Chapter 8: BODY MOVEMENTS

Transcription

1 Chapter 8: BODY MOVEMENTS P112 A. Very Short Answer Questions 1. What is a ball and socket joint?[ncert] Ans: A ball and socket joint allows movement of bone in all directions. The end of one bone rotates freely in socket of other bone. 2. Which of the skull bones are movable?[ncert] Ans: The lower jaw is movable. This movable joint helps us to open and close the mouth. 3. Why can our elbow not move backwards?[ncert] Ans: Our elbow has hinge joint due to which elbow cannot move backwards. 4. Animals walk, snake slithers and fish swims. How? Ans: Animals walk with their limbs and the whole body of a snake helps it to slither on the ground, while fish swims with its fins and tail. 5. Name the type of joint of your hand which helps you to grasp a badminton racquet. [NCERT Exemplar Problems] Ans: Hinge joint is present in fingers, which helps in grasping a badminton racquet while gliding joint is present in wrist. 6. Boojho fell off a tree and hurt his ankle. On examination the doctor confirmed that the ankle was fractured. How was it detected?[ncert Exemplar Problems] ans: Fracture in a bone can be detected by obtaining X-ray images of the bone. 7. Write the type of joint which is used for each of the following movements: (a) A cricket bowler bowls the ball. Ans: Ball and socket joint (b) A girl moves her head in right and left direction. Ans: Pivot joint (c) A person lifts weights to build up his biceps.[ncert Exemplar Problems] Ans: Hinge joint

2 P If our body had no joints, would it be possible for us to move? Ans: No, we would not be able to move at all if there were no joints. 9. Are all joints in our skull immovable? If not, name a movable joint in skull and state its importance. Ans: All joints in our skull are immovable except the lower jaw joint. This movable joint helps us to open and close mouth. It also helps us to speak and eat food. 10. What is the use of X-ray images of bones of the body? Ans: X-ray images of the bones help doctors to find out about any possible injuries that might have happened to bones. X-ray shows the shapes of the bone inside the body. 11. What would have happened if our backbone was made of one single bone? [NCERT Exemplar Problems] Ans: If our backbone was made of one single bone, it would not bend at all. 12. Mona made a fist and Sona held her arm of that hand. Mona opened and closed her fist repeatedly. Does Sona feel any movement in Mona's arm? How? Ans: Yes, Sona feels the movement in Mona s arm because as Mona opens and closes her fist, the muscular contractions occur in her arm. 13. How does a cockroach fly? Ans: Cockroach has two pairs of wings attached to the breast muscles move the wings and cockroach flies. 14. Why doesn't not a snake move straight? Ans: The snake curves its body to form loops. Each loop gives it a forward push by pressing it against the ground. As its body makes many loops so that the snake moves very fast but not in a straight line. B. Short Answer Questions 1. In what ways do animals move? Why are there so many differences in the way animals move from place to place? Ans: Animals move by walking, running, flying, jumping, creeping, crawling, slithering and swimming. There are differences in ways of movement because of the structure of each animal and hence their locomotory organs are different from each other. P Bones are hard structures and cannot be bent. But, we can still bend our elbow,

3 knee, etc. How is this possible?[ncert Exemplar Problems] ans: We bend our elbow, knee, etc. only at the joints where two bones are joined together and the movement bending at joints is possible. 3. While doing different exercises, how do you move your hands and legs? Ans: While doing exercises, hands and legs are bent or rotated or straightened in different directions. These are possible only at the joints in the skeleton. 4. Is the boy able to bend his elbow? Why? Ans: No, because the straight hard board will not allow any bending at all. 5. Why are we able to move/bend some body parts in various directions, some in one direction while some can't be moved at all? Ans: We can bend different body parts in different ways because different bones are joined to each other with different joints. At fixed joint, no movement is possible at all ; and at ball and socket joint, free movement in all directions is possible. Other joints help limited movement of the bones. 6. At which point can we bend our arm? Can we bend it upward and downward both? Ans: We bend our arm only in upward direction at the elbow. At the shoulders we can bend it in all directions. P Which type of movement would have been possible if: (a) our elbow had a fixed joint, Ans: No movement would be possible. (b) we were to have a ball and socket joint between our neck and head? [NCERT Exemplar Problems] Ans: Our head would rotate in all directions. 8. What are bones? How do we feel them in our body? Can bones be bent? Ans: Bones are the hard structures which form the framework of our body. We feel them as hard parts inside the body when we press our body by fingers. Bones cannot be bent. 9. What are joints? Name some types of joints. Ans: The places where two bones are joined together are called joints. Some types of joints are : ball and socket joint, hinge joint, pivot joint, gliding joint and fixed joint. 10. What is skeleton? What is its importance in our body?

4 Ans: A framework of bones which gives shape and support to our body is called skeleton. It protects the delicate organs of the body and helps to carry out different activities. 11. How is a ball and socket joint different from hinge joint? Ans: A ball and socket joint allows the movement of the bone in all directions. On the other hand, a hinge joint allows movement or bending in one direction only. In hinge joint, a bone rotates in a half cylindrical cavity of another bone. P (a) What is ribcage? Ans: Ribcage is a cage-like structure formed by bent bones that join the chest bone and backbone together. (b) How many bones does it have? Ans: Ribcage has twelve pairs of bones. The first ten pairs are attached at both ends, while last two pairs are attached at only one end called floating ribs. 13. What is cartilage? Where do we find it in our body? Ans: The parts of skeleton which are not as hard as bones and which can be bent are called cartilage. We find cartilage in the ear pinna, tip of nose and even in joints of the body. 14. Do all animals have bones? Explain with examples. Ans: No, all animals do not have bones. e.g. earthworm and snail do not have bones. 15. How does an earthworm fix its body parts to ground? Ans: An earthworm has a large number of tiny bristles projecting out under its body. These bristles are connected with the muscles, hence when the earthworm moves, they help it to get a good grip on the ground. 16. Earthworms are known as Farmer's friends. Why? [NCERT Exemplar Ans: The earthworm, actually, eats its way through the soil! Its body then throws away the undigested part of the material that it eats. This activity of an earthworm makes the soil more useful for plants. 17. Distinguish between skeleton and outer skeleton. Ans: The inner skeleton (endoskeleton) gives shape to the body of an organism and remains inside the body, while the outerskeleton (exoskeleton) protects the entire body like an outer covering. P How is the skeleton of a bird well-suited for flying? [NCERT Exemplar Problems]

5 Ans: Their bones are hollow 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. 19. How is the shape of a fish helpful in its movement? Ans: The streamlined shape of fish allows the fish to move faster in water as it cut through the water reducing resistance more efficiently.