Nutrition In Plants

1. Nutrition

1.1 Why is food essential?

The food contains several components such as carbohydrates, proteins, fats, vitamins, and minerals. These are called nutrients.

Nutrients are essential as they enable living organisms to build their bodies, to grow, to repair damaged parts of their bodies and provide the energy to carry out life processes.

1. Nutrition

1.1 Why is food essential?

The food contains several components such as carbohydrates, proteins, fats, vitamins, and minerals. These are called nutrients

Nutrition is the mode of taking food by an organism and its utilization by the body.

1.2 How is food produced?

Plants can make their own food, whereas animals including humans cannot and thus depend on plants and other animals for their food.

Animals are directly or indirectly dependent on plants for their food as animals get food either from plants or other animal-eating plants.

1.3 Different mode of nutrition

Nutrition is the mode of taking food by an organism and its utilization by the body.

A. The mode of nutrition in which organisms make food themselves from a simple substance is called autotrophic (auto = self; trophs = nourishment). Most plants are autotrophs.

B. The mode of nutrition in which organisms don't make their own food and depend on others is called heterotrophic (hetero = other; trophos = nourishment). Animals are heterotrophs.

2. Photosynthesis: The process of producing food in plants

2.1 What is photosynthesis?

Plants use water, minerals, carbon dioxide from their surroundings to make their food in the presence of sunlight and chlorophyll-containing pigment, this process is called photosynthesis. Photo means light, and synthesis means preparation of food.

2.2 Where is food produced in plants?

The synthesis of food takes place in the leaves. Therefore, it is called the food factory.

2.3 How does the raw material reaches the leaf?

A. Water and minerals from the soil are absorbed by the roots and transported to the leaves.

B. Carbon dioxide from air is taken through tiny pores, called stomata, present on the surface of the leaves.

C. The green pigment, called chlorophyll, on the leaves helps in capturing the energy of the sunlight to prepare food.

What is produced as a result of photosynthesis?

As a result of photosynthesis, oxygen and carbohydrates is formed in the plants.

Carbon dioxide + Water (in presence of sunlight and chlorophyll) gives Carbohydrates + Oxygen

2.4 Synthesis of other nutrients in plants:

A. Starch: Carbohydrates convert into starch.

B. Proteins and Fats: With the help of nitrogen, plants can synthesise components of food other than carbohydrates such as proteins and fats.

Where does the plant gets the nitrogen from?

Nitrogen is present in abundance in gaseous form in the air. However, plants cannot absorb nitrogen in this form. 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.

2.5 Can photosynthesis occur without sunlight?

Solar energy is used to prepare food, therefore, photosynthesis is not possible in the absence of sunlight. Thus, the sun is the ultimate source of energy for all living organisms.

Experiment to show sunlight is essential for photosynthesis

To verify our reasoning, we can perform an iodine test (an iodine test is used to confirm the presence of starch) on a part of leaf covered with a black paper to block sunlight (say, for 3-4- days). The iodine test fails proving that a plant away from sunlight has not made any food.

2.6 Can photosynthesis occur without chlorophyll?

Besides leaves, green parts of the plant — in green stems and green branches. The desert plants have scale- or spine-like leaves to reduce the loss of water by transpiration. These plants have green stems which carry out photosynthesis.

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

There are some plants which do not have chlorophyll. They cannot synthesise their food. Thus, they follow heterotrophic mode of nutrition.

3. Alternate mode of nutrition in plants:

There are some plants which do not have chlorophyll. They cannot synthesise their food. Thus, they follow alternate mode of nutrition.

3.1 Parasitic mode of nutrition

This is a plant called Cuscuta (Amarbel). 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. Since it deprives the host of valuable nutrients, it is called a parasite.

3.2 Insectivorous plants

Adaptation:

The pitcher-like structure is the modified part of the leaf. The apex of the leaf forms a lid which can open and close the mouth of the pitcher. Inside the pitcher there are hairs which are directed downwards.

Process:

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. Such insect-eating plants are called insectivorous plants.

3.3 Saprotrophic mode of nutrition

Have you seen fluffy umbrella-like patches growing on bread? These organisms are called fungi. Fungi also grow on pickles, leather, clothes and other articles that are left in hot and humid weather for long time.

Why fungi growth increases in rainy season?

This happens because the fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow.

They have a different mode of nutrition. They secrete digestive juices on the dead and decaying matter and convert it into a solution. Then they absorb the nutrients from it. This mode of nutrition is called saprotrophic nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs.

3.4 Symbiotic Relationship in Plants

Some organisms live together and share shelter and nutrients. This is called symbiotic relationship.

Examples of Symbiotic relationship:

1. Certain fungi live in the roots of trees. The tree provides nutrients to the fungus and, in return, receives help from it to take up water and nutrients from the soil.

2. Lichen: Symbiotic relationship between fungus and algae. Have you seen green patches on ponds? These are algae. They have chlorophyll.

In organisms called lichens, a chlorophyll-containing partner, which is an alga, and a fungus live together. The fungus provides shelter, water and minerals to the alga and, in return, the alga provides food which it prepares by photosynthesis.

3. Rhizobium and Legume

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. Most of the pulses (deals) are obtained from leguminous plants. In return, the plants provide food and shelter to the bacteria. They have a symbiotic relationship.

Why does farmers not need to put fertilizers on legumes?

The farmers do not need to add nitrogen fertiliser to the soil in which leguminous plants are grown because the Rhizobium bacteria is sufficient providing the necessary nitrogen.

4. Replenishing the soil with nutrients

4.1 Why are fertilisers added to soil after harvest?

Since plants absorb mineral nutrients from the soil, hence their amounts in the soil keep on declining. Fertilisers and manures contain plant nutrients such as nitrogen, potassium, phosphorous, etc. These nutrients need to be added from time to time to enrich the soil.