Body Movements

Why this chapter matters for UPSC: General-science questions on the human body start here: joint types and their examples, the number of bones and ribs, the difference between bone, cartilage, tendon and ligament, why a muscle can only pull. The second half, on how an earthworm, a fish or a bird moves, is the first lesson in adaptation, which biodiversity questions build on. In NCERT's rationalised 2023-24 edition this is Chapter 5, "Body Movements", with the text unchanged.

🧠 First Principles — Read This First

Sit absolutely still and you are still moving: blinking, breathing. NCERT separates two things. Parts of the body move while we stay in one place (writing, turning the head); and we also move from place to place (walking, running, jumping). Animals walk, run, fly, jump, creep, crawl, slither and swim. Why so many ways?

The chapter's answer has three parts.

1. Bones cannot bend, so we can bend or move only where bones meet: at joints. Different joints allow different movements.
2. The bones form a framework, the skeleton, which gives the body its shape and protects the organs inside.
3. Muscles move the bones. A contracting muscle becomes shorter, stiffer and thicker and pulls the bone. A muscle can only pull, it cannot push, so muscles work in pairs.

Animals without bones move with muscles alone, helped by bristles, slime or a shell, and every animal's body suits the way it moves.

PART 1 — Quick Reference

Joints in NCERT Class VI

The lower jaw is movable; the upper jaw is not (NCERT asks: "Which of the skull bones are movable?"). The elbow cannot bend backwards because it is a hinge.

The Skeleton in NCERT Class VI

How Animals Move (NCERT Class VI)

PART 2 — Concepts & Narrative

Why Joints Matter

NCERT's simplest experiment: tie a scale along your arm with the elbow at the centre and try to bend it. You cannot. The arm is not one long bone; different bones are joined at the elbow, and we can bend only where bones meet.

NCERT models the joints with household things: a paper cylinder stuck into a ball sitting in a bowl rotates freely (ball and socket); a rolled cylinder inside a half-cylinder moves only one way (hinge). The shoulder rotates the arm through a complete circle; the neck's pivotal joint lets the head turn and nod but not swing round; the elbow allows only back-and-forth movement.

Bones, Cartilage, Tendons and Ligaments (NCERT Class IX)

How Muscles Move Bones

Make a fist, bend your arm and touch your shoulder: the upper arm bulges. That swelling is a muscle, contracted (shorter in length). When contracted, a muscle becomes shorter, stiffer and thicker and pulls the bone. Muscles work in pairs: when one contracts and pulls the bone one way, its partner relaxes; to move the bone back, the partner contracts while the first relaxes. A muscle can only pull; it cannot push, so two muscles must work together to move a bone. You can feel the same contraction in the legs when you walk or run.

The Human Skeleton in Numbers (NCERT Class XI)

Classes of Joints and Joint Disorders (NCERT Class XI)

Skeletons Outside the Human Body (NCERT Class XI)

• Cartilaginous fishes (class Chondrichthyes, e.g. sharks) have a cartilaginous endoskeleton. Having no air bladder, "they have to swim constantly to avoid sinking".
• Bony fishes (Osteichthyes) have an air bladder "which regulates buoyancy".
• Birds (Aves): forelimbs modified into wings; long bones hollow with air cavities (pneumatic); most fly, except flightless birds such as the ostrich.
• Annelids (e.g. the earthworm): longitudinal and circular muscles help in locomotion.
• Arthropods (e.g. the cockroach): body covered by a chitinous exoskeleton.

Aristotle's Questions

NCERT closes with the Greek philosopher Aristotle, who in his book Gait of Animals asked the chapter's questions: why animals have the body parts they do, how those parts help them move, why humans have two legs and cows four, why so many animals have an even number of legs, and why our legs bend differently from our arms.

PART 3 — UPSC Integration

The chapter links structure to function at every scale. Joints explain why some movements are possible and others not; tissues explain why bone is rigid, cartilage bends and tendons and ligaments hold things together; muscle types explain the difference between voluntary and involuntary movement. Bone health connects to nutrition (calcium, vitamin D), to women's health (oestrogen and osteoporosis) and to yoga. Animal locomotion is the base of adaptation: the streamlined fish, the pneumatic bones of birds and the bristles of the earthworm each fit a way of life. Prelims tests the facts, often as pairs (joint and example, muscle and location, rib type and number); Mains uses them for health and ageing questions.

Exam Strategy

Prelims traps:

• Ball and socket: shoulder, hip. Hinge: elbow, knee. Pivot: neck (atlas and axis). Gliding: between carpals. Saddle: thumb. Fixed/fibrous: skull sutures, upper jaw.
• Bones: about 305 at birth, 206 in adults (NCERT VI). Vertebrae: 33 (NCERT VI) vs 26 units (NCERT XI).
• Ribs: 12 pairs; true 7, false 3, floating 2.
• Tendon = muscle to bone; ligament = bone to bone.
• A muscle can only pull; muscles work in pairs.
• Striated = voluntary; smooth and cardiac = involuntary; cardiac cells are branched.
• Sharks have cartilage skeletons and no air bladder; bony fishes have an air bladder for buoyancy.
• Tetany = low calcium; gout = uric acid crystals; osteoporosis = lower bone mass (oestrogen decline).
• International Day of Yoga: 21 June.

Mains angle: Explain how bones, joints and muscles work together to produce movement, or why osteoporosis is common in older women and how exercise and diet help prevent it.

Practice Questions

Practice (UPSC-pattern, not past papers).

Prelims:

1. Which of the following joints allows movement in all directions?
   (a) Hinge joint
   (b) Ball and socket joint
   (c) Pivotal joint
   (d) Fixed joint

2. Consider the following pairs:
   

   1. Hinge joint : knee
      
   2. Pivot joint : between atlas and axis
      
   3. Gliding joint : between the carpals
      How many of the pairs given above are correctly matched?
      (a) Only one
      (b) Only two
      (c) All three
      (d) None

3. Tendons connect:
   (a) Bone to bone
   (b) Muscle to bone
   (c) Muscle to muscle
   (d) Cartilage to bone

4. Which of the following muscles are involuntary?
   

   1. Muscles of the alimentary canal
      
   2. Muscles of the iris
      
   3. Muscles of the heart
      Select the correct answer using the code below:
      (a) 1 only
      (b) 1 and 2 only
      (c) 2 and 3 only
      (d) 1, 2 and 3

5. Cartilaginous fishes such as sharks must keep swimming to avoid sinking because they lack:
   (a) Fins
   (b) Gills
   (c) An air bladder
   (d) Scales

6. The floating ribs in humans are:
   (a) The first seven pairs
   (b) The 8th, 9th and 10th pairs
   (c) The 11th and 12th pairs
   (d) All twelve pairs

7. Tetany, a condition of rapid muscle spasms, is caused by:
   (a) Accumulation of uric acid crystals
   (b) Low calcium in body fluid
   (c) An autoimmune attack on the neuromuscular junction
   (d) Decreased oestrogen

Mains (UPSC-pattern):

1. "A muscle can only pull, not push." Explain how the body still produces movement in both directions at a joint. (150 words)
2. Discuss the causes of osteoporosis and the role of diet and exercise in preventing it. (150 words)

📦 Revision Capsule

Sources

Sources

• NCERT, Science (Class VI), ch. 8 "Body Movements" (2020-21 print) and ch. 5 in the Rationalised 2023-24 edition: NCERT's book archives as captured by the Wayback Machine, 2020 copy and 2023-24 copy.
• NCERT, Science (Class IX), ch. 6 "Tissues", Reprint 2025-26: book archive.
• NCERT, Biology (Class XI), ch. 4 "Animal Kingdom" and ch. 17 "Locomotion and Movement", Reprint 2025-26: book archive.
• PIB (Ministry of Labour and Employment), Labour Codes effective, 21-Nov-2025; see also Urban Livelihoods.