Page 1 Nutrition in Animals 2 Y ou 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 Table 2.1 Various modes of feeding Name of Kind of Mode of animal food feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) food into simpler substances is called digestion. 2.1 DIFFERENT WAYS OF T AKING 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. 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. Complex substance Simpler substances 2020-21 Page 2 Nutrition in Animals 2 Y ou 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 Table 2.1 Various modes of feeding Name of Kind of Mode of animal food feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) food into simpler substances is called digestion. 2.1 DIFFERENT WAYS OF T AKING 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. 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. Complex substance Simpler substances 2020-21 SCIENCE 12 Fig. 2.1 Starfish Amazing fact 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. 2.2 DIGESTION IN HUMANS We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. Have you ever wondered what happens to the food inside the body? The food passes through a continuous canal (Fig. 2.2) 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. Is it not a very long path? These parts together form the alimentary canal (digestive tract). 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. 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 Fig. 2.2 Human digestive system Buccal cavity Salivary gland Stomach Pancreas Small intestine Large intestine Rectum Anus Gall bladder Liver Oesophagus 2020-21 Page 3 Nutrition in Animals 2 Y ou 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 Table 2.1 Various modes of feeding Name of Kind of Mode of animal food feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) food into simpler substances is called digestion. 2.1 DIFFERENT WAYS OF T AKING 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. 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. Complex substance Simpler substances 2020-21 SCIENCE 12 Fig. 2.1 Starfish Amazing fact 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. 2.2 DIGESTION IN HUMANS We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. Have you ever wondered what happens to the food inside the body? The food passes through a continuous canal (Fig. 2.2) 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. Is it not a very long path? These parts together form the alimentary canal (digestive tract). 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. 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 Fig. 2.2 Human digestive system Buccal cavity Salivary gland Stomach Pancreas Small intestine Large intestine Rectum Anus Gall bladder Liver Oesophagus 2020-21 NUTRITION IN ANIMALS 13 Fig. 2.3 Arrangement of teeth and different type of teeth Milk teeth and permanent teeth Do you remember about falling of your teeth some years ago? 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. 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 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 Boojho is fascinated by the highly coiled small intestine seen in Fig. 2.2. He wants to know its length. Would you like to make a wild guess? We have given its approximate length on page 16. Just imagine how such a long structure is accommodated in a small space within our body! Type of teeth Number of teeth Total Lower jaw Upper jaw Cutting and biting teeth Piercing and tearing teeth Chewing and grinding teeth Table 2.2 Molar Canine Premolar Incisor 2020-21 Page 4 Nutrition in Animals 2 Y ou 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 Table 2.1 Various modes of feeding Name of Kind of Mode of animal food feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) food into simpler substances is called digestion. 2.1 DIFFERENT WAYS OF T AKING 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. 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. Complex substance Simpler substances 2020-21 SCIENCE 12 Fig. 2.1 Starfish Amazing fact 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. 2.2 DIGESTION IN HUMANS We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. Have you ever wondered what happens to the food inside the body? The food passes through a continuous canal (Fig. 2.2) 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. Is it not a very long path? These parts together form the alimentary canal (digestive tract). 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. 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 Fig. 2.2 Human digestive system Buccal cavity Salivary gland Stomach Pancreas Small intestine Large intestine Rectum Anus Gall bladder Liver Oesophagus 2020-21 NUTRITION IN ANIMALS 13 Fig. 2.3 Arrangement of teeth and different type of teeth Milk teeth and permanent teeth Do you remember about falling of your teeth some years ago? 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. 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 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 Boojho is fascinated by the highly coiled small intestine seen in Fig. 2.2. He wants to know its length. Would you like to make a wild guess? We have given its approximate length on page 16. Just imagine how such a long structure is accommodated in a small space within our body! Type of teeth Number of teeth Total Lower jaw Upper jaw Cutting and biting teeth Piercing and tearing teeth Chewing and grinding teeth Table 2.2 Molar Canine Premolar Incisor 2020-21 SCIENCE 14 Fig. 2.4 Effect of saliva on starch Iodine solution Water Boiled rice Boiled and chewed rice Sweets and tooth decay Normally bacteria are present in our mouth but they are not harmful to us. However, 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 (see Chapter 5 to know what an acid is). The acids gradually damage the teeth (Fig. 2.5). 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. Fig. 2.5 Gradual decay of tooth (a) (b) (c) (d) Our mouth has the salivary glands which secrete saliva. Do you know the action of saliva on food? Let us find out. Activity 2.3 Take two test tubes. Label them ‘A’ and ‘B’. In test tube ‘A’ put one teaspoonful of boiled rice; in test tube ‘B’ keep one teaspoonful of boiled rice after chewing it for 3 to 5 minutes. Add 3–4 mL of water in both the test tubes (Fig. 2.4). Now pour 2–3 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 A B 2020-21 Page 5 Nutrition in Animals 2 Y ou 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 Table 2.1 Various modes of feeding Name of Kind of Mode of animal food feeding Snail Ant Eagle Humming-bird Lice Mosquito Butterfly House fly (Scraping, chewing, siphoning, capturing and swallowing, sponging, sucking etc.) food into simpler substances is called digestion. 2.1 DIFFERENT WAYS OF T AKING 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. 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. Complex substance Simpler substances 2020-21 SCIENCE 12 Fig. 2.1 Starfish Amazing fact 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. 2.2 DIGESTION IN HUMANS We take in food through the mouth, digest and utilise it. The unused parts of the food are defecated. Have you ever wondered what happens to the food inside the body? The food passes through a continuous canal (Fig. 2.2) 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. Is it not a very long path? These parts together form the alimentary canal (digestive tract). 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. 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 Fig. 2.2 Human digestive system Buccal cavity Salivary gland Stomach Pancreas Small intestine Large intestine Rectum Anus Gall bladder Liver Oesophagus 2020-21 NUTRITION IN ANIMALS 13 Fig. 2.3 Arrangement of teeth and different type of teeth Milk teeth and permanent teeth Do you remember about falling of your teeth some years ago? 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. 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 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 Boojho is fascinated by the highly coiled small intestine seen in Fig. 2.2. He wants to know its length. Would you like to make a wild guess? We have given its approximate length on page 16. Just imagine how such a long structure is accommodated in a small space within our body! Type of teeth Number of teeth Total Lower jaw Upper jaw Cutting and biting teeth Piercing and tearing teeth Chewing and grinding teeth Table 2.2 Molar Canine Premolar Incisor 2020-21 SCIENCE 14 Fig. 2.4 Effect of saliva on starch Iodine solution Water Boiled rice Boiled and chewed rice Sweets and tooth decay Normally bacteria are present in our mouth but they are not harmful to us. However, 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 (see Chapter 5 to know what an acid is). The acids gradually damage the teeth (Fig. 2.5). 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. Fig. 2.5 Gradual decay of tooth (a) (b) (c) (d) Our mouth has the salivary glands which secrete saliva. Do you know the action of saliva on food? Let us find out. Activity 2.3 Take two test tubes. Label them ‘A’ and ‘B’. In test tube ‘A’ put one teaspoonful of boiled rice; in test tube ‘B’ keep one teaspoonful of boiled rice after chewing it for 3 to 5 minutes. Add 3–4 mL of water in both the test tubes (Fig. 2.4). Now pour 2–3 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 A B 2020-21 NUTRITION IN ANIMALS 15 Paheli wants to know how food moves in the opposite direction during vomiting. Fig. 2.6 Regions of the tongue for different tastes Fig. 2.7 Movement of the food in the oesophagus of the alimentary canal 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. 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 toothpick for each sample. 4. Ask the classmate which areas of the tongue could detect the sweet, salty, sour and bitter substances. 5. Now write down your observations and label Fig. 2.6. Repeat this activity with other classmates. The foodpipe/oesophagus The swallowed food passes into the foodpipe or oesophagus. Look at Fig. 2.2. The foodpipe runs along the neck 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. Food Oesophagus Stomach 2020-21Read More
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