GCSE AQA: Biology 1.5

Core science- biology 1.5

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Biology Unit B1.5 Energy in biomass
Radiation from the Sun is the initial source of energy for most communities of living organisms
The transfer from light energy to chemical energy occurs during photosynthesis
The equation for photosynthesis is:
Green plants and algae are the initial producers of food, after that its consumers; most food chains, and
therefore most life-forms, are therefore dependent on the initial input of sunlight energy.
The energy from photosynthesis produces sugars and other carbohydrates, which in turn a source of energy to
make fats and amino acids and proteins.
The carbohydrates and fats in the cells of plants and algae form part of the cell structure.
Plants are consumed by animals which in turn use the energy in respiration to build their fat and protein
structures etc.
The mass of living material (biomass) at each stage in a food chain is less than it was at the previous stage
In a biomass pyramid, each horizontal bar (drawn to scale) is proportional to the mass of the living material at
that producing level and feeding levels (trophic levels).
To draw to scale, you can keep the vertical height the same for each level and make the horizontal length of
the bar proportional to the biomass of that level in the pyramid
The bigger the bar, the greater the biomass at the producer/feeding-trophic level.
The food chain: producer primary consumer secondary consumer tertiary consumer etc.
Up the food chain and 'up the pyramid' the biomass gets less because of loss of organic material, waste
energy and even the energy from respiration, required to sustain life, eventually becomes waste energy too
e.g. heat energy to the surroundings
Butterflies feed off cabbage butterflies eaten by blue tit birds bird of prey catches smaller birds
o Some materials and energy are always lost in the organisms' waste materials by excretion, fallen leaves from
trees etc.
Respiration supplies all the energy needed for all life processes, including movement, maintaining
temperature and much of this energy is eventually transferred to the surroundings:
The equation for respiration is the opposite of photosynthesis: glucose + oxygen water + carbon dioxide (+
Only a small percentage of the mass is passed on, of a food chain/ biomass pyramid:
Plants producers (100%) primary consumers (caterpillars, 40%) secondary consumers (small birds 5%)
bird of prey (owl, 0.5%)
This means in this particular food chain, of all the mass /energy you start with, only 0.5% ends up as the owl
This is the reason that you rarely get food chains of more than five stages because there is so little
mass/energy left in the end

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Decay processes
Living things remove materials from the environment for growth and other processes
Plants need carbon as carbon dioxide from air, hydrogen as water, oxygen from air/water and nitrogen from
air/soil or as nitrates from the soil, plus other minerals via water through the roots. From these elements and
compounds plants can make carbohydrates, fats and proteins as well as a source of absorbed minerals.…read more

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When green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the
When green plants and algae are eaten by animals which are eaten by other animals, some of the carbon
becomes part of the fats and proteins that make up their bodies, so carbon based materials and energy are
moved up the food chain
When animals/plants respire some of this carbon becomes carbon dioxide and is released into the
atmosphere.…read more


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