Energy eaten isn't all absorbed
- The idea
- Predict
- See it
- Why
- Check
The idea
“Whatever an animal eats ends up in its body, so ingested and assimilated energy are equal.”
You probably pictured everything an animal swallows becoming part of it. Some of every meal passes straight through the gut instead.
The short version
The mistake: Whatever an animal eats ends up in its body, so ingested and assimilated energy are equal.
What's actually true: Assimilated energy is what gets absorbed across the gut wall. It's the energy eaten minus the energy lost in feces.
- Ingested energy is everything an animal swallows. Assimilated energy is the part that crosses the gut wall. Feces carry out what didn't.
- Much of the assimilated energy goes to cellular respiration and is lost as heat. A little leaves in urine. The rest builds new tissue, which a predator can eat.
- New tissue over assimilated energy is production efficiency. New tissue over ingested energy is the share of the meal that became body.
On the exam: Eaten minus feces is assimilated. Before you divide, check which one the question uses as the base.