Support and Movement in Humans and Animals, practice questions

C, A hydrostatic skeleton, as in the earthworm, uses fluid pressure that muscles squeeze against to move.

B, A tendon joins muscle to bone, so a contracting muscle pulls the bone; a ligament joins bone to bone.

B, Bending the arm needs the biceps to contract and pull the forearm up while the triceps relaxes.

A, The rigid exoskeleton cannot expand, so the insect sheds it and hardens a larger one to grow.

C, The tail fin provides most of the forward thrust; the other fins steer, balance and brake.

B, The keeled sternum gives a large surface area to anchor the powerful flight muscles.

C, Cartilage is soft and flexible, cushioning joint surfaces so they move smoothly.

B, Osteoporosis is a fall in bone density that makes bones fragile; arthritis is joint inflammation.

B, A ball-and-socket joint (shoulder, hip) allows movement in all directions; a hinge joint moves in one plane.

B, A sprain is an overstretched or torn ligament with the bone still in place; a dislocation forces the bone out.

• (a) Hinge joint.
• (b) The biceps.
• (c) The triceps relaxes.
• (d) A muscle can only pull, not push, so a second antagonistic muscle is needed to move the joint back the other way.

• (a) Myotomes.
• (b) It provides most of the forward thrust.
• (c) The bones are largely hollow (and fused).
• (d) The keeled sternum.

• (a) Bone density falls / bone breaks down faster than it is rebuilt.
• (b) Low calcium or vitamin D intake (or hormonal change / ageing).
• (c) The joint, usually the cartilage or the synovial membrane.
• (d) Regular weight-bearing exercise with a balanced diet rich in calcium and vitamin D.

Hydrostatic skeleton (e.g. earthworm), exoskeleton (e.g. insects) and endoskeleton (e.g. humans) each support and allow movement.

Bones give support, joints allow movement, and muscles attached by tendons produce the force.

A hinge joint (elbow, knee) allows movement in one plane; a ball-and-socket joint (shoulder, hip) allows movement in many directions.

Muscles work in pairs: when the biceps contracts to bend the arm, the triceps relaxes, and the reverse straightens it.

Muscle contraction pulls on bones across a joint to produce movement; locomotion is movement of the whole body.

Arthritis (joint inflammation) and osteoporosis (weak bones) affect the musculoskeletal system.

A fish bends its flexible vertebral column into side-to-side waves by contracting myotome muscle blocks arranged along both sides of the body, pushing against the denser medium of water. The tail fin provides most of the forward thrust, while the dorsal, pelvic and pectoral fins give stability, steering and braking as the fish swims.

A bird's skeleton is light because many bones are hollow and fused, reducing the number of separate joints and the overall mass that must be lifted. A keeled sternum, a ridge of bone on the chest, anchors large flight muscles that pull the wings down to generate lift and thrust, then relax as smaller muscles raise the wings again.

Bone is a hard, living tissue reinforced with calcium and phosphate salts, giving the skeleton the rigidity needed for support, movement and protection of organs such as the brain and heart. Cartilage is softer, more flexible connective tissue that cushions joint surfaces, allows smooth movement and forms flexible parts such as the outer ear, the nose tip and parts of the airway.

A skeletal muscle is joined to a bone by a tendon at each end, so contraction pulls the two bones of a joint closer together. Because a tendon cannot push, every movement in one direction needs a second muscle, or muscle group, to pull the joint back the other way once the first muscle relaxes.

Regular weight-bearing activity such as walking or jogging stimulates bone to stay dense, while an adequate daily intake of calcium and vitamin D supplies the minerals bone needs and helps the body absorb them. Correct posture when sitting, standing or lifting, together with avoiding repetitive strain, reduces the long-term risk of joint damage and bone loss.

At the knee, the quadriceps on the front of the thigh and the hamstrings at the back form another antagonistic pair: the quadriceps contracts to straighten the leg while the hamstrings relax, and the hamstrings contract to bend the leg while the quadriceps relaxes, the same principle as the biceps and triceps at the elbow.

Because an exoskeleton is a rigid outer casing, it cannot expand as the animal inside grows. An insect or crustacean must therefore periodically shed its old exoskeleton in a process called moulting, or ecdysis, and quickly harden a new, larger one underneath before the body can increase further in size.

A dislocation occurs when a bone is forced out of its normal position at a joint, often tearing the surrounding ligaments and requiring the bone to be manipulated back into place. A sprain is a milder injury in which a ligament is overstretched or partially torn, causing pain and swelling but without the bone leaving the joint.

A long bone such as the femur has a tough outer covering called the periosteum, which carries blood vessels and nerves and allows the bone to grow in width; beneath it lies dense compact bone for strength, surrounding a central marrow cavity that produces blood cells and stores fat, with spongy bone at each rounded end.