Showing posts with label CBSE-VII BIOLOGY. Show all posts
Showing posts with label CBSE-VII BIOLOGY. Show all posts

Sunday, January 10, 2021


To produce its kind is a characteristic of all living organisms. You have already learnt this in Class VI. The production of new individuals from their parents is known as reproduction. But, how do plants reproduce? There are different modes of reproduction in plants which we shall learn in this chapter. 

MODES OF REPRODUCTION In Class VI you learnt about different parts of a flowering plant. Try to list the various parts of a plant and write the functions of each. Most plants have roots, stems and leaves. These are called the vegetative parts of a plant. After a certain period of growth, most plants bear flowers. You may have seen the mango trees flowering in spring. It is these flowers that give rise to juicy mango fruit we enjoy in summer. We eat the fruits and usually discard the seeds. Seeds germinate and form new plants. So, what is the function of flowers in plants? Flowers perform the function of reproduction in plants. Flowers are the reproductive parts. 

There are several ways by which plants produce their offspring. These are categorised into two types: (i) asexual, and (ii) sexual reproduction. In asexual reproduction plants can give rise to new plants without seeds, whereas in sexual reproduction, new plants are obtained from seeds 

Plants have two kinds of parts: 
Vegetative Parts - These are the parts of the plant that plays a major role in the life cycle of a plant such as preparation of food, transportation of food, water and nutrients etc. For Example, roots, stems and leaves. 

Reproductive Parts - These are the parts of a plant that play a major role in the reproduction process in plants, For Example, flowers, fruits

Reproduction in plants can be categorized into two types:
Asexual Reproduction – The new plants are produced without using the seeds. In this process, generally, the leaves, stems and roots participate in reproduction. 

Cut a branch of rose or champa with a node. This piece of branch is termed a cutting. Bury the cutting in the soil. A node is a part of the stem/branch at which a leaf arises. Water the cutting every day and observe its growth. Observe and record the number of days taken for roots to come out and new leaves to arise. Try the same activity by growing money plant in a jar of water and record your observations. 

You must have seen flower buds developing into flowers. Apart from flower buds, there are buds in the axil (point of attachment of the leaf at the node) of leaves which develop into shoots. These buds are called vegetative buds. A bud consists of a short stem around which immature overlapping leaves are present. Vegetative buds can also give rise to new plants

Take a fresh potato. Observe the scars on it with the help of a magnifying glass. You may find bud(s) in them. These scars are also called “eyes”. Cut the potato into small portions, each with an eye and bury them in the soil. Water the pieces regularly for a few days and observe their progress. What do you find? 

Likewise you can also grow ginger or turmeric. Bryophyllum (sprout leaf plant) has buds in the margins of leaves. If a leaf of this plant falls on a moist soil, each bud can give rise to a new plant. Roots of some plants can also give rise to new plants. Sweet potato and dahlia are examples. Plants such as cacti produce new plants when their parts get detached from the main plant body. Each detached part can grow into a new plant. 

Plants produced by vegetative propagation take less time to grow and bear flowers and fruits earlier than those produced from seeds. The new plants are exact copies of the parent plant, as they are produced from a single parent. Later in this chapter you will learn that plants produced by sexual reproduction have characters of both the parents. Plants produce seeds as a result of sexual reproduction. 

Budding: You have already learnt about the tiny organisms like yeast can be seen only under a microscope. These grow and multiply every few hours if sufficient nutrients are made available to them. Remember that yeast is a single-celled organism. Let us see how they reproduce? 

The small bulb-like projection coming out from the yeast cell is called a bud. The bud gradually grows and gets detached from the parent cell and forms a new yeast cell. The new yeast cell grows, matures and produces more yeast cells. Sometimes, another bud arises from the bud forming a chain of buds. If this process continues, a large number of yeast cells are produced in a short time. 

Fragmentation: You might have seen slimy green patches in ponds, or in other stagnant water bodies. These are the algae. When water and nutrients are available algae grow and multiply rapidly by fragmentation. An alga breaks up into two or more fragments. These fragments or pieces grow into new individuals. This process continues and they cover a large area in a short period of time. 

Spore formation In Chapter 1 you learnt that the fungi on a bread piece grow from spores which are present in the air. Repeat Activity 1.2. Observe the spores in the cottonlike mesh on the bread. When spores are released they keep floating in the air. As they are very light they can cover long distances. Spores are asexual reproductive bodies. Each spore is covered by a hard protective coat to withstand unfavourable conditions such as high temperature and low humidity. So they can survive for a long time. Under favourable conditions, a spore germinates and develops into a new individual. Plants such as moss and ferns also reproduce by means of spores. 

Sexual Reproduction – The new plants are produced with the help of the seeds of a plant. In this process, the flowers of the plants participate in reproduction. You have learnt earlier the structure of a flower. You know that the flowers are the reproductive parts of a plant. Stamens are the male reproductive part and pistil is the female reproductive part.

Study the various parts of a stamen and pistil. Flowers which contain either only pistil or only stamens are called unisexual flowers. Flowers which contain both stamens and pistil are called bisexual flowers. Corn, papaya and cucumber produce unisexual flowers, whereas mustard, rose and petunia have bisexual flowers. Both male and female unisexual flowers may be present in the same plant or in different plants. Could you identify the anther and the filament of a stamen? 

Anther contains pollen grains which produce male gametes. A pistil consists of stigma, style and ovary. Ovary contains one or more ovules. The female gamete or the egg is formed in an ovule. In sexual reproduction a male and a female gamete fuse to form a zygote. 

Pollination Generally, pollen grains have a tough protective coat which prevents them from drying up. Since pollen grains are light, they can be carried by wind or water. Insects visit flowers and carry away pollen on their bodies. Some of the pollen lands on the stigma of a flower of the same kind. The transfer of pollen from the anther to the stigma of a flower is called pollination

If the pollen lands on the stigma of the same flower or another flower of the same plant, it is called self-pollination. When the pollen of a flower lands on the stigma of a flower of a different plant of the same kind, it is called cross-pollination

Fertilisation The cell which results after fusion of the gametes is called a zygote. The process of fusion of male and female fertilisation . The zygote develops into an embryo. Fruits and seeds form After fertilisation, the ovary grows into a fruit and other parts of the flower fall off. The fruit is the ripened ovary. The seeds develop from the ovules. The seed contains an embryo enclosed in a protective seed coat. Some fruits are fleshy and juicy such as mango and orange. Some fruits are hard like almonds and walnuts. 

SEED DISPERSAL: In nature same kind of plants grow at different places. This happens because seeds are dispersed to different places. Sometimes after a walk through a forest or a field or a park, you may have found seeds or fruits sticking to your clothes. 

Did you try to observe how these seeds were clinging to your clothes? What do you think will happen if all seeds of a plant were to fall at the same place and grow there? There would be severe competition for sunlight, water, minerals and space. As a result the seeds would not grow into healthy plants. 

Plants benefit by seed dispersal. It prevents competition between the plant and its own seedlings for sunlight, water and minerals. It also enables the plants to invade new habitats for wider distribution. Seeds and fruits of plants are carried away by wind, water and animals. Winged seeds such as those of drumstick and maple, light seeds of grasses or hairy seeds of aak (Madar) and hairy fruit of sunflower get blown off with the wind to far away places. 

     Some seeds are dispersed by water. These fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut. Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places. Examples are Xanthium and Urena. 

Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant. This happens in the case of castor and balsam.


One day Boojho was eagerly waiting to meet his grandparents who were coming to the town after a year. He was in a real hurry as he wanted to receive them at the bus-stop. He ran fast and reached the bus-stop in a few minutes. He was breathing rapidly. His grandmother asked him why he was breathing so fast. Boojho told her that he came running all the way. But the question got stuck in his mind. He wondered why running makes a person breathe faster. The answer to Boojho’s question lies in understanding why we breathe. Breathing is a part of respiration. Let us learn about respiration. 

WHY DO WE RESPIRE? In Chapter 2 you learnt that all organisms are made of small microscopic units called cells. A cell is the smallest structural and functional unit of an organism. Each cell of an organism performs certain functions such as nutrition, transport, excretion and reproduction. To perform these functions, the cell needs energy. Even when we are eating, sleeping or reading we require energy. But, where does this energy come from? Can you say why your parents insist that you should eat regularly? The food has stored energy, which is released during respiration. 

Therefore, all living organisms respire to get energy from food. During breathing, we breathe in air. You know that air contains oxygen. We breathe out air which is rich in carbon dioxide. The air we breathe in is transported to all parts of the body and ultimately to each cell. In the cells, oxygen in the air helps in the breakdown of food. The process of breakdown of food in the cell with the release of energy is called cellular respiration. Cellular respiration takes place in the cells of all organisms. In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen. When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration. 

 Food can also be broken down, without using oxygen. This is called anaerobic respiration. Breakdown of food releases energy. Human beings and many other animals undergo aerobic respiration. Carbon dioxide and water are also released in aerobic respiration. 

You should know that there are some organisms such as yeast that can survive in the absence of air. They are called anaerobes. They get energy through anaerobic respiration. In the absence of oxygen, glucose breaks down into alcohol and carbon dioxide, as given below: in the absence of oxygen Glucose → alcohol + carbon dioxide + energy. 

Our muscle cells can also respire anaerobically, but only for a short time, when there is a temporary deficiency of oxygen. During heavy exercise, fast running (Fig. 10.1), cycling, walking for many hours or heavy weight lifting, the demand for energy is high. But the supply of oxygen to produce the energy is limited. Then anaerobic respiration takes places in the muscle cells to fulfil the demand of energy: 

Have you ever wondered why you get muscle cramps after heavy exercise? The cramps occur when muscle cells respire anaerobically. The partial breakdown of glucose produces lactic acid. The accumulation of lactic acid causes muscle cramps. We get relief from cramps after a hot water bath or a massage. Can you guess why it is so? Hot water bath or massage improves circulation of blood. As a result, the supply of oxygen to the muscle cells increases. The increase in the supply of oxygen results in the complete breakdown of lactic acid into carbon dioxide and water. 

Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. The taking in of air rich in oxygen into the body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation. It is a continuous process which goes on all the time and throughout the life of an organism. 

The number of times a person breathes in a minute is termed as the breathing rate. During breathing inhalation and exhalation take place alternately. A breath means one inhalation plus one exhalation. As a result more oxygen is supplied to our cells. It speeds up the breakdown of food and more energy is released. 

A breath can be defined as an inhalation followed by an exhalation. Inhalation is the process of taking the air that contains oxygen inside the body. Exhalation is a process of releasing out air that contains carbon dioxide out of the body. Inhalation and exhalation take place alternatively in the breathing process. 

Let us now learn about the mechanism of breathing. Normally we take in air through our nostrils. When we inhale air, it passes through our nostrils into the nasal cavity. From the nasal cavity, the air reaches our lungs through the windpipe. Lungs are present in the chest cavity. This cavity is surrounded by ribs on the sides. A large, muscular sheet called diaphragm forms the floor of the chest cavity. Breathing involves the movement of the diaphragm and the rib cage. 

We take in the air present in the environment through our nostrils which travels through the nasal cavity. Then it moves through the windpipe and reaches the lungs. The lungs are located in the chest cavity which is surrounded by the ribs. On the floor of the chest cavity lays a muscle sheet called diaphragm. The lungs when releasing out air from the body which brings back the diaphragm and the ribs to their original positions. 

During inhalation, ribs move up and outwards and diaphragm moves down. This movement increases space in our chest cavity and air rushes into the lungs. The lungs get filled with air. During exhalation, ribs move down and inwards, while diaphragm moves up to its former position. This reduces the size of the chest cavity and air is pushed out of the lungs. These movements in our body can be felt easily. Take a deep breath. Keep your palm on the abdomen, feel the movement of abdomen. What do you find? 

To understand the expansion of the lungs, pull the rubbber sheet from the base downwards and watch the alloons. Next, push the rubber/plastic sheet up and observe the balloons. Did you see any changes in the balloons? What do the balloons in this model represent? What does the rubber sheet represent? Now, you should be able to explain the mechanism of breathing.

Breathing rate can be defined as the number of times a person breathes in a minute is called as breathing rate. An average adult human being breeds 15 to 18 times in a minute. While exercising, this rate can change up to 25 times a minute. 

When you inhale (breathe in), air enters your lungs and oxygen from the air moves from your lungs to your blood. At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs and is exhaled (breathe out). This process is called gas exchange and is essential to life. 

As we inhale the air present in the surroundings sometimes various unwanted elements such as smoke and dust are also included in it. However, they get stuck in the hair in our nostrils but some of them can get through the nasal cavity.They thus cause irritation in the nasal cavity which makes us sneeze. 
This helps in getting rid of the unwanted particles out of the nasal cavity.

Many animals have just cavities in their bodies just like human beings for example lions, elephants, goats, cows, snakes and birds. 

Breathing in cockroach:  A cockroach has small openings on the sides of its body. Other insects also have similar openings. These openings are called spiracles. Insects have a network of air tubes called tracheae for gas exchange. Oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissue, and reaches every cell of the body. Similarly, carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles. These air tubes or tracheae are found only in insects and not in any other group of animals. 

Earthworm: Recall from Chapter 9 of Class VI that earthworms breathe through their skins. The skin of an earthworm feels moist and slimy on touching. Gases can easily pass through them. Though frogs have a pair of lungs like human beings, they can also breathe through their skin, which is moist and slippery.

Can we breathe and survive in water? There are many organisms which live in water. How do they breathe under water? You have studied in Class VI that gills in fish help them to use oxygen dissolved in water. Gills are projections of the skin. You may wonder how gills help in breathing. Gills are well supplied with blood vessels for exchange of gases. 

Like other living organisms, plants also respire for their survival as you have learnt in Class VI. They also take in oxygen from the air and give out carbon dioxide. In the cells oxygen is used to break down glucose into carbon dioxide and water as in other organisms. 

In plants each part can independently take in oxygen from the air and give out carbon dioxide. You have already learnt in Chapter 1 that the leaves of the plants have tiny pores called stomata for exchange of oxygen and carbon dioxide. 

Like all other living cells of the plants, the root cells also need oxygen to generate energy. Roots take up air from the air spaces present between the soil particles Can you guess what would happen if a potted plant is overwatered? In this chapter you learnt that respiration is a vital biological process. All living organisms need to respire to get the energy needed for their survival process. All living organisms need to respire to get the energy needed 
for their survival.

Saturday, January 9, 2021


In plants, transport system is not complicated as in animals. Transport of water and minerals. Plants absorb water and minerals by the roots. The roots have root hair. The root hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in water. The root hair is in contact with the water present between the soil particles. 

Can you guess how water moves from the root to the leaves? What kind of transport system is present in plants? Well, Boojho is right. Plants have pipe-like vessels to transport water and nutrients from the soil. The vessels are made of special cells, forming the vascular tissue. A tissue is a group of cells that perform specialised function in an organism. The vascular tissue for the transport of water and nutrients in the plant is called the xylem. The xylem forms a continuous network of channels that connects roots to the leaves through the stem and branches and thus transports water to the entire plant. 

You know that leaves synthesise food. The food has to be transported to all parts of the plant. This is done by the vascular tissue called the phloem. Thus, xylem and phloem transport substances in plants. The transport system in plants consists of bundles of tubes in the stem, branches and roots. These tubes are called xylem and phloem. The main function of xylem is to transport water and dissolved minerals from the roots to rest of the plant body. 

Transport of substance in plants:
To circulate water, essential nutrients, excretory products, and gases within the plants for various purposes, transportation in plants is necessary. In vascular tissues, this transportation in the plant takes place. By a suction force, water and minerals are transported to various parts of the plant. 

Plants absorb water and minerals by the roots. The roots have root hair. The root hair increase the surface area of the root for the absorption of water and mineral nutrients dissolved in water. The root hair is in contact with the water present between the soil particles. 

In plants, there are pipe-like vessels through which water and minerals can enter the plants. These vessels are made up of elongated cells and thick walls. A group of cells forms a tissue that performs a specialized function within the organisms. These are conducting tissues. These conducting tissues are divided into two types which are xylem and phloem. 

Xylem: It is a vascular tissue that spreads from the top to bottom of the plant. For the transport of water molecules, it helps a lot. It also plays a vital role in the case of dissolved substances from the root hairs to aerial parts of the plant. It transfers water in one direction. Commonly, xylem occupies the central part of the vascular bundle. 

Phloem: It is also vascular tissue. In a plant where the necessity of food molecules is there, the use of the phloem transportation process will take place.

The food manufactured in the leaves is transported to different parts of the plant. This transpiration of food material from leaves to the others parts of plant is carried out by the tissue called phloem and process transport food material is called translocation. The phloem consists of those vessels known as sieve tubes. Xylem and phloem together form the vascular or connective tissue. 

Transpiration: Transpiration is a process that involves loss of water vapour through the stomata of plants. Transpiration is thought to be a 'necessary cost or evil' to allow the plant to absorb water from the soil. It is an inevitable process. 

Transpiration is important in plants for three major reasons: Cooling of the plant: the loss of water vapour from the plant cools down the plant when the weather is very hot. 
The transpirational pull: when the plant loses water through transpiration from the leaves, water and mineral salts from the stem and roots moves, or is `pulled', upwards into the leaves. Water and is therefore taken up from the soil by osmosis and finally exits the plants through the stomata. 

Plant structure: young plants or plants without woody stems require water for structural support. Transpiration helps maintain the turgidity in plants. 

Plants absorb mineral nutrients and water from the soil. Not all the water absorbed is utilised by the plant. The water evaporates through the stomata present on the surface of the leaves by the process of transpiration. The evaporation of water from leaves generates a suction pull (the same that you produce when you suck water through a straw) which can pull water to great heights in the tall trees. Transpiration also cools the plant.