2020-21 ISBN 81-7450-496-6 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 October 2006 Kartika 1928 transmitted, in any form or by any means, electronic, mechanical, photocopying, November 2007 Kartika 1929 recording or otherwise without the prior permission of the publisher. January 2009 Pausa 1930 q This book is sold subject to the condition that it shall not, by way of trade, be lent, re- 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 Pausa 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 and should be unacceptable. December 2012 Pausa 1934 December 2013 Agrahayana 1935 December 2014 Pausa 1936 May 2016 Vaishakha 1938 March 2017 Phalguna 1938 December 2017 Magha 1939 OFFICES OF THE PUBLICATION January 2019 Magha 1940 DIVISION, NCERT September 2019 Bhadrapada 1941 NCERT Campus Sri Aurobindo Marg PD 450T BS New Delhi 110 016 Phone : 011-26562708 108, 100 Feet Road © National Council of Educational Hosdakere Halli Extension Banashankari III Stage Research and Training, 2006 Bangaluru 560 085 Phone : 080-26725740 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 ````` 230.00 Publication Team Head, Publication : M. Siraj Anwar Division Chief Editor : Shveta Uppal Chief Production : Arun Chitkara Officer Chief Business : Bibash Kumar Das Manager Printed on 80 GSM paper with NCERT Assistant Editor : Shashi Chadha watermark Production Assistant : Prakash Veer Singh 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 Amit Illustrations Printing Press, D-12 and 13, Industrial Lalit Maurya Area, Site-A, Mathura- 281 001 (U.P.) 2020-21 F OREWORD 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. 2020-21 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) 2020-21 T D C EXTBOOK EVELOPMENT OMMITTEE C , A G T S M HAIRPERSON DVISORY ROUP FOR EXTBOOKS IN CIENCE AND ATHEMATICS J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee, Inter University Centre for Astronomy and Astrophysics (IUCAA), Pune University, Pune C A HIEF DVISOR K. Muralidhar, Professor, Department of Zoology, University of Delhi, Delhi M EMBERS 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 M -C EMBER OORDINATOR B.K. Tripathi, Reader, Department of Education in Science and Mathematics, NCERT. 2020-21 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. 2020-21 A N T S OTE FOR THE EACHERS AND 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 2020-21 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 2020-21 C ONTENTS FOREWORD iii A NOTE FOR THE TEACHERS AND STUDENTS vii U I NIT D L W 1-62 IVERSITY IN THE IVING ORLD Chapter 1 : The Living World 3 Chapter 2 : Biological Classification 16 Chapter 3 : Plant Kingdom 29 Chapter 4 : Animal Kingdom 46 U II NIT S O P A 63-122 TRUCTURAL RGANISATION IN LANTS AND NIMALS Chapter 5 :Morphology of Flowering Plants 65 Chapter 6 :Anatomy of Flowering Plants 84 Chapter 7 :Structural Organisation in Animals 100 U III NIT C : S F 123-172 ELL TRUCTURE AND UNCTIONS Chapter 8 : Cell : The Unit of Life 125 Chapter 9 : Biomolecules 142 Chapter 10 : Cell Cycle and Cell Division 162 2020-21