Biology HESI A2 2024

Correct Answer: A

Rationale: Beeswax is a lipid because it is a natural substance primarily composed of esters of fatty acids and long-chain alcohols. Lipids are hydrophobic molecules that include fats, oils, and waxes. Beeswax fits this description due to its insolubility in water and its role in providing a protective barrier for bees' hives. Carbohydrates are composed of sugars, proteins are made up of amino acids, and nucleic acids are the building blocks of DNA and RNA. Therefore, choices B, C, and D are incorrect as they do not align with the chemical composition and characteristics of beeswax.

Correct Answer: D

Rationale: Correct Answer: D - DNA cannot be altered. Rationale: 1. DNA can be altered through mutations, recombination, and other genetic processes. 2. DNA repair mechanisms exist to correct alterations. 3. Alterations in DNA are essential for evolution and genetic diversity. Summary: A: True - RNA is single-stranded. B: True - RNA contains uracil. C: True - DNA codes for proteins.

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: A

Rationale: Beeswax is a lipid because it is a natural substance primarily composed of esters of fatty acids and long-chain alcohols. Lipids are hydrophobic molecules that include fats, oils, and waxes. Beeswax fits this description due to its insolubility in water and its role in providing a protective barrier for bees' hives. Carbohydrates are composed of sugars, proteins are made up of amino acids, and nucleic acids are the building blocks of DNA and RNA. Therefore, choices B, C, and D are incorrect as they do not align with the chemical composition and characteristics of beeswax.

Correct Answer: C

Rationale: The correct answer is C: thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds. This is a fundamental principle known as Chargaff's rule, where A pairs with T and C pairs with G. Thymine is a pyrimidine base, complementing adenine, which is a purine base. Therefore, thymine is the most suitable choice for adenine in a DNA strand. Choices A, B, and D are incorrect because adenine does not pair with cytosine (A), uracil (B), or guanine (D) in DNA.