HESI A2 Biology Practice Test 2024

Correct Answer: B

Rationale: The correct answer is B: Cell Membrane. The cell membrane serves as a selectively permeable barrier that controls the passage of substances into and out of the cell. It is composed of a phospholipid bilayer with embedded proteins that regulate the transport of molecules. The other choices are incorrect because: A: Vacuole - Vacuoles are membrane-bound organelles that mainly store water, ions, and nutrients. They do not control the passage of substances into and out of the cell. C: Nuclear Membrane - The nuclear membrane surrounds the nucleus and regulates the passage of molecules between the nucleus and the cytoplasm. It does not control the passage of substances into and out of the entire cell. D: Cytoplasm - Cytoplasm is the gel-like substance inside the cell that contains organelles. It does not directly control the passage of substances into and out of the cell; instead, it provides a medium for cellular activities to occur.

Correct Answer: B

Rationale: The correct answer is B: Chloroplasts. Chloroplasts are the organelles responsible for photosynthesis in plant cells. They contain chlorophyll, the pigment that captures sunlight for photosynthesis. Mitochondria (A) are involved in cellular respiration, not photosynthesis. Ribosomes (C) are responsible for protein synthesis, not photosynthesis. Endoplasmic Reticulum (D) is involved in protein and lipid synthesis, not photosynthesis. Therefore, the correct answer is B because chloroplasts are specifically designed for photosynthesis in plant cells.

Correct Answer: B

Rationale: The correct answer is B: Lipids. The plasma membrane is primarily composed of lipids, specifically phospholipids, which form a lipid bilayer. This structure provides the membrane with its selective permeability properties. Proteins are also present in the membrane, but they are not the primary composition. Carbohydrates are found on the outer surface of the membrane for cell recognition and signaling. Nucleotides are the building blocks of nucleic acids and are not a major component of the plasma membrane.

Correct Answer: B

Rationale: In meiosis, sperm and egg cells produce haploid gametes with half the number of chromosomes as the parent cell. Since humans have 46 chromosomes in each somatic cell, sperm and egg cells produce 23 chromosomes each in meiosis. This ensures that when fertilization occurs, the resulting zygote has the correct diploid number of chromosomes. Choice A (46) is incorrect because somatic cells have 46 chromosomes, not gametes. Choice C (45) and D (24) are incorrect because they do not represent the correct haploid number of chromosomes produced in meiosis.

Correct Answer: B

Rationale: The correct answer is B: Nucleotides. DNA is made up of nucleotides, which are composed of a sugar molecule, a phosphate group, and a nitrogenous base. This structure forms the double helix shape of DNA. Proteins (option A) are not the building blocks of DNA, but they are involved in various cellular functions. Lipids (option C) and carbohydrates (option D) are not the primary components of DNA. Overall, nucleotides are the fundamental units of DNA, making option B the correct answer.