AQA GCSE Biology B2 3.1-3.5 Energy in Biomass

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B2 3.1 Pyramids of Biomass

Radiation from the sun is the main source of energy for living organisms.

This energy from the sun is captured and used in green plants during photosynthesis to make new biomass.

Biomass is the 'mass of material in living organisms'.

Biomass can be measured as the dry mass of biological material in grams.

At each stage in the food chain the mass of living material is less than the at the previous stage- this can be drawin to scale in  a 'pyramid of biomass'. This is because:

  • not all organisms at one stage are eaten than the one above
  • some material and energy is lost as waste by the organism
  • biomass can be lost through respiration or  growth

When an animal consumes another organism, its biomass gets passed onto the animal.

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B2 3.1 Pyramids of Biomass (Continued)


This template pyramid shows the pattern of decreasing biomass in ecosystems, as well as which type of organism would be found at each stage.

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B2 3.2 Energy Losses

Amounts of biomass in living things decrease as you progress through the food chain.

Energy is lost through waste- herbivores cannot digest all plant material, predators cannot digest all their prey, and urea (containing excess protein) is released through urine.

Energy is also lost through movement. This is because some biomass consumed is used by cells for respiration which provides energy to an organism for processes such as movement.

Energy is lost as heat because respiration is a process that produces heat which is lost to the surroundings. Warm-blooded animals need to keep their body at a constant temperature, and so they will have large heat losses.

Warm blooded animals need to consume more biomass in order to have enough energy to regulate their body temperature in hot or cold conditions.

Sankey diagrams can be used to show the proportion of energy losses from differnt types of animal: herbivore, carnivore, warm-blooded, and cold-blooded.

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B2 3.3 Energy in Food Production

The fewer the stages in a food chain, the less biomass is lost. Therefore it is inefficent for humans eat meat because the food chain goes plants --> livestock --> human instead of simply plants --> humans. 

There is also a limited amount of surface on Earth to grow food. It would be more efficient for humans to just grow and eat plants, and in theory everyone would have enough to eat.

Farmers artificially manage food production to reduce loss of biomass:

  • The movement of livestock is limited so less energy is lost through respiration
  • The control the temperature of the surroundings so energy is not lost through animals regulating their body temperature.

This means more animals are kept in tiny spaces so that they cannot move much at a constant warm temperature- these intensive methods are often described as 'factory farming'.

This happens because there is a greater demand for cheap meat, however these methods are cruel and unethical because the animals have unnatural and restricted lives.

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B2 3.4 Decay

Minerals are returned to the Earth when organisms die, because organisms known as 'decomposers' (bacteria and fungi) which feed on waste droppings and dead organisms.

'Detrius feeders' such as maggots and worms begin the process of eating dead animals and waste material, then the decomposers digest everything.

Decomposers also release waste products: carbon dioxide, water, & minerals which plants use.

'Decay' is the process of things being broken down and digested by decomposers.

This process ensures that soil is fertile for plants and that there aren't dead things everywhere

Decomposers work best in warm, moist conditions because they are controlled by enzymes. Many microbes also need oxygen to respire, grow, and reproduce.

Microorganisms are used in sewge treatment to break down excrement so it can be safely released in bodies of water. Similarly, many people use decomposers produce compost.

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B2 3.5 The Carbon Cycle

'The Carbon Cycle' is the constant circulation of carbon within nature. It is best displayed in a diagram showing how it released into and removed from the atmosphere:


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