OUR NUTRITION - BASICS

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1. Introduction :

  • Nutrition is one of the fundamental processes of living organisms, as it is essential for growth, development, and other vital functions in any living organism.
  • There are two types of living  organisms; unicellular organism, also known as single-celled organism and multi-cellular organisms such as plant and animal. 
  • Further, plant can be classified on the presence or absence of chlorophyll. Hence, the process of nutrition also varies from one type of organism to another.
  • The nutrition are classified into six major groups based on their role in the human body.

2. Concept Of Nutrition :

  • Every living organism requires energy and other nutrition for its growth, development, and other vital process. 
  • This energy is produced in the body of living organisms by the combustion of certain nutrition that they get from their food. Hence, food (nutrition) is essential for the survival of any living organism.
  • There are large diversity amongst the living organisms in terms of their cellularity level  (uni/multi-cellular), the presence of cell wall (plant/animal), and organisation.
  • This process of acquiring food or nutrition is called Nutrition.
  • On the basis of the presence of nutrition, Organisms can be divided into two major group:
    • Producers or Autotrophs.
    • Consumers or Heterotrophs.

2.1. Producers or Autotrophs :

The organism like green plants including algae and certain bacteria that produce their own food are called Producers or Autotrophs.

2.1.1. Type Of Autotrophs :

A. Photoautotrophs :

  • The green plants and algae produce their food by the process of Photosynthesis (photo=light) using light energy that gets converted into chemical energy of the food. 
  • As they use light energy to convert the inorganic materials (carbon dioxide and water) into organic compounds (carbohydrate), they are also called Photoautotrophs.
  • They produce food in the form of glucose (carbohydrate) that get stored in the plant cell in the form of starch grains.
How does Photosynthesis process takes place? Read more about Photosynthesis here.

B. Chemoautotrophs :    

  • Some autotrophs that reside in deep sea where the sunlight cannot penetrate and they produced their food with the help of chemicals. 
  • Due to the non-availability of light, they use chemical energy that is released from the inorganic chemical reactions, and this process is called Chemosynthesis. 
  • Some bacteria oxidise hydrogen sulphide or methane, and some reduce sulphide to produce sugar and other related by-products.
  • The chemosynthesis that occurs in organisms that oxidise hydrogen sulphide can be represented as follows:
         12H2S + 6CO2 à C6H12O6 + 6H2O + 12S

2.2. Consumers or Heterotrophs :

  • Organism that depend on other organism directly or in directly for their food are called consumers or heterotrophs.
  • In this case, the nutrients are acquired by digesting or breaking the complex organic compound into simpler organic or inorganic substances.
  • All animal and plants that cannot photosynthesise are heterotrophs.


2.2.1. Type Of Heterotrophs:

A. Holozoic Organisms:

  • Organisms that consume food in the form of solid or liquid complex matter that is further broken down into simpler molecules or nutrients are called  Holozoic organisms.
  • Thus, this kind of nutrition requires a series of steps for the conversion of complex organic matter into absorbable nutrients.
These step include the following:

INGESTION à DIGESTION à ABSORPTION à ASSIMILATION à EGESTION

Read detail about these different steps of Holozoic Nutrition here:

B. Parasitic Organisms : 

Organisms that depend on other living organisms for their food are called parasitic organisms. In this process, they depend on the other organism, which is referred  to as their host. These organisms absorb the digested or semi-digested food from their host, and in turn, harm in host in some way. 

Types of Parasitic Organisms :

a. Ectoparasites : 

  • These parasites live on the outer surface of the body of their hosts.
  • For example, lice or ticks living on animals and Dodder or Cuscuta  (amarbel) grows on trees and is completely dependent on its host as it lacks chlorophyll.
b. Endoparasites :
  • these parasites live inside the body of the host. 
  • For example, worms living in the human body (tapeworm, hookworm) or malarial parasite (Plasmodium) in human beings as well as in mosquitoes.
  • plasmodium is a parasite that requires two hosts to complete its life cycle.

C. Saprophytic Organisms :  

  • Organisms that depend on dead organisms and their decaying matter are called saprophytic organisms. 
  • They act as decomposers in the environment and are natural cleansers.
  • They help in recycling the nutrients in the environment.
  • For example, fungus (black mould) growing on the leather and fungus or bacteria acting on the dead animals and plants.

 D. Symbionts Organisms :

  • These organisms live in close association with organisms belonging to different species in such a way that both are mutually benefitted. This kind of relationship is referred to as symbiosis.
  • The most common example is lichens that are in association between algae and fungi and also they are mutually benefitting from each other. 
  •  bacteria like Lactobacillus living in human alimentary canal or Rhizobium bacteria in the root nodules of leguminous plants are also good examples of symbionts.

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