BiologyICSE Class 9 · Skeleton: Movement and Locomotion

Human Skeleton, Joints and Movement (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

The adult human skeleton has 206 bones in two parts: the axial skeleton (skull, vertebral column, ribs and sternum) and the appendicular skeleton (limbs and the girdles). Joints may be immovable, slightly movable or freely movable (ball and socket, hinge, pivot, gliding), and movement happens when muscles contract and pull on bones across a joint.

Understand Human Skeleton, Joints and Movement

1. Functions of the skeleton. Support, protection of organs (skull for the brain, rib cage for heart and lungs), movement with muscles, making blood cells in bone marrow, and storing calcium and phosphorus.

2. Axial skeleton (about 80 bones).

*Skull*: 22 bones, made of the cranium (8 bones, protecting the brain) and the face (14 bones). Only the lower jaw (mandible) is movable.
*Vertebral column*: 33 vertebrae: 7 cervical (neck; first is atlas, second is axis), 12 thoracic, 5 lumbar, 5 fused sacral and 4 fused coccygeal. It protects the spinal cord and gives support.
*Rib cage*: all 12 pairs of ribs join the thoracic vertebrae at the back. In front, 7 pairs (true ribs) join the sternum, 3 pairs (false ribs) join it through cartilage, and 2 pairs (floating ribs) are free.

3. Appendicular skeleton (about 126 bones). *Pectoral girdle* (collar bone and shoulder blade) and *pelvic girdle* (hip bones), and the limb bones: humerus, radius and ulna, carpals, metacarpals, phalanges in the arm; femur, tibia and fibula, tarsals, metatarsals and phalanges in the leg.

4. Joints.

*Immovable (fixed)*: bones of the skull.
*Slightly movable*: between vertebrae (cartilage discs).
*Freely movable (synovial)*: a capsule with synovial fluid, cartilage and ligaments.
Ball and socket: shoulder, hip (movement in all directions).
Hinge: elbow, knee (one direction).
Pivot: between atlas and axis (rotation of the head).
Gliding: wrist, ankle (sliding).

5. Movement. Muscles are joined to bones by tendons and work in pairs (antagonistic): when the biceps contracts the forearm bends and the triceps relaxes; when the triceps contracts the arm straightens. Ligaments join bone to bone.

Human Skeleton, Joints and Movement: key facts

Skeleton: Total 206
Axial about 80
Appendicular about 126
Vertebrae: $C er v i c a l 7∣ T h or a c i c 12∣ Lu mba r 5∣ S a cr a l 5 f u se d ∣ C occy g e a l 4 f u se d ∣ T o t a l 33$
Joints: Fixed skull
Slightly movable vertebrae
Ball and socket shoulder, hip
Hinge elbow, knee
Pivot neck
Muscles: Biceps flex
Triceps extend
Tendon: muscle to bone
Ligament: bone to bone

Fixed	skull
Slightly movable	vertebrae
Ball and socket	shoulder, hip
Hinge	elbow, knee
Pivot	neck

Human Skeleton, Joints and Movement in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Lifting a bag

Suppose a student lifts a heavy bag with the forearm and feels the front of the upper arm tighten.

Explain the action.

Try it first, then show the solutionSolution

The biceps contracts and shortens, pulling the forearm up at the elbow hinge.
The triceps relaxes during this.

Answer: Biceps contracts and triceps relaxes at the hinge joint.

Memory hook: Bend: biceps, straighten: triceps.

Tricks to remember Human Skeleton, Joints and Movement

Short memory aids. Say each one aloud once, then use it on a question the same day.

7-12-5
Cervical 7, thoracic 12, lumbar 5.
Use it when: Vertebrae.
Ball all ways
Ball and socket allows movement in all directions.
Use it when: Joint types.

Human Skeleton, Joints and Movement: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Count · 2 marks · Short answerBoard level

How many vertebrae are in the cervical, thoracic and lumbar regions together? [2]

Try it first, then show the solutionSolution

7 + 12 + 5.
= 24.

Answer: 24 vertebrae.

Example 2: Joints · 4 marks · Short answerBoard level

Name the type of joint at (a) the shoulder, (b) the knee, (c) the neck between atlas and axis, (d) the skull sutures. [4]

Try it first, then show the solutionSolution

(a) Ball and socket.
(b) Hinge.
(c) Pivot.
(d) Fixed.

Answer: (a) Ball and socket (b) Hinge (c) Pivot (d) Fixed.

Example 3: Why not a hinge at the hip · 3 marks · Short answerHarder board level

Why is the hip a ball and socket joint while the knee is a hinge joint? Relate to the movements needed. [3]

Try it first, then show the solutionSolution

The hip needs movement in many directions (walking, kicking, rotation).
The knee mainly bends and straightens.
The shape of the joint fits the movement and gives stability.

Answer: The hip needs multidirectional movement; the knee needs one-direction bending.

Example 4: Antagonistic muscles · 3 marks · Short answerHarder board level

Explain why muscles work in pairs, using the arm. [3]

Try it first, then show the solutionSolution

A muscle can only pull when it contracts; it cannot push.
Biceps flexes the arm; triceps extends it.
One contracts while the other relaxes.

Answer: Muscles pull only, so an opposing muscle is needed to reverse the movement.

Example 5: Case: injury · 6 marks · Case-basedHOTS / competency

Case. A player twists his knee and tears the tissue joining the thigh bone to the shin bone. (i) Name the tissue. [1] (ii) Name the joint. [1] (iii) Which fluid is in the joint cavity and what does it do? [2] (iv) Why may the joint become unstable? [2]

Try it first, then show the solutionSolution

(i) Ligament.
(ii) Hinge (knee) joint.
(iii) Synovial fluid; it lubricates.
(iv) Ligaments hold bones together; if torn, the bones are not held firmly.

Answer: (i) Ligament (ii) Knee, hinge (iii) Synovial fluid, lubrication (iv) Torn ligament cannot hold the bones.

Where students lose marks in Human Skeleton, Joints and Movement

The slips examiners see most often, and what to write instead.

Mistake: Counting only 7 cervical and 5 lumbar
Students mix up the numbers of vertebrae in each region (7, 12, 5, 5, 4).
Do this: Memorise 7, 12, 5, 5, 4.
Usually costs: 1 mark.
Mistake: Calling the knee a ball and socket
Types are confused.
Do this: Knee is a hinge.
Usually costs: 1 mark.
Mistake: Writing that muscles push bones
Muscles only pull.
Do this: State that they contract and pull.
Usually costs: 1 mark.

Exam tips

Draw the arm with biceps and triceps in both positions.
Give the example with every joint type.
Show totals for vertebrae.
Mention synovial fluid for movable joints.

Practice questions on Human Skeleton, Joints and Movement

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The bone of the upper arm is the:
(a) femur
(b) humerus
(c) tibia
(d) ulna
Hint
Arm.
Answer
(b) humerus.
Q2 · 2 marks · Very short answerBoard level
Name the two girdles of the appendicular skeleton. [2]
Hint
Shoulder and hip.
Answer
Pectoral girdle and pelvic girdle.
Q3 · 2 marks · Very short answerBoard level
State one function each of bone marrow and the rib cage. [2]
Hint
Blood/protection.
Answer
Bone marrow makes blood cells; the rib cage protects the heart and lungs.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The sacral vertebrae are fused.
Reason (R): The fused sacrum forms a strong base joining the vertebral column to the pelvic girdle.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Strength.
Answer
(a).
Q5 · 4 marks · Long answerHarder board level
Distinguish between a tendon and a ligament and between an immovable and a freely movable joint. [4]
Hint
Two points for each pair of terms.
Answer
Tendon: muscle to bone, ligament: bone to bone; immovable joints allow no movement (skull), freely movable joints allow wide movement and have synovial fluid.
Q6 · 2 marks · Very short answerBoard level
Why are the bones of the skull fixed? [2]
Hint
Protection.
Answer
Fixed joints form a rigid case to protect the brain.
Q7 · 3 marks · Short answerHarder board level
A person can nod the head but not rotate it to look sideways. Which joint may be injured? Explain. [3]
Hint
Neck.
Answer
The pivot joint between atlas and axis, which allows rotation, while the joint between the skull and atlas allows nodding.
Q8 · 3 marks · Short answerHarder board level
Describe the structure of a synovial joint and explain why it moves smoothly. [3]
Hint
Fluid.
Answer
It has a capsule enclosing synovial fluid with cartilage-covered bone ends; the fluid and smooth cartilage reduce friction.
Q9 · 3 marks · Case-basedHOTS / competency
Case. A child eats very little calcium and has bent leg bones. (i) Name the vitamin often involved. [1] (ii) Suggest a diet change. [1] (iii) Explain why bones bend. [1]
Hint
D.
Answer
(i) Vitamin D. (ii) Milk and sunlight. (iii) Soft bones cannot bear the body weight.
Q10 · 3 marks · Long answerHOTS / competency
Case. A cyclist asks why the knee does not bend backwards and the elbow does not bend sideways. Explain using joint type and ligaments. [3]
Hint
Hinge.
Answer
Both are hinge joints whose bone shape and ligaments allow bending in one direction only and stop movement beyond it.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Total bones in an adult?Show answer
206.
2.Joint of the elbow?Show answer
Hinge.
3.First cervical vertebra?Show answer
Atlas.
4.Muscle that bends the arm?Show answer
Biceps.
5.Where is blood made?Show answer
Bone marrow.

Human Skeleton, Joints and Movement: frequently asked questions

Why do babies have more bones?

Some fuse as they grow.

Is the jaw fixed?

The lower jaw is movable.

What is a girdle?

A bone set that joins the limb to the axial skeleton.