CLASS-7                      Chapter-2            Nutrition In Animal

Nutrition: – The breaking down of food into various nutrients by chemical processes in                        the body of all organisms to give out energy is called nutrition.

The process of nutrition is complex in animals that takes place in five steps:

The process of …………. is called ……………..

Ingestion: –  The process of taking in of food through the mouth is called ingestion.

Method of ingestion 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 animals, amoeba, etc.

Absorption: – The process of absorbing soluble food particles by intestine wall is called the absorption.

Assimilation: – The process of deriving energy from the absorbed food is called assimilation.

In assimilation our cells are supplied with oxygen and nutrients.

Egestion: –  The process of 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.

Different Ways of Taking Food

Different organism takes food in different ways.

1. A humming bird sucks nectar of plants.
2. Human beings use their hands to put food into their mouth and swallow the food after chewing.
3. Infants of human and many other animals feed upon their mother’s milk by sucking them.
4. A snake swallows the animals they prey upon without chewing them.
5. A frog captures prey with its sticky tongue.
6. An earthworm uses its muscular pharynx to swallow its food.
7. Spiders weave sticky web in which small insects get stuck.
8. Some aquatic animals filter tiny particles floating nearby and feed upon them.

Digestive System In Unicellular Organism

Those organisms which have only one cell in their body are called unicellular organism.    Ex: – Amoeba, Paramecium etc.

Amoeba: –   It is a microscopic, unicellular organism found in pound water. There is a finger-like projection found around its body called pseudopodia or false feet. Pseudopodia helps the amoeba to movement and capturing food particles.

Paramecium: –     The stiff hair-like structures are found all over its body are called cilia.

Cilia push the food particles into the mouth-like structure of paramecium.

Hydra: – It is multicellular organisms.

Hydra ingests its food with the help of tentacles present around its mouth. Hydra uses tentacles to surround its prey and kill them with its stinging cells. Then the food is pushed inside the body cavity.

Digestive System In Human

 

 

 

 

 

 

 

Human digestive system consists of an alimentary canal and associated glands. The process of digestion involves mastication, swallowing, digestion of food and elimination of undigested matter.

Alimentary canal: – The long, muscular and coiled hollow tub is called alimentary canal.

It starts from mouth and ends at anus.

The organs of alimentary canal are-  

Mouth, Buccal cavity, Oesophagus (food pipe), stomach, small intestine, large intestine rectum and anus.

Associated glands of alimentary canal are- Salivary glands, Liver, Pancreas

Mouth: –     The organ bounded by lower and upper lips and helps in ingestion of food is called mouth.

It is another opening part of alimentary canal that open into buccal cavity.

Buccal cavity: – The process of digestion starts in the buccal cavity.

The mouth cavity (buccal cavity) contains tongue, teeth and salivary glands (3-pairs).

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 an enzyme called the salivary amylase, which converts starch into sugar(maltose).
The tongue helps in mixing the food with saliva and swallowing it down the digestive system.

Teeth: –  The part of mouth that helps in cutting, tearing and grinding the food before swallowing is called tooth. There are four types of teeth in our mouth. 

Incisors: The front teeth which help mainly in biting the food are called incisors.

These are flat and chisel-shaped teeth.

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 in human.

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

Molars: –     At the back of our mouth, behind the premolars, molars are located.

There are two molars on both sides in both the jaws.

They have almost a flat surface with small projections.

These teeth are used for fine grinding of food.

There are 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.

Enamel is the hardest substance in the human body.

Milk teeth and Permanent teeth

Humans get two sets of teeth in their lifetime.

1. Milk teeth            2. Permanent teeth

Milk Teeth: – The first set of teeth comes out in babies are called milk teeth.

Milk teeth fall off at the age between 6 to 8 years.

Permanent Teeth: – The second set of teeth come out after milk teeth are called permanent teeth.

A child has 20 teeth in all, 10 in each jaw.   

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

These teeth may last through out life or fall off during old age or due to some dental diseases.

Tongue: –  The tongue is a muscular organ of mouth that helps in swallowing the food. 

Tongue perform the following functions-

It helps to push the food down in the food-pipe or oesophagus.

Tongue mixes the food with saliva and helps us to swallow it.

Taste buds are present on tongue that detects the four basics taste like sweet, sour, salty and bitter.

Tongue also helps us to speak.

Pharynx and Oesophagus (Gullet): – Oesophagus connects the mouth cavity with the stomach. It is also called food pipe whose length is 30 cm.

The upper part of tube is called pharynx and lower part is called oesophagus.

Oesophagus has powerful muscles which helps only in pushing the food in to stomach.

The oesophagus 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.

Digestion does not take place in oesophagus.

Vomiting takes place when the food is not accepted by the stomach.

Stomach: – Stomach is a flattened U/J- shaped and thick-wall bag like organ.

Stomach is the widest part of alimentary canal. It receives food at one end from food pipe and opens into the small intestine on the other end.

Functions of stomach-

The gland present in the wall of stomach secretes a digestive juice is called Gastric juice.

Gastric juice contains protein digesting enzyme (pepsin) which break down the proteins into simpler substances.

Gastric juice also contains hydrochloric acid which kills the harmful bacteria that enter along with the food and makes the medium in the stomach acidic so that enzymes may act on food.

The food in the stomach is churned into semi solid which is called chime.

NOTE: –   Food remains in stomach usually for 3-4 hours during which it gets partially digested.

Small intestine: –  Small intestine is a longest coiled tube in which last step of digestion takes place.

Intestine consists of three parts: duodenum, jejunum and Ileum.  The food leaves in the stomach at certain intervals of time and after that enters into the small intestine.

Consists of three parts: Duodenum, jejunum and Ileum. 

It Small intestine receives secretions from the liver and the pancreas. Besides, its wall also secreted digestive juice.

It is located below the stomach.

Small intestine is longer in length about 20 feet (7.5m) than the large intestine 4 feet (1.5m).

(a) Duodenum:-   Anterior short (25cm) and ‘C’ shaped part within which both bile duct

and pancreatic duct opens through ampulla of vater.

Note: – It is most active site for digestion.

 (b) Jejunum. Middle longer (2.5m), Thick wall and highly vascular part.

 (c) Ileum: – Posterior, Longest (3.5m).Thin wall and less vascular part.

Note: – Jejunum + Ileum are the site for complete digestion and absorption of digested food.

Absorption: -Digested food absorbs by villi pass into the blood vessels in the wall of intestine. This process is called absorption.

Villi–  Finger like projection on the inner wall of the small intestine are called villi.

Note:-Villi increase the surface area for absorption of digested food.

Assimilation: -The absorbed substances are transported via blood vessels to different organ of the body where they are used to build proteins required by body.                     In the cell, glucose breaks down with the help of oxygen into carbon dioxide, water and energy is released

Associated glands of Small intestine: –      

Liver and the Pancreas

Part of the digestive system	Enzymes/Digestive juice	Food acted Upon (substrate)	Product formed
Mouth	Saliva (Amylase)	Starch	Sugar (maltose)
Stomach	Digestive juice (pepsin)	Proteins	Peptides
Liver	Bile	Fats	Fatty acid and glycerol
Pancreas	Pancreatic juice	Protein and Starch	Amino acid, Maltose
Small intestine	Intestinal juice (several enzymes)	Partially digested Proteins, Carbohydrates and fats	Glucose and simple sugars (from carbohydrates) Amino acids (from proteins) Fatty acid and glycerol (from fats)

Large intestine: – (1.5m) It is last part of alimentary canal which is wider and shorter than small intestine.

It arranged around small intestine as ‘?’

It divided into three parts:-Caecum, Colon and Rectum

Caecum: – Highly reduce in man (as we cannot digest cellulose) and is small pouch like structure and give a blind tubular structure called VERMIFORM APPENDIX.

(b) Colon: – Highly develop in man and having four parts.

HAUSTRA;-Lateral pocket like structure of colon wall.

Note: – Colon is the site for absorption of water from undigested food.

(c) Rectum: – Sac like part of large intestine.

Within rectum faecal matter is temporarily store.

Rectum leads into small passage called Anul canal which opens outside through anus.

Digestion in Herbivores (Grass Eating Animals)

Ruminants: –      Those animals that send back the food from the reticulum to the mouth and chewed again is called rumination and such animals are called ruminants or ruminating animals.     OR

Chewing of the cud is called rumination and such animals are called ruminating animals or ruminants.

Ex: –  Cow, goat, buffaloes, sheep, bison, etc.

Ruminants are only herbivores animals. They digest their food in two steps. Their stomach is divided into four chambers like – 

Rumen,       Reticulum,           Omasum     and    abomasum.

1. Rumen: –  The first chamber of the stomach is called rumen. Firstly half chewed food is swallowed and it then goes from mouth to the rumen, Here, it is acted upon by

    bacteria. These microorganisms digest the cellulose.

2. Reticulum: –       The second muscular chamber of stomach is called reticulum.

      This half digested food goes to the reticulum. From the reticulum the food is sent back to the mouth; as cud; to be chewed again.

3. Omasum: – The third muscular chamber of stomach is called omasum. The re-chewed food is swallowed for the second time.

      After passing the first two chambers it enters the omasum. Here the food is further broken down into smaller pieces

4. Abomasum: –     The fourth muscular chamber of stomach is called abomasum.

        The smaller pieces finally enter the abomasum. Here, all enzymes act upon the food and the digestion is completed.

NOTE: –    Abomasum is the part of stomach that secrets gastric juice.      

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.