GCSE Biology AQA 8461

Levels of organisation

Students should understand that photosynthetic organisms are the producers of biomass for life on Earth.

Feeding relationships within a community can be represented by food chains. All food chains begin with a producer which synthesises molecules. This is usually a green plant or alga which makes glucose by photosynthesis.

A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem. hrIn relation to abundance of organisms students should be able to:

• understand the terms mean, mode and median
• calculate arithmetic means
• plot and draw appropriate graphs selecting appropriate scales for the axes. hrProducers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers. hrConsumers that kill and eat other animals are predators, and those eaten are prey. In a stable community the numbers of predators and prey rise and fall in cycles. hrStudents should be able to interpret graphs used to model these cycles.

How materials are cycled

Students should:

• recall that many different materials cycle through the abiotic and biotic components of an ecosystem
• explain the importance of the carbon and water cycles to living organisms.

All materials in the living world are recycled to provide the building blocks for future organisms.

The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis.

The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated.

Students are not expected to study the nitrogen cycle.

Students should be able to explain the role of microorganisms in cycling materials through an ecosystem by returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil.

Decomposition

Students should be able to explain how temperature, water and availability of oxygen affect the rate of decay of biological material. hrStudents should be able to:

• calculate rate changes in the decay of biological material
• translate information between numerical and graphical form
• plot and draw appropriate graphs selecting appropriate scales for the axes. hrGardeners and farmers try to provide optimum conditions for rapid decay of waste biological material. The compost produced is used as a natural fertiliser for growing garden plants or crops.

Anaerobic decay produces methane gas. Biogas generators can be used to produce methane gas as a fuel.

**Impact of environmental change

Students should be able to evaluate the impact of environmental changes on the distribution of species in an ecosystem given appropriate information.

Environmental changes affect the distribution of species in an ecosystem. These changes include:

• temperature
• availability of water
• composition of atmospheric gases.

The changes may be seasonal, geographic or caused by human interaction.**