Steps In The Process Of Nutrition in Animals

In this steps in the process of nutrition in animals post we have briefly explained about unicellular organisms, multi-cellular organism, lower vertebrate, and higher vertebrate.

Process of Nutrition in Animals and then using it to generate energy, grow, and heal the body is known as nutrition. Animals are classified as herbivores, carnivores, or omnivores depending on their eating patterns. Ingestion, Digestion, Absorption, Assimilation, and Egestion are the five primary processes involved in animal food consumption.

Steps In The Process Of Nutrition in Animals

Ingestion: Ingestion is the process of nutrition in animals by which food is taken inside (through the mouth), then chewed and broken down by teeth. The food that is taken in is broken down and mixes with saliva and this is known as bolus.

Digestion: Digestion is the process of nutrition in animals in which the food (it contains large, insoluble molecules, broken down into small, water soluble molecules) is then digested by secretion of certain enzymes and it is then used by the cells for producing energy.

Absorption: Absorption is the process of nutrition in animals in which the digested food passes (throughout the intestinal wall,) into the bloodstream. Our body cells use up the energy produced from the digested food; and then help in the building up various body tissues.

Assimilation: Assimilation is the process of nutrition in animals in which the digested food moves into the different cells of the body, for energy, growth and repair.

Egestion: Egestion is the process of nutrition in animals by which the undigested food is expelled out from the body through excretion. In the human body, kidneys help in purifying blood and removing metabolic wastes from it.

Feeding involves procurement as well as ingestion of food and nutrition. Depending upon the nature of food, feeding may be of three types in animals. 

Microphagy: This method is also known as filter feeding. Food particles smaller in size pass through filter along with water. The food particles are trapped and utilized whereas water is removed through body. Examples of organisms which show microphagy are paramecium, sponges, crustaceans, certain fishes and birds, blue whales, etc.

Macrophagy: This method involves the feeding of food particles which are large in comparison to the size of the organism. Organisms swallow whole food without chewing. Example of organisms which shows macrophagy are amoeba, hydra, certain amphibians, reptiles, fishes and birds.

Liquid feeding: Leeches, tape-worm, mosquitoes, bugs, spiders, flies, bats and mil-sucking young mammals shows different feeding behaviour where they ingest liquid food, known as liquid feeding or fluid-feeding.

Unicellular organisms


When food particles come in contact with the cell surface of amoeba, it slowly engulfs the whole food with the help of pseudopodia. This process of nutrition in amoeba animals takes place in approximately 2 min. Different modes of ingestion reported in amoeba is as follows:






Process Of Nutrition in Animals

Process of Nutrition in Animals: Steps of Digestion in Amoeba

Ingested food remains in food vacuole. The food vacuole is then transported deeper into the cytoplasm where they fuse with lysosome that contains amylase and certain proteinases. After digestion solid food is converted into liquid diffusible form and readily absorbed by cytoplasm through diffusion process of nutrition in animals. The undigested food is egested by exocytosis.

Multi-cellular Organism


Hydra is a fresh water diploblastic animal. Its body composed of two layers. Outer layer is protective and sensory epithelium and inner layer is gastrodermis act as a nutritive epithelium. The central body cavity known as coelenteron act as digestive tract. 

Process Of Nutrition in Animals

Process of Nutrition in Animals: Steps of Digestion in Hydra

Hydra catches the prey with the help of tentacles, a protrusion just outside the mouth. The circumference of mouth can extend according to the size of food particle. Thus it can swallow comparatively large animal. Soon after ingestion, digestion process of nutrition in animals starts with the help of enzymes secreted by granular glands, which appears just after ingestion. The undigested food is then egested through mouth. 


Sponges don’t have distinct digestive system. They engulf food by the support of water flow system. They show filter feeding behaviour, where food particle filter out of the water passing through them. Only particle smaller than 50 micrometre can enter through ostia. Sponges consume food by phagocytosis with the help of pinacocytes or archaeocytes. Food particles smaller than 0.5 micrometre can catch and consumed by choanocytes.

Lower Vertebrate


Cockroach searches the food with the help of antennae, maxillary and labial palps. These appendages bear sense organs. With the help of labium and labrum, the pro-legs pick up and bring food to the pre-oral cavity. Mandibles contain teeth which help in mastication of food in pre-oral cavity. The lacinia present in the maxillae also helps in mastication. 

Process Of Nutrition in Animals

Process of Nutrition in Animals: Digestive System of Cockroach

The food nutrition is mixed with saliva in pre-oral cavity. The saliva of cockroach contains amylase, chitinase and cellulose which digest carbohydrate partially in pre-oral cavity. Food from pre-oral cavity is then transported to esophagus and then into the crop. Crop is analogous to stomach of human, which store food for some time and also digestion takes place. 

Then food reaches to gizzard for crushing into fine particles, which then passes to midgut. Most of the digestion carried out in midgut. Digested food is absorbed by the inner lining of midgut through diffusion. The undigested food passes to hindgut. Water and electrolytes absorb here and undigested liquid food is converted to semisolid faeces, which the passed out through anus in the form of small dry pellets.

Higher Vertebrate


The amount of food and nutrition that an individual ingest in depend on the intrinsic desire for food (known as hunger) and the type of food that an individual seeks is determined by appetite. For maintaining an adequate supply of nutrition to the body these mechanisms are important. 


The foods engulfed or captured by most of the mammals are mechanically broken into smaller pieces. The teeth are perfectly designed for chewing. The anterior teeth (incisors) provide a strong cutting action and the posterior teeth (molars) a grinding action. Jaw bones and muscles help them in doing this work.

In herbivores animal (e.g. sheep, cow and horse) the premolar and molar teeth have well developed ridges for effective grinding of the food. In carnivores animals (e.g. tiger, cat, dog) the canine teeth are sharp and large for tearing the flesh. Chewing process of nutrition in animals is mainly caused by chewing reflex. The presence of bolus in mouth first initiates reflex inhibition of the muscles of mastication, which causes the lower jaw to drop. The drop of lower jaw initiate a stretch reflex of the jaw muscle that in turn initiate rebound contraction, which automatically raise the jaw upward to closure of the teeth. But again bolus compress against the lining of mouth, which inhibit the jaw muscles once again, allowing the jaw to drop again and rebound another time; this is repeated again and again.

Chewing is important for proper digestion of any king of food (except liquid food) but it is most important of fruits and raw vegetables because there indigestible cellulose membrane around the nutrients causes hindrance for digestion. Chewing also increase the surface area of food so that enzymes can act properly and increase the rate of digestion.


Swallowing is a complicated process of nutrition in animals because pharynx is involved both in respiration and swallowing. The pharynx is converted into food tract only for few seconds at a time without compromising respiration.

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