Chapter-01 Nutrition in Plants

Introduction

 All living organisms such as plants and animals require food. So food is essential for all living organisms.

 Plants are capable of Organisms needs food (nutrients) to – making their food obtain energy themselves but humans and animals cannot. obtain materials for growth  Carbohydrates, proteins, repair damaged body cells and parts fats, vitamins and minerals carry out life process. are essential components of food, these components are called nutrients.

Mode of nutrition in plants

 Plants prepare their food by using raw materials like water, carbon dioxide and minerals.  The process of utilization of food by a living organism to obtain energy is called nutrition.  There are two modes of nutrition as shown below in the figure

1. Autotrophs or Autotrophic: - Plants that have chlorophyll trap the energy from the sun and prepare their own food. Such nutrition wherein the food is prepared by the organisms itself is called autotrophic nutrition. The organisms capable of preparing their own food are called autotrophs. All green plants are Autotrophs (Auto means self and trophos means nourishment). They prepare their own food by a process called photosynthesis. 2. Heterotrophs or heterophobic: - Heterotrophic organisms are those who obtain food from other organisms. Since these organisms depend on other organisms for their food, they are called consumers. All animals and non-green plants like fungi come under this category. Organisms that follow the heterotrophic mode of nutrition are called heterotrophs.

Photosynthesis  Photosynthesis is food making process in plants from simple substances like carbon dioxide and water in the presence of sunlight.

 Oxygen is released during photosynthesis.

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:

1. Absorption of sunlight energy by chlorophyll. 2. Conversion of light energy into chemical energy, and splitting of water into hydrogen and oxygen by light energy. 3. Reduction of carbon dioxide by hydrogen to form carbohydrate like glucose by utilizing the chemical energy.

Conditions necessary for photosynthesis:

The conditions necessary for photosynthesis to take place are:

1. Sunlight 2. Chlorophyll 3. Carbon dioxide 4. Water Raw materials for photosynthesis:

The raw materials for photosynthesis are:

1. Carbon dioxide 2. Water 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. 1. The plants also need other raw materials such as nitrogen, phosphorus, iron and magnesium, etc., for building their body. 2. The plants take these materials from the soil. 3. 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 di oxide 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.

Other Notes on photosynthesis

 Photosynthesis in plants can also takes place in other green parts like green stems, green branches.  Glucose (simple carbohydrates) is the simplest food synthesized by plants. This glucose made by plants is converted into complex carbohydrates which are known as starch.  These simple carbohydrates are used to synthesise other components of food such as proteins and fats.  Proteins are nitrogenous substances. Plants prepare proteins with the help of nitrogen which is obtained from the soil.  Plants use the minerals dissolved in water to convert Glucose (simple carbohydrates) into carbohydrates, proteins and fats.  Photosynthesis is important because o It provides food to animals including human beings o It puts oxygen gas into the air which is essential for breathing and respiration in animals including human beings

Other modes of nutrition in plants(Heterotrophic nutrition)

 Most of the plants have green pigment called chlorophyll and can make their own food.  Some plants do not have chlorophyll and cannot synthesize their own food and are known as Heterotrophic plants  This type of nutrition can be categorized into 1. parasitic mode of nutrition 2. Insectivorous mode 3. saprophytic mode of nutrition 4. Symbiotic mode of nutrition

Parasites

 In parasitic mode of nutrition, plants depend on other plants or animals for their nourishment.  Such dependent plants are called as parasites and the ones on which parasites depend are called as hosts.  A parasite plant climbs on the host plant from which they get all the food.  The host does not get any benefit from the parasite.  Some examples of parasites are Cuscuta (akash-bel), Cassytha (amar-bel), hookworms, tapeworms, leeches, etc. More Notes

 Cuscuta (dodder) is a plant that does not have chlorophyll; it sucks food from the host plant through adventitious roots called haustoria, Cuscuta is therefore a complete parasite.  Mistletoe plant has green leaves and so can carry out photosynthesis. This plant mainly absorbs water and minerals from the host plant. Therefore, Mistletoe is called a partial parasitic plant.  Rafflesia is a parasite of the Tetrastigma plant. It is completely dependent on its host plant for food.

Insectivorous Plants

 The insectivorous mode of nutrition is observed in plants like pitcher plant and the Venus fly trap.  These types of plants purely depend on other insects and small animals for their nutrition.  Pitcher plants trap small insects inside the pitcher and insects are digested by the digestive juices secreted in the pitcher.  Insectivorous plants grow in those soils which do not contain sufficient nitrogen mineral.  These types of plants are green and carry out photosynthesis to obtain a part of food. More Notes

 The leaves of the Venus flytrap have stiff hair like projections on their edges and the entire leaf is divided into two parts, with the middle acting as a hinge. When an insect sits on the leaf, it shuts tightly, trapping the insect inside it.  The Pitcher plant has a pitcher- shaped structure filled with liquid. it has a flap -like structure on its mouth. The edge of the opening of the pitcher is slippery. The insect that sits on its slips and falls into the pitcher, getting trapped inside with the closing of the lid.  The sundew plant has long needle like structures called tentacles covered with sticky substance called mucous. Once an insect sits on it, it gets caught in the mucous and the tentacles fold inward, trapping the insect.

Saprotrophs

 Mode of nutrition in which organisms or plants that obtain their nutrition from dead and decaying organic matter is called Saprophytic mode  The plants which exhibit saprotrophic mode of nutrition are called as saprotrophs  Saprotrophs secrete digestive juices onto dead and decaying matter to dissolve it and then absorb nutrients from it.  Examples of saprotrophs are moulds, mushrooms, yeasts and some bacteria.

Symbiotic plants

 In this mode of nutrition there is a close association between two different plants of different categories.  In such type of association both the plants get benefited.  For example certain fungi live in the roots of the trees. In this case tree provides nutrients to fungi and in return receives help from it to take up water and nutrients from the soil.

How nutrients are replenished in the soil

 We know that plants continuously take nutrients from the soil in order to synthesize food. As a result of this amount of nutrients in the soil decreases.  Nutrients in the soil are replenished by adding fertilizers and manures.  Fertilizers 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.

Differences between a parasitic and a symbiotic relationship

Q1:Differentiate between nutrients and nutrition. Ans: Carbohydrates, proteins, fats, vitamins and minerals are essential components of food, these components are called nutrients, but Nutrition is the mode of taking food by an organism and its utilisation by the body.

Q2:Differentiate between autotrophs and heterotrophs.

Ans: Green plants are called autotrophs as they prepare their own food from simple substances, but animals and most other organisms are called heterotrophs as they take in ready-made food prepared by the plants

Q3: Explain the food factory of plants.

Ans: Leaves are called food factory of plants, as the synthesis of food takes place in leaves of plants. Water and minerals present in soil are absorbed by roots and transported to leaves via stem. Carbon dioxide from air is taken in through tiny pores on surface of leaves called stomata. Q4: How water and minerals are transported to leaves from roots?

Ans: There are vessels inside a plant which run like pipes throughout the root, stem branches and leaves, by going through these vessels water and minerals are transported to leaves from roots. Q5: Define chlorophyll.

Ans: Chlorophyll is the green colour pigment which helps leaves to capture energy from sunlight to carry out the food making process of plants by the leaves. Q6: Explain the role of chlorophyll in the process of photosynthesis.

Ans: Chlorophyll is the green colour pigment which helps leaves to capture energy from sunlight to carry out the food making process of plants by the leaves. It is the green photosynthesis pigment which provides energy necessary for photosynthesis. Q7: Define photosynthesis along with the equation for the same.

Ans: Photosynthesis is the food manufacturing process of green plants containing chlorophyll, in presence of sunlight, with the help of carbon dioxide and water to synthesise carbohydrates. The equation for the process is as follow: Carbon dioxide + water —————> carbohydrate + Oxygen Q8: What is the function of stomata in leaf of a plant?

Ans: Stomata are the tiny pores present on the surface of leaves which helps in exchange of gases, the pores in stomata are surrounded by guard cells. Q9: Why colours of algae are green?

Ans: Algae contain chlorophyll which gives them green colour and because of chlorophyll it can also prepare their own food by photosynthesis. Q10: From where do the plants obtain nitrogen?

Ans: Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. These soluble forms are absorbed by the plants along with water. By adding fertilizers rich in nitrogen to the soil farmers also made nitrogen available for plants. Q11: What do you mean by parasitic nutrition?

Ans: The mode of by which parasitic organism get and synthesize their food is called parasitic nutrition. Example Cuscuta. It does not have chlorophyll; it takes readymade food from the plant on which it is climbing. The plant on which it climbs is called a host. In a parasitic nutrition only one of the partners is benefited and other is not. Q12: What is saprotrophic mode of nutrition?

Ans: This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs. Example Fungi that secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the nutrients from it. Q13: How nutrients are replenished in soil?

Ans: Nutrients are replenished in soil by following ways:

 By spreading manure or fertilizers that contain nutrients such as nitrogen in the fields  By the bacterium Rhizobium that is commonly present in rot nodules of leguminous plant that can take atmospheric nitrogen and convert it into a soluble form like nitrates.

Q14: What is the role of leguminous plants in replenishing soil fertility?

 Ans:  Rhizobium is a type of bacteria that cannot make its own food and lives in the roots of gram, peas, moong beans and other legumes, it converts atmospheric nitrogen into useable form which increases the fertility of soil, and legumes provide food and shelter to the bacteria.

Q15: Explain how Pitcher plants get their nutrition?

 Ans:  When an insect lands in the pitcher, the lid closes and the trapped insect gets entangled into the hair. The insect is digested by the digestive juices secreted in the pitcher. Q16: Distinguish between a parasite and a saprotrophs.

Ans: Parasites Saprotrophs A parasite takes readymade They secrete the digestive food from the organism on juices on the matter they live which it feeds. and convert it into a solution They feed on a living and then absorb it. organism. They feed on dead and The organism on which it feeds decaying organism. is called host. They do not feed on a living It deprives the host of valuable organism. nutrients There is no host at all.

Q17: What are the main requirements of photosynthesis?

Ans: Chlorophyll, sunlight, carbon dioxide and water are necessary to carry out the process of Photosynthesis.

Q18: Draw a labelled diagram showing the process of photosynthesis.

Ans:

Q19: Nitrogen is an essential nutrient for plant growth. But farmers who cultivate pulse crops like green gram, Bengal gram, black gram, etc. do not apply nitrogenous fertilizers during cultivation. Why?

Ans: Roots of pulses have symbiotic relationship with bacteria called Rhizobium. This bacterium fixes atmospheric nitrogen which will be utilized by leguminous plants. Hence farmers don't apply nitrogen fertilizers while cultivating cereals. Q20: How would you test the presence of starch in leaves?

Ans: Take two potted plants of the same kind. Keep one in the dark for 72 hours and the other in sunlight. Perform the iodine test with the leaves of both the plants as given below. Now leave the pot which was earlier kept in the dark, undisturbed for 3 – 4 days and perform the iodine test again on its leaves. Iodine test: Put iodine solution on the leaf Observation: Blue-black colour will be observed on the leaves of the plant kept in sunlight, which indicates the presence of starch. Blue-black colour will not be observed on the leaves of plant kept in the darkroom. This indicates the absence of starch.