HESI A2 Practice Test Biology

Correct Answer: B

Rationale: The correct answer is B: Cell membrane. The cell membrane is a selectively permeable barrier that protects the cell, regulates communication with the external environment, and allows substances to enter and exit the cell. It is composed of a phospholipid bilayer with embedded proteins that facilitate transport and signaling. The other choices are incorrect because: A: Nucleus - The nucleus houses the cell's genetic material and is responsible for controlling cell activities, but it does not directly contribute to protection or substance passage. C: Endoplasmic reticulum - The ER is involved in protein synthesis and lipid metabolism, but it does not have a primary role in protection or communication. D: Cytoplasm - The cytoplasm is the fluid-filled region of the cell where organelles are suspended, but it does not play a direct role in protection or communication at the cell's boundary.

Correct Answer: A

Rationale: The correct answer is A: Carbohydrates, lipids, protein, and nucleic acids. These are considered the most important molecules in biology because they are essential for various biological functions. Carbohydrates provide energy, lipids are important for cell structure and energy storage, proteins are crucial for cell function and structure, and nucleic acids carry genetic information. Choices B, C, and D are incorrect because calcium, sulfur, and iron are important elements in biology but not considered the most important molecules for biological processes.

Correct Answer: D

Rationale: During meiosis I, the chromosome number is reduced from diploid to haploid. This occurs during the process of homologous chromosomes separating, resulting in two daughter cells with half the number of chromosomes. In contrast, in S phase, DNA replication occurs, while interphase is a period of cell growth and preparation for cell division. Mitosis is a process where a diploid cell divides into two identical diploid daughter cells, maintaining the same chromosome number. Thus, meiosis I is the only phase where the chromosome number is reduced from diploid to haploid, making it the correct answer.

Correct Answer: D

Rationale: The correct answer is D: gradient. A concentration gradient is necessary for cell diffusion to occur, as it drives the movement of particles from an area of higher concentration to an area of lower concentration. This process does not require ATP (choice C) as it is a passive transport mechanism. While water (choice A) is essential for life and plays a role in cell diffusion, it is not the sole requirement. The presence of a membrane (choice B) is important for regulating the diffusion process but is not the direct driving force behind it. Therefore, the concentration gradient is the critical factor necessary for cell diffusion to take place.

Correct Answer: B

Rationale: The correct answer is B: Golgi apparatus. The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids from the endoplasmic reticulum for transport throughout the cell. It receives materials from the ER, processes them, and then directs them to their final destinations. Ribosomes (choice A) are responsible for protein synthesis, lysosomes (choice C) are involved in digestion and waste removal, and vacuoles (choice D) are storage organelles. Therefore, B is the correct answer as it specifically functions in the transportation of materials within the cell.