(a) Muscles work.
1. Muscles of the body can only pull and they can not push.
2. Two muscles are required to move a bone at a joint.
3. When one muscle contracts, the other muscle relaxes.
4. For example to move the lower arm up and down biceps and triceps muscles are required.
5. When we raise our lower hand the biceps in front become short by contraction and the triceps at the back stretch to pull up the arm.
6. When we lower our arm the triceps at the back contract and biceps stretch to pull the arm down.
(b) Circulatory system – importance :
1. It is one of the important system consisting of heart, blood vessels and blood.
2. It transports respiratory gases, nutrients, hormones and waste materials within the body.
3. If protects the body from harmful pathogens.
4. Regulates the body temperature.
5. The heart pumps blood continuously throughout our lifetime.
