7th Class Science Nutrition in Plants Nutrition in Green Plants

     Introduction

Plants require water, sunlight, carbon dioxide and minerals for making their food. These nutrients in the plants are converted into glucose by the process of photosynthesis. The growth rate of a plant mainly depends on the availability of nutrients in the soil on which the plant grows. Lack of nutrients in the soil cause improper growth and shorter life-span of the plant. There are two modes of nutrition’s in plants. These are autotrophs and heterotrophs. Heterotrophic plants are further classified into three groups, saprophytes, parasite and insectivores. The living organisms, which make their own food by photo syntheses with the help of chlorophyll present in their body, have autotrophs mode of nutrition. The living organisms, which are unable to make their own food and depend on the autotrophs for their nutritional needs, is said to have heterotrophs mode of nutrition. In this chapter, we will study about the nutrition in different types of plants.

      Nutrition in Green Plants

Green plants are capable of making their own food by the process of photosynthesis, due to the presence of a pigment called chlorophyll in the plants. Leaves of a plant absorb carbondioxide and trap Sun rays which act as reactants in the process of photosynthesis. Different parts of a plant perform different functions. Root of a plant absorbs water and minerals from the soil .

Water and minerals absorbed by the root of the plant are transported throughout the plant through its stem, which is called transportation or conduction. Stem of a plant gives support to the plant to stand on the soil. The xylem and phloem tissues in the stem help the plant to transport essential substances from one part to another.

Look at the following picture to understand the process of photosynthesis in a plant:

The following reaction takes place between the reactants during the process of photosynthesis.

(Carbon dioxide)     (Water)   Chlorophyll    (Carbohydrates)    (Oxygen)  

          Function of Leaves

Leaves are the part of a green plant where the process of photosynthesis occurs.

        Absorption of Solar Energy through the Leaves of the Plant

Leaves absorb solar energy and carbon dioxide from air.

Look at the following picture of the structure of chlorophyll in a leaf:

 Chlorophyll transfers absorbed solar energy into the centre of the cell where, exchange of electrons between the water molecules and solar energy takes place. The result of the exchange of these electrons is the production of oxygen gas and hydrogen ions. ATP (adenosine triphosphate) is an enzyme. The function of ATP is to transport the energy within the cell for metabolism which is produced during the exchange of these electrons. ATP reduces a substance into its simpler form called, nicotinamide adenine dinucleotide phosphate (NADPH), which is used to convert the carbon dioxide into glucose for further use of the plant. Glucose or sugar is the product of the process of the photosynthesis.

       Respiration in Plant

Respiration is the process in which oxygen is taken in, for the oxidation of food to release energy. Plants release carbon dioxide during respiration. During the day time, when the process of photosynthesis occurs, plants release more oxygen as compare to the amount of oxygen taken by the plant for respiration. Therefore, the released amount of oxygen by plants is taken in by other living organism for respiration. During night, when there is no photosynthesis, plants release carbon dioxide.

The following reaction takes place during the process of respiration:

 Energy    

(Sugar)         (Oxygen)   (Carbondioxide)  (Water)

Carbohydrates is the product of respiration. Carbohydrates react with oxygen and oxidation of food takes place in the plant. Due to the oxidation of the food, carbohydrates break down into carbondioxide and water with releasing an amount of energy, which is used by the plant for their functions.  

        Function of Stem and Root in the Process of Photosynthesis

Stem and Root both play very important role in the process of photosynthesis.

       Function of Root in the Process of Photosynthesis

Root of a plant covers large area for the search of huge amount of water and minerals for absorption. Water and minerals enter through the cap holes of the root. The mechanism of entering water and minerals is the same as that of a small strip of cotton placed in a cup of water, which gets wet after sometime, absorbing the available water. If minerals are not available for the absorption of the plant, specific type of symptoms appear on the different parts of the plant. For example, magnesium helps for the formation of molecules of chlorophyll. Therefore, yellow colour of leaves appear due to the deficiency of magnesium.

Look at the following picture of root of a plant:

         Function of Stem in the Process of Photosynthesis

Plants absorb water and minerals from the soil through the root. The vessels in the stem and root of the plants are made of special cells which forming the vascular tissue. The xylem tissue transport water and minerals from the soil to the leaves. Every part of a plant is connected with xylem tissue which carry water and mineral throughout the plant. The synthesized food is transported by the phloem tissue

Look at the following picture of transportation mechanism in a plant:

        Requirement of Nutrients in a Plant

Nutrients of plants are classified into two groups as per the requirements, micronutrients or trace elements and macro-nutrients. The requirement of micro-nutrients in a plant is in less quantity therefore, called trace or micro- nutrients. The requirement of macro-nutrients in a plant is in huge quantity therefore, called macro nutrients. Micronutrients or trace elements for a plant are: magnesium, boron, copper, iron, zinc and chlorine, etc. Macro-nutrients are: carbon, hydrogen, oxygen, phosphorous, calcium, magnesium, nitrogen, sulfur, etc.

Plants obtain required nutrients from soil and air, carbon dioxide from air, oxygen from air and water from soil. Plants absorb nitrogen from soil in the form of nitrates ions  or as ammonium ions  or as ammonium ions . Some bacteria can fix nitrogen directly from air. Absorption of potassium, calcium, iron, etc. in a plant is done in ionic form like, .  

      Consider the following statements:

Statement 1: Water and minerals are transported throughout the plant through xylem tissue.

Statement 2: Synthesized food is transported throughout the plant through xylem tissue.

Which one of the following is correct about the above statements?

(a) Statement 1 is true and 2 is false

(b) Statement 1 is false and 2 is true

(c) Both statements are true

(d) Both statements are false

(e) None of these

Answer: (a)

Explanation

Water and minerals are transported throughout the plant through xylem tissue. Therefore, option (a) is correct and rest of the options is incorrect.

      Which one of the following products is made by the plant during the process of photosynthesis?

(a)

(b)

(c)

(d) All of these

(e) None of these  

Answer: (b)

Explanation 

Plant make sugar by the process of photosynthesis. Therefore, option (b) is correct and rest of the options is incorrect..