2022-23
,11080 – BIOLOGY ISBN 81-7450-496-6
Textbook for Class XI
First Edition
February 2006 Phalguna 1927
ALL RIGHTS RESERVED
Reprinted
October 2006 Kartika 1928 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,
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-
January 2010 Magha 1931 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.
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 OFFICES OF THE PUBLICATION
March 2017 Phalguna 1938 DIVISION, NCERT
December 2017 Magha 1939
January 2019 Magha 1940 NCERT Campus
Sri Aurobindo Marg
September 2019 Bhadrapada 1941 New Delhi 110 016 Phone : 011-26562708
February 2021 Magha 1942
108, 100 Feet Road
November 2021 Agrahayana 1943 Hosdakere Halli Extension
Banashankari III Stage
Bangaluru 560 085 Phone : 080-26725740
PD 260T RSP
Navjivan Trust Building
P.O.Navjivan
© National Council of Educational Ahmedabad 380 014 Phone : 079-27541446
Research and Training, 2006 CWC Campus
Opp. Dhankal Bus Stop
Panihati
Kolkata 700 114 Phone : 033-25530454
CWC Complex
Maligaon
Guwahati 781 021 Phone : 0361-2674869
Publication Team
` 230.00 Head, Publication : Anup Kumar Rajput
Division
Chief Editor : Shveta Uppal
Chief Production : Arun Chitkara
Officer
Chief Business : Vipin Dewan
Manager
Assistant Editor : Shashi Chadha
Printed on 80 GSM paper with NCERT Production Assistant : Om Prakash
watermark
Published at the Publication Division by the Cover and Layout
Secretary, National Council of Educational Shweta Rao
Research and Training, Sri Aurobindo Marg,
Illustrations
New Delhi 110 016 and printed at Esskay
Lalit Maurya
Press Pvt. Ltd. 220, Patparganj Industrial
Area, Delhi - 110 092
2022-23
,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.
2022-23
, 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)
2022-23
,11080 – BIOLOGY ISBN 81-7450-496-6
Textbook for Class XI
First Edition
February 2006 Phalguna 1927
ALL RIGHTS RESERVED
Reprinted
October 2006 Kartika 1928 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,
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-
January 2010 Magha 1931 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.
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 OFFICES OF THE PUBLICATION
March 2017 Phalguna 1938 DIVISION, NCERT
December 2017 Magha 1939
January 2019 Magha 1940 NCERT Campus
Sri Aurobindo Marg
September 2019 Bhadrapada 1941 New Delhi 110 016 Phone : 011-26562708
February 2021 Magha 1942
108, 100 Feet Road
November 2021 Agrahayana 1943 Hosdakere Halli Extension
Banashankari III Stage
Bangaluru 560 085 Phone : 080-26725740
PD 260T RSP
Navjivan Trust Building
P.O.Navjivan
© National Council of Educational Ahmedabad 380 014 Phone : 079-27541446
Research and Training, 2006 CWC Campus
Opp. Dhankal Bus Stop
Panihati
Kolkata 700 114 Phone : 033-25530454
CWC Complex
Maligaon
Guwahati 781 021 Phone : 0361-2674869
Publication Team
` 230.00 Head, Publication : Anup Kumar Rajput
Division
Chief Editor : Shveta Uppal
Chief Production : Arun Chitkara
Officer
Chief Business : Vipin Dewan
Manager
Assistant Editor : Shashi Chadha
Printed on 80 GSM paper with NCERT Production Assistant : Om Prakash
watermark
Published at the Publication Division by the Cover and Layout
Secretary, National Council of Educational Shweta Rao
Research and Training, Sri Aurobindo Marg,
Illustrations
New Delhi 110 016 and printed at Esskay
Lalit Maurya
Press Pvt. Ltd. 220, Patparganj Industrial
Area, Delhi - 110 092
2022-23
,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.
2022-23
, 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)
2022-23
