Body Movements
CBSE Class 6 Science - Chapter 8
Chapter Summary
- Every living organism, whether human or animal, shows some kind of movement. This can be walking, running, jumping, crawling, or even internal movements like breathing.
- The human body is capable of moving various parts. These movements are made possible by the skeletal system and the muscles.
- Skeletal System: The framework of bones in our body is called the skeleton. It gives shape and support to the body, protects internal organs, and allows for movement.
- Bones: Bones are hard and rigid structures. An adult human skeleton has about 206 bones.
- Cartilage: It is a soft, elastic tissue found between bones at joints, on the tip of the nose, and in the outer ear. Cartilage is softer than bone and provides flexibility while reducing friction.
- Joints: A joint is a place where two or more bones meet. Joints allow different parts of the body to move.
- Types of Joints:
- Ball and Socket Joint: Allows movement in all directions (e.g., shoulder joint, hip joint). One end of a bone has a ball-like shape that fits into a cup-like hollow of another bone.
- Pivotal Joint: Allows rotation (e.g., the joint where our neck joins the head). It allows us to bend our head forward and backward and turn it to the right or left.
- Hinge Joint: Allows only back-and-forth movement (e.g., elbow joint, knee joint, finger joints). It works like the hinges of a door.
- Fixed Joints: Some joints do not allow any movement (e.g., joints between the bones of the skull, except the lower jaw).
- Muscles: Muscles are tissues that are attached to bones. They work in pairs. When a muscle contracts, it pulls the bone, causing movement. To move the bone in the opposite direction, a different muscle contracts, and the first muscle relaxes. Muscles cannot push, they can only pull.
- Gait of Animals:
- Earthworm: Moves by extending and contracting its body muscles in rhythmic sequence. It has bristles on its underside that help in gripping the ground.
- Snail: Moves with the help of a strong, muscular foot. The foot produces wavy movements that push the snail forward very slowly.
- Cockroach: Has three pairs of legs for walking and two pairs of wings attached to its breast for flying. They have an outer skeleton (exoskeleton) made of chitin.
- Birds: Have lightweight, hollow bones. Their strong breast muscles help them flap their wings. They have streamlined bodies to aid flight.
- Fish: Move by making a curve on one side of their body and then quickly on the other side. This creates a thrust that pushes them forward. Fins also help in movement and maintaining balance.
- Snake: Has a long backbone and many muscles. The muscles are connected to the backbone, ribs, and skin. They make the body loop sideways, pushing against the ground to move forward in an 'S' shape.
Questions and Answers
1. Fill in the blanks:
(a) Joints of the bones help in the _______ of the body.
Answer: (a) Joints of the bones help in the movement of the body.
(b) A combination of bones and cartilages forms the _______ of the body.
Answer: (b) A combination of bones and cartilages forms the skeleton of the body.
(c) The bones at the elbow are joined by a _______ joint.
Answer: (c) The bones at the elbow are joined by a hinge joint.
(d) The contraction of the _______ pulls the bones.
Answer: (d) The contraction of the muscle pulls the bones.
2. Indicate true and false for the following statements:
(a) The movement and locomotion of all animals is exactly the same.
Answer: (a) False
(b) The cartilages are harder than bones.
Answer: (b) False
(c) The finger bones do not have joints.
Answer: (c) False
(d) The fore arm has two bones.
Answer: (d) True
(e) Cockroaches have an outer skeleton.
Answer: (e) True
3. Match the items in Column I with one or more items of Column II:
| Column I | Column II |
|---|---|
| Upper jaw | is an immovable joint |
| Fish | has fins on the body has a backbone |
| Ribs | has a backbone |
| Snail | show very slow movement |
| Cockroach | have an outer skeleton can fly in the air |
4. Answer the following:
(a) What is a ball and socket joint?
Answer: (a) A ball and socket joint is a type of joint where the rounded end of one bone fits into the cup-like hollow of another bone. This type of joint allows movement in all directions, such as the shoulder joint and the hip joint.
(b) Which of the skull bones are movable?
Answer: (b) Most of the bones of the skull are fixed joints and cannot move. However, the lower jaw bone is movable, allowing us to chew food and speak.
(c) Why can our elbow not move backwards?
Answer: (c) Our elbow cannot move backwards because it has a hinge joint. A hinge joint only allows back-and-forth movement, similar to the hinges on a door, which restricts movement in other directions.
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