What happens to the size of males gametes as they mature from spermatids to sperm cells?

Which of the following is one of the four conditions necessary for natural selection to occur in a population? fewer organisms are born than the habitat can support mutation does not occur organisms have identical characteristics variation is inherited

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Which to produce involved from a symbiotic relationship of organisms which resulted in eukaryotic organisms contain chloroplast