# Tutor profile: Cara M.

## Questions

### Subject: MCAT

How would you describes the direction of motion of alpha, beta, and gamma rays in the presence of an external magnetic field?

We must first recognize that magnetic fields exert a force on moving electric charge, and that the magnitude of this force is directly proportional to the electric charge. It is then important to know the charge possessed by each type of particle. Gamma particles possess 0 charge, and therefore will move in a straight line. Beta particles posses a negative charge, and alpha particles possess a positive charge, and will therefore move in opposite directions of one another.

### Subject: Biochemistry

Consider a certain initial concentration of urea, measured to be 200 ng/mL. If each half-life in this scenario is 10 minutes, how long will it take for the urea to reach 12.5 ng/mL?

The first step in solving this problem is understanding the definition of a half-life. A half-life is the amount of time it takes for half of a given substrate to decay. In this case, we know each half-life is 10 minutes, and the initial concentration is 200 ng/mL. Now, we can start by cutting the concentration in half, over and over, until we reach 12.5. 200 --> 100 --> 50 --> 25 --> 12.5. Here, we can see that it takes 4 half-lives to reach 12.5 ng/mL. Since each half-life takes 10 minutes, and there are 4 half-lives required, we multiply 4 x 10 to get 40 minutes as the correct answer.

### Subject: Biology

Consider a drug that prevents the formation of microtubules. How would this impact mitosis?

Here, one must first realize that in mitosis, the mitotic spindle is made up of microtubules. Therefore, a drug preventing microtubule formation would impact mitosis by preventing the formation of the mitotic spindle, leading to an inability to properly line up the chromosomes on the equator, or pull them towards opposite poles.