Nutrition in Plants Class 7

 Nutrition in Plants

➤ Carbohydrates, proteins, fats, vitamins, and minerals are components of food.

Nutrients: The components of food are called nutrients and are necessary for our body.

MODE OF NUTRITION IN PLANTS

Plants are the only organisms that can prepare food for themselves by using water, carbon dioxide, and minerals. The raw materials are present in their surroundings.

➤ The nutrients enable living organisms to build their bodies, to grow, repair damaged parts of their bodies, and provide the energy to carry out life processes.

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

Two modes of nutrition 

1. Autotrophic 
2. Heterotrophic 

1.  The mode of nutrition in which organisms make food themselves from simple substances is called autotrophic (auto = self; trophos = nourishment) nutrition. Therefore, plants are called autotrophs.

2. The mode of nutrition in which organisms do not make food themselves is called heterotrophic (heteros = others) nutrition. Animals and most other organisms take in food prepared by plants. They are called heterotrophs

PHOTOSYNTHESIS — FOOD MAKING PROCESS IN PLANTS

➤ Leaves are the food factories of plants. Therefore, all the raw materials must reach the leaf. Water and minerals present in the soil are absorbed by the roots and transported to the leaves. 

➤ Carbon dioxide from air is taken in through the tiny pores present on the surface of leaves. These pores are surrounded by ‘guard cells’. Such pores are called stomata

Source: NCERT

Q) How water and minerals absorbed by roots reach the leaves?

Water and minerals are transported to the leaves by the vessels which run like pipes throughout the root, the stem, the branches, and the leaves. They form a continuous path or passage for the nutrients to reach the leaf. They are called vessels.

Q) What is so special about the leaves that they can synthesise food but other parts of the plant cannot?

The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis (Photo: light; synthesis : to combine).

➤ The solar energy is captured by the leaves and stored in the plant in the form of food. Thus, sun is the ultimate source of energy for all living organisms

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

➤ During photosynthesis, chlorophyll-containing cells of leaves, in the presence of sunlight, use carbon dioxide and water to synthesise carbohydrates. The process can be represented in an equation:

➤ During the process, oxygen is released. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate.

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

Source: NCERT, Leaves of various colours

 ➤ Algae contain chlorophyll which gives them the green colour. It can also prepare its own food by photosynthesis.

Synthesis of plant food other than carbohydrates

● Plants synthesise carbohydrates through the process of photosynthesis. 

●The carbohydrates are made of carbon, hydrogen, and oxygen. 

●These are used to synthesise other components of food such as proteins and fats. But proteins are nitrogenous substances that contain nitrogen. 

Q) From where do the plants obtain nitrogen?

Plants cannot absorb nitrogen from the atmosphere. Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. These are absorbed by the plants along with water. Also, you might have seen farmers adding fertilisers rich in nitrogen to the soil. In this way, the plants fulfil their requirements of nitrogen along with the other constituents. Plants can then synthesise proteins and vitamins.

OTHER MODES OF NUTRITION IN PLANTS

➤ There are some plants that do not have chlorophyll. They cannot synthesise food. They use the heterotrophic mode of nutrition. 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 the host. Since it derives the nutrients from the host, Cuscuta is called the parasite.

Source: NCERT, Cuscuta on host plant

 ➤ In a pitcher plant, the pitcher-like or jug-like structure is the modified part of the leaf. The apex of the leaf forms a lid that can open and close the mouth of the pitcher. Inside the pitcher, there are hair which are directed downwards. When an insect lands in the pitcher, the lid closes and the trapped insect gets entangled into the hair. The lid closes and the insect is trapped. The insect is digested by the digestive juices secreted in the pitcher and its nutrients are absorbed. Such insect-eating plants are called insectivorous plants.

Source: NCERT, Pitcher plant 

SAPROTROPHS

Fungi, they have a different mode of nutrition. They secrete digestive juice on the dead and decay matter and convert it into a solution. Then they absorb nutrients from it. This mode of nutrition in which organisms take in nutrients in solution from dead and decaying matter is called saprotrophic nutrition. Such organisms with saprotrophic mode of nutrition are called saprotrophs. Another example mushroom.

Source: NCERT, Fungi

➤ The fungal spores are generally present in the air. When they land on wet and warm things they germinate and grow.

Symbiosis

➤ Some organisms live together and share both shelter and nutrients. This relationship is called symbiosis. For example, certain fungi live inside the roots of plants. The plants provide nutrients to the fungus and, in return, the fungus provides water and certain nutrients.

➤ An organism called lichen, 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 prepares and provides food to the fungus.

HOW NUTRIENTS ARE REPLENISHED IN THE SOIL

Usually, crop plants absorb a lot of nitrogen and the soil becomes deficient in nitrogen. Plants can not take nitrogen from the atmosphere, They need nitrogen in a soluble form. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a usable form.

But Rhizobium cannot make its own food. So it often lives in the roots of the gram, peas, moong, beans, and other legumes and provides them with nitrogen. In return, the plants provide food and shelter to the bacteria. They, thus, have a symbiotic relationship.

References

1. NCERT Science Class 7