AQA · Biology · 8461
GCSE Biology: Ecology notes (PDF)
AQA Topic 7 Ecology — ecosystems, food chains, the carbon and water cycles and biodiversity — detailed notes from Physics & Maths Tutor. Each card deep-links to the page.
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An ? is the interaction of a community with non-living (abiotic) parts of the environment.
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ecosystem
What is a stable community in ecology?
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One where all the biotic and abiotic factors are in balance, so population sizes remain roughly constant.
Why does soil pH affect the rate at which mineral ions return to soil?
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Soil pH affects the rate of decay, and decay returns mineral ions to the soil.
Why can a new pathogen rapidly wipe out a population?
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The population has no resistance to it.
? are organisms that live in environments with extreme conditions such as high temperature, pressure or salt concentration.
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Extremophiles
What type of organisms are always producers in a food chain?
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Photosynthetic organisms, usually green plants or algae.
What happens to predator populations after prey populations increase?
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The predator population will also increase (because more food is available).
How is CO₂ removed from the air in the carbon cycle?
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Through photosynthesis by green plants and algae.
Why must methane produced in biogas generators be used immediately?
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It cannot be stored as a liquid.
Why does high biodiversity make an ecosystem more stable?
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Species are less dependent on each other for things such as food and shelter.
Interdependence describes how organisms in a community depend on ? for vital services.
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other organisms
What is deforestation?
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The cutting down of a large number of trees in the same area, in order to use the land for something else.
Why does burning trees during deforestation contribute to global warming?
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Trees contain carbon, so burning them releases CO₂ into the environment, which contributes to global warming.
Trees take in ? when they photosynthesise, so fewer trees means less is taken in.
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CO₂
What are the two main greenhouse gases?
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Carbon dioxide and methane.
Why are peat bogs important habitats?
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They are a habitat for many species, in particular for migrating birds.
Only approximately ? of the biomass of each trophic level is transferred to the next.
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10%
What percentage of incident light energy do producers transfer for photosynthesis?
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About 1%, as not all the light lands on the green photosynthesising parts of the plant.
What is food security?
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Having sufficient food to feed the population.
Why do farmers raise livestock in small cages with high temperatures?
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To reduce energy transfer to the environment by limiting movement and reducing energy wasted on controlling body temperature, thus increasing biomass efficiency.
Why are fishing net sizes restricted to be bigger?
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So smaller fish are not caught and can reach breeding age and produce more fish, helping maintain sustainable populations.
The fungus ? can produce mycoprotein, a protein-rich food source.
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Fusarium
Give two advantages of genetically modifying crops.
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Making them resistant to pests or extreme weather to increase yields, and increasing their nutritional value to benefit areas lacking certain vitamins.
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