There are a total of 33 vertebrae in a human backbone.

Vertebrate + example : 1 Mark
Invertebrate + example : 1 Mark
The animals which have a backbone are called as vertebrates.  Example : Lions, fish, humans, etc
The animals that do not have a backbone are called invertebrates. Example : spiders, snails, bees, etc

The cranium, which is a part of the skull, covers and protects the brain.

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.

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 muscle relaxes.
3. A muscle can only pull. It cannot push.

Differences: 1 Mark each

$\begin{array}{cc}\text{BONES}& \text{CARTILAGES}\\ \text{They are hard}& \text{They are soft}\\ \text{They cannot bend}& \text{They can bend}\\ \text{They make the framework of the whole body}& \text{They are only used in some parts of the body}\end{array}$

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.

Cartilage is 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. Cartilage has widely spaced cells suspended in a matrix of proteins and sugars. It is found in the nose, ears and the rings of the trachea to give flexibility.

• 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.

Movement of earthworm: 1 Mark each.

1. Earthworm does not have bones. It has muscles.
2. During the movement, it first 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.

• 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.

• 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.