Respired energy is the part that's gone
- The idea
- Predict
- See it
- Why
- Check
The idea
“If an animal respires 75 percent of its energy, that 75 percent builds its body and feeds whatever eats it.”
Respiration is usually the biggest number in an energy budget. The animal really did use that energy, and using it sounds a lot like keeping it.
The short version
The mistake: If an animal respires 75 percent of its energy, that 75 percent builds its body and feeds whatever eats it.
What's actually true: Respired energy leaves as heat. Only what's left after respiration becomes new tissue the next level can eat.
- Assimilated energy is what an animal absorbs from food, which is what it ate minus what left in its feces. Apart from a little lost in urine, it splits two ways.
- Cellular respiration releases some of it to make ATP for moving, active transport and repair. It ends up as heat, which leaves the ecosystem. No predator can eat it.
- The rest becomes new tissue, as growth and offspring. It's the only energy the next trophic level can get. Its share of assimilated energy is production efficiency.
- Endotherms like birds and mammals often respire over 95 percent, mostly to keep warm. Ectotherms like insects and fish store a larger share.
On the exam: Respired means gone as heat. The next level gets what's left, assimilated minus respired.