Muscular System makes nearly what percent of the weight of the human body?

Correct Answer: D

Rationale: The muscular system accounts for about 50% of body weight, primarily from skeletal muscles, with smooth and cardiac adding less mass. This reflects their extensive presence over 600 muscles supporting movement and structure. Twenty percent is too low, ignoring skeletal bulk. Forty percent is close but underestimates, per anatomical data. Seventy percent overstates, leaving little for bones, organs, and fat. Fifty percent aligns with standard physiology, emphasizing muscles' role in force generation and mass, balancing the body's composition, distinct from lower or higher guesses misaligned with muscle distribution.

Correct Answer: C

Rationale: After ATP depletion in muscle contraction, creatine phosphate rapidly donates a phosphate to ADP, regenerating ATP in seconds via creatine kinase. This immediate source sustains short bursts of activity. Cellular respiration, in mitochondria, follows later, using oxygen for sustained ATP but takes time. Lactic acid breakdown isn't a process lactic acid forms in anaerobic conditions, not regenerating ATP. Fermentation (anaerobic glycolysis) produces ATP slowly, secondary to creatine phosphate. Its quick, oxygen-independent action distinguishes creatine phosphate, bridging energy gaps, unlike slower respiration or fermentation, vital for initial muscle energy demands.

Correct Answer: D

Rationale: The gluteus maximus is named for size (maximus, largest) and location (gluteus, buttock region), the biggest muscle there, extending and rotating the thigh. Shape (e.g., trapezius) or action (e.g., flexor) could apply elsewhere, but here, size and gluteal position define it. Combining both aspects highlights its prominence and placement, distinct from single-trait names, reflecting its anatomical and functional significance in the hip.

Correct Answer: A

Rationale: Rectus abdominis, along the abdomen, flexes the vertebral column, bending the spine forward, as in sit-ups. Serratus anterior protracts scapula. Sternocleidomastoid flexes the neck, not full column. Trapezius extends the head or adducts scapula. Rectus abdominis' anterior pull distinguishes it, key for trunk flexion, unlike scapular or neck-specific actions.

Correct Answer: B

Rationale: Quadriceps occupy the anterior thigh, comprising four muscles (rectus femoris, vastus lateralis, medialis, intermedius) that extend the knee. Anterior abdomen hosts rectus abdominis. Posterior thigh has hamstrings. Posterior arm holds triceps. Quadriceps' thigh-front location sets them apart, key for leg movement, distinct from other regions.