Modes of nutrition
March 15, 2018
Organisms obtain their food materials in different ways which are of two types generally. They are:
A) Autotrophic nutrition B) Heterotrophic nutrition.
A) Autotrophic nutrition
- Gr.autos=self, trophein=to nourish.
- Also known as holophytic.
- In this type, organisms synthesize their own nutrients from inorganic constituents of the environment.
- Typically found in all green plants.
- Some bacteria and protists also exhibit this type.
- This is of two types. They are:
a) Photosynthetic nutrition
- Chlorophyll bearing organisms synthesize their nutrients.
- Presence of light, water and carbondioxide is necessary.
- Organisms are termed phototrophs.
- Process is called photosynthesis.
- The process is represented as follow:
chlorophyll
6CO2 + 6H2O → C6H12O6 + 6O2.
Sunlight
b) Chemosynthetic nutrition
- Sulfur bacteria and iron bacteria follow this mode.
- They capture energy released during oxidation of simple inorganic compounds of sulfur iron, etc.
- Organic food is prepared without the use of sunlight.
- Organisms are called chemotrophs.
- The process is called chemosynthesis.
B) Heterotrophic nutrition
- Gr.Heteros- other, trophein– to nourish.
- Organisms obtain already synthesized nutrients.
- Chemical energy of organic compounds synthesized by other organisms are used.
- Typically exhibited by animals.
- Organisms are called heterotrophs.
- Food of heterotrophs come directly or indirectly from green plants.
- They may be classified as:
a) Holozoic nutrition
- The organisms feed on solid or liquid food.
- The food may be a whole plants or whole animals or their parts.
- Involves a number of processes like ingestion, digestion and absorption.
- Found commonly in free living organisms, including man.
- Such organisms are further classified as:
i) Herbivorous
- L.herba– herb, vorare- to eat.
- Feeds on plants and plant products.
- Include grazing animals like cows, goats,horses, rabbits, etc.
- Some are only fruits eating (frugivorous) while others are grains eating (gramnivorous).
ii) Carnivorous
- L.carnis- flesh,vorare- to eat.
- Feeds on other animals or animals products.
- Mostly preying and hunting animals fall under this group.
- They are called predators e.g. lion, tigers, vultures, etc.
- Some are only insects eating (insectivorous).
- Some others are blood sucking called sanguivorous.
iii) Omnivorous
- L.omnes- all, vorare- to eat.
- Derive food from both plants an animals.
- e.g. man, cockroach, crow, etc.
b) Saprophytic nutrition
- Derive food from dead and decaying matters.
- Fungi and many bacteria fall under this group.
- Enzymes are released to digest the dead organic food.
- The nutrients are absorbed through their body surface.
- Commonly called saprophytes or saprobes.
c) Parasitic nutrition
- Derive nutrients from body fluids or tissues of living animals or plants called hosts.
- Organisms are called parasites.
- They may be:
i) Ectoparasite
- Lives outside the body of animals or plants.
- e.g. leeches, bed bugs, body lice, etc.
ii) Endoparasite
- Lives inside the body of hosts (animals or plants).
- e.g. tapeworms, round worms, Plasmodium, etc.
Image source: ekuleducation
References:
ii) https://www.bartleby.com/subject/science/biology/concepts/modes-of-nutrition