Nutrition in Plants
Important topics covered in NCERT for Class 7 Science Chapter 1 – Nutrition in Plants
- Mode of Nutrition in Plants
- Photosynthesis – food making process in Plants
- The alternative mode of nutrition in Plants
- Nutrient replenishment in the soil
- Saprotrophic Nutrition : The mode of nutrition in which the organism decomposes the dead and decaying organic materials of the body by secreting enzymes and then absorbs the nutrients in solution.
- Saprotroph : Plants which use saprotrophic mode of nutrition.
- Some organisms live together and share shelter and nutrients. This is called symbiotic relationship.
- Lichens are the most common example of symbiotic relationship in which an algae and a fungus live together.
- Stomata : There are tiny pores present on the surface of the leaves for exchange of gases from atmosphere. Each pore is called stoma (stoma-singular form) and is surrounded by Guard cells.
- Leaves are called the food factory of the plants because the food is prepared in the leaves.
- Rhizobium : Rhizobium is a bacterium which lives on root nodules of pulses and other leguminous plants. It provides nitrogen to plants by the process known as ‘nitrogen fixation‘.
- Legumes : The plants related to pulses and having pods are called legumes like methi, urad.
- Iodine test : This test is performed to detect the formation of starch in the leaves. The starch gives blue – black colour with iodine.
- Fertilizers : The inorganic chemical compounds prepared in the industries and rich in the nutrients are called fertilizers.
Nutrition: The process by which an organism takes food and utilizes it is called nutrition.
Need of Nutrition: Organisms need energy to perform various activities. The energy is supplied by the nutrients. Organisms need various raw materials for growth and repair. These raw materials are provided by nutrients.
Nutrients: Materials which provide nutrition to organisms are called nutrients. Carbohydrates, proteins and fats are the main nutrients and are called macronutrients. Minerals and vitamins are required in small amounts and hence are called micronutrients. Plants make their food themselves but animals cannot. Hence, animals depend directly or indirectly on the plant.
Mode of Nutrition in Plants
- Autotrophic Nutrition: Auto means self and trophos means nourishment. Plants are called autotrophs because they make their food themselves. The making of food for themselves is called the Autotrophic nutrition. Autotrophic nutrition is found in green plants, and in some bacteria.
- Heterotrophic Nutrition: The word Heterotrophic is the combination of two words i.e. Hetero + Trophos. Hetero means ‘others’ and trophos means nourishment. If organisms depend on others for their food, such a mode of nutrition is called Heterotrophic Nutrition.
Animals cannot make their food themselves. They depend for food upon plants. Therefore, nutrition in animals is called Heterotrophic Nutrition. Animals are known as Heterotrophs.
Saprotrophic Nutrition: The uptake of nutrients by organism from dead and decaying matter in the form of solution is called the saprotrophic nutrition. The organisms which use saprotrophic mode of nutrition are
called saprotrophs. For example: fungi.
Plant Nutrition: Green plants prepare their own food. They make food in the presence of sunlight. Sunlight provides energy, carbon dioxide and water are the raw materials and chloroplast is the site where food is made.
Photosynthesis: The process by which green plants prepare food is called photosynthesis. During this process; the solar energy is converted into chemical energy and carbohydrates are formed. Green leaves are the main sites of photosynthesis. The green portion of the plant contains a pigment chloroplast; which contains chlorophyll.
The whole process of photosynthesis can be shown by following equation:
The process of photosynthesis can be represented as:
- The process of photosynthesis takes place in the green leaves of a plant. The food is prepared by the green leaves of a plant in the form of a simple sugar called glucose.
- The extra glucose is changed into another food called starch.
- This starch is stored in the leaves of the plant.
- The green plants convert sunlight energy into chemical energy by making carbohydrates.
The photosynthesis takes place in the following three steps:
- 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 utilizing the chemical energy.
Conditions necessary for photosynthesis:
- Carbon dioxide
Raw materials for photosynthesis:
- Carbon dioxide
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 carbon dioxide gas enters the leaves of the plant through the stomata present on their surface.
- Each stomatal pore is surrounded by a pair of guard cells. The opening and closing of stomatal pores is controlled by the guard cells.
How the plants obtain water for photosynthesis?
- The water required by the plants for photosynthesis is absorbed by the root of the plants from the soil through the process of osmosis.
- The water absorbed by the roots of the plants is transported upward through the xylem vessels to the leaves where it reaches the photosynthetic cells.
The plants also need other raw materials such as nitrogen, phosphorus, iron and magnesium, etc., for building their body. The plants take these materials from the soil. Nitrogen is essential element used by the plants to make proteins and other compound.
Site of photosynthesis: Chloroplasts
- Photosynthesis takes place in the leaves of the plants.
- Leaves have green pigment called chlorophyll
- It helps leaves capture the energy of the sunlight which is then used to prepare food from carbon dioxide and water.
- Here, you see that solar energy is captured by the leaves and is stored in the plant in the form of food.
- So, we can say that Sun is ultimate source of energy for all living organisms.
Significance of Photosynthesis:
- Photosynthesis is the main way through which the solar energy is made available for different living beings.
- Green plants are the main producers of food in the ecosystem. All other organisms directly or indirectly depend on green plants for food.
- The process of photosynthesis also helps in maintaining the balance of carbon dioxide and oxygen in the air.
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 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.
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 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 synthesize proteins and fats.
Modes of Nutrition in Non-Green Plants
Heterotrophic Mode of Nutrition in Plants: Some plants do not have the chlorophyll. Hence, they cannot synthesize their food by themselves. Such plants are known as non green plants. They depend on other organisms for food. Such plants use the heterotrophic mode of nutrition.
This type of nutrition can be categorized into
- Parasitic mode of nutrition
- Insectivorous mode of nutrition
- Saprophytic mode of nutrition
- Symbiotic mode of nutrition
Parasitic Mode of Nutrition: Plants that do not have chlorophyll are called non-green plants. Plants, which live on other plants for food, are called parasitic plants.
- Parasite (Parasitic Plant): Plants that get their food from other plants by living on them are called parasite. Example; Cuscuta, mistletoe.
- Cuscuta is a vine-like plant with yellowish stem. It twines around big trees, like banyan tree. Cuscuta gets nutrition from the tree on which it lives. The tree upon which it climbs and lives is called the host.
- Here, banyan is the host and cuscuta is the parasite.
- The adjacent figure shows a parasite plant (Cuscuta) climbing on the stem of its host plant.
- Some plants are total parasite while some are partial parasite.
- Total Parasite: A total parasite fully depends on other plants for their nutrition. For example – cuscuta.
- Partial parasite: Partial parasite is a parasite that receives a part of its nutrients from host. For example; mistletoe bears green leaves. It synthesizes its own food, but receives water and mineral from the host plant.
Insectivorous Mode of Nutrition: Some plants eat insects. Such plants are called insectivorous plants. They trap and digest the insects. Pitcher plant is the example of an insectivorous plant. In pitcher plant the leaf is modified to form a pitcher like structure. The bright colour of the pitcher makes it very attractive to insects. Inside the pitcher; there are several hair-like structures. These hairs direct the trapped insects downwards. When an insect sits on the pitcher of the plant, the lid closes and the insect gets trapped inside the pitcher. The insect is then digested by the enzymes secreted by the cells of the plants.
Cause of eating of insects by plants: The soil of marshy land is deficient in nitrogen. Plants living in marshy areas do not get nitrogen from the soil. Their nitrogen need is fulfilled by sucking the juice of insects. Venus flytrap, utricularia, drosera and Rafflesia are the other examples of insectivorous plants.
Saprophytic mode of Nutrition: Saprotrophs are non-green plants e.g. Agaricus (Mushroom) fungi, yeasts and bacteria. Saprotrophs get their food from dead or decaying organic matters. They grow on decaying organic matters such as cow-dung, wood, bread, etc.
The below figure shows a fungus (mushrooms) growing on the rotting wood of a dead tree.Saprotrophs secrete digestive juice over the decaying materials and absorb nutrients from them. This is called Saprotrophic Mode of Nutrition.
Symbosis Mode of Nutrition: Symbiosis is the combination of two Greek words ‘Sym’ means ‘with’ and ‘biosis’ means ‘living’, which means living together. In symbiosis or mutualism two different types of organisms live and work together for their mutual benefit from each other. They share shelter and nutrients, e.g. Lichens. Lichens are composite organisms composed of fungus and alga.
- Fungus is a saprophyte and alga is an autotroph. The Fungus supplies water and minerals to the cells of the alga while the alga supplies food; prepared by photosynthesis.
- A bird sitting on the back of a rhino is an example of symbiosis. The bird gets worms to eat, while the rhino gets rid of those worms.
Replenishment of Nutrients in Soil: We know that plants continuously take nutrients from the soil in order to synthesize food. As a result of this, the amount of nutrients in the soil decreases.
Nutrients in the soil are replenished by adding fertilisers and manures. Fertilisers and manures contain plants nutrients and minerals like nitrogen, phosphorus and potassium.
Another way to replenish soil is to grow leguminous crops (for example gram, peas, pulses etc.) in the soil. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form. But Rhizobium cannot make its own food. So it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen. In return plants provide food and shelter to the bacteria.
Thus plants and bacteria have a symbiotic relationship here.
Question 1: Why do organisms take food?
All living organisms require food to survive. It gives them energy to perform various activities. All activities such as playing, running, walking, studying, etc. require energy. The various components present in our food such as carbohydrates, proteins, fats, vitamins, and minerals provide energy to our body. These are also important for growth and development of the body.
Question 2: Distinguish between a parasite and a saprotroph.
Parasite (Parasitic Plant): Plants that get their food from other plants by living on them are called parasite. Example; Cuscuta, mistletoe. Cuscuta is a vine-like plant with yellowish stem. It twines around big trees, like banyan tree. Cuscuta gets nutrition from the tree on which it lives.
Saprotrophs: Saprotrophs are non-green plants e.g. Agaricus (Mushroom) fungi, yeasts and bacteria. Saprotrophs get their food from dead or decaying organic matters. They grow on decaying organic matters such as cow-dung, wood, bread, etc.
Question 3: How would you test the presence of starch in leaves?
Aim: To test for the presence of starch in leaf.
Materials Required: Green leaf, beaker, tripod stand, burner, test tube, alcohol, iodine solution, tap water and petri dish.
- Pluck a healthy green leaf of a plant which was kept in sunlight.
- Boil it in water contained in a beaker for about two minutes. This will make the leaf soft and stop any further chemical changes in it.
- Put the leaf in a test tube containing alcohol.
- Place the test tube in a beaker of boiling water.
- The alcohol will bleach the leaf and make it free from chlorophyll.
- Wash the leaf in water. Place it in a petri dish and add a few drops of iodine solution.
Observation : The leaf turns blue-black.
Conclusion : The leaf changes into blue-black colour due to presence of starch in it.
Question 4: Give a brief description of the process of synthesis of food in green plants.
Photosynthesis is defined as the process in which the chlorophyll-containing plant cells synthesise food in the form of carbohydrates, using carbon dioxide and water in the presence of solar energy.
Sources of raw materials required for photosynthesis:
(a) Water is taken in from the roots of the plant and is transported to the leaves.
(b) Carbon dioxide from the air enters the leaves through the tiny pores called stomata and diffuses to the cells containing chlorophyll.
(c) Solar energy is used to break water into hydrogen and oxygen. This hydrogen is combined with carbon dioxide to form food for the plants, which is ultimately used by the animals as well.Thus, photosynthesis can be represented by the following equation.
Question 5: Show with the help of a sketch that the plants are the ultimate source of food.
Question.9. Match the items given in Column I with those in Column II:
|Column I||Column II|
Question.11. Choose the correct option from the following:
Which part of the plant gets carbon dioxide from the air for photosynthesis.
(i) root hair
(iii) leaf veins
Question.13. Why do farmers grow many fruits and vegetable crops inside large greenhouses? What are the advantages to the farmers?
Fruits and vegetable crops are grown in large greenhouses because it protects crops from external climatic condition and to provide suitable temperature for the growth of crops.
Advantages to farmers while growing fruits and vegetable crops inside greenhouses are
- It protects crops from diseases and adverse climatic conditions.
- It protects crops from wind and rodents
Very Short Answer Type Questions
Question.7. What is heterotrophic mode of nutrition?
The mode of nutrition in which an organism takes food from another organism is called heterotrophic mode of nutrition. The nutrition in animals and non-green plants is the example of heterotrophic mode of nutrition.
Question.19. How water is transported to the leaves?
Question.22. Why do farmers add nitrogenous fertilizers to the soil?
Question.24. How do plants absorb nutrients other than carbohydrates from the soil?
Question.41. Give an example of symbiotic relationship.
A small bird, called plover, cleans the crocodile’s teeth. The crocodile keeps its mouth open and the bird takes out meat fibres stuck between the teeth. The bird gets food in lieu of providing dentist’s services to the crocodile.
Question.42. Write a brief note on pitcher plants?
In a pitcher plant, the leaf is modified into a pitcher like structure. The pitcher is complete with a lid. The inside of pitcher is full of hair-like structures. The pitcher is used to trap insects which may fall in it.
Question.43. What do you understand by saprotrophs?
An organism which feeds on dead and decaying material is called a saprotroph. In this mode of nutrition, digestive enzymes are secreted on the food. The digested food is then absorbed by the organism. In saprotrophs digestion takes place outside the body of the organism.
Question.44. How do nutrients get replenished in the soil?
There are two main means through which nutrients get replenished in the soil. One of them is the nitrogen fixation in soil. Nitrogen fixation replenishes nitrogenous nutrients in the soil. Another means is decomposition of dead remains of plants and animals (or farm waste). Decomposition of dead remains replenishes various other nutrients in the soil.