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: B

Rationale: The main component of blood plasma is water. Plasma is the liquid component of blood, making up about 55% of total blood volume. It serves as a carrier for various substances such as nutrients, waste products, hormones, and electrolytes. Water helps maintain blood volume, regulates body temperature, and facilitates the transport of essential components throughout the body. Proteins, red blood cells, and platelets are also present in blood plasma but are not the main component. Proteins play a role in clotting and immune function, red blood cells carry oxygen, and platelets aid in blood clotting. Water is the correct answer as it is the primary constituent of blood plasma.

Correct Answer: C

Rationale: The correct answer is C: 4. Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase. In prophase, chromosomes condense. In metaphase, chromosomes align at the cell equator. In anaphase, sister chromatids separate and move to opposite poles. In telophase, the nuclear envelope reforms. Choices A, B, and D are incorrect because mitosis is a complex process that involves more than 2 or 3 phases.

Correct Answer: C

Rationale: The correct answer is C: Cytoskeleton. The cytoskeleton provides structural support to the cell, helps maintain its shape, and allows it to adapt to external stimuli. It is composed of microfilaments, intermediate filaments, and microtubules. Microfilaments (choice A) play a role in cell movement but are not primarily responsible for maintaining cell shape. Cytoplasm (choice B) is the gel-like substance within the cell where organelles are suspended, but it does not directly contribute to maintaining cell shape. Centrioles (choice D) are involved in cell division and organization of microtubules, but they do not primarily help the cell maintain its shape and adapt.

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.