Hello!
Starting note: I am a GCSE student so I don't have any knowledge on how it is in higher levels, but I'm fairly sure it's more or less similar.
I'm in a similar situation, I understand most of the content in GCSE Biology but struggle to apply it to exam questions, got a nasty 4 on my mock despite having studied a lot. The best advice I can give you is to look for answer structures that tackle various questions. For example, in questions asking you to design an investigation, my teacher advised me to use an abbreviation called CORMMS which will help remember each point you need to tackle in order to get all the marks.
CORMMS is as follows:
CHANGE - State and explain the independent variable, what you will change in your investigation
ORGANISM - A control method related to the organism (if applicable), things such as using the same species
REPEAT - Mention that repeats must be done for reliable data, best to give a number of trials (eg. 3, 5, 10, anything reasonable really)
MEASURMENT 1 - Explain how you will measure your dependent variable
MEASUREMENT 2 - Explain how you will measure a second factor, usually time (remember that you must state
how you are measuring time, such as with a stopwatch)
SAME - Explain what you will control in the experiments, control variables
That abbreviation should help you hit all the marks (alongside talking about the method of course).
As for other little tips, it's good to try and get a grasp on what the question is asking from you. I don't really get most of the command words either, but another way to estimate what is needed is by looking at the marks. 1 mark just needs a definition, 2 marks is looking for two things (could be definition and example, two examples, you get the point), 3 marks wants you to mention 3 different things, and so on. It varies from question to question but as a general rule of thumb it should help in exam question comprehension.
I hope this advice is of use to you, I'm sure you'll do great! It's easier said than done but try not to feel disheartened, a lot of exams have really weirdly phrased questions I've noticed and the grade does
not define you. You know the content and just because the exam conditions aren't your forte that doesn't mean you're any less capable or smart.
Best wishes dear.