A) Crossing over is the mechanism of genetic variation that results from the exchange of gene segments between non-sister chomatids.
One of the differences between the cell membrane and the cell wall is in the type of organisms that they are found in. A cell wall is found in plants only. A cell membrane is found in all organisms including plants. Present only in plants, and in some fungi, bacteria, algae.
I think the answer is yes and No. . Yes, Fish are considered a sustainable resource. A sustainable resource is a resource an environmental resource that doesn't harm the environment. Fish are helping the environment. However fish have waste and the waste is dangerous to the environment.