Websink Prep UKKS2 ScienceYear 3 chaptersScience textbooksYear 1Year 2Year 3Year 4Year 5Year 6Year 7Year 8Year 9Browse allPast papersFind a tutorBecome a tutor
Primary Science · Year 3Chapter 6 · Skeletons and muscles
Year 3 Science · Skeletons and muscles · Lesson 6.5

Year 3 Science: Joints and muscles in pairs

Part of the Year 3 Science skeletons and muscles chapter. Chapter overview · whole chapter on one page

6.5

Joints and muscles in pairs

Year 3
A2: movement at joints; the biceps and the triceps work in pairs to bend and straighten the elbow
Story. Priya is drawing with a pencil. She bends her elbow to draw one line, then straightens it to draw the next. Mr Patel says, “Two different muscles do the work. One bends the arm, and the other straightens it.” Priya asks, “Which muscles are they?”

A joint is a place where two bones meet. Joints let the skeleton move. Two kinds of joint are shown here:

JointWhere it isHow it movesLike
hinge jointelbow, kneemoves in one directiona door hinge
ball and socket jointshoulder, hipmoves in many directionsa ball in a cup

Muscles work in pairs to move a joint in two directions. The upper arm has two main muscles:

When the biceps contracts, the triceps relaxes. When the triceps contracts, the biceps relaxes.

hinge jointmoves one way, like a doorball and socket jointmoves in many directions
Left: a hinge joint moves in one direction, like a door. Right: a ball and socket joint moves in many directions.
bicepstricepsArm bent:the biceps contracts,so it gets shorter and thicker.tricepsbicepsArm straight:the triceps contracts,so it gets shorter and thicker.
The arm seen from the side. Left: bent, with the biceps short and thick. Right: straight, with the triceps short and thick.

Key ideas

  • A joint is a place where two bones meet.
  • A hinge joint, such as the elbow or the knee, moves in one direction.
  • A ball and socket joint, such as the shoulder or the hip, moves in many directions.
  • Muscles work in pairs. The biceps bends the elbow, and the triceps straightens it.
Worked example 6.5.1
What is a place where two bones meet called? Write the word.

Method. Think about where bones meet in the body.

  1. Read the chapter. A place where two bones meet is called a joint.
    joint
  2. Name it. So the word is joint.
    joint
  3. Write the answer.
    joint

Check. The elbow and the shoulder are both joints. ✓

Worked example 6.5.2
Which muscle is at the front of the upper arm, and bends the elbow? Write the name.

Method. Find the muscle at the front of the upper arm.

  1. Read the chapter. The biceps is at the front of the upper arm, and it bends the elbow.
    biceps
  2. Name it. So the muscle is the biceps.
    biceps
  3. Write the answer.
    biceps

Check. The biceps bends the elbow when it contracts. ✓

Worked example 6.5.3
Is the knee a hinge joint or a ball and socket joint? Write the name of the joint.

Method. Look at the table of joints.

  1. Read the table. The knee is a hinge joint, which moves in one direction.
    hinge joint
  2. Write the answer. So the knee is a hinge joint.
    hinge joint
  3. Write the answer.
    hinge joint

Check. A knee bends like a door hinge. ✓

Watch out

Watch out: the biceps and the triceps do not both contract to bend the elbow. One muscle contracts, and the other relaxes.

Try it at home or school (with a grown-up). With a grown-up, put one hand on the front of your upper arm. Bend your elbow slowly, and feel the muscle get harder. Now straighten your arm slowly, and put your hand on the back of your upper arm. Feel that muscle get harder. Stop if your arm hurts.

Exam tip

Grown-up tip. Ask: “Which muscle is working when you bend your arm? Which one works when you straighten it?” Let your child say the words biceps and triceps.

Exercise 6E  Joints and muscles in pairs

1
FJoints let the skeleton move. What is the name for the place where two bones meet? Write the word.
2
FWhich kind of joint moves in one direction, like a door? Write the name of the joint.
3
FWhich joint is a ball and socket joint: the elbow or the shoulder? Write the joint.
4
FName a hinge joint in the leg. Write the name.
5
FWhich muscle is at the front of the upper arm? Write the name.
6
FWhich muscle is at the back of the upper arm? Write the name.
7
FLook at the picture. Which muscle is short and thick when the arm is bent? Write the name.
bicepstricepsArm bent:the biceps contracts,so it gets shorter and thicker.tricepsbicepsArm straight:the triceps contracts,so it gets shorter and thicker.
8
FLook at the picture. Which muscle is short and thick when the arm is straight? Write the name.
bicepstricepsArm bent:the biceps contracts,so it gets shorter and thicker.tricepsbicepsArm straight:the triceps contracts,so it gets shorter and thicker.
9
FFill in the gaps.
(a)When the biceps contracts, the elbow ___.
(b)When the triceps contracts, the elbow ___.
10
FTrue or false: when the biceps contracts, the triceps relaxes. Write true or false.
11
PSPriya says the shoulder is a hinge joint, like the elbow. Is she right? Write no or yes, and say why.
12
PSMo bends his elbow. Write which muscle contracts and which muscle relaxes.
13
PSWorking scientifically. Priya wants to test which muscle works when she straightens her arm. Plan how she could find out, using her own arm. Write one step.
14
RExplain why the bones and the muscles both need to work to bend the elbow. Write one or two sentences.

Websink Prep UK is an independent site. It is not affiliated with, endorsed by or sponsored by AQA, Pearson Edexcel, OCR, WJEC, Eduqas, CCEA, SQA, GL Assessment, CEM or the Department for Education. All exam board names and trademarks belong to their owners. Past papers are linked from the exam boards' own websites and are not hosted here.

About Websink Prep UK · Find a tutor · Privacy · Terms · Cookie settings