This chemical reaction is very dangerous.

Whenever he is feeling down, I always help him.

He always helps me when I'm in trouble.

He found out that there was a foreign object inside his body.

This enzyme helps with chemical reactions in the body.

He is majoring in chemistry at university.

This chemical reacts when heat is added.

This chemical reaction is very dangerous.

He is an expert in chemistry.

My biological clock is completely messed up.