A muscle can only pull, it cannot push. Thus, two muscles are required to work together to move a bone. When one muscle contracts, bone is pulled. When another muscle of the pair pulls, it brings the bone in its original position.

Our vertebral column is comprised of 31 small bones. These are joined together with soft tissue in the form of cartilage discs. This arrangement makes this bony structures to have some limited movements of the body.
If there is only one long bone instead of many in the vertebral column, the organism will not be able to avail the limited movements which are necessary for the organisms for its survival.

Yes, cartilages are the additional parts of the skeleton that are not as hard as the bones and which can bent. So, we can say that though most of the skeleton is made of bones but it has some cartilages too.

Under earthworm's body, it has a large number of tiny bristler projecting out. The bristles are connected with muscles. The bristles help to get a good grip on the ground.

Elbow and knee are not made up of a single bone rather they are made up of two or more bones which are joined to each other by a joint, i.e. hinge joint. This joint along with the muscles helps us to bend the elbow and knee.

(a) The doctor has diagnosed the fracture by taking photographs of bones, i.e. X-ray images.
(b) X-rays show us the images and shapes of different bones in our body.
(c) Friendly behaviour, sense of responsibility and kind nature are the values shown by Rishi's friends.

A snake form loops in its body while slithering. Each loop of the snake gives it a forward push by pressing against the ground. The snake with a larger number of loops will move much faster than the snake with lesser number of loops. Thus, the snake A will move faster than snake B as we can see that loops in snake A are more than in snake B.

(i) Movements in heart (ii) Movement in lungs.

The number of bones in each finger is three and are called phalanges.

The following adaptations are seen in the body of birds.
(i) Bones are hollow.
(ii) Forelimbs are modified into wings.
(iii) Body is streamlined.

Earthworm and snail move without the bones.

No, movement in the body of an animal is possible in the presence of joints only.