IMPORTANT TERMS

Carnivores -                      Animals which eat only flesh of other animals as their food.

Herbivores -                      Animals which eat only plants as their food.

Omnivores -                      Those animals which can eat both plants as well as animals.

Parasite -                          A plant or organism that lives on or inside other organism and derives its food from that organism. E.g. Ticks

Diarrhea -                         A condition of frequent passing of watery stool is called diarrhoea.

Churning -                         Mixing the food with various digestive juices inside the stomach.

Chyme -                           Semi digested food inside the stomach.

Autotrophic Nutrition -        Mode of nutrition in which organisms make their own food by simple substances is called autotrophic nutrition. E.g. Green plants

Saprophytic Nutrition -       Mode of nutrition in which organisms take in food from dead and decaying matter is called saprophytic nutrition. E.g. Fungi

Heterotrophic Nutrition-      Mode of nutrition in which organisms take their food from other plants or animals is called heterotrophic nutrition. E.g. Tiger

Holozoic Nutrition-             It is a type of heterotrophic nutrition where the digestion of food takes place inside the body with the help of enzymes. E.g. Man

NUTRITION IN ANIMALS

     Nutrition in animals takes place in five steps:-

‘1. Ingestion -     Process of taking in food into the body is called ingestion.

‘2. Digestion -     Process of breaking large insoluble particles of food to smaller soluble particles is called Digestion.

‘3. Absorption -   Process of passing digested food through the intestinal walls into the blood stream is called Absorption.

‘4. Assimilation - Process in which absorbed food is taken by body cells and used for energy, growth and repair is called Assimilation.

‘5. Egestion -      Process in which undigested food is removed from the body is called Egestion.

 

Methods of Ingestion

 

Animals take in food by different methods; every animal has some special structure or organ for taking food inside the body. Some of the examples are as follows -

 

• A frog uses its long and cleft tongue to catch its prey. Similarly a wall lizard and a chameleon have a fairly long tongue to catch their prey.
• The butterfly uses its long feeding tube to suck nectar from flowers. Other insects which use sucking mechanism are bees, humming bird, male and female mosquito, houseflies, lice.
• Eagle and crow use their long beak to put their food into their mouth.
• A spider weaves a web to catch its prey.
• An amoeba uses its pseudopodia to ingest its food.
• A hydra uses its tentacles with sting cells to kill its prey and put it into its mouth.
• A starfish pops out its own stomach through its own mouth to eat its food.
• Snakes swallow the whole animal on which they prey upon.

 

HUMAN DIGESTIVE SYSTEM

 

Alimentary Canal – It is a long tube running from mouth to anus of a human being in which digestion and absorption of food takes place. Its length is about 9 meters.

 

Human digestive system consists of following organs:-

1.Mouth or Buccal Cavity

Buccal cavity is the inner region of the mouth. It encloses teeth and tongue. The buccal cavity leads into pharynx.

a) TEETH are of different types namely, incisors, canines, premolars and molars.
• Incisors are used for cutting and biting food located at the centre of the Jaw. There are 4 incisors in each jaw. They are also called as biting teeth.

• Canines are sharp and pointed and are used to pierce or tear food located next to Incisors. There are 2 canines in each jaw.

• Premolars have broad grinding surfaces. Hence they help in chewing and grinding the food. There are 4 premolars in each jaw located between Canines and Molars.

• Molars are the principal grinders which help to chew and grind the food. There are 6 molars in each jaw located at the far end of the jaw after the premolars.

Teeth help in the process of mastication.

 

• Mastication involves proper chewing of food and mixing it with saliva.
   
• Food is broken into small pieces by chewing, which helps in increasing the surface area of food.
• Digestion of food starts in the mouth with the help of salivary amylase present in the saliva. 
   
• Salivary amylase (Ptylin) is the enzyme which digests starch, a form of carbohydrate present in the food.

Tooth decay- is a process in which tooth become rotten due to the formation of cavities insides it leading to toothache.

 

Tooth decay is caused by excessive eating of food containing sugars like sweets, ice-creams, chocolates, toffees and Cold drinks. The bacteria in the mouth feed on the sugar and causes cavities.

b) TONGUE

 

Tongue is a muscular organ attached to the floor of the buccal cavity at the back. 
 

• It is free at one end and helps in pushing the food inside while chewing. 
• It helps in mixing of food with saliva and swallowing it. 
• It has many taste buds on it which can taste different types of food.
• It is essential for talking.    

c) PHARYNX is at the back of buccal cavity. 

 

• Pharynx is the common channel for food and air.
• When we swallow food, a flap-like valve made up of cartilage called the epiglottis closes the wind pipe.
• Epiglottis prevents the entry of food particles into respiratory tract.

2. Oesophagus

 

• It is also called as food pipe or the Gullet and helps in conveying the food from buccal cavity to stomach. It is about 25 centimeters long.
• Food inside the oesophagus reaches the stomach by peristalsis movements. 
• Peristaltic movements are the alternate contractions and relaxations of wall of oesophagus which bring about movement of food from buccal cavity to the stomach. 
• Food conveyed to the stomach is called as bolus as it is round in shape.

3. Stomach

 

• It is the widest part of the alimentary canal. It is a J-shaped muscular organ.
• Stomach secretes fluids called as digestive juices. Digestive juice is made up of hydrochloric acid, mucous and some enzymes.
• Hydrochloric acid kills the bacteria present in the food and softens the molecules of food.
• Mucous protects inner lining of the stomach from the action of hydrochloric acid.
• Digestive enzymes partially digest some nutrients like proteins and fats. Pepsin is an enzyme which converts proteins into amino acids. Stomach churns the food into a milky paste.
• Chyme is send to small intestine for further digestion.

4. Small intestine

 

• It is made up of three regions namely Duodenum, Jejunum and Ileum. The length of small intestine is about 6-7 meter.
• Acidic chyme from the stomach is received by the duodenum for further digestion.
• Duodenum also receives bile from the liver.

Liver is the largest gland in our body. The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder. Bile provides an alkaline environment for many enzymes to get active. It also reduces the acidity of chyme. Bile plays an important role in the digestion of fats.

Duodenum also receives pancreatic secretions, which help in the digestion of food.  

The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose by amylase, proteins into amino acids by trypsin and chymotrypsin, and the lipids into fatty acids and glycerol by lipase. Also pancreas secrete enzyme insulin which helps in the regulation of sugar in the body.

 

• All these substances bring about digestion of food in the intestine. 
• The inner walls of small intestine are thrown into many folds which have millions of small finger like projections called villi.
• Villi increase the surface area for digestion as well as absorption of digested food by eight times. Small intestine this also helps in the process of absorption.
• Undigested food is sent into large intestine.

 

5. Large intestine

• It comprises of colon and rectum. The length of large intestine is about 1.5 meter. Large intestine receives undigested food from small intestine.
• Water from the undigested food is absorbed to a great extent in the large intestine.
• Semi-solid undigested waste is stored in the rectum for defecation.

6.  Anus

• It is the opening of the alimentary canal to the exterior. This helps in the elimination of faeces by the process of egestion.

 

DIGESTION IN GRASS-EATING ANIMALS

Ruminants: These are also called as grass-eating animals. These are hoofed animals whose body stands on four limbs. Ruminants include, cows, buffaloes, sheep, giraffe, camel, deer etc.

 

Rumination: Ruminants 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 as ruminants. Rumination is also called second chewing. The partially digested food in the Stomach of ruminants is called cud.

Ruminant stomach: The stomach of a ruminant is divided into four chambers –

• Rumen-        It helps in storing the large quantities of food that was quickly consumed. Rumen is the largest part of the stomach. 
• Reticulum-    It helps in moving the swallowed food back into the mouth for thorough chewing.
• Omasum-     It absorbs excess water.
• Abomasum-  Walls of Abomasum secrete digestive juices for food digestion.

 

 

Test for the presence of starch in food – Iodine solution, when mixed gives blue black colour with food stuffs containing starch like potato, bread, corn, boiled rice etc.

INTRESTING FACTS

• The only reason the acid in your stomach doesn't eat right through your body is because the stomach cells are renewed faster than they are destroyed.
• Your stomach acid is strong enough to dissolve razor blades.
• Your teeth start growing 6 months before you are born.