I have the same question. My hand writing is small and I can fit plenty of words in a line. So for me 1 page (both sides) would mean almost 400-450 words (given that there are about 23 lines per one side) and I think that is too much for a science related question.
My question is how many words could do justice to a 5 mark question? I don't want to extend an answer unnecessarily and waste my time on it. For example I could go on an and on about an open ended question like what causes environmental pollution, but for others I will have only limited knowledge.
So what is is the appropriate and justifiable length of an answer in terms of number of words? I don't want my answer to be too small because I don't want to give the examiner any reason to fail me.