Nutrition in Animals You have learnt in Chapter 1 that 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. Recall that 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. You have studied in Class VI that food consists of many components. Try to recall and list them below: 1. ______________________ 2. ______________________ 3. ______________________ 4. ______________________ 5. ______________________ 6. ______________________ 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 Complex substance Simpler substances food into simpler substances is called digestion. 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 motherís milk. Snakes like the python swallow the animals they prey upon. Some aquatic animals filter tiny food particles floating nearby and feed upon them. Activity 2.1 What is the type of food and mode of feeding of the following animals? Write down your observations in the given Table. You may find the list of modes of feeding given below the Table helpful. Table 2.1 Various modes of feeding Name of animal Kind of food Mode of feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) 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. Now, let us know what happens to the food in different parts of the digestive tract. The mouth and buccal cavity Food is taken into the body through the mouth. The process of taking food into SCIENCE the body is called ingestion. We chew the food with the teeth and break it down mechanically into small pieces. Each tooth is rooted in a separate socket in the gums (Fig. 2.3). Our teeth vary in appearance and perform different functions. Accordingly they are given different names (Fig. 2.3). Activity 2.2 Wash your hands. Look into the mirror and count your teeth. Use your index finger to feel the teeth. How many kinds of teeth could you find? Take a piece of an apple or bread and eat it. Which teeth do you use for biting and cutting, and NUTRITION IN ANIMALS type of teeth which ones for piercing and tearing? Also find out the ones that are used for chewing and grinding? Record your observations in Table 2.2 Table 2.2 of boiled rice; in test tube ëBí keep one teaspoonful of boiled rice after chewing it for 3 to 5 minutes. Add 3ñ4 mL of water in both the test tubes (Fig. 2.4). Now pour 2ñ3 drops of iodine solution in each test tube and observe. Why is there a change in colour in the test tubes? Discuss the results with your classmates and your teacher. The saliva breaks down the starch 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. Do you know the functions of the tongue? 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. We can find out the SCIENCE 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 foodpipe. But inside the throat, air and food share a common passage. Then how is food prevented from entering the windpipe? During the act of swallowing a flap-like valve closes the passage of the windpipe and guides the food into the foodpipe. If, by chance, food particles enter the windpipe, we feel choked, get hiccups or cough. 5. Now write down your observations and label Fig. 2.6. Repeat this activity with other classmates. The foodpipe/oesophagusFig. 2.6 Regions of the tongue for different tastes The swallowed food passes into the foodpipe or oesophagus. Look at Fig. 2.2. The foodpipe runs along the neck position of taste buds by the following activity. Activity 2.4 1. Prepare a separate sample each of (i) sugar solution, (ii) common salt solution, (iii) lemon juice and (iv) juice of crushed neem leaf or bitter gourd. Food 2. Blindfold one of your classmates and ask her/him to take out the tongue and keep it in straight and flat position. 3. Use a clean toothpick to put the above samples one by one on different areas of the tongue as shown in Fig. 2.6. Use a new Stomach toothpick for each sample. 4. Ask the classmate which areas of the Fig. 2.7 Movement of thetongue could detect the sweet, salty, food in the oesophagussour and bitter substances. of the alimentary canal NUTRITION IN ANIMALS food and makes the medium in the stomach acidic and helps the digestive juices to act. The digestive juices break down the proteins into simpler substances. The 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 (Fig. 2.2). The bile plays an important role in the digestion of fats. The pancreas is a large cream coloured gland located just below the stomach (Fig. 2.2). 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 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). Can you guess what the role of villi could be in the intestine? 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 Ruminants have a large sac-like structure called rumen between the oesophagus and the small intestine (Fig. 2.9). The cellulose of the food is digested here by the action of certain bacteria which are not present in humans. So far you have learnt about animals which possess the digestive system. But there are many small organisms which do not have a mouth and a digestive system. Then, how do they acquire and digest food? In the section below you will learn another interesting way of food intake. 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 (Fig. 2.10) 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 SCIENCE pushes out pseudopodia around the food particle and engulfs it. The food becomes trapped in a food vacuole [Fig. 2.10). 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 Keywords growth, maintenance and multiplication. The undigested residue of the food is expelled outside by the vacuole. The basic process of digestion of food and release of energy is the same in all animals. In a later chapter you will learn about the transport of food absorbed by the intestine to the various parts of the body. Absorption Amino acid Amoeba Assimilation Bile Buccal cavity Canine Cellulose Digestion Egestion What you have learntFatty acid Food vacuole Gall bladder Glycerol Incisor Ingestion Liver Milk teeth Molar Permanent teeth Oesophagus Pancreas Premolar Pseudopodia Rumen Ruminant Rumination Salivary glands Villi Saliva NUTRITION IN ANIMALS Digestion of carbohydrates, like starch, begins in the buccal cavity. The digestion of protein starts in the stomach. The bile secreted from the liver, the pancreatic juice from the pancreas and the digestive juice from the intestinal wall complete the digestion of all components of food in the small intestine. The digested food is absorbed in the blood vessels from the small intestine. The absorbed substances are transported to different parts of the body. Water and some salts are absorbed from the undigested food in the large intestine. The undigested and unabsorbed residues are expelled out of the body as faeces through the anus. The grazing animals like cows, buffaloes and deer are known as ruminants. They quickly ingest, swallow their leafy food and store it in the rumen. Later, the food returns to the mouth and the animal chews it peacefully. Amoeba ingests its food with the help of its false feet or pseudopodia. The food is digested in the food vacuole. Exercises 1. Fill in the blanks: (a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________. (b) The largest gland in the human body is __________. (c) The stomach releases hydrochloric acid and ___________ juices which act on food. (d) The inner wall of the small intestine has many finger-like outgrowths called _________. (e) Amoeba digests its food in the ____________ . 2. Mark ëTí if the statement is true and ëFí if it is false: (a) Digestion of starch starts in the stomach. (T/F) (b) The tongue helps in mixing food with saliva. (T/F) (c) The gall bladder temporarily stores bile. (T/F) (d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F) 3. Tick (v) mark the correct answer in each of the following: (a) Fat is completely digested in the (i) stomach (ii) mouth (iii) small intestine (iv) large intestine SCIENCE (b) Water from the undigested food is absorbed mainly in the (i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine 4. Match the items of Column I with those given in Column II: Column I Column II Food components Product(s) of digestion Carbohydrates Fatty acids and glycerol Proteins Sugar Fats Amino acids 5. What are villi? What is their location and function? 6. Where is the bile produced? Which component of the food does it help to digest? 7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also. 8. Why do we get instant energy from glucose? 9. Which part of the digestive canal is involved in: (i) absorption of food ________________. (ii) chewing of food ________________. (iii) killing of bacteria ________________. (iv) complete digestion of food ________________. (v) formation of faeces ________________. 10. Write one similarity and one difference between the nutrition in amoeba and human beings. 11. Match the items of Column I with suitable items in Column II Column I Column II (a) Salivary gland (i) Bile juice secretion (b) Stomach (ii) Storage of undigested food (c) Liver (iii) Saliva secretion (d) Rectum (iv) Acid release (e) Small intestine (v) Digestion is completed (f ) Large intestine (vi) Absorption of water (vii) Release of faeces NUTRITION IN ANIMALS 12. Label Fig. 2.11 of the digestive system. 13. Can we survive only on raw, leafy vegetables/grass? Discuss. Extended Learning — Activities and Project 1. Visit a doctor and find out: (i) Under what conditions does a patient need to be on a drip of glucose? (ii) Till when does a patient need to be given glucose? (iii) How does glucose help the patient recover? Write the answers in your notebook. 2. Find out what vitamins are and get the following information. (i) Why are vitamins necessary in the diet? (ii) Which fruits or vegetables should be eaten regularly to get vitamins? Write a one-page note on the information collected by you. You may take help of a doctor, a dietician, your teacher or any other person, or from any other source. SCIENCE 3. Collect data from your friends, neighbours and classmates to know more about ìmilk teethî. Tabulate your data. One way of doing it is given below: S. No. Age at which first tooth fell Age at which last tooth fell No. of teeth lost No. of teeth replaced 1. 2. 3. 4. 5. Find out from at least twenty children and find the average age at which children lose the milk teeth. You may take help of your friends. Did you know? Fats in goatís milk are much simpler than those in cowís milk. Therefore, the goatís milk is much easier to digest than the cowís milk. NUTRITION IN ANIMALS

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