Bones and Muscles: How Our Body Moves — Answers
Answer sheet with model answers and success criteria for the 3rd Grade the human body worksheet.
Success TutoringWorksheetsAnswer sheet3rd Grade · Science · The Human BodyBones and Muscles: How Our Body Moves — Answers
Part A: The skeleton
Read the passage. Then circle the best answer.
Your skeleton is made of bones. An adult has 206 bones. The skeleton has three main jobs: it supports your body so you can stand up, it protects soft parts inside, and it helps you move.
The skull protects the brain. The ribs protect the heart and lungs. The spine (backbone) holds you upright and protects the nerves that run down your back.
Bones meet at joints. The knee and elbow are hinge joints — they bend one way, like a door. The shoulder and hip are ball-and-socket joints — they can move in a circle.
Muscles move bones. Muscles can only pull, never push, so they work in pairs. When you bend your arm, the muscle at the front of your upper arm (the biceps) gets shorter and pulls. To straighten it, the muscle at the back (the triceps) pulls instead.
- Athe ribs
- Bthe skull
- Cthe spine
- Dthe thigh bone
Answer: the skull
The skull is a hard case of bone around the brain.
- Ayour heart and lungs
- Byour stomach only
- Cyour brain
- Dyour eyes
Answer: your heart and lungs
The ribs make a cage around the heart and lungs.
- Amuscle
- Btendon
- Cjoint
- Dskull
Answer: joint
Joints, like the knee and elbow, are where bones meet and let the body bend.
- Apushing them
- Bpulling them
- Cmelting them
- Dgrowing them
Answer: pulling them
Muscles can only pull. When a muscle gets shorter, it pulls on a bone.
- Athe shoulder
- Bthe hip
- Cthe neck
- Dthe elbow
Answer: the elbow
The elbow (and knee) are hinge joints. The shoulder and hip are ball-and-socket joints that move in many directions.
Part B: Bones and joints
- skull
- ribs
- spine
- protect the heart and lungs
- holds the body upright
- protects the brain
Answer: skull → protects the brain; ribs → protect the heart and lungs; spine → holds the body upright
Answer: 206
Answer: pairs
Answer: Hinge: elbow or knee. Ball-and-socket: shoulder or hip.
Part C: True or false?
Write True or False.
Answer: False
Muscles can only pull. That is why they work in pairs — one pulls one way, the other pulls back.
Answer: True
The heart is a special muscle that pumps blood all the time.
Answer: True
Bones are living parts of the body. They grow as you grow, and a broken bone can mend.
Answer: True
Calcium helps build strong bones, and exercise makes bones and muscles stronger.
Part D: Working scientifically: feel your muscles
Notice which muscle gets harder each time.
Rest one hand on the front of your other upper arm. Slowly bend that elbow, then straighten it. Now move your hand to the back of the upper arm and do it again.
Answer: It gets shorter and fatter (harder) as it pulls the lower arm up.
Answer: The muscle at the back of the upper arm (the triceps).
Model answer: Muscles can only pull, not push. The biceps pulls to bend the arm, but it cannot push it straight again. So the triceps on the back of the arm pulls to straighten it. The two muscles work as a pair.
Success criteria:
- States that muscles can only pull
- Names or describes the two muscles
- Explains that each muscle moves the arm one way
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.