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Support and movement: Class 10 Biology
Need for support and movement, the human skeleton and its functions, types of bones and joints, muscles and how they work in antagonistic pairs, and disorders of the skeletal system.
Key points
Support and movement are needed by living things. A skeleton gives shape and support, protects soft organs, and provides a place for muscles to attach. Animals move to find food, escape danger and find mates. Plants are supported by turgor pressure in cells and by tissues such as collenchyma and xylem, while most plants do not move from place to place.
Animals have three kinds of skeletons. A hydrostatic skeleton is a fluid filled body cavity, as in earthworms. An exoskeleton is a hard outer covering, as in insects and crabs. An endoskeleton is an internal skeleton of bone or cartilage, as in fish, birds and humans.
The human skeleton is an endoskeleton with 206 bones in an adult. It has two parts: the axial skeleton (skull, vertebral column, ribs and sternum) and the appendicular skeleton (the limbs and the girdles that join them to the axial skeleton).
Main parts of the human skeleton:
- Skull: protects the brain and holds the sense organs. The lower jaw is the only movable bone of the skull.
- Vertebral column: has 33 vertebrae in groups of cervical (7), thoracic (12), lumbar (5), sacral (5, fused) and caudal (4, fused). It protects the spinal cord and supports the body.
- Rib cage: 12 pairs of ribs joined to the sternum protect the heart and lungs and help in breathing.
- Pectoral girdle and pelvic girdle: join the arms and legs to the axial skeleton.
- Limbs: each arm has humerus, radius and ulna, carpals, metacarpals and phalanges; each leg has femur, tibia and fibula, tarsals, metatarsals and phalanges.
Bone is a living tissue made of cells in a hard matrix of calcium phosphate and collagen. Bone has a hard outer layer, and long bones have a central cavity filled with bone marrow, where blood cells are made. Cartilage is softer and more flexible than bone. It is found at the ends of bones, in the nose and ears, and between the vertebrae.
A joint is a place where two or more bones meet. Immovable (fixed) joints, such as those between skull bones, do not allow movement. Slightly movable joints, such as those between vertebrae, allow little movement. Freely movable (synovial) joints allow a wide range of movement.
Types of freely movable joints:
- Ball and socket joint: allows movement in all directions, as in the shoulder and hip.
- Hinge joint: allows movement in one plane only, as in the elbow, knee and fingers.
- Pivot joint: allows rotation, as between the first two vertebrae when the head turns.
- Gliding joint: allows sliding movement, as in the wrist and ankle.
A synovial joint is covered by a capsule. Its bone ends are covered with smooth cartilage, and synovial fluid inside the capsule acts as a lubricant and reduces friction. Ligaments are tough fibres that join bone to bone and keep the joint stable. Tendons join muscle to bone.
Muscles are tissues that contract to produce movement. Skeletal (voluntary) muscle is attached to bones and is striated. Smooth (involuntary) muscle is found in the walls of the stomach, intestine and blood vessels. Cardiac muscle forms the heart wall and works without rest and without conscious control.
Muscles can only pull by contracting, they cannot push. So they work in antagonistic pairs, where one muscle relaxes as the other contracts. In the arm the biceps contracts and the triceps relaxes to bend (flex) the forearm. The triceps contracts and the biceps relaxes to straighten (extend) it. The elbow joint acts as the pivot and the bones act as levers.
Disorders of the skeletal system include arthritis, where joints become painful and swollen. Osteoporosis is the loss of bone density that makes bones weak and easily broken, and it is common in older people and women after menopause. Rickets in children is caused by lack of vitamin D and calcium and gives soft, bent leg bones. A fracture is a broken bone, and a sprain is a torn or stretched ligament. Dislocation is displacement of a bone from its joint.
Study tip: Learn the human skeleton as axial and appendicular parts, and practise a quick sketch of the arm showing biceps, triceps, tendons and the elbow joint. Use a small table for the four joint types with one example each.
Definitions and flashcards
Say the meaning first, then open the card to check.
Endoskeleton
Internal skeleton of bone or cartilage.
Axial skeleton
Skull, vertebral column, ribs and sternum.
Ligament
Strong fibre that joins one bone to another bone.
Tendon
Tough cord that joins a muscle to a bone.
Cartilage
Flexible tissue found at joint ends, the nose and ears.
Synovial fluid
Lubricating fluid in freely movable joints.
Antagonistic muscles
Pair of muscles whose actions oppose each other.
Osteoporosis
Weakening of bones due to loss of bone mass.
Joint
Place where two or more bones meet.
Short questions with model answers
These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.
State two functions of the skeleton. (2 marks)
The skeleton supports the body and gives it shape. It also protects delicate organs such as the brain and heart, and it gives attachment to muscles for movement.
Differentiate between a ligament and a tendon. (2 marks)
A ligament joins one bone to another bone and keeps the joint stable. A tendon joins a muscle to a bone and transfers the pull of the muscle to the bone.
Why do muscles work in pairs? (3 marks)
A muscle can only pull when it contracts, and it cannot push. A second muscle is needed to pull the bone back to its first position. So muscles work as antagonistic pairs, where one contracts while the other relaxes, as biceps and triceps do in the arm.
Describe the structure of a synovial joint. (5 marks)
In a synovial joint the ends of the bones are covered with smooth cartilage that reduces friction. The joint is enclosed in a capsule that holds synovial fluid, which lubricates the surfaces. Ligaments hold the bones together. This structure allows free movement without wear.
Explain how the forearm is bent and straightened. (3 marks)
To bend the forearm, the biceps muscle contracts and pulls the radius upwards, while the triceps relaxes. To straighten it, the triceps contracts and pulls the ulna, while the biceps relaxes. The elbow joint acts as a hinge and the bones act as levers.
Name the types of joints with one example each. (5 marks)
Ball and socket joint is found in the shoulder and allows movement in all directions. Hinge joint is found in the elbow and allows movement in one plane. Pivot joint is found between the first two vertebrae and allows rotation. Gliding joint is found in the wrist and allows sliding. Fixed joints are found between the skull bones and allow no movement.
Common mistakes
- Writing that muscles push bones. Muscles only pull when they contract.
- Mixing up ligaments and tendons.
- Saying that the skull is one bone. It is made of many fused bones, and only the lower jaw moves.
- Giving the wrong count of vertebrae groups, for example writing 12 cervical vertebrae instead of 7.
- Forgetting that the biceps and triceps do opposite jobs, so both cannot contract at once.