NCERT NCERT Solutions Class 11 Biology Chapter 17 Locomotion and Movement

The class 11 biology NCERT solutions chapter 17 Locomotion and Movement cover every back-exercise question, according to the latest 2026-27 CBSE syllabus, and help students prepare for the CBSE Boards, NEET and CUET. Each answer is worked step by step, from the three types of cell movement and the build of a sarcomere, through the sliding filament theory of muscle contraction, to the 206 bones of the human skeleton and the joints that let them move.

This chapter sits in the coordination half of Class 11 Biology, and the muscle and bone vocabulary students learn here is tested again in the neural and chemical control chapters that follow.

• CBSE Weightage: 3 to 4 marks, part of the Human Physiology unit that carries the largest share of the Class 11 paper.
• Topics covered: types of movement, the three muscle types, the sarcomere and its bands, contractile proteins, the sliding filament theory, red and white fibres, the skeletal system, and the classification of joints.
• Exercise count: 10 back-exercise questions, a mix of diagram-drawing, describe, distinguish, match, true-or-false and fill-in-the-blank tasks.

These class 11 biology NCERT solutions chapter 17 Locomotion and Movement are curated by subject experts, based on the 2026-27 NCERT textbook, and checked against the last five years of CBSE Board and NEET papers.

Why Locomotion and Movement Matters and What the Chapter Covers

Every deliberate action, from lifting a pen to running for a bus, is movement, and movement that carries the whole body from one place to another is locomotion. NCERT makes the point that all locomotion is movement but not all movement is locomotion, and that locomotion needs the coordinated activity of the muscular, skeletal and neural systems working together. This chapter builds the language of that machinery, from a single contracting filament to the entire framework of bones.

• Everyday role: muscles moving against bones at joints are what let students walk, write, chew and even keep an upright posture.
• Core skill: tracing a contraction from a nerve signal, through calcium release, to the sliding of filaments that shortens a muscle.
• Why it matters for NEET: the sarcomere, the sliding filament theory, the bone count and the joint types are among the most frequently tested facts in the Human Physiology unit.

Almost every question in this chapter comes back to one idea: filaments that slide past each other to shorten a muscle, and a bony frame that turns that pull into motion. Students who understand that single mechanism can answer the sarcomere, contraction and muscle-type questions from the same base. The class 11 biology NCERT solutions chapter 17 Locomotion and Movement below follow the same order as the NCERT textbook so students can check their working line by line.

Types of Movement and the Three Muscle Types

NCERT opens the chapter by naming three types of movement shown by the cells of the human body: amoeboid, ciliary and muscular. Amoeboid movement uses pseudopodia formed by the streaming of protoplasm, as in the macrophages and leucocytes of blood. Ciliary movement occurs in the internal tubular organs lined by ciliated epithelium, so the trachea clears dust and the oviduct moves the ovum. Muscular movement uses the contractile property of muscle cells and moves the limbs, jaws and tongue.

Cardiac muscle is striated, so striation alone never separates it from skeletal muscle: the true separators are location, regulation and the branching pattern of cardiac cells. Muscle makes up 40 to 50 per cent of adult body weight and is mesodermal in origin. See Exercise Q7 and Q8 for the full answers on cell movements and on distinguishing skeletal from cardiac muscle.

The Sarcomere and the Structure of a Muscle Fibre

A muscle fibre is packed with parallel myofibrils, and the functional unit of contraction inside each is the sarcomere, the portion of the myofibril between two successive 'Z' lines. It is built from two proteins arranged as parallel rods: thin actin filaments attached to the 'Z' lines and thick myosin filaments lying in the centre. Every band that students must label in Exercise Q1 is simply a statement about which filaments are present there.

The thin filament is made of two 'F' (filamentous) actins helically wound together, each a polymer of globular 'G' actins, with tropomyosin running along them and troponin distributed at regular intervals on the tropomyosin. The thick filament is a polymer of meromyosins, each with a globular head and short arm (heavy meromyosin) and a tail (light meromyosin), and the head carries an ATPase and the binding site for actin. The sarcomere runs from one 'Z' line to the next, so it contains one full 'A' band and two half 'I' bands. Drawing a whole 'I' band inside the 'Z' lines is the commonest error in the diagram question.

Sliding Filament Theory and the Steps of Muscle Contraction

The sliding filament theory states that contraction of a muscle fibre takes place by the sliding of the thin filaments over the thick filaments. The word sliding does all the work: neither filament shortens, they change their positions relative to each other. Myosin cross bridges pull the actin towards the centre of the 'A' band, dragging the 'Z' lines inwards so the sarcomere shortens. Because the filaments keep their lengths, the 'I' band and 'H' zone shorten while the 'A' band stays constant, and that constant 'A' band is the proof that myosin did not shrink.

• The signal: the central nervous system sends an impulse along a motor neuron to the neuromuscular junction, where acetylcholine generates an action potential in the sarcolemma.
• The trigger: the action potential releases Ca⁺⁺ from the sarcoplasmic reticulum; the calcium binds troponin and unmasks the active sites on actin.
• The pull: the ATP-energised myosin head binds actin to form a cross bridge, rotates to slide the actin inward, then a fresh ATP breaks the cross bridge so the cycle repeats.
• Relaxation: Ca⁺⁺ is pumped back into the sarcoplasmic reticulum, the active sites are masked again, and the 'Z' lines return to their original position.

ATP is spent at two separate points: its hydrolysis energises the myosin head to bind and pull, and a fresh ATP binding is what breaks the cross bridge, while pumping calcium back costs still more. That is why a working muscle burns so much energy. Repeated activation builds up lactic acid from the anaerobic breakdown of glycogen, which is what causes fatigue. The full step-by-step chain is worked out in Exercise Q2 and Q3.

Red and White Muscle Fibres, Actin and Myosin

Skeletal muscle fibres are sorted into two kinds by their content of myoglobin, a red oxygen-storing pigment. Red fibres have a high myoglobin content and look reddish, while white fibres have very little and look pale. This single difference in a pigment sets up a whole chain of differences in how the two fibres make and spend energy, which is exactly what Exercise Q5 tests alongside the actin and myosin contrast.

The actin and myosin contrast runs the other way, as a comparison of two filaments. Actin is the thin filament, forms the light 'I' band, and carries the active sites that troponin masks. Myosin is the thick filament, forms the dark 'A' band, and its globular head is an active ATPase that pulls the actin. Colour is not the difference between red and white fibres; colour is the visible sign of the difference, which is really about oxygen storage and how ATP is made. Red fibres store oxygen in myoglobin and have the mitochondria to use it aerobically, so they keep going, while white fibres fall back on the anaerobic breakdown of glycogen and tire fast.

The Skeletal System: Bones, Ribs and the Skull

The human skeletal system is made up of 206 bones and a few cartilages, and it splits into the axial skeleton with 80 bones and the appendicular skeleton with 126 bones, so 80 plus 126 gives 206. The axial skeleton is the skull, vertebral column, sternum and ribs, while the appendicular skeleton is the limb bones and the two girdles. Several exact counts from this section are tested directly in Exercise Q4 and Q10.

• The skull: 22 bones in total, of which 8 form the cranium (the braincase) and 14 form the facial region; the cranium is not the same as the whole skull.
• The vertebral column: 26 vertebrae, of which 7 are cervical in almost all mammals, including human beings and the giraffe.
• The ribs: 12 pairs, with the first 7 pairs true ribs, the 8th to 10th false (vertebrochondral) ribs, and the 11th and 12th pairs floating ribs that are not connected ventrally.
• The limbs: each limb has 14 phalanges, and the sternum is a flat bone on the ventral midline of the thorax.

The chapter deliberately places similar numbers close together, so read the noun each figure is attached to: skull is 22 but cranium is 8, ribs are 12 pairs but only the last 2 pairs float. Reading which word the question uses before writing a number is the whole test in the fill-in-the-blank and true-or-false questions. The 11 versus 12 slip on ribs, and the cranium versus skull slip on bone counts, are the two errors that cost the most marks in this section.

Joints and Their Types

A joint is the point of contact between bones, and NCERT classifies joints into three structural forms by how much movement they allow. Fibrous joints allow no movement, cartilaginous joints allow limited movement, and synovial joints allow considerable movement because they have a fluid-filled synovial cavity. The naming question in Exercise Q9 works entirely from this three-way split, and most of its answers are synovial because synovial joints are the ones that help in locomotion.

To sort any joint, ask first how much it moves: none means fibrous, a little means cartilaginous, a lot means synovial. Then, if synovial, ask which way it moves: one plane is a hinge, rotation is a pivot, all planes is ball and socket. The pubic symphysis is the trap, because it contains fibrous cartilage, so students see the word fibrous and answer fibrous joint. Read the noun, not the adjective: the tissue joining the bones is cartilage, so the joint is cartilaginous. The skull sutures are the reverse case, joined by dense fibrous connective tissue and allowing no movement at all.

Locomotion and Movement Exercise-wise Breakdown

The NCERT back exercise has 10 questions, and they mix diagram drawing, describe-and-distinguish answers, matching, true-or-false and fill-in-the-blank tasks. The table below maps the question blocks to their topics so students can plan their practice by theme.

The chapter rewards precise wording, clean labelled diagrams and exact numbers rather than calculation. Learn the sarcomere bands as statements about which filaments are present, and fix the bone counts in blocks so the similar numbers stop being confusing. Every question in the class 11 biology NCERT solutions chapter 17 Locomotion and Movement PDF is solved with each step of reasoning shown, so students can compare their answers against the model working.

Common Mistakes Students Make in Locomotion and Movement

Most marks in this chapter are lost on small slips of wording and number, not on hard ideas. Each mistake below costs 1 to 2 marks, so watch for it at the exact step.

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