What is the role of the epiphyseal plate?

Correct Answer: C

Rationale: The epiphyseal plate, a cartilage layer in growing long bones, allows longitudinal growth as chondrocytes divide, ossify, and lengthen the bone until maturity. Remodeling occurs throughout bone. New formation is broader, not plate-specific. Its growth function, per skeletal development, makes 'c' correct.

Correct Answer: D

Rationale: False ribs (8-10) attach indirectly via shared cartilage, and floating ribs (11-12) don't attach to the sternum, unlike true ribs (1-7, direct). Both 'b' and 'c' fit false and floating lack direct connection. This distinction, per rib anatomy, makes 'd' correct.

Correct Answer: A

Rationale: The cell is the smallest independently functioning unit of life, capable of metabolism, reproduction, and homeostasis (e.g., a neuron firing), per cell theory. Molecules like DNA or proteins are components, not independently functional. Organs like the heart are multi-tissue structures, far larger. Tissues like muscle are cell groups, not individual units. The cell's standalone vitality, foundational in biology, makes 'a' the correct answer.

Correct Answer: C

Rationale: The heat-loss center (hypothalamus) activates sweat glands to increase output, cooling via evaporation when overheated. Blood vessels dilate (not constrict, a) to release heat. Breathing may adjust but isn't slow/shallow primarily. Not all only 'c' fits. Sweating's cooling role, per thermoregulation, makes 'c' correct.

Correct Answer: B

Rationale: In a sarcomere, the functional unit of skeletal muscle, contraction occurs via the sliding filament theory, where actin (thin) and myosin (thick) filaments slide past each other. During this process, the H zone the central region of the A band with only thick filaments shortens or vanishes as thin filaments overlap it. Similarly, the I band, containing only thin filaments on either side of the Z line, narrows as actin slides toward the sarcomere's center. The A band, spanning the thick filaments' full length, remains constant because myosin doesn't shorten, while Z lines, anchoring actin, move closer together but don't disappear. This dynamic reflects muscle shortening without altering filament lengths, driven by ATP-powered cross-bridge cycling. Electron microscopy and physiological studies confirm that contraction compresses these zones, distinguishing them from static structures like the A band. Misinterpreting these changes could confuse the sarcomere's architecture, but the consistent reduction of H zones and I bands aligns with observed muscle mechanics, critical for understanding force generation.