What is the linea alba?

Correct Answer: B

Rationale: The linea alba, a midline fibrous band, runs vertically, splitting rectus abdominis into left and right halves, formed by aponeuroses of abdominal muscles. It's tendinous, not muscular, and doesn't compress organs obliques do that. It's not a hip-knee connector (e.g., iliotibial band) or tendinous inscription (rectus abdominis crossbands). Its central tendon role distinguishes it, vital for abdominal wall unity.

Correct Answer: D

Rationale: Seaweeds concentrate iodine far above ocean levels, requiring energy to move it against its concentration gradient from low outside to high inside. Active transport, using ATP-powered pumps, achieves this, unlike diffusion or passive transport, which move substances down gradients without energy. Osmosis involves water, not solutes like iodine. Active transport's energy dependency enables seaweeds to accumulate iodine for metabolic needs, such as thyroid hormone precursors, showcasing a key adaptation in marine organisms for nutrient uptake.

Correct Answer: C

Rationale: A Foley catheter, a flexible tube inserted through the urethra into the bladder, primarily drains urine in patients unable to urinate naturally, such as post-surgery or with urinary retention. Its balloon tip secures it, allowing continuous drainage into a bag. It doesn't administer fluids or medications those use IVs or other catheters nor monitor pressure, which requires sensors. Draining urine, its core medical function, prevents complications like infection or kidney damage, distinguishing it in clinical practice.

Correct Answer: B

Rationale: Muscle structure descends from large to small: myofibrils (organelles within fibers) contain sarcomeres (contractile units), which comprise thin (actin) and thick (myosin) filaments. Muscle belly, the whole muscle, is larger, so starting there misorders scale. Sarcomeres, between Z-lines, house filaments, not vice versa filaments build sarcomeres, sarcomeres build myofibrils. Starting with filaments then sarcomere reverses this hierarchy, and myofibril as largest ignores its cellular role. The correct sequence reflects anatomical organization, distinguishing myofibril as a bundle of sarcomeres, each with filaments, key to understanding contraction's structural basis.

Correct Answer: D

Rationale: Myosin heads stay bound to actin post-power stroke until another ATP binds, detaching myosin by altering its conformation, allowing the cycle to repeat or relax. More Ca²⁺ affects troponin, not detachment Ca²⁺ sustains contraction. Troponin doesn't bind actin directly for release. More acetylcholine restarts excitation, not detachment. ATP's binding to myosin triggers release, distinguishing it from Ca²⁺ or neurotransmitter roles, key to cross-bridge cycling.