CBSE CLASS VII SCIENCE NOTE ON NUTRITION IN ANIMALS

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NUTRITION IN ANIMALS Carbohydrate, a complex component of food is broken down into simpler substances. The breakdown of complex components of food into simpler substances is called digestion.

DIFFERENT WAYS OF TAKING FOOD NAME OF ANIMAL KIND OF FOOD MODE OF FEEDING Snail(Vegetarian) Lower plants Scraping Ant Small particles of sugar and flour, etc Chewing Eagle Small animals like rat, birds Capturing, tearing and swallowing Humming bird Nectar of flower Sucking lice Blood Sucking Mosquito Blood Sucking Butterfly Nectar of flower Sucking Housefly Rubbish, many other solids and liquids Sucking Bee Nectar of flower Sucking Infants of human and other mammals Breast milk Sucking Python Prey animal Swallow prey animal Starfish feeds on animals covered by calcium carbonate shells. After opening the shell, starfish pops out its stomach through its mouth to eat the soft animal inside the shell. Stomach goes back into the body and food is slowly digested.

DIGESTION IN HUMANS

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Human ingest food through mouth which get digested in alimentary canal and utilize it. Unused food parts are defecated.

Alimentary canal/Digestive tract can be divided into various compartments 1) Buccal cavity 2) Food pipe or Oesophagus 3) Stomach 4) Small intestine 5) Large intestine ending in the rectum 6) Anus Digestive system constitutes digestive tract and its associated glands like salivary glands, liver and pancreas. Ingested food travels through the various compartments of digestive system and digested by digestive juice secreted by associated glands.

MOUTH AND BUCCAL CAVITY Ingestion is process of taking food into body.

Human ingest food through mouth and food is chewed with teeth and broken down mechanically into small pieces.

Tooth is rooted in a separate socket in gums. Teeth vary in appearance and perform different functions. Teeth are given various names like Incisor, canine, premolar and molar.

The first set of teeth grows during infancy and these fall off at the age between six to eight years. These teeth are termed milk teeth. The second set of teeth replacing milk teeth are the permanent teeth which last throughout life and fall off during old age.

TYPE OF TEETH

FUNCTION

NUMBER OF TEETH LOWER JAW

UPPER JAW

TOTAL

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INCISOR

Cutting and biting food.

4

4

8

CANINE

Piercing and tearing teeth.

2

2

4

PREMOLAR

Crushing and grinding food.

4

4

8

MOLAR

Crushing, grinding and mastication of food.

6

6

12

SWEETS AND TOOTH DECAY 

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Normally, harmless bacteria are present in our mouth. If we don’t wash our mouth properly after eating food, many harmful bacteria begin to live and grow in it. These bacteria break down sugar present from the leftover food and release acids. The acids gradually damage the tooth and are termed tooth decay. If it isn’t treated on time, it causes severe toothache and in extreme cases results in loss of tooth. Chocolates, sweets, cold drinks and other sugar products are the major culprits of tooth decay. Cleaning teeth with brush or dantun and dental floss (special strong thread which is moved between two teeth to take out trapped food particles) twice a day and rinsing mouth after every meal are good dental care habit. One shouldn’t put dirty fingers or any unwashed object in the mouth.

Human mouth has the salivary glands which secrete saliva. Saliva breaks down the starch into sugars.

Tongue is a fleshy muscular organ attaching its back to the floor of the buccal cavity. It is free at the front and can move in all directions. Tongue is used for talking, mixing saliva with food during chewing, and helps in swallowing food. It has taste buds that detect different tastes of food.

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THE FOODPIPE/OESOPHAGUS The swallowed food passes into the food pipe or oesophagus which runs along the neck and the chest. Food is pushed down by movement of the wall of the food pipe. Likewise the movement takes place throughout the alimentary canal and pushes the food downwards. Food is vomited out at the time it is not accepted by our stomach.

When food enters windpipe, hiccups or a choking sensation is experienced. The wind pipe running adjacent to food pipe carries air from the nostrils to the lungs. But, inside the throat air and food share a common passage. When food is swallowed, a flap like valve closes the passage of the wind pipe and guides the food into the food pipe.

THE STOMACH The stomach is thick walled bag, shaped like a flattened U and is the widest part of alimentary canal. It receives food from the food pipe at one end and opens into the small intestine at the other.

Inner lining of stomach secretes mucous, hydrochloric acid and digestive juices. The mucous protects the lining of the stomach.

The acid kills many bacteria entered along with food and makes the medium in the stomach acidic. Digestive juices break down the proteins into simpler substances.

Working of stomach was discovered by a strange accident by doctor William Beaumont in 1881. He found stomach is churning food with the help of fluid secreted by its wall. End of stomach is found opening in to intestine only after digestion of food is completed in stomach.

THE SMALL INTESTINE The small intestine is highly coiled measuring about 7.5 metres long. It receives secretions from the liver and the pancreas beside its own secretion.

The liver is reddish brown gland situated in the upper part of the abdomen on the right side. It is Largest gland in human body and secretes bile juice that is stored in a sac called gall bladder. The bile is essential for fats digestion.

Pancreas is a large cream coloured gland located just below the stomach. It secretes pancreatic juice which acts on carbohydrates and proteins and change them into simpler forms.

The partly digested food reaching lower part of small intestine gets digested by intestinal juice. Here, carbohydrates get broken into simple sugars like glucose, fats into fatty acids and glycerol and proteins into amino acids.

ABSORPTION IN THE SMALL INTESTINE Absorption is a process where digested food is passed into the blood vessels in the wall of the intestine. The inner walls of the intestine have thousands of finger like outgrowths which are known as villi(Plural).

Villi increase the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels close to its surface. The absorbed digested food materials by surface of villi are transported via blood vessels to different organs of the body where they used to build complex substances such as proteins required by body. This is called assimilation.

In the cells, glucose breaks down with the help of oxygen into carbon dioxide and water and energy is released. The remaining undigested and unabsorbed food materials enters large intestine.

LARGE INTESTINE The large intestine is wider and shorter than small intestine measuring about 1.5 metre in length. It functions to absorb water and some salts from the undigested food materials. The remaining waste passes into the rectum and remains there as semi solid faeces which are removed through anus from time to time.

Removal of faecal matter through anus on time to time is called egestion.

DIGESTION IN GRASS EATING ANIMALS Buffaloes and other grass eater swallow grass and store it in a separate par of stomach called rumen. In rumen, grass(food) get partially digested and is called cud. Later cud returns to mouth in small lumps and the animal chews it. This process is called rumination and these animals are known as ruminants. This is why buffaloes are found continuously chewing even after they finished eating grass.

Ruminants have large sac like structure between the small intestine and large intestine where cellulose of the food is digested by the action of certain bacteria.

DIARRHOEA Diarrhoea is a condition where a person passes watery stool frequently caused due to infection, food poisoning or indigestion.

Under severe condition it is fatal due to excessive loss of water and salts from body. Even before consulting doctor, person is given plenty of warm water with a pinch of salt and sugar dissolved in it. This is called oral rehydration solution(ORS).

FEEDING AND DIGESTION IN AMOEBA Amoeba is a microscopic single celled organism found in pond water. It has cell membrane, a round and dense nucleus, many small bubbles like vacuoles in its cytoplasm. It constantly changes in shape and position and it pushes out one or more finger like projections called pseudopodia or false feet for movement and capture of food.

Amoeba feeds on some microscopic organisms. When it senses food, it pushes out pseudopodia around the food particle and engulfs it. The food becomes trapped in a food vacuole. Digestive juices are secreted into the food vacuole and act on the food and break it down into simpler substances. Gradually the digested food is absorbed and is used for growth, maintenance and multiplication. The undigested residue of the food is expelled outside by the vacuole.