HESI A2 Biology Practice Test

Correct Answer: A

Rationale: The correct answer is A: A segment of DNA. Genes are segments of DNA that contain the instructions for building proteins and controlling various processes in an organism. DNA is the genetic material that carries hereditary information and is passed down from parents to offspring. Option B is incorrect because genes are not bead-like structures on chromosomes but are located within chromosomes. Option C is incorrect because genes are not protein molecules themselves but may code for proteins. Option D is incorrect because genes are not made up of RNA but rather DNA.

Correct Answer: B

Rationale: The correct answer is B because animal cells do not use chloroplasts to gain energy, they use mitochondria for cellular respiration. Lysosomes in animal cells break down old cells (A) and plant cells have a cell wall (C). Choice D is incorrect as B is false.

Correct Answer: A

Rationale: The correct answer is A because water is a raw material for the light reactions in photosynthesis, specifically in the process of photolysis where water is split to release electrons for the photosystems. Without enough water, this process is hindered, leading to a drop in photosynthetic rate. Choice B is incorrect because carbon dioxide availability affects the Calvin cycle, not the light reactions. Choice C is incorrect as carbon atoms for sugar come from carbon dioxide, not water. Choice D is incorrect because fermentation is not directly related to the availability of water in photosynthesis.

Correct Answer: B

Rationale: The correct answer is B: Create energy. Mitochondria are known as the powerhouse of the cell because they produce ATP, the primary energy source for cellular functions. They do this through a process called cellular respiration. Option A is incorrect as the nucleus controls the cell. Option C is incorrect as protein synthesis occurs in the ribosomes. Option D is incorrect as waste packaging is typically done by lysosomes.

Correct Answer: D

Rationale: The correct answer is D: They are denoted Aa. Heterozygous traits refer to the presence of different alleles at a specific gene locus. In this case, A and a represent two different alleles for the same trait. When an individual is heterozygous, one allele is dominant (A) and the other is recessive (a). Therefore, the correct notation for a heterozygous trait is Aa. Option A is incorrect because heterozygous traits are not haploid (having one set of chromosomes), but diploid (having two sets). Option B is incorrect as it denotes a homozygous dominant genotype. Option C is incorrect as it denotes a homozygous recessive genotype.