The movement depends on the type of joints which join two bones together. The body parts having ball and socket joint move in all directions while the body parts having hinge joint move only in one direction.

We can bend or move our body parts only at those places where two bones join together. Such places are called joints.
The amount of movement depends on the type of joint, e.g. ball and socket joint allows movement in all directions whereas hinge joint allows only one directional movement.

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.

(a) If our elbow had a fixed joint, we would not be able to bend/fold our arms. A fixed joint does not allow any movement.
(b) If we were to have a ball and socket joints between our neck and head, we would be able to rotate our head 360°. A ball and socket joint allows movement in all directions.

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.

(a) (i) Ribs X (ii) Breast bone Y (iii) Ribcage Z
(b) (i) Heart P (ii) Lungs Q (iii) Liver R

The streamlined shape of fish helps it to move in water. Skeleton and muscles present in front side of fish move it on one side while tail muscles move the body the other side. This makes a jerk and pushes the body forward. In this way, it moves in water.

An earthworm is called as farmer's friend as it eats its way through the soil thereby loosening the soil. Also, earthworm's body excretes the undigested materials that increase the fertility of soil.

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.

The doctor must have observed a swelling around his ankle and taken an X-ray of his ankle. X-ray images confirm any type of injuries/fractures in the bones.

Cockroaches walk and climb as well as fly in the air. They have three pairs of legs which help them in walking. The body is covered with a hard outer skeleton. This outer skeleton is made of different units joined together which permit movement. There are two pairs of wings attached to the thorax. The cockroaches have distinct muscles-those near the legs move the legs for walking. The thoracic muscles move the wings when the cockroach flies.

(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.

The skeleton of a bird is well-suited for flying because
(i) bones are hollow and light in weight
(ii) bones of hindlimbs are used for walking and perching.
(iii) bones of forelimbs are modified as wings.
(iv) shoulder bones are strong, thus helpful in flying.
(v) breast bones hold flight muscles and are used to move the wings up and down for flying.

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.

Earthworm fixes its front end and releases the rear end for movement. On a glass, it loses its grip.

The upper part of the human ear is made up of cartilage while the earlobe consists of only muscles.

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

An earthworm does not have bones or legs. It has muscles which help them to lengthen and shorten the body to move.

The hard and strong skull protects a delicate organ of our body called brain..

Fish, birds and snake have streamlined body.

Heart and lungs are protected by the rib cage.

If our backbone was made up of one single bone, then we would not have been able to bend our body (from waist).

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

Hinge joint of our hand helps us to grasp a badminton racquet.