The sum total of all the processes Involved in the taking and utilization of the elements for growth, repair and maintenance of activities in the organisms is called nutrition.
The nutrient is the food or elements or any substance that supplies the body elements, necessary for metabolism. All the organisms need nutrients for the maintenance of life. The nutrients like carbohydrates, fats and proteins perform following functions in the body.
- They provide energy.
- They provide raw material for the synthesis of protoplasm and other nutrients.
- Certain nutrients like water, electrolytes, minerals and vitamins are essential for the metabolic processes.
Types of Nutrition
Organisms can be divided into two groups on the basis of their mode of nutrition:
(a) Autotrophic nutrition
(b) Heterotrophic and Special Mode of Nutrition
(a) Autotrophic nutrition
The mode of nutrition in which the organisms can synthesize their food form inorganic salts is called autotrophic nutrition. So, autotrophic organisms can exist in an exclusively (completely) inorganic environment.
They synthesize their food in the form sugars, lipids and proteins from CO2 and water.
Mineral Nutrition in Plants
The carbon, oxygen and hydrogen are predominant elements of the plants. The plants obtain these elements from CO2 and water. There are many other mineral elements present in the composition of plants. These are:
- Nitrogen: It is present in protein.
- Phosphorus: It is present in ATP, nucleic acids and many other compounds.
- Magnesium: It is present in chlorophyll.
- Iron: Iron is present in Cytochromes.
Source of Mineral Elements
Soil is the main source of these nutrients. These nutrients are essential for the growth and life of the plant. If crops are grown repeatedly on the same field, these crops cannot flourish. Soil must be replenished with these nutrients. The farmers use animal manure sewage sludge or artificial fertilizers for this replenishment.
These materials are used in measured quantities over the field. Some chemical fertilizers like urea, super phosphate and ammonium nitrate are also commonly used in Pakistan.
Mineral Element Deficiencies
It is difficult to determine the effects of individual minerals in both plants and animals. However, the deficiencies of some elements cause serious diseases. These diseases show clear symptoms.
- If there is deficiency of nitrogen in soil, the growth of the plant is stunted. This deficiency of nitrogen also causes chlorosis mostly in older leaves. The lack of chlorophylls in the leaves is called chlorosis.
- The deficiency of phosphorus causes stunted growth of roots.
- The colour of leaf margins becomes yellow and brown due to deficiency of potassium in soil. It may cause early death of the plant.
- The deficiency of magnesium causes chlorosis.
So, the deficiency of minerals causes many important plant diseases. These diseases have been catalogued with the help of colour, photography. These catalogues help us to diagnose these diseases rapidly.
(b) Heterotrophic and Special Mode of Nutrition in Plants
The plants generally obtain their food from the air or water. However, there are following special methods of nutrition.
The feeding on dead and decaying matter is called saprophytic nutrition. This decaying matter includes dead leaves in the soil and rotting tree trunks. These saprophytic plants produce extracellular enzymes. These enzymes digest and decay the matter and the plants absorb the soluble products into their cells.
Some bacteria break down the proteins of dead plants and animals. They release nitrates. The roots of the plants absorb these nitrates. The plants synthesize new amino acids and proteins form these nitrates. So they play a role in the nitrogen cycle.
The feeding by living in or on other organisms (its host) belonging to different species is called parasitic nutrition. The parasites attach with the living hosts. The parasites penetrate their suckers into the conducting tissues of the host and absorb food. Puccinia is a parasitic fungus. It destroys the wheat plant. Dodder is a leafless plant. It lives as a twining parasite.
It is a mutual nutrition between the organisms belonging to different species, living in association with one another. Some important examples are lichens, mycorrhizae and root nodules.
Lichens are made up of fungus and algae cells. The algae make food for photosynthesis. The fungus supplies water and minerals. It also protects algae from desiccation (dehydration).
It is an association between the fungus and roots of higher plants. The fungus depends on the photosynthate (product of photosynthesis) of plant. The benefit derived by mycorrhiza plant is not properly understood.
However, the plants with mycorrhiza association show better growth than without this association. Possibly, the fungus decomposes the organic material in the soil for the plants. It also provides water and minerals like phosphorus to plant.
The leguminous plants develop nodules on their roots. These nodules contain nitrogen fixing bacteria. The bacteria live on the plant material and fix atmospheric nitrogen. They convert this nitrogen into nitrates. These nitrates are used by the plants.
Nutrition in Insectivorous Plants
There are a few plants which supplement their inorganic food with organic compounds. These organic compounds are obtained by trapping and digesting insects and small animals. All the Insectivorous plants are true autotroph. But they grow rapidly when they capture prey. The nitrogenous compounds of the animal bodies benefit these plants.
In some plants, these trapped insects are decomposed by bacteria. In other plants the leaves secrete enzymes. These enzymes digest the trapped insects and release nitrogenous compounds. The plant absorbs these nitrogenous compounds.
Pitcher Plant (Sarracenia Pupurea)
Its leaves are modified into a sac or a pitcher. This pitcher is partly filled with water. The end of the leaf is modified to form hood (cap). This hood partly covers the open mouth of the pitcher.
Small insects fall into the pitcher. They are prevented from climbing out by numerous stiff hairs. The bacteria or enzymes decompose the protein of the trapped insect. These decayed compounds are absorbed in the inner surface of the pitcher leaf.
Venus- fly trap (Dionaea Muscipula)
Their leaves are boiled with midrib between them. There is a row of long stiff bristles along the margin of each lobe. When an insect touches a small sensitive hair on the surface of the leaf, the lobes quickly come together. Their bristles interlock the lobes. The glands on the leaf surface secrete enzymes. These enzymes digest the insects. Their products are absorbed by the leaf.
Sundew (Drosera Intermedia)
There is another type of modification of leaf in sundew. The tiny leaves contain numerous hairs like tentacles. Each tentacle has gland at its tip. The insects are attracted by the odour of the plant. They are entangled in the tentacles. The plant secretes protein digesting enzymes. These enzymes break the protein and the products are absorbed by the plant.