Biology HESI A2 Practice Test

Correct Answer: A

Rationale: The correct answer is A: Atmosphere. The atmosphere is the layer of gases that surrounds a planet. It consists of different layers, including the stratosphere and troposphere mentioned in the other choices. The biosphere refers to the regions on Earth where living organisms exist, not the gases surrounding the planet. Therefore, the correct term for the mixture of gases surrounding a planet is the atmosphere.

Correct Answer: A

Rationale: The correct answer is A: TGAACGT. To find the matching DNA strand, we need to use complementary base pairing rules: A pairs with T, C pairs with G. Given the segment ACTTGCA, its complementary DNA strand would be TGAACTG. Therefore, the correct answer is A. Option B (GACCATG) is incorrect because it does not follow the complementary base pairing rules. Option C (ACTTGCA) is the same as the original segment given, so it is also incorrect. Option D (None of the above) is incorrect as the correct answer is A.

Correct Answer: C

Rationale: The correct answer is C: Tight junctions. Tight junctions are specialized connections between cells that form a barrier to prevent leakage of substances between cells. They are important for maintaining the integrity and function of epithelial and endothelial tissue. Separate desmosomes (choice A) are incorrect because desmosomes are anchoring junctions, not tight junctions. Ronofilaments (choice B) is not a term related to cell junctions. Fascia adherens (choice D) is incorrect as it refers to a type of adherens junction, not tight junctions.

Correct Answer: B

Rationale: The correct answer is B: mitochondria. Heart muscle cells require a significant amount of energy to constantly contract and pump blood, making mitochondria crucial for energy production through aerobic respiration. Mitochondria are abundant in heart muscle cells to meet their high energy demands. Lysosomes (A) are involved in cellular waste disposal, mRNA (C) carries genetic information, and ribosomes (D) are involved in protein synthesis, but they are not expected to be unusually high in heart muscle cells.

Correct Answer: A

Rationale: Enzymes can catalyze reactions by lowering the activation energy required for the reaction to occur, thus increasing the reaction rate. This is achieved through the formation of enzyme-substrate complexes. Inhibition refers to the process of preventing enzyme activity, which is contrary to the function of enzymes. Stopping reactions is not the role of enzymes. Therefore, the correct answer is A: Catalyze.