Muscles - Worksheet | Science Year 3 - Free Printable

Problem Analysis:

The worksheet is about understanding how muscles work during arm movements. The task involves filling in the blanks to describe what happens to the muscles when the arm is moved.

#### Key Concepts:
1. Biceps Muscle: Located on the front of the upper arm. It contracts (shortens) to bend the arm.
2. Triceps Muscle: Located on the back of the upper arm. It contracts to straighten the arm.
3. Contraction: When a muscle shortens and becomes tense, it pulls on the bones to move them.
4. Relaxation: When a muscle lengthens and becomes less tense, it allows the bones to move in the opposite direction.

Solution:

#### First Diagram:
The first diagram shows the biceps muscle contracting to pull the lower arm upward. This corresponds to bending the arm.

- To ______ your arm the ______ muscle ______ pulling ______ your ______ arm.
- To bend your arm, the biceps muscle contracts, pulling up your lower arm.

So, the completed sentence is:
"To bend your arm the biceps muscle contracts pulling up your lower arm."

#### Second Diagram:
The second diagram shows the triceps muscle contracting to pull the lower arm downward. This corresponds to straightening the arm.

- To ______ your arm the biceps muscle ______ while the ______ muscle contracts, pulling ______ the lower ______.
- To straighten your arm, the biceps muscle relaxes while the triceps muscle contracts, pulling down the lower arm.

So, the completed sentence is:
"To straighten your arm the biceps muscle relaxes while the triceps muscle contracts, pulling down the lower arm."

Final Answer:

1. First Diagram:
"To bend your arm the biceps muscle contracts pulling up your lower arm."

2. Second Diagram:
"To straighten your arm the biceps muscle relaxes while the triceps muscle contracts, pulling down the lower arm."

Boxed Final Answer:
\[
\boxed{
\text{To bend your arm the biceps muscle contracts pulling up your lower arm.}
}
\]
\[
\boxed{
\text{To straighten your arm the biceps muscle relaxes while the triceps muscle contracts, pulling down the lower arm.}
}
\]