OAT Biology 4 — Questions and Answers
Question 1: Which blood vessel type has the thinnest walls, facilitating gas and nutrient exchange?
- Arteries
- Veins
- Capillaries (Correct answer)
- Venules
Correct answer: Capillaries
Capillaries have walls only one cell thick (endothelium), allowing efficient diffusion of gases and nutrients.
Question 2: The process by which a cell engulfs large solid particles is called:
- Pinocytosis
- Exocytosis
- Phagocytosis (Correct answer)
- Receptor-mediated endocytosis
Correct answer: Phagocytosis
Phagocytosis ('cell eating') involves pseudopod extension to engulf large particles such as bacteria or debris.
Question 3: Which nitrogenous base is found in RNA but NOT in DNA?
- Adenine
- Guanine
- Uracil (Correct answer)
- Cytosine
Correct answer: Uracil
RNA contains uracil in place of the thymine found in DNA; uracil pairs with adenine.
Question 4: In the human excretory system, the loop of Henle is critical for:
- Glucose reabsorption
- Creating a concentration gradient in the medulla (Correct answer)
- Secreting hydrogen ions
- Producing renin
Correct answer: Creating a concentration gradient in the medulla
The loop of Henle establishes an osmotic gradient in the renal medulla that allows the collecting duct to concentrate urine.
Question 5: Which of the following best describes an exergonic reaction?
- Requires net energy input to proceed
- Releases net free energy and is thermodynamically spontaneous (Correct answer)
- Only occurs at high temperatures
- Involves the breaking of ATP
Correct answer: Releases net free energy and is thermodynamically spontaneous
Exergonic reactions have a negative ΔG, meaning they release free energy and occur spontaneously.
Question 6: Sensory neurons that carry impulses FROM sensory receptors TO the central nervous system are called:
- Efferent neurons
- Interneurons
- Motor neurons
- Afferent neurons (Correct answer)
Correct answer: Afferent neurons
Afferent (sensory) neurons transmit signals from receptors toward the CNS; efferent neurons carry signals away.
Question 7: Which phase of the cell cycle involves DNA replication?
- G1 phase
- S phase (Correct answer)
- G2 phase
- M phase
Correct answer: S phase
DNA replication occurs during the S (synthesis) phase of interphase, doubling the cell's genetic material.
OAT Biology 4
Which blood vessel type has the thinnest walls, facilitating gas and nutrient exchange?