Of all of the amino acids only 9 are essential and

Grasses--> mice--> cats--> coyotes suppose 10,000 units of energy are available at the level of the grasses. what is the total number of energy units lost by the time energy reaches the coyote?

Which environmental change would most likely result in bullfrog offspring that are able to store more water than bullfrogs in previous generations?

Why do the circulatory systems of land vertebrates have separate circuits to the lungs and to the rest of the body?