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Locomotion and Movement – Class 11 Biology notes, important questions and MCQs

NCERT Class 11 Biology, chapter 17. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Movement in humans uses muscles and the skeleton. Muscle contraction follows the sliding filament theory, and joints allow different kinds of motion.

Muscle

Types: skeletal (striated, voluntary), visceral (smooth, involuntary), cardiac (striated, involuntary).
Sarcomere (Z-line to Z-line) is the functional unit; actin (thin) and myosin (thick) filaments.
Sliding filament theory: Ca²⁺ binds troponin, myosin heads bind actin, ATP powers cross-bridge cycling; the I-band shortens, the A-band stays the same.

Skeleton and disorders

Human skeleton has 206 bones (axial 80, appendicular 126).
Joints: fibrous (skull sutures), cartilaginous (vertebrae), synovial (ball-and-socket, hinge, pivot, gliding, saddle).
Disorders: myasthenia gravis, tetany, muscular dystrophy, arthritis, osteoporosis, gout.

Key terms

Sarcomere: functional unit of a myofibril between two Z-lines
Synovial joint: freely movable joint with fluid-filled cavity
Motor unit: a motor neuron together with all the muscle fibres it supplies

Important questions with answers

Name the three types of movement shown by human cells.2 marks

Amoeboid (macrophages, leucocytes using pseudopodia), ciliary (cilia in the trachea and fallopian tubes) and muscular (limbs, jaws, tongue).

Differentiate between gout and arthritis.3 marks

Gout is inflammation of joints due to deposition of uric acid crystals. Arthritis is inflammation of joints in general, causing pain and stiffness, often due to wear of cartilage or autoimmune causes.

Describe the mechanism of muscle contraction step by step according to the sliding filament theory.5 marks

A motor neuron releases acetylcholine at the neuromuscular junction, creating an action potential that spreads along the sarcolemma. This makes the sarcoplasmic reticulum release Ca²⁺. Ca²⁺ binds to troponin, shifting tropomyosin and exposing myosin-binding sites on actin. Myosin heads, energised by ATP hydrolysis, bind to actin to form cross-bridges and pull the actin filaments towards the centre (power stroke), releasing ADP and Pi. A new ATP binds and the myosin head detaches; it is re-energised by ATP hydrolysis and the cycle repeats. The Z-lines come closer, the I-band and H-zone shorten, but the A-band stays the same. When stimulation stops, Ca²⁺ is pumped back, the binding sites are covered again and the muscle relaxes.

Quick revision

206 bones in adults.
Ca²⁺ triggers contraction.
Shoulder is a ball-and-socket joint.

Exam tips

During contraction, the H-zone and I-band shorten; the A-band length does not change.
Learn the parts of a sarcomere: Z-line to Z-line; A-band (dark, myosin), I-band (light, actin only), H-zone (myosin only), M-line (centre).

Practice MCQs

Number of bones in an adult human is
1. 106
2. 306
3. 206
4. 216
Show answer
Answer: (c) 206. 206.
Knee joint is a
1. ball-and-socket joint
2. pivot joint
3. hinge joint
4. gliding joint
Show answer
Answer: (c) hinge joint. Hinge.
The functional unit of a muscle fibre is the
1. neuron
2. tendon
3. sarcomere
4. ligament
Show answer
Answer: (c) sarcomere. Sarcomere.
The ion that triggers muscle contraction is
1. Na⁺
2. K⁺
3. Ca²⁺
4. Cl⁻
Show answer
Answer: (c) Ca²⁺. Binds troponin.
The number of ribs in humans is
1. 12
2. 24 pairs
3. 12 pairs
4. 10 pairs
Show answer
Answer: (c) 12 pairs. 7 true, 3 false, 2 floating pairs.
During muscle contraction, which band stays the same length
1. A-band
2. H-zone
3. I-band
4. sarcomere
Show answer
Answer: (a) A-band. Myosin length fixed.
Myasthenia gravis is
1. a bone disorder
2. a genetic joint disease
3. a vitamin deficiency
4. an autoimmune disorder affecting neuromuscular junctions
Show answer
Answer: (d) an autoimmune disorder affecting neuromuscular junctions. Autoimmune.
Rigor mortis after death is due to
1. excess ATP
2. calcium shortage
3. lack of ATP so myosin heads cannot detach from actin
4. nerve impulses
Show answer
Answer: (c) lack of ATP so myosin heads cannot detach from actin. Cross-bridges stay bound.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.