NCERT Class 7 Science Chapter 2 - Nutrition in Animals Notes

Chapter 2 - Nutrition in Animals Notes

1. All organisms including humans require food for growth, repair and functioning of the body.

2. Animal nutrition includes:
• nutrient requirement,
• mode of intake of food and,
• its utilisation in the body.

3. Different organisms have different ways of taking food. Example: Snakes swallow their prey, bees and hummingbirds suck nectar from the flowers, etc.

4. The human digestive system consists of the alimentary canal and secretory glands. The canal can be divided into various compartments
• The buccal cavity
• Food pipe or oesophagus
• Stomach
• Small intestine
• Large intestine ending in the rectum
• The anus

5. These parts together from the digestive tract.

6. The digestive tract and the associated glands (like salivary gland, liver, pancreas) together constitute the digestive system.

7. Nutrition is a complex process involving
• Ingestion
• Digestion
• Absorption
• Assimilation
• Egestion

8. Digestion is the breakdown of complex components of food into simpler substances.

9. Digestion of food begins in the buccal cavity. Carbohydrate, like starch is digested in buccal cavity. Digestion of protein starts in the stomach.

10. The bile secreted from the liver, pancreatic juice from the pancreas and digestive juice from intestinal wall of small intestine complete the digestion of all components of food in the small intestine.

11. The digested food now passes into the blood vessels in the wall of the intestine. This process is called absorption.

12. 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.

13. The removal of faecal matter through the anus time to time is called egestion.

14. Grass-eating animals quickly swallow grass which gets stored in the rumen. This partially digested food is called cud. This later returns to the mouth of animals in small lumps, and they chew it. This is called rumination and these animals are known as ruminants.

15. Amoeba ingests its food with the help of finger-like projections, called pseudopodia. The food is digested in the food vacuole.

16. Starfish feeds on animals covered by hard shells of calcium carbonate. After opening the shell, the starfish pops out its stomach through its mouth to eat the soft animal inside the shell. The stomach then goes back into the body and the food is slowly digested.

17. When we eat in a hurry, talk or laugh while eating, we may cough, get hiccups or a choking sensation. This happens when food particles enter the windpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacent to the food pipe. But inside the throat, air and food share a common passage. During the act of swallowing a flap-like valve closes the passage of the windpipe and guides the food into the food pipe. If, by chance, food particles enter the windpipe, we feel choked, get hiccups or cough.

18. In 1822, a man named Alexis St. Martin was badly hit by a shot gun. The bullet had seriously damaged the chest wall and made a hole in his stomach. He was brought to an American army doctor William Beaumont. The doctor saved the patient but he could not close the hole properly and left it bandaged. Beaumont took it as a great opportunity to see the inside of the stomach through the hole. Beaumont found that the stomach was churning food. Its wall secreted a fluid which could digest the food. He also observed that the end of the stomach opens into the intestine only after the digestion of the food inside the stomach is completed.

19. Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhoea. It may be caused by an infection, food poisoning or indigestion. This is because of the excessive loss of water and salts from the body. Even before a doctor is consulted the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS).

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