Nutrient provides energy which is necessary for carrying out the various functions of the body. Nutrients help to proper functioning and growth of all organisms. Some organisms feed on simple inorganic compounds to meet their nutrient requirement. On the other hand, Complex organisms utilise complex compounds. The mode of nutrition varies from one organism to another. There are two types of nutrition among living organisms termed as 

“Autotrophic mode of nutrition” and “Heterotrophic mode of nutrition”. Plants and animals are doing different types of nutrition. Plants have green pigment which helps to synthesize food, while animals depend on other organisms for food.

Based on modes of nutrition-

A. Autotrophic nutrition:

The term ‘autotroph’ means- autos (self) and trophy (nutrition). In autotrophic nutrition, an organism makes its food by using raw materials. Autotrophic organisms synthesize food through photosynthesis. Photosynthesis is a process by which green plants, having chlorophyll, synthesize glucose from water and carbon dioxide using the energy of sunlight. Oxygen is released in this process. Sugar is stored in plants in the form of starch. Food is stored in the form of glycogen in animals. Energy is provided by these food reserves. Autotrophic plants are regarded as “producers” because of this.

Site of Photosynthesis:

Green parts of a plant are performing “photosynthesis”. The leaves are in the kitchen of the plant. The cells of the leaves contain chloroplasts, which are responsible for photosynthesis. These are plastids that contain chlorophyll (the light-absorbing green pigment).

Requirements for Photosynthesis:

Chlorophyll, carbon dioxide, water and sunlight are essential for the process of photosynthesis.

1. Chlorophyll- Chlorophylls are green pigments found in autotrophs. They are responsible for their green colour. In plants, chlorophyll is present in the leaves, young stems and fruits. Algae take part in photosynthesis.

2. Water- Water is essential for photosynthesis. Plants absorb water from the soil. The water is then transported through their root hairs, up to the leaves.

4. Sunlight- Solar energy is used in splitting water molecules into hydrogen and oxygen. 
5. Carbon dioxide- Plants use atmospheric carbon dioxide in photosynthesis. Plants obtain carbon dioxide through the stomatal pore. That is present on the surfaces of leaves. 

B. Heterotrophic nutrition:

The word ‘heterotroph’ means- heteros (other) and trophy (nutrition). Some organisms are not capable of preparing their food. This type of organism depends on others for its nutrition. Heterotrophic organisms obtain food from other organisms. This is termed “heterotrophic nutrition”. That is why they are called “consumers”. Example- All animals, non-green plants like fungi, etc. 

Some organisms are heterotrophs (herbivores) and others eat animals (carnivores) while few eat both (omnivores). Simply it means consumers which consume herbs are called “herbivores”. Those organisms that consume animals are called “carnivores”. Based on their mode of nutrition heterotrophs are classified into different categories. They are-

1. Parasitic-

Parasitic organisms/parasites live on or inside “hosts,” which are other living species. They are the ones who provide them with food. Cassytha (Amar-bel), Cuscuta (Akash-bel), tapeworms, leeches, hookworms and other parasites are examples. They feed in a variety of ways, depending on their habits, habitat, and modifications.

1. Saprophytic:

 The organism that feeds on the nonliving organic matter is called saprophytes. Saprophytes derive their food from dead organisms. They obtain nutrients directly from dead organic matter or wastes. Examples- moulds, mushrooms, Indian pipe, Corallorhiza orchids, Mycorrhizal fungi, yeast and many bacteria.

1. Holozoic:

In this type of nutrition, complex organic substances are ingested without their being decomposed. After this, the digested food is absorbed into the body and the undigested product is ejected from the body. This kind of nutrition is found mainly in non-parasitic animals like Amoeba, human beings.

C. Mixotrophs

Certain unicellular organisms may use both forms of nutrition such as “autotrophic and heterotrophic”. This is depending on resource availability. Example- Euglena gracilis possess chlorophyll for photosynthesis but may also feed on detritus (heterotrophic).

modes of nutrition are found in prokaryotes

Prokaryotes are also known as “prokaryotes”. Any organisms whose cells lack a nucleus and other organelles due to the absence of internal membranes are called “prokaryotes”. Most prokaryotes are small, single-celled organisms. They have a simple structure. Prokaryotes are also microscopic entities. Examples- cyanobacteria, E. coli, mycoplasma etc. Different organisms obtain food in different ways. Nutrition in unicellular organisms, like Amoeba, involves 3 steps- ingestion, digestion and egestion.

• Amoeba takes in complex organic matter as food. Amoeba first identifies its food. It then spread small pseudopodia (false feet). These pseudopodia enclose the food particle. The food enclosed in a vacuole is known as “ a food vacuole”. The complex food is broken down into simpler forms with the help of enzymes. The digestive organelle is known as “ the lysosome”. The digested food is distributed in the body (cytoplasm) and the undigested food is removed through the plasma membrane

• In Paramecium food is ingested through a special opening. This is known as the cytostome (cell mouth). Food is brought to this opening. This is done by the lashing movement of cilia. Cilia is present in every part of paramecium.

Conclusion

The nutrition process includes the absorption of nutrients needed by the body for growth, development, and maintenance of life. Based on the mode of nutrition, there are mainly 2 types of organisms. i.e autotrophs and heterotrophs. Autotrophs are called producers while heterotrophs are called consumers. The nutrition in the prokaryotic organism (whose cells lack of nucleus and other organelles),  involves 3 steps. i.e. ingestion, digestion and egestion. Amoeba and paramecium undergo intracellular digestion. Both unicellular organisms engulf food material that comes on their way. Digestive juice helps them to digest food present in the food vacuole.