This community is for lovers (or haters) of the life-sciences. The main objective of this community is to assist students with their biology-related homework. This is set up as the sister community of chemistryhelp and it is currently maintained by cowbert.
Please include any work you have done/what you think the answer may be and rationale for that answer. That way we can help you approach your problem. This will only help you in the long run. Eric S. Raymond has written a good tutorial on How to ask Smart Questions. While it is intended for computer help, many of the concepts apply to common requests for help of all kinds.
In summary though, it helps to remember that Google and Wikipedia are your friends.