Science(Chap-2) Nutrition in Animals

Science(Chap-2)                               Nutrition in Animals

Ø  Plants can prepare their own food by the process of Photosynthesis but animals can not make their own food. For this, animals depend on plants to get food, either directly by eating plants or indirectly by eating animals.

Ø  Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body.

Ø  Food consists of many components like Carbohydrates, Proteins, Fats, Vitamins and Minerals. These components of food are complex substances which can not be utilized directly by the body and needs to be broken down into simpler substances.

Ø  The breakdown of complex components of food into simpler substances is called digestion.

Ø  The mode of taking food into the body varies in different animals.

·         Various ways of Feeding by different Animals

Name of Animal	Kind of Food	Mode of Feeding
Snail	Leaves & Insects	Scraping
Ant	Food particles	Chewing
Cow, Goat, Deer, Sheep	Plant parts: leaves, fruits, roots	Chewing
Eagle, Snakes, Lizards	Small animals	Swallowing
Humming bird, Butterfly	Nectar of flower	Sucking
Lice, Mosquito	Blood	Sucking
House fly	Nectar of food	Siphoning
Fish, Clam, Krill, Sponges	Particles suspended on water	Filtering

Ø  Starfish feeds on aquatic animals covered by its hard shells of calcium carbonate. After opening the shell, the starfish pops out its stomach through its mouth to eat soft animals such as mussels and clams inside the shell. The stomach than goes back into the body and the food is slowly digested.

·         Digestion in Humans

Ø  Humans take food through the mouth, digest and utilize it. The unused parts of the food are defecated by the anus.

Ø  When we take food, it passes through a continuous canal which begins at the buccal cavity and ends at the anus.

Ø  The compartments of the alimentary canal(digestive tract) is divided into-

(i)   Buccal cavity                               

(ii)  Food pipe or Oesophagus                                                             

(iii)  Stomach

(iv)  Small Intestine

(v)  Large Intestine &                          

 (vi)  Anus.                                          

Ø  The food components gradually get digested as food travels through various compartments.

Ø  The inner walls of the stomach and the Small Intestine and the various glands associated with the canal(such as Salivary glands, the Liver and the Pancreas) secrete digestive juices which convert complex substances of food into simpler ones.

Ø  The digestive tract and the associated glands together constitute the Digestive System.

·         The Mouth & the Buccal Cavity

Ø  Food is taken into the body through mouth. The process of taking food into the body is called Ingestion.

Ø  We chew the food with the teeth and break it down mechanically into small pieces. Each tooth is rooted in a separate socket in the gums.

Ø  Our teeth vary in appearance in order to perform different functions. Accordingly teeth are given different names. There are 4 Incisors, 2 Canines, 4 Premolars and 6 Molars found in each jaw of human mouth.

·         Types of Teeth:

Type of Teeth	Number of Teeth		Total
	Lower Jaw	Upper Jaw
Cutting & Biting teeth(Incisor)	4	4	8
Piercing & Tearing teeth(Canine)	2	2	4
Chewing & Grinding teeth(Molar & Premolar)	10	10	20

Ø  Humans have two sets of teeth: primary or milk teeth(between the ages 6-12) and permanent(adult) teeth, which develop in stages.

Ø  Our mouth has Salivary Glands which secretes Saliva that breaks down the starch into sugars.

Ø  The tongue is a fleshy muscular organ which mixes Saliva with the food during chewing & helps in swallowing food.

Ø  The tongue has many taste buds(papillae) that detects different tastes of food.

§  Bitter buds -  way in the back

§  Sour buds - between salty buds and bitter buds

§  Salty buds – either side of the front of the tongue

§  Sweet buds - on the tip of the tongue

·         The Food Pipe/ Oesophagus

Ø  The swallowed food from the mouth passes into the food pipe.

Ø  The food pipe runs through the neck and the chest. Food is pushed by movement of the wall of the food pipe. This movement takes place throughout the alimentary canal and pushes the food downwards.

Ø  When the food is not accepted by our stomach, it vomits out.

·         The Stomach

Ø  The Stomach is a thick walled bag like flattened ‘J’ shape and it is the widest part of the alimentary canal. It receives food from the food pipe at one end and opens into the small intestine at the other.

Ø  The inner lining of the stomach secretes mucous, hydrochloride acid and digestive juices.

Ø  The mucous protects the lining of the stomach.

Ø  The hydrochloride acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic and helps digestive juice to act.

Ø  The digestive juices break down the Proteins into simpler substances in the stomach.

·         The Small Intestine

Ø  The small intestine is highly coiled and is about 7.5 meters  long.  It receives secretions from the Liver and the Pancreas. Besides these, its wall also secretes juices.

Ø  Liver is the largest gland in the body which secretes Bile juice that is stored in a Sac called the Gall bladder. The Bile juice plays important role in the digestion of Fats.

Ø  The Pancreas is a large creamy coloured gland located just below the stomach. It secretes Pancreatic juice which acts on Carbohydrates, Proteins & Fats and changes them into simpler forms.

Ø  After partly digestion of  food by Pancreas, it reaches the lower part of the small intestine where the Intestinal juice completes the digestion of all components of food.

Ø  In the Small Intestine,

§  the Carbohydrates get broken into simple sugars such as Glucose,

§  the  Proteins get broken into Amino acids,

§  the Fats break down into Fatty acids and Glycerol .    

Ø  After break down of all the food particles in the Small Intestine, it passes into the blood vessels through the process of absorption.

Ø  The inner walls of the Small Intestine have thousands of finger-like outgrowths known as Villi.

Ø  The surface of the villi absorbs the digested food materials. When these absorbed simpler substances  transported through the  blood vessels to different organs of the body, it is called assimilation.

Ø  In the cells, Glucose breaks down with the help of Oxygen into Carbon dioxide and water, and energy is released.

Ø  The food that remains undigested and unabsorbed enters into the Large Intestine.

·         The Large Intestine

Ø  The Large Intestine is wider and shorter than the Small Intestine. Its length is about 1.5 metre.

Ø  The function of Large Intestine is to absorb water and some salts from the undigested food material. The remaining waste passes into the rectum and remains there as semi-liquid faeces.

Ø  The faecal matter is removed through the anus from time to time is called egestion.

·         Digestion in Grass-Eating Animals

Ø  Grass eating animals like cows, buffalos etc. while eating they swallow the grass and store in a part of the stomach called rumen. Here, the food gets partially digested and is called cud. Later on the cud returns to the mouth in small lumps and the animal chews it. This process is known as rumination. Hence, these animals are called ruminants.

Ø  The grass is rich in cellulose, a type of carbohydrate. In ruminants, bacteria present in rumen helps in digestion of cellulose.

Ø  Many animals, including humans, can not digest cellulose because of the lack of appropriate enzymes to break down the beta acetal linkages.

Ø  Animals like horses, rabbits etc. have a large sac-like structure called Caecum between the oesophagus and the small intestine. The cellulose of food is digested here by the action of certain bacteria which are not present in humans.

·         Digestion in Amoeba

Ø  Amoeba is a microscopic single-cell organism found in pond water.

Ø  Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble- like vacuoles in its cytoplasm.

Ø  Amoeba constantly changes its shape and position. It pushes out one, or more finger-like projections, called pseudopodia or false feet for movement and capture of food.

Ø  Amoeba ingests its food (some microscopic organisms)with the help of its false feet or pseudopodia. The food is digested in the food vacuole.

Ø  Digestive juices are secreted in to the food vacuole which breaks down the food into simpler substances. The absorbed substances are used for its growth, maintenance and multiplication. The undigested residue of the food is expelled outside by the vacuole.

Ø  The basic process of digestion of food and release of energy is the same in all animals.