Biology HESI A2 2024

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: 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: Parasitism. In parasitism, one organism benefits (the pneumonia bacterium) at the expense of the other (the human). The bacterium causes harm to the human by causing pneumonia, which is detrimental. In mutualism (A), both organisms benefit; in commensalism (C), one benefits while the other is unaffected; in competition (D), both organisms are harmed by vying for the same resources. Hence, parasitism is the most fitting description of the relationship between the pneumonia bacterium and the human in this scenario.

Correct Answer: C

Rationale: The purpose of phloem tissue in plant stems is to conduct food throughout the plant. Phloem is responsible for transporting sugars, amino acids, and other organic compounds produced through photosynthesis from the leaves to other parts of the plant for growth and energy. This process is known as translocation. Choice A is incorrect because water is transported by xylem tissue, not phloem. Choice B is incorrect as phloem does not conduct light energy. Choice D is incorrect as carbon dioxide is absorbed by the plant through stomata and transported through the plant via diffusion, not through phloem tissue.

Correct Answer: D

Rationale: In a lysosome, enzymes break down food particles through the process of digestion. This process helps to recycle nutrients and eliminate waste materials. Ribosomes are not made in lysosomes, as they are responsible for protein synthesis. Lysosomes do not produce food but rather break it down. Water storage does not occur in lysosomes. Therefore, the correct answer is D - food is digested in a lysosome.