What happens to sarcomeres when muscle fibers contract?

Correct Answer: B

Rationale: When muscle fibers contract, sarcomeres (the units between Z-lines) shorten as actin and myosin filaments slide past each other, per the sliding filament theory. This reduces sarcomere length, contracting the muscle, making 'Sarcomeres shorten' the correct answer.

Correct Answer: D

Rationale: Bones are classified by shape: long (e.g., femur), short (e.g., carpals), flat (e.g., scapula), irregular (e.g., vertebrae), and sometimes sesamoid (round, e.g., patella). 'Square,' 'cubed,' and 'triangular' are not standard categories; 'round' aligns with sesamoid bones, making 'long, short, flat, irregular and round' the most accurate.

Correct Answer: C

Rationale: The diaphysis, or shaft, of a long bone is primarily compact bone, providing strength and support. Spongy bone is in the epiphyses, hyaline cartilage covers joint surfaces, and fibrous tissue forms membranes like the periosteum, making 'compact bone' the correct answer.

Correct Answer: B

Rationale: Spongy bone consists of a network of trabeculae, bony plates that provide lightweight strength and house red marrow. Lamellae are in compact bone, lacunae contain osteocytes, and canaliculi connect them, making 'trabeculae' the correct answer.

Correct Answer: C

Rationale: The epiphyseal plate (growth plate), between the epiphysis and diaphysis, is where long bones grow in length via cartilage ossification. The epiphysis is the end, diaphysis the shaft, and periosteum the outer layer, making 'epiphyseal plate' correct.