Biology · Lesson 12

Support, skeleton & movement

JAMBWAECNECO

What the syllabus asks

JAMB: Support and movement in animals and plants

WAEC: Supporting systems in animals and plants: types of skeleton (hydrostatic, exo- and endoskeleton), functions of the skeleton, the mammalian skeleton (axial and appendicular), vertebrae, bones of limbs and girdles, joints, muscles and movement, supporting tissues in plants

NECO: Supporting systems in animals and plants: types of skeleton (hydrostatic, exo- and endoskeleton), functions of the skeleton, the mammalian skeleton (axial and appendicular), vertebrae, bones of limbs and girdles, joints, muscles and movement, supporting tissues in plants

What you will learn

Describe and give examples of the three types of skeleton.
State the functions of the skeleton.
Name the main bones of the axial and appendicular skeleton.
Describe and compare the regions of the vertebral column.
Describe the types of joints and the structure of a synovial joint.
Explain how antagonistic muscles produce movement, and describe support in plants.

Key points

Skeleton functions: support, shape, protection, movement, blood cell formation, mineral storage.
Hydrostatic (earthworm), exoskeleton (chitin, must moult), endoskeleton (bone and cartilage, grows).
Bone: calcium phosphate (hard) + collagen (flexible); cartilage cushions joints.
Axial: skull, 33 vertebrae, 12 pairs of ribs, sternum; appendicular: girdles and limbs.
Atlas (no centrum, nodding), axis (odontoid peg, rotation), cervical (vertebrarterial canals), thoracic (rib facets), lumbar (large centrum), sacrum (fused, pelvis).
Joints: immovable, slightly movable, synovial (ball-and-socket, hinge, pivot, gliding).
Synovial joint: cartilage, synovial membrane and fluid, capsule, ligaments; tendons join muscle to bone.
Muscles pull in antagonistic pairs (biceps flexor, triceps extensor); plants are supported by turgor, collenchyma, sclerenchyma and xylem.

Start here: Why organisms need support

Imagine a yam vine without a stake, or a human with no bones: both would collapse. Living things need support to keep their shape, hold organs in place, raise leaves towards light, and provide firm points for muscles to pull on during movement.

Small aquatic organisms are supported by water itself. Large land organisms face gravity without that help, so they need stronger supporting systems. In animals the main supporting system is the skeleton.

Functions of the skeleton
1. Support: holds up the body and gives it shape.
2. Protection: skull protects the brain; ribs protect heart and lungs; vertebrae protect the spinal cord.
3. Movement: bones act as levers for muscles.
4. Blood cell formation: red bone marrow makes red cells, white cells and platelets.
5. Mineral storage: calcium and phosphate.
6. Attachment for muscles.

Worked example 12.1

State the protective function of three named parts of the human skeleton.

Cranium (skull) — protects the brain.
Rib cage — protects the heart and lungs.
Vertebral column — protects the spinal cord.

Skull–brain; ribs–heart/lungs; vertebrae–spinal cord

⚠️ Common mistake: forgetting blood-cell formation and mineral storage when asked for "functions of the skeleton". WAEC often expects four or more.

Try it yourself. Where are red blood cells made in an adult?

Show solution

In the red bone marrow, especially of flat bones (sternum, ribs, pelvis, skull) and ends of long bones.

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Practice questions

1. The joint at the shoulder is a

ball and socket joint
hinge joint
pivot joint
gliding joint

Show answer

A: ball and socket joint
Ball and socket joints (shoulder, hip) allow movement in all directions.

2. Tissue connecting muscle to bone is called

ligament
cartilage
synovial membrane
tendon

Show answer

D: tendon
Tendon: muscle to bone. Ligament: bone to bone.

3. The skeleton of an insect is an

hydrostatic skeleton
endoskeleton of cartilage
exoskeleton made of chitin
endoskeleton of bone

Show answer

C: exoskeleton made of chitin
It is outside the body.

4. The earthworm has a

cartilaginous skeleton
hydrostatic skeleton
bony endoskeleton
chitinous exoskeleton

Show answer

B: hydrostatic skeleton
Fluid under pressure.

5. The joint at the elbow is a

hinge joint
ball-and-socket joint
pivot joint
gliding joint

Show answer

A: hinge joint
It allows movement in one plane.

Key words

Skeleton: A rigid or fluid framework that supports the body.
Hydrostatic skeleton: Support from fluid pressed by surrounding muscles.
Exoskeleton: A hard outer covering, e.g. of chitin in arthropods.
Endoskeleton: An internal skeleton of bone and cartilage.
Ecdysis (moulting): Shedding of the exoskeleton to allow growth.
Vertebra: One of the bones of the backbone.
Centrum: The solid body of a vertebra.
Neural canal: The hole in a vertebra through which the spinal cord passes.
Girdle: Bones attaching limbs to the axial skeleton (pectoral and pelvic).
Joint: A point where two or more bones meet.
Synovial joint: A freely movable joint with a fluid-filled cavity.
Ligament: Tough, slightly elastic tissue joining bone to bone.

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