MCAT missed bio qs

Question 1

The neural tube differentiates from?

Answer 1

ectoderm

Question 2

A drug is used that prevents the conversion of angiotensin I to angiotensin II. What is a likely effect of this drug?
a. Increased sodium reabsorption
b. Increased potassium reabsorption
c. Increased blood pressure
d. Increased blood pH

Answer 2

The correct answer is B

Normally, angiotensin II causes secretion of aldosterone from the adrenal cortex. Aldosterone serves to increase reabsorption of sodium, while promoting excretion of potassium and hydrogen ions. Thus, blocking the release of aldosterone should result in decreased reabsorption of sodium, while decreasing excretion of potassium and hydrogen ions. This eliminates choices (A) and (D) and makes choice (B) the correct answer. In the absence of aldosterone, less water reabsorption will occur, eliminating choice (C).

(A) Opposite. Sodium reabsorption will be decreased.

(C) Opposite. Blood pressure will be decreased because less water will be reabsorbed.

(D) Opposite. Blood pH will decrease because fewer hydrogen ions will be excreted.

Question 3

when the notochord causes differentiation of overlying ectoderm into the neural tube and neural crest cells

Answer 3

neurulation

Question 4

The neural tube becomes the

Answer 4

CNS

Question 5

T/F: Neural crest cells migrate from their original site. They differentiate into a number of different tissues

Answer 5

True

Question 6

Cellular respiration begins in the ____ and is completed in the _____.

Answer 6

cytoplasm, mitochondria

Question 7

C6H12O2 + O2 -> CO2 + H2O
This process is completed

in the cytoplasm.
in the area of the cell membrane.
in the mitochondria.
in the area around the ribosomes.

Answer 7

The correct answer is C

The process presented in the question stem is respiration; overall, in the presence of oxygen, a glucose molecule is broken down so as to give energy in the form of ATP, and two byproducts - carbon dioxide and water. Respiration begins in the cytoplasm but is completed in the mitochondria. The first step of respiration is glycolysis, which occurs in the cytoplasm. Pyruvate from this reaction is converted to acetyl CoA, which enters the Krebs cycle in the mitochondria. NADH and FADH2from the Krebs cycle enter the electron transport chain in the cristae, the inner membrane of the mitochondria. Therefore, the process described in the question stem is completed in the mitochondria, making choice (C) the correct answer.

(A) Opposite. The process begins in the cytoplasm, but is completed in the mitochondria.

(B) Distortion. Glycolysis is not associated with the area of the cell membrane.

(D) Distortion. Proteins are created by ribosomes. Glycolysis and protein production are not related to each other.

Question 8

Steps of respiration

Answer 8

1. glycolysis- in the cytoplasm
2. pyruvate -> acetyl CoA
3. acetyl CoA enters the Krebs cycle in the mitochondria
4. NADH and FADH2 from the Krebs cycle enter the electron transport chain in the cristae, the inner membrane of the mitochondria.

Question 9

The rate-determining step is simply the _____ step in a proposed mechanism.

Answer 9

slowest

Question 10

What is the response of the immune system to downregulation of MHC molecules on somatic cells?

a. B-cells are activated and antibodies are released.
b. T-cells are activated, resulting in a cytotoxic response.
c. Natural killer cells induce apoptosis of affected cells.
d. Macrophages engulf the pathogen and display its antigens.

Answer 10

The correct answer is C

Healthy cells exhibit MHC class I molecules. Natural killer cells monitor the expression of MHC molecules on the surface of cells. Viral infection and cancer often cause a reduction in the expression of MHC class I molecules on the cell surface. Natural killer cells detect this lack of MHC and induce apoptosis in the affected cells.

(A) Opposite. B-cells are activated by a presence, not absense, of MHC molecules.

(B) Distortion. Cytotoxic T-cells are activated by the display of foreign peptide fragments by MHC molecules, not by their downregulation.

(D) Distortion. Pathogen engulfing would precede, not follow, MHC downregulation.

Question 11

The number of genetically unique gametes produced by a given individual can be determined by using the formula

Answer 11

2^n
n= number of heterozygous gene pairs that the individual has

Question 12

molecule containing chiral carbon is optically ____?

Answer 12

is optically active

Question 13

no chiral carbon molecule

Answer 13

achiral and, thus, optically inactive

Question 14

function and location of adenylate cyclase

Answer 14

Through a G-protein intermediate, the enzyme adenylate cyclase is activated, and converts ATP into cAMP.

Adenylate cyclase is attached to the inner layer of the phospholipid bilayer; it is not located in the cytoplasm