HESI A2
HESI A2 Biology 2024
1. Ocean waves may tear sponges into pieces, each of which may grow into a new sponge. What is this form of reproduction called?
- A. Budding
- B. Vegetative propagation
- C. Binary fission
- D. Fragmentation
Correct answer: D
Rationale: Fragmentation is the form of asexual reproduction where an organism breaks into fragments, and each fragment can grow into a new individual. In the case of sponges being torn into pieces by ocean waves, each piece has the potential to develop into a new sponge, making fragmentation the correct answer in this scenario. Budding is a form of asexual reproduction where a new organism develops as an outgrowth from the parent organism. Vegetative propagation involves the growth of new individuals from plant parts like stems or roots. Binary fission is a method of reproduction seen in some single-celled organisms where one cell divides into two identical cells.
2. In a phospholipid molecule, the head:
- A. Is hydrophilic
- B. Is hydrophobic
- C. Is on the inner side of the layer
- D. Both A and C
Correct answer: D
Rationale: The head of a phospholipid is hydrophilic (water-loving) and is located on the outer side of the lipid bilayer, interacting with water molecules. This arrangement positions the hydrophobic tails inward, away from water. Therefore, the correct answer is D. Choice A is incorrect because the head is hydrophilic, not hydrophobic. Choice B is incorrect as the head is on the outer side, not the inner side of the layer.
3. How does an enzyme work on a chemical reaction that occurs in a substrate?
- A. An enzyme slows down the chemical reaction.
- B. An enzyme speeds up the chemical reaction.
- C. An enzyme has no effect on the chemical reaction.
- D. An enzyme stops most chemical reactions.
Correct answer: B
Rationale: Enzymes are biological catalysts that facilitate chemical reactions by lowering the activation energy required for the reaction to occur. This allows the reaction to proceed more quickly and efficiently. Enzymes do not change the overall outcome of the reaction, but they significantly increase the rate at which it takes place. Therefore, choice B, 'An enzyme speeds up the chemical reaction,' is the correct answer. Choices A, C, and D are incorrect because enzymes do not slow down, have no effect, or stop chemical reactions; instead, they accelerate the process by lowering the activation energy.
4. What type of cells possess a cell membrane?
- A. Prokaryotic cells only
- B. Eukaryotic cells only
- C. Both prokaryotic and eukaryotic cells
- D. None of the above
Correct answer: C
Rationale: Cell membranes are present in both prokaryotic and eukaryotic cells. The cell membrane serves as a barrier that encloses the cell contents and regulates the entry and exit of substances in and out of the cell. It is a fundamental structure found in all types of cells, regardless of whether they are prokaryotic (lacking a nucleus) or eukaryotic (containing a nucleus). Choice A is incorrect because eukaryotic cells also possess cell membranes. Choice B is incorrect as prokaryotic cells, such as bacteria, also have cell membranes. Choice D is incorrect as both prokaryotic and eukaryotic cells have cell membranes.
5. How do animal cells divide?
- A. Through a contractile ring
- B. Via a cell plate
- C. Both methods
- D. None of the above
Correct answer: A
Rationale: Animal cells divide through a contractile ring made of actin and myosin filaments. The ring contracts, pinching the cell membrane in the middle to form two daughter cells. Plant cells use a cell plate due to their rigid cell walls, making choices B and C incorrect. Choice D is incorrect as animal cells do use the contractile ring method for division.
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