The process of making of food by green plants in the presence of sunlight and chlorophyll is known as photosynthesis.
Photosynthesis is the combination of two words- Photo + Synthesis. ‘Photo’ means light and ‘Synthesis’ means to make.
Process of food-making in green plants:
1. Green plants make their food themselves. Green leaves make food from Carbon dioxide and water in the presence of sunlight and chlorophyll.
2. Hence, for taking place of photosynthesis carbon dioxide, water and sunlight must be reached at the green leaves in addition to presence of chlorophyll.Fig. Guide to photosynthesis
3. Leaves have several tiny pores like structure on its lower surface. These are called stomata through which leaves absorb carbon dioxide from air. Water is transported to the leaves through hair like pipelines from the roots. These pipelines are present throughout the plant, i.e. from roots to branches and leaves.
4. These pipe-lines are known as Xylem. Xylem is a type of tissues. Chlorophyll, a green pigment, is found in green leaves. Chlorophyll absorbs sunlight and gives energy.
5. Chlorophyll absorbs sunlight, carbon dioxide and water and convert them to carbohydrate and oxygen. Carbohydrate is used as food and oxygen is emitted out to atmosphere.
6. This whole process of making food by plants is called photosynthesis.
7. The reaction takes place in the process of photosynthesis can be written as:
8. Carbohydrate which is produced in the process of photosynthesis is ultimately converted into starch and stored into leaves. From leaves it is transported to the parts of plants. Starch is a type of carbohydrate. The oxygen so produced is released into atmosphere through the stomata.
9. Leaves are known as the kitchen or food factories of the plants because photosynthesis takes place in leaves. Leaves look green because of the presence of chlorophyll.
Besides leaves, photosynthesis takes place in other green parts of the plant also, such as in green stems. Chlorophyll is necessary for photosynthesis; hence photosynthesis takes place only in green plants.
10. The leaves of plants that grow in desert areas are modified in spine like structure or scales to reduce the loss of water in the course of transpiration. In such plants photosynthesis takes place in green stems.
11. The photosynthesis helps to maintain a balance between oxygen and carbon dioxide in the atmosphere as it absorbs carbon dioxide and release oxygen.
Sunlight is necessary for photosynthesis. Thus sun is the ultimate source of energy for all living organism.
12. Our earth is the only unique planet, where photosynthesis takes place. In the absence of photosynthesis life would not be possible on earth.
Following are necessary for photosynthesis to be taken place:
(i) Presence of sunlight
(ii) Presence of Chlorophyll
(iii) Presence of Water
(iv) Presence of carbon-dioxide
PHOTOSYNTHESIS IN ALGAE Fig. Photosynthesis in algae
Green patches in ponds or near the stagnant water can be seen easily. These green patches are living organism called algae. Algae are plants. Often algae grow near the shallow waterlogged areas such as near tube-wells, taps, etc. One may slip over it. Algae look green because of presence of Chlorophyll. Algae prepare their own food by the process of photosynthesis.
Ques 1: What is photosynthesis?
Ans: The process of making food in green plants in the presence of sunlight is known as photosynthesis.
Ques 2: What are the essentials factors for the photosynthesis?
Ans: Carbon dioxide, water, chlorophyll and sunlight are essentials factors for the photosynthesis to take place.
Ques 3: What is chlorophyll?
Ans: Chlorophyll is the green pigment present in green leaves.
Ques 4: Why do leaves look green?
Ans: Leaves look green because of the presence of chlorophyll, which is a green pigment.
Ques 5: What is the function of chlorophyll?
Ans: Chlorophyll absorbs the sunlight for photosynthesis.
Ques 6: What are the final products made after photosynthesis?
Ans: Glucose and oxygen are the final products after photosynthesis.
Ques 7: What are stomata?
Ans: The small pores present on the lower surface of leaf, are called stomata.
Ques 8: What is function of stomata?
Ans: Stomata absorbs carbon dioxide from air for photosynthesis.
Fig: StomataQues 9: What is the ultimate source of energy?
Ans: Sun is the ultimate source of energy.
Ques 10: How water is transported to the leaves?
Ans: Water is transported to the leaves through pipe like structures from the roots of plant. These pipe-like structures are present from root to leaves through branches throughout.
SYNTHESIS OF PLANT FOOD OTHER THAN CARBOHYDRATES
Plants need proteins and fats besides the carbohydrate. Proteins are nitrogenous substances which contain nitrogen. Although nitrogen is present in abundance in atmosphere, but plant cannot absorb atmospheric nitrogen. Plant gets nitrogen from soil. Certain types of bacteria called rhizobium, are present in soil. They convert gaseous nitrogen into usable form and release it into the soil. Plants absorb these soluble forms of nitrogen along with water and other minerals through their roots.
Sometimes farmers add nitrogenous fertilizer to their field to fulfill the need of nitrogen. In this way plants gets fulfillment of nitrogen along with other nutrients. After the fulfillment of all nutrients plants synthesis proteins and fats.
Ques 1: What are the nutrients other than carbohydrates which are required by plants?
Ans: Proteins and fats are the nutrients; other than carbohydrates; which are required by plants.
Ques 2: In which form do plants absorb nitrogen?
Ans: Plants absorb soluble form of nitrogen.
Ques 3: Why do farmers add nitrogenous fertilizers to the soil?
Ans: Farmers add nitrogenous fertilizers to the soil to fulfill the requirement of nitrogen of the plants. Nitrogen is necessary to synthesise proteins.
Ques 4: Which microorganism help to provide nitrogen to the plants?
Ans: A certain type of bacteria called rhizobium helps to provide nitrogen to the plants.
Ques 5: How do plants absorb nutrients other than carbohydrates from the soil?
Ans: Other nutrients are available in the soil in the form of minerals. Plants absorb these minerals from the soil; along with water.