CHAPTER – 1 NURITION IN PLANTS

 CHAPTER – 1 NURITION IN PLANTS

TOPICS:

1.     Introduction

2.     Modes of nutrition in plants

3.     Photosynthesis – Food making process in plants

4.     Other modes of nutrition in plants

5.     Saprotrophs

6.     How nutrients are replenished in the soil

1.  INTRODUCTION:

·       Food is essential for all living organisms.

·       Carbohydrates, proteins, fats, vitamins and minerals are components of food.

·       These components of food are called nutrients and are necessary for our body.

·       Plants can synthesise food for themselves but animals including humans cannot. They get it from plants or animals that eat plants.

·       Thus, humans and animals are directly or indirectly dependent on plants.

2.  MODES OF NUTRITION IN PLANTS:

Plants are the only organisms that can prepare food for themselves by using water, carbon dioxide and minerals. 

Nutrients may be defined as the process of obtaining, and utilising food by an organism, is known as nutrition. The process of obtaining food is not the same in all organisms. 

On the basis of food habits, the modes of obtaining the required nutrition, by the body, have been divided into the following two categories:·

  Autotrophic Nutrition (In Greek, auto = self, trophe = nutrition): It is the mode of nutrition in which organisms can make their own food from simple raw materials. Example-All green plants and some bacteria are autotrophs.

·Heterotrophic Nutrition (In Greek, heterone = (an) other) : It is the mode of nutrition in which organisms cannot prepare their food on their own and depend on others for it. Example-All animals, and a few plants, are heterotrophs.

3. PHOTOSYNTHESIS – (photo = light, synthesis = to combine)

FOOD MAKING PROCESS IN PLANTS:

· The synthesis of food in plants occurs in their leaves. Hence, leaves are called the food factories of the plants. The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used by the plants to synthesise their food using carbon dioxide and water

·This process is called photosynthesis as it takes place in the presence of sunlight. This process can be written in the form of the following equation:

  

Raw Materials for Photosynthesis

These are as-

·  Water and Minerals: These are absorbed by the roots from the soil. From here, water and minerals are transported to other parts of the plant by the ‘vessels’. Vessels are tubes that run throughout the root, the stem, the branches and the leaves.

· Carbon dioxide: Plants take carbon dioxide from the atmosphere. Carbon dioxide enters the leaves through tiny pores present on the surface of leaves. Such pores are called stomata. The stomata are surrounded by special cells called guard cells.

·  Sunlight: Sunlight is the light and energy that comes from the Sun. During photosynthesis the plants use the energy of sunlight to prepare food. That is why the food making process, in plants, is called photosynthesis. (Photo = light, synthesis = to combine)

·  Chlorophyll: The leaves are green due to the presence of a pigment—chlorophyll. It helps the leaves to capture solar energy. This energy is used to prepare food from carbon dioxide and water.

Photosynthesis is a unique process. It is this process that supplies food, directly or indirectly, for all living organisms. The energy of the sun, thus, gets passed on to all organisms through plants. Plants also provide oxygen, needed by all living organisms, for respiration.

Products of Photosynthesis

· The initial product of photosynthesis is a carbohydrate—glucose. It next gets converted to starch whose presence, in the leaves,

·  Some carbohydrates are also converted to proteins and fats. Besides carbon, hydrogen and oxygen, proteins also contain nitrogen.

Stomata

•          Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves.

•          These pores are surrounded by ‘guard cells’. Such pores are called stomata.

•     Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem, the branches and the leaves

•      They form a continuous path or passage for the nutrients to reach the leaf.

Cell structure:   

•      Buildings are made of bricks. Similarly, the bodies of living organisms are made of          tiny units called cells.

•      Cells can be seen only under the microscope.

•     Some organisms are made of only one cell.

•     The cell is enclosed by a thin outer boundary, called the cell membrane.

•      Most cells have a distinct, centrally located spherical structure called the nucleus.

The nucleus is surrounded by a jelly-like substance called cytoplasm.

Leaves of various color:

The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments makes the green colour &  Photosynthesis takes place in these leaves also.

4.  OTHER MODES OF NUTRITION IN PLANTS:

There are some plants which do not have chlorophyll. Like humans and animals such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition.

Parasite:

•   They use the heterotrophic mode of nutrition.

•   It does not have chlorophyll in it.

•   It takes readymade food from the plant which it is climbing.

•    The plant on which it climbs is called a host.

•      Since it deprives the host of valuable nutrients, it is called a parasite.

Cuscuta    

   

Insectivorous plants:

•  There are a few plants which can trap insects and digest them.

•  Such insect-eating plants are called insectivorous plants.

•   Such plants do not get all the required nutrients from the soil in which they grow.

Pitcher plant   (Nepenthes)                        Sun dew   

                                                                                  

       

                                  

Venus fly trap                                               

5.  SAPROTROPHS:

·       ‘Sapros’ means rotten and ‘trophic’ means food.

·       Saprotrophic nutrition is the process in which the organisms feed on dead and decaying matter.

·       The food gets digested outside the cells, or sometimes, even outside the body of the organism.

·       This type of digestion is called extracellular digestion.

·       The organism secretes digestive juices directly onto the food.

·       These digestive juices make the food soluble; the organism then directly absorbs it.

Some organisms, which have saprotrophic nutrition, are Rhizopus (bread mould), Mucor (pin mould), Yeast, Agaricus (mushroom) and many bacteria.

·     

Symbiotic Relationship: (In Greek, symbion = “to live together”)

Sometimes two organisms live in close association and develop a relationship that is beneficial to both. This is called symbiotic relationship. 

 Some algae and fungi live in the roots of trees. They receive shelter and nutrition from the tree; in return, they help the trees to absorb water and minerals more efficiently.

·   Lichen is a living partnership between a fungus and an alga. The fungus absorbs water and provides shelter. The alga prepares food by photosynthesis.

 ·  Rhizobium is a bacterium that lives in the roots of leguminous plants. It converts nitrogen, from the atmosphere, into a usable form that can be utilised by the plants. The plants, in turn, provide food and shelter to the bacterium.

6.  HOW NUTRIENTS ARE REPLENISHED IN THE SOIL:

Plants remove nutrients from the soil as they grow. These nutrients need to be reintroduced into the soil so that the soil remains productive. Farmers usually enrich the soil by adding manures and fertilisers; these are materials that contain one or more of the nutrients that plants need.

 

 

Usually crop plants absorb a lot of nitrogen and the soil becomes deficient in nitrogen. You learnt that though nitrogen gas is available in plenty in the air, plants cannot use it in the manner they can use carbon dioxide. They need nitrogen in a soluble form. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a usable form. But Rhizobium cannot make its own food. So it often lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. In return, the plants provide food and shelter to the bacteria.  

They, thus, have a symbiotic relationship. This association is of great significance for the farmers. They can reduce the use of nitrogenous fertiliser where leguminous plants are grown. Most of the pulses (dals) are obtained from leguminous plants.

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