Class 6 Science Notes Chapter 8 (Chapter 8) – Examplar Problem Book
Alright class, let's get straight into Chapter 8: Body Movements from your Science Exemplar book. This chapter is crucial for understanding how we and other animals move, and questions often appear in competitive exams based on these fundamental concepts. Pay close attention!
Chapter 8: Body Movements - Detailed Notes for Exam Preparation
1. Introduction to Movement:
- Movement is a fundamental characteristic of living organisms.
- Animals move for various reasons: finding food, shelter, escaping danger, finding mates.
- Plants also show movement (e.g., opening/closing of flowers, growth towards light), but locomotion (moving from one place to another) is primarily seen in animals.
- Different animals exhibit different types of movements: walking, running, flying, swimming, crawling, slithering, jumping, etc.
2. The Human Body and its Movements:
- Our body can move various parts like arms, legs, head, neck, etc. Some parts can move in multiple directions, while others have limited movement or no movement at all.
- Joints: The points where two or more bones meet are called joints. Joints allow for movement. The nature of the joint determines the type and extent of movement possible.
3. Types of Joints in the Human Body:
* Ball and Socket Joint:
* Description: The rounded end (ball) of one bone fits into a cup-like cavity (socket) of another bone.
* Movement: Allows movement in almost all directions (circular movement).
* Examples: Shoulder joint, Hip joint. (Think about how you can swing your arm or leg around).
* Pivotal Joint:
* Description: A cylindrical bone rotates within a ring formed by another bone.
* Movement: Allows rotation around an axis (forward, backward, left, right turning).
* Example: The joint between the neck and the head. (Allows you to nod 'yes' and turn your head 'no').
* Hinge Joint:
* Description: Works like the hinge of a door.
* Movement: Allows only back-and-forth movement in one plane (like opening and closing a door).
* Examples: Elbow joint, Knee joint, Finger joints, Toe joints.
* Fixed Joint (Immovable Joint):
* Description: Bones are fused together and do not allow any movement.
* Function: Provide strength and protection.
* Examples: Joints between the bones of the skull (except the lower jaw), Joint between the upper jaw and the rest of the head, Joints in the pelvis (largely fixed).
4. The Human Skeleton:
- Definition: The framework of all the bones in our body is called the skeleton.
- Functions:
- Gives shape and support to the body.
- Protects vital internal organs (e.g., skull protects the brain, rib cage protects the heart and lungs).
- Allows movement (along with muscles).
- Bone marrow (inside some bones) produces blood cells.
- Key Parts:
- Skull: Bony structure protecting the brain. Made of many bones fused together (fixed joints), except for the lower jaw which is movable.
- Backbone (Vertebral Column): Runs from the neck to the lower back. Made of 33 small bones called vertebrae. It is flexible and protects the spinal cord.
- Rib Cage: A cage-like structure formed by 12 pairs of curved ribs. Joined to the backbone at the back and the breastbone (sternum) in the front (except for the last two pairs, called floating ribs). Protects the heart and lungs.
- Shoulder Bones (Pectoral Girdle): Consists of the collar bone and shoulder blade. Connects the arm bones to the trunk.
- Pelvic Bones (Pelvic Girdle): Encloses the portion of the body below the stomach. Supports the abdomen and provides attachment points for leg bones. You sit on this part.
- Limb Bones: Bones of the arms and legs.
- X-rays: Images used to see the shapes of bones inside the body, helpful in identifying fractures.
5. Cartilage:
- A firm but flexible connective tissue.
- Not as hard as bone.
- Found in some parts of the skeleton (e.g., covering the ends of bones at joints to reduce friction).
- Also found in the upper part of the ear (pinna) and the tip of the nose.
6. Muscles:
- Bones cannot move on their own. Movement is caused by the action of muscles attached to the bones.
- Muscles work in pairs: When one muscle contracts (shortens), the other relaxes (lengthens), pulling the bone in a specific direction.
- Example: To bend the arm at the elbow, the biceps muscle (front of upper arm) contracts, and the triceps muscle (back of upper arm) relaxes. To straighten the arm, the triceps contracts, and the biceps relaxes.
7. Gait of Animals (How Animals Move):
- Earthworm:
- Body: Made of many rings joined end-to-end. No bones.
- Movement: Uses muscle expansion and contraction to shorten and lengthen its body. Tiny bristles called setae under its body grip the ground. Secretes slime to help movement.
- Snail:
- Has a hard outer shell (protection, not for movement).
- Moves using a large, flat, muscular foot.
- Secretes mucus (slime) to reduce friction and aid movement. Moves very slowly.
- Cockroach:
- Has a hard exoskeleton (outer skeleton).
- Movement: Walks and climbs using three pairs of legs. Can also fly using two pairs of wings (though they are not strong fliers). Distinct muscles move legs for walking and wings for flying.
- Birds:
- Movement: Fly, walk, hop, perch.
- Adaptations for Flight:
- Streamlined body: Reduces air resistance.
- Hollow and light bones: Reduces body weight.
- Wings: Forelimbs modified into wings with feathers.
- Strong chest muscles: Power the flapping of wings.
- Fish:
- Movement: Swimming.
- Adaptations for Swimming:
- Streamlined body: Reduces water resistance.
- Fins: Help in balancing, changing direction, and stopping.
- Tail (Caudal fin): Helps in propulsion (moving forward) and steering.
- Strong muscles: Create waves along the body to push against the water.
- Snakes:
- Body: Long backbone, many thin muscles connected to backbone, ribs, and skin. No legs.
- Movement: Slithering. Moves by forming loops. Each loop pushes against the ground, moving the snake forward very fast. Scales on the underside also help in gripping the ground.
8. Yoga:
- Often mentioned in context. Yoga involves postures (asanas) and breathing techniques that help keep joints and muscles healthy and flexible.
Multiple Choice Questions (MCQs) for Practice:
-
Which type of joint allows movement in almost all directions?
(a) Hinge joint
(b) Pivotal joint
(c) Ball and socket joint
(d) Fixed joint -
The joint between the head and the neck is an example of a:
(a) Hinge joint
(b) Pivotal joint
(c) Ball and socket joint
(d) Fixed joint -
Which part of the skeleton protects the brain?
(a) Rib cage
(b) Backbone
(c) Pelvic bones
(d) Skull -
Cartilage is NOT found in which of these body parts?
(a) Tip of the nose
(b) Upper part of the ear (Pinna)
(c) Between vertebrae
(d) Lower jaw bone -
How do muscles cause movement of bones?
(a) By pushing the bones
(b) By working in pairs - contracting and relaxing
(c) By secreting lubricants at the joints
(d) By expanding equally on both sides -
An earthworm moves with the help of:
(a) Muscular foot and slime
(b) Legs and wings
(c) Muscle contractions/expansions and setae
(d) Fins and tail -
Which of the following animals has an outer skeleton (exoskeleton)?
(a) Fish
(b) Bird
(c) Cockroach
(d) Human -
Which adaptation helps birds to fly?
(a) Solid, heavy bones
(b) Muscular foot
(c) Hollow bones and streamlined body
(d) Presence of scales -
A fish swims primarily using its:
(a) Fins for propulsion
(b) Gills for direction
(c) Streamlined body shape alone
(d) Muscles and tail fin for propulsion -
Fixed joints are found in the:
(a) Elbow
(b) Shoulder
(c) Skull (except lower jaw)
(d) Knee
Answer Key:
- (c) Ball and socket joint
- (b) Pivotal joint
- (d) Skull
- (d) Lower jaw bone (This is bone, not cartilage)
- (b) By working in pairs - contracting and relaxing
- (c) Muscle contractions/expansions and setae
- (c) Cockroach
- (c) Hollow bones and streamlined body
- (d) Muscles and tail fin for propulsion
- (c) Skull (except lower jaw)
Make sure you revise these notes thoroughly. Understanding the types of joints and how different animals move are key takeaways from this chapter. Good luck with your preparation!