Biology · Edexcel Paper 2
Ecosystems and Communities
How living things are organised into populations, communities and ecosystems, how organisms depend on each other (parasitism and mutualism), how abiotic and biotic factors shape a community, how to sample a habitat with quadrats and belt transects, and how energy is lost along a food chain. Matches Edexcel Topic 9 statements 9.1 to 9.8. The first three lessons are for both Combined Science and separate Biology; the last lesson (9.7B and 9.8B, energy transfer and pyramids of biomass) is for separate Biology only. There is no Higher tier only content in this chapter.
Lessons
Ticks are remembered on this device only.
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1
Levels of Organisation and Interdependence
No living thing lives on its own. This lesson is for both Combined Science and separate Biology. It covers the levels of organisation from a single organism up…
10 terms -
2
Abiotic and Biotic Factors
Why are there cacti in a desert, mosses in a damp wood and almost nothing growing under a dense pine plantation? This lesson is for both Combined Science and…
9 terms -
3
Fieldwork: Quadrats and Transects
You cannot count every daisy in a field, so ecologists count a sample and scale it up. This lesson is for both Combined Science and separate Biology. It covers…
10 terms -
4
Energy Transfer and Pyramids of Biomass
A lion needs a huge territory, yet a field of wheat can feed far more people than a field of cattle. The reason is energy loss along food chains. This lesson…
10 terms -
Knowledge organiser
The whole chapter on a page or two of A4 — to revise from on screen or print.
Key terms in this chapter
All 39, gathered from every lesson.
- Population
- All the organisms of one species living in the same place at the same time.
- Community
- All the populations of the different species living in the same place.
- Ecosystem
- A community of living organisms together with the non-living parts of their environment.
- Interdependence
- The way the organisms in a community depend on each other, for food, shelter, pollination and other needs.
- Parasitism
- A relationship in which one organism, the parasite, lives on or in another and feeds on it, harming the host.
- Parasite
- An organism that lives on or in a host and gets its food from it, harming the host.
- Host
- The organism that a parasite lives on or in, and which is harmed by it.
- Mutualism
- A relationship between two organisms of different species in which both of them benefit.
- Nitrogen-fixing bacteria
- Bacteria in the root nodules of plants such as peas that convert nitrogen gas into compounds the plant can use.
- Pollinator
- An animal, such as a bee, that carries pollen from one flower to another and so pollinates it.
- Abiotic factor
- A non-living part of the environment, such as temperature, light, water or a pollutant.
- Biotic factor
- A living part of the environment, such as competition, predation or disease.
- Competition
- The struggle between organisms for the same limited resource, such as food, light, water or space.
- Predator
- An animal that kills and eats other animals.
- Prey
- An animal that is killed and eaten by a predator.
- Predation
- The killing and eating of prey by a predator.
- Pollutant
- A harmful substance added to the environment, usually by human activity.
- Stable community
- A community in which the populations stay roughly constant over time because the factors that raise and lower them balance.
- Resource
- Something an organism needs, such as food, water, light, space or a mate.
- Quadrat
- A square frame that marks out a known area, used to sample the organisms in a habitat.
- Sample
- A small part of a habitat or population that is studied to represent the whole.
- Random sampling
- Choosing the positions to sample by chance, such as with random numbers, so that there is no bias.
- Belt transect
- A strip of fixed width along a line across a habitat, sampled with quadrats at regular intervals.
- Abundance
- The number of individuals of a species in a given area.
- Percentage cover
- The percentage of the area of a quadrat that is covered by a species.
- Mean
- The total of all the values divided by the number of values.
- Bias
- A fault in sampling or measuring that makes results favour one outcome.
- Distribution
- Where in a habitat a species is found, and how it is spread out.
- Correlation
- A relationship between two variables, shown by a scatter graph.
- Trophic level
- A feeding stage in a food chain, such as producer, primary consumer or secondary consumer.
- Biomass
- The mass of living material in organisms, usually measured as dry mass.
- Pyramid of biomass
- A diagram with a bar for each trophic level, the width in proportion to its biomass, producers at the base.
- Producer
- An organism that makes its own food by photosynthesis, at the start of a food chain.
- Primary consumer
- An animal that eats producers, at the second trophic level.
- Secondary consumer
- An animal that eats primary consumers, at the third trophic level.
- Efficiency of energy transfer
- The percentage of the energy available at one trophic level that is transferred to the next.
- Dry mass
- The mass of an organism with the water removed, used as a measure of biomass.
- Decomposer
- A microorganism, such as a bacterium or fungus, that breaks down dead organisms and waste.
- Respiration
- The process in cells that transfers energy from food, releasing much of it as heat.