Make sure you answer the question with close reference to the verb. Explain means to give cause and effect while evaluate means you would have to make a judgement. People who disregard these usually lose marks for 'not answering the question.' This is especially important in those last 6-7 mark questions. Your answer to this would need to be in the structure of a mini essay with an introduction, body and conclusion. For example:
Discuss the impacts of genetic engineering techniques on society and the environment. (8)
For this sort of question first I would define genetic engineering in my introduction and then use a specific example to discuss the advantages and disadvantages it has had on society and the environment. Then follow it up with a basic conclusion which summarises your ideas.
