NCERT Solutions for Class 11 Biology Chapter 17: Locomotion and Movement (NCERT 2026–27)

These Class 11 Biology Chapter 17 solutions cover Locomotion and Movement with complete, exam-ready answers to every NCERT exercise question. The chapter explains the three types of movement in human cells, the structure of skeletal muscle and contractile proteins, the sliding filament theory of muscle contraction, the human skeletal system (axial and appendicular), the joints, and the common disorders of the muscular and skeletal systems. All questions are reproduced verbatim and solved in clear CBSE-style prose, updated for session 2026–27.

Class: 11 Subject: Biology Chapter: 17 Chapter Name: Locomotion and Movement Exercises: 10 questions (all solved) Session: 2026–27
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Class 11 Biology Chapter 17 Solutions – Overview

Movement is one of the defining features of living beings. In humans, cells show three kinds of movement — amoeboid (macrophages, leucocytes), ciliary (lining of internal tubular organs such as the trachea and oviduct) and muscular (limbs, jaws, tongue). A voluntary movement that changes an animal’s location is called locomotion; thus all locomotions are movements, but all movements are not locomotion. Locomotion requires the coordinated action of the muscular, skeletal and neural systems. The chapter studies the three muscle types (skeletal, visceral, cardiac), the detailed structure of a skeletal muscle fibre and its sarcomere, the contractile proteins actin and myosin, the mechanism of contraction by the sliding filament theory, the 206 bones of the human skeleton divided into the axial and appendicular skeleton, the three structural types of joints (fibrous, cartilaginous, synovial), and disorders like myasthenia gravis, muscular dystrophy, tetany, arthritis, osteoporosis and gout.

Key Concepts & Definitions

Locomotion: a voluntary movement that results in a change of place or location (walking, running, swimming, flying).

Types of cell movement (human): amoeboid (by pseudopodia, using cytoskeletal microfilaments), ciliary (by cilia of ciliated epithelium), and muscular (by contractile muscle tissue).

Muscle properties: excitability, contractility, extensibility and elasticity; muscle is a mesodermal tissue making up ~40–50% of adult body weight.

Three muscle types: Skeletal (striated, voluntary), Visceral / smooth (non-striated, involuntary), Cardiac (striated, branched, involuntary).

Sarcomere: the functional unit of contraction — the part of a myofibril between two successive ‘Z’ lines, containing a central ‘A’ band of thick (myosin) filaments and two half ‘I’ bands of thin (actin) filaments.

Contractile proteins: Actin (thin filament, made of F-actin + tropomyosin + troponin) and Myosin (thick filament, made of meromyosin with a head bearing ATPase and actin-binding sites).

Sliding filament theory: contraction occurs by the thin filaments sliding over the thick filaments, shortening the sarcomere; the ‘A’ band length stays constant while the ‘I’ band and H-zone shorten.

Skeleton: 206 bones — Axial (80: skull, vertebral column, sternum, ribs) and Appendicular (126: limb bones + pectoral and pelvic girdles).

Joints: Fibrous (immovable, e.g. skull sutures), Cartilaginous (slightly movable, e.g. between vertebrae), Synovial (freely movable, e.g. ball-and-socket, hinge, pivot, gliding, saddle).

NCERT Exercises — Solutions

All questions below are reproduced verbatim from the NCERT textbook; the answers are original and exam-ready.

1. Draw the diagram of a sarcomere of skeletal muscle showing different regions.

ANSWER A sarcomere is the segment of a myofibril lying between two successive ‘Z’ lines. In a labelled diagram, the regions are arranged in the following order along the length of the myofibril, which you should sketch and label clearly: ‘Z’ line: the elastic line bounding each end of the sarcomere; thin (actin) filaments are firmly attached to it. ‘I’ band (Isotropic / light band): contains only thin filaments. Each sarcomere has two half ‘I’ bands, one at each end, with the ‘Z’ line in the middle of every ‘I’ band. ‘A’ band (Anisotropic / dark band): the central band; contains the thick (myosin) filaments together with the overlapping ends of the thin filaments. ‘H’ zone: the central part of the ‘A’ band where only thick filaments are present (not overlapped by thin filaments). ‘M’ line: the thin fibrous membrane at the centre of the ‘A’ band (and of the H-zone) that holds the thick filaments together. Sequence to draw (left to right): Z line — half I band — A band (with central H zone bisected by the M line) — half I band — Z line. Show thin filaments running from the Z lines inward and thick filaments lying in the A band.

2. Define sliding filament theory of muscle contraction.

ANSWER The sliding filament theory states that the contraction of a muscle fibre takes place by the sliding of the thin (actin) filaments over the thick (myosin) filaments, which are pulled towards the centre of the ‘A’ band. During this sliding the thin filaments and the attached ‘Z’ lines are drawn inwards, so the sarcomere shortens (contraction). The length of the ‘A’ band remains unchanged, while the ‘I’ bands and the ‘H’ zone get reduced. The filaments themselves do not change length — only their degree of overlap increases.

3. Describe the important steps in muscle contraction.

ANSWER 1. Neural signal: Contraction is initiated by a signal from the central nervous system carried by a motor neuron. The junction between the motor neuron and the sarcolemma (the neuromuscular junction or motor-end plate) releases the neurotransmitter acetylcholine. 2. Action potential: Acetylcholine generates an action potential in the sarcolemma, which spreads through the muscle fibre. 3. Calcium release: The action potential causes the release of Ca++ from the sarcoplasmic reticulum into the sarcoplasm. 4. Unmasking of active sites: The increased Ca++ binds to a subunit of troponin on the actin filament, removing the masking of the active (myosin-binding) sites on actin. 5. Cross-bridge formation: Using energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin to form a cross bridge. 6. Power stroke (sliding): The cross bridge pulls the attached actin filaments towards the centre of the ‘A’ band; the ‘Z’ lines are pulled inwards, shortening the sarcomere — the ‘I’ bands shorten while the ‘A’ band length is retained. 7. Cross-bridge breaking: The myosin head releases ADP and Pi and returns to its relaxed state; a new ATP binds and the cross bridge breaks. The ATP is again hydrolysed, and the cycle of cross-bridge formation and breakage repeats, causing further sliding. 8. Relaxation: The process continues until Ca++ is pumped back into the sarcoplasmic cisternae, re-masking the actin active sites. The ‘Z’ lines return to their original positions, i.e. the muscle relaxes.

4. Write true or false. If false change the statement so that it is true.

(a) Actin is present in thin filament

(b) H-zone of striated muscle fibre represents both thick and thin filaments.

(c) Human skeleton has 206 bones.

(d) There are 11 pairs of ribs in man.

(e) Sternum is present on the ventral side of the body.

ANSWER (a) True. Actin makes up the thin filament. (b) False. Corrected: The H-zone of a striated muscle fibre represents only the thick filaments (the central part of the ‘A’ band not overlapped by thin filaments). (c) True. The human skeleton has 206 bones. (d) False. Corrected: There are 12 pairs of ribs in man. (e) True. The sternum is a flat bone present on the ventral midline of the thorax.

5. Write the difference between :

(a) Actin and Myosin

(b) Red and White muscles

(c) Pectoral and Pelvic girdle

ANSWER (a) Actin vs Myosin
ActinMyosin
Forms the thin filament.Forms the thick filament.
Made of two F-actins, with tropomyosin and troponin attached.Made of polymerised meromyosin monomers.
Present in the ‘I’ band (and overlaps into the ‘A’ band).Present only in the ‘A’ band.
Lacks ATPase; carries the active sites for myosin.Head bears ATPase activity and binding sites for ATP and actin.
(b) Red vs White muscles
Red fibresWhite fibres
High myoglobin content, hence reddish.Low myoglobin content, hence pale/whitish.
Plenty of mitochondria.Few mitochondria.
Less sarcoplasmic reticulum.Abundant sarcoplasmic reticulum.
Aerobic — rely on oxygen for ATP production.Anaerobic — depend on anaerobic process for energy.
(c) Pectoral vs Pelvic girdle
Pectoral girdlePelvic girdle
Articulates the upper limbs (arms) with the axial skeleton.Articulates the lower limbs (legs) with the axial skeleton.
Each half consists of a clavicle and a scapula.Consists of two coxal bones, each formed by fusion of ilium, ischium and pubis.
Has the glenoid cavity that articulates with the head of the humerus.Has the acetabulum that articulates with the head of the femur.
The two halves are not fused ventrally.The two halves meet ventrally to form the pubic symphysis.

6. Match Column I with Column II :

Column IColumn II
(a) Smooth muscle(i) Myoglobin
(b) Tropomyosin(ii) Thin filament
(c) Red muscle(iii) Sutures
(d) Skull(iv) Involuntary
ANSWER (a) Smooth muscle → (iv) Involuntary (b) Tropomyosin → (ii) Thin filament (c) Red muscle → (i) Myoglobin (d) Skull → (iii) Sutures

7. What are the different types of movements exhibited by the cells of human body?

ANSWER The cells of the human body exhibit three main types of movement: 1. Amoeboid movement: shown by specialised cells like macrophages and leucocytes in blood; it is brought about by pseudopodia formed by the streaming of protoplasm (as in Amoeba) and involves cytoskeletal elements such as microfilaments. 2. Ciliary movement: occurs in internal tubular organs lined by ciliated epithelium; the coordinated beating of cilia in the trachea helps remove dust and foreign particles, and ciliary movement also helps pass ova through the female reproductive tract. 3. Muscular movement: movement of limbs, jaws, tongue, etc., is brought about by the contractile property of muscle tissue; it is used for locomotion and other movements.

8. How do you distinguish between a skeletal muscle and a cardiac muscle?

ANSWER
Skeletal muscleCardiac muscle
Closely associated with skeletal components of the body.Forms the muscle of the heart.
Striated; cylindrical, unbranched fibres.Striated; cells assemble in a branching pattern.
Voluntary — under direct control of the nervous system.Involuntary — the nervous system does not control its activity directly.
Primarily involved in locomotion and changes of body posture.Involved in the continuous, rhythmic pumping of blood by the heart.

9. Name the type of joint between the following:-

(a) atlas/axis

(b) carpal/metacarpal of thumb

(c) between phalanges

(d) femur/acetabulum

(e) between cranial bones

(f) between pubic bones in the pelvic girdle

ANSWER (a) atlas/axis → Pivot joint (synovial) (b) carpal/metacarpal of thumb → Saddle joint (synovial) (c) between phalanges → Hinge joint (synovial) (d) femur/acetabulum → Ball and socket joint (synovial) (e) between cranial bones → Fibrous joint (sutures — immovable) (f) between pubic bones in the pelvic girdle → Cartilaginous joint (pubic symphysis)

10. Fill in the blank spaces:

(a) All mammals (except a few) have __________ cervical vertebra.

(b) The number of phalanges in each limb of human is __________

(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________.

(d) In a muscle fibre Ca++ is stored in __________

(e) __________ and __________ pairs of ribs are called floating ribs.

(f) The human cranium is made of __________ bones.

ANSWER (a) seven (7) cervical vertebrae. (b) 14 phalanges in each limb. (c) tropomyosin and troponin. (d) the sarcoplasmic reticulum. (e) the 11th and 12th pairs of ribs are called floating ribs. (f) 8 bones.

Extra Practice Questions

Short Answer Type Questions

Q1. Name the four properties of muscle tissue.

ANSWERExcitability, contractility, extensibility and elasticity. Muscle is of mesodermal origin and forms about 40–50% of an adult’s body weight.

Q2. What is a sarcomere and why is it called the functional unit of contraction?

ANSWERA sarcomere is the part of a myofibril between two successive ‘Z’ lines. It is the smallest repeating segment that contains all the components (thick and thin filaments) needed for contraction, so it is the structural and functional unit of muscle contraction.

Q3. Differentiate between the axial and the appendicular skeleton.

ANSWERThe axial skeleton comprises 80 bones along the main body axis — the skull, vertebral column, sternum and ribs. The appendicular skeleton comprises 126 bones — the limb bones along with the pectoral and pelvic girdles. Together they make up the 206 bones of the human skeleton.

Q4. Why are red muscle fibres also called aerobic muscles?

ANSWERRed fibres are rich in the oxygen-storing pigment myoglobin and contain plenty of mitochondria. They use the stored oxygen for ATP production through aerobic respiration, and hence are called aerobic muscles.

Q5. What causes muscle fatigue?

ANSWERRepeated, prolonged activation of muscles leads to anaerobic breakdown of glycogen and accumulation of lactic acid in them. This build-up of lactic acid causes the condition of muscle fatigue.

Long Answer Type Questions

Q1. Classify the three types of muscles on the basis of location, appearance and regulation, giving one function of each.

ANSWERSkeletal muscles are located close to the skeletal components; they are striated (striped) under the microscope and are voluntary, being under the control of the nervous system. They are primarily involved in locomotion and changes of body posture. Visceral (smooth) muscles are located in the inner walls of hollow visceral organs such as the alimentary canal and reproductive tract; they are non-striated (smooth) in appearance and involuntary. They help in the transport of food through the digestive tract and gametes through the genital tract. Cardiac muscles are the muscles of the heart, with cells assembled in a branching pattern; they are striated in appearance but involuntary in nature, and carry out the continuous rhythmic pumping of blood. Thus muscles differ in location, appearance and the nature of regulation of their activity.

Q2. Describe the structure of the human vertebral column and rib cage.

ANSWERThe vertebral column is dorsally placed and formed of 26 serially arranged vertebrae, extending from the base of the skull to form the main framework of the trunk. Each vertebra has a central neural canal through which the spinal cord passes. The column is differentiated, from the skull downwards, into cervical (7), thoracic (12), lumbar (5), sacral (1, fused) and coccygeal (1, fused) regions. The first vertebra, the atlas, articulates with the occipital condyles. The column protects the spinal cord, supports the head and gives attachment to the ribs and back muscles. The rib cage consists of 12 pairs of ribs; each rib is a thin flat bone, bicephalic, connected dorsally to a thoracic vertebra. The first seven pairs (true ribs) join the sternum directly via hyaline cartilage; the 8th, 9th and 10th pairs (vertebrochondral / false ribs) join the seventh rib; and the 11th and 12th pairs (floating ribs) are not connected ventrally. The thoracic vertebrae, ribs and sternum together form the rib cage.

Q3. Explain the three structural types of joints with suitable examples and their degree of movement.

ANSWERJoints are points of contact between bones, or between bone and cartilage, and act as fulcrums for the force generated by muscles. Fibrous joints do not allow any movement; the flat skull bones fuse end to end by dense fibrous connective tissue forming sutures, e.g. joints between cranial bones. Cartilaginous joints join bones with the help of cartilage and permit only limited movement, e.g. the joints between adjacent vertebrae. Synovial joints have a fluid-filled synovial cavity between the articulating surfaces and allow considerable, free movement; they are vital for locomotion and include the ball-and-socket joint (between humerus and pectoral girdle), hinge joint (knee), pivot joint (between atlas and axis), gliding joint (between carpals) and saddle joint (between carpal and metacarpal of the thumb). Thus movability ranges from none (fibrous) to limited (cartilaginous) to free (synovial).

MCQs

1. The functional unit of contraction in a skeletal muscle is the:

(a) myofibril    (b) sarcomere    (c) sarcolemma    (d) fascicle

2. Calcium ions required for muscle contraction are stored in the:

(a) sarcolemma    (b) mitochondria    (c) sarcoplasmic reticulum    (d) Golgi body

3. During muscle contraction, which band remains unchanged in length?

(a) I band    (b) A band    (c) H zone    (d) Z line gap

4. The neurotransmitter released at the neuromuscular junction is:

(a) adrenaline    (b) acetylcholine    (c) dopamine    (d) serotonin

5. The total number of bones in the human skeleton is:

(a) 200    (b) 206    (c) 212    (d) 226

6. Which of the following is an example of a pivot joint?

(a) knee joint    (b) between atlas and axis    (c) between carpals    (d) shoulder joint

7. The cranium of the human skull is made up of how many bones?

(a) 6    (b) 8    (c) 14    (d) 22

8. Which pairs of ribs are called floating ribs?

(a) 1st and 2nd    (b) 8th, 9th and 10th    (c) 11th and 12th    (d) 1st to 7th

9. The disorder caused by an autoimmune attack on the neuromuscular junction is:

(a) gout    (b) osteoporosis    (c) tetany    (d) myasthenia gravis

10. The thin filament of a myofibril is made of F-actin together with:

(a) myosin and meromyosin    (b) tropomyosin and troponin    (c) myoglobin and ATPase    (d) actin and myosin

Answer key: 1-(b), 2-(c), 3-(b), 4-(b), 5-(b), 6-(b), 7-(b), 8-(c), 9-(d), 10-(b).

Assertion–Reason Questions

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: During contraction the I band of the sarcomere shortens.

Reason: The thin filaments slide over the thick filaments and the Z lines are pulled inwards.

A-R 2. Assertion: Cardiac muscles are striated but involuntary.

Reason: The nervous system does not directly control the activity of cardiac muscle.

A-R 3. Assertion: Red muscle fibres can sustain prolonged activity.

Reason: Red fibres are rich in myoglobin and mitochondria and produce ATP aerobically.

A-R 4. Assertion: Fibrous joints allow free movement of bones.

Reason: Synovial joints have a fluid-filled cavity between the articulating bones.

A-R 5. Assertion: Tetany is characterised by rapid muscle spasms.

Reason: Tetany is caused by a low level of Ca++ in the body fluid.

Answer key: 1-(A), 2-(A), 3-(A), 4-(D), 5-(A).

Common Mistakes to Avoid

Watch out for these

  • Saying the A band shortens during contraction — it does not; only the I band and H zone shorten.
  • Confusing thick and thin filaments — actin is thin (I band), myosin is thick (A band).
  • Writing 11 pairs of ribs — humans have 12 pairs.
  • Mixing up girdle cavities — the glenoid cavity (pectoral) takes the humerus; the acetabulum (pelvic) takes the femur.
  • Calling cardiac muscle voluntary — it is striated but involuntary.
  • Stating Ca++ is stored in mitochondria — it is stored in the sarcoplasmic reticulum.
  • Forgetting that cranium = 8 bones while the whole skull = 22 bones (8 cranial + 14 facial).

Exam tips for this chapter

Memorise the sarcomere band sequence (Z — I — A with H zone & M line — I — Z) and exactly which regions shorten during contraction. Learn the eight steps of contraction in order, highlighting the roles of acetylcholine, Ca++, troponin, ATP and cross bridges. Keep bone numbers ready: 206 total, 80 axial + 126 appendicular, 22 skull (8 cranial + 14 facial), 26 vertebrae, 12 rib pairs, 14 phalanges per limb. For joint questions, link each named example to its joint type. Write difference questions as neat two-column tables for full marks.

Frequently Asked Questions

What is Class 11 Biology Chapter 17 about?

Chapter 17, Locomotion and Movement, deals with the types of movement in human cells (amoeboid, ciliary, muscular), the three muscle types, the structure of skeletal muscle and the sarcomere, the contractile proteins actin and myosin, the sliding filament theory of contraction, the axial and appendicular skeleton, the types of joints, and disorders of the muscular and skeletal systems.

What is the difference between movement and locomotion?

Movement is any change shown by a part of the body, while locomotion is a voluntary movement that causes the animal to change its place or location. Therefore all locomotions are movements, but all movements are not locomotion.

What is the sliding filament theory in simple terms?

It states that a muscle fibre contracts when the thin (actin) filaments slide over the thick (myosin) filaments, pulling the Z lines inward and shortening the sarcomere, while the A band length stays the same.

Are these Class 11 Biology Chapter 17 solutions free?

Yes. All solutions are free and follow the official NCERT Biology textbook for session 2026–27, with every exercise question reproduced and answered.

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