Nutrition In Living Organisms & Modes Of Nutrition

Generally, our days are packed with numerous activities. To perform these activities we need huge chunks of energy. The energy we utilize comes from the food we consume. Hence, food is vital as it provides the energy needed for growth, repair, and sustaining life. All these come under the life process called nutrition. Let’s learn about nutrition and its different modes in detail.

What is Nutrition?

Nutrition is the process of taking in food and converting it into energy and other vital nutrients required for life. Nutrients are the substances which provide nutrition. All living organisms need nutrients for proper functioning and growth. But they show divergence in how they fulfil this demand. Some animals use simple inorganic compounds to obtain their food. While other animals use complex compounds as their source of food. The mode of nutrition varies from one species to another.

Types of Nutrition

Broadly, there are two types of nutrition among living organisms, namely:

  • Autotrophic mode
  • Heterotrophic mode

Autotrophic Nutrition

In the autotrophic mode, organisms use simple inorganic matters like water and carbon dioxide in the presence of light and chlorophyll to synthesize food on their own. In other words, the process of photosynthesis is used to convert light energy into food such as glucose. Such organisms are called autotrophs. Plants, algae, and bacteria (cyanobacteria) are some examples where autotrophic nutrition is observed.

During photosynthesis, carbon dioxide and water get converted into carbohydrates. These carbohydrates are stored in the form of starch in plants. Plants later derive the energy required from the stored starch. The process of photosynthesis can be explained in three stages:

  1. Absorption: The chlorophyll present in leaves traps the light coming from the sun.
  2. Conversion: The absorbed light energy gets converted into chemical energy. And water absorbed will split into hydrogen and oxygen molecules.
  3. Reduction: At last, carbon dioxide gets reduced i.e. hydrogen molecules combine with carbon, to form carbohydrates (sugar molecules).


All three events are not a continuous process. They may or may not take place sequentially.

In plants, stomata are the openings on leaves where gaseous exchange takes place and is regulated by guard cells. Plants take in and release out gases through these stomatal pores. In desert-like habitats, to avoid water loss, guard cells keep these pores closed during the daytime. Later, during the night time, stomata will be opened to absorb carbon dioxide and store in the vacuoles. During daytime, they will use this stored carbon dioxide to perform photosynthesis.

Other than photosynthesis, plants also depend on soil for micro and macro elements. These elements are used to synthesize proteins and other essential compounds required for the proper functioning and growth of the plants.

Heterotrophic Nutrition


Every organism is not capable of preparing food on its own. Such organisms depend on others for their nutrition. The organisms which cannot produce food on their own and depend on other sources/organisms are called heterotrophs. This mode of nutrition is known as heterotrophic nutrition. Fungi and all the animals including humans are heterotrophs. Heterotrophs can be of many varieties depending upon their environment and adaptations. Some may eat plants (herbivores) and others eat animals (carnivores) while few eat both (omnivores). Thus we can say survival of heterotrophs depends directly or indirectly on plants.

Heterotrophs are classified into different categories based on their mode of nutrition. They are:

  • Parasites (e.g. leeches, ticks)
  • Saprophytes (e.g. mushrooms)
  • Holozoic (e.g. humans, dogs)

To learn more about different modes of nutrition, download Byju’s-The Learning App.

Practise This Question

Which of the following can be an indication of contraction and relaxation of the heart?