Nutrition In Organisms

The process by which organisms obtain and utilize food for their growth, development, and maintenance is called nutrition and the chemical substances present in the food are called nutrients.  

  • Every organism needs energy to perform its life processes, and these energies are acquired by proteins and ATP formation, for this, we need raw material in the form of food.
  • So food is the source of energy by which we get energy. This is different in plants and animals as Plants manufacture their own food by photosynthesis, but animals including humans have to take in ready-made food.

Nutrients: Types and Function

Nutrients are the substances used by organisms to survive, grow, and reproduce. The seven basic components of nutrients are carbohydrates, protein, fat, vitamins, minerals, fiber, and water.

Nutrients can be divided into two groups:

  1. Macronutrients: These are the components that humans consume in the largest quantities. These are mainly classified into carbohydrates, proteins, and fats. The macronutrients mainly provide energy to organisms.
  2. Micronutrients: These are substances introduced in small quantities, but they are required for adequate growth. eg. Vitamins, minerals

On the basis of function nutrients are of three types:

  • Energy-Giving Nutrients: Carbohydrates and fats provide us energy to carry out biological processes and other daily activities of life.
  • Body Building Nutrients: Proteins help in the growth of organisms by the formation of new cells, increasing the size of cells, and repairing or replacement of damaged or worn-out cells. The raw materials for these processes are provided by various food components.
  • Protective and regulating Nutrients: Vitamins and minerals are used to perform different functions in the body. 

Mode of Nutrition:

There are two types of nutrition, Autotrophic nutrition and heterotrophic nutrition.

Autotrophic nutrition:

In autotrophic nutrition, the organisms manufacture their own food (organic material) from simple inorganic raw materials. The organisms involved in autotrophic nutrition are called autotrophs.

  • In autotrophic nutrition, the food is synthesized by the organism itself, and in the process of food, production photosynthesis takes place in the presence of sunlight and carbon dioxide with the help of chlorophyll. With the help of chlorophyll, carbohydrates are produced as the product of photosynthesis. The remaining carbohydrates which are not utilized by the plant, are stored in the form of starch. The starch serves as the internal energy reserve to be used as and when required by the plant.
  • The resultant products of photosynthesis are utilized by plants to obtain energy to carry on their life processes like growth, repair, and reproduction.
  • The unused Carbohydrates are stored mainly in the form of starch for future use.
  • Examples of autotrophs are green plants and a few bacteria.

Process of photosynthesis:

These are the events that occur during photosynthesis:

  • Chlorophyll absorbs light energy.
  • Conversion of light energy into chemical energy and water molecules split into hydrogen and oxygen.
  • Reduction of carbon dioxide to carbohydrates.


In the whole process of photosynthesis chlorophyll, water, carbon dioxide, and sunlight are the essential elements. Water for photosynthesis is taken from the soil by the roots in terrestrial plants, from the soil other important materials like nitrogen, phosphorus, iron, and magnesium are taken.

Heterotrophic nutrition

As we know nutrition differs depending on the type and availability of food materials as well as how it organism obtains that food.

  • In single-celled organisms, the food may be taken in by the entire surface. But as the organism becomes complex, different parts become specialized to perform different functions.
  • For example, Amoeba takes food using a temporary finger- Food particles such as minute bacteria are enclosed (caught) by pseudopodia (pseudo = false, podia = feet) to form a food vacuole (Ingestion).

Difference between Autotrophs and Heterotrophs:

Autotrophs Heterotrophs
(AUTO: self, TROPHOS: food)   (Hetero: different, Trophos: food)
They manufacture their own food (organic substances) from inorganic substances like CO2 and H2O using energy from sunlight

Heterotrophs depend on other organisms for their nutrition.

Food – Organic and inorganic substances obtained by feeding on other organisms are called heterotrophic. In other words, the organisms cannot produce their food and are dependent on others.

These utilize simple inorganic materials for their nutrition

The autotrophs are called primary producers as they manufacture their own food by photosynthesis.

These utilize complex organic substances for their nutrition

Heterotrophs are called consumers because they consume autotrophs or other heterotrophs for their nutrition

These convert simple substances into complex food substances (anabolism) These break down complex food substances into simple substances (catabolism) during digestion.
These store unused food mainly as starch The unutilized food is stored in the form of glycogen and fat
All autotrophs have chloroplast which contains chlorophyll The chloroplasts are absent in heterotrophs
Example: Green plants and certain bacteria Examples: All animals, fungi, most of the bacteria and non-green plants

Types of heterotrophic nutrition

Holozoic nutrition:

The animals with holozoic nutrition obtain complex organic food materials by consuming other organisms i.e. plants or animals or their products through ingestion. The ingested food is digested and absorbed into the body by a specialized digestive system.

The undigested and unabsorbed part of food is thrown out of the body of the organism by the process of egestion. Most of the animals such as Amoeba, frogs, reptiles, birds, and human beings; exhibit the holozoic type of nutrition.

On the basis of food habits, the holozoic animals are divided into three groups:

  1. Herbivores: These are animals that consume only plants or plant products i.e. grass, leaves, grains, fruits, etc. Some common examples are cow, sheep, goat, buffalo, horse, deer, camel, elephant, etc.
  2. Carnivores: These animals feed on the other animals for their nutrition. They are also called meat or flesh eaters. Some of the common examples are lion, tiger, kite, snake, frog, etc.
  3. Omnivores: These animals consume plants as well as animals for their nutrition. Some common examples are crows, sparrows, dogs, bears, cockroaches, humans, etc.

Saprophytic nutrition: (sapro = rotten; phytos = plants)

Saprophytes obtain their food from dead and rotten plants and animals or their products, and other decaying organic matter. 

  • These organisms secrete digestive enzymes onto dead organic material which break down the complex decaying organic material into simpler compounds.
  • The soluble end products are then absorbed by them, generally by their body surface or through some specialized absorptive structures. 
  • Examples of saprophytes are some bacteria, and fungi such as moulds (Rhizopus, Mucor) and mushrooms.

Parasitic nutrition: (para = other; sitos = food)

The parasitic organisms obtain their food from the other living organism called the host. 

  • Food is derived from other living organisms by living on or inside their body
  • In this process, the parasite is benefited and the host is generally harmed.
  • The host may be a plant or an animal.
  • e.g., certain bacteria, roundworms, tapeworms, Cuscuta, etc.

Endoparasites: The parasite that lives inside the body of the host is called an endoparasite. Examples: Plasmodium (malarial parasite), Taenia (a flatworm), Ascaris (roundworm)

Ectoparasite: The parasite lives outside the body of the host. Example: Cuscuta (a plant parasite), mosquitoes, and leeches are some examples of ectoparasites.


Mutualism is a close association between two organisms, in which both organisms are benefited from each other. Some examples of mutualism:

  • Sea anemone (a cnidarian) attaches itself to the shell of a mollusc, inside the shell of which lives a hermit crab. The sea anemone obtains nutrition from the crab and the crab gets protection with the help of the sea anemone.
  • The association of nitrogen-fixing bacteria present in the root nodules of leguminous plants is also an example of mutualism.

Steps of Nutrition in Animals

The steps of nutrition in animals are as follows:

  • Ingestion: Through this process, the animals take food inside the body.
  • Digestion: The process of breaking down complex organic food substances into simpler, smaller, and soluble substances is called digestion.
  • Absorption: After the digestion is completed, the soluble, digested food is absorbed into the body fluid through the process of absorption.
  • Assimilation: The absorbed food substances are transported to the tissues and cells in different parts of the body. They are utilized for getting energy, synthesis of new protoplasm for growth and development, or are stored for future use.
  • Egestion: The undigested and unabsorbed solid residue of food is expelled from the body in the form of feces through this process.



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