2.8.5Inquiry Process
Movement of Joints- Skills — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 90 of 160
Section 1 of 5Parts of a Synovial Joint
Cartilage
- Smooth hyaline cartilage covers the bone ends, reducing friction and absorbing shocks.
Synovial fluid
- A lubricating fluid secreted by the synovial membrane reduces friction and nourishes the cartilage.
Joint capsule
- A tough fibrous capsule surrounds the joint and keeps the synovial fluid in place.
Ligaments
- Strong fibrous bands join bone to bone, stabilising the joint and limiting its range of movement.
Tendons
- Tendons attach muscles to bones so that muscle contraction pulls on the skeleton.
Section 2 of 5Joint Types and Muscle Action
Hinge joint
- Found at the elbow and knee, it allows movement in one plane, like a door opening and closing.
Ball and socket joint
- Found at the hip and shoulder, it allows movement in many directions, including rotation.
Elbow flexion
- The biceps contracts and the triceps relaxes to bend the arm.
Elbow extension
- The triceps contracts and the biceps relaxes to straighten the arm.
| Joint | Example | Movement |
|---|---|---|
| Hinge | Elbow, knee | One plane |
| Ball and socket | Hip, shoulder | Many planes |
Section 3 of 5Levers and Measurement
Levers and Measurement
Lever
- The bone acts as a rigid bar, the joint as the pivot, and the muscle supplies the effort force.
Moments
- Moment equals force multiplied by perpendicular distance from the pivot;
- balance occurs when moments are equal.
Range of movement
- A goniometer measures the angle through which a joint can move.
Variables
- Compare ages or activities by measuring angle at maximum flexion and extension with repeated trials.
Section 4 of 5Worked Example
Question
- The biceps attaches 4 cm from the elbow pivot.
- A 5 N weight is held in the hand 30 cm from the pivot.
- Ignoring the forearm's weight, calculate the force the biceps must exert to hold the arm still.
- Moment of load = 5 N × 0.30 m = 1.5 N m.
- Moment of effort = F × 0.04 m.
- At balance, F × 0.04 = 1.5.
- F = 1.5 ÷ 0.04 = 37.5 N.
Answer The biceps must exert 37.5 N, seven and a half times the weight held.
Section 5 of 5Exam Checklist & Tips
2.8.5 – Key Points for the Exam
- Synovial joint A joint with a fluid-filled cavity between bones, allowing free movement.
- Ligament Tissue that connects bone to bone.
- Tendon Tissue that connects muscle to bone.
- Flexor A muscle that bends a joint.
- Extensor A muscle that straightens a joint.
Common Mistakes
- Mixing up tendons and ligaments.
- Saying both antagonistic muscles contract together to move the joint.
- Writing that cartilage is bone.
- Measuring the lever distance to the bone's end rather than to the pivot.
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