What is the ten percent rule of ecology

law

Explanation:

10% law. When organisms are consumed, approximately 10% of the energy in the food is fixed into their flesh and is available for next trophic level (carnivores or omnivores). When a carnivore or an omnivore in turn consumes that animal, only about 10% of energy is fixed in its flesh for the higher level.

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they deliver oxygen to the blood

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.