7th Class Science Transportation in Animals and Plants NCERT Summary - Structures and Functions of the Living Body

Structures and Functions of the Living Body

All animals and plants have different organs to perform various functions. Each part of the body of an animal or plant is different in structure. The organs, however, function in coordination with one another.

SPECIFIC PARTS OF PLANTS

• Plants have two main systems: (i) the root system (ii) the shoot system

The Root System

The root system grows mainly underground. Root systems are of two types:

(i) Tap root system

(ii) Fibrous root system

(i) Tap root system: It is a main root and grows vertically down into the soil. The tap root gives out branches. For example, pea, neem, mango.

(ii) Fibrous root system: Some plants do not have main root. They have many fibre-like roots. These are called fibrous roots. These roots spread out in the soil and give firm support to the plant. For example, wheat, grass, maize and millet.

Advantages of the root system: As roots grow normally underground, they fix the plant to the ground. They absorb the mineral salts and water from the ground, which are needed for the plant to grow. Roots also help hold the soil together. They save the soil from being blown off or washed away.

The Shoot System

The shoot system grows above the ground. It consists of the main stem, its branches and leaves.

(i)   The stem: The stem holds the plant upright. The stem is the strongest part of a tree and is known as the trunk. Most trunks are observed with bark. The bark protects the inner part of the tree. The stems-of some plants are weak. They cannot stand erect.

Stems carry water from the roots to the leaves and flowers. They also carry food from the leaves to other parts of the plant. They hold the leaves in such a way that the leaves get plenty of light from the sun.

(ii) The leaves: Leaves are important parts of plants. They manufacture food for the plants. They are green because they contain a green pigment. This pigment is called chlorophyll. To manufacture food, the green leaves need sunlight, air and water. The process of making food in the presence of sunlight is called photosynthesis.

(iii) Flowers and fruits: In a flower, the green leaf-like parts in the outermost circle are called sepals. Towards the centre of a flower many little stalks with swollen tops are present and they called stamens. The swollen tops are called anthers. They contain a powdery substance called pollen. The stamen is the male part of a flower. In the centre of the flower, there is a flesh-shaped organ called the carpel. The carpel is the female part of a flower. The little swollen portion at the base is called the ovary. The ovary contains egg-like structures called ovules. Pollen are transferred to the carpel in a process called pollination. This is done by insects, wind and water. Eventually, the ovules of the flower turn into seeds and the ovary into fruits.

• Seeds: A seed contains a baby plant and food for the new plant. Corn, peas and beans are seeds.

SPECIFIC PARTS OF ANIMALS

All animals, including human beings, have definite organs and systems to carry out various functions. The main systems are: (i) digestive system (ii) respiratory system (iii) circulatory system (iv) nervous system (v) urinary system and (vi) reproductory system.

(i)   Digestive system: When we eat food, it is broken down into smaller particles. Then these particles get changed into absorbable forms in the body. This process is called digestion. The digested food is absorbed and used in the body. The unabsorbed portion is removed from the body as faeces. There are several organs that are involved in carrying out these processes. These are the mouth, oesophagus, stomach, small intestine, large intestine, anus, liver, gall bladder, pancreas.

• Mouth: The mouth contains tongue, teeth and salivary glands. Digestion of food starts in the mouth as soon as saliva mixes with the food. Saliva is secreted by the salivary glands. The mixing of saliva with the food takes place when the food is chewed by the teeth. Most adults have 32 teeth.

There are four types of teeth in our mouth—

The tongue has many functions. It helps in mixing the saliva with the food swallowing the food and experiencing the taste. It is also essential for speaking.

• Oesophagus: It acts as a passage or a tube which takes the food from the mouth to the stomach.
• Stomach: The stomach is like a bag. Food is churned in the stomach and turned into a semi-solid paste. The stomach helps in digesting food. The food goes to the small intestine from here.
• Small intestine: It is arranged in the form of a coil in our belly. Digestion of food also takes place here. This intestine also absorbs the digested food.

(ii) Respiratory system: Living organisms need oxygen. Oxygen helps break down the absorbed food in our body to release energy required for our life. The process is known as respiration. Carbon dioxide is formed as a waste during the process.

Breathing is an important part of respiration. We breathe in air rich in oxygen. When this air reaches the lungs, oxygen enters the blood. Carbon dioxide and water vapour from the blood are released into the lungs. These are removed from the lungs with the air we breathe out. The main organs of breathing are—nostrils, passages in the nose, trachea, bronchi and the lungs. Together, they are known as the respiratory system.

Note: The muscles of the chest and diaphragm help in the process of breathing in and breathing out.

(iii) Circulatory system: It supplies blood to all the organs of the body. The heart, blood and the blood vessels are its main components. The blood vessels are of three types - (a) arteries (b) veins (c) capillaries. Numerous greenish-blue lines just below the skin are the veins. Veins are very easily visible. They carry blood from all the organs of the body to the heart. Arteries lie a little deeper under the skin, so they are not easily visible. These carry blood from the heart to all parts of the body. A network of capillaries forms the connection between the arteries and the veins.

(iv) Nervous system: There are special sense organs that are sensitive to light (eyes), sound (ears), gaseous chemicals (nose), liquid chemicals (tongue), heat, cold and touch (skin).

The sensations are carried from these sense organs through the nerves to the brain or spinal cord. On receiving a message, the body's reaction to the changes is decided by the brain. The brain then sends out commands to different parts of the body for action, again through nerves. The main organs of the nervous system are—the brain, the spinal cord and the nerves. These organs help in coordinating all the functions of the body. This system helps the other systems to work together.

Note: The brain is located inside the skull. The spinal cord runs inside the bony structure of the backbone, while the nerves are distributed all over the body.

(v) Urinary system: The urinary system collects the liquid wastes and helps the body get rid of them. It comprises of two kidneys, two ureters, the bladder and the urethra. The function of the kidneys is to filter the wastes from the blood, producing a yellowish liquid called urine. The ureters convey urine from the kidneys to the bladder. Where it gets stored. It is passed out from the body through the urethra.

(vi) Reproductive system: All living organisms have the capacity to produce their offsprings which have characteristics similar to them. This process of producing individuals of one's own kind is called reproduction. If there is no reproduction, all life on the Earth would come to an end. Both males and females are required for reproduction.

• Other systems: There are several other systems that perform major functions. The muscular system helps in movement and locomotion. The movement of the internal organs like the heart, the limbs and the digestive system is all due to muscles. The skin helps in protection of the body. It also has sense organs and sweat glands.
• The skeletal system consists of the skull, the backbone, and the limb bones. The skeleton protects the inner body parts. It also helps in movement and in making the body rigid.