This set of notes cover year 9 IGCSE topics including ecology and environment. With detailed information, student that had used the notes scored a 9 in her IGCSE Biology.
Unit 3. Ecology and the Environment (year 9)
- Producers – plants which photosynthesise to produce food
- Consumers – animals that eat plants or other animals
- Decomposers - organisms that break down dead material and help to recycle nutrients
Biotic components: living.
Abiotic components: non-living.
A habitat is the place where an organism lives. All the organism of a particular species found in an ecosystem at a certain time form the
population of that species. The population of all species found in an ecosystem at a particular time form the community.
Quadrat sampling-
The sampling in an area is carried out at random to avoid bias. EG. Number of daisies in each. Quadrat in a field.
The chosen study area measured 10 m x 10 m (100 m2).
Pupils placed 8 quadrats, each 50 cm x 50 cm (a total of 2 m2).
A total of 24 daisy plants were found in the quadrats.
So there were 12 daisies per m2.
The amount of variation shown by species in an ecosystem is called the ecosystem’s biodiversity.
Factors that influence the numbers and distribution of organisms in an ecosystem
Biotic factors
- Availability of food and competition for food resources
- Predation
- Parasitism
- Disease
- Presence of pollinating insects
- Availability of nest sites
Abiotic factors
- Climate, light intensity, temperature, humidity
- Hours of daylight
- Soil conditions
Food chain/ web:
Trophic levels --
Producer Primary consumer (herbivore) secondary consumer (carnivore) tertiary consumer quaternary consumer
The top one is called top carnivore
Ecological pyramids
- Pyramids of numbers, which represents the numbers of organisms in each trophic level in a food chain, irrespective of their mass
- Pyramids of biomass, which show the total mass of the organisms in each trophic level, irrespective of their numbers.
Why are diagrams of feeding relationships a pyramid shape?
- Some parts of the grass are not eaten.
- Some parts are not digested and so are not absorbed.
- Some of the materials absorbed form excretory products
- Many of the materials are respired to release energy, with the loss of carbon dioxide and water
So therefore energy lost from food chains and webs at each trophic level.
Flow of energy through ecosystems
- Photosynthesis turns sunlight energy into chemicals such as glucose and starch.
- Respiration releases energy from organic compounds such as glucose.
- Almost all other biological processes (muscle contraction, growth, reproduction, excretion, active transport) uses the energy released
in respiration.
Cycling nutrients through ecosystems
Microorganisms break down complex organic molecules in the bodies of dead animals and plants into simple substances which they
release into the environment.
The Carbon Cycle
Why is carbon important
Carbon is the main constituent of all living cells. It makes DNA, RNA and enzymes in living things.
Plants take in CO2 for photosynthesis. Through photosynthesis, plants make glucose and other substances such as protein. When animals eat
plants, they use some of the carbon containing compounds to grow. Some carbon-containing compounds are used to release energy by
respiration. Organic compounds in green plants death organic compounds in dead organisms Decay and decomposition releases CO2
as microbes respire. Carbon dioxide in the air and dissolved in water.
Organic compounds can also be converted to fossil fuels burning carbon dioxide in the air and dissolved in water.
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