Chapter 1 – Nutrition in Plants

1.1 Mode of Nutrition in Plants
Among all living beings, plants are the only ones who can make their own food. They prepare their food from sunlight, minerals, water and carbon dioxide that exist in the surrounding. The nutrients help the plant to grow, build itself and repair damaged body parts. The nutrients also provide the required energy to perform vital life processes. The mode is nutrition by which an organism takes nutrients from its surroundings and utilizes it in its body.

There are two modes of nutrition- autotrophic and heterotrophic nutrition mode. Autotrophic nutrition mode enables the organisms to make their food from simpler substances from the surrounding. For example, plants are autotrophs. Heterotrophic nutrition mode allows the organism to derive their nutrients from other animals. For example, all animals are heterotroph.

Since plants are autotrophs, the next questions that will come to you are how do plants make their food.

1.2 Photosynthesis- Food Making Process in Plants
You must have learned that leaves are considered as food factories in plants. They synthesize the food for all parts of the plant. The different body parts transport different raw materials to the parts of the leaves. The roots absorb water and minerals from the soil and send it to leaves through vessels that run all over the root, stem and leaves. Tiny pores on the leaves, called stomata, absorb carbon dioxide. The guard cells control the opening and closing of stomata on the leaves.

All leaves contain chlorophyll. The chlorophyll is responsible for the green colour of the leaves. The chlorophyll traps sunlight and uses solar energy to produce food from carbon dioxide and water. Therefore, to produce food, plants require sunlight, water and carbon dioxide. The process by which plants produce their own food from sunlight, carbon dioxide and water is called photosynthesis. Photosynthesis is an exclusive process that takes place in plants and some algae. It uses solar energy.

Therefore, you can imagine the importance of photosynthesis for maintaining life on earth. Without photosynthesis, there will be no food, since all animals depend indirectly or directly on the plants for food. Without food for plants, life is impossible on earth.

At the time of photosynthesis, the chlorophyll present on the leaves uses sunlight, water and carbon dioxide to produce carbohydrates. Carbohydrate or starch is the food for the plant. The equation for photosynthesis is:

Carbon dioxide + water−→−−−−−ChlorophyllSunlightCarbohydrate + oxygen

As you can see in the equation, oxygen is known to release during photosynthesis. The carbohydrate thus formed is converted to starch, which is another carbohydrate. Photosynthesis is indicated by the presence of starch in the leaves.

Green plants do not only conduct photosynthesis. Yellow, red or multicoloured leaves also perform photosynthesis. Chlorophyll is also present in the leaves that are of other colours.

If you look at the pond or any other stagnant water bodies, you will observe green slimy patches on the water surface. These slimy patches are algae and contain chlorophyll, which makes them green coloured. With the help of these chlorophylls, algae, too, can make their food by the process of photosynthesis.

Every living body is made up of numerous tiny building blocks called cells. Cells play numerous functions in the body. During photosynthesis, the stomata are responsible for gaseous exchange. The opening and closing of stomata are controlled by the guide cells.

1.3 Other Modes of Nutrition in Plants
Not all plants contain chlorophyll. For example, you will often find yellow tubular plants twining around the stem of other plants. It is called Cuscuta and they do not contain chlorophyll. Then how exactly do they get their food? Such plants that lack chlorophyll obtain food by heterotrophic nutrition mode. That means that the plants obtain food from other living organisms. The other living organism is called the host. If the plants deprive the valuable nutrients of the host, they are called parasites. You have often come across the word parasite in terms of insects and other animals. But can plants also be a parasite? Well, yes!

Do you know that plants can also eat animals? Yes, they do so. For example, a pitcher plant has a pitcher shaped structure which is a modification of a leaf. It has a lid at the top which closes when any insect (prey) falls into the pitcher. Some hairs directed downwards on the inside of the pitcher. These plants are insect-eating and known as insectivorous plants.

1.4 Saprotrophs
You must have seen mushrooms selling in the market. They are club-shaped structures mostly white or cream in colour. If they do not contain chlorophyll, then how do they prepare their food?

Mushrooms are fungi. They are not plants and they obtain food from other nutrition modes. They secrete digestive juices and chemicals on decaying or dead organic matters and extract nutrients from them. Such nutrition mode is called the saprophytic nutrition mode and the fungi are known as saprotrophs.

You will also find fungi growing on leather, pickle, bread and other surfaces, which are kept in hot and humid weather for a long time.

You will find most fungi in rainy seasons. These saprotrophs are the reasons why most food and clothes get spoiled in this season. The fungi propagate with the help of spores that can travel through the air. Once these spores come in contact with a wet surface, they can settle down, germinate and grow. So now you can understand why your food or wet clothes get spoiled in the rainy season.

There are other types of relationships between organisms. In one relationship, two organisms stay together since both of them are benefiting. For example, some fungi living in close association with the roots of some plants. They derive their nutrients from plants while providing nitrogen to the plants in return. Such a type of relationship where both the organisms are benefitted is called a symbiotic relationship.

In lichens, fungi and algae stay together. The alga delivers food it makes by photosynthesis. The fungus provides water, minerals, and shelter.

1.5 How Nutrients are Replenished in the Soil
If plants use all the minerals and nutrients from the soil, the levels of these nutrients in the soil are supposed to go down. To replenish the nutrient content of the soil, farmers often add manures and fertilizers to the soil. In this way, the nutrients are replenished, and it will support the continued growth of plants on this soil.

In general, soils require plenty of nitrogen for their growth. After each harvest, the soil gets devoid of nitrogen. To have further plantation on these soils, farmers often grow leguminous crops that can increase the nitrogen content of the soil. These leguminous crops like pulses, grams, dal, etc. are in a symbiotic relationship with a bacteria called rhizobium, which fixes atmospheric nitrogen into the soil. The bacteria obtain food and shelter in return from the plants. Growing leguminous crops in the field reduce the need to add nitrogen-containing artificial fertilizers in the soil.

In this CBSE Class 7 Science Chapter 1 nutrition in plants, you learned about plants that are autotrophs. You also learned about different nutrition modes amongst plants like heterotrophic, saprophytic, parasitic, insectivorous and symbiotic.

Facts that Matter
All organisms take food and utilize it to get energy for growth, maintenance and various life processes.

Based on the mode of getting food, organisms are classified as autotrophs and heterotrophs.

Autotrophs prepare their own food using simple inorganic materials like carbon dioxide and water.

The essential requirements for photosynthesis are chlorophyll and sunlight.

Heterotrophs are the organisms that cannot make food on its own and so they depend on autotrophs directly or indirectly for food.

Parasitic, saprophytic, insectivorous and symbiotic are the different modes of heterotrophic nutrition in plants.

Plants like Cuscuta are parasites as they take nutrition from the host plant.

Saprotrophs like Fungi obtain nutrition from dead and decaying organic matter.

Symbiotic relationship between Rhizobium and legumes helps in enriching the soil of the nitrogen that was lost.

Leaves of the plants prepare the food so they are called the food factory of the plant.

The important components of food are carbohydrates, fats, proteins, vitamins and minerals.

Sun is the fundamental source of energy for all living organisms.

Exercise 1.5 Total Solutions: 12 Questions (12 short questions).
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