oxygen Demand (BOD)
➢ The degree of pollution of a river by organic matter is measured by its BOD level.
➢ This is the amount of oxygen used by aerobic bacteria (decomposers) which live the
river.
➢ The higher the BOD level the more polluted the river is by organic matter such as
sewage, excretory matter, and dead bodies.
How to reduce eutrophication:
➢
➢
➢
➢
➢
Use detergent with low phosphate.
Minimize the use of chemical fertilizers.
Use chemical fertilizers in correct dose.
Use chemical fertilizers that do not dissolve easily.
Do not discharge animal waste to rivers.
Effects of enhanced greenhouse gasses:
It causes global warming.
Global warming causes many problems.
Conservation:
Conservation is an active process of developing strategies to prevent the loss of Earth biological
diversity.
9
Conservation of a forest:
There are several ways of sustaining the number of tree species in a natural forest.
➢
➢
➢
➢
Education
Protected areas.
Legal quotas.
Replanting
Conservation of fish stocks:
➢
➢
➢
➢
➢
➢
Education.
Closed seasons.
Protected areas.
Control of net type and mesh size.
Legal quotas.
Monitoring.
Conservation of endangered species:
➢
➢
➢
➢
Education.
Captive breeding and reintroduction.
Seed banks.
Conservation programs.
Risks to a species of decreasing population size:
•
•
•
If the population is large there will be a minimal reduction in the genetic variation
present.
A smaller population would be affected because the genetic variation in the gene pool
would be reduced.
It can affect the ability of the species to cope with environmental change and put it at
greater risk of extinction.
Set by Ms.A.J.Sriyani.
10