Answer: (c) both bones and cartilage
Explanation:
Bones and cartilage form the skeleton of human body.

Answer: (d) All of these
Explanation:
All are the part of human skeleton.

Answer: (b) skull
Explanation:
Joints in skull are immovable.

Answer: (a) hinge joints
Explanation:
Knee joints are very similar to the hinges of a door.

Answer: (a) forming loops alternately on two sides of the body
Explanation:
During swimming, the front part and the tail part of the body curve in opposite directions. This makes a jerk and pushes the body forward. So fish forms loops alternately on two sides of the body.

Answer: (d) All of these
Explanation:
These are the adaptations of birds for flying.

Answer: (a) three pairs of legs and two pairs of wings
Explanation:
Three pairs of legs are the characteristics of insects.

Answer: (a) snakes
Explanation:
With the help of muscles, ribs, and scales, snake moves from place to place.

Answer: (a) skull
Explanation:
Skull has 22 bones in cranium and 14 on the face. These protect the brain and sensory organs.

Answer: (c) seven
Explanation:
Seven cervical vertebrae are found in neck region.

Answer: organs

Answer: cells and tissues

Answer: cells

Answer: unit

Answer: Out side

Answer: internal

Important Questions

Question 1.
How many types of joints are there in our body? Name them.
Answer:
There are five types of joints in our body:

1. Ball and socket joints
2. Hinge joints
3. Gliding joints
4. Pivotal joints
5. Fixed joints.

Question 2.
Name the three components of skeleton.
Answer:
Skeleton is made up of different bones, joints and cartilage.

Question 3.
Name various parts of skeletal system.
Answer:
The skeletal system can be divided into following main parts:

• Skull
• Back bone
• Limb bones
• Chest bones
• Shoulder bones
• Hip bones.

Question 4.
What is the function of skeleton?
Answer:
The function of skeleton is:

• It forms the framework of body,
• It gives shape and structure to the body.
• It protects the internal organs.
• It helps in the movement and keeping body erect.
• Ribs of chest help in breathing.

Question 5.
At which point does the arm rotate?
Answer:
The arm rotates on the round pit like structure.

Question 6.
Which is the longest bone in your body? Measure it with your scale.
Answer:
Femur is the longest bone in our body. It is a thigh bone.

Question 7.
Name the bones which protect the heart from all sides.
Answer:
Breastbone from front and the backbone at the back make a type of box to protect the heart.

Question 8.
Does the shoulder bone also move when you move your arm?
Answer:
The shoulder bone does not move when we move our arm. Only arm moves, the shoulder bone remains fixed.

Question 9.
Keeping your arm straight, move it forwards and backwards, up and down. Can the arm move freely in all directions?
Answer:
Yes, the arm can move forward, backward down and up.

Question 10.
Do the bones of the upper jaw move?
Answer:
The bones of the upper jaw are joined with fixed joints. So they do not move.

Question 11.
Which important organ is fully protected inside the bones of the skull (head)?
Answer:
The bones of the skull form the structure similar to a box. The bones are joined with strong joints. It is not easy to break them. The bones of the skull protect the most important organ, i.e., the brain.

Question 12.
Do the bones on top of the skull move?
Answer:
The bones on top of the skull form the structure similar to the structure of teeth. They are joined strongly with one another. So these bones are also fixed. These bones do not move.

Question 13.
Try to eat your food without moving the lower jaw. Do you find this difficult to do?
Answer:
Without moving the lower jaw, we cannot chew the food. Without chewing, we cannot engulf the food into food pipe. It would be difficult to digest unchewed food.

Question 14.
Draw a labelled diagram of a ball and socket joint.
Answer:

Question 15.
Identify and label the different bones in the skeleton shown in the figure.
Answer:

Question 16.
What is exoskeleton? Explain giving examples.
Answer:
The bodies of crabs, insects and spiders are covered and protected by hard coverings. These hard parts outside are called exoskeleton (ekso-skel-e-ton). Nails and hair are also exoskeleton found in our body. Similarly the scales of cockroach, fish, outer shell of snails and oyster are also exoskeleton of these animals.

Question 17.
How can we get photograph of a bone? What is the use of such photographs?
Answer:
We can get photograph of a bone by a machine called X-ray machine. Doctors use these photographs to examine the dislocations and fractures in the bone.

Question 18.
Why are bones in the foot normally set in an arch? What is a flat-foot?
Answer:
The bones in the foot are normally set in an arch (Fig. 8.12). The feet arches give good support to the body. They also bend and spring back each time one steps out. The smaller toe bones also help in walking and running. In some cases, the foot is flat instead of being arched and are called flat-foot. Not all flat-feet cause trouble, but sometimes they give trouble or cause pain. Then it may need special care.

Question 19.
Do all animals have bones?
Answer:
No, all animals do not have bones. Bones are present only in the backboned animals. Even among the backboned animals, the skeleton of sharks are made entirely of cartilage.
The jellyfish, leeches and worms have no hard structure to support their bodies.

Question 20.
What is dislocation and fracture of a bone? What precaution should one take when one gets a fracture?
Answer:
Dislocation and fracture: Any careless, sudden movement—a jump, fall or knock—may cause an injury to the skeleton. It may be a dislocation or a fracture. In case of dislocation the bones at the joint are dislodged from their normal position. The ligaments may be torn apart or injured causing pain and swelling.

A fracture is a break in the bone. The break may be of a hair line crack or serious break in one or more points (Fig. 8.13). Fracture also causes pain and swelling. In all these cases, the patient should soon be taken to a doctor or a hospital.

• Never try to reset the bones.
• Place the injured part in a comfortable position.
• Care should be taken to avoid jerk or movement of the injured part.

Question 21.
How a bone is formed? What kind of food should we take for proper growth and upkeep of bones?
Answer:
Before our birth, the skeleton forms as soft and elastic pieces of cartilage. Some of these cartilages, not all, are changed to bones. With the deposition of a substance containing calcium and phosphorus, the bones become hard and strong. When a baby is born its skeleton is soft. At old age, the bones become hard and brittle.

For proper growth and upkeep of bones, we need to take food which are rich in calcium, phosphorus, vitamins and proteins. Milk, curd, fruits, vegetables and eggs ^contain the needed nutrient.

Question 22.
What is a bone marrow? Give its main function.
Answer:
The long bones such as the thigh bone, upper arm bones have hollow spaces inside which contains bone marrow (Fig. 8.14). The bone marrow produces red blood cells. They also form some kinds of white blood cells.

Question 23.
Discuss the mechanism of bone movement. What is the role of muscles in the movement of bones?
Answer:
Two muscles work for the movement of a bone. When one muscle contracts, it becomes shorter, stiffer and thicker. It pulls the bone in that direction. The other muscle of the pair relaxes. A muscle can only pull. It cannot push. Hence to move the bone in opposite direction, the relaxed muscle contracts to pull the bone towards its original position, while the first relaxes.

Question 24.
Differentiate between bone and cartilage with examples.
Answer:
Bone: They are hard and rigid structure in our body that cannot be bent but give shape to our body, e.g. pelvic bone, shoulder bone, etc.

Cartilage: They are semi-hard structures that are elastic tissue and present in an animal body.
e.g., upper part of ear, etc.

Question 25.
What are floating ribs?
Answer:
The last two pairs of ribs that are not joined in front of the breast bone/sternum. So, they are called floating ribs.

Question 26.
Differentiate between ligament and tendon.
Answer:
Ligament joins bone to bone together, whereas the tendon joins muscles to bone.

Question 27.
Differentiate between exoskeleton and endoskeleton.
Answer:
Exoskeleton: The skeleton, if it covers the body from the outside, or is situated in the skin, is known as exoskeleton. For example, insects.

Endoskeleton: The skeleton, if it lies inside the body and is covered by soft parts like flesh, is known as endoskeleton. For example, animals.

Question 28.
What is cartilage? Give one example.
Answer:
These are some additional parts of the skeleton that are not as hard as the bones and which can be bent. For example, the upper part of our ear has cartilage.

Question 29.
What is a bone joint? Describe various kinds of joints found in our body.
Joints: The place where two or more bones meet together is called a joint. There are five main types of joints in our body.
(i) Fixed joints: Some attachments of bones do not allow movement. They are fixed joints. Joint of the cranium is a fixed joint.

(ii) Ball and socket joints: The rounded end of one bone fits into the hollow space of the other bone (Fig. 8.18). Such a kind of joint allows movements in all directions and is called ball and socket joint. For example, the joint between the upper arm and the shoulder; the thigh and the hip.

(fit) Pivotal joints: The skull is joined to the first two vertebrae of the backbone like a ball to a stick. This type of joints allows movements in many planes—up and down, to the side and all other planes.
iv) Hinge joints: These joints allow movement only in one plane like a door hinge and not more than 180 degree. For example, the fingers, the knee. The wrist is a double hinge joint (Fig. 8.19).

(v) Gliding joints: These joints allow only a limited amount of movement of sliding nature of cartilages (Fig. 8.20). For example, the joints in backbone.

Question 30.
Write short notes on the following.

1. skull
2. chest bones
3. Backbone
4. Hip bone
5. The shoulder bone
6. limb bone

Answer:
1. The skull: The skull has two main parts. They are the cranium (cra-ni-um) or the brain case and the facial bones. The bones of the cranium are flat. They are held firmly like a zipper. The cranium covers and protects the brain. The facial bones comprise of the upper and lower jaws and a few other bones. The lower jaw is movable. The movement of the lower jaw enables us to eat, talk, and sing. The skull also includes a pair of eye sockets. These form a safe pocket for the eyes.

2. The chest bones: The chest is a cone-shaped cage (Fig. 8.21). It encloses the heart and the lungs. At the back are the vertebrae, 12 pairs of ribs curve surround the sides. Ribs are attached to the sides of each vertebrate. Ten of them are also attached by cartilage to the breast bone at the front. Two ribs are free. These are called floating ribs.

The ribs are joined in such a way that they allow the necessary movement of the chest during breathing.

3. Backbone: Vertebral column or backbone is composed of 33 small, ring-like vertebrae joined end to end. Thus it forms a hollow bony tube. The main nerve cord passes through it. The backbone has five regions from top to bottom, they are the neck, chest, belly, hip and tail. Five vertebrae of the hip and four vertebrae of tail are fused to form 1 bone [turn 26 bones of vertebrae in an adult (Fig. 8.2)].

4. Hip bone: The hip bone is formed by the fusion of three bones (Fig. 8.5). The hip bones together with the last two parts of the backbone form a large bony bowl. It is called the pelvis (pel-vis). It is the lowest and strongest part on which we sit on. The thigh bones are attached to the hip bones.

5. Shoulder bones: The shoulder bone is formed by the collar bone and the shoulder blades (Fig. 8.4). It connects the upper part of the chest and the bones of the hand. The bones of the upper arm attach with the shoulder bones.

6. Limb bones: The hand comprises of the upper arm, fore arm, wrist, palm and fingers. The leg includes the thigh, lower leg, ankle, feet, and the toes. The bones in hand and leg are in same pattern and are called limb bones, upper arm and thigh has one long bone. The thigh bone is strongest and longest bone in the body. In the fore arm and lower leg, there are two long bones. Wrist and ankle are made up of several small bones. Palm and foot have five longer bones. Each finger and toe are made up of three small bones, except thumb, which has two bones.

Question 31.
How do incorrect sitting postures harm us? What are the correct sitting and standing postures?
Answer:
Incorrect sitting postures cause stresses and strains on the muscles and bones [Fig. 8.22(a)].It may turn fatigue and painful

In correct position, one should sit straight and relaxed. One should not bend in front or lean backwards [Fig. 8.22 (b)]. The fore arms should be at the same level. The feet should rest flat on the floor. The lower leg should be erect making a right angle at the knee.

Similarly, one should stand straight and erect and not droop in front for a long time [Fig. 8.22 (c)]. The habit should be checked from childhood when the bones are soft. Otherwise the curvature or bend of the backbone may become permanent with age as the bones gradually harden.

Question 32.
Name organs that are protected by rib cage.
Answer:
heart and lungs