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Definition: 1 Mark 
Example: 1 Mark
An exoskeleton is the hard and stiff outer covering made up of chitin that protects an animal's body.
Examples - crab and snail.

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A tissue is a group of cells that together perform a particular function.

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Types of joints: 1 Mark each
1. Fixed or immovable joints are the joints which do not allow the bones to move but they offer protection for the structure in which they are present. Examples are the sutures between the bones of the cranium, ribs in the breastbone and bones of the hip girdle.
2. Slightly movable joints provide support to the structure in which they are present. They also help the structure to move slightly. An example is the joint in the lower jaw which is slightly movable.
3. Freely movable joints are the joints which help in the movement of the part in which they are present. There are four freely movable joints present in our body - ball and socket joint, Pivot joint, hinge joint and the gliding joint.

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Bone: 1 Mark
Cartilage: 1 Mark
Bone: Bone is a hard and non- flexible structure. It forms the skeleton
Cartilage : Cartilage is soft and flexible structure. It provides flexibility to the joints. It is found in the nose, ears and the rings of the trachea to give flexibility. 

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There are a total of 206 bones in a healthy adult human body.

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Types: 1 Mark each
Location: 1 Mark
Bones can be of different types based on their rigidity.

Round and long bones: Found in limbs. 
Ring-like bones with outgrowths: Found in the vertebral column.
Flat and strong bones: Found in the skull.
Girdles: Found in the shoulder region and pelvic region.

 

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Body structure : 2 Marks
Movement : 1 Mark
Snakes are vertebrates with a vertebral column. Its body is supported by a skeleton made up of vertebrae which run continuously from head to tail. As they do not have any limbs, snakes do not have appendicular skeleton. They have a long back bone and many interconnected muscles that help them to slither. They have muscles connecting the backbone, ribs and skin.
Snakes move in grass, sand and water. Though the snakes do not have arms or legs, they can climb trees. They move in a loop-like, zig-zag manner. They cannot move in a straight line. They have difficulty in moving on very smooth surfaces.

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Animal movements: 1 Mark each
Snakes :
Snakes have a backbone and many interconnected muscles that help them to slither. They have muscles connecting the backbone, ribs and skin. Snakes move in a loop-like, zig-zag manner. They cannot move in a straight line, and have difficulty in moving on very smooth surfaces.
Cockroaches :
Cockroach is an arthropod with six jointed legs. These legs aid in walking, and two pairs of wings are used to fly. A cockroach moves its legs with the help of muscles near the limbs. It uses its breast muscles to move its wings and fly.
Snails : 
Snail moves with the help of a single muscular foot. The under surface of the foot is lubricated with mucus which helps the snail to move easily. The rhythmic contractions and relaxations of the foot brings about a moving action in the body. The entire body except the foot lies inside the shell. 
Earthworms: 
Earthworms move with help of tiny, stiff hair-like projections called bristles. Every segment of the earthworm's body possesses "setae" which help in their movement. They move forward by repeated contractions and relaxations of their muscles in the skin. A slimy substance secreted by the earthworm helps in its movement.
Fish: 
Fish possess a streamlined body which helps them to swim in water. They swim with the help of their fins and their tails. The tail flaps from side to side to propel in the right direction. Some fish, however, move by bending their bodies from one side to another in quick succession. This produces a thrust that helps it move forward.

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Functions: 1 Mark each.
Any three: 

• It protects the spinal cord.


• It serves as an attachment for the ribs.


• It provides support and place of attachment for the pectoral and pelvic girdle.


• It provides movement for the human skeleton.


• It helps in walking and standing erect and maintaining correct posture.

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Definition: 1 Mark
Types: 1 Mark each
Freely movable joints are the joints which solely help in the movement of the structure or organ in which they are present. Four freely movable joints present in our body are Ball and socket joint, Pivot joint, hinge joint and gliding joint.

Ball and socket joint: This joint is formed by two bones in which one end of a bone is rounded and ball-like. It fits into a cup-like depression of the other bone. This joint provides movement in any direction. Examples of a ball and socket joint are shoulder joints and hip joints.
Pivot joint: This is the joint in which one bone fits into a ring formed by the other bone. It rotates over the pivot-like end of the other bone. An example is the joint between the neck and the head
Hinge joint: This is a joint which moves like a hinge in a single plane, not more than 180 degrees.  It provides back and forth movement of the structure. This can be compared the hinge in a door. Examples of a hinge joint are the elbow joint and the knee joint.
Gliding joints: This is a joint which allows bones to glide over each other. These types of joints provide little movement in all directions. These are the joints present at the ankles, wrist and between the  vertebrae.