Knowing your way around Krebs Cycle is no excuse for handing in a badly written essay. Basically the results are often very similar too, with a very low standard of grammar from students in every single discipline, including those studying English. Writing one word instead of two, such as 'infact' rather than in fact and 'alot' instead of a lot . Believing implicitly that the spellchecker is always right and will correct your every error. Pffffft, you wish.
Facts are easy-pickings for any undiscerning student.
As ever it's quality not quantity that matters and the big marks will rest on how you put them to use. Use that logical mind that everyone keeps saying you have because you're a scientist. Know what conclusion you are heading towards, from the moment you start writing That way, you won't get bogged down in a fog of facts or a sea of statistics. Having decided on which facts to use, make sure they flow together - imagine you're adding gravy to the factual meat and two veg of your essay. However, a science essay is not the place to be flip or flamboyant.