Ask about my undergraduate research internship I’m planning to apply for an internship. There is a professor who represents the school who asked me to submit some necessary documents. He wanted me write a detailed paper about the project I am interested in, and then he will choose the host supervisor for me. 

Before that, I checked the list of professors for this school, and I noticed a professor whose main project is about antimicrobial biochemistry. I want to work with this group, but I am worried about whether or not he will accept any students this year. 

At any rate: this “antimicrobial” topic is my favorite, but I do not know any details about what the project entails. How do I write this type of paper? Does he want expect a full proposal? What should I do?
You should ask the professor you want to work with for instructions.  If he is open to supervising your work, then in addition to helping you apply for the internship, he can also contact the coordinator.  This will increase your chance of success.  If he says he does not want to supervise you, then you will save a lot of time applying for something that cannot work.