Something which is 'living' (not dead) is said to be 'alive'. In most simple terms, 'alive' means 'having life'. Alive is called 'jeevit'or 'zinda' in Hindi. We are alive and you are also alive. Those things which are alive are called 'living things'. All the plants and animals (including human beings) are alive or living things. Now, an important question arises : What criteria do we use to decide whether something is alive ? This is discussed below.

The most important criterion to decide whether something is alive (or not) is the• movement. Movement is one of the most important signs  in an organism. All the living things (which are alive) move by themselves without any external help. In some cases the movements of living things are quite fast which can be easily observed by us but in other cases the movements are very slow and hence observed with difficulty. For example, the movements in most of the animals are fast and can be observed easily but the movements in plants are usually slow and observed with difficulty. Animals and plants move in different ways. This will become clear from the following discussion.

Animals can move from one place to another or they can move their body parts. For example, a frog moves when it jumps into a pond . A bird moves when it flies in the sky, we move when we go to school and a fish moves when it swims in water. We move our hands when we clap and our chest moves up and down when we breathe.

Life processes

the organisms perform some basic functions to keep themselves alive,The basic performed by living to maintain their lire on this earth are called

life proccsses.The basic Transport life processes and common Excretion; to all Control the living and organism and  Coordination are

to stimuli); Growth; Movement and Reproduction. The process of nutrition the taking of food inside the body and converting it into smaller molecules which absorbed by the body. Respiration is the process which releases energy from the absorbed by the body. Transportation is the process in which a substance absorbed or de one part of the body is moved to other parts of the body. Excretion is the process h the waste materials produced in the cells of the body are removed from the

control and coordination (or response to stimuli) is a process which helps the living to survive in the changing environment around them. The process of growth the change from a small organism to a big organism (or an adult organism). In the organism either moves from one place to another or moves its body parts remaining at the same place. The process of reproduction involves the making of organisms from the existing ones, so that organisms could live on this earth for

Energy is Needed for the Life Processes

All the living organisms need energy to perform various life processes. They get this from food. Food is a kind of fuel which provides energy to all the living organisms. The living organisms use the chemical energy for carrying out various life processes. They get this chemical energy from food through chemical reactions. Actually, organisms continuously need energy for their various life processes and other activities which they perform. For example, energy is required by an organism even during This is because whey we are asleep, a number of biological processes keep on  in the body which require energy. Our heart beats non-stop even when we are deep to pump blood throughout the body. And this beating of heart requires energy. the working of heart requires a continuous supply of energy.

The energy required by an organism comes from the food that the organism eats.

food is the basic requirement of all the living organisms for obtaining energy. In Is chapter we will first study the process of intake and utilisation of the food by an ism (called nutrition) and the liberation of energy from the food (called respiration).

that we will study the process of moving the digested food and other materials to various Pans of the body (called transport) and the removal of waste materials from body (called excretion). Let us start with nutrition.


Food is an organic substance. The simplest food is glucose. It is also called simple

stances like complex glucose food (sugar) is starch, and starch Starch is 'carbohydrates'. is made from glucose. Carbohydrates The general are the name of foods for getting energy. Fats and proteins are also foods. (A wider definition of also includes mineral salis, vitamins and water which are essential for the 90wth and development of an organism). The process of taking in food (consuming).

food) and utilising it is called nutrition. It is a process in which food is obtained in order to utilise it to provide energy for performing various metabolic activities of the Organism. Actually, the term 'nutrition' comes from the word 'nutrient'. A nutrient is an organic or inorganic substance required for the maintenance of life and survival of a living organism. In most simpler terms, a nutrient can be said to be a particular type of food. A nutrient can be defined as a substance which an organism obtains from its surroundings and uses it as a source of energy or for the biosynthesis of its body constituents (like tissues and organs). For example, carbohydrates and fats are the nutrients which are used by an organism mainly as a source of energy whereas proteins and mineral salts are nutrients used by an organism for the biosynthesis of its body constituents like skin blood, etc.

The food taken in by an organism contains a large number of nutrients like carbohydrates, fats, proteins, minerals, vitamins and water, etc. We can now say that • Nutrition is a process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilisation of these nutrients by the organism. We will now describe the various ways of procuring food (or obtaining food) by the different organisms. In other words, we will now describe the different modes of nutrition of the various organisms.

Modes of Nutrition

Modes of nutrition means methods of procuring food or obtaining food by an organism. All the organisms do not obtain their food in the same way. Different organisms have different methods of procuring food or obtaining food. In other words, organisms differ in their modes of nutrition. Depending on the mode (or method) of obtaining food, all the organisms can be classified into two groups: autotrophic and heterotrophic. Thus :

There are mainly two modes of nutrition :

Autotrophic, and


We will now discuss the autotrophic mode of nutrition and the heterotrophic mode of nutrition in detail, one by one.

Autotrophic Mode of Nutrition

The word 'auto' means 'self' and 'trophe' means 'nutrition'. Thus, autotrophic means 'selfnutrition'. In autotrophic nutrition, the organism makes (or synthesizes) its own food from the inorganic raw materials like carbon dioxide and water present in the surroundings using the sunlight energy. we can now say that : Autotrophic nutrition is that or nutrition in which an organism makes (or synthesizes) its own food fn)nl the simple inorganic materials like carbon dioxide and water present in  (with the help of sunlight energy). Please note that food is an organic material glucose, etc.). This means that, in autotrophic nutrition, organic material (food) is (or synthesized) from inorganic like carbon dioxide and water by utilising sunlight energy. The green plants have an autotrophic mode of nutrition• the autotrophic bacteria also obtain (heir food by the autotrophic mode of nutrition (though most bacteria are not autotrophic). The organisms having autotrophic Of nutrition are called autotrophic organisms or just autotrophs.

Just like other organisms, plants also require food which can supply energy for their various metabolic activities. Though animals can move from one place to another in search of food, plants just stand still at one place and make their own food. Green plants are autotrophic and synthesize their own food by the process of photosynthesis. 'Photo' means 'light' and 'synthesis' means 'to build', thus 'photosynthesis' means 'building up by light'. The plants use the energy in sunlight to prepare food from carbon dioxide and water in the presence of chlorophyll. Chlorophyll is present in the green coloured bodies called 'chloroplasts' inside thé plant cells. In fact, the leaves of a plant are green because they contain tiny green coloured bodies called chloroplasts (which contain chlorophyll). Keeping these points in mind, we can now define the process of photosynthesis as follows :

Tbe process by which green plants make their own food (like glucose) from carbon dioxide and water by using sunlight energy in the presence of chlorophyll, is called photosynthesis.
. Oxygen gas is released during photosynthesis. The process photosynthesis can be represented as : —-------Chl-------.---.-----> chlorophyll C6H1206 + 602

6C02 + 61420 + Light energy sun) (Photosynthesis)Glucose Oxygen

Carbon dioxide Water (From (A food)

The fool procéss of photosynthesis takes place in the green leaves of a plant. In other words, is made in the green leaves of the plant. The green leaves of a plant make food by combining carbon dioxide and water in the presence of sunlight and chlorophyll.

provides energy required to carry Figure 2. Green plants make their own food by photosynthesis.

reactions involved in the preparation of food. The green pigment called chlorophyll in green leaves helps in absorbing energy from sunlight. Oxygen gas is produced as product during the preparation of food by photosynthesis. This oxygen gas goes into the air.

The food prepared by the green leaves of a plant is in the form of a simple sugar called glucose. This glucose food made in the leaves is then sent to the different of the plant (see Figure 2). The extra glucose is changed into another food called starch' This starch is stored in the leaves of the plant. Glucose and starch belong to a of foods called carbohydrates. The foods like carbohydrates prepared by contain chemical energy stored in them. Thus, the green plants convert sunlight into chemical energy by making carbohydrates (foods). The food prepared b! photosynthesis provides all the energy to a plant which it needs to grow. And

plant foods (like foodgrains, fruits and vegetables), the chemical energy stored in is released in our body during respiration.

We will now describe what actually happens during the process of photosynthesis. photosynthesis takes place in the following three steps (i) Absorption of sunlight energy by chlorophyll.

conversion of light energy into chemical energy, and splitting of water into hydrogen and oxygen by light energy.

Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose by utilising the chemical energy (obtained by the transformation of light energy).

please note that the three steps involved in photosynthesis need not take place one after the other immediately. They can take place at different times. For example, desert plants take up carbon dioxide at night and prepare an intermediate product which is acted upon by the sunlight energy absorbed by chlorophyll when the sun shines during the next day.

Conditions Necessary for Photosynthesis

It has been found by experiments that the presence of sunlight, chlorophyll, carbon dioxide and water is necessary for the process of photosynthesis. So, we can say that : The conditions necessary for photosynthesis to take place are .

l. Sunlight,


Carbon dioxide, and


Please note that the conditions necessary for photosynthesis are also the conditions necessary for autotrophic nutrition.We will now describe some experiments to show that 9anlight, chlorophyll and carbon dioxide are necessary for photosynthesis by green plants.

These experiments will also show that leaves finally make 'starch' as food by


The experiments on photosynthesis depend on the fact that green leaves make starch food. And that starch gives a blue-black colour with iodine solution. Now, ordinarily all the Plants have starch in their green leaves, so before we can use a plant in a experiment, the initial starch present in its leaves must be removed. In other words, we should destarch the leaves of a plant before using it in a photosynthesis

dark place in The a room green for leaves at least of a three plant are days.destarched by keeping this plant in a completely

When the plant is kept in a dark place, it cannot make more starch (food) by because there is no sunlight. so, the plant kept in dark place uses the stored already stored in its leaves during respiration. The plant will use up in its leaves in about days' time. so, after about three days, the plant will not have any starch left in them. And we say that the leaves have been experiments. This Please plant note with that we destarched will be using leaves a plant can growing now in used a pot in in the these photosynthesis experitnents. The 'plant growing in a pot' is called spotted plant'.
The upper half part of the leaf (which was outside the glass bottle, having carbo dioxide around it) turns blue-black on adding iodine solution showing that iodine present in this upper half of the leaf [see Figure 5(c)]. From this observation conclude that photosynthesis (to make starch) takes place in the presence of carbon dioxide. In other words, carbon dioxide is necessary for the process photosynthesis to take place.

Raw Materials for Photosynthesis:-

The preparation of carbohydrates (food) by plants by the process of Photosynthesis requires two materials (or substances) : carbon dioxide, and water. Thus, the raw material; for photosynthesis are :

(i) Carbon dioxide, and (ii) Water.

We will now describe how these two raw materials become available to plants for photosynthesis.

1. How the Plants Obtain Carbon Dioxide. There are a large number of tiny pores called stomata on the surface of the leaves of plants (The singular of stomata is stoma). The green plants take carbon dioxide from air for photosynthesis. The carbon dioxide gas enters the leaves of the plant through the stomata present on their surface [see figur: 6(a)]. Each stomatal pore (or stoma) is surrounded by a pair of guard cells. The opening



cells of a leaf

Guard cells (curved)

Open stoma

(a) Open stomata (b) Closed stomata Figure 6. Stomata (tiny pores) are present on the surface of a leaf.

and closing of stomatal pores is controlled by the guard cells. When water flows into guard cells, they swell, become curved and cause the pore to open [see Figure the other hand, when the guard cells lose water, they shrink, become and the stomatal pore [see Figure A large amount of water is also lost from the the plant leaves through open stomatal pores. So, when the plant does not need dioxide and wants to conserve water, the stomatal pores are closed. The Produced during photosynthesis also goes out through the stomatal pores of the Please note that in addition to leaves, the stomata are also present in the green shoots) of a plant. So, the green stems (or shoots) of a plant also carry out photosyn It is clear from the above discussion that stomata allow the movement of gases in afl of plant cells. In other words, the gaseous exchange in plants takes place stomata in leaves (and other green parts).

occur only in the lower surface oc the leaf but in narrow-plants, the are equally distributed on both the sides of the leaf Another point to be noted is the aquatic plants (or water plants) use the carbon dioxide gas dissolved in water for out photosynthesis.

the Plants Obtain Water for Photosynthesis. The water required by the for photosynthesis is absorbed by the roots of the plants from the soil through the of osmosis. The water absorbed by the roots of the plants is transported upward the xylem vessels to the leaves where it reaches the cells and utilised in photosynthesis.

The two raw materials, carbon dioxide and water, are required by the plants to prepare foods called carbohydrates (such as glucose and starch). But the plants also need materials such as nitrogen, phosphorus, iron and magnesium, etc., for building body. The plants take materials like nitrogen, phosphorus, iron and magnesium, from the soile For example, nitrogen is an essential element used by the plants to proteins and other compounds. The plants take up nitrogen from the soil in the form inorganic salts called nitrates (or nitrites), or in the form of organic compounds which produced by bacteria from the atmospheric nitrogen.

Site of Photosynthesis : Chloroplasts

Chloroplasts are the organelles in the cells of green plants which contain chlorophyll here photosynthesis takes place. Thus, photosynthesis occurs in the organelles called Chloroplasts present in the photosynthetic cells (or mesophyll cells) of green plants. In other words, the site of photosynthesis in a cell of the leaf are chloroplasts. Chloroplasts be seen easily by using a light microscope. In a cross-section of a leaf, chloroplasts be seen as numerous disc-like organelles in the photosynthetic cells (or mesophyll cells) of the palisade tissue just below the upper epidermis.


upper epidermis

Palisade layer


Spongy layer

Lower epidermis

Guard cells

The structure of a leaf to show chloroplasts in it (The small in the above diagram are all chloroplasts).

the Structure of a leaf shown., we can see that the middle layers in the layer and spongy layer) contain photosynthetic cells called mesophyll cells.

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