Community Level Systems | OCR GCSE Biology A, Foundation tier (J247)

Community Level Systems

86 questions
5 subtopics
Paper 2
Paper 2

Community Level Systems is examined in Biology A Paper 2.

It covers cycling materials, and the role of microorganisms, the carbon and water cycles, and decomposition, levels of organisation, and abiotic and biotic factors, interdependence, competition and trophic levels and pyramids of biomass and the efficiency of transfer.

Sample questions from Community Level Systems

Answer each one closed book first, then open the answer.

Cycling materials, and the role of microorganisms

Explain why materials such as carbon and nitrogen must be recycled in an ecosystem.

Show the answer
The supply of them is limited, so they have to be returned to the non-living surroundings for other organisms to take up and use again.
Cycling materials, and the role of microorganisms

How do decomposers return carbon to the air?

Show the answer
They respire as they break down dead material, releasing carbon dioxide.
The carbon and water cycles, and decomposition

Explain why the carbon cycle is important to living organisms.

Show the answer
It keeps returning carbon to the air as carbon dioxide so plants can photosynthesise, and that supplies the carbon compounds every other organism feeds on.
The carbon and water cycles, and decomposition

Explain why decomposition is slow in waterlogged soil.

Show the answer
Water fills the air spaces and excludes oxygen, so aerobic decomposers cannot respire fast and break material down only slowly.
Levels of organisation, and abiotic and biotic factors

All the oak trees growing in one wood are an example of which level of organisation?

Show the answer
A population.
Levels of organisation, and abiotic and biotic factors

Explain how light intensity affects the plants growing on a woodland floor.

Show the answer
Plants in deep shade photosynthesise less, so they grow more slowly and fewer of them survive than in a bright gap.
Interdependence, competition and trophic levels

What is parasitism?

Show the answer
A relationship in which a parasite lives on or in a host, gaining from it while harming the host.
Interdependence, competition and trophic levels

What is a consumer?

Show the answer
An organism that gets its energy and nutrients by eating other organisms.

The 5 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
Cycling materials, and the role of microorganisms	What it means for a material to cycle, carbon, nitrogen and water as cycled materials and why they must be recycled, the abiotic and biotic components of an ecosystem, bacteria and fungi as decomposers, how extracellular digestion and respiration release nutrients and carbon dioxide, why decomposers matter for soil minerals and nitrogen, and calculating mass loss and decay rate in a leaf bag investigation.	19
The carbon and water cycles, and decomposition	How photosynthesis removes carbon dioxide and respiration, combustion and decomposers return it, how water evaporates, transpires, condenses and falls as fresh rain, why the carbon and water cycles matter to organisms and habitats, what aerobic and anaerobic mean, how temperature, water and oxygen affect the rate of decomposition, turning a compost heap, and calculating rates of decay.	19
Levels of organisation, and abiotic and biotic factors	The levels of organisation from individual organism to population, community and ecosystem, what a habitat is, the difference between abiotic and biotic factors, how temperature, light intensity, soil pH and moisture affect where plants grow and which species live in a habitat, and how predators and food shortage act on populations.	16
Interdependence, competition and trophic levels	What interdependence is and why losing one species changes a community, predation, mutualism and parasitism with examples such as bees and tapeworms, what plants and animals compete for, trophic levels, producers and primary, secondary and tertiary consumers, placing organisms in a food chain, and apex predators.	16
Pyramids of biomass and the efficiency of transfer	What biomass is, what a pyramid of biomass shows, why biomass is lost through egestion, excretion and respiration, calculating the efficiency of a transfer, and why food chains stay short.	16

Community Level Systems is 86 of the 981 questions in the guide.Get the guide, £7

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.