Chapter 5: Body Movements
शरीर में गति (संधियाँ, कंकाल, केंचुआ, घोंघा, तिलचट्टा, मछली, पक्षी एवं सर्प की गति)
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- Joints in Human Body:
- - Ball and Socket Joint (कंदुक-खल्लिका संधि): Rounded end of one bone fits into hollow cavity of another; permits movement in ALL directions (Shoulder joint and Hip joint).
- - Pivotal Joint (धुराग्र संधि): Cylindrical bone rotates inside a ring; enables head to bend forward/backward and rotate left/right (Neck joining the skull).
- - Hinge Joint (हिंज / कब्जा संधि): Allows movement only in a single plane back and forth like a door hinge (Elbow joint, Knee joint, finger knuckles).
- - Fixed Joints (अचल संधि): Bones fused immovably together (Upper jaw fused to cranium/skull; suture joints of skull).
- Skeleton & Cartilage: Skeleton gives form, anchors muscles, and shields organs (Brain protected by skull, heart/lungs by ribcage). Cartilage (उपास्थि) is flexible tissue softer than bone found in the ear pinna, nose tip, and intervertebral discs.
- Animal Locomotion Modes:
- - Earthworm (केंचुआ): Possesses NO bones. Body composed of multiple muscular rings. Movement occurs through alternating contraction and expansion of circular and longitudinal muscles. Tiny hair-like bristles (setae / शूक) project underneath to grip the soil.
- - Snail (घोंघा): Has a hard non-cellular outer calcium shell (exoskeleton) dragged along. Locomotion is carried out by a thick, muscular foot producing wavy muscular ripples.
- - Cockroach (तिलचट्टा): Has a chitinous exoskeleton, three pairs of jointed walking legs, and two pairs of wings powered by distinct breast flight muscles.
- - Fish (मछली): Streamlined body shape minimizes water drag; body muscles form opposing curves while the caudal (tail) fin sweeps sideways to propel forward.
- - Birds (पक्षी): Forelimbs modified into wings; bones are hollow and pneumatic (air-filled) to reduce weight; strong breast muscles anchor flight feathers.
- - Snake (सर्प): Has a long backbone and interconnected muscle bands. Curves into alternating lateral loops pressing against the ground; slithers fast in a zigzag path. SNAKES NEVER MOVE IN A STRAIGHT LINE.
- Trap: CBSE assertion: 'Snakes move forward in a straight line.' Correct: FALSE. Snakes propel themselves forward by pushing loops sideways against the ground; their path is wavy/curved.
- Trap: Earthworms do not have an internal skeleton; their movement is hydrostatic, gripping soil with bristles (setae).
- Trap: The joint between upper jaw and skull is a FIXED joint; the only movable joint in the skull is the lower jaw (mandible).
NCERT Core Facts: Joints & Biomechanics of Animal Locomotion
Joint classifications and comparative animal mechanics represent high-yield question clusters in CTET Paper 2:
1. Human Articulations / Joint Types
| Joint Type | Mechanical Analogy | Permissible Motion | Anatomical Location |
|---|---|---|---|
| Ball and Socket (कंदुक-खल्लिका) | Mortar and pestle | Multidirectional rotation (360^circ circle) | Shoulder (Scapula-Humerus), Hip (Pelvis-Femur) |
| Pivotal (धुराग्र) | Ring rotating on a pin | Forward, backward, lateral pivot | Neck joint (Atlas-Axis vertebrae connecting head) |
| Hinge (कब्जा संधि) | Door hinge | Unidirectional flexion and extension | Elbow (Humerus-Ulna), Knee (Femur-Tibia) |
| Fixed (अचल संधि) | Interlocking tongue-and-groove | Zero movement | Upper jaw (Maxilla) to Cranium bones |
2. High-Yield Comparative Locomotion Matrix
| Animal | Skeletal Structure | Engine of Movement | Distinctive Locomotion Trait |
|---|---|---|---|
| Earthworm | No bones (Hydrostatic) | Alternating circular & longitudinal muscle waves | Bristles (Setae) provide ground traction |
| Snail | Outer calcified shell (No joints) | Thick muscular foot | Secretes lubricating slime trail |
| Cockroach | External chitinous skeleton | 3 pairs legs + 2 pairs wings + flight muscles | Can walk, climb vertical walls, and fly |
| Fish | Flexible internal vertebral column | Body curves into opposing loops; tail fin whips | Streamlined (धारारेखीय) body reduces water friction |
| Bird | Hollow pneumatic bones | Pectoral breast muscles flapping modified forelimbs | Light frame engineered for flight |
| Snake | Long flexible spine | Loops push against surface sideways | Advances rapidly in S-shaped curves; never straight |
Test Your Mastery: Body Movements
Authentic CBSE exam questions tested directly from this NCERT chapter.
Which of the following statements regarding locomotion in animals is INCORRECT according to NCERT Class 6 Science?
NCERT कक्षा 6 विज्ञान के अनुसार जंतुओं में गति के संबंध में निम्नलिखित में से कौन-सा कथन गलत है?
Match the joints in List I with their body locations in List II: (a) Ball and Socket Joint - (i) Neck and head (b) Pivotal Joint - (ii) Knee and Elbow (c) Hinge Joint - (iii) Shoulder and Hip (d) Fixed Joint - (iv) Upper jaw and skull
सूची I में दिए गए जोड़ों को सूची II में दिए गए उनके स्थानों से सुमेलित कीजिए: (a) कंदुक-खल्लिका संधि - (i) गर्दन और सिर (b) धुराग्र संधि - (ii) घुटना और कोहनी (c) हिंज संधि - (iii) कंधा और कूल्हा (d) अचल संधि - (iv) ऊपरी जबड़ा और खोपड़ी
Why are bird bones light yet strong enough for flight?
Bird bones have hollow, air-filled cavities (pneumatic bones) that drastically reduce body weight while maintaining structural strength.
How do earthworms grip slippery ground while crawling?
Earthworms have microscopic hair-like structures called setae (शूक) underneath their body rings, connected to muscles that anchor into the soil.