Body movements (part 2)

 Body movements

Q.5. Write a short note on cartilage.

Ans. Cartilage:

  • Cartilage is a kind of softer and elastic bone which can be bent and are not as hard as the bones.
  • Cartilage is found in some elastic organs; like Upper part of ear has cartilage, nose etc.
  • Cartilage is also found in the joints of the body and layer of cartilage reduces friction, hence allows the bones to move easily over each other without damaging them.
Q.6. Muscles work in pairs. Explain.
Ans. Muscle is a fibrous tissue in the body that has ability to contract and relax. Muscles are attached to do so by the brain. The muscle bulges due to contraction (it became smaller in length). When contracted, the muscle becomes shorter, stiffer and thicker. It pulls the bone.

Muscles work in pairs. When one of them contracts, the bone is pulled in that direction. The other muscle of the pair relaxes. To move the bone in the opposite direction, the relaxed muscle contracts to pull the bone towards its original position, while the first relaxes. A muscle can only pull. It cannot push. Thus, two muscles have to work together to move a bone.

Q.7. Explain the movement in following animals.

        i) Bird        ii) Fish

Ans. i) Bird

  • A bird has streamlined body.
  • Their bones are hallow and light.
  • The bones of the hind limbs are typical for walking and perching. The bony parts of the forelimbs are modified as wings. The shoulder bones are strong.
  • The breastbones are modified to hold muscles of flight which are used to move the wings up and down. 

        ii) Fish

  • The head and tail of the fish are smaller than the middle portion of the body – the body tapers at both ends. This body shape is called streamlined. This type of shape allows the fish to move easily in the water.
  • The skeleton of the fish is covered with strong muscles.
  • During swimming, muscles make the front part of the body curve to one side and the tail part swings towards the opposite side. The fish forms a curve. Then quickly, the body and tail curve to the other side. This makes a jerk and pushes the body forward. A series of such jerks make the fish swim ahead. This is helped by the fins of the tail.
  • Fish also have other fins on their body which mainly help to keep the balance of the body and to keep direction, while swimming.

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