Make sure that what you write is closely related to the question and requirements for your essay.
Read the question carefully so that you understand what is expected from you. Pay attention to any words that tell you how to answer the question, anything that identifies the topic and anything that limits the scope of your answer.
The science may be complicated but you don't always have to write in a complicated way to describe it. Try and write plainly and clearly for someone with a similar level of knowledge to yourself. Think about what you have learned while studying on your module and how this relates to the essay question: this is what you will need to write about in sufficient detail to show your understanding. Your lecturer will know more about the subject than you but is looking for you to demonstrate your understanding and progress through your studies. You may also be using research for your essay that your lecturer has not seen so you must make sure that your explanations will stand on their own. Reading out loud can help you appreciate if what you have written will be clear to your reader.
'Evaluate the benefits and disadvantages of self-regulation and self-treatment for young adolescents with diabetes.'
To answer this question you would need to pay attention to assessment criteria and any available guidance from your tutors but this is one possible approach: