Marine mammals and diving – how do they do it?

I want the structure of my essay like this:

1. Introduction: Answer the question and provide a summary or of the essay. Tell the reader what you are going to talk about and what you believe the answer to be. Keep it brief, but mention all your main ideas.

2. Body: The body of the essay is where you answer the question by developing a discussion. Here you show your knowledge and grasp of the material you have read. Offer exposition and evidence. Use relevant examples and quotes to support your argument. If your essay question has more than one part, structure the body into sections that deal with each part of the question.

3. Conclusions: the conclusion rounds off the essay. Relate it back to your main ideas or points and restate your answer to the question. NEVER introduce new information in your conclusion. The conclusion from specific to general.

Essay Paragraphs:
Each paragraph in the body of the essay should contain a topic sentence (or main idea sentence of a paragraph) that states your point. It should be followed by an explanation of the point you are making, and (most of the time) it should be supported by some form of evidence from your reading, Or by an example drawn from subject area. Do not just leave the evidence hanging there  analyse it! Comment on the implication\ significance\ impact and finish off the paragraph with critical conclusion you have drawn from the evidence.

Important: just one of the 4 sources can be from web sites. And make the essay like that a new student at first year makes it.