HESI A2 Biology 2024

Correct Answer: B

Rationale: The correct answer is B: Virus. A virus is a structure composed of a core of nucleic acid (either RNA or DNA) surrounded by a protein coat. This structure allows viruses to infect host cells and replicate. Blue-green algae (option C) are photosynthetic organisms composed of cells with chlorophyll. RNA (option A) is a type of nucleic acid but does not necessarily have a protein coat. Saprophytes (option D) are organisms that obtain nutrients from decaying organic matter and do not typically have a core of nucleic acid surrounded by a protein coat.

Correct Answer: B

Rationale: The correct answer is B because enzymes speed up chemical reactions by lowering the activation energy required for the reaction to occur. This is achieved by binding to the substrate, forming an enzyme-substrate complex, and facilitating the conversion of substrate into product. Enzymes do not slow down or stop reactions, as suggested in choices A and D. Choice C is incorrect as enzymes play a crucial role in catalyzing reactions.

Correct Answer: C

Rationale: The correct answer is C: Order. Classification starts from the broadest category (Kingdom) to the most specific (Genus). Carnivora is an Order in the classification hierarchy, encompassing various families of carnivorous mammals, including dogs. Therefore, the correct classification for dogs within the Carnivora group is Order. Choices A, B, and D are incorrect because Kingdom refers to the highest taxonomic rank, Class is a level below Order, and Genus is a more specific category than Order.

Correct Answer: B

Rationale: During glycolysis, glucose is broken down into molecules of pyruvic acid through a series of enzymatic reactions. This process occurs in the cytoplasm of cells and is the first step in cellular respiration. Pyruvic acid can then enter the citric acid cycle (Kreb's cycle) to further generate ATP. Choice A is incorrect because glucose's energy is not entirely lost but rather partially captured in the form of ATP. Choice C is incorrect as glucose is not stored in NADH but rather NADH is generated during glycolysis. Choice D is incorrect as glucose does not join with molecules of citric acid during glycolysis but rather pyruvic acid is the end product.

Correct Answer: D

Rationale: To facilitate active transport through a membrane, ATP (adenosine triphosphate) is necessary. ATP provides the energy required for active transport processes to move molecules against their concentration gradient. Glucose (Choice A) and Sodium (Choice C) are often transported through active transport mechanisms, but they are not the energy source themselves. Oxygen (Choice B) is typically transported through passive diffusion due to its small size. Therefore, the correct answer is D (ATP) as it directly supplies the energy needed for active transport to occur.