CLEP Biology Organismal Biology & Physiology 4 — Questions and Answers
Question 1: Which hormone, produced by the thyroid gland, lowers blood calcium levels by inhibiting osteoclast activity?
- Parathyroid hormone (PTH)
- Calcitonin (Correct answer)
- Calcitriol
- Thyroxine (T4)
Correct answer: Calcitonin
Calcitonin is secreted when blood calcium is high and reduces calcium levels by inhibiting bone resorption by osteoclasts.
Question 2: In a CAM plant such as a cactus, when are the stomata open to take in CO₂?
- During the day only
- At night only (Correct answer)
- Continuously throughout the day and night
- Only during early morning hours
Correct answer: At night only
CAM plants open stomata at night to fix CO₂ into organic acids, storing it for daytime photosynthesis with stomata closed to reduce water loss.
Question 3: The countercurrent exchange mechanism in fish gills maximizes oxygen uptake because:
- Blood and water flow in the same direction
- Blood and water flow in opposite directions, maintaining a diffusion gradient along the entire gill (Correct answer)
- Oxygen binds to hemoglobin irreversibly at high temperatures
- Gill lamellae have thick epithelium to slow diffusion
Correct answer: Blood and water flow in opposite directions, maintaining a diffusion gradient along the entire gill
Countercurrent flow keeps blood encountering progressively more oxygenated water throughout the gill, sustaining a concentration gradient for diffusion along the entire length.
Question 4: Which part of the brain is primarily responsible for maintaining balance and coordinating muscle movements?
- Cerebrum
- Medulla oblongata
- Cerebellum (Correct answer)
- Hypothalamus
Correct answer: Cerebellum
The cerebellum integrates sensory information from the vestibular system and proprioceptors to fine-tune motor commands and maintain equilibrium.
Question 5: Aldosterone, secreted by the adrenal cortex, primarily acts on the kidney to:
- Increase water reabsorption by inserting aquaporins in the collecting duct
- Increase sodium reabsorption in the distal tubule, driving water retention (Correct answer)
- Decrease potassium reabsorption in the proximal tubule
- Inhibit ADH release from the posterior pituitary
Correct answer: Increase sodium reabsorption in the distal tubule, driving water retention
Aldosterone upregulates sodium-potassium pumps and channels in the distal convoluted tubule, causing Na⁺ retention and K⁺ excretion, which raises blood volume and pressure.
Question 6: In a flowering plant, fertilization involves two sperm cells. What does the second sperm nucleus fuse with to produce the endosperm?
- The egg cell
- The two polar nuclei (Correct answer)
- The antipodal cells
- The synergid cells
Correct answer: The two polar nuclei
Double fertilization in angiosperms involves one sperm fusing with the egg (forming the zygote) and the other fusing with two polar nuclei to form the triploid (3n) endosperm.
Question 7: Which of the following best describes the role of the thymus in the immune system?
- Producing red blood cells for oxygen transport
- Maturing T lymphocytes and establishing self-tolerance (Correct answer)
- Filtering bacteria from the lymph before returning it to blood
- Secreting antibodies into the bloodstream
Correct answer: Maturing T lymphocytes and establishing self-tolerance
The thymus is the site where T cells develop, undergo positive and negative selection, and learn to distinguish self from non-self antigens.
CLEP Biology Organismal Biology & Physiology 4
Which hormone, produced by the thyroid gland, lowers blood calcium levels by inhibiting osteoclast activity?