7th Class Science Nutrition in Animals Nutrition in Animals

Nutrition in Animals

Category : 7th Class

Learning Objectives

  1. Different types of nutrition
  2. Nutrition in amoeba-digestion is intracellular,
  3. Nutrition in humans
  4. Nutrition in ruminants- has four chambered stomach
  5. Different types of teeth in relation to food habits.
  6. Humans have two sets of teeth- milk teeth and permanent teeth.



Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly. All organisms require food for survival and growth. Requirement of nutrients, mode of intake of food and its utilization in body are collectively known as nutrition. Animals are heterotrophic in nutrition as they cannot make their own food. Euglena is an exception. It has chlorophyll and is capable of synthesizing food. But in the absence of light it feeds on dead organic matter and is a saprophyte. Animals are also holozoic because they swallow or ingest food. Examples of some holozoic method of intake of food by heterotrophic animals:

  1. Herbivores- These animals feed on plants and plant products, e.g cow, goat, horse, deer.
  2. Carnivores- These are also called meat eaters, e.g snakes, lions, tigers, eagle, frog etc.
  3. Omnivores- They feed on both plants and animal flesh. Man is an omnivore. e.g pigs, bears, crow, etc.


  1. Parasites- These live on or inside the body of ether living organisms

(a) Ectoparasite- These live on the body of the host. These are blood Slicking parasites, e.g lice, bedbugs, ticks, leeches etc

(b) Endoparasite- These live inside the body of the host. e.p tapeworm, liook v/orm, malaria parasite lives inside mosquito and man.

  1. Saprotroph- These feed on dead organic matter, e.g earthworm.
  2. Scavengers- They feed on flesh of dead matter, e.g vulture.


Nutrition in complex animals involves following steps:






Ingestion - The intake of food is called ingestion Method of ingestion, i.e., taking of food, varies from one animal to another.


Digestion- The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animations, amoeba, etc.

Absorption- The process of passing of digested food into blood vessels in the intestine is called the absorption.

Assimilation- The Conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation. In other words, assimilation is the conversion of absorbed food (Nutrients) into living tissues. Through the process of assimilation our cells are supplied with oxygen and nutrients.

Egestion- Removal of waste materials from the body is called egestion. The faecal matter is removed through the anus from time-to-time.

Since the waste- of food left after digestion is also called faeces, hence the process of egestion is also known as defecation.


Do you know?

During warm months a grizzly bear eats 40 kg of food each day gaining over 1 kg of body weight a day.


Different Ways of Taking Food: Ingestion

Different organisms take food in different ways:

A humming bird sucks nectar of plants.

Human beings use their hands to put food into their mouth and swallow the food after chewing

Infants of human and many other animals feed upon their mother’s milk by sucking them.

A snake swallows the animals they prey upon without chewing them.

A frog captures prey with its sticky tongue.

An earthworm uses its muscular pharynx to swallow its food.

Spiders weave sticky web in which small insects get stuck

Some aquatic animals filter tiny particles floating nearby and feed upon them.

Amoeba, a unicellular animal, engulfs tiny particles of food by using pseudopodia. Amoeba surrounds the food by pseudopodia and then makes a food vacuole to engulf the food.

In multi cellular organisms; like hydra there are numerous tentacles around their mouth. Hydra uses tentacles to surround its prey and kill them with its stinging cells. Then the food is pushed inside the body cavity.

Do you know?

An average person bites and chews food more than 1000 times a day. This keeps the jaw muscles strong and healthy.



After taking in food, food is digested and then it is passed to the different parts of body for the growth, repair and other vital functioning of body. The food we take is primarily in the form of complex substances. Food in such complex form is not used as such by animals. Hence, they need to absorb by the cells of the body.

The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, hydra, etc.

Enzymes help in the breakdown of complex molecules like carbohydrates, protein, fats, etc. Into simple molecules.

Digestion in unicellular animals; like Amoeba; is intracellular. The digestive enzymes are secreted in the food vacuoles.


Digestion in Amoeba

The amoeba is a microscopic unicellular organism. It belongs to the group protozoa. The name comes from the Greek word amoibe, meaning change. The habitat of the amoeba is fresh water. The amoeba contains jelly-like cytoplasm, Inside the cytoplasm are cell organelles like the nucleus, food vacuoles and contractile vacuole. An amoeba takes in oxygen and gives off carbon dioxide through the cell membrane by a mechanism of diffusion. It takes in oxygen dissolved in water.


Do you know?

Lions have sharp deged molar that called carnassials for cutting into tough meat.

An amoeba can move in all directions and can change its shape with the help of pseudopodia as a locomotary organ. An amoeba engulfs its prey along with a droplet of water with the help of pseudopodia, and then forms a food vacuole inside the cytoplasm. The prey can be killed and digested with the help of the digestive juice secreted by the food vacuole. Digestion in amoeba is intracellular takin place within the cell. The food takn in remains in a food vacuole or gastric vacuole formed by the cell membrane and small part of the cytoplasm. The vacuoles are transported deeper into the cells by cytoplasmic movements. Here they fuse with lysosomes that contain enzymes. Two enzymes amylase and proteins have been reported. Thus, amoeba can digest sugars, cellulose and proteins. Fats, however, remain undigested.

The contents of the vacuole become lighter and the outline of the vacuole becomes indefinite indicating that the digestion is complete. The undigested food is thrown out by changing the shape of the body. Amoeba forms a cyst in unfavorable conditions.


Amoeba ingesting food  



The digestive system of humans is well developed. It consists of the gut or alimentary canal, along with many associated digestive glands. The alimentary canal is divided into mouth, oesophagus, stomach, small intestine, large intestine and rectum. Mouth: The food is ingested through the mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands. Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar.


Salivary glands are present inside the Buccal Cavity .They secrete saliva. This saliva plays an important role in breaking down complex components like starch, which is further simplified into sugars.

Teeth: Our teeth cut, tear and grind the food before we swallow it. There are four types of teeth in our mouth.

Incisors: These are flat and chisel-shaped teeth. They lie in the front of the mouth. There are eight incisor teeth; four in the upper jaw and four in the lower jaw. The incisor teeth are well adapted for cutting and biting of food items.

Canines: These are round shaped, sharp and pointed teeth. Canines are well adapted to hold and tear the food. There are four canine teeth found inhuman.

Premolars: There are two premolars on each side of each jaw. Premolars help in crushing and grinding the food. There are total 8 premolar teeth in an adult human.

Molars: There are two molars on both sides in both the jaws. They have almost a flat surface with small projections. These teeth are meant for fine grinding of food.

There are total 12 molar teeth including the wisdom teeth in an adult human. The 4 molar teeth are also called wisdom teeth. Wisdom teeth usually grow between the ages of 18 to 21.

The tooth is covered with a white substance called enamel. It is the hardest substance in the human body.


Milk teeth and Permanent teeth

Humans get two sets of teeth in their lifetime. The first set erupts when we are babies, and are called milk teeth. Milk teeth last until we are about 8 years old. Milk teeth are replaced by the second set of teeth and are called permanent teeth.

An adult human has 32 teeth in all; 16 in each jaw.

Tongue- The tongue is a muscular organ. Tongue helps to mix saliva in the food. It also helps to push the food down the food-pipe or oesophagus. Taste receptors are present in tongue and give us the sense of taste.

Oesophagus- It is a tube-like structure connecting the mouth and the stomach. It is about 30 cm. long. Oesophagus has powerful muscles which gently push the food down to the stomach. The oseophagus contracts and relaxes in a rhythmic fashion to facilitate the forward movement of food. This movement happens in other parts of the alimentary canal as well and is called peristalsis. There is no digestion taking place in oesophagus.

Stomach- It is a muscular J- shaped thick walled bag. Stomach is the widest part of alimentary canal. It receives food at one end from food pipe and open into the small intestine from other end. Stomach chums the food to mix digestive juices. The food in the stomach is churned into semi solid. The churned semi-solid food is called chyme. Gastric juice is secreted from the wall of stomach and mixed with food. Gastric juice contains some enzymes and hydrochloric acid. The enzymes present in the gastric juices break down protein from food. The hydrochloric acid kills the harmful bacteria present if any in the food and helps the gastric enzymes to work.

Small intestine - The food leaves the stomach at certain intervals of time and enters into the small intestine.


Do you know?

At about 20 feet, if the small intestine was straight instead of bent, a person would need to be almost 26 feet long.

The small intestine is the longest part of the digestive system. It is about 20 feet or seven meters long in an adult human. Small intestine is a highly coiled tube. It consists of three parts: duodenum, jejunum and ileum. In the duodenum, the liver and pancreas pour their secretions. Liver secretes bile juice and pancreas secretes the pancreatic juice. The bile juice contains the bile which carries out emulsification of fat. In this process, the fat is broken into tiny droplets. The pancreatic juice contains several enzymes. The enzymes of the pancreatic juice break down starch into simple sugars and proteins into amino acids.

Minerals and vitamins do not need to be changed because cells are able to absorb them easily From duodenum the food goes to the lower part of the intestine. There are numerous finger-like projections on the wall of the small intestine. These projections are called villi. They have fine blood capillaries to absorb the food/after absorption; food mixes in me blood stream and is carried to all the cells of me body. The cells utilize this food to release energy.

Large intestine: The digested food enters into large intestine after small intestine. The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length. In large intestine excess of water from the materials is absorbed. The semi solid residue’s stored in the last part of the large intestine called rectum and finally thrown out of the body through-the anus time to time. The throwing out of waste of digested food from rectum is called egestion.


Do you know?

In an average person more than half of the faeces, or solid-wste in water. Much of the rest is undigested food material such as fiber.

The brown colour of faeces is due to a substance called bilirubin that comes from liver.

Some important points:

  • Egestion is also known as defecation.
  • A flap-like valve called the epiglottis closes the windpipe. It prevents the entry of food particles into tracheae.
  • Movement of food inside the oesophagus in the stomach is by peristalsis movement.
  • Stomach is u-shaped and it is the widest part of the alimentary canal.
  • Pancreas is the mixed gland. It acts as a both endocrine and exocrine gland.
  • The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the fats to fatty acids and glycerol.
  • The inner walls of the small intestine have millions of small finger like projections called the Villi. Due to their presence the surface area for digestion as well as absorption of digested food increases by eight times. Energy needed for various activities is obtained from glucose.

• This process of utilisation of absorbed food, such as glucose, amino acids, fatty acids and glycerol is called as Assimilation.


Digestion in Ruminants

Cellulose is an important component in the diet of herbivorous animals. Cellulose is an important component in the diet of herbivorous animals. It is present in the cell wall of plant cells. Humans cannot digest cellulose. Grass eating animals like the cow, ox, buffalo and sheep swallow the food without chewing. After feeding, they bring the food from the stomach back into the mouth and chew it leisurely. This process is called rumination, and such animals are called ruminants.

  • The stomach of a ruminant is divided into four chambers – the rumen, reticulum, omasum and abomasums. Among these, the rumen is the largest.
  • The partially digested food in the rumen is called cud.
  • Micro-organisms present in the stomach of the cow help digest the cellulose.
  • Digestion in ruminants is a good example of symbiosis.

None of the animal can digest cellulose which is a major component of the food eaten by herbivores. The plant eating animals digest their food in two steps. Their stomach is divided into four chamber the rumen, reticulum, omasum and abomasum.

First of all, half chewed food is swallowed and it then goes from mouth to the rumen, the first chamber of the stomach. Here, it is acted upon by bacteria. These microorganisms digest the cellulose. This half digested food goes to the second muscular chamber; the reticulum. From the reticulum the food is sent back to the mouth; as cud; to be chewed again. Chewing of the cud is called rumination and such animals are called ruminating animals or ruminants. Cow, goat, buffaloes, sheep, bison, etc. are good example of ruminating animals. The re-chewed food is swallowed for the second time. After passing the first two chambers it enters the third chamber; the omasum. Here the food is further broken down into smaller pieces and finally enters the fourth chamber, the abomasum. Here, all enzymes act upon the food and the digestion is completed. After digestion and absorption, nutrients from food are taken to the cells in all parts of the body the cells oxidize the food to release energy.


Do you know?

Ruminants eat 2 kinds of food. They eat grains and roughage. A typical food mix consist of corn, soyabean meal calcium, vitamin A, D, E and extra fat for energy.

Digestive system in Cow


Types of Teeth

There are four main kinds of teeth in mammals (incisors, canines, premolars and molars). Herbivores tend to have well-developed flat premolars and molars, often with sharp ridges on the tops. Generally herbivores do not have canine teeth, and their incisors are usually large and used to snip off foliage from branches.

Do you know?

When you enter a cattle farm, you may smell a strong acid smell. This sour smell is of vinegar or acetic acid which cows produce when they digest food.

Carnivores tend to have long canines which are used to rip and tear meat, sometimes in a scissors like action. In addition, carnivores have sharp molars toward the back of the mouth, used to further rip and shred meat. Omnivores usually have a variety of all kinds of teeth. Humans, bears and raccoons are omnivores, since they eat all kinds of food (both meat and plant material) they need all kinds of teeth



Holozoic nutrition- the process of taking in complex food matter by animals.

Saprozoic nutrition- a type of nutrition in which organism feeds on dead remains of living organisms

Herbivore- a plant eating animal

Carnivore- a meat eating animal

Omnivore- animal that can eat both plant and animal products.

Ingestion- the process of taking in of food into the body through mouth.

Egestion- the process of eliminating undigested food

Ruminant- an animal with a four chambered stomach that chews food two times by bringing the food back into its mouth.




Other Topics

Notes - Nutrition In Animals
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