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LESSON B13 · EXPLAINER
Movement, the Skeleton and Locomotion
A sunflower turns toward the sun. You turn your head. Both are movement — but they’re not the same.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Explore in 3D
Antagonistic muscles in 3D
Bend the elbow and watch the biceps and triceps work as a pair.
Step 2 · Read
Key notes
Copy these into your notebook in your own words — that is how they stick.
Movement
Change in position of the whole or part of an organism.
Plant movement
Growth movements (tropisms): slow, irreversible, part of the plant.
Animal movement
Muscle contraction on a skeleton: fast, reversible, whole body (locomotion).
Skeleton functions
Support, protection, movement, blood cell production, mineral storage, breathing.
Ligament vs tendon
Ligament: bone to bone (slightly elastic). Tendon: muscle to bone (inelastic).
Antagonistic muscles
Biceps (flexor) raises forearm; triceps (extensor) lowers it; elbow hinge joint is the pivot.
“Plants: irreversible, growth or part movement” — this is the correct P1 description.
When describing forearm movement, say which muscle CONTRACTS and which RELAXES, plus the joint and bones.
For skeleton functions, name the bone for each function — the mark scheme pairs them.
Step 2 · Learn from examples
Worked examples & study resources
The kind of support a teacher gives after the lesson: worked examples to attempt first, a board illustration, key terms, common misconceptions and memory aids.
Worked example 1
Raising and lowering the forearm
Explain how the biceps and triceps raise and lower the forearm.
Try it in your notebook first, then reveal the solution one step at a time.
Muscles can only pull (contract); they cannot push. So two muscles are needed, working as an antagonistic pair.
To raise the forearm: the biceps contracts and pulls on the radius through its tendon, while the triceps relaxes. The arm bends at the elbow (a hinge joint).
To lower the forearm: the triceps contracts and pulls on the ulna, while the biceps relaxes. The arm straightens.
Tendons are strong and inelastic, so the full pull of the muscle is passed to the bone.
Answer. Raising: biceps contracts, triceps relaxes. Lowering: triceps contracts, biceps relaxes. They are antagonistic because they produce opposite movements at the elbow (hinge) joint.
Examiner’s tip. Always state BOTH muscles and what each is doing (contracting or relaxing).
Worked example 2
Ball-and-socket and hinge joints
Compare the shoulder joint with the elbow joint, and explain the roles of cartilage, synovial fluid and ligaments.
Try it in your notebook first, then reveal the solution one step at a time.
The shoulder (and hip) is a ball-and-socket joint: the rounded head of the humerus fits into a cup, allowing movement in all directions and rotation.
The elbow (and knee) is a hinge joint: movement in one plane only, like a door.
Cartilage covers the ends of the bones — smooth, so it reduces friction, and it absorbs shock.
Synovial fluid lubricates the joint, reducing friction. Ligaments hold the bones together, keeping the joint stable while allowing movement.
Answer. Shoulder: ball-and-socket (movement in all planes, rotation). Elbow: hinge (one plane). Cartilage reduces friction and absorbs shock; synovial fluid lubricates; ligaments join bone to bone and hold the joint together.
Examiner’s tip. Ligaments join bone to bone; tendons join muscle to bone. Mixing them up is a very common lost mark.
On the board · Functions of the human skeleton
Function
Example
Support
The vertebral column holds the body upright; gives shape
Protection
Skull protects the brain; ribs protect the heart and lungs
Movement
Bones act as levers; muscles are attached to them by tendons
Making blood cells
Red bone marrow in long bones, ribs and sternum
Mineral store
Calcium and phosphate are stored in bone
Five functions; give an example for each — examples turn a 1-mark answer into a 2-mark answer.
Key terms
Joint
A place where two bones meet.
Ligament
Tough, slightly elastic tissue joining bone to bone.
Tendon
Strong, inelastic tissue joining muscle to bone.
Cartilage
Smooth tissue covering bone ends; reduces friction and absorbs shock.
Synovial fluid
Liquid that lubricates movable joints.
Antagonistic muscles
A pair of muscles producing opposite movements.
Locomotion
Movement of the whole organism from place to place.
Common misconceptions
✗ Muscles can push bones as well as pull them.✓ Muscles only pull. A second muscle is needed to move the bone back.
✗ Tendons and ligaments are the same thing.✓ Tendons join muscle to bone; ligaments join bone to bone.
✗ Bones are dead, dry structures.✓ Living bone has cells, blood vessels and nerves, and it grows and repairs itself.
Memory aid
Ligaments Link bones; Tendons Tie muscle To bone.
Real-life link
Strong bones need calcium (milk, fish with bones, green vegetables) and vitamin D, which the skin makes in sunlight. Weight-bearing exercise also strengthens bones and reduces the risk of osteoporosis later in life.
Try this
Rest one hand on the front of your upper arm and lift a full bag with the other hand, bending the elbow. Feel the biceps tighten. Now push down on a table — which muscle tightens now?
Play & practise
Games
4 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness.
Step 3 · Practise
Paper 1 practice — multiple choice
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better.
Step 4 · Apply
Paper 2 practice — structured questions
Write full answers, then reveal the mark scheme and tick the points you earned (19 marks in total). Your answers are saved on this device.
Based on CSEC P2 January 2022, Question 3
Question 1 [11 marks]
Movement in plants and animals.
(a) Define the term “movement”. [1]
MARK SCHEME — (a) (max 1)
(b) Outline TWO distinctions between movement in plants and animals. [4]
MARK SCHEME — (b) (max 4)
(c) List THREE major functions of the skeleton (other than locomotion) and name ONE bone responsible for each. [6]
MARK SCHEME — (c) (max 6)
Based on CSEC P2 January 2022 Q3(d) and SO B6.4
Question 2 [8 marks]
Corals are completely immobile.
(a) Outline TWO disadvantages of complete immobility and ONE consequence of each. [4]
MARK SCHEME — (a) (max 4)
(b) Describe how the forearm is raised. [4]
MARK SCHEME — (b) (max 4)
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Sources
Where this topic appears in CSEC papers
Find these in your own past-paper booklets for extra timed practice. The practice above is adapted from them.