MAT help!

For long questions, e.g. 2-7, the mark scheme only says how many marks each question worths, so does it mean that if you don't get the answer right, you will lose all the marks instantly (let say first part of question 2 worths 4 marks), regardless of getting some part of the question right?

I would assume so, but it's rare for marks to be given solely for the answer of a part of a question unless that part is really basic (eg. plugging numbers into a function etc.) You'd probably get people better advised to answer here:
https://www.thestudentroom.co.uk/showthread.php?t=4814360

Also Cambridge doesn't ask for the MAT, so it's an interesting choice of forum.

For long questions, e.g. 2-7, the mark scheme only says how many marks each question worths, so does it mean that if you don't get the answer right, you will lose all the marks instantly (let say first part of question 2 worths 4 marks), regardless of getting some part of the question right?

Part marks are available for all parts of the long answer questions (2-7). So it's perfectly possible to get 3 marks out of 4 on the first part, and (say) 3 marks out of 6 for the second part.