Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
The Skeleton
The human body has a framework of bones called the skeleton. Functions: 1. Gives shape to the body. 2. Protects internal organs (skull → brain; ribs → heart and lungs). 3. Helps in movement along with muscles.
Bone facts:
- An adult human has 206 bones.
- Bones are hard and cannot bend.
- Bones meet at joints.
Cartilage
- Soft, flexible material found between bones at joints.
- Acts as a cushion and prevents wear and tear.
- Found at: tips of ears, nose, between backbones (vertebrae).
Joints
Joints are places where two or more bones meet.
Types of Joints
| Joint | Movement | Example |
|---|---|---|
| Ball and Socket | Movement in all directions | Shoulder, hip |
| Pivotal Joint | Rotation only | Neck (head turns/nods) |
| Hinge Joint | Back and forth only (like a door hinge) | Knee, elbow, fingers |
| Fixed Joint | No movement | Skull (cranium) bones |
Muscles
- Bones cannot move on their own — muscles pull them.
- Muscles work in pairs (one muscle contracts, the other relaxes).
- When you bend your arm: bicep contracts (shortens), tricep relaxes.
- When you straighten your arm: tricep contracts, bicep relaxes.
Muscles can only pull, not push.
Movement in Different Animals
Earthworm
- No bones or legs.
- Has circular and longitudinal muscles.
- Circular muscles contract → body becomes long and thin.
- Longitudinal muscles contract → body becomes short and fat.
- Tiny bristles (setae) grip the ground as it moves.
Snail
- Moves using a large muscular foot underneath its body.
- The foot muscles contract in waves.
- Snail secretes mucus to reduce friction.
- Movement is very slow.
Cockroach
- Has 3 pairs of legs (6 legs).
- Also has 2 pairs of wings.
- Walks, climbs, and flies.
- Hard outer skeleton (exoskeleton) — no internal bones.
Fish
- Moves by bending its body and tail fin sideways.
- Streamlined (boat-shaped) body helps reduce friction in water.
- Fins help balance, steer, and maintain position.
Bird
- Bones are hollow and lightweight — helps in flight.
- Strong chest muscles control wing movement.
- Wings are like arms — when wings flap down, bird is pushed up.
- Streamlined body reduces air resistance.
Comparison: Movement in Animals
| Animal | Organ Used | Special Feature |
|---|---|---|
| Earthworm | Muscles (circular, longitudinal) | Setae for grip |
| Snail | Muscular foot | Secretes mucus |
| Cockroach | Legs + wings | Exoskeleton, 6 legs |
| Fish | Body + tail + fins | Streamlined body |
| Bird | Wings + legs | Hollow bones, strong chest muscles |
Key Vocabulary
| Term | Meaning |
|---|---|
| Skeleton | Framework of bones |
| Joint | Where two bones meet |
| Cartilage | Flexible material cushioning bones |
| Ligament | Connects bone to bone at joint |
| Tendon | Connects muscle to bone |
| Exoskeleton | External hard covering (cockroach, crab) |
| Streamlined | Shape that reduces friction with water/air |
| Setae | Small bristles on earthworm that help grip |
Exam Tips
- The 4 types of joints table (with examples) is a very common 4-mark question.
- Muscles work in pairs — bicep/tricep example is the standard answer.
- For earthworm movement, mention both muscles (circular AND longitudinal) and the role of setae.
- Hollow bones in birds for lightweight is a standard 1-mark question.
- Cockroach has 6 legs (3 pairs), 4 wings (2 pairs) — both may be asked.
Frequently Asked Questions
Ball and socket joint — shoulder, hip (movement in all directions). Pivotal joint — neck (nodding/turning head). Hinge joint — knee, elbow, fingers (back-and-forth movement only). Fixed joint — skull bones (no movement).