The answer is true. They cannot only replicate themselves within cells, but they cannot outside of a cell.
I believe the example of an environmental variation in the above question is, A. Marge dyes her hair blue. Variation represents any difference between cells, individual organisms, or groups of organisms of any species caused by either genetic differences or by the effect of environmental factors. Environmental variation is the ability of an organism to alter its phenotype depending on environmental conditions.
The same copies of the dna with the genes is distributed in all the cells of the body. This makes all the cells of the body to have the same genetic material. In lower organisms, dna replication is necessary for reproduction in order to have the same genes in the progeny.
The two ways the endocrine system and the nervous system are different in communication, is that the nervous system responds rapidly to short-term changes in the body by sending electrical impulses. And with the endocrine system, it takes longer, so it's a long-term effect until it notices any changes and when it does, it sends chemical messengers known as hormones into the body.
Now, how they are similar, is because both the nervous and endocrine systems work together to maintain homeostasis.
Muscles and internal organs
