Movement: skeleton, joints and musclesIB MYP Biology: Revision notes
Section 1
Functions of the skeleton
The skeleton has several jobs:
- Support: it gives the body its shape and holds up the soft organs.
- Protection: the skull protects the brain, the rib cage protects the heart and lungs, and the backbone protects the spinal cord.
- Movement: bones act as levers, and muscles pull on them to move the body.
- Making blood cells: red and white blood cells are made in the bone marrow of some bones.
- Storage: bones store minerals such as calcium.
Section 2
Joints: ball and socket and hinge
A joint is where two or more bones meet.
- Ball and socket joint (shoulder, hip): the rounded end of one bone fits into a cup-shaped socket in another. It allows movement in all directions, including rotation.
- Hinge joint (elbow, knee): it allows bending and straightening in one plane only, like a door hinge.
Some joints, such as those between the bones of the skull, are fixed and do not move.
Link joint to movement: hinge = back and forth in one plane, ball and socket = all directions.
Section 3
Ligaments, tendons and cartilage
Three tissues keep a joint working well:
- Ligaments join bone to bone. They hold the joint together and limit how far it can move, so the bones do not come apart.
- Tendons join muscle to bone. They transmit the pull of a muscle to the bone so the bone moves.
- Cartilage is smooth, rubbery tissue that covers the ends of bones. It reduces friction and absorbs shocks.
When cartilage wears away the bones rub together, causing pain and damage.
Do not mix up ligaments and tendons. Ligaments = bone to bone, tendons = muscle to bone.
Section 4
Antagonistic muscles
Muscles can only pull (contract); they cannot push. So muscles work in pairs that pull in opposite directions. These are antagonistic muscles.
At the elbow:
- To bend the arm, the biceps contracts and the triceps relaxes. The biceps pulls the forearm up through its tendon.
- To straighten the arm, the triceps contracts and the biceps relaxes.
When one muscle of the pair contracts, the other relaxes.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Movement: skeleton, joints and muscles
- A handball goalkeeper in Denmark dives across the goal to block a shot. Her shoulder swings her arm in a wide circle to reach the ball, and her elbow bends and straightens as she stretches out and pulls her hand back.Explain how the biceps and triceps work together to bend and then straighten her elbow.2 marks
- A physiotherapist is explaining knee injuries to a young runner who twisted her knee during a cross-country race in Kenya. The scan shows no broken bones, but there is some damage to the soft tissues in and around the joint where her thigh bone meets her shin bone. Her Achilles tendon, which joins her calf muscle to her heel bone, is also sore.State the function of a tendon and explain why a torn Achilles tendon would stop the runner pushing off the ground with her foot.2 marks
- A sports science student wants to find out whether eight weeks of daily biceps curls, lifting a 2 kg weight by bending the elbow, increases the number of curls a person can do in one minute. She tests six volunteers from her class at the start and again after the eight weeks. The mean number of curls rises from 18 to 27.State a testable hypothesis for this investigation with a scientific reason, and identify one variable that the student must control.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).