Description 2 describes a commensal symbiosis. The answer is D, commensalism.
If organisms can not adapt they become extinct.
Numerous barriers can prevent sperm from reaching and fertilizing the egg, this can be that the Sperm may be defected, or lack the required number of mitochondria needed to help move the sperm. Also, if sperm had already fertilized the egg, there is a change that takes place to the membrane surrounding the egg preventing further sperm from fertilizing.
When a nucleus of an unstable atom loses energy by emitting radiation.
Cells,tissue, organ , organ system
