do people make more than 1 or 2 silly mistakes in GCSEs?

no, everyone gets 100%

That is clearly sarcasm but a lot of people might not get really high mark because they didn't revise enough rather than just making a lot of mistakes.

Yep I meant 'I'. Yh I understand, especially when its via text or online. So my bad if it did come across as a problem

Yup, I am aware of that. OP seems to think that you need to be perfect in exams and not make mistakes which is TOO idealistic, they're worrying too much. this will have more of a negative impact on their exams.

Yes I made a few stupid mistakes... I was fortunate enough that my all my GCSEs results turned out to be at least at a C grade (June 2016)

One specific mistake that stands out was in one of the biology papers. You had to explain the evolution of horse bones from what looked like a human foot to a horse's hoof, and I explained it the opposite way round...

There's a process. That's why practice is essential.
1. Make mistakes (not intentionally)
2. Identify those mistakes (some way or the other)
3. Fix those mistakes.
4. Enjoy a better grade. i.e Given that you do make mistakes and possibly a lot.

Persons who make mistakes don't necessarily deserve a better grade. But the less you make them the better you're bound to do. i.e what tests are about, you have to be able to make little to no mistakes to guarantee success in a test/exam, you have to be able to work well under pressure.
So, no. If you are well prepared, you become a master or something. You will not make 'dumb' mistakes.

Yes I made a few stupid mistakes... I was fortunate enough that my all my GCSEs results turned out to be at least at a C grade (June 2016)

One specific mistake that stands out was in one of the biology papers. You had to explain the evolution of horse bones from what looked like a human foot to a horse's hoof, and I explained it the opposite way round...

My teacher calls them muppet moments. Best way to avoid them is often to triple check the question you’re reading. In my last mock for English we had to write an article for or against snow (yeah.) and I threw in crude jokes and anecdotes and got halfway through before seeing it was supposed to be broadsheet

That is clearly sarcasm but a lot of people might not get really high mark because they didn't revise enough rather than just making a lot of mistakes.

Yes but it isn't all detrimental to your overall grade-those one or two marks would be super costly at A-level but down at GCSE nothing much would happen. Obviously there are times where you could be one or two marks off a a better grade so always try to identify and rectify them nonetheless!

So what's the difference between it in grade 1-9, yeah for subjects like science it makes a big difference especially with combined, so it would be around 7 marks difference between each grade. Don't worry, I know how you feel, if you revise a lot as long as you don't panic and get really nervous, you won't make a lot of silly mistakes and check your work in case you do, it's normal to make some silly mistakes because of exam pressure, and it's fine to get a bit nervous but not too much.

i wrote diaphanous instead of diatherminous in my physics exam

How much did it cost you lol

i scraped through

After having my maths mock this week, I think this the case even more that if you are good at something or just with practice you are less likely to make mistakes, as I made a lot less. However, there were a few questions I would have got wrong but I realised when I checked my work that it was wrong, I still made a silly mistake but it was only on a 2 mark question. Also compared to previous exams I basically was not worried at all even before the exam so I wasn't too worried in the exam, As soon as you start worrying a simple question will seem hard and. A hard question you might actually be able to do you will think you can't or it's too hard. Also when you are working for algebra and specifically equations you can check if your answer is right, I know I definitely got a 6 mark question right because I plugged in the value of x and it did equal the number in the question