HESI A2 Biology 2024

Correct Answer: B

Rationale: The correct answer is B (25%). When two heterozygous parents (Hh) with Huntington's disease reproduce, they can produce offspring with genotypes HH, Hh, or hh. The only genotype that results in the disease is HH. Therefore, 25% of the offspring are predicted to be disease-free (hh), as they would inherit the recessive allele from both parents. The other choices are incorrect because 0% is not possible since the parents are heterozygous, 50% would mean all offspring are disease-free which is not the case, and 100% would mean all offspring have the disease, which is also not true.

Correct Answer: D

Rationale: The correct answer is D: Citric acid. Citric acid is not a component of DNA nucleotides. A DNA nucleotide consists of a simple sugar (deoxyribose), a nitrogen base (adenine, thymine, cytosine, or guanine), and a phosphate group. Citric acid is not part of the structure of DNA; it is a component of the citric acid cycle in cellular respiration. Therefore, it is not found in the nucleotide of DNA. The other choices (A, B, and C) are all components that make up a DNA nucleotide, making them incorrect options.

Correct Answer: D

Rationale: The correct answer is D (2 females : 1 male) because in this scenario, the male offspring will inherit the X chromosome without the hemophilia gene from the mother. The female offspring will inherit one X chromosome with the hemophilia gene from the carrier mother and one X chromosome without the gene from the father. Therefore, 2 out of 3 offspring are predicted neither to carry nor manifest the disease. Choice A (0 females : 1 male) is incorrect because females can also be carriers of hemophilia. Choice B (1 female : 1 male) is incorrect because it doesn't account for the possibility of female carriers. Choice C (1 female : 0 males) is incorrect because it doesn't consider the transmission of the X chromosome from the mother to the sons.

Correct Answer: B

Rationale: The correct answer is B: Vacuole. Vacuoles are organelles that provide storage space for the cell, storing water, nutrients, and waste products. They help maintain the cell's internal pressure and shape. Mitochondria (A) are responsible for energy production, not storage. The cell membrane (C) is a protective barrier, and ribosomes (D) are involved in protein synthesis, not storage. Therefore, only the vacuole fits the role of providing storage space for the cell.

Correct Answer: B

Rationale: The correct answer is B: Glycerol. Phospholipids are composed of a phosphate group, two fatty acids, and a glycerol molecule. Triglycerides, on the other hand, consist of three fatty acid chains attached to a glycerol molecule. Therefore, phospholipids lack the monosaccharide component, not glycerol. Monosaccharides are simple sugars and are not typically found in phospholipids. Phosphates are actually a key component of phospholipids, as indicated by their name. Fatty acids are present in both phospholipids and triglycerides, so they are not the component lacking in phospholipids.