HESI A2 Biology Practice Test 2024

Correct Answer: B

Rationale: The correct answer is B: Vacuoles (contractile). Contractile vacuoles are responsible for pushing excess water out of the cell through a process called osmoregulation. They maintain the cell's internal water balance by collecting and expelling water to prevent the cell from bursting due to osmotic pressure. Lysosomes (A) are involved in cellular waste disposal, mitochondria (C) are the powerhouse of the cell, and the nucleus (D) contains genetic material but does not play a role in expelling water from the cell.

Correct Answer: C

Rationale: The correct answer is C: Lipids. Plasma membranes are primarily composed of phospholipids, which form a lipid bilayer structure. This lipid bilayer provides a barrier that separates the internal and external environments of the cell. Proteins are also present in the plasma membrane, but they are not the main component. Carbohydrates are found on the surface of the membrane for cell recognition and signaling, but they do not make up the majority of the membrane. Nucleotides are building blocks of nucleic acids like DNA and RNA, not the main constituents of plasma membranes. In summary, lipids are the key component of plasma membranes, forming the structural basis for its function, making choice C the correct answer.

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: DNA. DNA, or deoxyribonucleic acid, is the molecule that stores the genetic code for each person. It is located in the cell nucleus and organized into structures called chromosomes. DNA contains the instructions for building and maintaining an organism, including traits and characteristics. RNA (choice A) is involved in protein synthesis but does not store the complete genetic information. The nucleus (choice C) is the cellular organelle where DNA is located, not the genetic code itself. Chromosomes (choice D) are made up of DNA and proteins and contain the genetic material in a condensed form. Therefore, the correct choice is DNA as it is the primary storage location for the genetic code.

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.