Nutrition in Animals:

As we discussed nutrition in plants in previous sections. Nutrition in animals will be discussed in this section. When we see animals several questions arise in our mind. What happens to the food we eat? How our body utilizes it?  Why different animals eat different types of food? 

The fact about animals that is different from plants is the mode of nutrition. Nutrition in animals and plants is one of the vital life processes. Plants make their own food, so they are called autotrophs. But animals can’t synthesize their own food, they are dependent on autotrophs or other heterotrophs for their food, that is why they are said to possess heterotrophic mode of nutrition.

Heterotrophic Nutrition:

• The mode of nutrition in living organism who can’t make their own food but is dependent on other living organisms for their food is heterotrophic mode of nutrition.
• The living creature which follows heterotrophic mode of nutrition is said to be heterotrophs.
• A lot of creatures, human beings, giraffes, dogs, fish, horses, and lizards follows heterotrophic mode of nutrition.

Types of Heterotrophic Nutrition in Animals:

The nutrition by dependence of heterotrophs on other organisms are of three types:

• Saprophytic Nutrition:
  In saprophytic nutrition, the organisms obtain their food from dead and decaying plants, animals and other decomposing organic matters.
  The organisms which obtain their food through this process is called saprophytes.
  Fungi, mushrooms, bread mould, some protistas and many bacteria follow saprophytic in nutrition.
• Parasitic Nutrition:
  In this type of nutrition, the organisms depend on the body of other living organisms (host body) for getting their food.
  The organisms which depend on other living organisms (host organisms) for food are called parasites.
  Leech and Many viruses, fungi, bacteria and animals have this mode of nutrition.
• Holozoic Nutrition:
  This mode of nutrition in animals is followed by those organisms which take solid or liquid food inside their body.
  The complex organic material (food) which when ingested than is broken down into simple inorganic substances by the process of digestion. After digestion, it is absorbed in our body cells. 
  Human beings, dog, cat, lion, deer, crow, frog have holozoic mode of nutrition.

On the basis of eating habits animals are classified into 5 types:

• Herbivorous animals: The animals which depend on green plants for their food are herbivorous animals.
  Example: Deer, cow etc.
• Carnivorous animals: The animal that gets food from killing and eating other animals are carnivores.
  Example: Tiger, cat, snakes etc.
• Omnivorous animals: The animal that eats both, other animals and plants are omnivorous animals.
  Example: Human beings, bears, squirrels, racoons etc.
• Parasites: The organisms which depend on other living organisms (host organisms) for food are called parasites.
  Example: Leech.
• Scavengers: The animals which eat dead animals are called scavengers.
  Example: Vultures, Hyenas, and wolves.

Nutrition in Amoeba:

• Amoeba is a microscopic unicellular organism. It mostly resides in places like pond water.
• It follows holozoic mode of nutrition and the process of taking food is known as “phagocytosis”.
• The process of taking food includes:

• Ingestion: It pushes out its pseudopodia to encircle the food. After this, it engulfs the food by forming a bag-like structure (vacuole).
• Digestion: The enzymes (in vacuoles) break down large insoluble foodstuffs into simple soluble molecules.
• Absorption: There is the absorption of the digested food material into the cytoplasm.
• Assimilation: Now, the absorbed food is utilized for energy production, growth, repair as well as for multiplication.
• Egestion: Finally, the undigested food material is removed out of the body by the rupturing of the cell membrane.

INGESTION ⇒ DIGESTION ⇒ ABSORPTION ⇒ ASSIMILATION ⇒ EGESTION

Nutrition in Paramecium:

• Paramecium is a unicellular aquatic organism.
• The paramecium has thin, hair-like cilia all over its body.
• The cilia move back and forth rapidly in water.
• When the cilia are present around, the mouth region of paramecium move, back and forth. They sweep the food particles present in water into the mouth of the paramecium.
• This is the first step in the nutrition of paramecium which is called ingestion and is followed by digestion, absorption, assimilation and egestion.

Nutrition in human beings:

There are 5 stages of nutrition in human beings. They are

1. Ingestion
2. Digestion
3. Absorption
4. Assimilation
5. Egestion

• The digestive system begins with the mouth where food enters and is placed into the alimentary canal. This process is
• After the food enters the alimentary canal it is in form of complexes. The breakdown of complex food into their simple soluble molecules to be done. This process is
• The food must be broken down so that they can be absorbed into the bloodstream and then taken to the body cells. This process is
• After the food is absorbed the essential nutrients are reached to the body cells. Here the process of assimilation converts the absorbed nutrients into complex molecules for growth, repair and defence.
• Finally, there is removal of waste products which remain behind, from the body. This is done by the process of egestion.

The biochemical process involved in digestion of food: nutrition in animals

As you are now aware that nutrition in animals so now takes a look at human digestive system.

• At first, with the help of tongue and teeth food is chewed and mixed with saliva in the mouth.
• Saliva contains an enzyme “salivary amylase” acts on the starch present in food.
• As elementary canal is soft so food is converted to smaller particles and wet it with the help of mucus and saliva to make it smooth.
• The lining of the canal has muscles that contract rhythmically to push the food forward.
• From the mouth, the food is taken to the stomach through the food-pipe or
• The stomach is a large organ which expands when food enters it.
• The gastric glands present in the wall of the stomach release hydrochloric acid, a protein-digesting enzyme called pepsin and mucus.
• The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin.
• Pepsin has a great role in converting proteins into peptides.
• The mucus has an important role as it protects the inner lining of the stomach from the action of the acid under normal conditions.
• Sphincter muscle regulates the exit of food from the stomach, it releases it in small amounts into the small intestine.
• The small intestine is the longest part of the alimentary canal which is fitted into a compact space because of extensive coiling.
• Herbivores who eats grass need a longer small intestine to allow the cellulose to be digested.
• Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.
• Bile salts (from liver) acts on the fat molecules and breaks them into smaller globules. By this, the action of lipase on the fats eased. This process is called emulsification.
• The pancreas secretes pancreatic juice which contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.

• Enzymatic action:

Protein – Amino Acid
Fat – Fatty Acid and Glycerol
Complex carbohydrates – Glucose

• The inner lining of the small intestine has a large number of finger-like projections called “villi”. Villi increase the surface area for absorption.
• Villi has sufficient blood vessels in it by which nutrients get absolved in the blood.
• The unabsorbed food is sent into the large intestine where more villi absorb water.
• The rest of the material left as waste is removed from the body via the anus.

Nutrition in animals thus concluded. Also, you can refer life processes and nutrition in plants.

Also read,
Life processes	Nutrition in plants
Respiration in plants	Human respiratory system
Transportation in plants	Human circulatory system
Excretion