Class 6 Science Chapter 5 Important Questions

Hinge joint allows the movement of bones in only one direction as forwards and backwards. In hinge join the movement of bones is restricted to one direction by the shape of the ends of the bones which form the joints and by the ligaments which holds the bone together at the joint. Open and close a door a few times. Observe the hinges of the door carefully. They allow the door to move back and forth. Make a cylinder with cardboard or thick chart paper. Attach a small pencil to the cylinder by piercing the cylinder at the centre. Make a hollow half cylinder from cardboard such that the rolled-up cylinder can fit inside it easily. The hollow half cylinder with the rolled-up cylinder sitting inside it, allows movement like a hinge. But, it illustrates the direction in which a hinge allows movement. The elbow has a hinge joint that allows only a back and forth movement.

There are so many differences in the way that animals move from place to place because different animals move through or on four different types of environment aquatic, terrestrial, fossorial (underground) and aerial.

The joint present at the elbow is hinge joint that helps in its bending. The large muscle of the upper arm flexes the arm and powerfully twists the forearm, turning the palm upward.

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 have fixed joint at certain parts of the body, therefore we are unable to move some parts at all.

Technically, human have four legs but after evolution the muscles in human legs group stronger and longer alloying them to be able to stand upright. While the body of cows and buffaloes are designed such as that they do not able to stand up right.

Elbow has a relatively simple hinge joint which allows only flexion and extension whereas legs have modified hinge joint at knee composed of three functional compartments.

Sometimes when we are hurt, or have an accident, doctors use these X-ray images to find out about any possible injuries that might have happened to the bones. The X- rays show the shapes of the bones in our bodies.

The human body has two shoulders one on each side of the neck as collarbone and shoulder blade. Collar bone keeps the shoulders apart.
The upper arm fits into the socket of shoulder blade forming ball and socket joint. The main functions of the shoulder bones are:
i)Collar bones on the two sides of the neck keep our shoulders apart.
ii)Shoulder blades attached the arms to our body.
iii)Shoulder blades provide sites for muscle attachments which move the arms, neck and upper part of our body.

In human body, most of the skeleton consists of hard bones. Some additional parts of the skeleton that are not as hard as the bones and which can be bent. These are called cartilage. In fact, cartilage is a kind of softer and elastic bone.
Bones are rigid and non-flexible whereas cartilage is semi-rigid but flexible. Bones form frame work of whole body whereas cartilage form framework only for a little part of body.

Cartilage is a firm but flexible material found at some places in the skeleton. Cartilage is present in the following places in our body. Cartilage is found at the end of nose. Cartilage is present in the pinnae of ears. This is found on the end of bones where they meet one another at a joint. Cartilage is also present as cartilage disc between the vertebrae of backbone.

The fibrous tissue in the body that has the ability to contract or expand, called muscle. The muscle bulged due to contraction (it became smaller in length). Muscles are attached to the bones of our skeleton through strong fibres called tendons. 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 musle 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.

Gait of animals refers to the way of movement in animals. Different animals have different body parts that help them to move. Aristotle an ancient Greek philosopher, wrote the book “Gait of Animals”. In the other words, gait is the pattern of movement of the limbs of animal and humans, during locomotion over a solid substrate. Most animals use a variety of gaits, based on speed, terrain, the need to manoeuvre, and energetic efficiency. Different animal species may use different gaits due to differences in anatomy that prevent use of certain gaits.
As an example, the birds fly in the following manner:
i)Downstroke: The feathers overlap so that the bird can push itself along through the air.
ii)Upstroke: The feathers twist open, allowing the bird to lift its wings easily.
iii)Landing: The bird lands by spreading out its wings and tail as a brake.

The body of an earthworm is made up of many rings joined end to end. An earthworm does not have bones. It has muscles which help to extend and shorten the body. During movement, the earthworm first extends the front part of the body, keeping the rear portion fixed to the ground. Then it fixes the front end and releases the rear end. It then shortens the body and pulls the rear end forward. This makes it move forward by a small distance. Repeating such muscle expansions and contractions, the earthworm can move through soil. The body secretes a slimy substance to help the movement. Under its body, it has a large number of tiny bristles (hair like structures) projecting out. The bristles are connected with muscles. The bristles help to get a good grip on the ground.

Snail is a very slow-moving animal. The body of a snail is soft and consists of a head, a foot and a shell. The head of snail has two pairs of tentacles for catching prey. The body of the snail is covered with hard shell, which is outer skeleton of snail but it is not made of bones. This shell does not help the snail in movement. The foot of snail is large, flat and disc-shaped which is made of strong muscles, called muscular foot. These muscular food contract and expand alternately, producing a kind of wave effect from back to front. A series of waves in the muscles of foot make the snail move forward. The movement of snail is called creeping. Snail is also referred as “gastropods” which means “belly-footed animals”. But remember, an earthworm moves much faster than a snail.

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 join together which permits 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.

The skeleton of a bird is well-suited for flying because:
i)Their bones are hollow and light in weight.
ii)Their forelimbs are modified as wings.
iii)The shoulder bones are strong, thus, helpful in flying.
iv)The breast bone are modified to hold flight muscles which are used to move the wings up and down for flying.
v)They have a streamlined body, which reduces the air resistance.

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. The shape is such that water can flow around it easily and allow the fish to move in 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.

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 stabilize 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 friend.

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.

Hip bone forms a large, basin-shaped frame at the lower end of the backbone, to which the legs are attached. The hip bone is also known as pelvic bone. The hip bone is not a single bone. It is made up of a number of bones fused together by fixed joints.
Hip bone supports and protects the lower organs of the body such as intestine, urinary bladder and internal sex organs. Hip bone attaches the legs to our body. Hip bone provides sites for the attachment of muscles that move legs, hips and trunk.