Energy Flows

A brief summary of the third chapter in the AQA textbook.

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Biomass = mass of living material in an animal or plant, ultimatly all built up from the suns energy, normally measured as the dry mass of biological material in grams.

Energy in biomass is passed through food chains/webs into consumers.

Pyramid of numbers = The number of organisms at each level, however often not accurate at showing what is happening.

Pyramid of biomass = More accurate, shows total amount of biomass in living organisms proportionally at each stage of the food chain.

Interpretation of Pyramids of Biomass = The biomass found at each stage is less than the previous because:
-->Not all organisms are eaten by the stage above
-->Some material is excreeted as waste
-->When a herbivore eats a plant, some plant material becomes new herbivore
-->Some biomass is wasted in respiration, which isn't passed from herbivore to carnivore

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Energy Loss Through Waste

  • Material which cannot be digested is passed out of the body in faeces. Plant is particularly hard to digest, and so much of it comes out in a herbivores faeces.
  • Carnivores eat easily digested meat containing protein, but their bodies cannot normally handle bone, teeth, hooves and claws.
  • When more protein is consumed than is needed in the body, the excess is passed out in the urea in urine.
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Energy Loss Through Movement

  • The biomass which is consumed is partly used for respiration.
  • Movement requires a lot of energy and therefore lots of respiration.
  • Muscles use energy to contract, and in this process they produce heat and waste energy.
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Energy Loss Through Temperature

  • Lots of the energy we comsume is lost as heat after cellular respiration.
  • Heat losses are particularly large in warm blooded mammals and birds.
  • It takes energy to maintain the crucial internal body temperature of an organism.
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Biomass In The Food Industry

Lots of the origional biomass of our food never actually reaches us due to the extensive stages in our food chain. The more stages there are, the less energy we take in from our food! We can gain this energy back by using intensive farming methods known as factory farming. This involves:

  • Restricting the animals movements so they don't waste energy on respiration.
  • Controlling their surrounding temperature, so they don't have so much trouble maintaining their own internal temperature.

Using these methods, animals can be farmed within weeks to meet the demands for cheap, fat meat. However, the animals subject to this farming experience unatural lives. As more people realise this, they become more willing to pay for more expensive, but well brought about, meat.

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Intensive (Factory) Farming - Pros and Cons


  • Lots of animals in a small space.
  • Little or no food wastage.
  • Wasted energy in animals minimalised, so maximum weight/produce gain.
  • Cheap prduce.
  • Animals develop faster.
  • Food carefully monitored.
  • Kept safely indoors, away from the harsh outer environments.


  • Unnatural behaviour which may lead to lack of natural skill (perching etc.)
  • Expensive to light and heat large barns.
  • Bones may break as animals bodies cannot handle the fast weight gain.
  • Risk of fast spreading disease in such crampt conditions.
  • Feed must be bought instead of naturally found by the animals.
  • Sheds need maintanence (watching, cleaning etc.)
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Free Range Farming - Pros and Cons


  • Animals are allowed to behave more naturally.
  • No heating/lighting costs for the large barns.
  • No food needs supplying, the animals find their own.
  • Farmers can charge more for their produce.
  • Animals have natural development.


  • Animals are more vulnerable to the weather and predators.
  • More land is needed to care for the animals.
  • Milk and eggs need manual collection.
  • Animal products fluctuate in quantity according to the weather.
  • Animals take longer to gain weight.
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Decaying = the breaking down of a substance to be digested by microorganisms.

Decomposers are a group of microorganisms (bacteria, fungi, etc) which feed on waste and the dead. Detritus feeders such as maggots start the decaying proces by eating dead animals and producing waste material for the decomposers to consume. Some of their gained nutrients is used to grown and produce, and some is just released as waste suc as carbon dioxide, water and plant minerals.

Ideal Conditions for Decay:

  • Warm: faster chemical reaction = faster decay. Respiration in microorganisms is controlled by enzymes, so too hot and they will be denatured.
  • Moist: moisture makes dissolving food easier and prevents drying out.
  • Plenty of oxygen: for the decomposers to respire and thus energize, grow and reproduce.
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Decay and Recycling

In sewage treatment plants, microorganisms break down waste so that it is safe for release into the sea. In these treatment plants, microorganisms are in artificially enhanced conditions for the fastest possible decay rate.

A compost heap contains plant waste which are decomposed to form compost full of mineral nutrients released by the decomposers, so it makes an excellent fertaliser.

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Had some good information

well done

however i dont know whether it is just me or not but there seems to be nothing on the last card..




The last card has now been deleted as it only contained a heading. The cards contain a number of useful key facts on energy flow that could be used alongside a set of revision notes and flashcards to make a complete set of resources for this topic.

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