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#Biology and biochemistry will have a stronger focus on the MCAT that debuts in 2015.

Prospective medical students anticipating taking the new MCAT can look at the following sample questions and explanations to help prepare for the new test's stronger focus on biology and biochemistry. The changes, set to debut in 2015, will in part make the exam two hours longer.

Question 1. What is the function of the movement of urea in renal tissue?

A. It aids in nitrogen excretion

B. It is an intermediate in anabolism of amino acids

C. It maintains blood pH

D. It aids in the metabolism of amino acids

Answer: A is correct. This question asks you to recall the function of urea in the kidneys. Urea is created as a byproduct in the metabolism of nitrogen containing compounds like amino acids. Urea serves as a relatively nontoxic waste product and is useful in that it removes excess nitrogen from the body.

Urea is a product of the metabolism, not anabolism – building – of amino acids, which is why answer B is incorrect. Urea does not play a significant role in blood pH regulation. Dissolved in water, it is neither acidic nor basic – so, answer C is incorrect. For answer D, urea does not aid in metabolism of amino acids, it is a product of their metabolism.

Difficulty Level: 1

Question 2. A cell is placed in a medium containing radioactively labeled thymidine. After the cells undergo replication three times, what percentage of the cells will have both strands of DNA labeled?

A. 25 percent

B. 50 percent

C. 75 percent

D. 100 percent

Answer: C is correct. This question asks you to determine the percentage of cells with both strands of DNA labeled after three replications of one cell in radioactive thymidine. After three rounds of replication, there will be eight cells: 2 3 =8. After the first round, each cell will have one labeled strand and one not labeled. After the second round, two cells will have one labeled and one unlabeled strand, and two cells will have both strands labeled. After the third round, six cells will have both strands labeled. No matter how many rounds of replication occur, there will always only remain two cells that contain one labeled DNA strand and one unlabeled DNA strand.

Answer A is the percentage of cells that do not have both strands labeled; B and D are both the result of miscalculation.

Difficulty: 2

Concept Category: 1B

Question 3. Which of the following is least likely to be impaired if a patient has liver disease?

A. Fat digestion

B. Bile production

C. Hematocrit levels

D. Albumin concentration

Answer: C is correct. This question asks you to predict the possible effects of a liver disease. We need only determine which of the four factors is not directly controlled by the liver. Hematocrit is a blood test that measures the percentage of the volume of whole blood that is made up of red blood cells. This measurement depends on the number of red blood cells and the size of red blood cells. Thus, hematocrit is not directly dependent on any function of the liver. Even if you weren’t aware of what a hematocrit test is, you can still arrive at the correct answer.

Answer A, fat digestion, depends on bile and bile is produced in the liver. Bile answer B, emulsifies fats to aid in their enzymatic breakdown and is produced in the liver. Albumin, referred to in the last answer, is a protein made by the liver. Its main function is to regulate the osmotic pressure of blood.