Grade 7 - Science

SCIENCE NAME SEC SCHOOL 7

Saarthi Pedagogy Private Limited is a result of enormous amount of research which is imprinted in the book to develop scientific literacy. The content is curated for developing Science related attitudes, skills and knowledge required by students for problem-solving and decision making abilities to; n become lifelong learners n maintain a sense of wonder about the world around them The book provides myriad learning experiences for students to use, speculate, theorize, summarize, discover connections, describe processes, express understandings, raise questions and make sense of science around them. Science book stresses the need to design and implement a curriculum that provides opportunities for all students to their abilities, needs and interests. The activities provided by this book would help children in their visual association, observation, classification, analytical reasoning, cognitive, social, emotional and environmental development. We hope and definitely know that children would enjoy this book. Happy learning! Have fun!! All rights reserved - Saarthi Pedagogy Pvt. Ltd., reserves the copyright of its ‘The Wizz Kit’ series. Saarthi Pedagogy Pvt. Ltd. has applied for copyright permission wherever possible. Designed by the editorial team of Saarthi Pedagogy Pvt. Ltd. Version: SP22

TABLE OF CONTENT 1 | NUTRITION IN PLANTS 4 2 | NUTRITION IN ANIMALS 16 3 | FIBRE TO FABRIC: ANIMAL FIBRE 32 4 | HEAT AND TEMPERATURE 46 5 | ACIDS, BASES, AND SALTS 65 6 | PHYSICAL AND CHEMICAL CHANGES 85 7 | WEATHER, CLIMATE, AND ADAPTATIONS IN ANIMALS 104 8 | WINDS, STORMS, AND CYCLONES 122 9 | ALL ABOUT SOIL 138 10 | RESPIRATION IN ORGANISMS 153 11 | TRANSPORTATION IN ANIMALS AND PLANTS 167 12 | REPRODUCTION IN PLANTS 182 13 | MOTION AND TIME 197 14 | ELECTRIC CURRENT AND ITS EFFECTS 211 15 | LIGHT 225 16 | WATER: A PRECIOUS RESOURCE 247 17 | FORESTS: OUR LIFELINE 259 18 | WASTEWATER STORY 272

4 61 NUTRITION IN PLANTS What do we all eat? How do plants obtain food? Get Set Go! All living organisms obtain the energy to perform various activities from the food they eat. Energy is stored in the food materials as chemical energy. Food has various components such as carbohydrates, fats, proteins, vitamins, minerals, roughage, and water, etc., These components are called nutrients. These components provide us energy for growth, reproduction, metabolism, and other day-to-day activities. Different organisms take food from different sources. Green plants prepare their own food by a process called photosynthesis. Humans and animals get their food from plants or other smaller animals. Hence, we can say that humans and animals are directly or indirectly dependent on plants for their food. NUTRIENTS CARBOHYDRATE PROTEIN FAT VITAMIN MINERAL WATER MODES OF NUTRITION Food stores energy in the form of chemical energy. To make the food energy available to living organisms, it is broken down into smaller and soluble molecules inside the body. These smaller molecules then react with oxygen inside the cell to release energy. The process of intake of food and its proper utilisation by the body to obtain energy is called nutrition. Based on the food habits, the modes of nutrition in all living organisms are divided into two categories: - Autotrophic Heterotrophic Modes of nutrition

5 AUTOTROPHIC NUTRITION The mode of nutrition in which the organism makes its food itself from simple inorganic substances is called autotrophic nutrition (auto means self and “trophos” means nourishment). ƒ The organisms which make their own food from the simple substances present in the environment are called autotrophs. ƒ Autotrophs are the producers of food, so they are also called producers. Green plants make their food from carbon dioxide and water in the presence of chlorophyll and sunlight. So, the mode of nutrition in green plants is autotrophic. HETEROTROPHIC NUTRITION The mode of nutrition in which the organisms cannot make their food and depend on others for their food is called heterotrophic nutrition (‘heteros’ means ‘others’ and ‘trophos’ means nourishment). ƒ The organisms showing heterotrophic mode of nutrition are called heterotrophs. ƒ As all the animals and humans eat food prepared by plants or eat the flesh of other animals, they are called heterotrophs. Depending on the food they eat, heterotrophs can be divided into the following three types: ƒ Herbivores ƒ Carnivores ƒ Omnivores HERBIVORES The animals which eat only grass, plants, or plant products are called herbivores. Examples: Elephant, Camel, Cow, Deer, Goat, Grasshopper, etc. CARNIVORES (MEAT EATERS) The animals which eat meat or flesh of other animals are called carnivores. Examples: Lion, Tiger, Hawk, Jackal, Frog, Snake, Vulture, Lizard, etc. OMNIVORES The animals which eat both plants and meat are called omnivores. Examples: Birds, Dog, Bear, Fox, etc. AUTOTROPHS AND HETEROTROPHS

6 PHOTOSYNTHESIS Green plants make their own food from carbon dioxide and water in the presence of chlorophyll and sunlight. The process by which green plants make their food is called photosynthesis, (photo means light, and synthesis means combining). ƒ During photosynthesis, the plants use the sun’s energy to prepare food in the presence of a green colour pigment called “chlorophyll” present in the leaves of the green plant. ƒ Plants take carbon dioxide from the air through tiny pores called stomata. The stomata are present on the surface of the leaves. ƒ Water and minerals are absorbed through their roots. ƒ Plants convert solar energy of food into chemical energy of food. ƒ The process of photosynthesis first produces a simple carbohydrate called ‘glucose’ as food. The synthesized food is distributed to different parts of the plant/tree. ƒ The glucose carbohydrate then gets converted into a complex carbohydrate called starch. Starch gets stored as food in the various parts of a plant including leaves. ƒ Some of the glucose is also converted into other types of plant foods such as fats and oils, proteins as well as vitamins. ƒ Oxygen gas is produced during photosynthesis which is very important for all living organisms for their survival. The photosynthesis can be represented by following equation. Carbon dioxide + Water Glucose + Oxygen (from the air) (from the soil) (food stored (Released into in the plant) the atmosphere) 6CO2 + 6H2O C6H12O6 + 6O2 (g) Sunlight Chlorophyll Sunlight Chlorophyll

7 Activity 1 Aim: To show that green plant produce oxygen during photosynthesis. Materials required: A beaker, glass funnel, boiling tube and a cutting of water plant. Procedure: Place Hydrilla plant ( Waterthyme) in a beaker containing pond water and cover it by a short-stemmed funnel. (Make sure the level of water in the beaker is above the level of the stem of the funnel). Invert a test tube full of water over the stem of the funnel. Place the set up in the sun light for a few hours. Observation: Bubbles appear in the stem which rise and are collected in the test tube. When sufficient gas gets collected, a glowing splinter will be introduced in the test tube, which will burst into flames. Conclusion: The splinter glows due the presence of oxygen in the test tube which proves that the gas collected in the test is released by hydrilla during photosynthesis. Activity 2 Aim: To identify the green plants produces food during the photosynthesis. Materials required: A leaf, foil stencil, iodine solution, Procedure: Take a leaf of any plant and place it in a dark place where there is no light for two to three days. This will destarch the leaves. It is necessary to remove starch present in the leaves otherwise presence of starch confirms that photosynthesis has taken place. Select a leaf of a plant and cover it with stencil made of foil. Now keep the plant in sunlight for five to six hours. pluck the leaf and test it for the presence of starch by pouring iodine solution over it. Observation: The whole leaf except the part that was covered with the foil stencils becomes blue black. The covered portion did not turn blue black because there was no starch formed in that portion. This shows that only in those part of the leaf that were exposed to the sun photosynthesis occurs. Conclusion: We conclude that sunlight is necessary for photosynthesis

8 FACTORS AFFECTING PHOTOSYNTHESIS Photosynthesis is affected by a number of environmental factors. These are: 1. Light intensity-Photosynthesis increases with increase in light intensity up to a certain point. 2. Availability of carbon dioxide- Photosynthesis increases with increase in carbon dioxide concentration 3. Temperature- Up to a certain temperature value, rate of photosynthesis increases with increase in temperature. This value ranges generally between 20degree to 35 degree Celsius. 4. Availability of water-Less availability of water reduce photosynthesis through closure of stomata. 5. Chlorophyll- Photosynthesis requires the pigment chlorophyll. Without chlorophyll photosynthesis does not take place. 6. Inorganic mineral ions- Each inorganic ions have different function in the process of photosynthesis. Some of the elements are required in higher quantities (macro nutrients) while others are required in lower quantities (micronutrients or trace elements) Macronutrients: Carbon, hydrogen, nitrogen, phosphorus, sulphur, potassium, calcium, iron and magensium Micronutrients: Copper, zinc, boron, maganese and molybdenum. IMPORTANCE OF PHOTOSYNTHESIS ƒ Photosynthesis is important for the existence of life on this earth because photosynthesis by plants provides food to animals (including human beings) and it is very important for the survival of animals (including human beings). In the absence of photosynthesis, there would be no plants on this earth and hence no animals will survive. ƒ The process of photosynthesis by plants puts oxygen gas into the air; It is this oxygen gas that animals (including human beings) use for breathing and respiration. In the absence of photosynthesis, there would be no oxygen in the air and hence no animals would exist on this earth. 1. PRACTICE QUESTIONS A. What do you understand by nutrition? B. All green plants have __________ mode of nutrition. C. What is the green pigment present in the green leaves? D. What are saprophytes? E. Can plants use an artificial source of light for preparing food? F. What energy transformations take place during photosynthesis? G. Name the site of photosynthesis in plants. H. From where does carbon dioxide enter a leaf? I. What do plants synthesize other than glucose? J. Write one example of herbivore, carnivore and omnivore.

9 SYNTHESIS OF PLANT FOOD OTHER THAN CARBOHYDRATES First plants synthesise glucose through photosynthesis. Carbohydrates are made of carbon, hydrogen and oxygen. These are used to synthesise other components of foods such as protein and fats. Plants synthesise other food nutrients such as fats and proteins (through amino acids). Proteins also contain nitrogen. This nitrogen is obtained by plants from soil. ƒ The atmospheric nitrogen cannot be utilised by plants as such. However, certain bacteria such as symbiotic bacteria present in the root nodules of leguminous plants can convert atmospheric nitrogen into soluble salts of nitrogen e.g., ammonium and nitrates. These salts being soluble, are absorbed by the plants through their root system. In this way, plants get nitrogen to prepare proteins needed for their growth and for the animals deriving their food from plants. 2. OTHER MODES OF NUTRITION IN PLANTS Plants that do not contain chlorophyll (nongreen plants) depend on other living organisms for their food. Thus, the plants which do not contain chlorophyll are heterotrophs and their mode of nutrition is heterotrophic. Various types of heterotrophic nutrition are described below: ƒ Saprophytic nutrition ƒ Parasitic nutrition ƒ Insectivorous nutrition ƒ Symbiotic nutrition 3. SAPROPHYTIC NUTRITION ƒ The plants which derive their food from the dead and decaying organic matter are called saprophytes or saprophytic plants or saprotrophs and the mode of nutrition is called saprophytes. ƒ Examples of saprophytes are fungi (bread mould), mushrooms, and some bacteria (e.g., Lactobacillus, Acetobacter). They are saprophytic, because they derive their food from the dead and decaying organic matter. ƒ Saprotrophs releases digestive juices on the dead and decaying matter and convert them into a solution. These Do you k now? In some plants, photosynthesis also takes place in other parts of plants such as green stem and green branches. The green stems and green branches can do photosynthesis because they contain chlorophyll. For example- Cactus. Mushrooms Do you k now? Fungi also grow on pickles, leather etc., if left in hot and humid weather.

10 juices act upon and convert organic matter into liquid form. Then, they absorb the nutrients from it. 4. PARASITIC NUTRITION ƒ The mode of nutrition in which plants derive their food from the bodies of some other green plants and animals is called parasitic mode of nutrition. The green plant or the animal which provides the food is called the host. ƒ The plants which derive their food from the bodies of the host plants and animals are called parasites or parasitic plants. The parasitic plants may be total parasites or partial parasites. ƒ The plants which depend wholly on the host plant, for their food are called totally parasitic plants. ƒ Plants such as Cuscuta (Amarbel), Apodanthes, and certain bacteria and fungi are totally parasitic. ƒ The plants which make a part of their food themselves by photosynthesis but derive other components such as water, minerals, etc., of food from the host plant are called partial parasitic. ƒ The mode of nutrition in some plants like, Mistletoe is partially parasitic, because they make their food themselves but get water and minerals from the host plant. INSECTIVOROUS NUTRITION ƒ The mode of nutrition in which green plants make their own food but depend on insects for nitrogenous food is called insectivorous nutrition. ƒ The green plants which make their own food but depend on insects for nitrogenous food are called insectivorous plants. ƒ Plants such as pitcher plants (Nepenthes), sundew, and bladderwort derive their nutrition partly from the soil and the atmosphere and partly from small insects. These plants are called insectivorous plants. ƒ Most of these plants are found in the environment where nitrogen is not readily available. They use insects because they grow in soil that is usually thin and is also poor in nutrients. So to make themselves rich in nutrients they eat insects. Cuscuta on a host tree Apodanthes Mistletoe Do you k now? A parasitic plant called Rafflesia in Sumatra bears the largest flower diameter: 106 cm weight up to 10 kg. Rafflesia Pitcher plant

11 SYMBIOTIC NUTRITION ƒ The two plants which live together as parts of the same plant and mutually help each other are called symbionts. ƒ Such a relationship of mutually helping each other is called symbiosis. ƒ The mode of nutrition in lichens is symbiotic. A lichen is made up of a fungus and an alga living together. ƒ Lichen is an association between algae and fungi. Algae is an autotroph that synthesizes food and fungi is a saprophyte which absorb water and minerals and supply to the algal partner with shelter. HOW NUTRIENTS ARE REPLENISHED IN THE SOIL Plants get their mineral nutrients from the soil. The plant nutrients like nitrogen (N), Phsophorus (P) and Potassium (K) are present in the soil. When plant grows, they absorb the nutrients from the soil due to which amount of plant nutrient in soil goes on decreasing. When same plants are grown in the same field again and again then the soil become deficient in N,P and K. Due to this the plant nutrients are replenished in the soil. It is important to replenish (to make up for the loss) these nutrients in the soil. Fertile soil produces higher yields and greater plant quality. Fertile soil is rich in essential components and minerals, has good aeration, holds water well, and has a pleasant texture. Nutrients can be replenished in the following ways: Fertilisers and manures contain plant nutrients such as nitrogen, phosphorous and potassium, etc. So, when fertilisers and manures are added to the soil in the fields, then the soil gets enriched. Nutrients are replenished by certain different microorganisms that are found in the soil or also by the death of certain bacteria such as the rhizobium. 1. PRACTICE QUESTIONS A. Are non green plants autotrophic or heterotrophic? B. What is the saprophytic mode of nutrition? Give examples. C. What is lichen? Write the name of the components of the lichen thallus? D. What is crop rotation method? E. From where do the plants such as pitcher plants get their nutrients? Quick revision ƒ Energy is stored in the food materials as chemical energy. ƒ Food has various components such as carbohydrates, fats, proteins, vitamins, minerals, roughage, and water, etc., These components are called nutrients. ƒ Green plants prepare their own food by a process called photosynthesis. ƒ Food stores energy in the form of chemical energy. Lichens Do you k now? Lichens are the great indicator of air quality.

12 ƒ The process of intake of food and its proper utilisation by the body to obtain energy is called nutrition. ƒ The organisms which make their own food from the simple substances present in the environment are called autotrophs. ƒ Green plants make their food from carbon dioxide and water in the presence of chlorophyll and sunlight. ƒ The mode of nutrition in which the organisms cannot make their food and depend on others for their food is called heterotrophic nutrition. ƒ The animals which eat only grass, plants, or plant products are called herbivores. ƒ The animals which eat meat or flesh of other animals are called carnivores. ƒ The animals which eat both plants and animals are called omnivores. ƒ Plants convert solar energy of food into chemical energy. ƒ The glucose carbohydrate gets converted into a complex carbohydrate called starch. ƒ Plants get nitrogen in the form of soluble salts such as nitrates, urea, ammonium sulphate, etc. from the soil through their root system. ƒ The plants which derive their food from the dead and decaying organic matter are called saprophytes or saprophytic plants or saprotrophs. ƒ The mode of nutrition in which plants derive their food from the bodies of some other green plants and animals is called parasitic mode of nutrition. ƒ The mode of nutrition in which green plants make their own food but depend on insects for nitrogenous food is called insectivorous nutrition. ƒ The mode of nutrition in lichens is symbiotic. ƒ Rhizobium can convert atmospheric nitrogen into soluble salts of nitrogen. Š Chlorophyll: A green coloured pigment present in the leaves. Š Photosynthesis: The process green plants synthesise using carbon dioxide, water and mineral in the presence of sunlight. Š Nutrition: The process of intake of food and its utilisation by the body of an organism. Š Autotrophs: Organisms that can make their food from simple inorganic substances. Š Heterotrophs: Organisms that cannot make their food and depend on green plants (or autotrophs) for their food. Š Saprophytes: Plants that derive their food from dead and decaying organic matter. Š Parasites: Organisms that derive their food from the body of the host plant or animal. Š Insectivorous plants: Green plants which make their own food but depend on insects for nitrogenous food. Š Symbionts: Two plants that live together as part of the same plant and mutually help each other. Š Symbiosis: The mode of nutrition in which two different organisms work together for their mutual benefit. Š Stomata: Tiny openings on the lower surface of leaf that allow the exchange of gases. KEY TERMS

13 Exercise OBJECTIVE TYPE QUESTIONS A. Fill in the blanks. 1. Autotrophic plants are also _________. 2. Green plants are called _________ since they synthesise their own food. 3. The small pores on the lower side of a leaf are called _________. 4. During photosynthesis plants take in _________ and release _________. 5. Leguminous plants are examples of _________ association. B. State whether the following statements are true or false. 1. Carbon dioxide is released during photosynthesis. 2. Solar energy is converted into chemical energy during photosynthesis. 3. The product of photosynthesis is not a protein. 4. Plants which synthesise their food are called saprotrophs. 5. The mode of nutrition in lichens is symbiotic. C. Match the columns. Column A 1. Cuscuta 2. Pitcher plant 3. Green plants 4. Rhizobium Column B A. Autotrophs B. Bacteria C. Insectivorous D. Parasitic D. Write one word for the following. 1. The energy is stored by the leaves with the help of chlorophyll. 2. It derive nutrition from, dead, decaying matter. 3. The process by which green plants make their food. 4. It is called as small pores on the under-surface of the leaves. 5. It is the site of reception of light energy in leaves. E. Tick () the odd-one out. 1. Autotrophs, hetrotrophs, nutrition, nitrogen, Carbon dioxide 2. Pitchet plant, bladderwort, cuscuta, sunflower 3. Water, Chlorophyll, Root hair, Carbon dioxide 4. Herbovores, carnivores, omnivores, sunlight 5. Nitrogen, phosphorus, potassium, photosynthesis SUBJECTIVE TYPE QUESTIONS A. Very short-answer questions. 1. What is process by which green plants make food? 2. What do plants synthesize other than glucose?

14 3. What are the small pores in a leaf called? 4. What is the mode of nutrition in mushroom? 5. Where does the bacterium Rhizobium live? B. Define the terms. 1. Nutrition 2. Autotrophic and hetrotrophic nutrition 3. Saprophytic nutrition 4. Photosynthesis 5. Symbiosis C. Short-answer questions. 1. What are humans and animals called together? 2. Name the factors which affect photosynthesis. 3. What are parasites name one total parasitic and one partial parasitic plant? 4. How are nutrients replenished in the soil? 5. How does a pitcher plant get its nutrients? D. Long-answer type questions. 1. How would you test the presence of starch in leaves? 2. Teena is discussing with her friend that wild animals like tiger, wolf, lion and leopard do not eat plants. Does this mean that they can survive without plants? Can you provide a suitable explanation? 3. Explain the mode of nutrition in fungi. 4. How farmer is benefited from symbiotic relationship between rhizobium bacteria and legumes? 5. Explain symbiotic relationship with the help of example. 1. Why do farmers grow a leguminous crop in between two main crops? Explain? 2. Some plants have deep red, violet or brown coloured leaves. Can these leaves perform the photosynthesis process? 3. Name the members associated in lichen. How does each member benefit from the other? Higher order thinking skills (HOTS)

15 Explore more 1. GROUP DISCUSSION 1. Discuss the different type of nutrition in plants. Link: https://www.britannica.com/science/nutrition/Nutrition-in-plant Link: http://keralaagriculture.gov.in/wp-content/uploads/2021/04/Plant-NutritionsMar-2018_PDF.pdf 2. COLLABRATIVE PROJECT 1. Students make a trip to visit a zoo. List the animals present there. Find out the food they eat and classify them on the basis mode of nutrition. Link 1: https://www.boddunan.com/education/24-arts-a-science/13246-nutrition-inplants-and-animals.html Link 2: https:/www.preservearticles.com/201101042478/complete-information-onthe-dict-of-herbivores-carnivores-Omnivores-and-carryanimals.html 2. Perform any experimental activity given in the chapter. Link 1: http://en.wikipedia.org/wiki/Photosynthesis Link 2: http://www.ftexploring.com/photosyn/chloroplast.html Lets crack in accordance with 'Blooms Taxonomy' CREATE Validate that plants are the ultimate source of food with a sketch. EVALUATE Justify your response. Autotrophs are all types of green plants. APPLY Explain why sunlight is essential for photosynthesis. ANALYSE Demonstrate a schematic of a leaf section and label each component. UNDERSTAND Describe the steps taken by plants to produce their food utilising various raw components. REMEMBER What exactly is chlorophyll and what does it do?

16 62 NUTRITION IN ANIMALS What do we eat? Do you remember that food consists of many components? Write them below. Get Set Go! We know that all animals require food for their growth and development, repair of damaged parts, and functioning of the body. In the previous chapter, we learnt that plants can prepare their own food by the process of photosynthesis but animals are dependent on plants for their food, either directly by eating plants or indirectly by eating other animals that eat plants; this is the heterotrophic mode of nutrition. They are called herbivores (eat plants), carnivores (eat other animals) and omnivores (eat both plants and other animals). The components of food such as carbohydrates, fats, and protein are complex substances that cannot be utilised by the body directly. The process of breaking down the complex components of food into simpler substances is called digestion. The carbohydrates get broken down into simple sugar called glucose, while fats in fatty acid and glycerol and proteins get broken down into amino acids during digestion. Then, these simpler compounds are easily absorbed into the body for growth and development. This process starts only after the food intake. There are various methods by which different animals take their food.

17 VARIOUS MODES OF TAKING FOOD The first step in the process of nutrition in animals is ingestion which means taking food into the body (or eating of food). Every animal has some special structure or organs for taking food inside its body. Few examples are described below:- ƒ Animals such as cows, horses, etc., pick up food directly into their mouth. ƒ Human beings use their hands to put food into their mouth. ƒ Amoeba is a tiny aquatic animal which ingests its food with the help of its pseudopodia (false feet). ƒ A Paramecium has brush-like body structures called cilia. It sweeps food particles from water with the help of these structures. ƒ A frog uses its tongue to catch its prey. ƒ The butterfly uses its feeding tube to suck the nectar. ƒ Hydra is an animal which uses its tentacles to catch its prey and put it into mouth (body cavity). ƒ A spider weaves a web around it to catch its prey. Amoeba Paramecium Do you k now? The digestion that occurs inside the cell is called intracellular digestion. The digestion that takes place outside the cell is called extracellular digestion. In more complex multicellular animals such as fishes, frogs, and humans, all the steps in the process of nutrition are performed by specific organs and organ systems. Various ways of taking food We use our hands to put food into our mouth A butterfly sucks nectar with its feeding tube The web of the spider traps its prey A cow directly eats the grass The sticky tongue of a frog helps to catch the prey

18 Activity 1 Aim: To identify the different ways of taking food. Materials required:- Pictures/video clips of animals (housefly, butterfly, mosquito,ant, lice, snail, eagle, snake and humming bird) Procedure: Watch the video clips of different ways of food taken by different animals and fill the blank details in the given below table. Name of animal Kind of food Mode of feeding Eagle Flesh Swallowing Snail Grass Chewing Lice Blood Sucking Ant Mosquito Humming bird Housefly Decaying matter Brewing Butterfly PROCESS OF NUTRITION Nutrition is the sum total of the processes involved in taking in and the utilization of food by which growth, repair, and maintenance of the body of the organism are achieved. The various steps involved in the process of nutrition are: Intake of food through mouth. (Ingestion) Travels through the alimentary canal and breakdown of food. (Digestion) Nutrients from the food are absorbed. (Absorption) The absorbed food is used for producing energy and growth (Assimilation) Remaining waste material are ejected out from anus. (Egestion)

19 THE HUMAN DIGESTIVE SYSTEM The system that consists of the gastrointestinal tract plus the accessory organs of digestion and salivary glands is called the digestive system. The hollow organs that make up the gastrointestinal tract (GI tract) include the mouth, oesophagus, stomach, small intestine and large intestine that contains the rectum and anus. TEETH IN HUMAN BEINGS Before we describe the nutrition in human beings, it is very important to know about the teeth and their care because the intake of food is done with the help of teeth. In humans, teeth grow twice in their lifetime. The first set of 20 teeth appears by the age of 2 years. These teeth are called milk teeth. These milk teeth fall off one by one. These teeth begin to fall off at the age between 6 and 8 years. A new set of 32 permanent teeth is formed by the age of 12. These 32 teeth are called permanent teeth and last for the rest of our life. These 32 teeth (for an adult) can be classified into four types. Teeth Teeth present Teeth in each type Function in each jaw (Total number) Incisors 4 8 Biting/cutting Canines 2 4 Tearing Premolars 4 8 Chewing, Grinding Molars 6 12 Chewing, Grinding Total 32 Human digestive system Arrangement of different types of teeth in human beings Molar Premolar Canine Incisor

20 ƒ The front teeth which help us in cutting or biting food are called incisors. These are chisel shaped teeth. There are four incisors in the centre of each jaw. ƒ Next to each incisor, there is one canine on each side. These are the large and pointed teeth. Canines help in tearing the food. So, there are 2 canines in each jaw one behind the left incisor and the other behind right incisor. ƒ The next to canines, two teeth on each side of the jaw are premolars. Premolars have large, flat surfaces. There are four premolars in each jaw. These are helpful in chewing and grinding food. ƒ In the end, there are three molars on each side of the jaw. Thus, there six molars in each jaw. Four of those are wisdom teeth, which is also called the third molar, which come in between the ages of 17 to 25. ƒ Molars help in chewing and grinding the food. Molars are present only in the permanent set of teeth. They are not present in the temporary set of teeth called milk teeth. Activity 2 Aim: To understand position of our teeth. Procedure: Open your mouth, look into a mirror and try to count the different types of teeth in your mouth. RECORD THE NUMBER OF TEETH IN THE TABULAR FORM. Observation: 1. Incisors- Number of ____________ present in my mouth. 2. Canines- Number of ______________present in my mouth. 3. Premolars-Number of ______________present in my mouth. 4. Molars-Number of ______________present in my mouth. Conclusion: To know the difference of different types of teeth present in our mouth. STRUCTURE OF A TOOTH A tooth that is visible in your mouth is only a part of the entire tooth. The root of the tooth is completely buried into the jaw bone. A tooth consists of enamel, dentin, cementum and pulp tissue. The portion of a tooth exposed to the oral cavity is known as the dental crown, and the portion below the dental crown is known as the tooth root. ƒ ROOT: The part of a tooth embedded into the jaw. ƒ CROWN: The top part of the tooth outside the gums. ƒ NECK: The part between the root and the crown. Structure of a tooth

21 The tooth internally is made up of- ƒ ENAMEL: The hardest bodily tissue covering the surface of the dental crown. It is the hardest substance in our body. ƒ DENTIN: The tissue that forms the tooth from the dental crown to the tooth root, situated inside the enamel and cementum. It is softer than the enamel. A small tube filled with tissue fluid, called the dentinal tubule, runs inside the dentin. ƒ PULP CAVITY: The tissue is called the nerve. Blood vessels and the lymph vessels, as well as nerve fibers, are located in the dental pulp, supplying nutrients to the dentin. DIGESTIVE TRACT The food components pass through a continuous canal and get digested in each compartment. This is called an alimentary canal, it is ‘the tract or canal running from mouth to anus where digestion and absorption of food take place.’ In humans, the alimentary canal is about 9 m long. The alimentary canal can be divided into various compartments in human beings. ƒ buccal cavity ƒ food pipe or oesophagus ƒ stomach ƒ small intestine ƒ large intestine ƒ rectum ƒ anus Along with the alimentary canal, several glands play an equally important role in the digestion of food. ƒ DIGESTIVE GLANDS ƒ salivary glands ƒ liver ƒ pancreas ƒ gall bladder Now we will discuss the journey of food through different parts of the digestive tract. INGESTION OF FOOD IN HUMANS Humans take in food through the mouth. It is the first step in the process of nutrition which involves the intake of food through the mouth. The mouth contains teeth, tongue, and salivary glands. CARE OF THE TEETH (OR ORAL HYGIENE) Healthy teeth are white and healthy gums are pink. If proper care is not taken, teeth become yellowish due to the formation of a sticky layer containing food particles, saliva, and bacteria. This is called plaque. Do you k now? Tooth enamel is the hardest material in our body. This is also chemically the most stable tissue in the body. That is why teeth are selectively preserved after the death teeth of ancient humans and animals have provided the most useful data for studying the process of evolution. Mouth Salivary gland Oesophagus Stomach Small interstine Large interstine Pancreas Gall Bladder Liver Reetum Anus

22 Proper brushing of teeth keep them healthy Before brushing After brushing A soft thread called floss is used to clean between the teeth. The plaque absorbs sugary and starchy food materials. The bacteria in the plaque convert sugar and starch into acids. This acid dissolves the tooth enamel and leads to the formation of a cavity in the tooth. Gums hold the teeth. The soft tissue covering the alveolar bone is generally called “gum”. Given below are some helpful suggestions for the proper care of teeth and gums: ƒ Properly brush your teeth every day in the morning and night before going to bed. Massage your gums gently with a soft brush. ƒ Rinse the mouth with water or mouthwash after eating every meal. ƒ Eat self-cleansing foods such as raw vegetables, carrots, radishes, cabbage, and fresh fruits, particularly citrus fruits. ƒ Avoid eating sticky and starchy foods, sweets, chocolates, toffees ice-cream etc. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. The main functions of the tongue are: ƒ It helps in mixing saliva with food. ƒ It allows chewing and swallowing of the food. ƒ It bears the taste buds that allow tasting the food. ƒ It is also responsible for the speech. The tongue has small taste buds on its surface. The taste buds in a location detect a particular taste. DIGESTION OF FOOD The process of digestion starts in the mouth with the help of saliva secreted by the salivary glands. MOUTH OR BUCCAL CAVITY: The food is chewed and masticated with the help of premolars and molars and tongue. Mastication (chewing), in which food is crushed and mixed with saliva to form a bolus for swallowing. The salivary glands (three pairs) release a digestive juice called saliva in the buccal cavity. Saliva makes the chewed food wet Correct ways of brushing the teeth Salivary glands Tongue-taste buds

23 Do you k now? l The process of digestion involves enzymes such as amylase, pepsin, trypsin, lipase, and sucrose. These are called digestive enzymes. l Amylase breaks down starch to sugars e.g., glucose. l Pepsin and trypsin break proteins into peptides l Lipase helps in the breaking down of fats/ oils. l Sucrase breaks down sucrose to glucose. Activity 3 Aim: To show the effect of saliva on starch. Materials required: Boiled rice, chewed rice, dropper, iodine solution. Procedure: Two test tubes were taken and were labelled as A and B. In test tube A, one teaspoon full of boiled rice was kept. In test tube B one teaspoon full of boiled rice which were chewed for 3-5 minutes were kept. 3-4 ml of water was added to both the tubes. Add 2-3 drops of iodine solution in both test tubes A and B. Observation: The test tube A shows blue – black colour whereas test tube B does not show this colour. Conclusion: Test tube A (Boiled rice) contains starch and starch shows blue/black colour with iodine solution and slippery. This makes the swallowing of food easier. During digestion in the buccal cavity starch present in the food gets converted into sugar maltose. ƒ IN THE OESOPHAGUS (OR FOOD PIPE): Oesophagus is a hollow tube (about 25 cm long) made up of muscles. It connects the mouth (buccal cavity) to the stomach. 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. This movement takes place throughout the alimentary Movement of food through oesophagus into the stomach oesophagus

24 canal and pushes the food downwards. At times the food is not accepted by our stomach and is vomited out. ƒ IN THE 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 mucus protects the stomach lining from the action of enzymes and acid. Hydrochloric acid kills bacteria that might enter the food. The acid makes the food acidic to promote the action of enzymes. The stomach muscles churn the food with gastric juices secreted by the glands in the stomach wall. The food stays in the stomach for 2-4 hours. Most of the food is digested in the stomach. ƒ IN 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. 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 OF DIGESTED FOOD IN THE SMALL INTESTINE ƒ The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption. ƒ The inner walls of the small intestine have thousands of finger -like outgrowths. These are called villi (singular villus). ƒ 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. ƒ 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. ƒ 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. Do you k now? Bile juice makes the food alkaline and helps in the digestion of fat.

25 ƒ IN LARGE INTESTINE: Large intestine is about 1.5 m long in length. The undigested food (called the waste) moves from the small intestine to the large intestine. ABSORPTION IN THE LARGE INTESTINE AND EGESTION ƒ The large intestine removes most of the water and certain salts from the waste by absorption. ƒ The almost solid wet waste is then sent to the rectum. ƒ EGESTION: This wet solid waste in the rectum called faeces leaves the body through the anus. This process of throwing solid waste out of the body is called egestion. 1. PRACTICE QUESTIONS A. Which of these structure(s) help amoeba to capture food? a. Cell membrane b. Cilia c. Pseudopodia B. Name two animals that live on liquid food only. C. What is a long coiled tube in our digestive system? D. Which type of teeth help us in biting food? E. How many teeth are present in the lower jaw of human beings? F. Name the structure used by the butterfly to procure food. G. What is the unabsorbed portion of the food thrown out of our body called? (Chyme/Bolus/ Faeces) H. What is the name given to the process by which absorbed nutrients are utilized by the body? I. In which part of the human body does the absorption take place? NUTRITION IN ANIMALS Different animals have different body structures. The process of nutrition in different animals is different. In this section, we will learn the process of nutrition in some unicellular and multicellular animals. DIGESTION IN GRASS-EATING ANIMALS ƒ It is very common to see grass-eating animals chewing leisurely continuously even when they are not eating. ƒ Grass-eating animals such as cows, buffaloes, horses, etc swallow half-chewed grass quickly and store it in a part of their stomach called rumen. ƒ Here the food gets partially digested. The partially digested food is called cud. When the animals are not eating, the cud returns to the mouth in small lumps and is chewed again. This process is called rumination. ƒ These animals are called ruminants. DIGESTION OF CELLULOSE ƒ The grass is rich in cellulose. Most animals and human beings cannot digest cellulose. ƒ Ruminants have a large sac-like structure called a caecum between the small intestine and large intestine. The cellulose of the grass is digested here by the action of cellulose-digesting bacteria.

26 ƒ This bacterium is not present in humans. It is due to this, that humans cannot digest grass/ cellulose. FEEDING AND DIGESTION IN AMOEBA ƒ Amoeba is a unicellular organism found in pond water. It has a cell membrane, a rounded dense nucleus, and many small vacuoles in its cytoplasm. It has an irregular shape which keeps on changing slowly. It has projections on its body. These are called pseudopodia. ƒ It feeds on some microscopic organisms. ƒ It engulfs tiny particles of food with the help of its false feet called pseudopodia. ƒ The pseudopodia close to form a small cavity called a food vacuole. ƒ The food vacuole moves around in the cytoplasm. Here, the digestive enzymes help in the break-down of food into simpler and soluble molecules. ƒ The digested food is then absorbed and assimilated and the Amoeba grows in size. The nutritional process in amoeba ƒ After the Amoeba reaches a critical size, it divides into two daughter cells. ƒ The undigested food is thrown out of the body through the contractile vacuole at any point because amoeba has no anus. The digestive system of a ruminant (cow) 2. ORAL QUESTIONS A. From which part of the body, undigested food is egested in Amoeba? B. Why humans cannot digest cellulose? C. Partially digested food mixed with digestive juices in the stomach is called ______________.

27 So now you k now ƒ The process of breaking down the complex components of food into simpler substances is called digestion. ƒ The carbohydrates get broken down into simple sugar called glucose. ƒ The first step in the process of nutrition in animals is ingestion which means taking food into the body. ƒ Nutrition is the sum total of the processes involved in taking in and the utilization of food by which growth, repair, and maintenance of the body of the organism are achieved. ƒ The system that consists of the gastrointestinal tract plus the accessory organs of digestion and salivary glands is called the digestive system. ƒ In humans, teeth grow twice in their lifetime. ƒ The first set of 20 teeth appears by the age of 2 years. These teeth are called milk teeth. ƒ In humans, the alimentary canal is about 9 m long. ƒ If proper care is not taken, teeth become yellowish due to the formation of a sticky layer containing food particles, saliva, and bacteria. This is called plaque. ƒ The tongue has small taste buds on its surface. ƒ The process of digestion starts in the mouth with the help of saliva secreted by the salivary glands. ƒ During digestion in the buccal cavity starch present in the food gets converted into sugar maltose. ƒ Oesophagus connects the mouth (buccal cavity) to the stomach. ƒ The stomach is a thick-walled bag. Its shape is like a flattened U and it is the widest part of the alimentary canal. ƒ The process of throwing solid waste out of the body is called egestion. ƒ Amoeba is a unicellular organism found in pond water. ƒ Amoeba engulfs tiny particles of food with the help of its false feet (called pseudopodia). The food is digested in the food vacuole. The digested food is then absorbed and assimilated. ƒ Amoeba grows in size and after reaching a critical size, it divides into two daughter cells. ƒ The undigested food is thrown out of the body through the contractile vacuole. ƒ Amoeba has no anus. Š Nutrition: the process in which living organism takes in nutrients from the food they eat and these nutrients are needed for energy, maintenance of tissues and regulation of bodily processes. Š Ingestion: the first step in the process of nutrition which involves the intake of food through the mouth. Š Egestion: the process of throwing solid waste out of the body is called egestion. Š Assimilation: process in which the absorbed food is used for producing energy and for growth. Š Plaque: sticky layer containing food particles, saliva, and bacteria. Š Alimentary canal: the digestive system from oesophagus to the anus. KEY TERMS

28 Exercise OBJECTIVE TYPE QUESTIONS A. Fill in the blanks. 1. The carbohydrates get broken down into simple sugar called ____________. 2. ____________ are for biting and cutting food in humans. 3. Digestion of food starts in ____________ and gets completed in ____________. 4. Amoeba takes in food by the use of ____________. 5. The digested food moves from the stomach to the ____________. 6. Grass is rich in carbohydrates known as ____________. 7. The organ that stores bile is ____________. B. State whether the following statements are true or false. 1. The process of taking food is called digestion. 2. Digestion of starch starts in the stomach. 3. Undigested food cannot be assimilated by the body. 4. The ruminants bring back swallowed grass into their mouth and chew it for sometime. 5. The tongue helps in mixing saliva with food. C. Match the columns. Column A 1. Amoeba 2. Paramecium 3. Frog 4. Taste buds Column B A. Catches insects with its tongue B. Tongue C. Engulfs food by false feet D. Uses cilia for ingestion of food D. Write one word for the following. 1. The act of getting and eating food. 2. The inner walls of the small intestine have thousands of finger-like outgrowths. 3. It causes severe toothache. 4. The process of taking food into the body. 5. The grazing animals quickly swallow the grass and store it in a part of the stomach. Š Faeces: unabsorbed portion of the food that is thrown out of the body. Š Taste buds: taste-sensitive locations on the surface of the tongue. Š Villi: finger-like projections on the inner wall of the small intestine. Š Cud: partially digested food stored in a part of the stomach called the rumen. Š Ruminants: plant/grass-eating animals that digest their food in two steps. Š Contractile vacuole: the point from where the undigested food is thrown out of the body by Amoeba.

29 E. Tick () the odd-one out. 1. Camel, Cow, Horse, Human beings, Hydra 2. Molars, Canines, Premolars, Incisors, Ingestion 3. Root, Pulp cavity, Crown, Dentin, Nutrition 4. Large intestine, Small intestine, Swallow, Rectum 5. Liver, Salivary gland, Starch, Intestine SUBJECTIVE TYPE QUESTIONS A. Very short-answer questions. 1. Name the parts of amoeba which help it in moving and capturing food. 2. What is a gall bladder? What is its role? 3. What is the difference between ingestion and egestion? 4. Name the process in which absorbed food is used for producing energy. 5. What is the hard substance that covers the tooth known as? B. Define the terms. 1. Digestion 2. Rumination 3. Plaque 4. Dentin 5. Gum 6. Absorption C. Short-answer questions. 1. Name the glands relative to digestive system along with their functions. 2. Write the function of the large intestine? 3. How do you differentiate between absorption and assimilation? 4. Where is saliva produced? Write about its main functions. 5. How is the process of digestion different in ruminants? D. Long-answer type questions. 1. Briefly describe the process of nutrition in amoeba. 2. Write the functions of different types of teeth. 3. Cows and buffaloes swallow their food hurriedly and then sit restfully and chew their food. Can you reason why? 4. Why grass eating animals can digest cellulose whereas human beings can not? 5. Draw a labelled diagram of human alimentary canal. Teena was eating dinner. Suddenly she got hiccups. Her brother Sachin gave her water and suggested not to eat too fast. Raghav was sitting with Sachin and he got confused as he first time heard the new word ‘hichki’ that comes when someone remembers. He asked his father and his father said that it is only a myth. He also explained him the proper scientific reason behind it. A. What is hiccup and why do we get hiccup? B. What do we know about Raghav? Life Skill

30 Ingestion Colour the part where this process starts Function of ingestion Digestion Colour the part where this process starts Function of digestion Absorption Colour the part where this process starts Function of absorption Assimilation Colour the part where this process starts Function of assimilation Egestion Colour the part where this process starts Function of egestion Value Based Questions Take a printout of the image given below. Use different colours for marking in the diagram. (a) Blue colour for ingestion, (b) Green colour for digestion, (c) Yellow colour for absorption, (d) Red colour for assimilation and pink colour for egestion. Write your name, class and section on paper. Submit the printout to your subject teacher. 1. The long structure of small intestine is accommodated in small space within our body. Explain. 2. Anurag got his gall bladder removed surgically as she was diagnosed with stones in his gall bladder. After the surgery, he faced problems in digestion of certain food items when consumed in bulk. Which kind of food items would they be and why? Higher order thinking skills (HOTS)

31 Explore more 1. GROUP DISCUSSION 1. Is the following statement true or false? Why? The epiglottis prevents food from entering the lungs when you swallow. Link 1: http://kidshealth.org/kid/watch/er/choking.html Link 2: http://www.sciencebob.com/research/digestion.php 2. COLLABRATIVE PROJECT 1. Study the teeth arrangement and make a model of the two jaw and label incisor, canines, molars and premolars, with the help of models of the two jaws. Discuss amongst your friends. Link: https://www.medicalnewstoday.com/articles/326754 2. Write an activity to show the effect of saliva on starch. Link 1: https://www.youtube.com/watch?v=OVjWJxV2zig 3. SYMPOSIUM 1. What is root canal therapy, write its history and its role in the treatment of teeth? Link 1: https://my.clevelandclinic.org/health/treatments/21759-root-canal Lets crack in accordance with 'Blooms Taxonomy' CREATE In comparison to carnivores, herbivores have a longer small intestine. Do you agree? Support your answer. EVALUATE Distinguish between incisors and canines. APPLY Explain why a piece of Chapati tastes sweet after chewing for a long time? ANALYSE Choose the odd one out and give reasons. Oesophagus, small intestine, large intestine, rectum UNDERSTAND Discuss the function of the hydrochloric acid that the gastric glands secrete. REMEMBER What is the name of the condition that causes a person to pass out watery stools?

32 FIBRE TO FABRIC: ANIMAL FIBRE 63 Why do you wear different clothes in different weather? What type of clothes will you wear if you attend a party in winter? What are these clothes made of? Get Set Go! In the previous class we studied that natural fibres are obtained from plants and animals. We also know about synthetic fibres which are man-made such as rayon, nylon, and polyesters. We know that wool and silk fibres are obtained from animals and are known as animal fibres. Now, in this chapter, we will understand how these animal fibres are converted into the wool that we buy from the market to knit sweaters. We will also learn how silk fibres are made into silk. ANIMAL FIBRES—WOOL AND SILK Animal fibres that are extracted from different animals usually have different properties. The wool comes from animals such as sheep, goats, rabbits and yak, etc., whereas silk comes from silkworms. Wool is used for knitting sweaters, weaving shawls, and other woollen clothes. Silk is used for making saris and other dresses. Characteristics of Wool and Silk ƒ WOOL: It is off-white to light cream in colour. It is soft, smooth, absorbent, and wrinkle-free. Woollen fabrics are used in winter as it is a good insulator. It is a weak and brittle fibre that required special care during washing.

33 ƒ SILK: It is soft, shiny, lustrous, smooth, and stronger than wool. It is also called the ‘Queen of fibres’ and is majorly used for formal wear. WOOL The term ‘wool’ generally refers to the fibres and yarn derived from the hair of various animals. Wool is soft and hairy in texture. Wool is the most commonly used natural fibre obtained from different animals. It is commonly obtained from the hair of sheep, goats, yaks, rabbits, and camels. These animals are therefore called wool-yielding animals. ANIMALS THAT YIELD WOOL Animals from which fur or fleece is extracted to make wool fibres are wool-yielding animals. Most animals found in mountain regions are being used to extract wool because their body is covered with a thick coat of hair or fur. Have you ever thought about why these animals have a thick coat of hair? Actually, their hair or fur traps a lot of air and the air is a poor conductor of heat, that does not allow the body heat to go out and keeps these animals warm, protecting them from cold weather. For example, sheep, goats, rabbits, llamas, alpacas, camels, bison, and yak. Some wool-yielding animals Sheep Goat Camel Llama Yak ƒ SHEEP: Most sheep have two types of hair from which the wool is obtained. The outer coarse hair is known as the kemp and the fine soft structure undercoat close to the skin from which wool fibre is obtained. ƒ CASHMERE GOAT: The fine soft fibre obtained from under a layer of cashmere goat is called cashmere. The outer coat of hair fibre is quite coarse and high-quality Cashmere is obtained by ‘dehairing’ or combing. Cashmere goats are found only in the mountain regions of China and Tibet. Do you k now? HISTORY OF WOOL First-time sheep were brought to North America in 1493. New England was the first region to establish a spinning and weaving industry and the first textile factory was established in the year 1788. During first civil war there was a great demand of wool for making uniforms for soldiers. Merino sheep were bred in large numbers to meet the demand.

34 ƒ YAK: Yaks are found in Ladakh and Tibet. The outer coat consists of long hair and an undercoat consists of soft and silky wool. The colour ranges from brown to black. ƒ CAMEL: Camel fleece consists of a soft and fine undercoat and a long and coarse overcoat that grows up to 15 inches long. It has excellent property of insulation. ƒ ANGORA RABBIT: Soft white fibre called Angora wool is obtained from the angora rabbit. The soft white fur obtained is then spun into yarn that is used to make sweaters. Sheep, goats, alpacas, and llama are the main sources of wool production. The hairy coating of a sheep, i.e., a thin layer on the skin giving a blanket-like appearance, is called fleece. HOW DOES WOOL KEEP US WARM? Wool is used for making winter clothing. Do you know why? Because it is very soft and warm due to its high insulating properties. Wool fibres are packed together, forming millions of tiny air pockets which trap air inside and keep us warm. The crimp in wool fibres makes it soft and springy to the touch. The length of each fibre ranges from 38 mm to 380 mm depending on the breed of sheep. The quality of wool depends on the breed of sheep. It is judged on the basis of the thickness, length, shine, strength, and colour of the fibre. Pashmina is a fine, fluffy, light, and warm wool from Kashmir and nearby Himalayan areas. It is obtained from the underfur of Cashmere goat. There are six important wool-yielding breeds of Indian sheep. Do you k now? Fibres obtained from plant sources are cellulosic fibre whereas fibres obtained from animal sources are called protein fibres. Wool is a protein fibre, and cotton is a carbohydrate (cellulose). That is why wool burns with a bad smell (burning of proteins) not cotton. Do you k now? Have you ever thought why these animals have thick coat of hair? Air is a poor conductor of heat, so hair traps a lot of air and keeps these animals warm during colder conditions. Some Indian breeds of sheep Breed Quality of Wool State where it is found Bakharwal Woollen shawl Jammu and Kashmir Lohi Superior wool Rajasthan, Punjab Nali Carpet wool Rajasthan, Haryana, Punjab Rampur bushair Brown fleece Uttar Pradesh, Himachal Pradesh Patanwadi Hosiery Gujarat Marwari Coarse wool Gujarat Research MAKE A SCRAPBOOK FOR WOOL-YIELDING ANIMALS. Search for pictures of wool-yielding animals either from books on animals or from the internet and paste them into your scrapbook. Also, give some relevant information about each of them. Paste a piece of wool thread obtained from the respective animal. For this, you may have to visit the wool market.

35 FROM FIBRES TO WOOL In this section, you will understand and learn about the journey of wool from the rearing and breeding of wool-yielding animals (such as sheep) to the final finished wool. Getting wool fibre from sheep (or in general any wool-yielding animal) involves the steps given below: REARING AND BREEDING OF SHEEP (SHEEP FARMING OR SHEEP HUSBANDRY) Have you seen shepherds looking after the grazing herds of sheep in the hills of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Arunachal Pradesh, and Sikkim, or in the plains of Haryana, Punjab, Rajasthan and Gujarat? Sheep are reared in many parts of our country for wool, meat, and milk. Rearing means taking care of wool-bearing animals by providing them food, shelter, and health care facilities. The entire process of raising and breeding sheep for wool, meat, and milk is known as Sheep Farming or Sheep Husbandry. Sheep are herbivores and prefer grass and leaves. However, the wool-yielding sheep are given protein-rich food such as a mixture of corn, pulses, jowar, and oil-cake. Sheep fed on such a diet develop good growth of curly and shiny hair. Depending upon the quality of wool required, the sheep are selectively bred by choosing the parents of the ‘sheep’ with the desired characteristics. This process is called ‘Selective breeding’. In winter, sheep are kept indoors and fed on leaves, grain, and dry fodder. For yielding good quality wool, proper rearing of sheep is very important. PROCESSING OF WOOL Once sheep are reared, and their fleece grows well, wool fibres are extracted. The wool which is used for knitting sweaters or for weaving shawls is the finished product of a long process, which involves multiple steps. ƒ SHEARING: The fleece of sheep or other wool-yielding animals is removed along with a thin layer of skin with the help of a hair-cutting machine or even manually. Shearing does not hurt the sheep; this process is just like shaving the beard. Shearing is done only once a year, preferably during summer because, in hot weather, sheep can survive without their protective covering of hair. The fleece provides woollen fibres that are further processed to produce woollen yarns. After the shearing, the sheep is immediately dipped into an antiseptic to prevent any skin infection. Remember The major steps required in the processing of wool from sheep to fabric are: 1. Rearing and breeding of sheep 2. Shearing 3. Cleaning or Scouring 4. Grading and Sorting 5. Carding and Drawing 6. Dyeing 7. Spinning and weaving Shearing of sheep

36 ƒ CLEANING OR SCOURING: Hair in an animal body contain dust and dirt. So, after the hair are removed, they are rigorously washed and cleaned to remove any dust, dirt, or grease. The small, fluffy burrs often observed in our sweaters also appear on the hairs extracted from sheep, which are also removed. After this, long and continuous woollen fibres are made. Nowadays, scouring is done mostly by machines. The scoured hair are then dried. Scouring Scouring by machine Cleaning of burrs ƒ GRADING AND SORTING: After scouring, the hairy skin is sent to a factory where the hair of different textures, colours, and quality is sorted. The dried hair of different textures is sorted out here. Grading means the breaking up of fleece, whereas sorting means the division of the wool into sections as per the quality of fibre obtained from different parts of the body. The best quality of fibres obtained from the shoulder are used for clothing and the inferior quality fibres come from the legs that are used to make rugs. The small fluffy fibres called burrs are picked out and sent for reprocessing. ƒ CARDING AND DRAWING: The process by which selected curly wool fibres are straightened by passing through rollers is called carding. In this process, fibres are passed through metal teeth which make them straight and blend them into slivers. It also removes dirt and leftover matter. From carding, yarn is taken to combing, where short fibres are removed and long fibres are placed parallel to each other. Now the thin slivers are compacted through a process called drawing. ƒ DYEING: Natural fleece obtained from animals are primarily black, white, or brown. To give desirable colour to the fibres, they are dyed. ƒ SPINNING AND FINISHING: Finally, woollen yarns are made by rolling or spinning them into yarns. Fibres are straightened, combed, and rolled into yarn. Wonder box Have you ever thought about why it hurts when someone pulls your hair but not when you go for a haircut? Wonder box A good breed of sheep yields about 4-5 kg fleece per year. Steps involved in the processing of wool

37 y Longer fibres give wool yarn for sweaters. y Shorter fibres are spun and woven into woollen cloth. PHYSICAL PROPERTIES OF WOOL ƒ SMOOTHNESS: Wool fibres are smooth, shiny, and soft in nature. ƒ STRENGTH: Wool fibres have high tensile strength. It can increase in length up to 70% when soaked in water. ƒ ABSORPTION OF WATER: Wool absorbs a maximum amount of water than other fibres, it can absorb one-third of its weight water. CHEMICAL PROPERTIES OF WOOL ƒ Action of acid and base – It easily dissolves in acid and alkali. ƒ Action of bleaching agents – The wool fibre can be bleached without losing its strength. Practice Time! 1. Practice questions A. What is the process of removing wool from the sheep called? B. What are the quality of best wool? C. Why is scouring of the sheep’s hair done? D. Name any two animal fibres. E. Which type of wool fibres are used for making sweaters? 2. Answer in one word A. Angora wool is obtained from this animal ___________________. B. The process of removing any stained, damaged, and inferior wool from the fleece ___________________. C. The process of cleaning sheared skin ___________________. D. Wool-yielding animal found in Tibet ___________________. Occupational hazard The wool industry is an important means of livelihood for many people in our country. But sorter’s job is risky as sometimes they might get infected by a bacterium, Anthrax, which causes a fatal blood disease called sorter’s disease. The risks faced by people working in industry are called occupational hazards. CURIOSITY GENERATION-BASED ACTIVITY 1. What type of cloth material are you wearing today? 2. What will you wear when going to bed, when going to the birthday party? 3. Have you noticed any difference in the fabric you are wearing on both the occasion? 4. Which one is softer? Do you know… where it comes from? Higher order thinking skills (HOTS)

38 SILK Silk is a fine, strong, soft, and shining fibre produced by silkworms. It is a luxurious fibre obtained from the cocoon of a moth, Bombax mori. Silk is regarded as a “natural” protein fibre. The protein produced by moths from which fibre is formed is called sericin. HOW SILK IS OBTAINED FROM SILKWORMS? Fibre obtained from silkworms is animal fibre. The process of silkworm’s rearing is often referred to as Sericulture. Silkworm culture or sericulture is a very old occupation in India. On a commercial scale, India produces a lot of silk. Before we learn how silk is processed, let us discuss the life cycle of the silk moth, and spinning of the ‘silk fibres’. LIFE CYCLE OF SILK MOTH When a female silk moth lays eggs, the life cycle of the silk moth begins. The caterpillars or larvae of the silk moth are hatched from the silk moth’s eggs. Silkworms produce pupa by feeding on mulberry leaves. To keep itself alive during the pupa stage, the silkworm weaves a net around itself. The time span of the life cycle of a silkworm ranges from 66 to 88 weeks. ƒ STAGE 1: EGG: An egg is the first stage of the life cycle of the silkworm. The female silk moth lays about 300–400 eggs, which are mostly the size of small dots. In the springtime, the eggs hatch due to the warmth in the air. This procedure happens once every year. ƒ STAGE 2: CATERPILLAR- THE SILKWORM: The caterpillars or hairy silkworms come out as the eggs hatch. This stage is known as the larval stage. In this stage of silkworms, growth happens. They feed on mulberry leaves and consume a large amount of these leaves for around 30 days before going to the next stage. ƒ STAGE 3: COCOON: In this stage, the silkworm deposits filaments in concentric layers around its body by spinning its head in a pattern of eight, forming a structure called the cocoon. The silkworm takes around 3–7 days to prepare the cocoon, formed by about 20−40 concentric layers of a single thin thread. It is the size of a small cotton ball. In this stage, the silkworm secretes fine filaments from two silk glands located on its head. These thin filaments are made Explore Prepare a List of the different kinds of silks. Ask your mother/aunt/grandmother to show you the kind of silk saris they have. Do you k now? Most historians conclude that origin of silk and sericulture is associated with China in nearly 2500 BC when Empress Si-Ling-Chi, queen learned how to rear silkworms and unwind their cocoons to produce filament fibres. China kept secret and had a monopoly on the silk industry for more than 4,000 years. After this, sericulture spread to Korea and Japan and then to the rest of the world. Eggs

39 of a protein that hardens to form silk fibres when exposed to air. Soon the caterpillar completely covers itself with silk fibres and turns into a pupa. ƒ STAGE 4: PUPA: Inside the cocoon, the silkworm develops and enters the second stage of its life, i.e., ‘the pupa stage’. The pupa stage is a motionless stage. This is the stage between larvae and adult moths. After 14−15 days, the pupa emerges from the cocoon as an adult moth. But for obtaining silk, this stage has no importance because cocoons are drown into boiling water, and silk threads are unwounded from cocoons. ƒ STAGE 5: MOTH: In the final stage or after 10−14 days of developing into a moth in its cocoon, the silk moth comes out of the cocoon and excretes a brownish fluid while emerging. Silk moths cannot fly. Male and female silk moths can be easily separated as female silk moths have large abdomens and males have small abdomens. After mating with the male moth, the female moth will lay eggs and die. In this manner, the life cycle of silkworms continues. TYPES OF SILK FIBRE ƒ There are various kinds of silk, according to their chemical composition. They are divided into two types- natural silk and artificial silk. Natural silk is obtained from cocoons or silkworms and is made up of protein. Artificial silk is made up of wood pulp such as rayon. The silk thread is made from the silk moth cocoon. ƒ Silk moths look very different from one another, and the silk yarn they produce has different textures (coarse, smooth, shiny, etc.). Tassar silk, Mooga silk, Kosa silk, and other silks are derived from cocoons spun by various types of moths. The mulberry silk moth is the most common silk moth. The silk fibre from this moth’s cocoon is soft, lustrous, and elastic, and it can Life cycle of silk moth Wonder box Silk fabrics are tightly woven which leaves less room in between for insects to bite through. You’re all protected from mosquitoes during summer months! Activity 1 1. Collect pieces of different silk cloth and paste them in your activity book. Do you k now? Can you think of which is strong among silk, steel, and wool?

40 be dyed in a variety of beautiful colours. PROCESSING OF SILK Extracting silk from the cocoon is known as the processing of the silk. It is separated from the cocoon by exposing it to sunlight. Taking out threads from cocoons is called reeling of the silk. After the reeling of silk is done, the process of unwinding silk from a cocoon takes place. The silk thread is then bleached. Silk fibre are spun into thread to make cloth or fabric. The processing of silk from cocoons follows: ƒ STEP 1: The cocoons are sorted out according to their colour, size, shape, and texture. ƒ STEP 2: Separation of the silk fibre from the cocoon. For this, it is needed to be exposed to warmth. Piles of cocoons are kept under the sun, boiled, or exposed to steam. The warmth causes the silk fibre to separate from the rest of the cocoon. ƒ STEP 3: The cocoons are given a series of hot and cold immersions. This makes the silk-gum soft. ƒ STEP 4: Reeling the silk, which is the process of delicately unwinding the fibre from the cocoon. Reeling is also done with special machines. The resulting fibre is known as raw silk. ƒ STEP 5: The silk thread is then bleached and dyed into many shades. Activity 2 Materials required for the activity: Cutting of tactile diagram of stages of life history of silk moth/cut-outs having names of each stage of the silk moth. Use the cut-out pictures of the life history of the silk moth and jumble them. Ask students to arrange the sequence of the life history of silkworms in a cyclic form, who ever will do first will win. Students can show and tell the life history of the silkworm in a form of storytelling/poem. SILK SOME FACTS! Silk cloth can uphold water equals to 30% of its weight when dipped in water before it feels moist. It is an excellent electrical insulator. Silk is stronger per weight than steel wire. Silk thread can be used for stitches wound and incisions. It can be used for wide variety of fabrics from bridal wear to bulletproof.

41 ƒ STEP 6: The silk fibre is then spun into silk thread, which is woven into silk cloth by weavers. USES OF SILK FIBRE ƒ Silk is antibacterial and can resist bacterial infection when worn during sweat or wet conditions. ƒ It is a natural material and breathable. ƒ It is durable, hygienic, and keeps away dirt and sweat from the skin. ƒ Due to its comfortable wear, it helps in blood circulation. ƒ Silk has high levels of hydrogen peroxide which keeps hair frizzy less. ƒ Silk is good for sensitive skin wear as it does not require any harsh chemicals. SOME DIFFICULTIES IN SILK PRODUCTION ƒ Silk production requires the rearing of thousands of silkworms, Bombax mori. ƒ It requires more land to produce silk than cotton which makes them more expensive. ƒ Silk is more difficult to dye. ƒ Silk-making is labour-intensive work. Do you k now? Can you suggest how the workers prevent themselves from diseases while working in the textile industry? OCCUPATIONAL HAZARDS IN THE SILK INDUSTRY l Chemical used for degreasing, dyeing, and bleaching of silk cloth cause skin infection and eye irritation. l Small particles of silk fibre or moth cause serious asthmatic problems and lung infections. l Working in hot and cold water for reeling causes skin softening and burns and scalds in hands. l Dyes used for colouring fabric are being absorbed by our digestive system, if ingested, and may cause serious health hazards. Points to remember Practice Time! 1. Practice questions A. Which fibre is obtained from an organism that feeds on mulberry leaves? B. When the eggs of silkworm hatch what comes out? C. Where does a female silk moth lay eggs? D. What is the primary reason to boil the cocoons of the silkworm? E. Name the sticky fluid secreted by the larva (caterpillar) from its salivary glands.

42 2. Fill in the blanks A. The production of raw silk by raising silkworms is known as _________. B. The process of shedding the skin by the larvae of silkworms is known as _________. C. The caterpillar spins fine silk filament around it in layers to form _______. D. _________ is an infectious disease caused by a bacterium present in the fleece of infected animals. Quick revision ƒ Silk and wool are obtained from animals. That’s why these are called animal fibres. ƒ Wool is obtained from the hair of sheep, camels, goats, and rabbits. Wool is a suitable fibre for making winter clothes. ƒ The process of removing hair from the sheep is called shearing. ƒ Shearing can be done either manually or with a shearing machine. ƒ The sheared skin with hair is thoroughly washed in a soap solution to remove grease, dust, and dirt. This process is called scouring. ƒ After scouring, the hair is dried and sorted depending on the texture of the wool. ƒ The selected curly wool fibres are then straightened by passing through rollers. ƒ Then the wool fibres are dyed and finally sent for spinning and weaving. ƒ Silk is a natural fibre made from the cocoons of silkworms. ƒ Silk moth is a large, white insect, which passes through different stages in its life cycle-eggs, larva, pupa, and moth. ƒ Silk is soft, smooth, and lustrous. ƒ Silk is obtained from the cocoon stage. ƒ Silk is of various types- Tassar silk, Mooga silk, and Kosa silk. ƒ The rearing of silkworms is called Sericulture. ƒ Silk fibres are made of protein. ƒ Silk fibres from cocoons are separated out and reeled into silk threads. ƒ Weavers weave silk threads into silk cloth. Š Fleece: The wool coating of a sheep i.e., a thin layer on skin is called fleece. It is very soft and warm due to its high-insulating properties. Š Shearing: Removal of wool along with a thin layer of skin from the body of sheep. Š Sorting: Separating defective and damaged wool. Š Scouring: The process of cleaning raw wool, making it free from dust, grease, and other residues present as impurities. Š Dyeing: Colouring of textile materials such as fibres, and yarns to obtain colourful fabric. Š Spinning: The process of twisting fibre together to form a continuous thread. Š Carding: A process of separation of individual fibres. Š Sericulture: Rearing of silk moth. Š Cocoon: An envelope-like protective covering made up of silk threads where larva grows into adult form. Š Reeling: Getting silk fibre from cocoons. Š Weaving: A method of textile making in which two different threads are arranged into yarn to form a fabric or cloth. KEY TERMS

43 Exercise OBJECTIVE TYPE QUESTIONS A. Fill in the blanks. 1. Angora wool is obtained from __________________. 2. The process of taking out threads from the cocoons for use as silk is called ______________ the silk. 3. The thread obtained in the reeling process is called __________________. 4. Silk fibres come from __________________ of silk moth. B. State whether the following statements are true or false. 1. Silk is non lustrous. 2. Wool is made from plant cellulose. 3. Silk is a natural fibre. 4. Egg is the second stage of silkworm’s life cycle. 5. Cahmere goats provide us Merino wool. C. Match the columns. Column A 1. The wool coating of a sheep 2. Rearing of silk moth 3. Separating defective and damaged wool 4. Colouring of textile materials Column B A. Fleece B. Dyeing C. Sericulture D. Sorting D. Write one word for the following. 1. It absorbs good amount of moisture without becoming damp. 2. It is secreted by a caterpillar. 3. It is fire resistant. 4. It is a popular fabric for tailoring fine garments. 5. It can be dyed easily and is very elastic. E. Tick () the odd-one out. 1. Wool, scouting, rearing, reeling. 2. Larvae, caterpillar, eggs, silk. 3. Dog, Sheep, Angora, goat. 4. Spinning, weaving, carding, silkworm 5. Fiber, jute, coir, Industrial hemp. SUBJECTIVE TYPE QUESTIONS A. Very short-answer questions. 1. What are silkworms? 2. What is sericulture? 3. Why are the sheep after shearing dipped into an antiseptic?

44 4. What are occupational hazards? 5. What is the process of taking out silk thread or filaments from cocoons called? B. Define the terms. 1. Removing fleece from the body of animals: _______________. 2. Washing fleece to free it from grease, dirt and dust:_________________. 3. Grouping of wool as per length, colour and texture: ______________. 4. Colouring of the fibres: ____________. 5. Twisting of fibre into yarns: ___________. C. Short-answer questions. 1. Distinguish between silk and wool fibres. 2. Define the following terms a. Scouring b. Sorting c. Grading 3. What keeps the wool yielding animals warm? 4. How are the silkworms reared? 5. Write the four stages in the life cycle of a silk moth. D. Long-answer type questions. 1. Describe in brief about the animals that yield wool. 2. What are the various steps for processing fibres into wool? 3. What are the characteristics of silk fibres? Describe the stages involved in the life cycle of a silkworm with a neat and labelled diagram? 4. Explain the life history of a silk moth with the help of figures of each stage. 5. What happens when the silk caterpillar stops feeding? Collect your wollen clothes and donate them in help age home or NGO. Life Skill Value Based Questions Value based- Naina got upset on learning that for obtaining 1 kg of raw silk arou nd 5,000 cocoons are killed. But her father explained her that silkworms are also conserved in this process for obtaining silk next time. He also explained to Naina that it is the source of income to many rural and needy person. a. Why silk are famous? b. Whom do you agree- Naina or her father? Justify? c. If you get an option to select between a silk dress and a dress made of synthetic fibre which one will you select and why?

45 1. Tina wear nylon clothes while lighting diyas, candles and bursting green crackers. Do you think nylon cloth is safe while doing any fire related activity. 2. Why natural fibres are costlier than synthetic fibres? Higher order thinking skills (HOTS) Explore more 1. GROUP DISCUSSION 1. Safety and health issues in the textile industry. Make a poster and each group will brief on the above topic. Link: https://www.ask-ehs.com/blog/occupational-health-safety-in-textile/ Link: http://researchjournal.co.in/upload/assignments/9_267-271.pdf 2. COLLABRATIVE PROJECT 1. Research and compile the list of different types of silk moths and the varieties of silk produced by them. Link 1: http//schmidling.com/silkmoth.htm 3. SYMPOSIUM 1. Prepare a presentation on “Fibres from Animals and plant” Search from internet/local newspaper/animal fiber and plant fiber book to compile the data in the presentation. Link: https://www.fibre2fashion.com/industry-article/2943/plant-and-animal-fibres Lets crack in accordance with 'Blooms Taxonomy' CREATE Create a diagram illustrating the silk moth’s life cycle with welllabelled stages. EVALUATE Evaluate the statement, we wear different types of clothes in different weathers. APPLY Distinguish between silk and wool fibres. ANALYSE Explain what spinning is. UNDERSTAND Give examples of two fibres made of protein. REMEMBER Describe the occupational hazards associated with Sorter’s disease.

46 64 HEAT AND TEMPERATURE When you sip hot coffee, what do you feel? When you open the door of the refrigerator, what do you feel? Get Set Go! Heat is a form of energy that makes things hot. The things become hotter when they gain heat and they become colder when they lose heat. People use their sense of touch to know the hotness or coldness of an object. When you rub your hands against each other, they get warm. Rubbing of hands produce heat. Water become hot when kept on a gas stove burner. Here, gas stove is the source of heat and water is gaining this heat energy. Therefore, heat is a form of energy that causes the sensation of hotness and coldness. When a body is heated, its energy increases, and when it is cooled, its energy decreases. Heat is measured by the change in the degree of hotness or coldness. HOT AND COLD The hotness or coldness of an object depends on the flow of heat energy. Heat energy always flow from a hot object to a cold object. For example when we add ice cubes in a glass of juice (as shown in the image), ice cubes start melting. It is because the juice has high temperature than ice cubes and so heat energy from juice flows to ice cubes. It shows that when a hot object (object with high temperature) and a cold object (an object with low temperature) are in contact, the hot object loses its heat energy while the cold object gains the heat energy. The differences between the temperature of two objects results in the flow of a type of energy from a hot object to a cold object. This energy is called heat energy. Rubbing of hands produces heat Water is gaining heat energy

47 Our sense of touch tells only whether the object is hot or cold. It cannot tell how hot or cold the objects are. To compare the hotness or coldness of different objects, we need to know the temperature of the objects. Need to k now The SI unit of Heat is Joule (J). It is also measured in calorie (cal) and kilocalorie (kcal). Heat energy flows from an area of higher temperature to an area of lower temperature Juice containing ice cubes Is our sense of touch always reliable to the degree of hotness and coldness of an object? Let us find out. Activity 1 Aim: To find out if our sense of touch is reliable enough to determine the hotness and coldness. Materials required: Three bowls, bearable hot water, lukewarm water and cold water. Procedure: Proceed as follows: Label the three bowls as A, B, and C. Now, fill bowl A with hot (It should be bearable, not too hot that you burn your hand) water, bowl B with lukewarm water and bowl C with icecold water. Now, dip your right hand in bowl A and left hand in bowl C for 2-3 minutes. Then, remove your hands from bowls A and C and dip them together in bowl B. Notice the feel of touch of your left and right hands. Do both the hands have the same feeling? You must be feeling as given below: Fingers of right-hand Fingers of the left hand Bowl A: Hot   Bowl C: Cold Fingers of right-hand Fingers of the left hand Bowl B: Cold   Bowl B: Warm

48 The right-hand feels the water in bowl B to be colder. The left-hand fingers feel the water in bowl B to be warmer. Which is right? Conclusion: Our sense of touch is not reliable in finding out the degree of hotness or coldness. TEMPERATURE When we touch an object, it may appear hot or cold. When you take ice cream, it appears cold and when you sip a hot cup of tea, it feels hot. The terms hot or cold are relative and not absolute. But why things appear hot or cold? How can we measure the hotness and coldness of an object? Actually, we get a reliable measure of the hotness of an object through its temperature. We can define the temperature as the measurement of hotness or coldness. Generally, an object appears hot if its temperature is higher than that of our body and vice-versa. MEASUREMENT OF TEMPERATURES Temperature is measured by a device called as thermometer. All thermometers contain a special material (mercury) that has a unique property of expansion on heating and contraction on cooling. There are three temperature scales on which temperature is measured. These are: ƒ Celsius scale (earlier called as centigrade scale) ƒ Fahrenheit scale ƒ Kelvin scale (Absolute scale) For practical reasons, most thermometers measure temperature on the Celsius scale. About Celsius scale About Fahrenheit scale Thermometer for a room Digital Thermometer ƒ A thermometer measuring a temperature of 22° Celsius is shown here. ƒ Celsius scale was designed by Sir Anders Celsius. ƒ This scale is indicated by °C. ƒ On the Celsius scale, water freezes at 0°C and boils at 100°C. The difference between these two points is divided into 10°. ƒ A thermometer measuring a temperature of 72° Fahrenheit is shown here. ƒ Fahrenheit scale was developed by Daniel Gabriel Fahrenheit and his colleague. ƒ This scale is indicated by °F. ƒ On the Fahrenheit scale, water freezes at 32°F and boils at 212°F. The difference between these two points divides into 180°. Celsius Fahrenheit

49 Presently, Doctor’s thermometer (called a clinical thermometer) is also marked on the basis of Celsius scale. THERMOMETERS There are different kinds of thermometers. On the basis of materials used inside the thermometer, these are of two different types: mercury and digital thermometer. The most commonly used thermometers are mercury thermometers, used in laboratories and by doctors. THE MERCURY THERMOMETER The first mercury thermometer was invented by Gabriel Fahrenheit in 1714. He used mercury in the thermometer because of its certain properties. These are: 1. It remains in liquid state for a wide temperature range from -38.87 degree celsius (melting point) to 365.58 degree celsius (boiling point). 2. It does not stick to the glass. 3. It has a uniform rate of expansion. 4. It is easy to see due to its grey shiny colour. Clinical and laboratory thermometers are two common examples of mercury thermometer. THE LABORATORY THERMOMETER To measure the temperature of objects other than body temperature, there are other thermometers such as the laboratory thermometer. The range of temperature in a laboratory thermometer is from –10°C to 110°C. HOW TO USE A LABORATORY THERMOMETER? It is important to know how to use a laboratory thermometer without breaking it. Correct way to read the temperature is: ƒ First of all wash the thermometer and bring it to normal room temperature. ƒ Now the temperature mark should be below 37°C or 98°F. ƒ Hang the thermometer from a stand with the help of a hook. ƒ Place a beaker just below the thermometer. ƒ Now pour tap water/liquid into the beaker in such a way that the bulb of the thermometer is completely dipped into the water. A laboratory thermometer Explore All thermometers have liquid material inside them. What would happen if the thermometers are filled with gases? Measuring the temperature of water with a laboratory thermometer

50 ƒ Now observe the mercury thread in the thermometer. ƒ Read the temperature when it becomes constant and record it in your notebook. PRECAUTIONS While using a laboratory thermometer, the following precautions should be taken. ƒ Held the thermometer vertically straight so that you can take the correct reading. ƒ The bulb should be dipped fully in the liquid or the substance of which temperature is to be measured. ƒ Make sure the bulb does not touch bottom or sides, handle it with care. ƒ Take the reading while the thermometer bulb is immersed inside because if it is taken out the level of mercury thread will begin to fall. ƒ Keep your eyes at the mercury level. ƒ Do not place the thermometer in too hot or too cold liquid. THE CLINICAL THERMOMETER A clinical thermometer (or Doctor’s thermometer) is used for measuring the body temperature of humans and animals. It is a long narrow glass tube with a bulb containing mercury inside the tube. The features of mercury clinical thermometer are: 1. There is a little arrow at 98.4 or 98.6°F showing the normal body temperature. The level of mercury tells our body temperature in °C. 2. There is a kink in the tube near the bulb which ensures that the mercury in thermometer does not contract and flow back into the bulb before the temperature has been read. The mercury can be brought back into the bulb by giving it a jerk after the thermometer has been read. HOW TO USE A CLINICAL THERMOMETER? To use a clinical thermometer, follow the steps given below: ƒ Determine the value of one small division on the thermometer scale. For this, count the number of small divisions between two bigger marks (i.e., a difference of 1°C). Then Clinical thermometer Value of one small division = Difference of temperature between two big marks Number of small divisions = 1 5 °C = 0.2°C (assuming there are 5 small divisions) Zoomed portion of a clinical thermometer Do you k now? An earlier clinical thermometer was based on Fahrenheit scale. On this scale the body temperature of a normal healthy person is 98.6o F.