Food is an organic substance where carbohydrates are the most common food for getting energy. Fats and proteins are also food. The simplest carbohydrate food is glucose, which is also called simple sugar. A more complex food is starch; it is also made from glucose. The process of taking in and utilizing food is called nutrition. In this process, obtained food is used to provide energy for performing various metabolic activities of the organism.
The mode of nutrition means methods of procuring food or obtaining food by an organism. All the microorganisms do not get their food in the same way. Different organisms have different methods of procuring food or obtaining food. In other words, organisms differ in their modes of nutrition. Depending on the mode of obtaining food, all the organisms can be classified into two groups:
NCERT Solutions For Class 10 Science Chapter 6 Life Processes discusses Nutrition and various modes of nutrition in both plants and human beings.
The word autotroph is derived from two words, i.e. 'auto' means self and 'trophe' implies nutrition. Hence, autotrophic means 'self nutrition'. In autotrophic nutrition, the organism produces its food from inorganic raw materials like CO2 and H2O present in the surroundings by using sunlight energy.
In autotrophic nutrition, organic material is made from inorganic materials. The green plants have an autotrophic mode of nutrition. The autotrophic bacteria also obtain their food by the autotrophic way of nutrition. The organisms having an autotrophic mode of nutrition are called autotrophic organisms or autotrophs.
All green plants are autotrophs because they can make their food from inorganic substances like carbon dioxide and water present in the environment. Non-green plants are, however, not autotrophs. Certain bacteria called 'autotrophic bacteria' are also autotrophs. The autotrophic organisms contain the green pigments called chlorophyll which is capable of trapping sunlight. The autotrophs utilize the trapped sunlight to make food by combining inorganic materials like carbon dioxide and water present in the environment by photosynthesis. Thus, autotrophs make their food by photosynthesis.
Autotrophs are the producers of food. The food produced by autotrophs is also used by human beings and many, many other animals. Based on the source of energy, autotrophs are of the following types:
Photosynthetic autotrophs: These bacteria use light energy for food synthesis. In these bacteria, photosynthesis is non-oxygenic. Therefore, photosynthetic pigments are present in the cytoplasm for photosynthesis. These can be of following three types:
Chemosynthetic autotrophs: They use chemical energy instead of light energy for food synthesis. Chemical energy is obtained by oxidation of chemical compounds, i.e. organic or inorganic. Chemosynthetic bacteria play a significant role in recycling nutrients like nitrogen, phosphorus, iron, and sulfur. These can be of following sub-types:
1. Nitrifying bacteria: They oxidize nitrogenous compounds and obtain energy. It performs nitrifying action in the following two steps:
STEP 1. Conversion of NH3 to NO2- by Nitrosomonas and Nitrococcus
STEP 2. Conversion of NO2- to NO3- by Nitrobacter and Nitrocystis
1. Iron bacteria: e.g. Ferrobacillus, which converts Fe2+ to Fe3+
2. Hydrogen bacteria: e.g. Hydrogenomonas, which converts H2 to H2O
3. Methane bacteria: e.g. Methanomonas, which converts CH4 to CO2
4. Sulfur bacteria: These are of the following two types-
Heterotrophic nutrition is that mode of nutrition. An organism cannot make its food from simple inorganic materials like carbon dioxide and water and depends on other organisms. A heterotrophic organism is a consumer which derives its nutrition from other organisms. All the animals have a heterotrophic mode of nutrition. Most bacteria and fungi also have a heterotrophic way of nutrition. The non-green plants like yeast are also heterotrophs.
Heterotrophs are categorized into different categories based on their mode of nutrition. They are listed below: