PPT FOR CBSE CLASS 7 SCIENCE UNIT 2 SCIENCE.pdf
- 2. CONTENTS •2.1- Different ways of taking food •2.2- Digestion in humans •2.3- Digestion in grass eating animals •2.4- Feeding & Digestion in Amoeba
- 3. KEYWORDS Absorption Fatty acid Amino acid Amoeba Assimilation Bile Buccal cavity Canine Cellulose Digestion Egestion Food vacuole Gall bladder Glycerol Incisor Ingestion Liver Milk teeth Permanent teeth Molar Oesophagus Pancreas Premolar Rumen Ruminant Rumination Salivary glands Villi Saliva Pseudopodia
- 4. ANIMAL NUTRITION • Plants can prepare their own food by the process of photosynthesis but animals cannot. • 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 utilization in the body.
- 5. Digestion
- 6. 2.1 DIFFERENT WAYS OF TAKING FOOD • The mode of taking food into the body varies in different organisms. • Bees and humming-birds suck the nectar of plants. • Infants of human and many other animals feed on mother's milk. • Snakes like the python swallow the animals they prey upon. • Some aquatic animals filter tiny food particles floating nearby and feed upon them.
- 7. STARFISH • Starfish feeds on animals covered by hard shells of calcium carbonate. • After opening the shell, the star fish 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.
- 8. 2.2 DIGESTION IN HUMANS • We take in food through the mouth, digest and utilize it. • The unused parts of the food are defecated. • The food passes through a continuous canal called Alimentary canal, which begins at the buccal cavity and ends at the anus.
- 9. Human digestive system consist of Alimentary canals & Associated glands. The Alimentary canal (Digest tract) can be divided into various compartments: (1) Buccal cavity (2) Foodpipe or oesophagus (3) Stomach (4) Small intestine (5) Large intestine ending in the rectum (6) Anus The Associated glands are: (1) Salivary glands Saliva (2) Liver Bile (3) Pancreas Pancreatic Juice HUMAN DIGESTIVE SYSTEM
- 10. • The food components gradually get digested as food travels through the various compartments. • 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.
- 11. 1. The mouth and buccal cavity • Food is taken into the body through the mouth. • Mouth contains teeth, tongue & salivary glands. • The process of taking food into the body is called ingestion. • We chew the food with the teeth and break it down mechanically into small pieces. • Our mouth has the salivary glands which secrete saliva. i.Salivary glands
- 12. • Each tooth is rooted in a separate socket in the gums. • Our teeth vary in appearance and perform different functions. • Accordingly they are given different names, There are four types of teeth. • They are incisors, canines, premolars and molars. • Incisors - help in biting and cutting the food. • Canines - help in piercing and tearing the food. • Premolars and molars - help in chewing and grinding the food. • The first set of teeth grows during infancy and they fall off at the age between six to eight years. These are termed milk teeth. • The second set that replaces them are the permanent teeth. • The permanent teeth may last throughout life or fall off during old age or due to some dental disease. ii.Teeth
- 14. • Normally bacteria are present in our mouth but they are not harmful to us, if we do not clean our teeth and mouth after eating, many harmful bacteria also begin to live and grow in it. • These bacteria break down the sugars present from the leftover food and release acids. The acids gradually damage the teeth. This is called tooth decay. • If it is not treated in time, it causes severe toothache and in extreme cases results in tooth loss. • Chocolates, sweets, soft drinks and other sugar products are the major culprits of tooth decay. • Therefore, one should clean the teeth with a brush or datun and dental floss (a special strong thread which is moved between two teeth to take out trapped food particles) at least twice a day and rinse the mouth after every meal. • Also one should not put dirty fingers or any unwashed object in the mouth.
- 15. • Sometimes when you eat in a hurry, talk or laugh while eating, you 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.
- 16. iii.Tongue • 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.
- 17. 2. The foodpipe/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 and is called Peristalsis (Wave like movement caused by alternate contraction and relaxation of muscles of alimentary canal). • 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.
- 18. 3. The Stomach • The stomach is a thick-walled bag. Its shape is like a flattened J 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 substances. • The digestive juices breakdown the proteins into simpler substances.
- 19. 4. The Small Intestine • The small intestine is highly coiled and is about 7.5m 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 colored 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.
- 20. Absorption in the 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. • 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.
- 21. 5. Large intestine • The large intestine is wider and shorter than small intestine. It is about 1.5m 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.
- 22. Diarrhoea • 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. It is very common in India, particularly among children. • 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).
- 24. 2.3 DIGESTION IN GRASS-EATING ANIMALS • Cows, buffaloes and other grass-eating animals chewing continuously even when they are not eating. Actually, they quickly swallow the grass and store it in a part of the stomach called rumen. • Here 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. In ruminants like cattle, deer, etc., bacteria present in rumen helps in digestion of cellulose. • Many digest cellulose, including humans cannot digest cellulose. • Animals like horses, rabbit, etc., have a large sac-like structure called Caecum 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.
- 25. 2.4 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.
- 26. • 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.
- 27. What you have learnt • Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body. • The human digestive system consists of the alimentary canal and secretory glands. It consists of the buccal cavity, oesophagus, stomach, small intestine, large intestine ending in rectum and anus. • The main digestive glands which secrete digestive juices are (i) the salivary glands, (ii) the liver and (ii) the pancreas. The stomach wall and the wall of the small intestine also secrete digestive juices. • The modes of feeding vary in different organisms. • Nutrition is a complex process involving: (1) ingestion, (i) digestion, (ii) absorption, (iv) assimilation and (v) egestion.