Chapter 17: Locomotion and Movement Long Questions | biology Class 11 CBSE

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Chapter 17: Locomotion and Movement Long Questions | biology Class 11 CBSE | ByteNotes.in

Long Answer

Medium difficulty • Structured explanation

Medium

Question 1

Long Form

Describe the structure of a skeletal muscle, starting from the whole muscle down to the level of the myofibril. Include all key structural components.

Each skeletal muscle is made of muscle bundles called fascicles, held together by a collagenous connective tissue layer called fascia.
Each fascicle contains many muscle fibres (cells), each lined by the plasma membrane called sarcolemma, which encloses the sarcoplasm. The muscle fibre is a syncitium (multinucleate).
The sarcoplasmic reticulum within each fibre is the storehouse of calcium ions, critical for contraction.
The sarcoplasm contains numerous parallelly arranged filaments called myofibrils (myofilaments). Each myofibril displays alternating dark A bands (anisotropic, containing myosin) and light I bands (isotropic, containing actin).
The functional unit between two successive Z lines is the sarcomere. The Z line bisects each I band; the M line holds thick filaments in the middle of the A band; the H zone is the portion of the A band not overlapped by thin filaments at rest.
Actin filaments are thin and attached to Z lines; myosin filaments are thick and held by the M line. Both proteins are arranged as parallel rod-like structures along the longitudinal axis of the myofibril.

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Long Answer

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Hard

Question 2

Long Form

Explain in detail the mechanism of muscle contraction according to the sliding filament theory, from the arrival of a neural signal to complete relaxation.

A signal from the CNS via a motor neuron reaches the neuromuscular junction (motor-end plate), causing release of acetylcholine, which generates an action potential in the sarcolemma.
The action potential spreads through the muscle fibre and triggers release of Ca++ ions from the sarcoplasmic reticulum into the sarcoplasm.
Ca++ binds to a subunit of troponin on the actin filaments, removing the masking of active sites for myosin. The myosin head, using energy from ATP hydrolysis, binds to these exposed sites to form a cross bridge.
The cross bridge pulls the actin filaments towards the centre of the A band; the attached Z lines move inward causing sarcomere (and hence muscle) shortening. During this, I bands reduce but A bands retain length.
After the power stroke, ADP and Pi are released from the myosin head; a new ATP binds, breaking the cross bridge. The ATP is hydrolysed again, and the cycle repeats for further sliding.
When Ca++ is pumped back into the sarcoplasmic cisternae, the active sites on actin are masked again by troponin; cross bridge cycling stops, Z lines return to their original position, and the muscle relaxes.

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Long Answer

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Medium

Question 3

Long Form

Compare and contrast the three types of muscles in humans — skeletal, visceral, and cardiac — with respect to location, appearance, voluntary/involuntary nature, and function.

Skeletal muscles are closely associated with the skeletal components of the body. They appear striated (striped) under the microscope due to the organised arrangement of actin and myosin filaments.
Skeletal muscles are voluntary — their activities are under the direct control of the nervous system. They are primarily involved in locomotion and changes in body posture.
Visceral (smooth) muscles are located in the inner walls of hollow visceral organs like the alimentary canal and reproductive tract. They appear smooth (non-striated) with no visible striations.
Visceral muscles are involuntary — not under voluntary nervous control. They function in transporting food through the digestive tract and gametes through the genital tract.
Cardiac muscles are exclusively the muscles of the heart. Like skeletal muscles, they are striated, and like smooth muscles, they are involuntary — the nervous system does not directly control them.
Cardiac muscle cells assemble in a branching pattern, which is a unique structural feature. They contract rhythmically throughout life without fatigue, unlike skeletal muscles.

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Long Answer

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Hard

Question 4

Long Form

Describe the structure of the contractile proteins actin and myosin. How does the structure of these proteins enable muscle contraction?

Each actin (thin) filament is made of two F (filamentous) actins helically wound together. Each F actin is itself a polymer of monomeric G (Globular) actins.
Two filaments of tropomyosin run close to the F actins along their entire length. Troponin, a complex protein, is distributed at regular intervals on tropomyosin, and in the resting state its subunit masks the active binding sites for myosin.
Each myosin (thick) filament is a polymerised protein composed of many monomeric meromyosins. Each meromyosin has a globular head with a short arm (HMM) and a tail (LMM).
The HMM component projects outward from the surface of the polymerised myosin to form cross arms. The globular head is an active ATPase enzyme with binding sites for ATP and for actin.
When Ca++ unmasks the active sites on actin, the myosin head binds using ATP energy to form a cross bridge and undergoes a rotation (power stroke) to pull the actin filament, enabling contraction.
The ATPase activity of the myosin head is critical — it hydrolyses ATP to provide the energy for each cycle of cross bridge formation, rotation, and detachment that drives the sliding of thin over thick filaments.

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Long Answer

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Medium

Question 5

Long Form

Describe the axial skeleton of the human body, including the skull, vertebral column, and rib cage, with relevant numbers.

The axial skeleton comprises 80 bones distributed along the main axis of the body. It includes the skull, vertebral column, sternum, and ribs.
The skull is composed of 22 bones — 8 cranial bones forming the protective cranium for the brain, and 14 facial bones forming the front of the skull. A single U-shaped hyoid bone is present at the base of the buccal cavity; each middle ear has 3 ear ossicles (Malleus, Incus, Stapes).
The vertebral column has 26 serially arranged vertebrae differentiated into cervical (7), thoracic (12), lumbar (5), sacral (1 fused), and coccygeal (1 fused) regions. It protects the spinal cord, supports the head, and provides attachment for ribs and back musculature.
There are 12 pairs of ribs. The first 7 pairs (true ribs) connect dorsally to thoracic vertebrae and ventrally to the sternum via hyaline cartilage. Pairs 8–10 (false/vertebrochondral ribs) connect to the 7th rib via cartilage.
Pairs 11 and 12 are floating ribs — they are not connected ventrally. Thoracic vertebrae, ribs, and sternum together constitute the rib cage.
The sternum is a flat bone on the ventral midline of the thorax. Each rib is a thin flat bone with two articulation surfaces on its dorsal end, making it bicephalic.

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Medium

Question 6

Long Form

Describe the appendicular skeleton with reference to the pectoral girdle, pelvic girdle, and the bones of the limbs.

The appendicular skeleton consists of the limb bones and their girdles. Each limb is made of 30 bones. The pectoral and pelvic girdles help in the articulation of upper and lower limbs, respectively, with the axial skeleton.
Each half of the pectoral girdle has a clavicle (long slender collar bone with two curvatures) and a scapula (large triangular flat bone between the 2nd and 7th ribs). The acromion of the scapula articulates with the clavicle, and the glenoid cavity articulates with the humerus to form the shoulder joint.
The pelvic girdle has two coxal bones, each formed by fusion of ilium, ischium, and pubis. The acetabulum (cavity at their junction) articulates with the femur. The two halves meet ventrally at the pubic symphysis (fibrous cartilage).
Upper limb bones: humerus, radius, ulna, 8 carpals (wrist), 5 metacarpals (palm), and 14 phalanges (digits). The femur (longest bone), tibia, fibula form the thigh and leg.
Lower limb bones also include 7 tarsals (ankle), 5 metatarsals, and 14 phalanges. The patella (knee cap) is a cup-shaped bone covering the knee ventrally.
Both girdles are each formed of two halves, and each girdle has structural adaptations that support the weight and movement demands of the respective limbs.

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Long Answer

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Medium

Question 7

Long Form

Classify joints in the human body on the basis of their structure and the degree of movement permitted. Give examples for each type.

Joints are points of contact between bones, or between bones and cartilages, where force generated by muscles causes movement, with the joint acting as a fulcrum. Three structural types are recognised: fibrous, cartilaginous, and synovial.
Fibrous joints are formed by dense fibrous connective tissue; they do not allow any movement. The flat skull bones fuse end-to-end via sutures to form the cranium — this is a classic fibrous joint.
Cartilaginous joints involve bones joined by cartilage; they permit limited movement. The joints between adjacent vertebrae in the vertebral column are of this type.
Synovial joints are characterised by a fluid-filled synovial cavity between the articulating surfaces; they allow considerable movement and are critical for locomotion.
Types of synovial joints: ball and socket (humerus/pectoral girdle), hinge (knee joint), pivot (atlas/axis), gliding (between carpals), and saddle (carpal/metacarpal of thumb).
The degree of movability increases progressively from fibrous (none) to cartilaginous (limited) to synovial (considerable). Synovial joints are the most functionally important for locomotory movements.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 8

Long Form

Analyse the disorders of the muscular and skeletal system discussed in the chapter. For each disorder, state its cause and the system it primarily affects.

Myasthenia gravis is an auto-immune disorder that affects the neuromuscular junction. The immune system attacks the junction, leading to fatigue, progressive weakening, and eventual paralysis of skeletal muscles.
Muscular dystrophy is a disease involving progressive degeneration of skeletal muscle. It is mostly due to a genetic disorder and results in gradual loss of muscle function.
Tetany affects the muscular system — it is characterised by rapid spasms (wild contractions) caused by low levels of calcium ions (Ca++) in body fluids, disrupting normal calcium-dependent regulation of contraction.
Arthritis is the inflammation of joints, affecting the skeletal/joint system. It reduces movement and causes pain at joint surfaces.
Osteoporosis is an age-related disorder of the skeletal system characterised by decreased bone mass and increased risk of fractures; decreased estrogen levels are a common cause.
Gout is inflammation of joints due to the accumulation of uric acid crystals in joint spaces, also affecting the skeletal/joint system and causing significant pain and restricted movement.

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Long Answer

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Hard

Question 9

Long Form

Distinguish between red muscle fibres and white muscle fibres at the structural and functional levels. Relate their properties to their respective energy pathways.

Red muscle fibres have a high content of myoglobin, the red-coloured oxygen-storing pigment, which gives them their characteristic reddish colour.
They contain a large number of mitochondria, which enables them to efficiently utilise the large amount of oxygen stored in myoglobin for aerobic ATP production.
Because they rely primarily on aerobic respiration, red fibres are suited for sustained, continuous, and prolonged muscular activity without rapid fatigue.
White muscle fibres contain very little myoglobin and therefore appear pale or whitish. They have fewer mitochondria but a high amount of sarcoplasmic reticulum.
White fibres depend on anaerobic processes for energy generation; they can contract rapidly but fatigue quickly due to lactic acid accumulation.
The reaction time of white fibres is shorter, making them suited for rapid, powerful, short-duration activities, while red fibres support endurance-based activities — both serve complementary roles in the musculature.

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Long Answer

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Hard

Question 10

Long Form

Explain the role of the three systems — muscular, skeletal, and neural — in achieving locomotion in humans.

Locomotion is a coordinated voluntary movement requiring the integrated activity of muscular, skeletal, and neural systems; no single system alone can achieve it.
The neural system (CNS and motor neurons) initiates and controls the process by sending signals via motor neurons to the neuromuscular junction, triggering acetylcholine release and generating action potentials in muscle fibres.
The muscular system executes movement — muscles contract by the sliding filament mechanism (Ca++-mediated, ATP-dependent cross-bridge cycling), generating the necessary force.
The skeletal system provides the rigid framework on which muscular force acts. Bones act as levers and joints act as fulcrums; without this system, muscular force cannot produce directional movement.
The type of joint involved (especially synovial joints like ball-and-socket, hinge, and pivot) determines the range and direction of movement achievable at each body region.
Any disorder in one system — such as myasthenia gravis (neural-muscular junction), muscular dystrophy (muscular), or arthritis and osteoporosis (skeletal) — disrupts this coordination and impairs locomotion, illustrating the interdependence of all three systems.

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Chapter 17: Locomotion and Movement | Long Questions

Describe the structure of a skeletal muscle, starting from the whole muscle down to the level of the myofibril. Include all key structural components.

Explain in detail the mechanism of muscle contraction according to the sliding filament theory, from the arrival of a neural signal to complete relaxation.

Compare and contrast the three types of muscles in humans — skeletal, visceral, and cardiac — with respect to location, appearance, voluntary/involuntary nature, and function.

Describe the structure of the contractile proteins actin and myosin. How does the structure of these proteins enable muscle contraction?

Describe the axial skeleton of the human body, including the skull, vertebral column, and rib cage, with relevant numbers.

Describe the appendicular skeleton with reference to the pectoral girdle, pelvic girdle, and the bones of the limbs.

Classify joints in the human body on the basis of their structure and the degree of movement permitted. Give examples for each type.

Analyse the disorders of the muscular and skeletal system discussed in the chapter. For each disorder, state its cause and the system it primarily affects.

Distinguish between red muscle fibres and white muscle fibres at the structural and functional levels. Relate their properties to their respective energy pathways.

Explain the role of the three systems — muscular, skeletal, and neural — in achieving locomotion in humans.

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