Science Textbook for Class 7 (2018-19) PDF

SCIENCE TEXTBOOK FOR CLASS VII 2018-19  ISBN 81-7450-654-3 First Edition ALL RIGHTS RESERVED January 2007 Magha 192...

SCIENCE TEXTBOOK FOR CLASS VII 2018-19  ISBN 81-7450-654-3 First Edition ALL RIGHTS RESERVED January 2007 Magha 1928 q No part of this publication may be reproduced, stored in a retrieval system or Reprinted transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the publisher. November 2007 Kartika 1929 q This book is sold subject to the condition that it shall not, by way of trade, be lent, re- January 2009 Pausa 1930 sold, hired out or otherwise disposed of without the publisher’s consent, in any form January 2010 Magha 1931 of binding or cover other than that in which it is published. January 2011 Magha 1932 q The correct price of this publication is the price printed on this page, Any revised January 2012 Magha 1933 price indicated by a rubber stamp or by a sticker or by any other means is incorrect December 2012 Agrahayana 1934 and should be unacceptable. October 2013 Asvina 1935 December 2014 Pausa 1936 December 2015 Agrahayana 1937 February 2017 Phalguna 1938 OFFICES OF THE PUBLICATION DIVISION, NCERT December 2017 Agrahayana 1939 NCERT Campus Sri Aurobindo Marg New Delhi 110 016 Phone : 011-26562708 PD 750T+100T RPS 108, 100 Feet Road Hosdakere Halli Extension Banashankari III Stage © National Council of Educational Bengaluru 560 085 Phone : 080-26725740 Research and Training, 2007 Navjivan Trust Building P.O.Navjivan Ahmedabad 380 014 Phone : 079-27541446 CWC Campus Opp. Dhankal Bus Stop Panihati Kolkata 700 114 Phone : 033-25530454 CWC Complex Maligaon Guwahati 781 021 Phone : 0361-2674869 ` 55.00 Publication Team Head, Publication : M. Siraj Anwar Division Chief Editor : Shveta Uppal Chief Business : Gautam Ganguly Manager Chief Production : Arun Chitkara Printed on 80 GSM paper with NCERT Officer watermark Editor : Bijnan Sutar Published at the Publication Division by the Production Assistant : Prakash Veer Singh Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg Cover, Layout and Illustrations New Delhi 110 016 and printed at Amit Printing Press, D-12 and 13, Industrial Area, Site-A, Ashwani Tyagi Mathura- 281 001 (U.P.) 2018-19  FOREWORD The National Curriculum Framework (NCF), 2005, recommends that children’s life at school must be linked to their life outside the school. This principle marks a departure from the legacy of bookish learning which continues to shape our system and causes a gap between the school, home and community. The syllabi and textbooks developed on the basis of NCF signify an attempt to implement this basic idea. They also attempt to discourage rote learning and the maintenance of sharp boundaries between different subject areas. We hope these measures will take us significantly further in the direction of a child-centred system of education outlined in the National Policy on Education (1986). The success of this effort depends on the steps that school principals and teachers will take to encourage children to reflect on their own learning and to pursue imaginative activities and questions. We must recognise that, given space, time and freedom, children generate new knowledge by engaging with the information passed on to them by adults. Treating the prescribed textbook as the sole basis of examination is one of the key reasons why other resources and sites of learning are ignored. Inculcating creativity and initiative is possible if we perceive and treat children as participants in learning, not as receivers of a fixed body of knowledge. These aims imply considerable change in school routines and mode of functioning. Flexibility in the daily time-table is as necessary as rigour in implementing the annual calendar so that the required number of teaching days are actually devoted to teaching. The methods used for teaching and evaluation will also determine how effective this textbook proves for making children’s life at school a happy experience, rather than a source of stress or boredom. Syllabus designers have tried to address the problem of curricular burden by restructuring and reorienting knowledge at different stages with greater consideration for child psychology and the time available for teaching. The textbook attempts to enhance this endeavour by giving higher priority and space to opportunities for contemplation and wondering, discussion in small groups, and activities requiring hands-on experience. The National Council of Educational Research and Training (NCERT) appreciates the hard work done by the Textbook Development Committee responsible for this book. We wish to thank the Chairperson of the advisory group in Science and Mathematics, Professor J.V. Narlikar and the Chief Advisor for this book, Prof. V.B. Bhatia for guiding the work of this committee. Several teachers contributed to the development of this textbook; we are grateful to their principals for making this possible. We are indebted to the institutions and organisations which have generously permitted us to draw upon their resources, material and personnel. We are especially grateful to the members of the National Monitoring Committee, 2018-19  iv appointed by the Department of Secondary and Higher Education, Ministry of Human Resource Development under the Chairpersonship of Professor Mrinal Miri and Professor G.P. Deshpande, for their valuable time and contribution. As an organisation committed to systemic reform and continuous improvement in the quality of its products, the NCERT welcomes comments and suggestions which will enable us to undertake further revision and refinement. Director New Delhi National Council of Educational 20 November 2006 Research and Training 2018-19  PREFACE This book is the outcome of the efforts of the Textbook Development Committee appointed by the NCERT. The committee met a few times to interact with one another to improve the draft. Then there was a review meeting in which many experts and practicing school teachers were invited to review the draft and suggest improvements. By and large we have stuck to the format of the Class VI book. By now, famous characters, Boojho and Paheli, have been used to make the text interactive. Attempt has been made to recall children’s own experiences and build concepts around them. This is designed to connect science that they study in the school with their every-day life. Many activities have been suggested to clarify concepts. Some of these activities are so simple that children can perform them on their own. The requirement of the apparatus required for the activities is minimal. We performed all the activities ourselves to ensure that there was no difficulty in performing them in the school situation. The activities should also help children in developing skills such as presentation of data in tabular and graphical forms, reasoning and drawing inference from the given data. The language of the book has been kept as simple as possible. A large number of photographs, illustrations, cartoons, etc. have been included to make the book attractive. To help teachers evaluate children effectively, a large number of exercises have been given at the end of each chapter. The teachers are encouraged to frame additional exercises to test children’s understanding. Some challenging exercises have also been devised for those children who would like to appear for the National Talent Search Examination conducted by the NCERT. We are conscious of the fact that there is a paucity of additional reading material for children. We have tried to address this problem by providing non-evaluative boxes. These boxes, in blue, contain additional information, anecdotes, stories, strange facts and other such interesting materials. We all know that children are mischievous and playful by nature. Therefore, in order to prevent any untoward incident during the performance of the activities in the school or outside, necessary cautions, in red, have been inserted at various places in the book. To prepare children to assume their roles as responsible citizens of tomorrow, attempt has been made to sensitise them to the issues concerning gender, religion, environment, health and hygiene, water scarcity and energy conservation. We have sought to weave into the text the value of cooperation and the importance of peer learning. An important feature of the book is what we call ‘Extended Learning’. These are totally non-evaluative, and purely voluntary activities and projects. Some of the projects in this section have been designed to enhance children’s interaction with the experts, teachers, even parents, and society at large. The children are required to collect information of various kind and draw conclusions of their own. My request to teachers and parents is to use the book in the spirit in which it has been written. Encourage children to perform activities and learn by doing, rather than by rote. 2018-19  vi You can supplement, or even replace, the activities given here. If you feel that you have better alternatives, especially with your local/regional flavour, please write to us so that these activities could be used in the future editions of the book. We have been able to include only a small subset of children’s experiences. You have a better knowledge of their experiences because you are in touch with them. Use them to illustrate the concepts being taught. Above all, please do not stifle children’s natural curiosity. Encourage them to ask questions, even if sometimes you feel uncomfortable. If you do not know the answer to a question on the spot, do not feel embarrassed. You can promise them to find the answer and deal with it later. Make a genuine attempt to get the answer from whatever resources are within your reach, such as senior school or college teachers, experts, libraries, internet, etc. If, in spite of your efforts, you cannot get the answer to some question, you could write to NCERT. I must thank the NCERT for enabling us to talk to children through the medium of this book. Every member of the NCERT has been courteous and helpful to us. If you find this book useful and enjoy teaching/learning science through this book, the Editing Team and I shall consider ourselves well-rewarded. V.B. BHATIA Chief Advisor Textbook Development Committee 2018-19  TEXTBOOK DEVELOPMENT COMMITTEE CHAIRPERSON, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS J.V. Narlikar, Emeritus Professor, Inter University Centre for Astronomy and Astrophysics (IUCCA), Ganeshkhind, Pune University, Pune CHIEF ADVISOR V.B. Bhatia, Professor, Retd. (Physics), Delhi University, Delhi MEMBERS Bharati Sarkar, Reader, Retd. (Zoology), Maitreyi College, Delhi University, Delhi C.V. Shimray, Lecturer, Department of Education in Science and Mathematics (DESM), NCERT, Sri Aurobindo Marg, New Delhi D. Lahiry, Professor, Retd, DESM, NCERT, Sri Aurobindo Marg, New Delhi G.P. Pande, Uttarakhand Seva Nidhi, Paryavaran Shiksha Sansthan, Jakhan Devi, Almora, Uttaranchal Harsh Kumari, Headmistress, CIE Experimental Basic School, Department of Education, Delhi University, Delhi J.S. Gill, Professor, DESM, NCERT, Sri Aurobindo Marg, New Delhi Kamal Deep Peter, TGT (Science), Kendriya Vidyalaya, Bangalore Kanhiya Lal, Principal, Retd., Directorate of Education, Delhi Lalita S. Kumar, Reader (Chemistry), School of Sciences, Indira Gandhi National Open University (IGNOU), Maidan Garhi, New Delhi Mohd. Iftikhar Alam, TGT (Science), Sarvodaya Bal Vidyalaya (No.1), Jama Masjid, Delhi P.S. Yadava, Professor, Department of Life Sciences, Manipur University, Imphal R. Joshi, Lecturer (Selection Grade), DESM, NCERT, Sri Aurobindo Marg, New Delhi Rachna Garg, Lecturer, DESM, Central Institute of Educational Technology, NCERT, Sri Aurobindo Marg, New Delhi Ranjana Agrawal, Principal Scientist and Head, Division of Forecasting Techniques, Indian Agricultural Statistics Research Institute, IARI Campus, Pusa, New Delhi R.S. Sindhu, Professor, DESM, NCERT, Sri Aurobindo Marg, New Delhi Ruchi Verma, Lecturer, PPMED, NCERT, Sri Aurobindo Marg, New Delhi Sarita Kumar, Reader (Zoology), Acharya Narendra Dev College, Delhi University, Delhi Sunila Masih, Teacher, Mitra GHS School, Suhagpur, P.O. Hoshangabad, Madhya Pradesh V.K. Gupta, Reader (Chemistry), Hans Raj College, Delhi University, Delhi MEMBER-COORDINATOR R.K. Parashar, Lecturer, DESM, NCERT, Sri Aurobindo Marg, New Delhi 2018-19 2018-19  ACKNOWLEDGEMENTS The National Council of Educational Research and Training (NCERT) acknowledges the valuable contribution of the individuals and organisations involved in the development of Science textbook for Class VII. The Council acknowledges the valuable contribution of the following academics for reviewing and refining the manuscripts of this book: Sushma Kiran Setia, Principal, Sarvodaya Kanya Vidyalaya, Hari Nagar (Clock Tower), New Delhi; Mohini Bindra, Principal, Ramjas School, Pusa Road, New Delhi; D.K. Bedi, Principal, Apeejay Senior Secondary School, Pitampura, Road No. 42, Sainik Vihar, New Delhi; Chand Vir Singh, Lecturer (Biology), GBSS School, Rajouri Garden (Main), New Delhi; Renuka Madan, TGT (Physics), Air Force Golden Jubilee Institute, Subroto Park, Delhi Cantt; Reena Jhani, TGT (Science), Darbari Lal DAV Model School, Pitam Pura, New Delhi; Geeta Bajaj, TGT (Science), K. V. No. 3, Delhi Cantt., New Delhi; Gagandeep Bajaj, Lecturer, Department of Education, S.P.M. College, Delhi University, Delhi; Shashi Prabha, Lecturer, DESM, NCERT, New Delhi; A.K. Bakhshi, Professor, Department of Chemistry, University of Delhi, Delhi; N. Rathnasree, Director, Nehru Planetarium, Teen Murti Bhavan, New Delhi; S.B. Singh, TGT (Science), J.N.V. Sonikpur, P.O. Trivediganj, Distt. Barabanki, Uttar Pradesh; Madhur Mohan Ranga, Lecturer (Selection Scale), (Zoology), Govt. College, Ajmer, Rajasthan; K.G. Ojha, Associate Professor, Department of Chemistry, M.D.S. University, Ajmer, Rajasthan; Puneeta Sharma, TGT (Science), L.D. Jain Girls Senior Secondary School, Pahari Dhiraj, Delhi; Manohar Lal Patel, Teacher, Govt. R.N.A. Exc. H.S.S. Pipariya, Distt. Hoshangabad, Madhya Pradesh; Bharat Bhushan Gupta, PGT (Biology), Sarvodaya Vidyalaya, No.1, Shakurpur, Delhi; Sushma Jairath, Reader, Department of Women Studies (DWS), NCERT, New Delhi; Mina Yadav, Lecturer, DWS, NCERT, New Delhi; Swadesh Taneja, Ex-Reader (Life Sciences), IGNOU, New Delhi and M.M. Kapur, Professor, Retd. (Chemistry), Delhi University, Delhi. The contributions of Pramila Tanwar and Ashish K. Srivastava, Assistant Professors, are acknowledged for being a part of the review of this textbook. The council is highly thankful to the India Meteorological Department, New Delhi, for providing some illustrations for the Chapter 8: Winds, Storms and Cyclones. The Council gratefully acknowledges the valuable suggestions received from the National Monitoring Committee in the development of the manuscript of this textbook. The dynamic leadership of Professor Hukum Singh, Head, DESM, for providing guidance in the final editing of the manuscript and extending infrastructure facilities is highly acknowledged. Special thanks are due to Shveta Uppal, Chief Editor; and Bijnan Sutar, Assistant Editor, for going through the manuscript and suggesting relevant changes. 2018-19  x The Council also acknowledges the efforts of Deepak Kapoor, Incharge, Computer Station; Purnendu Kumar Barik, Musarrat Parveen and Satish Kumar Mishra, Copy Editors; Neelam Walecha and Muhammad Aiyub, DTP Operators; and Randhir Thakur, Proof Reader. The contribution of APC-office, administration of DESM, Publication Department and Secretariat of NCERT is also acknowledged. 2018-19  A NOTE FOR THE STUDENTS The team of Paheli and Boojho will be with you as you journey through this textbook. They love to ask questions. All kind of questions come to their minds and they collect them in their sacks. Sometimes, they may share some of these questions with you, as you read through the chapters. Paheli and Boojho are also on the lookout for answers to many questions — sometimes the questions seem answered after they discuss them with each other, sometimes through discussions with other classmates, teachers or their parents. Answers to some questions do not seem available even after all these. They might need to experiment on their own, read books in the library, send questions to scientists. Just dig and dig and dig into all possibilities and see if the questions can be answered. Perhaps, they would carry some of the unanswered questions in their sacks to higher classes. What will really thrill them would be your adding questions to their sacks or answers to their questions. Sometimes, activities are suggested in the textbook, results or findings of these by different groups of students would be of interest to other students and teachers. You can complete the suggested activities and send your results or findings to Paheli and Boojho. Do keep in mind that activities that involve using blades, scissors or fire need to be done strictly under the care of your teachers. Stick to the precautions given and then enjoy doing all the suggested activities. Mind, the book will not be able to help you much, if the activities are not completed! We would like to advise you that you must make observations yourself and record whatever results you get. Keen and true observations are necessary for exploring any subject of study. For some reason your results may turn out to be different from those of your classmates. To Do not worry. Try to find out the reason The Head for these results instead of disregarding Department of Education in them. Do not ever copy results from your Science and Mathematics, classmate. NCERT, Sri Aurobindo Marg, New Delhi 110 016 You can send your feedback for Paheli and Boojho at: 2018-19  CONSTITUTION OF INDIA Part IV A (Article 51 A) Fundamental Duties Fundamental Duties – It shall be the duty of every citizen of India — (a) to abide by the Constitution and respect its ideals and institutions, the National Flag and the National Anthem; (b) to cherish and follow the noble ideals which inspired our national struggle for freedom; (c) to uphold and protect the sovereignty, unity and integrity of India; (d) to defend the country and render national service when called upon to do so; (e) to promote harmony and the spirit of common brotherhood amongst all the people of India transcending religious, linguistic and regional or sectional diversities; to renounce practices derogatory to the dignity of women; (f) to value and preserve the rich heritage of our composite culture; (g) to protect and improve the natural environment including forests, lakes, rivers, wildlife and to have compassion for living creatures; (h) to develop the scientific temper, humanism and the spirit of inquiry and reform; (i) to safeguard public property and to abjure violence; (j) to strive towards excellence in all spheres of individual and collective activity so that the nation constantly rises to higher levels of endeavour and achievement; (k) who is a parent or guardian, to provide opportunities for education to his child or, as the case may be, ward between the age of six and fourteen years. 2018-19  CONTENTS FOREWORD iii PREFACE v Chapter 1 Nutrition in Plants 1 Chapter 2 Nutrition in Animals 11 Chapter 3 Fibre to Fabric 24 Chapter 4 Heat 35 Chapter 5 Acids, Bases and Salts 49 Chapter 6 Physical and Chemical Changes 58 Chapter 7 Weather, Climate and Adaptations of Animals to Climate 68 Chapter 8 Winds, Storms and Cyclones 80 Chapter 9 Soil 96 Chapter 10 Respiration in Organisms 108 Chapter 11 Transportation in Animals and Plants 121 Chapter 12 Reproduction in Plants 133 2018-19  xiv Chapter 13 Motion and Time 143 Chapter 14 Electric Current and its Effects 160 Chapter 15 Light 174 Chapter 16 Water: A Precious Resource 193 Chapter 17 Forests: Our Lifeline 206 Chapter 18 Wastewater Story 220 INDEX 231 2018-19  1 Nutrition in Plants I n Class VI you learnt that food is utilisation by the body. The mode of essential for all living organisms. nutrition in which organisms make food You also learnt that carbohydrates, themselves from simple substances is proteins, fats, vitamins and minerals are called autotrophic (auto = self; trophos components of food. These components = nourishment) nutrition. Therefore, of food are called nutrients and are plants are called autotrophs. Animals necessary for our body. and most other organisms take in food All living organisms require food. prepared by plants. They are called Plants can make food for themselves but heterotrophs (heteros = other). animals including humans cannot. They get it from plants or animals that eat plants. Thus, humans and animals are directly or indirectly dependent on Paheli wants to know why plants. our body cannot make food from carbon dioxide, water and minerals like plants do. Boojho wants to know how plants prepare Now we may ask where the food their own food. factories of plants are located: whether food is made in all parts of a plant or only in certain parts? How do plants 1.1 MODE OF NUTRITION IN PLANTS obtain the raw materials from the Plants are the only organisms that can surroundings? How do they transport prepare food for themselves by using them to the food factories of plants? water, carbon dioxide and minerals. The raw materials are present in their 1.2 PHOTOSYNTHESIS — FOOD surroundings. MAKING PROCESS IN PLANTS The nutrients enable living Leaves are the food factories of plants. organisms to build their bodies, to grow, Therefore, all the raw materials must to repair damaged parts of their bodies reach the leaf. Water and minerals and provide the energy to carry out life present in the soil are absorbed by the processes. Nutrition is the mode of roots and transported to the leaves. taking food by an organism and its Carbon dioxide from air is taken in 2018-19  Cells You have seen that buildings are made of bricks. Nucleus Similarly, the bodies of living organisms are made of tiny units called cells. Cells can be seen only under the microscope. Some organisms are made of only one cell. The cell is enclosed by Cytoplasm a thin outer boundary, called the cell membrane. Most cells have a distinct, centrally located Cell membrane spherical structure called the nucleus (Fig. 1.1). The nucleus is surrounded by a jelly-like substance called cytoplasm. Fig. 1.1 Cell through the tiny pores present on the The leaves have a green pigment surface of leaves. These pores are called chlorophyll. It helps leaves to surrounded by ‘guard cells’. Such pores capture the energy of the sunlight. This are called stomata [Fig. 1.2 (c)]. energy is used to synthesise (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the Boojho wants to know how water presence of sunlight, it is called and minerals absorbed by roots photosynthesis (Photo: light; synthesis : reach the leaves. to prepare). So we find that chlorophyll, sunlight, carbon dioxide and water are Water and minerals are transported to the leaves by the vessels which run necessary to carry out the process of like pipes throughout the root, the stem, photosynthesis. It is a unique process on the earth. The solar energy is the branches and the leaves. They form a continuous path or passage for the captured by the leaves and stored in the nutrients to reach the leaf. They are plant in the form of food. Thus, sun is the ultimate source of energy for all called vessels. You will learn more about transport of materials in plants in living organisms. Chapter 11. Can you imagine life on earth in the absence of photosynthesis! In the absence of photosynthesis there would not be any food. The Paheli wants to know what is so survival of almost all living organisms special about the leaves that they directly or indirectly depends upon the can synthesise food but other food made by the plants. Besides, parts of the plant cannot. oxygen which is essential for the survival 2 SCIENCE 2018-19  Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and green branches. The desert plants have scale- or spine-like leaves to reduce loss of water by transpiration. These plants have green stems which carry out photosynthesis. of all organisms is produced during Light energy photosynthesis. In the absence of photosynthesis, life would be impossible on the earth. During photosynthesis, chlorophyll Carbon containing cells of leaves (Fig. 1.2), in dioxide the presence of sunlight, use carbon Chlorophyll Oxygen in leaf dioxide and water to synthesise carbohydrates (Fig. 1.3). The process can be represented in an equation: Water and sunlight Carbon dioxide + water  → minerals chlorophyll Carbohydrate + oxygen Fig. 1.3 Diagram showing photosynthesis Chlorophyll During the process oxygen is released. The presence of starch in leaves indicates the occurrence of photosynthesis. Starch is also a carbohydrate. Guard Cells Stoma Boojho has observed some (b) Section of a leaf plants with deep red, violet or brown leaves. He wants to Guard cells know whether these leaves also carry out photosynthesis. (a) Leaf Activity 1.1 Stomatal opening Take two potted plants of the same kind. (c) Stoma Keep one in the dark (or in a black box) Fig. 1.2 for 72 hours and the other in sunlight. NUTRITION IN PLANTS 3 2018-19 Perform iodine test with the leaves of carbohydrates are made of carbon, both the plants as you did in Class VI. hydrogen and oxygen. These are used Record your results. Now leave the pot to synthesise other components of food which was earlier kept in the dark, in such as proteins and fats. But proteins the sunlight for 3 – 4 days and perform are nitrogenous substances which the iodine test again on its leaves. contain nitrogen. From where do the Record your observations in your plants obtain nitrogen? notebook. Recall that nitrogen is present in The leaves other than green also have abundance in gaseous form in the air. chlorophyll. The large amount of red, However, plants cannot absorb nitrogen brown and other pigments mask the in this form. Soil has certain bacteria that green colour (Fig. 1.4). Photosynthesis convert gaseous nitrogen into a usable takes place in these leaves also. form and release it into the soil. These are absorbed by the plants along with water. Also, you might have seen farmers adding fertilisers rich in nitrogen to the soil. In this way the plants fulfil their requirements of nitrogen along with the other constituents. Plants can then synthesise proteins and vitamins. 1.3 OTHER MODES OF NUTRITION IN PLANTS Fig. 1.4 Leaves of various colours There are some plants which do not have chlorophyll. They cannot synthesise You often see slimy, green patches food. How do they survive and from in ponds or stagnant water bodies. These where do they derive nutrition? Like are generally formed by the growth of humans and animals such plants organisms called algae. Can you guess depend on the food produced by other why algae are green in colour? They plants. They use the heterotrophic contain chlorophyll which gives them mode of nutrition. Look at Fig. 1.5. Do the green colour. Algae can also prepare you see a yellow wiry branched structure their own food by photosynthesis. twining around the stem and branches of a tree? This is a plant called Cuscuta Synthesis of plant food other (Amarbel). It does not have chlorophyll. than carbohydrates It takes readymade food from the plant You have just learnt that plants on which it is climbing. The plant on synthesise carbohydrates through the which it climbs is called the host. Since process of photosynthesis. The it deprives the host of valuable nutrients, 4 SCIENCE 2018-19  the pitcher. Inside the pitcher there are hair which entangle the trapped insect. The lid closes and the insect is trapped. The insect is killed by the juices secreted in the pitcher and its nutrients are absorbed. Such insect-eating plants are called insectivorous plants. Is it possible that such plants do not get all the required nutrients from the soil in which they grow? Boojho is confused. If the Fig. 1.5 Cuscuta (Amarbel) on host plant pitcher plant is green and carries out photosynthesis, then Cuscuta is called the parasite. Are we why does it feed on insects? and other animals also a kind of parasites? You should think about it and discuss with your teacher. Lid Paheli wants to know whether mosquitoes, bed bugs, lice and leeches that suck our blood are also parasites. Have you seen or heard of plants that can eat animals? There are a few plants Leaf modified which can trap insects and digest them. into pitcher Is it not amazing? Such plants may be green or of some other colour. Look at Fig. 1.6 Pitcher plant showing lid and pitcher the plant in Fig. 1.6. The pitcher-like or jug-like structure is the modified part 1.4 SAPROTROPHS of leaf. The apex of the leaf forms a lid You might have seen packets of which can open and close the mouth of mushrooms sold in the vegetable NUTRITION IN PLANTS 5 2018-19 market. You may have also seen fluffy umbrella-like patches growing in moist soils or on rotting wood during the rainy season (Fig. 1.7). Let us find out what type of nutrients they need to survive and from where they get them. Fig. 1.8 Fungi growing on bread These organisms are called fungi. They have a different mode of nutrition. They absorb the nutrients from the Fig. 1.7 Packet of mushrooms, a mushroom bread. This mode of nutrition in which growing on decayed material organisms take in nutrients from dead and decaying matter is called saprotrophic nutrition. Such organisms with saprotrophic mode of nutrition are Boojho wants to know how called saprotrophs. these organisms acquire Fungi also grow on pickles, leather, nutrients. They do not have clothes and other articles that are left mouths like animals do. They are in hot and humid weather for long time. not like green plants as they lack During the rainy season they spoil many chlorophyll and cannot make food things. Ask your parents about the by photosynthesis. menace of fungi in your house. The fungal spores are generally present in the air. When they land on Activity 1.2 Take a piece of bread and moisten it with water. Leave it in a moist warm place Paheli is keen to know for 2–3 days or until fluffy patches whether her beautiful shoes, appear on them (Fig. 1.8). What is the which she wore on special colour of these patches? Observe the occasions, were spoiled by fungi patches under a microscope or a during the rainy season. She magnifying glass. Write down your wants to know how fungi appear observations in the notebook. You will suddenly during the rainy see cotton-like threads spread on the season. piece of bread. 6 SCIENCE 2018-19  1.5 HOW NUTRIENTS ARE REPLENISHED IN THE SOIL Have you seen farmers spreading Boojho says once his manure or fertilisers in the fields, or grandfather told him that his gardeners using them in lawns or in wheat fields were spoiled by a pots? Do you know why this is done? fungus. He wants to know if You learnt that plants absorb fungi cause diseases also. minerals and nutrients from the soil. Paheli told him that many fungi So, their amounts in the soil keep on like yeast and mushrooms are declining. Fertilisers and manures useful, but some fungi contain nutrients such as nitrogen, cause diseases in plants, potassium, phosphorous, etc. These animals including nutrients need to be added from time to humans. Some time to enrich the soil. We can grow fungi are also plants and keep them healthy if we can used as medicines. fulfil the nutrient requirement of plants. Usually crop plants absorb a lot of nitrogen and the soil becomes deficient wet and warm things they germinate and in nitrogen. You learnt that though grow. Now, can you figure out how we nitrogen gas is available in plenty in the can protect our things from getting air, plants cannot use it in the manner spoiled? they can use carbon dioxide. They need Some organisms live together and nitrogen in a soluble form. Hence, share both shelter and nutrients. This addition of fertilisers and manures relationship is called symbiosis. For enriches the soil. The bacterium called example, certain fungi live inside the Rhizobium can take atmospheric roots of plants. The plants provide nitrogen and convert it into a usable nutrients to the fungus and, in return, form. But Rhizobium cannot make its the fungus provides water and certain own food. So it often lives in the roots of nutrients. gram, peas, moong, beans and other In organisms called lichens, a legumes and provides them with chlorophyll-containing partner, which is nitrogen. In return, the plants provide an alga, and a fungus live together. The food and shelter to the bacteria. They, fungus provides shelter, water and thus, have a symbiotic relationship. This minerals to the alga and, in return, the association is of great significance for the alga prepares and provides food to the farmers. They can reduce the use of fungus. nitrogenous fertiliser where leguminous NUTRITION IN PLANTS 7 2018-19 plants are grown. Most of the pulses (dals) from other organisms. All animals are are obtained from leguminous plants. categorised as heterotrophs since In this chapter you learnt that they depend on plants and other most of the plants are autotrophs. animals for food. Can we say that Only a few plants are parasitic or the insectivorous plants are partial saprotrophic. They derive nutrition heterotrophs? Keywords Autotrophic Insectivorous Photosynthesis Chlorophyll Nutrient Saprotrophs Heterotrophs Nutrition Saprotrophic Host Parasite Stomata What you have learnt All organisms need food and utilise it to get energy for growth and maintenance of their body. Green plants synthesise food for themselves by the process of photosynthesis. They are autotrophs. Plants like Cuscuta are parasites. They take food from the host plant. Plants use simple chemical substances like carbon dioxide, water and minerals for the synthesis of food. Chlorophyll, water, carbon dioxide and sunlight are the essential requirements for photosynthesis. Complex chemical substances such as carbohydrates are the products of photosynthesis. Solar energy is absorbed by the chlorophylls present in leaves/plants. Oxygen is produced during photosynthesis. Oxygen released in photosynthesis is utilised by living organisms for their survival. Many fungi derive nutrition from dead and decaying matter. They are saprotrophs. A few plants and all animals are dependent on others for their nutrition and are called heterotrophs. 8 SCIENCE 2018-19  Exercise 1. Why do organisms take food? 2. Distinguish between a parasite and a saprotroph. 3. How would you test the presence of starch in leaves? 4. Give a brief description of the process of synthesis of food in green plants. 5. Show with the help of a sketch that plants are the ultimate source of food. 6. Fill in the blanks: (a) Green plants are called _________________ since they synthesise their own food. (b) The food synthesised by plants is stored as _________________. (c) In photosynthesis solar energy is absorbed by the pigment called ___________. (d) During photosynthesis plants take in ______________________ and release __________________ gas. 7. Name the following: (i) A parasitic plant with yellow, slender and branched stem. (ii) A plant that is partially autotrophic. (iii) The pores through which leaves exchange gases. 8. Tick the correct answer: (a) Cuscuta is an example of: (i) autotroph (ii) parasite (iii) saprotroph (iv) host (b) The plant which traps and feeds on insects is: (i) Cuscuta (ii) china rose (iv) pitcher plant (iv) rose 9. Match the items given in Column I with those in Column II: Column I Column II Chlorophyll Rhizobium Nitrogen Heterotrophs Cuscuta Pitcher plant Animals Leaf Insects Parasite 10. Mark ‘T’ if the statement is true and ‘F’ if it is false: (i) Carbon dioxide is released during photosynthesis. (T/F) (ii) Plants which synthesise their food are called saprotrophs. (T/F) NUTRITION IN PLANTS 9 2018-19  (iii) The product of photosynthesis is not a protein. (T/F) (iv) Solar energy is converted into chemical energy during photosynthesis. (T/F) 11. Choose the correct option from the following: Which part of the plant takes in carbon dioxide from the air for photosynthesis? (i) Root hair (ii) Stomata (iii) Leaf veins (iv) Petals 12. Choose the correct option from the following: Plants take carbon dioxide from the atmosphere mainly through their: (i) roots (ii) stem (iii) flowers (iv) leaves 13. Why do farmers grow many fruits and vegetable crops inside large green houses? What are the advantages to the farmers? Extended Learning — Activities and Projects 1. Project Take a potted plant with broad leaves. Take two strips of black paper and cut out a small square in the centres. Cover a part of two leaves with these papers and secure them with paper clips (Fig. 1.9). Keep the plant in sunlight for 2–5 days. Observe the difference in the colour of the covered and the uncovered portions on the leaf. Perform iodine test on this leaf. Did Fig. 1.9 Experiment to test the the two parts show different occurrence of photosynthesis results? Now take second leaf. Remove the strip and expose the covered part to the sunlight for 2–3 days and do the iodine test again. Describe your observations. 2. Visit a green house if there is one near your place. Observe how they grow plants. Find out how they regulate the amount of light, water and carbon dioxide to grow the plants. 3. Try growing a sweet potato just in water. Describe your experiment and observations. You can read more on the following website: www.phschool.com/science/biology_place/biocoach/photosynth/ overview.htm Did you know? Light is so important to plants that their leaves grow in many patterns so as to absorb maximum sunlight. 10 SCIENCE 2018-19  2 Nutrition in Animals Y ou have learnt in Chapter 1 that food into simpler substances is called plants can prepare their own food digestion. by the process of photosynthesis 2.1 DIFFERENT WAYS OF TAKING FOOD but animals cannot. Animals get their The mode of taking food into the body food from plants, either directly by varies in different organisms. Bees and eating plants or indirectly by eating humming-birds suck the nectar of animals that eat plants. Some animals plants, infants of human and many eat both plants and animals. Recall that other animals feed on mother’s milk. all organisms including humans require Snakes like the python swallow the food for growth, repair and functioning animals they prey upon. Some aquatic of the body. Animal nutrition includes animals filter tiny food particles floating nutrient requirement, mode of intake nearby and feed upon them. of food and its utilisation in the body. You have studied in Class VI that food Activity 2.1 consists of many components. Try to What is the type of food and mode of recall and list them below: feeding of the following animals? Write 1. ______________________ down your observations in the given 2. ______________________ Table. You may find the list of modes of feeding given below the Table helpful. 3. ______________________ Table 2.1 Various modes of feeding 4. ______________________ 5. ______________________ Name of Kind of Mode of animal food feeding 6. ______________________ Snail The components of food such as Ant carbohydrates are complex substances. Eagle These complex substances cannot be Humming-bird utilised as such. So they are broken Lice down into simpler substances. The Mosquito breakdown of complex components of Butterfly House fly (Scraping, chewing, siphoning, capturing Complex substance Simpler substances and swallowing, sponging, sucking etc.) 2018-19  Amazing fact of the stomach and the small intestine, and the various glands associated with the Starfish feeds on animals covered by canal such as salivary glands, the liver hard shells of calcium carbonate. and the pancreas secrete digestive juices. After opening the shell, the starfish The digestive juices convert complex 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. Buccal cavity Salivary gland Oesophagus Liver Fig. 2.1 Starfish Stomach Gall bladder 2.2 DIGESTION IN HUMANS Pancreas We take in food through the mouth, Small digest and utilise it. The unused parts intestine of the food are defecated. Have you ever Large wondered what happens to the food intestine inside the body? The food passes Rectum through a continuous canal (Fig. 2.2) Anus which begins at the buccal cavity and Fig. 2.2 Human digestive system ends at the anus. The canal can be divided into various compartments: substances of food into simpler ones. The (1) the buccal cavity, (2) foodpipe or digestive tract and the associated glands oesophagus, (3) stomach, (4) small together constitute the digestive system. intestine, (5) large intestine ending in Now, let us know what happens to the rectum and (6) the anus. Is it not a the food in different parts of the digestive very long path? These parts together tract. form the alimentary canal (digestive tract). The food components gradually The mouth and buccal cavity get digested as food travels through the Food is taken into the body through the various compartments. The inner walls mouth. The process of taking food into 12 SCIENCE 2018-19  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. Molar Boojho is fascinated by the Premolar highly coiled small intestine seen in Fig. 2.2. He wants to know its length. Would you like to make a Canine wild guess? We have given its approximate length on page 16. Just imagine how such a long Incisor structure is accommodated in a small space within our body! the body is called ingestion. We chew Fig. 2.3 Arrangement of teeth and different the food with the teeth and break it type of teeth down mechanically into small pieces. Each tooth is rooted in a separate socket which ones for piercing and tearing? in the gums (Fig. 2.3). Our teeth vary in Also find out the ones that are used for appearance and perform different chewing and grinding? functions. Accordingly they are given Record your observations in Table 2.2 different names (Fig. 2.3). Table 2.2 Activity 2.2 Type of teeth Number of teeth Total Wash your hands. Look into the Lower jaw Upper jaw mirror and count your teeth. Use Cutting and your index finger to feel the teeth. biting teeth How many kinds of teeth could you Piercing and find? Take a piece of an apple or tearing teeth bread and eat it. Which teeth do Chewing and you use for biting and cutting, and grinding teeth NUTRITION IN ANIMALS 13 2018-19  Our mouth has the salivary glands of boiled rice; in test tube ‘B’ keep one which secrete saliva. Do you know the teaspoonful of boiled rice after chewing action of saliva on food? Let us find out. it for 3 to 5 minutes. Add 3–4 mL of Activity 2.3 water in both the test tubes (Fig. 2.4). Now pour 2–3 drops of iodine solution Take two test tubes. Label them ‘A’ and in each test tube and observe. Why is ‘B’. In test tube ‘A’ put one teaspoonful 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 Iodine solution you know the functions of the tongue? We use our tongue for talking. Besides, Water it mixes saliva with the food during Boiled rice chewing and helps in swallowing food. We also taste food with our tongue. It Boiled and chewed rice A B has taste buds that detect different Fig. 2.4 Effect of saliva on starch tastes of food. We can find out the 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, (a) 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 (b) 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 (c) 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. (d) Fig. 2.5 Gradual decay of tooth 14 SCIENCE 2018-19  Sometimes when you eat in a hurry, talk or laugh while eating, you may cough, get hiccups or a choking sensation. This happens when food particles enter the windpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacent to the foodpipe. But inside the throat, air and food share a common passage. Then how is food prevented from entering the windpipe? During the act of swallowing a flap-like valve closes the passage of the windpipe and guides the food into the foodpipe. If, by chance, food particles enter the windpipe, we feel choked, get hiccups or cough. 5. Now write down your observations and label Fig. 2.6. Repeat this activity with other classmates. Fig. 2.6 Regions of the The foodpipe/oesophagus tongue for different tastes The swallowed food passes into the foodpipe or oesophagus. Look at Fig. 2.2. The foodpipe runs along the neck position of taste buds by the following activity. Paheli wants to know how Activity 2.4 food moves in the opposite direction during vomiting. 1. Prepare a separate sample each of (i) sugar solution, (ii) common salt solution, (iii) lemon juice and (iv) juice of crushed neem leaf or bitter gourd. Food 2. Blindfold one of your classmates and ask her/him to take out the tongue and keep it in straight and flat position. Oesophagus 3. Use a clean toothpick to put the above samples one by one on different areas of the tongue as shown in Fig. 2.6. Use a new Stomach toothpick for each sample. 4. Ask the classmate which areas of the tongue could detect the sweet, salty, Fig. 2.7 Movement of the food in the oesophagus sour and bitter substances. of the alimentary canal NUTRITION IN ANIMALS 15 2018-19 and the chest. Food is pushed down by food and makes the medium in the movement of the wall of the foodpipe. stomach acidic and helps the digestive Actually this movement takes place juices to act. The digestive juices break throughout the alimentary canal and down the proteins into simpler pushes the food downwards (Fig. 2.7). substances. At times the food is not accepted by our The small intestine stomach and is vomited out. Recall the instances when you vomited after eating The small intestine is highly coiled and and think of the reason for it. Discuss is about 7.5 metres long. It receives with your parents and teacher. secretions from the liver and the pancreas. Besides, its wall also secretes juices. The stomach The liver is a reddish brown gland The stomach is a thick-walled bag. Its situated in the upper part of the shape is like a flattened J and it is the abdomen on the right side. It is the widest part of the alimentary canal. It largest gland in the body. It secretes bile receives food from the food pipe at one juice that is stored in a sac called the end and opens into the small intestine gall bladder (Fig. 2.2). The bile plays at the other. an important role in the digestion of fats. The inner lining of the stomach The pancreas is a large cream secretes mucous, hydrochloric acid and coloured gland located just below the digestive juices. The mucous protects stomach (Fig. 2.2). The pancreatic juice the lining of the stomach. The acid kills acts on carbohydrates, fats and proteins many bacteria that enter along with the and changes them into simpler forms. The working of the stomach was discovered by a strange accident. In 1822, a man named Alexis St. Martin was badly hit by a shot gun. The bullet had seriously damaged the chest wall and made a hole in his stomach. He was brought to an American army doctor William Beaumont. The doctor saved the patient but he could not close the hole properly and left it bandaged (Fig. 2.8). Beaumont took it as a great opportunity to see the inside of the stomach through the hole. He made some wonderful observations. Beaumont found that the stomach was churning Fig. 2.8 Alexis St. Martin’s shotgun wound food. Its wall secreted a fluid which could digest the food. He also observed that the end of the stomach opens into the intestine only after the digestion of the food inside the stomach is completed. 16 SCIENCE 2018-19 The partly digested food now reaches the proteins required by the body. This is lower part of the small intestine where called assimilation. In the cells, glucose the intestinal juice completes the breaks down with the help of oxygen digestion of all components of the food. into carbon dioxide and water, and The carbohydrates get broken into energy is released. The food that simple sugars such as glucose, fats into remains undigested and unabsorbed fatty acids and glycerol, and proteins enters into the large intestine. into amino acids. Large intestine Absorption in the small The large intestine is wider and shorter intestine than small intestine. It is about 1.5 metre The digested food can now pass into the in length. Its function is to absorb water blood vessels in the wall of the intestine. and some salts from the undigested food This process is called absorption. The material. The remaining waste passes inner walls of the small intestine have into the rectum and remains there as thousands of finger-like outgrowths. semi-solid faeces. The faecal matter is These are called villi (singular villus). removed through the anus from Can you guess what the role of villi could time-to-time. This is called egestion. be in the intestine? The villi increase the surface area for absorption of the 2.3 DIGESTION IN GRASS-EATING digested food. Each villus has a network ANIMALS of thin and small blood vessels close to Have you observed cows, buffaloes its surface. The surface of the villi and other grass-eating animals absorbs the digested food materials. The chewing continuously even when absorbed substances are transported they are not eating? Actually, they via the blood vessels to different organs quickly swallow the grass and store of the body where they are used to build it in a part of the stomach called complex substances such as the rumen (Fig. 2.9). Here the food gets Diarrhoea Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhoea. It may be caused by an infection, food poisoning or indigestion. It is very common in India, particularly among children. Under severe conditions it can be fatal. This is because of the excessive loss of water and salts from the body. Diarrhoea should not be neglected. Even before a doctor is consulted the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS). NUTRITION IN ANIMALS 17 2018-19  helps in digestion of cellulose. Many animals, including humans, cannot Paheli wants to know why digest cellulose. these animals cannot chew Animals like horses, rabbit, etc., have food properly at the time they a large sac-like structure called Caecum take it in? between the oesophagus and the small intestine (Fig. 2.9). The cellulose of the food is digested here by the action of certain bacteria which are not present in Boojho wants to know why humans. we cannot digest cellulose So far you have learnt about animals like the cattle do. which possess the digestive system. But there are many small organisms which do not have a mouth and a digestive system. Then, how do they acquire and digest partially digested and is called cud. food? In the section below you will learn But later the cud returns to the mouth another interesting way of food intake. in small lumps and the animal chews it. This process is called rumination and 2.4 FEEDING AND DIGESTION IN these animals are called ruminants. AMOEBA The grass is rich in cellulose, a type Amoeba is a microscopic single-celled of carbohydrate. In ruminants like cattle, organism found in pond water. Amoeba deer, etc., bacteria present in rumen has a cell membrane, a rounded, dense nucleus and many small bubble-like Small Intestine Oesophagus vacuoles (Fig. 2.10) in its cytoplasm. Rumen Amoeba constantly changes its shape and position. It pushes out one, or more finger-like projections, called pseudopodia or false feet for movement and capture of food. Nucleus Pseudopodium Food particle (ingestion) Food vacuole Stomach Large Intestine Caecum Egested waste Fig. 2.9 Digestive system of ruminant Fig. 2.10 Amoeba 18 SCIENCE 2018-19  Amoeba feeds on some microscopic The absorbed substances are used for organisms. When it senses food, it growth, maintenance and multiplication. pushes out pseudopodia around the The undigested residue of the food is food particle and engulfs it. The food expelled outside by the vacuole. becomes trapped in a food vacuole The basic process of digestion of [Fig. 2.10). food and release of energy is the same Digestive juices are secreted into the in all animals. In a later chapter you food vacuole. They act on the food and will learn about the transport of food break it down into simpler substances. absorbed by the intestine to the various Gradually the digested food is absorbed. parts of the body. Keywords Absorption Fatty acid Oesophagus Amino acid Food vacuole Pancreas Amoeba Gall bladder Premolar Assimilation Glycerol Pseudopodia Bile Incisor Rumen Buccal cavity Ingestion Ruminant Canine Liver Rumination Cellulose Milk teeth Salivary glands Digestion Molar Villi Egestion Permanent teeth Saliva What you have learnt Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body. The human digestive system consists of the alimentary canal and secretory glands. It consists of the (i) buccal cavity, (ii) oesophagus, (iii) stomach, (iv) small intestine, (v) large intestine ending in rectum and (vi) anus. The main digestive glands which secrete digestive juices are (i) the salivary glands, (ii) the liver and (iii) the pancreas. The stomach wall and the wall of the small intestine also secrete digestive juices. The modes of feeding vary in different organisms. Nutrition is a complex process involving: (i) ingestion, (ii) digestion, (iii) absorption, (iv) assimilation and (v) egestion. NUTRITION IN ANIMALS 19 2018-19  Digestion of carbohydrates, like starch, begins in the buccal cavity. The digestion of protein starts in the stomach. The bile secreted from the liver, the pancreatic juice from the pancreas and the digestive juice from the intestinal wall complete the digestion of all components of food in the small intestine. The digested food is absorbed in the blood vessels from the small intestine. The absorbed substances are transported to different parts of the body. Water and some salts are absorbed from the undigested food in the large intestine. The undigested and unabsorbed residues are expelled out of the body as faeces through the anus. The grazing animals like cows, buffaloes and deer are known as ruminants. They quickly ingest, swallow their leafy food and store it in the rumen. Later, the food returns to the mouth and the animal chews it peacefully. Amoeba ingests its food with the help of its false feet or pseudopodia. The food is digested in the food vacuole. Exercises 1. Fill in the blanks: (a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________. (b) The largest gland in the human body is __________. (c) The stomach releases hydrochloric acid and ___________ juices which act on food. (d) The inner wall of the small intestine has many finger-like outgrowths called _________. (e) Amoeba digests its food in the ____________. 2. Mark ‘T’ if the statement is true and ‘F’ if it is false: (a) Digestion of starch starts in the stomach. (T/F) (b) The tongue helps in mixing food with saliva. (T/F) (c) The gall bladder temporarily stores bile. (T/F) (d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F) 3. Tick () mark the correct answer in each of the following: (a) Fat is completely digested in the (i) stomach (ii) mouth (iii) small intestine (iv) large intestine 20 SCIENCE 2018-19  (b) Water from the undigested food is absorbed mainly in the (i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine 4. Match the items of Column I with those given in Column II: Column I Column II Food components Product(s) of digestion Carbohydrates Fatty acids and glycerol Proteins Sugar Fats Amino acids 5. What are villi? What is their location and function? 6. Where is the bile produced? Which component of the food does it help to digest? 7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also. 8. Why do we get instant energy from glucose? 9. Which part of the digestive canal is involved in: (i) absorption of food ________________. (ii) chewing of food ________________. (iii) killing of bacteria ________________. (iv) complete digestion of food ________________. (v) formation of faeces ________________. 10. Write one similarity and one difference between the nutrition in amoeba and human beings. 11. Match the items of Column I with suitable items in Column II Column I Column II (a) Salivary gland (i) Bile juice secretion (b) Stomach (ii) Storage of undigested food (c) Liver (iii) Saliva secretion (d) Rectum (iv) Acid release (e) Small intestine (v) Digestion is completed (f ) Large intestine (vi) Absorption of water (vii) Release of faeces NUTRITION IN ANIMALS 21 2018-19  12. Label Fig. 2.11 of the digestive system. Fig. 2.11 A part of human digestive system 13. Can we survive only on raw, leafy vegetables/grass? Discuss. Extended Learning — Activities and Project 1. Visit a doctor and find out: (i) Under what conditions does a patient need to be on a drip of glucose? (ii) Till when does a patient need to be given glucose? (iii) How does glucose help the patient recover? Write the answers in your notebook. 2. Find out what vitamins are and get the following information. (i) Why are vitamins necessary in the diet? (ii) Which fruits or vegetables should be eaten regularly to get vitamins? Write a one-page note on the information collected by you. You may take help of a doctor, a dietician, your teacher or any other person, or from any other source. 22 SCIENCE 2018-19  3. Collect data from your friends, neighbours and classmates to know more about “milk teeth”. Tabulate your data. One way of doing it is given below: S. No. Age at which Age at which No. of teeth No. of teeth first tooth fell last tooth fell lost replaced 1. 2. 3. 4. 5. Find out from at least twenty children and find the average age at which children lose the milk teeth. You may take help of your friends. Did you know? Fats in goat’s milk are much simpler than those in cow’s milk. Therefore, the goat’s milk is much easier to digest than the cow’s milk. NUTRITION IN ANIMALS 23 2018-19  3 Fibre to Fabric I n Class VI you have learnt about Like us, the hairy skin of the sheep some fibres obtained from plants. has two types of fibres that form its You also learnt that wool and silk fleece: (i) the coarse beard hair, and fibres are obtained from animals. Wool (ii) the fine soft under-hair close to the is obtained from the fleece (hair) of skin. The fine hair provide the fibres for sheep or yak. Silk fibres come from making wool. Some breeds of sheep cocoons of the silk moth. Do you know possess only fine under-hair. Their which part of the sheep’s body yields parents are specially chosen to give birth fibres? Are you aware how these fibres to sheep which have only soft under- are converted into the woollen yarn that hair. This process of selecting parents we buy from the market to knit sweaters? for obtaining special characters in their Do you have any idea how silk fibres are offspring, such as soft under hair in made into silk, which is woven into saris? sheep, is termed ‘selective breeding’. In this Chapter we shall try to find answers to these questions. Animal fibres — wool and silk 3.1 WOOL Wool comes from sheep, goat, yak and some other animals. These wool-yielding animals bear hair on their body. Do you know why these animals have a thick coat of hair? Hair trap a lot of air. Air is a poor conductor of heat, as you would learn in Chapter 4. So, hair keeps these animals warm. Wool is derived from Fig. 3.1 Sheep with thick growth of hair these hairy fibres. Animals that yield wool Activity 3.1 Several breeds of sheep are found in Feel the hair on your body and arms different parts of our country (Table 3.1). and those on your head. Do you find However, the fleece of sheep is not the any difference? Which one seems coarse only source of wool, though wool and which one is soft? commonly available in the market is 24 SCIENCE 2018-19 sheep wool (Fig. 3.1). Yak (Fig. 3.2) wool Activity 3.3 is common in Tibet and Ladakh. Mohair Procure outline maps of India and the is obtained from angora goats, (Fig. 3.3) world. Find out and mark the places on found in hilly regions such as Jammu the map where you find animals that and Kashmir. provide wool. Use different colours to Wool is also obtained from goat hair denote the location for different wool (Fig. 3.4). The under fur of Kashmiri yielding animals. goat is soft. It is woven into fine shawls called Pashmina shawls. The fur (hair) on the body of camels is also used as wool (Fig. 3.5). Llama and Alpaca, found in South America, also yield wool (Fig. 3.6 and 3.7). Activity 3.2 Collect pictures of animals whose hair Fig. 3.3 Angora goat Fig. 3.4 Goat is used as wool. Stick them in your scrap book. If you are unable to get pictures, try and draw them from the ones given in this book. Find out words for sheep, goat, camel and yak in your local language and also in other languages of our country. Fig. 3.5 Camel Fig. 3.2 Yak Fig. 3.6 Llama Fig. 3.7 Alpaca FIBRE TO FABRIC 25 2018-19 From fibres to wool mentioned earlier, these sheep are For obtaining wool, sheep are reared. “selectively bred” with one parent being Their hair is cut and processed into a sheep of good breed. wool. Let us learn about this process. Once the reared sheep have developed a thick growth of hair, hair is Rearing and breeding of sheep: If you shaved off for getting wool. travel to the hills in Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Processing fibres into wool Arunachal Pradesh and Sikkim, or the The wool which is used for knitting plains of Haryana, Punjab, Rajasthan sweaters or for weaving shawls is the and Gujarat, you can see shepherds finished product of a long process, taking their herds of sheep for grazing. which involves the following steps: Sheep are herbivores and prefer grass and leaves. Apart from grazing sheep, Step I: The fleece of the sheep along with a rearers also feed them on a mixture of thin layer of skin is removed from its pulses, corn, jowar, oil cakes (material body [Fig. 3.8 (a)]. This process is called left after taking out oil from seeds) and shearing. Machines similar to those used minerals. In winter, sheep are kept by barbers are used to shave off hair. indoors and fed on leaves, grain and dry Usually, hair are removed during the hot fodder. weather. This enables sheep to survive Sheep are reared in many parts of without their protective coat of hair. The our country for wool. Table 3.1 gives the hair provide woollen fibres. Woollen names of some breeds of sheep reared fibres are then processed to obtain in our country for producing wool. The woollen yarn. Shearing does not hurt quality and texture of the fibres obtained the sheep just as it does not hurt when from them is also indicated in the table. you get a hair cut or your father shaves his Certain breeds of sheep have thick beard. Do you know why? The uppermost coat of hair on their body which yields layer of the skin is dead. Also, the hair of good quality wool in large quantities. As sheep grow again just as your hair does. Table 3.1 Some Indian breeds of sheep S.No. Name of breed Quality of wool State where found 1. Lohi Good quality wool Rajasthan, Punjab 2. Rampur bushair Brown fleece Uttar Pradesh,Himachal Pradesh 3. Nali Carpet wool Rajasthan, Haryana, Punjab 4. Bakharwal For woollen shawls Jammu and Kashmir 5. Marwari Coarse wool Gujarat 6. Patanwadi For hosiery Gujarat 26 SCIENCE 2018-19 Step II: The sheared skin with hair is sometimes appear on your sweaters. The thoroughly washed in tanks to remove fibres are scoured again and dried. This grease, dust and dirt. This is called is the wool ready to be drawn into fibres. scouring. Nowadays scouring is done Step V: The fibres can be dyed in various by machines [Fig. 3.8 (b) and (c)]. colours, as the natural fleece of sheep Step III: After scouring, sorting is done. and goats is black, brown or white. The hairy skin is sent to a factory where Step VI: The fibres are straightened, hair of different textures are separated combed and rolled into yarn or sorted. [Fig. 3.8 (d)]. The longer fibres are Step IV: The small fluffy fibres, called made into wool for sweaters and the burrs, are picked out from the hair. shorter fibres are spun and woven These are the same burrs which into woollen cloth. Fig. 3.8 (a) Shearing a sheep Fig. 3.8 (b) Scouring in tanks Fig. 3.8 (c) Scouring by machines Fig. 3.8 (d) Rolling into yarn The processing of fibre into wool can be represented as follows: Shearing → Scouring → Sorting → Cleaning of burrs ↓ Rolling ← Dyeing FIBRE TO FABRIC 27 2018-19  Occupational hazard your mother/aunt/grandmother the kind of silk saris they have. List the Wool industry is an important kinds of silk. means of livelihood for many people Before we discuss the process of in our country. But sorter’s job is obtaining silk, it is necessary to know the risky as sometimes they get infected interesting life history of the silk moth. by a bacterium, anthrax, which causes a fatal blood disease called Life history of silk moth sorter’s disease. Such risks faced by The female silk moth lays eggs, from workers in any industry are called which hatch larvae which are called occupational hazards. caterpillars or silkworms. They grow in size and when the caterpillar is ready to enter the next stage of its life history called pupa, it first weaves a net to hold Boojho is wondering why it itself. Then it swings its head from side hurts when someone pulls his to side in the form of the figure of eight (8). hair but not when he goes for a During these movements of the head, haircut. the caterpillar secretes fibre made of a Boojho is wondering why a cotton garment cannot keep us (a) Male (b) Female as warm in winter as a woollen Adult silk moths sweater does. Activity 3.4 Debate amongst your classmates (c) Eggs on mulberry leaves (d) Silkworm whether it is fair on the part of humans to rear sheep and then chop off their hair for getting wool. 3.2 SILK Silk fibres are also animal fibres. Silkworms spin the ‘silk fibres’. The (e) Cocoon (f) Cocoon with developing moth rearing of silkworms for obtaining silk is called sericulture. Find out from Fig. 3.9 (a to f ) Life history of silk moth 28 SCIENCE 2018-19 protein which hardens on exposure to Take help of your mother, aunt or air and becomes silk fibre. Soon the teacher and identify the types of silk caterpillar completely covers itself by such as mulberry silk, tassar silk, eri silk fibres and turns into pupa. This silk, mooga silk, etc. Compare the covering is known as cocoon. The further texture of these silks with that of the development of the pupa into moth artificial silk pieces, which contain continues inside the cocoon (Fig. 3.9). Silk synthetic fibres. Try and collect pictures fibres are used for weaving silk cloth. Can of different moths whose caterpillars you imagine that the soft silk yarn is as provide the various types of silk. strong as a comparable thread of steel! Activity 3.6 The silk yarn (thread) is obtained from the cocoon of the silk moth. There Take an artificial (synthetic) silk thread is a variety of silk moths which look very and a pure silk thread. Burn these different from one another and the silk threads carefully. Did you notice any yarn they yield is different in texture difference in the smell while burning? (coarse, smooth, shiny, etc.). Thus, Now, burn a woollen fibre carefully. tassar silk, mooga silk, kosa silk, etc., Did it smell like burning of artificial are obtained from cocoons spun by silk or that of pure silk? Can you different types of moths. The most explain why? common silk moth is the mulberry silk To remember when the cocoon stage moth. The silk fibre from the cocoon of is reached in the life history of the silk this moth is soft, lustrous and elastic moth, try the following activity. and can be dyed in beautiful colours. Activity 3.7 Sericulture or culture of silkworms Photocopy Fig. 3.9. Cut out pictures of is a very old occupation in India. India the stages of the life history of the silk produces plenty of silk on a commercial moth, and paste them on pieces of scale. cardboard or chart paper. Jumble Activity 3.5 them. Now try and arrange the stages in the correct sequence in a cyclic form. Collect pieces of silk cloth of various Whoever does it fastest wins. types and paste them in your scrap You may also describe the life history book. You can find them in a tailor’s in your own words. Write it down in your shop among the heap of waste cut pieces. scrap book. In India, women are significantly involved in various kinds of industries related to silk production. These are rearing of silkworms, reeling of silk from cocoons and processing of raw silk into fabrics. By their enterp