What the largest endogenous substrate source in the body?

Correct Answer: D

Rationale: Adipose tissue is the body's largest endogenous substrate source, storing vast triglyceride reserves thousands of grams far exceeding other stores, providing energy via lipolysis during prolonged activity. Muscle glycogen, about 300-500 grams in trained individuals, fuels local contraction but is limited. Liver glycogen, around 100 grams, maintains blood glucose but depletes quickly. Intramuscular lipids, small triglyceride droplets, contribute modestly, far less than adipose's capacity. Adipose tissue's sheer volume and energy density (9 kcal/g) dwarf glycogen's stores (4 kcal/g), distinguishing it as the primary reserve, key for sustained energy needs beyond glycogen's scope.

Correct Answer: C

Rationale: Erector spinae, along the spine, extends and stabilizes it, providing postural support for standing and lifting. Arm movement involves deltoid or biceps. Pelvic stabilization uses gluteals or obliques. Rotation involves rotatores or obliques, not erector spinae's primary extension. Its role in maintaining upright posture distinguishes it, essential for spinal integrity, unlike arm, pelvic, or twisting functions.

Correct Answer: B

Rationale: Vastus intermedius, a quadriceps muscle, lies deep to rectus femoris, which overlays it on the anterior thigh, both extending the knee. Biceps femoris, a hamstring, is posterior. Vastus medialis and lateralis flank it laterally and medially, not superiorly. Rectus femoris' superficial position distinguishes it, key for quadriceps layering.

Correct Answer: D

Rationale: Water's ability to mound above a glass rim results from surface tension, a property arising from cohesive forces between its molecules. Hydrogen bonds create a strong, elastic 'skin' at the surface, resisting external disruption and allowing water to hold together against gravity briefly. Specific gravity relates to density, not this behavior. Cohesion contributes but isn't the complete mechanism. Opacity, transparency-related, is irrelevant. Surface tension's role in forming this temporary barrier, driven by molecular attraction, explains the phenomenon, a key feature in water's physical behavior.

Correct Answer: C

Rationale: Acidity depends on ion concentration affecting pH. Hydronium ions (H₃O⁺), formed when protons (H⁺) bond with water, increase in acidic solutions, lowering pH below 7, as in vinegar. Hydroxyl ions (OH⁻) raise pH, making solutions basic. Sodium and potassium ions, from salts, are neutral, minimally shifting pH unless paired with strong acids or bases. Hydronium's direct link to proton donation defines acidity, distinguishing it in chemical equilibria and pH measurement.