Holozoic Nutrition 

             

                               Or

What is Holozoic Nutrition?

                                 Or

Explain Holozoic mode of nutrition in organisms.

Nutrition is the sum of processes involved in taking all the nutrients ( i.e. food or chemical substance obtained by an organism from its surroundings) which is required by the body, their internment, distribution and utilisation for obtaining energy, repair, growth materials and body protection.

Depending upon the taking in of food, there are two modes of nutrition, 

Autotrophic Nutrition:

Autotrophs,manufacturing food  by photosynthesis ( manufacturing in the presence of light) or by chemosynthesis ( in the absence of light by some simple molecules). Examples: plants, bacteria and cyanobacteria.

Heterotrophic Nutrition: 

Obtaining their food by some mode other than the autotrophic one i.e. from dead or living plants or animals.Example: all animals, fungi and most prokaryotes including bacteria.

Depending upon the mode of obtaining food, heterotrophic nutrition is of four different types:

1. Holozoic Nutrition

2. Saprophytic Nutrition

3. Parasitic Nutrition

4. Mutualistic Nutrition

Holozoic Nutrition:

(Holo- complete + zoon- animal)

In this type of nutrition, all the animals including humans, obtain their nourishment by ingesting the whole food (complex organic matter in the form of plant or animal part) through mouth or some similar structure by the process of ingestion.

Holozoic Nutrition in Amoeba and Paramecium- Diagram

Holozoic Nutrition definition:

Engulfment of the whole or a part of a plant or an animal, either in a solid or in a liquid state. e.g. most of the free-living protozoans and animals.

The ingested matter is,

•  subsequently digested (complex to simple molecules), 
•  absorbed in the body, and
•  finally egested out of the body, e.g., all animals including vertebrates (fishes, birds, mammals etc.) and invertebrates (insects,  molluscs etc.).

Steps of Holozoic Nutrition:

The various steps involved in Holozoic Nutrition are:

I. Ingestion: 

Method of feeding based on gross size of food ingested is of two types:

1.  Microphagy: Feeding on microscopic organisms e.g. Amoeba, paramecium.
2. Macrophagy: Feeding on larger forms of organism e.g. the majority of non-chordates and some chordates.

II. Digestion:

Breaking down of the covalent bonds in the organic food molecules (carbohydrates, lipids, proteins and nucleic acids) by hydrolysis. 

In heterotrophs, two types of digestion i.e.

1. Intracellular digestion: Takes place inside the individual cells with the help of lysosomal enzymes, found in unicellular protozoans  (e.g. amoeba, paramecium) and sponges.

2. Extracellular digestion: Digestion takes place outside cells within a cavity e.g. sac-like coelenteron or gastrovascular cavity in cnidarians ( Hydra, Aurelia etc,).

 The gastrovascular cavity is lined by endoderm cells which secrete their enzymes into the cavity and digest the food extracellularly. 

The partly digested, fragmented food particles are digested by nutritive cells for intracellular digestion. i.e. cnidarians perform both intra- and extracellular digestion.

• Free-living Platyhelminthes or flatworms (e.g., planaria) employ both types of digestion.
• In most non-chordates and chordates, a developed complete digestive tract, with two openings is present. The entire alimentary canal and its associated glands together constitute the alimentary or digestive system.

III. Absorption:

The digested food is absorbed. The absorbed food is circulated in the body through the blood-vascular system to meet the needs of living cells. The absorbed food is used for energy liberation and anabolic processes.

IV. Egestion:

Elimination of undigested food through food vacuole (exocytosis) in protozoans,  single opening in cnidarians and anus in most non-chordates and chordates. 

Depending upon the type of whole food taken or the food habit holozoic nutrition have different types.

Types of Holozoic Nutrition ( Ingestive Nutrition) :

Mainly they are:

1. Herbivores: Consume only algae or plant material e.g. cow, horse and rabbit.
2. Carnivores: Flesh-eating animals e.g. lions, tigers, crocodile etc.
3. Omnivores:Feed both on plants and animals e.g. cockroaches, rats, crows, humans etc. Some other types include,
4. Cannibals: Eat upon the members of their species e.g. some fish, cockroaches, certain snakes etc.
5. Predators:  When the larger animals feed upon the smaller animal species e.g. birds like eagles, kites etc.
6. Piscivores: Feed on fishes e.g. crocodiles, penguins, kingfishers etc.
7. Insectivores: Feed upon insects, e.g. frogs, lizards, small bats etc.
8. Scavengers or Carrian eaters: Feed on other dead and decaying material e.g.vultures, crows, hyenas etc.
9. Grainivorous: Feed upon grains e.g. pigeon.
10. Coprophagous: Feed upon faeces e.g. dung beetle, pigs etc.
11. Detritivores: Feed chiefly upon dead organic matter present in the mud e.g. earthworms.
12. Myrmecophagous: Take ants as prey e.g. spiny ant eater, scaly ant eater.
13. Larvaevorous: Feed on larvae e.g. Gambusia fish.
14. Sanguinivores: Suck blood of other animals e.g. leeches, mosquitoes, fleas etc.
15. Folivorous: Eat leaves e.g. sheep, goat etc.
16. Frugivores: Eat fruits e.g. birds, monkeys etc.
17. Fluid feeders: Feeding on plant fluids e.g. butterflies, male mosquitoes etc.

Related QnA:

Question:

What is Saprophytic or Saprozoic Nutrition?

Answer: 

Organisms obtain food from dead and decaying organic material by first pouring digestive juices ( hydrolysing enzymes) over the same and then sucking the digested food.

Note: Saprobiotic Nutrition, referred to as Saprozoic, if carried out by an organism considered to be an animal and Saprophytic if the organism is a plant or fungus.

(Sapro: rotten+ phyton- plant, trophos - feeder)

Question:

What is the Parasitic and symbiotic or mutualism mode of nutrition?

Answer:

Parasitic Nutrition: It refers to nutrition by obtaining food manufactured or synthesized by others. Here always two types of organisms are involved. A smaller organism called parasite, derives its nutrition or food from another organism called host. The host can be plant or animal. The parasite lives either inside the body called endoparasite or one body, called ectoparasite. e.g. Plasmodium, Taenia, Typanosoma, Ascaris.

Symbiotic Nutrition or Mutualism or Mutualistic Nutrition: It is a type of interdependent nutrition, in which each organism is dependent mutually on the other. Here two organisms or animals live in association and derive nutrition from each other. e.g. 

1. The lichens share mutualistic nutrition between fungus and a cyanobacterium or alga. The algal partner manufacture the food with the help of photosynthesis while the fungal Partner provides protection and also absorbs water and mineral salts.

2. E.coli and human. E.coli synthesize vitamin B12 for humans while, human provide food to bacterium.

Question:

Difference between Saprophytic and holozoic nutrition.

Answer:

The major differences between Saprophytic and Holozoic Nutrition are:

Features	Saprophytic Nutrition	Holozoic Nutrition
Nature of Food	Liquid food is ingested ( dead decaying organic matter).	Solid food is ingested ( whole plant or animal or their parts)
Site of digestion	Always outside the body as enzymes are released on the food.	Always inside the body, whether intracellular or intercellularly
Examples	Fungi and some bacteria	Most animals including human beings.

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About the Author: This educational content on Zoology is written by Rekha Debnath, M.Sc. & M.Phil. in Zoology, with a focus on university-level academic topics. Read the full Author Credentials and Background here.