Energy Flows

Biology B2 Unit 3

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Pyramids of biomass


  • Is the mass of living material in an animal or plant.
  • Also known as dry mass (biomass is an animal or plant with all the water removed)
  • Biomass from plants is passed on to the rest of the food chain

You can compare the numbers in a food chain using a pyramid of numbers

  • Doesn't accurately reflect what is happening in a food chain.

To show what is happening more accurately, we use a pyramid of biomass

  • Biomass at each stage of the food chain is less then the previous stage because:
    • Not all the organisms in one stage is eaten by the stage above
    • Some material is lost through movement, waste products and maintaining a constant body temp.
    • Some is used to make a new organism within the stage
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Energy losses

Energy is lost as:

  • Waste:
    • Herbivores can't digest all of the plant material so it is passed out as waste
    • Carnivores can't digest bones, claws etc. so passed out as waste
    • When an organism has excess proteins, it is broken down and passed out as waste
  • Movement:
    • Some biomass is used for respiration in cells
    • Supplies the energy needed in the body (including growth)
    • Lots of it used to move
  • Maintaining a constant body temp:
    • Uses lots of energy in mammels and birds, regardless of surroundings
    • Because of this, warm blooded animals eat more to gain same increase in biomass
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Energy in food production - intensive farming

Because the world population is increasing, people are gaining a smaller amount of biomass. This is because we eat more meat and the meat (when it was alive) gained their biomass from plants and they waste some of it so we gain less.

Theoretically, it would be better to eat more plants as we would gain more biomass seeing as there is no organism between the two stages that would waste biomass.

Another way which we can maximise the biomass we gain from the meat we eat is intensive farming:

  • intensive farming tries to retain as much biomass as possible within an organism
  • it does this by:
    • restricting their movement, preventing energy loss
    • providing heating, preventing energy wasted on maintaining a body constant temp
  • cheap meat is produced quickly
  • animals live an unnatural life
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Energy in food production - free range farming

Free range farming:

  • focuses on providing animals with a natural life
  • it does this by:
    • allowing them to roam freely  in fields
  • the animals grow slowly but live a long, natural life
  • it is less expensive then intensive farming because there are no costs of artificial heating and lighting.
  • uses more land than intensive farming so more money in that aspect
  • more labour is needed
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Decay is the recycling of materials and minerals from dead organisms. It is returned to the environment

This is done by decomposers, a group of micro-organisms which includes bacteria and fungi

They feed on waste droppings and dead organisms. They release waste products which include carbon dioxide, water and minerals which plants can use

Conditions for decay:

  • Temperature of around 40ºC for the enzymes to function at their best
  • Moist conditions make it easier for enzymes to digest their food by dissolving it and preventing it from drying out
  • Oxygen for respiration although some microbes work without it
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Carbon cycle - diagram


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Carbon cycle - explanation

1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion

2. Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis

3. Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide made during respiration.

4. The animals and plants eventually die. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions, decomposition is blocked. The plant and animal material may then be available as fossil fuels in the future for combustion

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