Modes of nutrition

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.

LIFE PROCESSES - EKUL EDUCATION

Image source: ekuleducation

References: 

i) https://www.simply.science/images/content/biology/plant_form_and_function/nutrition_in_plants/conceptmap/Modes_nutrition.html

ii) https://www.bartleby.com/subject/science/biology/concepts/modes-of-nutrition

Modes of nutrition