Respiration always runs warm: Respiration is not 100% efficient. Some of the energy released from glucose is transformed into heat instead of the usable chemical form.
The points to remember
- Respiration is not 100% efficient.
- It cannot move all the energy in glucose (a carbohydrate) into the usable chemical form.
- The rest is transformed into heat: roughly 60% of the energy released.
- Every organism that respires makes heat: animals, plants, fungi and bacteria.
- The faster an organism respires, the more heat it makes.
Remember it as: Every cell that respires is a tiny heater.
Real example: a person sitting still gives off about 100 watts of heat, as much as an old light bulb. That is why a crowded classroom warms up.
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Once energy has become heat inside an organism, the organism cannot use it again for its cells' work.
Heat is a one-way exit
- Heat cannot be turned back into chemical energy inside the organism.
- It is lost from the body to the air, water or ground around it.
- So energy lost as heat is not stored in biomass and cannot be passed on when the organism is eaten.
- Mammals and birds use this heat to keep warm, but it still leaves the body in the end.
- So they must keep respiring, and keep eating, to replace the heat they lose.
Remember it as: Heat out, never back in.
Real example: before farmers mow a field in the UK, volunteers fly drones with heat-sensing cameras over it. Deer fawns hiding in the grass glow on the screen because of the heat their bodies give off, so they can be moved to safety.
Lost, not destroyed: Say the energy is 'lost as heat' or 'transformed into heat'. It is not 'used up' or 'destroyed': energy cannot be destroyed (see 2.2.2). Why this makes every transfer inefficient is 2.2.8.
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How this could come up: Paper 2, Section A: a chart of where an animal's energy goes. Explain one part of it [2].
Figure 1 shows where the energy in the milk drunk by a lamb goes.
Explain why the energy lost as heat cannot be passed on to a fox that eats the lamb.
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