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Locomotion and Movement – Class 11 Biology Chapter 17 Notes & NCERT PDF

Class 11BiologyChapter 17NCERT book: Biology - Class 11

Notes and a simple summary of Chapter 17 of the NCERT Class 11 Biology book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 17: Locomotion and Movement

Introduction

Movement is a significant feature of living beings — from protoplasmic streaming in Amoeba to cilia, flagella and tentacles. Voluntary movements that change place or location are locomotion (walking, running, climbing, flying, swimming). The same structure may do both jobs: cilia of Paramoecium move food through the cytopharynx and also help locomotion; Hydra uses tentacles for capturing prey and for locomotion.

All locomotions are movements, but all movements are not locomotions.

Animals move to search for food, shelter, mate, breeding grounds or favourable climate, or to escape enemies.

Key Concepts

17.1 Types of Movement

Cells of the human body show three types:

  • Amoeboid — macrophages and leucocytes; pseudopodia formed by streaming protoplasm; microfilaments are involved.
  • Ciliary — ciliated epithelium of internal tubular organs; cilia in the trachea remove dust; cilia move ova through the female reproductive tract.
  • Muscular — movement of limbs, jaws, tongue; locomotion needs coordinated muscular, skeletal and neural systems.

    • Flagellar movement helps swimming of sperm, water current in sponges and locomotion of Euglena.

    17.2 Muscle

    Muscle is a specialised tissue of mesodermal origin forming about 40–50% of adult body weight. Properties: excitability, contractility, extensibility and elasticity.

  • Skeletal — attached to skeleton; striated, voluntary; locomotion and posture.
  • Visceral — inner walls of hollow organs (alimentary canal, reproductive tract); smooth (non-striated), involuntary.
  • Cardiac — heart; striated, branching, involuntary.

    • Structure of skeletal muscle: muscle → fascicles (bundles) held by the collagenous fascia → muscle fibres. Each fibre is lined by the sarcolemma enclosing the sarcoplasm; it is a syncitium (many nuclei). The sarcoplasmic reticulum stores calcium ions. The fibre has many parallel myofibrils with alternate bands:

  • I-band (isotropic, light) — contains actin (thin filaments); bisected by the elastic Z line.
  • A-band (anisotropic, dark) — contains myosin (thick filaments), held together at the M line.
  • Sarcomere — portion between two successive Z lines; the functional unit of contraction.
  • H zone — central part of the thick filaments not overlapped by thin filaments.

    • #### 17.2.1 Contractile proteins

  • Actin (thin) filament — two F-actins helically wound; each F-actin is a polymer of G-actin monomers. Two filaments of tropomyosin run alongside; troponin lies at regular intervals on tropomyosin. At rest a troponin subunit masks the myosin-binding sites on actin.
  • Myosin (thick) filament — polymer of meromyosins. Each has a globular head with short arm (heavy meromyosin, HMM) and a tail (light meromyosin, LMM). The projecting head and short arm form the cross arm. The head is an ATPase with ATP-binding sites and actin-binding sites.

    • #### 17.2.2 Sliding filament theory

    Contraction occurs by the sliding of thin filaments over thick filaments.

  • CNS sends a signal via a motor neuron. Motor neuron + its muscle fibres = motor unit; the junction is the neuromuscular junction / motor-end plate.
  • Acetylcholine is released, generating an action potential in the sarcolemma.
  • Ca²⁺ is released into the sarcoplasm; it binds a troponin subunit and unmasks the active sites on actin.
  • Using energy from ATP hydrolysis, the myosin head binds actin → cross bridge.
  • The cross bridge pulls actin towards the centre of the A band; Z lines move inwards → sarcomere shortens.
  • Myosin releases ADP and Pi; a new ATP binds and the cross bridge breaks; the cycle repeats.
  • When Ca²⁺ is pumped back into the sarcoplasmic cisternae, actin is masked again and Z lines return — relaxation.
    • During contraction the I band shortens while the A band retains its length.
  • Fatigue — repeated activation leads to lactic acid accumulation from anaerobic breakdown of glycogen.
  • Red fibres — high myoglobin, many mitochondria; aerobic muscles.
  • White fibres — little myoglobin, few mitochondria, much sarcoplasmic reticulum; depend on anaerobic metabolism.

    • 17.3 Skeletal System

    Bones (hard matrix due to calcium salts) and cartilages (pliable matrix due to chondroitin salts). 206 bones in humans.

    Axial skeleton — 80 bones

  • Skull — 22 bones: 8 cranial + 14 facial. Plus a U-shaped hyoid at the base of the buccal cavity and three ear ossicles in each middle ear (malleus, incus, stapes). Two occipital condyles → dicondylic skull.
  • Vertebral column — 26 vertebrae: cervical (7), thoracic (12), lumbar (5), sacral (1 fused), coccygeal (1 fused). First vertebra: atlas, articulates with the occipital condyles. Almost all mammals have 7 cervical vertebrae.
  • Sternum — flat bone on the ventral midline of the thorax.
  • Ribs — 12 pairs, each bicephalic. True ribs: first 7 pairs (joined to sternum by hyaline cartilage). Vertebrochondral (false) ribs: 8th, 9th, 10th (join the 7th rib). Floating ribs: 11th and 12th.

    • Appendicular skeleton — limbs and girdles. Each limb has 30 bones.

  • Fore limb: humerus, radius, ulna, carpals (8), metacarpals (5), phalanges (14).
  • Hind limb: femur (longest bone), tibia, fibula, tarsals (7), metatarsals (5), phalanges (14), and the patella (knee cap).
  • Pectoral girdle — each half: clavicle (collar bone) and scapula (triangular, between the 2nd and 7th ribs; spine → acromion; glenoid cavity articulates with the humerus to form the shoulder joint).
  • Pelvic girdle — two coxal bones, each a fusion of ilium, ischium and pubis; the acetabulum receives the femur; the halves meet ventrally at the pubic symphysis (fibrous cartilage).

    • 17.4 Joints

    Points of contact between bones, or bones and cartilages; the joint acts as a fulcrum.

  • Fibrous — no movement; sutures of flat skull bones.
  • Cartilaginous — limited movement; between adjacent vertebrae.
  • Synovial — fluid-filled synovial cavity; considerable movement:

    • - Ball and socket — humerus and pectoral girdle

    - Hinge — knee joint

    - Pivot — atlas and axis

    - Gliding — between carpals

    - Saddle — carpal and metacarpal of thumb

    17.5 Disorders

  • Myasthenia gravis — autoimmune; affects the neuromuscular junction; fatigue, weakening, paralysis.
  • Muscular dystrophy — progressive degeneration of skeletal muscle, mostly genetic.
  • Tetany — rapid spasms due to low Ca²⁺ in body fluid.
  • Arthritis — inflammation of joints.
  • Osteoporosis — age-related decreased bone mass; decreased estrogen a common cause.
  • Gout — joint inflammation from accumulated uric acid crystals.

    • Diagrams to Know (in words)

  • Sarcomere: Z line – half I band – A band (with H zone and central M line) – half I band – Z line; thin filaments anchored on Z lines overlapping thick filaments.
  • Actin filament: two twisted F-actins with tropomyosin strands and periodic troponin; meromyosin with head, short arm and tail.
  • Skull, vertebral column (right lateral view), rib cage, pectoral and pelvic girdles.

    • Key-Facts Sheet

  • Muscles: 40–50% of body weight
  • Human skeleton: 206 bones; axial 80; skull 22 (8 cranial + 14 facial); each limb 30
  • Vertebrae 26: 7 + 12 + 5 + 1 + 1
  • Ribs 12 pairs: 7 true, 3 vertebrochondral, 2 floating
  • Carpals 8, tarsals 7, metacarpals/metatarsals 5, phalanges 14 per limb

    • Exam Focus

  • Draw and label a sarcomere; define the sliding filament theory; list the steps of contraction.
  • True/False from the exercises: actin is in the thin filament (true); H zone has both thick and thin filaments (false — only thick); human skeleton has 206 bones (true); 11 pairs of ribs (false — 12); sternum is ventral (true).
  • Joint types: atlas/axis — pivot; carpal/metacarpal of thumb — saddle; femur/acetabulum — ball and socket; cranial bones — fibrous; between phalanges — hinge; pubic bones — cartilaginous.
  • Differences: actin vs myosin; red vs white fibres; pectoral vs pelvic girdle.

    • Key Terms

  • Locomotion (गमन)
  • Sarcomere (सार्कोमियर)
  • Sarcolemma (पेशीचोल)
  • Sarcoplasmic reticulum (पेशीद्रव्य जालिका)
  • Actin (एक्टिन)
  • Myosin (मायोसिन)
  • Tropomyosin (ट्रोपोमायोसिन)
  • Troponin (ट्रोपोनिन)
  • Cross bridge (अनुप्रस्थ सेतु)
  • Myoglobin (मायोग्लोबिन)
  • Axial skeleton (अक्षीय कंकाल)
  • Appendicular skeleton (उपांगीय कंकाल)
  • Synovial joint (साइनोवियल संधि)
  • Pectoral girdle (अंस मेखला)
  • Pelvic girdle (श्रोणि मेखला)

    • Common Mistakes

  • Saying the A band shortens — it keeps its length; the I band and H zone shorten.
  • Confusing troponin (masks binding sites, binds Ca²⁺) with tropomyosin.
  • Counting the sacrum and coccyx as several vertebrae — each is one fused unit in the book's count of 26.
  • Mixing vertebrochondral (8th–10th) with floating ribs (11th–12th).

    • 💡 Key Learning Points

    • ✓Human cells show amoeboid, ciliary and muscular movement; all locomotions are movements but not vice versa.
    • ✓Skeletal, visceral and cardiac muscles differ in location, striation and voluntary control.
    • ✓The sarcomere (Z line to Z line) is the functional unit; actin–tropomyosin–troponin and myosin are the contractile proteins.
    • ✓Muscle contraction follows the sliding filament theory, triggered by acetylcholine, Ca²⁺ and ATP-driven cross bridges.
    • ✓The 206-bone skeleton has axial (80) and appendicular parts; joints are fibrous, cartilaginous or synovial.

    👨‍🏫 Teaching Tips

    • →Model a sarcomere with two combs sliding into each other to show why I band and H zone shorten.
    • →Sequence cards: students order the eight steps of contraction from motor signal to relaxation.
    • →Use a skeleton model or chart to count ribs and vertebrae region by region.
    • →Have students move their own joints to identify hinge, pivot, ball and socket, gliding and saddle types.
    • →Compare red and white fibres using everyday examples of endurance vs sprint activity.
    • →Revise disorders with a quick match-the-cause game (e.g., gout — uric acid, tetany — low Ca²⁺).
    • →Link acetylcholine release to synaptic transmission in Chapter 18.

    📋 Assessment Questions

    1. Draw a labelled sarcomere and explain which bands change during contraction.
    2. Describe the sliding filament mechanism step by step.
    3. Classify ribs into true, vertebrochondral and floating ribs with numbers.
    4. Name the joint type between given pairs of bones.
    5. Differentiate red and white muscle fibres.

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    Keep learning

    All chapters in Biology - Class 11

    1. 1. The Living World
    2. 2. Biological Classification
    3. 3. Plant Kingdom
    4. 4. Animal Kingdom
    5. 5. Morphology of Flowering Plants
    6. 6. Anatomy of Flowering Plants
    7. 7. Structural Organisation in Animals
    8. 8. Cell: The Unit of Life
    9. 9. Biomolecules
    10. 10. Cell Cycle and Cell Division
    11. 11. Photosynthesis in Higher Plants
    12. 12. Respiration in Plants
    13. 13. Plant Growth and Development
    14. 14. Breathing and Exchange of Gases
    15. 15. Body Fluids and Circulation
    16. 16. Excretory Products and their Elimination
    17. 17. Locomotion and Movement
    18. 18. Neural Control and Coordination
    19. 19. Chemical Coordination and Integration