Answer: Option A. -> hollow and light
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A
The bones of the birds are hollow and light. This makes their body light in weight which helps them to fly in the air. The bones in their hindlimbs are designed for walking and perching. The bony part of their forelimbs are modified for flying.

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The working of muscles: 1 Mark each
1. The muscles work in pairs.
2. When one of them contracts, the bone is pulled in that direction, the other muscle of the pair relaxes. To move the bone in the opposite direction, the relaxed muscle contracts to pull the bone towards its original position, while the first musclerelaxes.
3. A muscle can only pull. It cannot push.

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Each point : 1 Mark
Any 5:

• Rib cage occupies the chest region. It is cone-shaped structure made up of 12 pairs of ribs.


• Ribs are attached to vertebrae at the back which curve around to form a cage.


• 10 pairs of ribs are attached to the breast bone at the front.


• 2 pairs of lower ribs are free at front. These are called as free-floating ribs.


• Rib cage is set up in such a way that it can contract and expand during the process of breathing.


• Rib cage protects the underlying lungs, heart and some part of liver etc.

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Definition: 1 Mark
Each constituent: 2 Marks
The skeleton is an internal framework of all the bones and cartilage in the human body. It is made up of 206 bones. It gives the shape and structure to support the body. Babies at birth possess 300 separate bones. Later some of the bones fuse together and finally an adult has 206 bones making up the skeleton.
Boneis a type of fibrous connective tissue. Bones provide support to the structures in the body. Bone cells are embedded in a hard matrix composed of calcium and phosphorus compounds. Bones also anchor the muscles. The strongest, longest and the heaviest bone in the human body is femur. It is located in the thigh region of the leg.
Cartilageis a soft elastic tissue that covers the bones at the region of the joints. It offers support to the structure. It connects the bones together.Cartilagehas widely spaced cells suspended in a matrix of proteins and sugars. It is found in the nose, earsand the rings of the trachea to give flexibility.

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Movement of earthworm: 1 Mark each.
1. Earthworm does not have bones. It has muscles.
2. During the movement, itfirst extends the front part of the body keeping the rear portion fixed to the ground. Then it fixes the front and releases the rear end.
3. It then shortens the body and pulls the rear end forward. In this way, by repeating such muscular expansions and contractions earthworm moves.

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Adaptations: 1 Mark each
Any two :

1. The bones of a bird are hollow and light.


2. The wings are made of strong flight muscles that help in long flights.


3. They have tails that control the direction of their flight.

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Vertebral column : 3 Marks
Functions : 2 Marks
Any three:

• Vertebral column running at the back of the body is also called as spine or the backbone.


• It is in the trunk region to offer support to the upper part of the body.


• Vertebral column is made up of individual bones called as vertebrae.


• Total vertebral column consists of 7 cervical vertebrae, 12 lumbar vertebrae, 5 fused sacral and 3 fused coccygeal vertebrae.


• Vertebral column runs from the base of the skull to the hip bone forming a tube. Spinal cord passes through this hollow tube.


• Movement of neck can be up, down or sidewards.


• Vertebrae are joined by gliding joints which offer spring movement to the backbone. Body can be bent back, front or sidewards.

Functions (any two) :

• It protects the spinal cord.


• It supports the head.


• 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, correct posture.

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

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There are a total of 206 bones in a healthyadult 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.