Biology HESI A2 2024

Correct Answer: B

Rationale: To determine the percentage of offspring that are carriers but not manifesting the disease, we need to consider the Punnett square. When both parents carry the recessive gene, there is a 25% chance of producing homozygous recessive offspring with cystic fibrosis. This means the remaining 75% will be carriers (heterozygous) but not show symptoms. Therefore, the correct answer is B (25%). A: 0% - Incorrect, as carriers are present. C: 50% - Incorrect, as it does not account for the probability of being a carrier. D: 100% - Incorrect, as not all offspring will manifest the disease.

Correct Answer: B

Rationale: The correct answer is B: shape. Enzyme activity is highly dependent on the enzyme's specific three-dimensional shape. Changes in temperature and pH can disrupt the hydrogen bonds and other interactions that maintain the enzyme's shape, leading to denaturation. This alters the active site of the enzyme, making it unable to bind effectively with its substrate and catalyze the reaction. Incorrect options: A: Acidity is related to pH, which can affect enzyme activity, but the primary reason for the alteration is the change in shape. C: While changes in pH can affect the chemical properties of enzymes, the main impact on enzyme activity is the alteration of shape. D: Substrate is the molecule upon which the enzyme acts, and while changes in substrate concentration can affect enzyme activity, alterations in temperature and pH primarily impact the enzyme's shape, not the substrate itself.

Correct Answer: A

Rationale: The correct answer is A: It will swell and possibly burst. This is because the solution outside the cell is hypotonic compared to the inside, causing water to move into the cell through osmosis, leading to swelling. If the influx of water is excessive, the cell may burst. Explanation for other choices: B: It will shrivel and shrink - This would happen if the solution outside the cell is hypertonic, causing water to move out of the cell, leading to shrinkage. C: It will maintain its current size - In an isotonic solution, there would be no net movement of water, so the cell would maintain its size. D: It will grow a supportive cell wall - Cell walls are typically found in plant cells and serve different functions. The growth of a cell wall is not directly related to the concentration of solutes inside and outside the cell.

Correct Answer: C

Rationale: The correct answer is C because yeast carries out fermentation, producing ethanol and carbon dioxide. During fermentation, yeast breaks down sugars in the dough into ethanol and carbon dioxide gas. The carbon dioxide gas gets trapped in the dough, causing it to rise. Choice A is incorrect because yeast does not engage in photosynthesis. Choice B is incorrect because yeast does not carry out photosynthesis at all. Choice D is incorrect because yeast primarily produces carbon dioxide through fermentation, not aerobic respiration.

Correct Answer: A

Rationale: The correct answer is A because chlorophyll appears green due to its absorption spectrum. It absorbs light most efficiently in the blue and red regions of the spectrum, while reflecting or transmitting green light. This selective absorption of light wavelengths results in chlorophyll appearing green to our eyes. Choice B is incorrect because chlorophyll does not primarily absorb green light. Choice C is incorrect as chlorophyll actually does absorb green light, just not as efficiently as blue and red light. Choice D is incorrect because chlorophyll primarily absorbs red and blue light, not red light alone.