Holozoic Nutrition (Definition, 5 Steps, Types & Examples for Class 7 & Class 10 Science): Holozoic nutrition is a mode of heterotrophic nutrition in which an organism takes in complex solid or liquid organic food and breaks it down internally through five sequential stages: Ingestion, Digestion, Absorption, Assimilation, and Egestion.
| Step # | Stage of Holozoic Nutrition | What Happens in This Step? | Example in Humans / Amoeba |
|---|---|---|---|
| 1 | Ingestion | Taking solid or liquid food into the body. | Mouth in humans; pseudopodia in Amoeba. |
| 2 | Digestion | Breaking down complex, insoluble food molecules into simple, soluble molecules using digestive enzymes. | Alimentary canal (stomach & small intestine); food vacuole in Amoeba. |
| 3 | Absorption | Passing digested soluble nutrients through the intestinal wall into the blood or cytoplasm. | Villi in the small intestine; diffusion into cytoplasm in Amoeba. |
| 4 | Assimilation | Utilizing absorbed nutrients inside body cells for energy (respiration), growth, and tissue repair. | Glucose oxidized in cells to release ATP; amino acids build proteins. |
| 5 | Egestion | Expelling undigested and unabsorbed waste food material out of the body. | Anus in humans; rupture of cell membrane in Amoeba. |
Holozoic Nutrition
Definition of Holozoic Nutrition :It is mode of heterotrophic nutrition which involves intake of solid pieces of food. Since solid food is taken in, holozoic nutrition is also called ingestive nutrition. Holozoic Nutrition(Gk. holo-whole ,zoon-animal) is found in animals and protozoans protists. The food may consist of another animal, plants or its parts. Depending upon the source of food, holozoic organisms are of three types-herbivores, carnivores ,omnivores.
Herbivores (L. herba-plant, vorare-to eat). They are holozoic organisms which feed on plants or plant parts, e.g., Cow, Buffalo, Deer Goat, Rabbit, Grasshopper, Elephant, Squirrel, Hippopotamus.
Carnivores (L. carne-flesh, vorare-to eat). They are animals which feed on other animals. Carnivores are also called predators as they hunt kill and feed on their preys, e.g., Lion, Tiger, Leopard, Snake, Hawk
Omnivores (L. omnis-all, vorere-to eat). They are holozoic organism which feed on both plant and animal materials, e.g., Cockroach, Ant,Pig, Crow, Rat, Bear, Dog, Humans.
A fourth category of holozoic organisms is detrivores.
Detrivore (L, detritue-dead, vorare to eat) are animals which feed on dead bodies of other animals. They are also called carrion feeders or scavenger e.g., Vulture, Hyaena, Kite,
A heterotrophic organism can obtain its food from other organisms in following three ways:
- Holozoic nutrition
- Saprophytic nutrition
- Parasitic nutrition
There are five steps in holozoic nutrition -ingestion, digestion, absorption, assimilation and egestion.
This process takes place in the following steps:
Ingestion.
- Ingestion. The process of taking food inside the body is called ingestion. Different animals use different organs for catching, holding and putting the food into mouth. Cutting and tearing the solid food into small pieces is common for ingestion.
Digestion
- Digestion. The ingested food consists of complex insoluble organic substances. The conversion of complex insoluble food ingredients into simple absorbable form is called digestion. It is a catabolic process which occurs with the help of digestive enzymes. Digestion can be intracellular or intercellular. Intracellular digestion is found in protozoan protists (e.g., Amoeba, Paramecium), simple animals and certain cells of higher animals leg., macrophages, monocytes). Here the ingested food particle is digested in a food vacuole. In higher animals the ingested food is taken to a digestive tract where digestive enzymes are poured over it. As it occurs outside the cells, the digestion is intercellular or extracellular, e.g., fish, frog, lizard, lion, human.
Absorption
- Absorption. The digested food is absorbed from the digestive tract and transported to all body parts. It is picked up by all the living cells.
Assimilation
- Assimilation. Inside the living cells, the absorbed food materials are used in obtaining energy and formation of new components for repair and growth of cells. Assimilation is an anabolic process as it takes part in synthesis of proteins, polysaccharides, fats and other macromolecules.
Egestion
- Egestion (L. egestus-discharge). The whole of ingested food is seldom digested. The undigested components of food are thrown out of the body as faecal matter. The process is called egestion.
Also See Difference between Holozoic and Holophytic Nutrition