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Biology Organismal Biology & Physiology Flashcards

7 cards from real CLEP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which hormone, produced by the thyroid gland, lowers blood calcium levels by inhibiting osteoclast activity?

    Answer: Calcitonin

    Calcitonin is secreted when blood calcium is high and reduces calcium levels by inhibiting bone resorption by osteoclasts.

  2. In a CAM plant such as a cactus, when are the stomata open to take in CO₂?

    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.

  3. The countercurrent exchange mechanism in fish gills maximizes oxygen uptake because:

    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.

  4. Which part of the brain is primarily responsible for maintaining balance and coordinating muscle movements?

    Answer: Cerebellum

    The cerebellum integrates sensory information from the vestibular system and proprioceptors to fine-tune motor commands and maintain equilibrium.

  5. Aldosterone, secreted by the adrenal cortex, primarily acts on the kidney to:

    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.

  6. In a flowering plant, fertilization involves two sperm cells. What does the second sperm nucleus fuse with to produce the endosperm?

    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.

  7. Which of the following best describes the role of the thymus in the immune system?

    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.