Biology Textbook for Class XI PDF

2024-25 11080 – BIOLOGY ISBN 81-7450-496-6 Textbook for Class XI First Edition February 2006 Phalguna 1927 ALL RIGHTS RESERVED Reprinted...

2024-25 11080 – BIOLOGY ISBN 81-7450-496-6 Textbook for Class XI First Edition February 2006 Phalguna 1927 ALL RIGHTS RESERVED Reprinted q No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, October 2006, November 2007, recording or otherwise without the prior permission of the publisher. January 2009, January 2010, q This book is sold subject to the condition that it shall not, by way of trade, be lent, re- January 2011, January 2012, sold, hired out or otherwise disposed of without the publisher’s consent, in any form of binding or cover other than that in which it is published. December 2012, December 2013, q The correct price of this publication is the price printed on this page, Any revised December 2014, May 2016, price indicated by a rubber stamp or by a sticker or by any other means is incorrect and should be unacceptable. March 2017, December 2017, January 2019, September 2019, February 2021, November 2021 OFFICES OF THE PUBLICATION Revised Edition DIVISION, NCERT November 2022 Kartika 1944 NCERT Campus Reprinted Sri Aurobindo Marg New Delhi 110 016 Phone : 011-26562708 March 2024 Chaitra 1946 108, 100 Feet Road Hosdakere Halli Extension Banashankari III Stage Bangaluru 560 085 Phone : 080-26725740 PD 270T SU Navjivan Trust Building P.O.Navjivan © National Council of Educational Ahmedabad 380 014 Phone : 079-27541446 Research and Training, 2006, 2022 CWC Campus Opp. Dhankal Bus Stop Panihati Kolkata 700 114 Phone : 033-25530454 CWC Complex Maligaon Guwahati 781 021 Phone : 0361-2674869 Publication Team ` 240.00 Head, Publication : Anup Kumar Rajput Division Chief Editor : Shveta Uppal Chief Production : Arun Chitkara Officer Chief Business : Amitabh Kumar Manager (In charge) Assistant Editor : Shashi Chadha Printed on 80 GSM paper with NCERT Assistant Production : Om Prakash watermark Officer Published at the Publication Division by the Secretary, National Council of Educational Cover and Layout Research and Training, Sri Aurobindo Marg, Shweta Rao New Delhi 110 016 and printed at Illustrations Raas T echnoprint, A-93, Sector -65, Lalit Maurya Noida-201 301 (UP) 2024-25 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, Professor K. Muralidhar, Department of Zoology, University of Delhi, Delhi for guiding the work of this committee. 2024-25 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, 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, NCERT welcomes comments and suggestions which will enable us to undertake further revision and refinement. Director New Delhi National Council of Educational 20 December 2005 Research and Training (iv) 2024-25 RATIONALISATION OF CONTENT IN THE TEXTBOOK In view of the COVID-19 pandemic, it is imperative to reduce content load on students. The National Education Policy 2020, also emphasises reducing the content load and providing opportunities for experiential learning with creative mindset. In this background, the NCERT has undertaken the exercise to rationalise the textbooks across all classes. Learning Outcomes already developed by the NCERT across classes have been taken into consideration in this exercise. Contents of the textbooks have been rationalised in view of the following: Overlapping with similar content included in other subject areas in the same class Similar content included in the lower or higher class in the same subject Difficulty level Content, which is easily accessible to students without much interventions from teachers and can be learned by children through self-learning or peer-learning Content, which is irrelevant in the present context This present edition, is a reformatted version after carrying out the changes given above. 2024-25 2024-25 TEXTBOOK D EVELOPMENT C OMMITTEE C HAIRPERSON, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee, Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune University, Pune CHIEF ADVISOR K. Muralidhar, Professor, Department of Zoology, University of Delhi, Delhi MEMBERS Ajit Kumar Kavathekar, Reader (Botany), Sri Venkateswara College, University of Delhi, Delhi B.B.P. Gupta, Professor, Department of Zoology, North-Eastern Hill University, Shillong C.V. Shimray, Lecturer, Department of Education in Science and Mathematics, NCERT Dinesh Kumar, Reader, Department of Education in Science and Mathematics, NCERT J.S. Gill, Professor, Department of Education in Science and Mathematics, NCERT K. Sarath Chandran, Reader (Zoology), Sri Venkateswara College, University of Delhi, Delhi Nalini Nigam, Reader (Botany), Ramjas College, University of Delhi, Delhi Pratima Gaur, Professor, Department of Zoology, University of Allahabad, Allahabad Ratnam Kaul Wattal, Reader (Botany), Zakir Hussain College, University of Delhi, Delhi R.K. Seth, UGC Scientist C, Department of Zoology, University of Delhi, Delhi R.P. Singh, Lecturer (Biology), Rajkiya Pratibha Vikas Vidyalaya, Kishan Ganj, Delhi Sangeeta Sharma, PGT (Biology), Kendriya Vidyalaya, JNU, New Delhi Savithri Singh, Principal, Acharya Narendra Dev College, University of Delhi; Former Fellow, Centre for Science Education and Communication, University of Delhi, Delhi S.C. Jain, Professor, Department of Education in Science and Mathematics, NCERT Sunaina Sharma, Lecturer (Biology), Rajkiya Pratibha Vikas Vidyalaya, Dwarka, New Delhi Tejinder Chawla, PGT (Biology), Guru Harkrishan Public School, Vasant Vihar, New Delhi T.N. Lakhanpal, Professor (Retd.), Department of Bio Sciences, Himachal Pradesh University, Shimla U.K. Nanda, Professor, Regional Institute of Education, Bhubaneshwar MEMBER-COORDINATOR B.K. Tripathi, Reader, Department of Education in Science and Mathematics, NCERT. 2024-25 A CKNOWLEDGEMENTS National Council of Educational Research and Training (NCERT) gratefully acknowledges the contribution of the individuals and organisations involved in the development of the Biology textbook for Class XI. The Council is grateful to Arvind Gupte, Principal (Retd.), Government Collegiate Education Services, Madhya Pradesh; Shailaja Hittalmani, Associate Professor (Genetics), University of Agricultural Sciences, Bangalore; K.R. Shivanna, Professor (Retd.), Department of Botany, University of Delhi, Delhi; R.S. Bedwal, Professor, Department of Zoology, University of Rajasthan, Jaipur; P.S. Srivastava, Professor, Department of Biotechnology, Hamdard University, New Delhi and Pramila Shivanna, former Teacher, D.A.V. School, Delhi, for their valuable suggestions. The Council is also thankful to V.K. Bhasin, Professor and Head, Department of Zoology, University of Delhi, Delhi; P.P. Bakre, Professor and Head, Department of Zoology, University of Rajasthan, Jaipur and Savithri Singh, Principal, Acharya Narendra Dev College, New Delhi for their support. The Council is also grateful to B.K. Gupta, Scientist, Central Zoo Authority, New Delhi for providing pictures of zoological parks and Sameer Singh for the pictures on the front and back cover. All the other photographs used in the book provided by Savithri Singh and taken at either at NCERT, IARI Campus or Acharya Narendra Dev College is gratefully acknowledged. NCERT sincerely acknowledges the contributions of the members who participated in the review of the manuscripts – M.K. Tiwari, PGT (Biology), Kendriya Vidyalaya, Mandsaur, Madhya Pradesh; Maria Gracias Fernandes, PGT (Biology), G.V.M.S. Higher Secondary, Ponda, Goa; A.K. Ganguly, PGT (Biology), Jawahar Navodaya Vidyalaya, Roshnabad, Haridwar; Shivani Goswami, PGT (Biology), The Mother’s International School, New Delhi and B.N. Pandey, Principal, Ordinance Factory Sr. Sec. School, Dehradun. The Council is highly thankful to M. Chandra, Professor and Head, DESM; Hukum Singh, Professor, DESM, NCERT for their valuable support throughout the making of this book. The contributions of V. V. Anand, Professor (Retd), Regional Institute of Education (RIE), Mysuru; A.K. Mohapatra, Professor, RIE, Bhubaneswar; Abhay Kumar, Assistant Professor, CIET, NCERT; G.V. Gopal, Professor, RIE, Mysuru; Ishwant Kaur, AHM, DMS, Ajmer; Sunita Farkya, Professor, DESM, NCERT; Pushplata Verma, Assistant Professor, DESM, NCERT; C. Padmaja, Professor, RIE, Mysuru and Jaydeep Mandal, Professor, RIE, Bhopal in the review of this textbook in 2017-18 are acknowledged. The Council also gratefully acknowledges the contribution of Deepak Kapoor, Incharge, Computer Station; Mohd. Khalid Raza and Arvind Sharma, DTP operators; Saswati Banerjee and Hari Darshan Lodhi, Copy Editor; Archana Srivastava, Proof Reader and APC office and administrative staff of DESM, NCERT. The efforts of the Publication Department, NCERT in bringing out this publication are also appreciated. 2024-25 A NOTE FOR THE TEACHERS AND S TUDENTS Biology is the science of life. It is the story of life on earth. It is the science of life forms and living processes. Biological systems, often appear to challenge physical laws that govern the behaviour of matter and energy in our world. Historically, biological knowledge was ancillary to knowledge of human body and its function. The latter as we know, is the basis of medical practice. However, parts of biological knowledge developed independent of human application. Fundamental questions about origin of life, the origin and growth of biodiversity, the evolution of flora and fauna of different habitats, etc., caught the imagination of biologists. The very description of living organisms, be it from morphological perspective, physiological perspective, taxonomical perspective, etc., engaged scientists to such an extent that for sheer convenience, if not for anything else, the subject matter got artificially divided into the sub- disciplines of botany and zoology and later into even microbiology. Meanwhile, physical sciences made heavy inroads into biology, and established biochemistry and biophysics as new sub- disciplines of biology. Mendel’s work and its rediscovery in the early twentieth century led to the promotion of study of genetics. The discovery of the double-helical structure of DNA and the deciphering of three dimensional structures of many macromolecules led to the establishment of and phenomenal growth in the dominating area of molecular biology. In a sense, functional disciplines laying emphasis on mechanisms underlying living processes, received more attention, support, intellectual and social recognition. Biology, unfortunately, got divided into classical and modern biology. To the majority of practising biologists, pursuit of biological research became more empirical rather than a curiosity and hypothesis driven intellectual exercise as is the case with theoretical physics, experimental physics, structural chemistry and material science. Fortunately and quietly, general unifying principles of biology were also being discovered, rediscovered and emphasised. The work of Mayr, Dobhzhansky, Haldane, Perutz, Khorana, Morgan, Darlington, Fisher and many others brought respect and seriousness to both classical and molecular biological disciplines. Ecology and Systems biology got established as unifying biological disciplines. Every area of biology began developing interface with not only other areas of biology but also other disciplines of science and mathematics. Pretty soon, the boundaries became porous. They are now on the verge of disappearing altogether. Progress in human biology, biomedical sciences, especially the structure, functioning and evolution of human brain brought in respect, awe and philosophical insights to biology. Biology even stepped out of laboratories, museums and natural parks and raised social, economic and cultural issues capturing the imagination of general public and hence political attention. Educationists did not lag behind and realised that biology should be taught as an interdisciplinary and integrating science at all stages of educational training especially at school and undergraduate levels. A new synthesis of all areas of basic and applied areas of biology is the need of the hour. Biology has come of age. It has an independent set of concepts which are universal just like physics and chemistry and mathematics. The present volume is the first time presentation of the integrated biology for the school level children. One of the lacunae in biology teaching and study is the absence of integration 2024-25 with other disciplinary knowledge of physics, chemistry etc. Further many processes in plants, animals and microbes are similar when looked from physico-chemical perspective. Cell biology has brought out the unifying common cellular level activities underlying apparently diverse phenomena across plants, animals and microbes. Similarly, molecular science (e.g. biochemistry or molecular biology) has revealed the similar molecular mechanisms in all these apparently diverse organisms like plants, animals and microbes. Phenomena like respiration, metabolism, energy utlisation, growth, reproduction and development can be discussed in a unifying manner rather than as separate unrelated processes in plants and animals. An attempt has been made to unify such diverse disciplines in the book. The integration achieved however, is partial and not complete. Hopefully along with changes in the teaching and learning context, to be brought out in the next few years, the next edition of this book will reveal more integration of botany, zoology and microbiology and truly reflect the true nature of biology – the future science of man by man and for man. This new textbook of Biology for class XI is a completely rewritten book in view of the syllabus revision and restructuring. It is also in accordance with the spirit of the National Curriculum Framework (2005) guidelines. The subject matter is presented under twenty-two chapters which are grouped under five thematic units. Each unit has a brief write up preceding the unit highlighting the essence of the chapters to follow under that unit. Each unit also has a biographical sketch of a prominent scientist in that area. Each chapter has, on the first page, a detailed table of contents giving sub-headings within the chapter. Decimal system using arabic numerals has been employed to indicate these sub-headings. At the end of each chapter a brief summary is provided. This brings to the notice of the student, what she/he is supposed to have learnt by studying the chapter. A set of questions is also provided at the conclusion of each chapter. These questions are essentially to enable the student to test herself/himself as to how much she/he has understood the subject matter. There are questions which are purely of information recall type; there are questions which need analytical thinking to answer and hence test true understanding; there are questions which are problems to solve and finally there are questions which need analysis and speculation as there is no one to answer to such questions. This tests the critical understanding of the subject matter in the mind of the student. Special emphasis has been given on the narrative style, illustrations, activity exercises, clarity of expression, coverage of topics within the available time in school. A large number of extremely talented and dedicated people including practising teachers helped in bringing out this beautiful book. Our main purpose was to make sure that school level biology is not a burden for students and teachers. We sincerely wish that teaching biology and learning biology would become an enjoyable activity. PROFESSOR K. Muralidhar Department of Zoology University of Delhi (x) 2024-25 C ONTENTS FOREWORD iii RATIONALISATION OF CONTENT IN THE TEXTBOOK V A NOTE FOR THE TEACHERS AND STUDENTS ix U NIT I D IVERSITY IN THE LIVING WORLD 1-54 Chapter 1 : The Living World 3 Chapter 2 : Biological Classification 10 Chapter 3 : Plant Kingdom 23 Chapter 4 : Animal Kingdom 37 U NIT II S TRUCTURAL ORGANISATION IN PLANTS AND ANIMALS 55-84 Chapter 5 : Morphology of Flowering Plants 57 Chapter 6 : Anatomy of Flowering Plants 71 Chapter 7 : Structural Organisation in Animals 79 U NIT III C ELL : STRUCTURE AND FUNCTIONS 85-130 Chapter 8 : Cell : The Unit of Life 87 Chapter 9 : Biomolecules 104 Chapter 10 : Cell Cycle and Cell Division 120 2024-25 U NIT IV PLANT PHYSIOLOGY 131-180 Chapter 11 : Photosynthesis in Higher Plants 133 Chapter 12 : Respiration in Plants 153 Chapter 13 : Plant Growth and Development 166 U NIT V HUMAN PHYSIOLOGY 181-250 Chapter 14 : Breathing and Exchange of Gases 183 Chapter 15 : Body Fluids and Circulation 193 Chapter 16 : Excretory Products and their Elimination 205 Chapter 17 : Locomotion and Movement 217 Chapter 18 : Neural Control and Coordination 230 Chapter 19 : Chemical Coordination and Integration 239 2024-25