Science [3 Marks Each] QUE-ANS

Earthworms make their way through the soil, by loosening the soil and allowing more air to get in. Their body excretes undigested materials that also increases the fertility of soil.
They also help in the decomposition of organic wastes and stabilise a wide variety of wastes. This is called vermicomposting. All this helps the crops to grow, that is why earthworms are regarded as farmer’s friends.

Birds can fly because their bodies are well-suited for flying. Main adaptations for flying in birds are given as follows:

1. Body is streamlined.
2. Bones have air spaces.
3. Fore limbs are modified as wings.
4. Shoulder bones are strong.
5. Breast bones are modified to hold massive muscles of flight.
6. Wings and tail are reinforced with big feathers.
7. Air sacs are connected with the lungs to make the body light and buoyant.

Before our birth, the skeleton forms as soft and elastic pieces of cartilage. Some of these cartilages, not all, are changed to bones. With the deposition of a substance containing calcium and phosphorus, the bones become hard and strong. When a baby is born its skeleton is soft. At old age, the bones become hard and brittle.
For proper growth and upkeep of bones, we need to take food which are rich in calcium, phosphorus, vitamins and proteins. Milk, curd, fruits, vegetables and eggs contain the needed nutrient.

The bodies of fish are usually spindle-shaped and streamlined. This makes it easy to move in water. There are also air filled swim bladders to make the body buoyant.
The skeleton of the body axis is covered by strong muscles. They are arranged serially, segment by segment. During swimming, the front part of the body curves in one side and the tail part remains in the opposite side. It forms a loop. 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 aided by the fins of the tail.
The paired and unpaired fins mainly help to keep the balance of the body and to keep direction.

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 help us to bend the elbow and knee. Hinge joint allows the movement of bones in only one direction.