People need to realize that the examination system is flawed and they aren't testing you on your knowledge of biology as a whole subject, they're testing you on how good you are at writing and remembering bull**** useless stuff that is written on their mark schemes / syllabus.
Don't write something that is beyond the syllabus because you think you know better (even if you do), you're just going to be upset.
Having said that I had a discussion about this with my chemistry teacher when I was doing my A levels and she told me that markers of that subject can use their "professional judgement" to add additional correct answers if the situation is suitable, although I'm not sure how true this is.