Complete Notes on Food for CTET / TET - Part II || Nutrition in Animals (including Human) || NCERT Based
This article summarizes the important contents on Food topic based on NCERT. This highlights important points which may be useful for competitive exams such as TET / CTET.
This article covers topics like Nutrition in Animals, Digestion in Humans etc. Refer to below link to read about Sources of Foods, Components of Food, Test for Carbohydrates, Proteins and Fats, Nutrition in Plants, etc.
Nutrition in Animals:
Animals get their food from plants, either directly by eating plants or indirectly by eating animals that eat plants. Some animals eat both plants and animals. All organisms including humans require food for growth, repair and functioning of the body. Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
The components of food such as carbohydrates are complex substances. These complex substances cannot be utilised as such. So they are broken down into simpler substances. The breakdown of complex components of food into simpler substances is called digestion.
Digestion in Humans:
We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. The food passes through a continuous canal. which begins at the buccal cavity and ends at the anus .
The canal can be divided into various compartments: (1) the buccal cavity, (2) foodpipe or oesophagus, (3) stomach, (4) small intestine, (5) large intestine ending in the rectum and (6) the anus. These parts together form the alimentary canal (digestive tract).
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. The digestive juices convert complex substances of food into simpler ones. The digestive tract and the associated glands together constitute the digestive system. Let us know what happens to the food in different parts of the digestive tract.
1: Mouth and Buccal Cavity: Food is taken into the body through the mouth. The process of taking food into the body is called ingestion. Our mouth has the salivary glands which secrete saliva. The saliva breaks down the starch into sugars. Boiled rice contains starch but when you chew it, then chew rice will not have starch, as it is broken into sugars.
The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. It is free at the front and can be moved in all directions. We use our tongue for talking. Besides, it mixes saliva with the food during chewing and helps in swallowing food. We also taste food with our tongue. It has taste buds that detect different tastes of food.
2: Foodpipe or Oesophagus: The swallowed food passes into the foodpipe or oesophagus. The foodpipe runs along the neck and the chest. Food is pushed down by movement of the wall of the foodpipe. Actually this movement takes place throughout the alimentary canal and pushes the food downwards. At times the food is not accepted by our stomach and is vomited out.
3: Stomach: The stomach is a thick-walled bag. Its shape is like a flattened U 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.
The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices. The mucous protects the lining of the stomach. The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic and helps the digestive juices to act. The digestive juices breakdown the proteins into simpler substances.
4: Small Intestine: The small intestine is highly coiled and is about 7.5 metres long. It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices. The liver is a reddish brown gland situated in the upper part of the abdomen on the right side. It is the largest gland in the body. It secretes bile juice that is stored in a sac called the gall bladder. The bile plays an important role in the digestion of fats.
The pancreas is a large cream coloured gland located just below the stomach. The pancreatic juice acts on carbohydrates, fats and proteins and changes them into simpler forms.
The partly digested food now reaches the lower part of the small intestine where the intestinal juice completes the digestion of all components of the food. The carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and proteins into amino acids.
Absorption in Small Intestine:
The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption . The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi (singular villus). The 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 surface of the villi absorbs the digested food materials. The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by the 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 food that remains undigested and unabsorbed enters into the large intestine.
5. Large Intestine: The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length. Its function is to absorb water and some salts from the undigested food material. The remaining waste passes into the rectum and remains there as semi-solid faeces. The faecal matter is removed through the anus from time-to-time. This is called egestion.
In short, This whole Process can be written sequentially as :
INGESTION -> DIGESTION -> ABSORPTION -> ASSIMILATION -> EGESTION
Digestion in Grass eating Animals:
Actually, grass eating animals like cows quickly swallow the grass and store it in a part of the stomach called rumen. the food gets partially digested and is called cud. But later the cud returns to the mouth in small lumps and the animal chews it. This process is called rumination and these animals are called ruminants.
The grass is rich in cellulose, a type of carbohydrate. Many animals, including humans, cannot digest cellulose.
Ruminants have a large sac-like structure called rumen between the oesophagus and the small intestine. The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.
Feeding and Digestion in Amoeba:
Amoeba is a microscopic single-celled organism found in pond water. Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles in its cytoplasm. 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.
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. They act on the food and break it down into simpler substances. Gradually the digested food is absorbed. The absorbed substances are used for growth, maintenance and multiplication. The undigested residue of the food is expelled outside by the vacuole.
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