Locomotion and Movement (MCQs)

Correct Answer: (d)
Both swimming and flying rely on generating lift by pushing against a fluid medium (water or air). By exerting a downward force on the surrounding fluid, an upward lift force is generated, allowing the organism to remain suspended or move efficiently against gravity.

Correct Answer: (d)
Muscles generate movement by contracting and by being attached to bones across joints. When a muscle contracts, it pulls one bone toward another, resulting in movement of the hand through space. Muscles do not actively lengthen; they relax.

Correct Answer: (a)
The first statement is false because skeletal muscles at rest primarily obtain energy through the aerobic metabolism of fatty acids. Glucose and glycogen become the primary fuel sources only when the muscle becomes active and the demand for ATP increases.

Correct Answer: (d)
Intramembranous ossification occurs when bone forms directly from embryonic mesenchymal tissue (common in flat bones of the skull). Endochondral ossification occurs when bone replaces a pre-existing hyaline cartilage model (common in long bones like the femur).

Correct Answer: (b)
During muscle contraction, calcium ions bind to troponin. This binding causes tropomyosin to shift away from actin’s myosin-binding sites, allowing cross-bridge formation. If Ca2+ cannot bind to troponin, the binding sites remain blocked, preventing muscle contraction.

Correct Answer: (c)
Bone is a dynamic tissue that responds to mechanical stress. Weight-bearing and resistance exercises stimulate osteoblast activity, leading to increased bone density and thickness. Therefore, Ray’s bones would appear thicker and stronger due to long-term physical stress, unlike Ben’s sedentary lifestyle.

Correct Answer: (a)
During muscle contraction, the individual protein filaments (actin and myosin) maintain their original length. The sarcomere shortens because the thin actin filaments are pulled over the thick myosin filaments, increasing the degree of overlap.

Correct Answer: (b)
A hydrostatic skeleton consists of a fluid-filled cavity (coelom) surrounded by muscles. When these muscles contract, they put pressure on the incompressible fluid, changing the animal's shape and allowing for movement like peristalsis.

Correct Answer: (b)
A twitch is a single, brief contraction and relaxation cycle of a muscle fiber in response to a single action potential. This makes it the ideal unit for studying the molecular events and energy consumption of one contraction cycle.

Correct Answer: (d)
The fundamental structural difference is placement. An exoskeleton (like that of an arthropod) provides a hard outer covering for soft internal tissues, while an endoskeleton (like that of a human) is a framework located inside the body's soft tissues.

Correct Answer: (d)
The correct sequence starts with the stimulus (Action potential arrives, 3), which triggers the release of calcium from storage (SR releases Ca²⁺, 1). The calcium then binds to the regulatory protein (Ca²⁺ binds to troponin, 4), which reveals the binding sites, allowing the cross-bridge to form (Myosin binds to actin, 2).

Correct Answer: (b)
Acetylcholine is released at the neuromuscular junction to stimulate muscle fiber depolarization. If ACh release is inhibited, the nerve impulse cannot trigger muscle contraction, even though the neuron itself may still fire action potentials.

Correct Answer: (b)
Osteocytes are living bone cells housed in lacunae. They receive nutrients and oxygen through blood vessels present in Haversian canals. These canals form an organized network that maintains the viability of osteocytes deep within bone tissue.

Correct Answer: (c)
Motor neurons release the neurotransmitter acetylcholine (ACh) into the synaptic cleft at the neuromuscular junction. ACh binds to receptors on the muscle fiber's sarcolemma, triggering an action potential that leads to contraction.