Summary AQA Biology A Level Revision - Energy and Ecosystems - Unit 13
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Course
Unit 1 BIOL1 - Biology and disease (7402)
Institution
AQA
Book
AQA Biology A Level Student Book
These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification -
Very comprehensive notes and enabled me to achieve an A* in my A Level Biology exams.
Biology revision - Energy and ecosystems (Unit 13)
Food chains and energy transfer
- The ultimate source of energy for almost all organisms is the sun which is conserved
as chemical energy by plants
- Most plants use sunlight in making organic compounds from CO 2 in the air or water
that surrounds them
o These include sugars
- The remained are used to make other groups of bio molecules
o These form the biomass of plants that is the means by which energy is passed
between other organisms
- Organisms can be divided into three groups according to how they obtain their energy
and nutrients
Producers:
- Are photosynthetic organisms that manufacture organic substances using light energy,
water, CO2 and mineral ions
Consumers:
- Organisms that obtain their energy by feeding on other organisms rather than using
the energy of direct sunlight – such as animals
- Those that directly eat producers are called primary consumers as they are the first
in the chain of consumers
- Those animals eating primary consumers are called secondary consumers
- Those eating secondary consumers are called tertiary consumers
Saprobionts:
- Aka decomposers
- Are a group of organisms that break down the complex materials in dead organisms
into simple ones
- In this process, they release valuable minerals and elements in a form that can be
absorbed by plants and thus contribute to recycling
- The majority of the work is carried out by fungi and bacteria
- A food chain describes a feeding relationship in which the producers are eaten by
primary consumers
- These are in trun eaten by secondary consumers, which are then eaten by teritiary
consumer
- In a long food chain the tertiary consumers may in turn by eather by further consumers
called quaternary consumers
o However, this is rare as usually there isn’t enough energy left in the chain to
sustain these consumers
- Each stage in this chain is referred to as a trophic level
- A food web shows the link between different food chains
- However, these often become very complex
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