Organisms that use the same resources because there may not be enough for all, so it then becomes a competition of who gets it and who doesn't.
Answer:
The answer is:
A. An organism whose cells each contain a membrane-bound nucleus.
Hope that helps. :)
Q1: The answer is seasonal changes.
Q3: The answer is sodium.
Q4: Not sure, sorry.
Q5: And then I think it is A for this one, but I am not sure.
I mean each Animal has a purpose in order to keep the food chain in line, for example sharks if they went extinct there would be more seals and more fish and less of this and that. Each animal plays a certain part on earth in order to keep everything normal.