Locomotion and Movement
This domain examines how organisms move from place to place and how the human skeleton and muscles produce movement. The exam tests types of joints with examples, antagonistic muscle action, the sliding filament idea, and locomotion in earthworm, fish and birds.
Locomotion in other organisms
- Amoeba: pseudopodia and cytoplasmic flow. Paramecium: cilia beating in coordinated waves.
- Earthworm: circular and longitudinal muscles act alternately against a hydrostatic skeleton, with setae gripping the soil.
- Fish: myotomes bend the body, fins stabilise and the swim bladder adjusts buoyancy. Birds: pneumatic bones, keeled sternum, powerful flight muscles, feathers and air sacs.
Human skeleton and joints
- Axial skeleton: skull, vertebral column, ribs, sternum. Appendicular: limb bones with pectoral and pelvic girdles.
- Fibrous or immovable joints: skull sutures. Cartilaginous, slightly movable: between vertebrae. Synovial, freely movable: ball and socket at shoulder and hip, hinge at elbow and knee, pivot between atlas and axis, gliding between carpals, saddle at the base of the thumb.
Muscles
- Skeletal (striated, voluntary), smooth (unstriated, involuntary), cardiac (striated, involuntary).
- Muscles work in antagonistic pairs: the biceps flexes the elbow while the triceps relaxes, and the reverse extends it.
- Sliding filament theory: actin filaments slide over myosin filaments, the sarcomere shortens, powered by ATP and calcium.
Worked example
When you bend your arm at the elbow, the biceps contracts and shortens while the triceps relaxes and lengthens. Straightening the arm reverses the roles. Muscles can only pull, never push, which is exactly why they must act in pairs across a joint.
Traps that cost marks
- Muscles pull on bones; they never push them.
- Both members of an antagonistic pair do not contract at the same time.
- Rickets is caused by vitamin D deficiency; osteoporosis is loss of bone mass, commoner with age.