I am preparing for a university extrance test, so I must improve my writing skills. But for now I still feel unsure in writing a sentence. Would you mind correcting my paragraph and showing me some skills of writing?
Learning biology
Biology is considered one of the hardest subjects that students have to learn. It is because biology exercises are impossible to solve if we don't have a strong basic knowledge. Even if we have, there are a lot of difficulties in solving them without mastering exercise skills. For instance, a student who knows a lot about biology theory still can't reach 5/10 marks in his contest just because he hasn't ever solved the kind of exercises given in the test before. Another reason explains why students feel sick of biology is lack of learning equipment. This factor makes the students confused in what they've already learned. For example, we must learn about " DNA definition" but we still don't have an imagination on its sharp, its color, its structure... In conclusion, studying biology is not an easy work for most students all over the world
Learning Biology -- capitalize all the main words of a title.

Biology is considered one of the hardest subjects that students have to learn.-- Try to use more formal vocabulary for essays; here, hardest should be replaced with most difficult.

It is because biology exercises are impossible to solve if we don't have a strong basic knowledge.-- It does not refer clearly to anything here; when referring back to a complex statement, use this. Do not use contractions in essay-writing; change don't to do not.

Even if we have, there are a lot of difficulties in solving them without mastering exercise skills.-- a lot of is too informal; use considerable or another synonym (but not much in affirmative sentences).

For instance, a student who knows a lot about biology theory still can't reach 5/10 marks in his contest just because he hasn't ever solved the kind of exercises given in the test before.-- 5/10 marks is unclear, though it must be the way your school marks scores; be sure that you use words and phrases generally understood by your reader. An examination is not a contest.

Another reason explains why students feel sick of biology is lack of learning equipment.-- reason and explains and why are redundant: Another reason is...

This factor makes the students confused in what they've already learned.-- this sentence displays shaky logic: lack of equipment does not explain student confusion.

For example, we must learn about " DNA definition" but we still don't have an imagination on its sharp, its color, its structure... -- the definition of 'DNA'. We still cannot imagine. Do not use ellipses except to show omitted words of a quotation.

In conclusion, studying biology is not an easy work for most students all over the world -- delete all over the world as redundant. Work here is uncountable.

Overall, your essay has good basic structure, but it is not long enough; you must explain each point more thoroughly before you introduce your examples. Your conclusion also needs more than a simple repetition of the thesis.
Thank you very much, Mister Micawber.
But I still have some questions :
1> How can we know which words are formal, and which words are not?
2> How can I draw conclusion and make it different to the thesis?
Kind regards,
Khai Minh
Students: We have free audio pronunciation exercises.
Hello Khai Minh,

1-- Getting to know formal from informal vocabulary requires considerable reading experience, but one basic guideline is to avoid slang (of course) and phrasal verbs (pick up, go over, make out) in favour of their formal equivalents (acquire, review, succeed), which are usually of Latin or Greek origin. Many words and phrases from conversational English (too many to list here) should also be avoided if possible in writing, such as: a lot of, really, wonderful, get (meaning obtain), awesome, mom, etc.

2-- The conclusion is not different from the thesis; it makes a final expansion on the thesis. The conclusion is the last thing your reader reads, so it should be striking in some way. Try to find a way to make the thesis more general in application, more immediate, or more thought-provoking; for instance:

In conclusion, although biology is the study of life, and life is a part of ourselves and is all around us, studying biology is not easy work for most students.