We walk, run, jump, swim, and play every day. All these activities are possible because our body can move. Movement is one of the most important features of living organisms. Even animals that stay still can move their body parts. In this chapter, we study how our body moves, what parts are involved, and how animals move in different ways.
The movement of our body is possible because of a system of bones and muscles. The framework of bones inside our body is called the skeleton. The bones are joined together at joints, and muscles pull on these bones to cause movement. In this chapter, we learn about the human skeleton, joints, and the movement of different animals.
We also explore how different animals move. Some swim, some fly, some walk, and some crawl. Each animal has a body structure suited to its way of movement. Earthworms crawl, snails glide on a slimy foot, birds fly with wings, and fish swim with fins and tails. Understanding body movements helps us appreciate the amazing design of living organisms.
The skeleton is the framework of bones in our body. It performs many important functions: - It gives shape and support to the body. - It protects the delicate internal organs. The skull protects the brain, the ribcage protects the heart and lungs, and the backbone protects the spinal cord. - It helps in movement by providing attachment points for muscles. - It produces blood cells in the bone marrow.
The skeleton is like the frame of a building. Without it, our body would be a shapeless mass. A human baby is born with around 300 bones, but by adulthood many of them join together, and an adult has about 206 bones.
The human skeleton consists of many bones that are grouped into parts: - Skull: The bones of the head. The skull protects the brain. The skull has a movable lower jaw bone called the mandible, which helps in chewing and speaking. - Ribcage: The ribs form a cage that protects the heart and lungs. The ribs are attached to the backbone at the back and to the breastbone (sternum) at the front. - Backbone (vertebral column): The backbone is made of many small bones called vertebrae. It supports the body and protects the spinal cord. The backbone allows us to bend and twist. - Shoulder bones (pectoral girdle): The collar bones (clavicles) and shoulder blades (scapulae) connect the arms to the body. - Pelvic bones (pelvic girdle): These bones connect the legs to the body and support the body weight. - Arm bones: The upper arm bone (humerus), the two forearm bones (radius and ulna), and the bones of the wrist and fingers. - Leg bones: The thigh bone (femur, the longest and strongest bone), the shin bones (tibia and fibula), and the bones of the ankle and toes.
The skeleton is covered by muscles, and together they form the musculoskeletal system.
A joint is the place where two bones meet. Joints allow the bones to move and give flexibility to the body. There are different types of joints, each allowing a different kind of movement.
Joints can be movable or immovable. The ball and socket, hinge, and pivot joints are movable, while the skull joints are fixed.
Muscles are the fleshy tissues attached to the bones. Muscles work in pairs to cause movement. When we bend our arm, the muscle at the front of the upper arm contracts (becomes shorter and thicker), while the muscle at the back relaxes (becomes longer). When we straighten the arm, the two muscles exchange their actions.
Muscles are attached to bones by tough bands called tendons. When a muscle contracts, it pulls on the bone, and the bone moves at the joint. Muscles can only pull; they cannot push. This is why they work in pairs. One muscle pulls the bone one way, and the other muscle pulls it back.
Different animals move in different ways depending on their body structure and habitat. Let us look at some examples:
The cockroach is an insect with a well-defined body. It has a hard outer skeleton made of a material called chitin. The body of a cockroach is divided into three parts: head, thorax, and abdomen. - Head: Has antennae and eyes. - Thorax: Has three pairs of legs and two pairs of wings. - Abdomen: Contains the internal organs.
The cockroach walks with its six legs. The legs have small joints that allow the cockroach to walk, climb, and run. The cockroach can also fly using its wings. Its hard outer skeleton protects the body and provides support.
Birds are the masters of flight. They fly with the help of their wings and strong flight muscles. The body structure of birds is specially adapted for flying: - Wings: Broad wings help the bird push against the air and lift itself. - Feathers: Feathers make the body light and help in steering. - Hollow bones: The bones of birds are hollow and light, which reduces the body weight. - Streamlined body: The body shape of a bird is streamlined, which reduces air resistance.
These adaptations allow birds to fly efficiently over long distances. Not all birds can fly, though. Birds like ostriches and emus cannot fly because they are heavy and their wings are small.
Fish live in water and move with the help of fins and their tail. The body of a fish is streamlined, which means it is narrow at both ends and broader in the middle. This shape helps the fish move through water easily, reducing water resistance.
The parts that help fish move are: - Tail fin: The tail fin and the tail push against the water and help the fish move forward. - Other fins: The pectoral, pelvic, and dorsal fins help the fish steer, balance, and change direction. - Scales: The scales protect the fish's body and reduce friction with water.
The muscles of the fish contract in a wave-like pattern from head to tail, pushing the water backwards and moving the fish forward.
| Type of Joint | Movement Allowed | Example |
|---|---|---|
| Ball and socket | Movement in many directions | Shoulder, hip |
| Hinge | Movement in one direction | Elbow, knee |
| Pivot | Rotational movement | Between skull and backbone |
| Fixed | No movement | Bones of the skull |
| Animal | Organ/Part for Movement | Mode of Movement |
|---|---|---|
| Earthworm | Setae and body muscles | Crawling |
| Snail | Flat muscular foot | Gliding slowly |
| Cockroach | Legs and wings | Walking, climbing, flying |
| Fish | Fins and tail | Swimming |
| Bird | Wings | Flying |
| Frog | Hind legs and webbed feet | Jumping and swimming |
In this chapter, we explored the wonderful machinery that makes movement possible. We learned about the human skeleton, which gives shape, support, and protection to the body, and about the joints that allow our bones to move in different ways. We understood how ball and socket, hinge, pivot, and fixed joints work, and how muscles in pairs pull on bones to cause movement. We also studied the amazing variety of movement in animals: the crawling earthworm, the gliding snail, the flying bird, the swimming fish, and the jumping frog. Every living organism has a body structure perfectly suited to its way of moving. Body movements remind us of the beauty and design of living things all around us.