How many fused bones make up each hip bone in an adult skeleton?

Correct Answer: B

Rationale: Each hip bone (os coxa) in an adult is formed by the fusion of three bones: ilium, ischium, and pubis, which unite at the acetabulum during development.

Correct Answer: B

Rationale: Osteoclasts are specialized cells that break down (resorb) bone tissue, releasing minerals like calcium into the bloodstream during remodeling or repair. Osteoblasts build bone, hematopoietic cells in marrow produce blood, and chondroblasts form cartilage—none match 'osteoclast.'

Correct Answer: B

Rationale: The sliding filament theory describes how muscle contraction occurs when actin and myosin filaments slide past each other, shortening the muscle. This process happens within the sarcomere, the functional unit of contraction between Z-lines in a myofibril. While myofibrils contain sarcomeres and myosin heads facilitate the sliding, the theory specifically applies to the sarcomere level, making 'Sarcomeres' the correct answer.

Correct Answer: C

Rationale: Irregular bones, like the vertebrae, have complex shapes and primarily function to protect internal organs. The vertebrae form the vertebral column, which encases and protects the spinal cord, a critical nervous system component. While some bones produce blood cells, protection is the primary role here, making 'Protecting internal organs' the correct answer.

Correct Answer: B

Rationale: Compact bone, also called cortical bone, is the dense, hard outer layer of bone tissue that provides strength and structural support. Spongy bone (with trabeculae) is lighter and found inside, often in the epiphysis, but 'compact bone' specifically denotes the dense type, making 'Dense and hard' the correct answer.