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ICSE Class X Board Exam 2018 : Science

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ICSE Analysis of Pupil Performance SCIENCE Research Development and Consultancy Division Council for the Indian School Certificate Examinations New Delhi Year 2018 __________________________________________________________________________________ Published by: Research Development and Consultancy Division (RDCD) Council for the Indian School Certificate Examinations Pragati House, 3rd Floor 47-48, Nehru Place New Delhi-110019 Tel: (011) 26413820/26411706 E-mail: council@cisce.org Copyright, Council for the Indian School Certificate Examinations All rights reserved. The copyright to this publication and any part thereof solely vests in the Council for the Indian School Certificate Examinations. This publication and no part thereof may be reproduced, transmitted, distributed or stored in any manner whatsoever, without the prior written approval of the Council for the Indian School Certificate Examinations. FOREWORD This document of the Analysis of Pupils Performance at the ISC Year 12 and ICSE Year 10 Examination is one of its kind. It has grown and evolved over the years to provide feedback to schools in terms of the strengths and weaknesses of the candidates in handling the examinations. We commend the work of Mrs. Shilpi Gupta (Deputy Head) of the Research Development and Consultancy Division (RDCD) of the Council and her team, who have painstakingly prepared this analysis. We are grateful to the examiners who have contributed through their comments on the performance of the candidates under examination as well as for their suggestions to teachers and students for the effective transaction of the syllabus. We hope the schools will find this document useful. We invite comments from schools on its utility and quality. Gerry Arathoon Chief Executive & Secretary October 2018 i PREFACE The Council has been involved in the preparation of the ICSE and ISC Analysis of Pupil Performance documents since the year 1994. Over these years, these documents have facilitated the teaching-learning process by providing subject/ paper wise feedback to teachers regarding performance of students at the ICSE and ISC Examinations. With the aim of ensuring wider accessibility to all stakeholders, from the year 2014, the ICSE and the ISC documents have been made available on the Council s website www.cisce.org. The documents include a detailed qualitative analysis of the performance of students in different subjects which comprises of examiners comments on common errors made by candidates, topics found difficult or confusing, marking scheme for each answer and suggestions for teachers/ candidates. In addition to a detailed qualitative analysis, the Analysis of Pupil Performance documents for the Examination Year 2018 have a component of a detailed quantitative analysis. For each subject dealt with in the document, both at the ICSE and the ISC levels, a detailed statistical analysis has been done, which has been presented in a simple user-friendly manner. It is hoped that this document will not only enable teachers to understand how their students have performed with respect to other students who appeared for the ICSE/ISC Year 2018 Examinations, but also provide information on how they have performed within the Region or State, their performance as compared to other Regions or States, etc. It will also help develop a better understanding of the assessment/ evaluation process. This will help teachers in guiding their students more effectively and comprehensively so that students prepare for the ICSE/ ISC Examinations, with a better understanding of what is required from them. The Analysis of Pupil Performance document for ICSE for the Examination Year 2018 covers the following subjects: English (English Language, Literature in English), Hindi, History, Civics and Geography (History and Civics, Geography), Mathematics, Science (Physics, Chemistry, Biology), Commercial Studies, Economics, Computer Applications, Economic Applications, Commercial Applications. Subjects covered in the ISC Analysis of Pupil Performance document for the Year 2018 include English (English Language and Literature in English), Hindi, Elective English, Physics (Theory), Chemistry (Theory), Biology (Theory), Mathematics, Computer Science, History, Political Science, Geography, Sociology, Psychology, Economics, Commerce, Accounts and Business Studies. I would like to acknowledge the contribution of all the ICSE and the ISC examiners who have been an integral part of this exercise, whose valuable inputs have helped put this document together. I would also like to thank the RDCD team of, Dr. M.K. Gandhi, Dr. Manika Sharma, Mrs. Roshni George and Mrs. Mansi Guleria who have done a commendable job in preparing this document. Shilpi Gupta Deputy Head - RDCD October 2018 ii CONTENTS Page No. FOREWORD i PREFACE ii INTRODUCTION 1 QUANTITATIVE ANALYSIS SCIENCE 3 QUALITATIVE ANALYSIS Physics (Paper-1) 10 Chemistry (Paper-2) 34 Biology (Paper 3) 54 INTRODUCTION This document aims to provide a comprehensive picture of the performance of candidates in the subject. It comprises of two sections, which provide Quantitative and Qualitative analysis results in terms of performance of candidates in the subject for the ICSE Year 2018 Examination. The details of the Quantitative and the Qualitative analysis are given below. Quantitative Analysis This section provides a detailed statistical analysis of the following: Overall Performance of candidates in the subject (Statistics at a Glance) State wise Performance of Candidates Gender wise comparison of Overall Performance Region wise comparison of Performance Comparison of Region wise performance on the basis of Gender Comparison of performance in different Mark Ranges and comparison on the basis of Gender for the top and bottom ranges Comparison of performance in different Grade categories and comparison on the basis of Gender for the top and bottom grades The data has been presented in the form of means, frequencies and bar graphs. Understanding the tables Each of the comparison tables shows N (Number of candidates), Mean Marks obtained, Standard Errors and t-values with the level of significance. For t-test, mean values compared with their standard errors indicate whether an observed difference is likely to be a true difference or whether it has occurred by chance. The t-test has been applied using a confidence level of 95%, which means that if a difference is marked as statistically significant (with * mark, refer to t-value column of the table), the probability of the difference occurring by chance is less than 5%. In other words, we are 95% confident that the difference between the two values is true. t-test has been used to observe significant differences in the performance of boys and girls, gender wise differences within regions (North, East, South and West), gender wise differences within marks ranges (Top and bottom ranges) and gender wise differences within grades awarded (Grade 1 and Grade 9) at the ICSE Year 2018 Examination. The analysed data has been depicted in a simple and user-friendly manner. 1 Given below is an example showing the comparison tables used in this section and the manner in which they should be interpreted. The table shows comparison between the performances of boys and girls in a particular subject. The t-value of 11.91 is significant at Comparison on the basis of Gender Gender Girls Boys *Significant at 0.05 level N 2,538 1,051 Mean 66.1 60.1 SE 0.29 0.42 t-value 11.91* 0.05 level (mentioned below the table) with a mean of girls as 66.1 and that of boys as 60.1. It means that there is significant difference between the performance of boys and girls in the subject. The probability of this difference occurring by chance is less than 5%. The mean value of girls is higher than that of boys. It can be interpreted that girls are performing significantly better than boys. The results have also been depicted pictographically. In this case, the girls performed significantly better than the boys. This is depicted by the girl with a medal. Qualitative Analysis The purpose of the qualitative analysis is to provide insights into how candidates have performed in individual questions set in the question paper. This section is based on inputs provided by examiners from examination centres across the country. It comprises of question wise feedback on the performance of candidates in the form of Comments of Examiners on the common errors made by candidates along with Suggestions for Teachers to rectify/ reduce these errors. The Marking Scheme for each question has also been provided to help teachers understand the criteria used for marking. Topics in the question paper that were generally found to be difficult or confusing by candidates, have also been listed down, along with general suggestions for candidates on how to prepare for the examination/ perform better in the examination. 2 QUANTITATIVE ANALYSIS STATISTICS AT A GLANCE Total Number of Candidates: 1,65,331 Highest Marks: 100 Mean Marks: Lowest Marks: 06 66.0 3 PERFORMANCE (STATE-WISE & FOREIGN) West Bengal Uttarakhand Uttar Pradesh Tripura Telangana Tamil Nadu Sikkim Rajasthan Punjab Puducherry Odisha New Delhi Nagaland Meghalaya Manipur Maharashtra Madhya Pradesh Kerala Karnataka Jharkhand Himachal Pradesh Haryana Gujarat Goa Chhattisgarh Chandigarh Bihar Assam Arunachal Pradesh Andhra Pradesh Foreign 66.0 64.3 62.1 61.8 66.6 70.5 55.1 67.8 60.8 70.1 64.3 58.7 54.6 60.4 54.3 76.1 59.8 71.7 70.4 62.4 64.3 70.9 67.0 72.3 59.3 70.2 64.6 66.3 52.0 64.4 79.7 The States of Maharashtra, Goa and Kerala secured highest mean marks. Mean marks secured by candidates studying in schools abroad were 79.7. 4 GENDER-WISE COMPARISON GIRLS BOYS Mean Marks: 67.0 Mean Marks: 65.3 Number of Number of Candidates: 74,430 Candidates: 90,901 Comparison on the basis of Gender Gender Girls Boys N Mean SE t-value 74,430 90,901 67.0 65.3 0.07 0.06 18.74* *Significant at 0.05 level Girls performed significantly better than boys. 5 REGION-WISE COMPARISON East North Mean Marks: 64.7 Mean Marks: 62.3 Number of Candidates: 51,791 Number of Candidates: 59,535 Highest Marks: 100 Lowest Marks: 15 Highest Marks: 100 Lowest Marks: 06 Mean Marks: 69.6 REGION Number of Candidates: 34,163 Highest Marks: 100 Lowest Marks: 21 South Mean Marks: 74.5 Number of Candidates: 19,459 Mean Marks: 79.7 Number of Candidates: 383 Highest Marks: 99 Lowest Marks: 34 Foreign 6 Highest Marks: 100 Lowest Marks: 21 West Mean Marks obtained by Boys and Girls-Region wise 63.5 61.4 North 64.9 70.6 64.5 East 75.3 68.6 South 79.4 73.9 West 80.0 Foreign Comparison on the basis of Gender within Region Region North (N) East (E) South (S) West (W) Foreign (F) Gender Girls Boys Girls Boys Girls Boys Girls Boys Girls Boys *Significant at 0.05 level N Mean SE 25,454 34,081 23,030 28,761 17,092 17,071 8,666 10,793 188 195 63.5 61.4 64.9 64.5 70.6 68.6 75.3 73.9 79.4 80.0 0.11 0.10 0.12 0.12 0.13 0.13 0.18 0.17 1.09 1.21 REGION (N, E, S, W) 7 t-value 13.74* 2.78* 10.85* 5.37* -0.37 MARK RANGES : COMPARISON GENDER-WISE Comparison on the basis of gender in top and bottom mark ranges Marks Range Top Range (81-100) Bottom Range (0-20) Gender Girls Boys Girls Boys N Mean SE 21,201 24,395 6 7 89.1 89.1 16.0 17.3 0.03 0.03 2.18 1.48 Boys Girls t-value -0.13 -0.49 All Candidates 89.1 81 - 100 89.1 89.1 70.4 61 - 80 70.6 70.5 50.8 41 - 60 51.2 51.0 35.0 21 - 40 35.5 35.2 17.3 0 - 20 16.0 16.7 8 GRADES AWARDED : COMPARISON GENDER-WISE Comparison on the basis of gender in Grade 1 and Grade 9 Grades Grade 1 Grade 9 Gender Girls Boys Girls Boys N Mean SE 9,820 11,440 6 7 93.8 93.8 16.0 17.3 0.03 0.02 2.18 1.48 Boys Girls t-value 0.62 -0.49 All Candidates 93.8 93.8 93.8 1 No significant difference was observed between the average 84.5 84.6 84.5 2 performance of girls and boys. 75.5 75.5 75.5 3 66.5 66.6 66.5 4 56.5 56.5 56.5 5 47.6 47.7 47.6 6 37.9 38.1 38.0 7 8 9 9 26.0 26.3 26.1 17.3 16.0 16.7 QUALITATIVE ANALYSIS PHYSICS (PAPER-1) SECTION I (40 Marks) Attempt all questions from this Section Question 1 (a) (i) State and define the S.I. unit of power. [2] (ii) How is the unit horse power related to the S.I. unit of power? (b) State the energy changes in the following cases while in use: [2] (i) An electric iron. (ii) A ceiling fan. (c) The diagram below shows a lever in use: (i) [2] To which class of levers does it belong? (ii) Without changing the dimensions of the lever, if the load is shifted towards the fulcrum what happens to the mechanical advantage of the lever? (d) (i) Why is the ratio of the velocities of light of wavelengths 4000 and 8000 in [2] vacuum 1:1? (ii) Which of the above wavelengths has a higher frequency? (e) (i) Why is the motion of a body moving with a constant speed around a circular path said to be accelerated? (ii) Name the unit of physical quantity obtained by the formula Where K: kinetic energy, V: Linear velocity. 10 2 2 . [2] Comments of Examiners Suggestions for teachers (a)(i) Majority of the candidates were able to answer this question. However, some - Teach units with their definitions and candidates either did not define the unit conversions. Emphasise on their or defined an incorrect unit. A few correct spellings. candidates made spelling errors while - Explain energy conversion giving stating and defining the unit watt. common day to day examples to the students. Lay stress on important (ii) Most candidates answered this sub-part energy changes that occur, with the correctly. Some candidates, however, proper names of energies. wrote either 1 H.P. = 0.746 watt or 1 watt Illustrate change in the mechanical = 746 H.P. Some candidates were unsure advantage of a lever giving daily life about the exact value of H.P. in watt. A examples. few candidates did not write the unit. - Clarify to the students the difference (b)(i) Some candidates stated the energy between electromagnetic waves and change in case of an electric iron mechanical waves. electrical to mechanical or vice versa. A - Lay stress on the concept that few candidates gave irrelevant answers. frequency of a wave is inversely proportional to its wavelength i.e., (ii) Majority of the candidates answered this 1 . sub-part correctly. However, some candidates stated the energy change in - Interpret the concept of the motion of case of a ceiling fan, mechanical to wind a body moving with a constant speed energy instead of electrical to kinetic around a circular path thoroughly. energy. - Train the students to read the (c)(i) Most of the candidates wrote second questions and answer as per their requirements. class lever but a few candidates did write Class I or Class III lever. (ii) Majority of the candidates were unable to answer what happens to the mechanical advantage of the lever if the load is shifted towards the fulcrum without changing the dimensions of the lever! They just mentioned mechanical advantage is greater than one without realizing that the mechanical advantage of lever is already > 1 which increases further. (d)(i) Most of the candidates were able to answer this question. A few candidates however, arrived at the correct answer or an incorrect answer after long calculations. 0 0 (ii) Most of the candidates answered it correctly as 4000 but some candidates wrote 8000 . A few candidates did huge calculations to arrive at the answer. (e)(i) Several candidates explained the centripetal and centrifugal forces. Some candidates diagrammatically showed that motion is tangential to the curved path but were unable to make it clear that the motion of a body moving with a constant speed around a circular path, would be accelerated. (ii) Most of the candidates could name the unit of physical quantity obtained by the given formula correctly, however, a few candidates were unable to name the unit. 11 MARKING SCHEME Question 1 (a) (i) watt If 1joule of work is done in 1 second then the power spent/developed / expended is 1watt. (b) (c) (d) (e) (ii) 1H.P. = 746 W /750 W (i) Electrical energy to heat energy (ii) Electrical energy to kinetic/mechanical energy. (i) Second order (or class) lever. (ii) Mechanical advantage of the lever increases. (i) In vacuum their speed/velocity is the same. (ii) 4000 has higher frequency. (i) Because on a circular path the direction of motion changes continuously which changes the velocity of the body continuously. (ii) kg or kilogram/g/ any unit of mass can be accepted. Question 2 (a) The power of a lens is 5D. [2] (i) Find its focal length. (ii) Name the type of lens. (b) (c) State the position of the object in front of a converging lens if: (i) It produces a real and same size image of the object. (ii) It is used as a magnifying lens. (i) State the relation between the critical angle and the absolute refractive index of a medium. [2] [2] (ii) Which colour of light has a higher critical angle? Red light or Green light. (d) (i) Define scattering. [2] (ii) The smoke from a fire looks white. Which of the following statements is true? 1. Molecules of the smoke are bigger than the wavelength of light. 2. Molecules of the smoke are smaller than the wavelength of light. 12 (e) The following diagram shows a 60o, 30o, 90o glass prism of critical angle 42o. Copy the diagram and complete the path of incident ray AB emerging out of the prism marking the angle of incidence on each surface. [2] Comments of Examiners (a)(i) Most of the candidates answer this sub-part Suggestions for teachers correctly. However, some candidates calculated the focal length of the given lens incorrectly or - Explain clearly the sign convention expressed the focal length in incorrect unit. for the nature of lens, relating it to the (ii) Most candidates named the type of lens correctly. spectacle numbers of the students Some candidates, however, were unaware that the being negative for most of them. focal length of a lens with negative sign is for a - Emphasise the unit while writing a physical quantity or an answer. concave lens. - Teach different cases of image (b)(i) Many candidates gave the incorrect position of the formation by lenses, giving relevant object. Some candidates even drew an incorrect examples from daily life. diagram. A few candidates got confused due to the - Train students to write labelling seen in question 6 (b). mathematically correct statement (ii) Majority of the candidates made the same error as rather than the generalised in Q6(b). mathematical statement in terms of (c)(i) Only a few candidates wrote the correct increases and decreases. mathematical relation between the critical angle - Explain the difference between and the absolute refractive index of a medium. scattering and dispersion Also give a Many candidates simply mentioned increases and practical demonstration. decreases. - Train the students to complete the (ii) Most of the candidates wrote correct colour of path of the ray of light by calculating light which has a higher critical angle. However, the angle of incidence at every new surface when the ray hits the surface. some candidates mentioned the colour as green Give adequate practice to the students which was incorrect. in drawing the ray diagrams. (d) (i) Majority of the candidates stated the definition of - Instruct students to focus on the dispersion which was incorrect. Some candidates requirement of the question and to did not state absorption and reemission without draw diagrams only when asked for. the change in the wavelength. Some candidates even changed the order and wrote reemission and absorptio (ii) Almost all candidates identified the correct statement except a few who chose statement 2 as the correct option. (e) Majority of the candidates showed total internal reflection Some candidates showed the ray bending towards normal. The diagram drawn by a few candidates was ambiguous. 13 MARKING SCHEME Question 2 (a) 1 1 (i) = = 5 = 0.2 20 (substitution expressed with negative sign is also acceptable) (ii) Concave/diverging lens (b) (i) at 2F (ii) Between the optical centre and principal focus. (c) 1 (i) = sin (ii) Red (d) Bending away at surface XZ Angle of incidence = 30o (e) (i) Scattering is the absorption and then reemission of light without the change in the wavelength. (ii) Statement 1 Question 3 (a) Displacement distance graph of two sound waves A and B, travelling in a medium, are as shown in the diagram below. Study the two sound waves and compare their: 14 [2] (i) Amplitudes (ii) Wavelengths (b) You have three resistors of values 2 , 3 and 5 . How will you join them so that [2] the total resistance is more than 7 ? (i) Draw a diagram for the arrangement. (ii) Calculate the equivalent resistance. (c) (i) What do you understand by the term nuclear fusion? [2] (ii) Nuclear power plants use nuclear fission reaction to produce electricity. What is the advantage of producing electricity by fusion reaction? (d) (i) What do you understand by free vibrations of a body? [2] (ii) Why does the amplitude of a vibrating body continuously decrease during damped vibrations? (e) (i) How is the e.m.f. across primary and secondary coils of a transformer related [2] with the number of turns of coil in them? (ii) On which type of current do transformers work? Comments of Examiners (a) A number of candidates were unable to comprehend the diagram. Many candidates, instead of calculating proper ratios of amplitudes and wave lengths, just compared them by stating more or less. Some candidates left the answer in the fractional form without bringing it to the lowest form. A few candidates stated the values of the quantities for the two waves. (b) (i) Many candidates showed a straight line instead of a wavy line to depict the resistor in the diagram. Some candidates showed various combinations of series and parallel resistors. A few candidates considered 7 as one of the resistors in the circuit (ii) Many candidates showed series combination but used the formula of parallel combination and vice versa. Several candidates tried out different combinations as they overlooked the word more than 7 and tried to get it equal to 7 . Some candidates did not write the unit in the final answer. 15 Suggestions for teachers Explain to the students that if the numerical figures are given in the question then compare means ratio. Train students to interpret the information of waves from graph. rill students for expressing the final answer as per the requirement of the question. Encourage students to learn the definitions with proper understanding keeping in mind the importance of keywords like periodic force, constant frequency and amplitude in the definition of free vibrations. Ensure that the students understand the difference between external force and external resistive force (c) (i) Many candidates, instead of writing lighter and heavier nuclei, wrote smaller and bigger - Point out clearly the distinction atoms/nuclei. Some candidates wrote the - among free, forced and damped definition of nuclear fission. vibrations with a variety of (ii) Majority of the candidates were unable to answer examples. this question correctly. A few candidates - Adequate practice should be given expressed that only nuclear fission can be used to to students for comprehension of produce electricity. Some candidates gave various terms and related aspects in advantages of fission reaction. transformers correctly. (d)(i) Many candidates did not write the key words - Give adequate practice to the students in solving numerical such as without influence of external periodic problems based on force, constant frequency and constant combination(series/parallel/mixed) amplitude in the definition. of resistors. (ii) Most candidates did not write that external force Clarify the terms Nuclear fusion and is resistive in nature or that it causes loss of fission in detail giving relevant energy. Some candidates wrote the definition of examples for comprehension damped vibrations. A few candidates wrote that damped vibrations are due to the removal of external force. (e)(i) Several candidates were unable to answer this question. Most of them wrote how voltage or current increases or decreases in step-up and step-down transformer. A large number of candidates wrote = . Several candidates wrote only primary or only secondary coil without giving clear relation between number of turns and e.m.f. (ii) Majority of the candidates wrote d.c or induced current or high voltage current or eddy currents. MARKING SCHEME Question 3 (a) (i) Amplitudes of A and B are in the ratio 2:1. (ii) Wavelengths of A and B are in the ratio 1:2. (b) (i) (c) (ii) = 2 + 3 + 5 = 10 (Only 10 can be accepted if the diagram is shown else substitution is a must.) (i) Nuclear fusion The process in which two lighter nuclei of lighter atoms combine to form a heavy and more stable nucleus with the liberation of large amount of heat. (ii) The product formed is not radioactive hence less harmful to human/ energy produced per nucleon (for same mass of nuclear material) is more than fission. (d) (i) Vibrations of a body in absence of any external periodic force with constant frequency and amplitude. (ii) The energy is lost to the surrounding due to the friction of the surrounding medium. 16 (e) (i) e.m.f. and the number of turns of the coil are directly proportional. (ii) A.C. or alternating current. Question 4 (a) (i) How can a temperature in degree Celsius be converted into S.I. unit of [2] temperature? (ii) A liquid X has the maximum specific heat capacity and is used as a coolant in Car radiators. Name the liquid X. (b) A solid metal weighing 150 g melts at its melting point of 800 o C by providing heat [2] at the rate of 100 W. The time taken for it to completely melt at the same temperature is 4 min. What is the specific latent heat of fusion of the metal? (c) Identify the following wires used in a household circuit: (i) [2] The wire is also called as the phase wire. (ii) The wire is connected to the top terminal of a three-pin socket. (d) (i) What are isobars? [2] (ii) Give one example of isobars. (e) State any two advantages of electromagnets over permanent magnets. 17 [2] Comments of Examiners Suggestions for teachers (a)(i) Majority of the candidates could not express a temperature in degree Celsius in S.I. unit of Teach the basic physical quantities temperature. Several candidates wrote 10C = and their corresponding conversions. 273 K. Some candidates wrote t0C-273 or T = While doing calorimetry numerical, 273 t0C or t = 273+K, 10C=1 K. ask the students to express the (ii) Most of the candidates named the liquid X temperature in K or vice versa. correctly. However, some candidates wrote Clearly explain the properties of water and the advantages of its high hydrogen or kerosene, or petrol or diesel can specific heat capacity. be used as a coolant in car radiators. Tell the students that every piece of (b) Majority of the candidates used melting point 800 0 information given in the sum need C in their calculation. Most candidates substituted not be used in the calculations 150 800 on one side of the equation. Some involving change of state. Give candidates solved the specific latent heat of fusion adequate practice on the heat of the metal equation using incorrect numerical. expressions = only or = only or Make the students aware of the using = + . A few candidates wrote colloquial terms. Practically show the incorrect unit. the students the connections to the (c)(i) Most of the candidates were unaware of the three-pin socket. word phase. Some candidates wrote the Clearly explain the difference between isotopes and isobars. Ensure answer in terms of colours of wire. A few that the students are clear that the candidates wrote options such as hot wire or reactant and product during beta live/earth or neutral/earth. emission are always isobars. Teach (ii) This question was attempted well by most of the topic by giving sufficient the candidates. However, some candidates examples. wrote live wire or live/neutral. Some Encourage the students to think over candidates wrote the answer in terms of the statement and check its validity colours of wire. in different situations. Clearly (d) Many candidates answered sub-parts (i) and (ii) explain the advantages of correctly. However, some common errors made electromagnets as compared to the by a few candidates were as follows: permanent magnets. confused between isotopes and isobars. wrote examples with incorrect mass number and atomic number.wrote the elements without atomic number and mass numbers. gave examples of isotopes. (e) Some candidates, instead of writing the advantages of electromagnets over permanent magnets, wrote the differences between the two. Some candidates wrote only one advantage. Some candidates repeated the points. A few candidates wrote incorrect advantages. 18 MARKING SCHEME Question 4 (a) (i) o (ii) Water C + 273 = K = => 100 4 60 = 150 (b) = 160 J g-1 (c) (i) (both side correct substitutions.) (answer is accepted in any unit.) Live wire (ii) Earth wire (d) (i) (ii) (e) Elements of same mass number but different atomic numbers are called isobars. 14 14 6 , 7 , 23 23 12 , 11 (Any one correct example) Permanent Magnet Electromagnet Magnetic Strength cannot be easily altered Magnetic strength can be easily altered. Polarity cannot be reversed easily Polarity can be reversed easily. SECTION I (40 Marks) Attempt any four questions from this Section Question 5 (a) (i) Derive a relationship between S.I. and C.G.S. unit of work. [3] (ii) A force acts on a body and displaces it by a distance S in a direction at an angle with the direction of force. What should be the value of to get the maximum positive work? (b) A half metre rod is pivoted at the centre with two weights of 20 gf and 12 gf suspended [3] at a perpendicular distance of 6 cm and 10 cm from the pivot respectively as shown below. 50 cm 20gf 12gf 6 cm 19 10 cm (i) Which of the two forces acting on the rigid rod causes clockwise moment? (ii) Is the rod in equilibrium? (iii) The direction of 20 kgf force is reversed. What is the magnitude of the resultant moment of the forces on the rod? (c) (i) Draw a diagram to show a block and tackle pulley system having a velocity ratio [4] of 3 marking the direction of load(L), effort(E) and tension(T). (ii) The pulley system drawn lifts a load of 150 N when an effort of 60 N is applied. Find its mechanical advantage. (iii) Is the above pulley system an ideal machine or not? Comments of Examiners (a)(i) Some candidates, instead of deriving the Suggestions for teachers relation between S.I. and C.G.S. unit of work Lay stress on the derivations for wrote the relation. Some candidates showed conversions with key steps. the derivation between newton and dyne. The Clearly explain the work done for derivations done by a few candidates were = 00 , 900 , 1800 . Ensure that the the substitution on R.H.S of equation making basic concept of trigonometry is it meaningless. 0 0 clear to the students. (ii) Several candidates wrote = 90 180 or 0 Drill students on the concept of 90 = 1. Some candidates identified the clockwise and anticlockwise angle correctly but made contradictory moment. Give adequate practice on statements like 0 = 0. numerical of moments. (b)(i) Majority of the candidates were able to Train students to answer the answer this question. However, some questions as per the requirement of candidates were confused and wrote both 20 the question. gf and 12 gf. Ensure that the students are given (ii) This part of the question was attempted well regular practice of drawing pulley by most candidates. However, some diagrams. Clearly explain the candidates arrived at the conclusion after difference between ideal and long, elaborate and unnecessary calculations. practical pulley. Tell the students A few candidates guessed the answer to be that if the mechanical advantage is either a yes or no. less than the number of strands (iii) This question was performed well by most supporting the load, then it is not an candidates. ideal pulley system. (c)(i) The common anomalies in most of the answer scripts were: Direction of load and tension were missing. There were no proper number of pulleys in the fixed and movable block. No distinction between fixed and movable block. No support was shown. The strands of the tackle were shown loose. 20 (ii) Majority of the candidates were able to get the calculations correct but left the answer in fraction form. Some candidates added the units. The calculations done by a few candidates were vague. (iii) Majority of the candidates were able to answer this question. Some candidates, however, wrote it is an ideal pulley system. MARKING SCHEME Question 5 (a) (i) 1J=1Nx1m 1 J = 10 5 dyn x 100 cm 1 J = 10 7 ergs (ii) 0 (b) (i) 12 kg f (ii) Yes (iii) On reversing the direction of 20 kg f, the magnitude of the resultant forces on the (c) (i) rod = 20 6 + 12 10 = 240 Two pulleys in block and one pulley(movable) in tackle, their proper connection, marking directions of load(L) and effort(E) and at least one tension and the support. Strands should be stretched. (ii) . . = = 150 60 = 2.5 (iii) No, it is not an ideal system. 21 Question 6 (a) A ray of light XY passes through a right angled isosceles prism as shown below. [3] (i) What is the angle through which the incident ray deviates and emerges out of the prism? (ii) Name the instrument where this action of prism is put into use. (iii) Which prism surface will behave as a mirror? (b) An object AB is placed between O and F 1 on the principal axis of a converging lens [3] as shown in the diagram. Copy the diagram and by using three standard rays starting from point A, obtain an image of the object AB. (c) An object is placed at a distance of 12 cm from a convex lens of focal length 8 cm. Find: (i) the position of the image (ii) nature of the image 22 [4] Comments of Examiners (a) Majority of the candidates answered sub-parts (i),(ii) and (iii) of this question well. However, some common miscues made by candidates were: - Reported the angle through which the incident ray deviates and emerges out of the prism as 00 or 450 - named binoculars as the instrument. - the prism surface BC and AC will behave as a mirror. - all the three surfaces will behave as a mirror. (b) Many candidates were unsure of the answer due to the third standard ray which was asked. Suggestions for teachers The common anomalies in most of the answer scripts were: - Ray after refraction did not pass through F. - Virtual intersection or the image was not shown by dotted lines. - Arrows were missing on either incident or refracted rays. - Two rays were drawn but the image was not drawn. - Arrows were drawn on the dotted lines to show the path of the ray. (c)(i) Majority of the candidates were unable to answer this question. The common flaws observed in most of the answer scripts were: - use of incorrect lens formula incorrect use of sign convention. incorrect substitutions. incorrect characteristics of the images. incorrect answer with correct unit or correct answer with incorrect unit or without unit. Teach the students the angle of deviation with respect to any phenomenon of light and not only with respect to refraction through prism. Discuss with the students, the total internal reflection through the right angled isosceles prism in detail. Illustrate lenses including characteristics of the images formed, location of images using ray diagrams, sign convention lens formula thoroughly. Ensure that the students understand the sign convention clearly. Give sufficient practice to the students to draw ray diagrams using three standard rays even if the object is lying between the optical centre and the focus. Insist on the arrows on the rays before and after the refraction. Guide students that apparent intersection and virtual image has to be shown by dotted lines. Give sufficient practice to the students to solve the numerical problems. MARKING SCHEME Question 6 (a) (i) 900 (ii) refracting periscope. (iii) Surface AB 23 (b) Image of the object AB, using three standard rays starting from point A (c) (i) 1 1 1 1 (ii) (iii) 1 - = 1 1 - 12 = 8 1 1 = 8 - 12 = 3 2 24 Real or inverted 1 = 12 ; image distance v = +24cm Image is bigger than object. Question 7 (a) Draw the diagram of a right angled isosceles prism which is used to make an inverted [3] image erect. (b) [3] The diagram above shows a wire stretched over a sonometer. Stems of two vibrating tuning forks A and B are touched to the wooden box of the sonometer. It is observed that the paper rider (a small piece of paper folded at the centre) present on the wire flies off when the stem of vibrating tuning fork B is touched to the wooden box but the paper just vibrates when the stem of vibrating tuning fork A is touched to the wooden box. (i) Name the phenomenon when the paper rider just vibrates. (ii) Name the phenomenon when the paper rider flies off. (iii) Why does the paper rider fly off when the stem of tuning fork B is touched to the box? 24 (c) A person is standing at the sea shore. An observer on the ship which is anchored in [4] between a vertical cliff and the person on the shore fires a gun. The person on the shore hears two sounds, 2 seconds and 3 seconds after seeing the smoke of the fired gun. If the speed of sound in the air is 320 ms-1 then calculate: (i) the distance between the observer on the ship and the person on the shore. (ii) the distance between the cliff and the observer on the ship. Comments of Examiner (a) Many candidates performed well barring a few exceptions who could not show: - 900 Deviation - Inversion of image. - Arrows on incident, refracted, reflected and emergent rays. Suggestions for teachers Drill students in drawing correct ray (b) Most candidates answered sub-parts (i), (ii) and (iii) correctly, however a few candidates wrote: (i) damped and forced or resonant vibrations. (ii) forced vibrations. (iii) that the frequency of the tuning fork B becomes more than the natural frequency of the stretched wire and vibrates with greater amplitude or vice versa or the explanation of increased amplitude was missing. (c) Most of the candidates attempted this part well, however, some candidates made mistakes in calculations. 25 diagrams. Insist on necessary labelling and specifications of the diagrams. Explain to the students, the reason for total internal reflection taking place at the lower surface and not at the side surfaces. Illustrate free vibrations, forced vibrations and resonance with relevant examples. Train students to read and analyse the question gingerly and then take logical steps towards solving it. Instruct students to refrain themselves from simply substituting the data in the formula. MARKING SCHEME Question 7 (a) (Any other correct ray diagram) (b) (i) Forced vibrations (ii) Resonance. (iii) Frequency of the tuning fork B matches the natural frequency of the stretched wire and vibrates with greater amplitude. (c) (i) = = 320 2 = 640 m (ii) = 2 = 320 1 = 160 m 2 Question 8 (a) (i) A fuse is rated 8A. Can it be used with an electrical appliance rated 5 KW, 200 [3] V? Give a reason. (ii) Name two safety devices which are connected to the live wire of a household electric circuit. (b) (i) Find the equivalent resistance between A and B. [3] (ii) State whether the resistivity of a wire changes with the change in the thickness of the wire. (c) An electric iron is rated 220V, 2kW. [4] 26 (i) If the iron is used for 2h daily find the cost of running it for one week if it costs ` 4.25 per kWh. (ii) Why is the fuse absolutely necessary in a power circuit? Comments of Examiners (a) Sub-parts (i) and (ii) were correctly attempted by Suggestions for teachers most of the candidates except for some who: Explain the concepts on electrical (i) answered the question without calculating power and energy, fuse and its current. calculated the current but made rating and its use in power circuits calculation errors. were unable to in detail. comprehend the meaning of the term fuse Ask students to show the rating and hence could not write a proper calculations in the numerical reason. simply wrote No as the answer. problems. (ii) wrote the names of the appliances. wrote Ensure that the students are clear earthing /earth wire without realising that the about the safety devices and their safety devices connected to the live wire had functions. been asked. Illustrate the concept of resistors (b) (i) This sub-part was correctly attempted by most in combination (series, parallel candidates. The common anomalies in most and mixed) with adequate of the answer scripts were: number of numerical problems. Series resistor formula was used. Guide students about the L.H.S of the parallel resistor formula was possible errors also. 1 written R in place of which resulted Point out the difference between resistance and resistivity. in incorrect mathematical step. Give regular practice to the students Unit was missing in the answer. in solving the numerical problems (ii) Majority of the candidates wrote that the based on different topics in resistivity changes as they were unsure about Electricity. the factors affecting it. (c) (i) The common lapses observed in some of the answer scripts were: calculation errors. time (one week) was not taken into consideration. kW was converted into watt. (ii) Many candidates could not write about the absolute necessity of the fuse in power circuits correctly. MARKING SCHEME Question 8 (a) (i) = = 5000 200 = 25 No, it cannot be used. Maximum current drawn by the appliance is greater than the fuse rating. (ii) M.C.B. Fuse, switch, ELCB 27 6 3 (i) 1 = 6+3 = 2 (b) (c) Or 4 12 2 = 4+12 = 3 (ii) = 2 + 3 = 5 (i) E = P x t = 2 x 2 =4 kW h No, it does not change. [Correct substitution] Cost for running it for a week = 4 x 7 x 4.25 = ` 119/(ii) Power circuits draw large amount of current/ Electric shock in this circuit is very fatal hence to avoid it fuse is necessary in the power circuit/ to safeguard. Question 9 (a) (i) Heat supplied to a solid change it into liquid. What is this change in phase called? [3] (ii) During the phase change does the average kinetic energy of the molecules of the substance increase? (iii) What is the energy absorbed during the phase change called? (b) (i) State two differences between Heat Capacity and Specific Heat Capacity . [3] (ii) Give a mathematical relation between Heat Capacity and Specific Heat Capacity. (c) The temperature of 170g of water at 50 C is lowered to 5 C by adding certain amount of ice to it. Find the mass of ice added. Given: Specific heat capacity of water = 4200 J kg-1 C-1 and Specific latent heat of ice = 336000 J kg-1 28 [4] Comments of Examiners (a)(i) Majority of the candidates were able to answer this question. However, some candidates wrote melting point, boiling point, boiling, liquification, and vaporization A few candidates explained about specific heat capacity. (ii) Most of the candidates wrote yes for this part, missing out on the word average in the question. (iii) Majority of the candidates wrote specific heat or specific latent heat or heat energy or kinetic energy or potential energy or specific latent heat capacity. (b)(i) Many candidates made errors in the definitions of Heat Capacity and Specific Heat Capacity. Several candidates stated incorrect units. Some candidates did not write corresponding points of difference. (ii) Many candidates were confused in the use of symbols such as C, C and H. Several candidates deviated from the usual symbols but did not explain them. (c) The common inaccuracies observed in most of the answer scripts were: Required conversions were not done. Proper equation was not formed. Heat absorbed by melted ice was not considered. Unit was incorrect or not mentioned in the final answer. Suggestions for teacher - Familiarize students with conceptual - - - - - - questions through oral questioning and regular written tests. With the help of the heating curve, discuss the various processes of phase change and the difference between them. Explain phase change on the basis of the kinetic theory. Explain the differences between Heat Capacity and Specific Heat Capacity. Tell the students that the formula is nothing but the mathematical statement of definition and so is not a point of difference. Train students to explain the symbols in an answer given in the form of a formula/mathematical equation. Give adequate practice to students in solving a variety of questions based on calorimetry. Also, ask them to use only the values given in the question. Give adequate practice in constructing the equation involving change of state and principle of mixtures as well as substitution in the equation. Use the Heating curve to construct an equation. MARKING SCHEME Question 9 (a) (i) Melting (ii) No. (iii) Latent heat of melting/fusion. 29 (b) (i) Heat capacity Specific heat capacity Heat absorbed by the mass of a body Heat absorbed by unit mass of a body to raise its temperature by 1o C. to raise its temperature by 1o C. S.I. Unit is J K-1 S.I. unit is J kg-1 K-1 Depends on mass and (specific Heat capacity/material) Does not depend on mass (but depends on material) (Any two points) (ii) Heat capacity(C') = mass of the body(m) x specific heat capacity (c) mw cw w = mi L + mi cw w (c) 170 x 4.2 x 45 = m i [ 336 + 4.2 x 5 ] m i = 90 g Question 10 (a) [3] The diagram shows a coil wound around a U shape soft iron bar AB. (i) What is the polarity induced at the ends A and B when the switch is pressed? (ii) Suggest one way to strengthen the magnetic field in the electromagnet. (iii) What will be the polarities at A & B if the direction of current is reversed in the circuit? (b) The ore of Uranium found in nature contains 238 92 U and 235 92 U . Although both the isotopes are fissionable, it is found out experimentally that one of the two isotopes is more easily fissionable. (i) Name the isotope of Uranium which is easily fissionable. 30 [3] (ii) Give a reason for your answer. (iii) Write a nuclear reaction when Uranium 238 emits an alpha particle to form a Thorium (Th) nucleus. Comments of Examiners (a)(i) Majority of the candidates were unable to Suggestions for teacher write the correct polarity induced at the ends A and B of the coil wound around a U shape soft - Explain to the students the correct method of determining the polarity iron bar AB on pressing the switch. Some induced at any end of a coil wound candidates wrote that the answer is not around a magnetic substance, on possible. passing the current through the coil. (ii) Most of the candidates answered this sub-part - Discuss the isotopes of Uranium and correctly. fission of uranium thoroughly to the (iii) Majority of the candidates who were unable to students. answer sub-part (i) of this question correctly, - Train students to write balanced could not answer this sub-part correctly. nuclear equations. (b)(i) Many candidates named the easily fissionable 238 - Discuss radioactivity and changes in U. Some candidates isotope of Uranium, 238 235 92 the nucleus, comparative properties wrote U or U or U. of , and along with the reasons. (ii) Majority of the candidates were unable to Explain in detail the important uses answer this question. of nuclear radiations (iii) Many candidates wrote the nuclear equation but were unable to balance it. Several candidates wrote above the arrow in the equation. (c)(i) Most candidates were able to answer this question. However, some candidates wrote or which was incorrect. (ii) Majority of the candidates, instead of relating it to the negligible mass of , related it to its speed or negative charge. (iii) Majority of the candidates wrote either beta or gamma. Candidates seemed to be confused by the word externally. (iv) Majority of the candidates either did not attempt this question or wrote incorrect answer. MARKING SCHEME Question 10 (a) (i) South and south. (ii) Increasing the strength of current through the coil. (iii) The polarities at the two ends become North. (b) (i) 235 92 U (ii) Fission of 238 92 U is possible only by fast neutrons while the fission of even possible by the slow neutrons. 31 235 92 U can be (iii) (c) 238 92 234 90 + 42 (i) B (gamma) (ii) C has less mass compared to A (iii) A (iv) C Note: For questions having more than one correct answer/solution, alternate correct answers/solutions, apart from those given in the marking scheme, have also been accepted. Topics found difficult/ confusing by candidates Change in mechanical advantage when the load is shifted towards fulcrum in class II lever. Speed of light for all wavelengths in vacuum is the same. Problems on calorimetry. Conversion of units. Heat capacity and specific heat capacity. Ray diagrams of lenses. Numerical problem on lens formula. Total internal reflection through right angled isosceles prism. Specific resistance and its unit. Differentiation between resistance and specific resistance. Difference between the use of a fuse in a normal circuit and a power circuit. Numerical on reflection of sound. Confusion between the use of = and = 2 . Beta emission during carbon dating. Nuclear fusion. Concept of isobar. Identification of magnetic poles in electromagnets. Substitution in a numerical which required some conversion. 32 Suggestions for candidates Avoid selective study. Learn tables and squares up to 30. Read the questions heedfully and write answer in brief and to the point. Express the answer only in SI units unless otherwise asked. Learn the principles, laws and definitions accurately. Focus more on conceptual learning rather than the rote learning. Make observations and try to relate your learning with it. State the meaning of the symbols if the answer is given in terms of any formula/mathematical equation. Use abbreviations/symbols which are standard/acceptable. Solve at least the last five years I.C.S.E. question papers. Write in a neat and legible handwriting. Avoid changing the order of sequence of questions and numbering system while attempting the paper. Express final answer with proper unit as per the requirement of the question. 33 QUALITATIVE ANALYSIS CHEMISTRY (PAPER-2) SECTION I (40 Marks) Attempt all questions from this Section Question 1 (a) Choose the correct answer from the options given below: (i) (ii) (iii) (iv) The salt solution which does not react with ammonium hydroxide is: A. Calcium Nitrate B. Zinc Nitrate C. Lead Nitrate D. Copper Nitrate The organic compound which undergoes substitution reaction is: A. C 2 H2 B. C 2 H4 C. C 10 H 18 D. C 2 H6 The electrolysis of acidified water is an example of: A. Reduction B. Oxidation C. Redox reaction D. Synthesis The IUPAC name of dimethyl ether is: A. Ethoxy methane B. Methoxy methane C. Methoxy ethane 34 [5] D. (v) (b) Ethoxy ethane The catalyst used in the Contact Process is: A. Copper B. Iron C. Vanadium pentoxide D. Manganese dioxide Give one word or a phrase for the following statements: [5] (i) The energy released when an electron is added to a neutral gaseous isolated atom to form a negatively charged ion. (ii) Process of formation of ions from molecules which are not in ionic state. (iii) The tendency of an element to form chains of identical atoms. (iv) The property by which certain hydrated salts, when left exposed to atmosphere, lose their water of crystallization and crumble into powder. (v) The process by which sulphide ore is concentrated. (c) Write a balanced chemical equation for each of the following: (i) [5] Action of concentrated sulphuric acid on carbon. (ii) Reaction of sodium hydroxide solution with iron (III) chloride solution. (iii) Action of heat on aluminum hydroxide. (iv) Reaction of zinc with potassium hydroxide solution. (v) Action of dilute hydrochloric acid on magnesium sulphite. (d) (i) Give the IUPAC name for each of the following: 1. 2. 3. (ii) Write the structural formula of the two isomers of butane. 35 [5] (e) State one relevant observation for each of the following: [5] (i) Lead nitrate solution is treated with sodium hydroxide solution drop wise till it is in excess. (ii) At the anode, when molten lead bromide is electrolyzed using graphite electrodes. (iii) Lead nitrate solution is mixed with dilute hydrochloric acid and heated. (iv) Anhydrous calcium chloride is exposed to air for some time. (v) Barium chloride solution is slowly added to sodium sulphate solution. (f) Give a reason for each of the following: (i) [5] Ionic compounds have a high melting point. (ii) Inert gases do not form ions. (iii) Ionisation potential increases across a period, from left to right. (iv) Alkali metals are good reducing agents. (v) Conductivity of dilute hydrochloric acid is greater than that of acetic acid. (g) Name the gas that is produced in each of the following cases (i) [5] Sulphur is oxidized by concentrated nitric acid. (ii) Action of dilute hydrochloric acid on sodium sulphide. (iii) Action of cold and dilute nitric acid on copper. (iv) At the anode during the electrolysis of acidified water. (v) Reaction of ethanol and sodium. (h) Fill up the blanks with the correct choice given in brackets. (i) Ionic or electrovalent compounds do not conduct electricity in their _____________ state. (fused / solid) (ii) Electrolysis of aqueous sodium chloride solution will form _____________ at the cathode. (hydrogen gas / sodium metal) (iii) Dry hydrogen chloride gas can be collected by _____________ displacement of air. (downward / upward) (iv) The most common ore of iron is _____________. (calamine / haematite) (v) The salt prepared by the method of direct combination is _____________. (iron (II) chloride / iron (III) chloride 36 [5] Comments of Examiners (a) (i) Some candidates chose the salt copper nitrate while others selected lead nitrate instead of calcium nitrate. (ii) Many candidates made random choices indicating they did not associate the fact that alkanes show substitution reactions or did not apply the general formula to select the correct alkane. (iii) A few candidates either wrote oxidation or reduction instead of redox reaction. (iv) Many candidates were unsure of the correct name and gave varied names. (v) Most candidates selected the correct option of vanadium pentoxide. However, a few chose iron which was incorrect. (b) (i) Instead of electron affinity, many candidates wrote electronegativity or ionization potential. (ii) Many candidates wrote dissociation instead of ionization. (iii) Some candidates wrote self-linking instead of Catenation. (iv) Majority of the candidates answered correctly. However, a few candidates got confused between efflorescence and deliquescence. Spelling errors were also noticed in some answers. Some referred to it as effervescence. (v) Many candidates wrote roasting or calcination instead of froth floatation. (c) (i) Many candidates erred by writing H 2 SO 3 or H 2 CO 3 among the products. Some left the equation unbalanced. A few wrote Cu instead of C. (ii) Some candidates wrote the equation with FeCl 2 instead of FeCl 3. (iii) Some candidates incorrectly wrote the products as Al and H 2 O. (iv) Some candidates wrote incorrect formula of potassium zincate and many wrote one of the products as Zn(OH) 2 or ZnO or K 2 O. (v) Many candidates got confused between magnesium sulphite, sulphide and sulphate. Some others erred by writing one of the products as H 2 SO 3 instead of H 2 O +SO 2 . (d) (i) Some candidates wrote trivial or common names. (1) methanone instead of methanal. 37 Suggestions for teachers Encourage students to read the question carefully and state complete answers. Familiarize students with the help of practical work that NH4OH forms precipitate with Pb2+, Zn2+, Cu2+ Fe2+, Fe3+ but not with Ca2+. Ask students to learn hydrocarbons (alkanes, alkenes and alkynes) their general formulae, methods of preparation and main properties thoroughly. Stress upon revising the concepts based on oxidation and reduction frequently. Train students in naming of compounds, both the trivial names (where possible) and IUPAC names. Instruct students to learn industrial processes like Haber s, Ostwald s and Contact with conditions, reactions and precautions (if any) in detail. Advise students to learn the differentiation between terms such as: ionization potential and electron affinity; electron affinity and electronegativity; dissociation and ionization; ionic compounds and covalent compounds; self-linking and catenation; efflorescence and deliquescence; efflorescence and effervescence; roasting and calcination; roasting and froth floatation; calcination and froth floatation Teach various methods of concentration of ores with the help of diagrams/charts etc, for better retention of the content. Test regularly or conduct quizzes on topics that require memorization for better retention. (2) Name ended by al instead of ol while some incorrectly wrote prop-l-ol. (3) 1,2-dimethlyethene instead of 2-butene or but-2-ene. Some wrote simply butane or butan-2-ene. (ii) Many candidates did not understand the difference between straight and branched chains clearly. Some showed the Carbon skeleton and missed showing the complete structural formula. (e) (i) Many candidates wrote white Pb(OH) 2 instead of white precipitate soluble. Thus, the answer was left incomplete. For solubility of the precipitate in excess NaOH some wrote: Insoluble in excess instead of soluble in excess. White solution instead of colourless solution. (ii) Colour of bromine was written as orange/red by some candidates; some forgot to add the word vapour or gas with the colour of bromine; A few candidates wrote that grey metal is deposited at the anode. Several candidates wrote equations instead of observations. (iii) Instead of white precipitate many candidates wrote reddish brown fumes of NO 2 . Some wrote the equation without stating the colour of the precipitate. A few candidates expressed the answer by leaving out the effect of heating on the solubility of PbCl 2. (iv) Instead of writing that CaCl 2 turns into colourless solution, candidates wrote that it turns hydrated. Some candidates stated that it turns powdery having got confused with efflorescent substances. (v) Most candidates answered correctly. However, a few candidates identified the product BaSO 4 but missed out the word precipitate or the colour white (f) (i) Intermolecular force of attraction instead of strong electrostatic force of attraction between ions was stated to be responsible for the high melting point in ionic compounds. (ii) Some candidates wrote that inert gases are stable without mentioning electronic configuration / 8 electrons in the valence shell. 38 - - - Advise students to learn the chemical reactions with necessary conditions and their balanced chemical equations assiduously and practise by writing again and again. Draw the attention of students to the difference in the symbols of radicals especially when the names sound similar. Ensure students grasp the fact that alcohols end in ol and aldehydes end in al that the e of an alkane is replaced by ol or al Instruct students that numbering of chain is essential to assign the number to the functional group. Clarify straight and branched chains with sufficient examples and by giving repeated practice. Insist upon students recording the observation on their own during practical and then ask them to compare their observations with the observations expected. Discuss the reason for the difference (if any) in their observations. Demonstrate the what happens when type of possible cases to students to enable them to write relevant observation/s with confidence. Give practice in answering reasoning questions in different units. Explain the possible reasoning questions in the class at the time of discussing a topic. Train students to write answers to the point. While writing a chemical equation, gas should be highlighted with an upward arrow and precipitation with a downward arrow. Instruct students to be specific as per the requirement of the question in writing the correct gas or precipitate instead of giving multiple answers or all products. Guide students to learn the chemical names correctly especially the various oxides of nitrogen, etc. (iii) Many candidates could not explain the reason for increase in ionisation potential Ask students to first name the across a period, from left to right. electrode and then give the equation (iv) Many candidates did not write the correct or product while answering questions reason to explain alkali metals are good on reaction at electrode. reducing agents. Ask students to read the given (v) Most candidates wrote about the statements and choices supplied conductivity of dilute HCl or acetic acid but carefully. could not compare the conductivity of both the acids. (g) (i) Instead of NO 2 some candidates wrote SO 2 , H 2 S or N 2 while some others wrote NO 2 and SO 2 . (ii) Most of the candidates answered this sub-part correctly. (iii) While most candidates were able to give correct answer, but a few could not name the gas correctly called it nitrogen oxide instead of nitric oxide or gave the incorrect answer NO 2. (iv) While writing the name of the gas produced at the anode during the electrolysis of acidified water many candidates overlooked the term anode and wrote hydrogen and oxygen. (v) Several candidates wrote ethane/ethene is evolved with the reaction of ethanol and sodium which was an incorrect answer. (h) This question was attempted well by most candidates, but a few candidates made errors in subparts(i), (ii) and (v). MARKING SCHEME Question 1 (a) (i) (ii) (iii) (iv) (v) A or calcium nitrate D or C 2 H 6 C or redox reaction B or methoxy methane C or Vanadium pentoxide (b) (i) (ii) (iii) (iv) (v) Electron affinity/electron gain enthalpy Ionisation Catenation Efflorescence/efflorescent Froth floatation method (c) (i) C + 2H 2 SO 4 CO 2 + 2SO 2 + 2H 2 O (ii) FeCl 3 + 3NaOH Fe(OH) 3 + 3NaCl (iii) 2Al(OH) 3 Al 2 O 3 + 3H 2 O (iv) Zn + 2KOH K 2 ZnO 2 + H 2 (v) MgSO 3 + 2HCl MgCl 2 + SO 2 + H 2 O 39 (d) (i) (ii) 1. 1. Methanal or methan-1-al 2. 1Propanol or Propane 1 OL 3. 2Butene or but 2 ene OR 2. (e) (i) CH 3 -CH 2 -CH 2 -CH 3 CH 3 | H 3 C CH CH 3 OR White precipitate soluble in excess of sodium hydroxide solution. (ii) Reddish brown vapour at the anode. (iii) A white precipitate is formed which dissolves on heating or initially white precipitate is formed but on heating colourless solution is observed. (iv) Colourless solution or solid CaCl 2 turns into solution. (v) A white precipitate is formed. (correct relevant observations accepted) (f) (i) Oppositely charged ions are held by strong force of attraction or energy is required to separate the ions/ particles held by strong electrostatic force of attraction (ii) Inert gases have stable electronic configuration or have 8 electrons in the valence shell (last shell) / do not lose or gain electrons to form ions/complete outermost or valence shell. (iii) Nuclear charge increases / nucleus exerts greater force of attraction on the valence electrons of same shell or atomic size decreases / the force of attraction on the valence electrons are more i.e., increases. (iv) Alkali metals have low ionization potential / have one electron in their valence shell /and hence they easily lose or donate electron. (v) Dilute hydrochloric acid undergoes complete ionization/ dissociation whereas acetic acid undergoes incomplete or partial ionization or dilute HCl has higher concentration of ions than acetic acid./Dilute hydrochloric acid is a stronger acid than acetic acid/ Dilute hydrochloric acid is a strong electrolyte and acetic acid is a weak electrolyte/ Dilute hydrochloric -only ions, acetic acid- ions and molecules/ Dilute hydrochloric acid has higher degree of dissociation than acetic acid. 40 (g) (i) Nitrogen dioxide or NO 2 (ii) Hydrogen sulphide or H 2 S (iii) Nitric oxide / nitrogen monoxide or NO (iv) Oxygen or O 2 (v) Hydrogen or H 2 (h) (i) solid (ii) hydrogen (gas) (iii) upward (iv) Haematite (v) iron III chloride SECTION II (40 Marks) Attempt any four questions from this Section Question 2 (a) (i) What do you understand by a lone pair of electrons? [3] (ii) Draw the electron dot diagram of Hydronium ion. (H=1; O=8) (b) In Period 3 of the Periodic Table, element B is placed to the left of element A. [3] On the basis of this information, choose the correct word from the brackets to complete the following statements: (i) The element B would have (lower / higher) metallic character than A. (ii) The element A would probably have (lesser / higher) electron affinity than B. (iii) The element A would have (greater / smaller) atomic size than B. (c) Copy and complete the following table which refers to the conversion of ions to neutral particles. Conversion Ionic Equation Oxidation / Reduction Chloride ion to chlorine molecule (i) __________ (ii) __________ Lead (II) ion to lead (iv) __________ (iii)__________ 41 [4] Comments of Examiners (a)(i) Many candidates could not define a lone pair of electrons completely. They missed out the key words in the definition like pair of electrons or not shared/unshared or covalent molecule. (ii) Observations in the electron dot diagram of hydronium ion drawn by some candidates were as follows: the lone pair or the charge was missing. same kind of dots were used for electrons of both O and H the coordinate bond was not indicated by an arrow. (b) Majority of the candidates attempted subparts (i), (ii) and (iii) of this question well barring a few exceptions who could not choose the correct word from the brackets to complete the given statements. (c) Common errors observed in this question were: in ionic equations such as of Cl 2 formation, equation Cl - + eCl was given and the next equation was missed out. Pb 2+ - 2e Pb. the term oxidation/reduction was incorrectly associated with the ionic equations. Suggestions for teachers Stress upon using the necessary key words and insist on underlining them at the time of regular practice in class. Train students to draw both dot structure and bond structure separately. Instruct students about the periodic properties of elements in the Periodic table and variations of properties in detail. Use charts displayed with pictorial representation of the trends to enhance understanding and retention. Give regular exercises in application of the knowledge of trends of the following periodic properties in groups and periods: atomic size, metallic character, electron affinity, etc. Illustrate the concept of oxidation and reduction based on loss and gain of electrons in detail. MARKING SCHEME Question 2 (a) (i) The pair of electrons which is not yet shared with other atoms in a covalent molecule is known as lone pair of electrons. (ii) (b) (i) (ii) (iii) higher higher smaller (c) (i) 2Cl1- 2e Cl 2 or Cl- e Cl (or Cl- Cl + e-) and Cl + Cl Cl 2 or 2Cl Cl 2 (ii) Oxidation (iii) Pb2+ + 2e Pb (iv) Reduction 42 Question 3 (a) (i) Write the balanced chemical equation to prepare ammonia gas in the laboratory by [3] using an alkali. (ii) State why concentrated sulphuric acid is not used for drying ammonia gas. (iii) Why is ammonia gas not collected over water? (b) (i) Name the acid used for the preparation of hydrogen chloride gas in the laboratory. [3] Why is this particular acid preferred to other acids? (ii) Write the balanced chemical equation for the laboratory preparation of hydrogen chloride gas. (c) For the preparation of hydrochloric acid in the laboratory: (i) [2] Why is direct absorption of hydrogen chloride gas in water not feasible? (ii) What arrangement is done to dissolve hydrogen chloride gas in water? (d) For the electro-refining of copper: (i) [2] What is the cathode made up of? (ii) Write the reaction that takes place at the anode. 43 Comments of Examiners (a) (i) Many candidates wrote the required balanced chemical equation to prepare ammonia gas in the laboratory using an alkali correctly but some wrote methods of preparation of NH 3 gas using NaOH or using (NH 4 ) 2 SO 4 instead of NH 4 Cl. Some showed the formation of NH 4 OH instead of NH 3 . Most candidates answered sub parts (ii) and (iii) of this question correctly. (b) (i) Many candidates did not specify whether sulphuric acid used for the preparation of hydrogen chloride gas in the laboratory should be concentrated or dilute. In response to the preference of this acid over other acids, some wrote that it does not react with HCl gas. (ii) Some candidates did not mention the necessary condition of temperature i.e., below 200 oC to ensure Na 2 SO 4 is not formed which has a tendency to get fused with the glass and ended up writing the equation which was not required as per the question asked : 2NaCl + H 2 SO 4 Na 2 SO 4 +2HCl (c)(i) Many candidates gave inadequate explanation without mentioning the effect back suction. (ii) Most candidates answered correctly. However, a few candidates wrote thistle funnel instead of inverted funnel arrangement. (d) (i) Majority of the candidates wrote that the cathode is made up of copper. A few candidates missed out associating the word pure with it or wrote impure copper. (ii) Some candidates wrote incorrect reactions such as: Cu + 2e- Cu2+ Or Cu2+ - 2e- Suggestions for teachers Insist upon students sticking to the choice of appropriate reactants for laboratory preparations. Explain thoroughly the study of compounds with laboratory preparation of hydrogen chloride gas, ammonia, etc., and their physical and chemical properties. Besides this, also discuss all possible reasoning questions related to their physical and chemical properties at length. Instruct students to read the question carefully and answer to the point as per the requirement of the question. Clarify the technical terms used in the question. Train students to write dilute or concentrated whenever reference is made to any acid. Habituate students to write chemical equations with necessary conditions Show a presentation on back suction will give clarity to students. Discuss electrorefining and also give practice in writing reactions taking place at cathode and anode. Cu MARKING SCHEME Question 3 (a) (i) 2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2H 2 O + 2NH 3 (ii) Concentrated sulphuric acid reacts with ammonia / form ammonium sulphate or NH 3 being basic combines with concentrated H 2 SO 4 /correct chemical equation. (iii) NH 3 is highly soluble in water or dissolves in water. (b) (i) Concentrate sulphuric acid. It is nonvolatile / has high boiling point / displaces the volatile hydrogen chloride from the salt sodium chloride. (c) 200 NaCl + H 2 SO 4 NaHSO 4 + HCl (conc.) (i) Back suction occurs (or the description of back suction) / HCl gas dissolves in water at a faster rate than it is produced. (ii) 44 (ii) Inverted funnel arrangement/ the rim of the funnel just touches the surface of water taken in the trough or correct diagram. (d) (i) Pure copper (ii) Cu 2e Cu2+ / Cu Cu2+ + 2e- Question 4 (a) The percentage composition of a gas is: [2] Nitrogen 82.35%, Hydrogen 17.64%. Find the empirical formula of the gas. (b) [N = 14, H = 1] Aluminum carbide reacts with water according to the following equation: [4] Al 4 C 3 + 12H 2 O 4Al (OH) 3 + 3CH 4 (i) What mass of aluminum hydroxide is formed from 12 g of aluminum carbide? (ii) What volume of methane at s.t.p. is obtained from 12 g of aluminum carbide? [Relative molecular weight of Al 4 C 3 = 144; Al(OH) 3 = 78] (c) (i) If 150 cc of gas A contains X molecules, how many molecules of gas B will be [2] present in 75 cc of B? The gases A and B are under the same conditions of temperature and pressure. (ii) Name the law on which the above problem is based. (d) Name the main component of the following alloys: (i) [2] Brass (ii) Duralumin Comments of Examiners (a) Some candidates calculated the number of atoms by dividing atomic weight by the individual percentage. Therefore, empirical formula went incorrect. In the last step, some candidates stated the empirical formula as N 3 H instead of NH 3. (b) (i) Many candidates ignored the stoichiometric coefficients and did not consider 4 moles of Al(OH) 3 . 45 Suggestions for teachers Train students to work out numericals step by step and give enough practice in solving them. Explain Mole concept and Stoichiometry in detail (ii) A few candidates ignored the fact that 3 moles of CH 4 were released with every mole of Al 4 C 3 . (c) (i) Most candidates answered correctly. However, a few candidates wrote number of molecules of gas B as 2x instead of x/2. (ii) Many candidates named the law as Gay Lussac s law which was incorrect. (d) In sub-parts (i) and (ii), most candidates listed all the components of the alloys Brass and Duralumin instead of giving the main components as asked in the question. Familiarize students with the equivalent correspondence between number of moles, molar mass and molar volume. Give adequate practice to students in solving numerical problems based on Mole and Stoichiometry. Ensure that students understand Gay Lussac s law of combining volumes, Avogadro s law, their statements, explanation and numerical problems based on them. Train students to read the question carefully and answer only whatever is asked in the question. MARKING SCHEME Question 4 (a) (b) % Composition Atomic Mass No. of atoms N 82.35 14 82.35/14=5.88 5.88/5.88=1 H 17.64 1 17.64/1=17.64 17.64/5.88=3 Empirical Formula N 1 H 3 Al 4 C 3 + 12H 2 O 4Al(OH) 3 + 3CH 4 144 4 x 78 = 312 1. 144 g Al 4 C 3 312 g of Al(OH) 3 Mass of Al(OH) 2 = 2. (d) 144 x 12 = 26 g 144 g Al 4 C 3 3 x 22.4l of CH 4 Volume of CH 4 = (c) 312 3 22.4 144 (i) No. of molecules of B = (ii) Avogadro s law (i) Copper (ii) Aluminum 12 = 5.6l CH 4 75 150 =2 46 Simplest formula Question 5 (a) Complete the following table which relates to the homologous series of hydrocarbons. General formula C n H 2n 2 C n H 2n + 2 (b) IUPAC name of the homologous series Characteristic bond type IUPAC name of the first member of the series (A) __________ (B)__________ (C)__________ (D)__________ (E)__________ (F)__________ (i) Name the most common ore of the metal aluminum from which the metal is [6] [4] extracted. Write the chemical formula of the ore. (ii) Name the process by which impure ore of aluminum gets purified by using concentrated solution of an alkali. (iii) Write the equation for the formation of aluminum at the cathode during the electrolysis of alumina. Comments of Examiners (a) Some candidates made the following mistakes in completing the table which relates to the homologous series of hydrocarbons: - Name of compound was written in place of homologous series; - The characteristic bond was referred to as unstaturated/saturated instead of triple covalent bond and single covalent bond respectively; - The IUPAC name of the first member of the alkynes was given as methyne. (b) Most candidates wrote the name of the common ore of aluminum from which the metal is extracted as alumina or cryolite instead of Bauxite. Some candidates gave chemical formula of Bauxite as Al 2 O 3 .5H 2 O wherein the number of water molecules was incorrect. (i) A few candidates named the process by which impure ore of aluminum gets purified by using concentrated solution of an alkali as Hall s process or Hoope s Process in place of Baeyer s process. 47 Suggestions for teachers - Develop an understanding of the general formula of hydrocarbons. Train students to apply general formula to various component and point out the formation of a homologues series with its special features like successive members differing by CH2 and so on. - Write the name or formula of any organic compound using the IUPAC system of nomenclature. - Give enough practice to students in writing the name of compounds and their structures. - Clarify electrolysis and its applications in detail with examples. Instruct students to commit to memory the names and formulae of important ores of metals (listed in the syllabus) and the processes for extraction of metals from ores (ii) Most candidates wrote the correct equation for the formation of aluminum at the cathode during the electrolysis of alumina. However, a few got confused and wrote equations like: Al 3eOr Al + 3eOr 2Al3+ +6e- - Advise students to ensure instructions are read carefully. that Al3+ Al3+ Al MARKING SCHEME Question 5 (a) (b) (A) Alkyne (B) Triple covalent bond/ triple/ / C C/ CH CH (C) Ethyne (D) Alkane (E) Single covalent bond/ single / / C C (F) Methane (i) Bauxite Al 2 O 3 . 2H 2 O (ii) Baeyer s Process (iii) Al3+ + 3e Al Question 6 (a) A compound X (having vinegar like smell) when treated with ethanol in the presence [4] of the acid Z, gives a compound Y which has a fruity smell. The reaction is: C 2 H 5 OH + X Y + H 2 O (b) (i) Identify Y and Z. (ii) Write the structural formula of X. (iii) Name the above reaction. Ethane burns in oxygen to form CO 2 and H 2 O according to the equation: 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O. If 1250 cc of oxygen is burnt with 300 cc of ethane. Calculate: 48 [4] (c) (i) the volume of CO 2 formed. (ii) the volume of unused O 2 . Three solutions P, Q and R have pH value of 3.5, 5.2 and 12.2 respectively. Which [2] one of these is a: (i) Weak acid? (ii) Strong alkali? Comments of Examiners (a)(i) Many candidates identified compound Y as C 2 H 5 COOCH 3 while some identified it as ester.A few candidates did not mention the strength of the acid. (ii) Some candidates drew an incorrect structure of compound X. (iii) Majority of candidates named the reaction correctly. However, a few called it catalysis which was not correct. (b) (i) While majority of candidates answered correctly, a few candidates incorrectly used volume of O 2 to calculate the volume of CO 2 . Some copied the volume of ethane incorrectly. (ii) Many candidates did not calculate the volume of unused O 2 . (c) (i) Some candidates wrote solution P having value of pH 3.5 as that of a weak acid. (ii) Most candidates answered correctly. Suggestions for teachers - Clarify that the H of acid is replaced by the alkyl group of alcohol and to prevent the backward reaction conc.H2SO4 (a strong dehydrating agent) is used to remove the moisture content. - Train students in naming as well as drawing various kinds of structural formulae. - Ensure that students know the reaction is called esterification. - Provide adequate practice to students in numerical problems. Insist on stepwise working. - Guide students about pH scale to test for acidity, neutrality and alkalinity. MARKING SCHEME Question 6 (a) (i) Y: Ethyl acetate / Ethyl ethanoate / CH 3 COOC 2 H 5 Z: Concentrated H 2 SO 4 (ii) (b) (iii) (i) (ii) Esterification 4 Volume of CO 2 formed = 2 x 300 = 600 cc 7 Volume of O 2 used = 2 x 300 = 1050 cc Volume of unused oxygen = 1250 1050 = 200 cc 49 (c) (i) Solution Q (ii) Solution R Question 7 (a) (b) (c) (d) Give a chemical test to distinguish between the following pairs of chemicals: (i) Lead nitrate solution and Zinc nitrate solution (ii) Sodium chloride solution and Sodium nitrate solution Write a balanced equation for the preparation of each of the following salts: [4] [2] (i) Copper sulphate from Copper carbonate. (ii) Zinc carbonate from Zinc sulphate. (i) What is the type of salt formed when the reactants are heated at a suitable [2] temperature for the preparation of Nitric acid? (ii) State why for the preparation of Nitric acid, the complete apparatus is made up of glass. Which property of sulphuric acid is shown by the reaction of concentrated sulphuric [2] acid with: (i) Ethanol? (ii) Carbon? Comments of Examiners (a) (i) Many candidates ignored the solution state of both Pb(NO 3 ) 2 and Zn(NO 3 ) 2 and gave dry heating test for each, which was contrary to the requirement of the question. Some candidates used, the reagent solution NaOH in place of NH 4 OH for distinguishing one from the other. (ii) A few candidates used concentrated H 2 SO 4 to distinguish between NaCl and NaNO 3 overlooking the fact that both were in solution form and not in solid state. (b)(i) Instead of reaction with H 2 SO 4 , a few candidates used Na 2 SO 4 solution. Some candidates wrote two equations first using HCl and then using H 2 SO 4 . 50 Suggestions for teachers - Demonstrate chemical tests to distinguish between the pairs of chemicals for better understanding and recall. Simultaneously, explain other technicalities related to use of those chemicals/reagents, etc. - Guide students to learn the typical reactions of acid in word form also such as Carbonate +Acid Salt +H2O +CO2 (ii) Instead of Na 2 CO 3 solution or another soluble carbonate solution, a few candidates used H 2 CO 3 solution. Some used two steps to obtain ZnCO 3 : - first reaction of ZnSO 4 with HCl and - second reaction of ZnCl 2 with Na 2 CO 3 . (c)(i) Instead of acid salt, some candidates wrote normal salt. (ii) Most candidates answered correctly but a few stated that rubber will melt due to heat or cork will break. (d)(i) Many candidates wrote drying instead of dehydration. (ii) Several candidates stated acidic property instead of oxidising property. - Discuss most of the reasoning questions (wherever it is possible), with demonstration in the laboratory or in the class through actual observation to develop students inquisitiveness. - Explain thoroughly the preparation of nitric acid, equations with conditions, setting up of apparatus, precautions, material suitable for its storage, etc. - Stress on the essential difference between drying and dehydration i.e. in the former process only physically combined water/moisture is removed but in dehydration chemically combined H2O is removed. - Explain about the behavior of sulphuric acid in its dilute and concentrated forms, and its volatile nature with illustrations. MARKING SCHEME Question 7 (a) (b) (i) By adding ammonium hydroxide in excess. Lead nitrate solution gives a white precipitate while Zinc Nitrate solution gives a colourless solution. (ii) By adding silver nitrate / lead nitrate solution. Sodium chloride gives a white precipitate while sodium nitrate gives no precipitate / colourless solution / remains unchanged. (alternate correct chemical test) (i) CuCO 3 + H 2 SO 4 CuSO 4 + H 2 O +CO 2 (c) (ii) ZnSO 4 + Na 2 CO 3 ZnCO 3 + Na 2 SO 4 Or ZnSO 4 + (NH 4 ) 2 CO 3 (NH 4 ) 2 SO 4 + ZnCO 3 (i) Acid Salt/ bisulphate/ hydrogen sulphate/ NaHSO 4 / KHSO 4 (d) (ii) The vapour of nitric acid being highly corrosive/ HNO 3 vapours attack rubber, cork etc./ HNO 3 vapours do not react with glass. (i) (ii) Dehydrating agent/dehydration Oxidizing agent/oxidation Note: For questions having more than one correct answer/solution, alternate correct answers/solutions, apart from those given in the marking scheme, have also been accepted. 51 GENERAL COMMENTS Topics found difficult/ confusing by candidates Concepts in which candidates got confused Specific tests to identify/distinguish between substances. IUPAC names of organic compounds. Scientific terms for process/properties. Observations of different reactions based on practical chemistry. Reasons behind trends in properties across or down the periodic table. Ionic equations, especially involving the discharge of ions/formation of ions. Selective discharge of ions during electrolysis. Definition if lone pair of electrons. Scientific reasons for certain observations. Electron affinity and Ionization potential. Froth floatation and roasting. Method of preparations of salts in the lab. Dissociation and Ionization. Gases involved in reactions. Structural formulae of organic compounds. Difference between precipitate and solution. 52 Suggestions for Candidates Read the questions carefully and then answer accordingly what has been asked. Avoid selective study. Prepare charts to study topics at a glance, such as Industrial processes, comparative study of Homologous series of hydrocarbons, etc. Practice numerical problems regularly, solve the numericals stepwise with correct formula and write the answer with correct unit. Learn definitions verbatim and highlight key words. Learn symbols of elements and their valencies. Practice writing balanced chemical equations with necessary conditions. In a chemical equation, write an acid with its strength(dilute/concentration) Name organic chemical compounds only using IUPAC nomenclature. In laboratory listen to the teacher s instructions carefully, read the experiment thoroughly and then perform it. Select only one reagent when distinguishing between substances and state the result with each substance. Study the typical reactions of acids as word equations such as Metal + Acid ---> Salt + H2 OR Carbonate + Acid ---> Salt + H2O + CO2 Practice structural formulae of hydrocarbons. Solve past years papers to understand the pattern of the paper. 53 QUALITATIVE ANALYSIS BIOLOGY (PAPER-3) SECTION I (40 Marks) Attempt all questions from this Section Question 1 (a) Name the following: [5] (i) The organization which procures and supplies blood during an emergency. (ii) The blood vessel which supplies blood to the liver. (iii) The number of chromosomes present in a nerve cell of a human being. (iv) The layer of the eyeball that forms the transparent Cornea. (v) The wax-like layer on the epidermis of leaves which reduces transpiration. (b) Choose the correct answer from each of the four options given below: (i) (ii) (iii) The number of Spinal nerves in a human being are: A. 31 pairs B. 10 pairs C. 21 pairs D. 30 pairs Which one of the following is non-biodegradable? A. DDT B. Vegetable peel C. Cardboard D. Bark of trees Aqueous humour is present between the: 54 [5] A. Lens and Retina B. Iris and Lens C. Cornea and Iris D. Cornea and Lens (iv) A strong chemical substance which is used on objects and surfaces in our surroundings to kill germs: (v) (c) A. Cresol B. Carbolic acid C. Iodine D. Mercurochrome Which one of the following is a Greenhouse gas? A. Oxygen B. Methane C. Sulphur dioxide D. Nitrogen Complete the following paragraph by filling in the blanks (i) to (v) with appropriate [5] words: To test a leaf for starch, the leaf is boiled in water to (i)__________. It is then boiled in Methylated spirit to (ii)__________. The leaf is dipped in warm water to soften it. It is placed in a petri dish, and (iii)__________ solution is added. The region of the leaf which contains starch, turns (iv)__________ and the region which does not contain starch, turns (v)__________. (d) Match the items given in Column A with the most appropriate ones in Column B and rewrite the correct matching pairs. Column A Column B (i) Cretinism (a) Hypersecretion of adrenal cortex (ii) Diabetes insipidus (b) Hyposecretion of Thyroxine 55 [5] (iii) Exophthalmic Goitre (c) Hyposecretion of growth hormone (iv) Adrenal virilism (d) Hyposecretion of Vasopressin (v) Dwarfism (e) Hyposecretion of adrenal cortex (f) Hypersecretion of Growth hormone (g) Hypersecretion of Thyroxine (e) Correct the following statements by changing the underlined words: [5] (i) Normal pale yellow colour of the urine is due to the presence of the pigment Melanin. (ii) The outermost layer of Meninges is Pia mater. (iii) The cell sap of root hair is Hypotonic. (iv) Xylem transports starch from the leaves to all parts of the plant body. (v) Nitrogen bonds are present between the complementary nitrogenous bases of DNA. (f) Choose between the two options to answer the question specified in the brackets for the [5] following: An example is illustrated below. Example: Corolla or Calyx (Which is the outer whorl?) Answer: Calyx (i) Blood in the renal artery or renal vein (Which one has more urea?) (ii) Perilymph or endolymph (Which one surrounds the organ of Corti?) (iii) Lenticels or stomata (Which one remains open always?) (iv) Sclerotic layer or choroid layer (Which one forms the Iris?) (v) Blood in the pulmonary artery or pulmonary vein (Which one contains less oxyhaemoglobin?) (g) Given below is a representation of a type of pollution. Study the picture and answer the questions: 56 [5] (i) Name the type of pollution shown in the picture. (ii) Name one source of this pollution. (iii) How does this pollution affect human health? (iv) Write one measure to reduce this pollution. (v) State one gaseous compound that leads to the depletion of the ozone layer and creates Ozone holes . (h) Choose the ODD one out from the following terms given and name the CATEGORY to which the others belong: Example: Nose, Tongue, Arm, Eye Answer: Odd Term Arm, Category Sense organs (i) Detergents, X-rays, sewage, oil spills (ii) Lumen, muscular tissue, connective tissue, pericardium (iii) Dendrites, Medullary Sheath, Axon, Spinal cord (iv) Centrosome, Cell wall, Cell membrane, Large vacuoles (v) Prostate gland, Cowper s gland, seminal vesicle, seminiferous tubules. 57 [5] Comments of Examiners (a) (i) Most candidates wrote the correct answer. WHO was written as an incorrect answer by some candidates. (ii) Majority of candidates wrote the correct answer. However, some candidates were confused between Hepatic artery and Hepatic vein. (iii) Most candidates answered correctly. Some candidates, however, wrote the chromosome number of gametes instead of number of chromosomes present in a nerve cell. (iv) Many candidates wrote choroid instead of sclera. Some candidates could not spell the term correctly. (v) Most candidates wrote the correct answer. (b) (i) Most candidates wrote the number of Spinal nerves in a human being correctly. (ii) Most candidates chose the correct nonbiodegradable from the options given. (iii) Many candidates were unsure of the location of aqueous humour. (iv) Most candidates wrote the correct answer. (v) Most candidates wrote the correct option from the given four alternatives for a Greenhouse gas. (c) In the given paragraph, most candidates filled in the appropriate words in the blanks (i), (iii)-(v). However, a few candidates could not fill in the appropriate word in the blank (ii), which shows that some candidates did not know the usage of methylated spirit in the starch test. (d) Most candidates wrote the most appropriate matching pairs for the items given in column A and column B. Suggestions for teachers - Give importance to each step of the Starch Test which is done at the end of an experiment on photosynthesis along with its significance. - Give a number of examples of plants having variegated leaves and tell the students which parts of such leaves give a positive test for the presence of Starch. - Advise students to read the instructions given for each question very carefully. - Explain the parts and functions of the eye and ear using charts, models and interactive boards. - Emphasise on the differences between Plant and Animal Cells. - Train students to know the location and function of stomata and lenticels. - Familiarise students with the location and function of the different parts of testis and accessory glands. - Acquaint students with the hormones secreted by the endocrine glands and the disorders caused due to their Hypo and Hyper secretions. - Explain the differences between Biodegradable and NonBiodegradable substances, Antiseptics and Disinfectants and the kind of blood flowing in Pulmonary artery and Pulmonary vein. - Draw the attention of the students towards the activities of WHO and Red Cross and guide them to express these correctly. (e) (i) Majority of the candidates, instead of writing Urochrome, wrote Bilirubin. (ii) Many candidates were confused with the location of the three meninges. In sub-parts (iii)-(v), most candidates corrected the statements by changing the underlined words correctly. However, a few candidates changed the underlined word in statement (v) to Covalent instead of Hydrogen. (f) (i) Majority of the candidates chose the correct option to answer the question specified in the bracket. However, a few candidates were confused between renal artery and renal vein. 58 (ii) Most candidates wrote the incorrect option to answer the question specified in the bracket which clearly implies that the candidates were unaware of the fluid surrounding the organ of Corti. (iii) Most candidates answered correctly. (iv) Many candidates were unsure of the layer of eyeball which forms the Iris. (v) Majority of the candidates wrote an incorrect answer as they were confused with the oxygen content in pulmonary artery and pulmonary vein. (g) In sub-parts (i-iv), most of the candidates answered the questions based on the study of a picture on type of pollution, correctly. For sub-part (v), only a few candidates wrote the correct answer. Most of them were unsure of the gases causing ozone holes. (h) In sub-parts (i) (iii) & (v), most of the candidates chose the ODD one out from the given terms correctly and named the category to which the others belong appropriately. However, in sub-part(iv), majority of the candidates were unsure of the difference between plant and animal cell. MARKING SCHEME Question 1 (a) (b) (c) (d) (i) Red Cross / Red Cross Society (ii) Hepatic artery/Hepatic Portal Vein (iii) 46 or 23 pairs (iv) Sclera/Sclerotic layer (v) Cuticle/cutin (i) A.31 pairs (ii) A. DDT (iii) D. Cornea and Lens (iv) A. Cresol (v) B. Methane/CH 4 (i) kill the cells (ii) remove chlorophyll/decolourise the leaf (iii) Iodine/Potassium iodide/K1/I2 (iv) blue black/blackish blue/dark blue/Indigo (v) yellowish brown/reddish brown/yellow /golden brown (i) Cretinism - (b) Hyposecretion of thyroxine (ii) Diabetes insipidus - (d) Hyposecretion of Vasopressin (iii) Exophthalmic Goitre - (g) Hypersecretion of thyroxine 59 (e) (iv) Adrenal virilims - (a) Hypersecretion of adrenal cortex (v) Dwarfism - (c) Hyposecretion of growth hormones (i) Urochrome/Urobilin (ii) Duramater (iii) Hypertonic/Concentrated (iv) Phloem (v) Hydrogen/ H (f) (i) Renal artery (ii) Endolymph (iii) Lenticels (iv) Choroid (v) Pulmonary artery (g) (i) Air/Gaseous Pollution (ii) Factories / industries / motor vehicles / cars / buses/ burning of garbage / brick kilns/trucks/lorries/Power Plant/oil refineries/burning crop residues/bursting crackers. (iii) Respiratory problems / difficulty in breathing / Asthma / poor visibility / damages lungs / bronchitis/Respiratory inflammation/cough/sneezing/wheezing/eye irritation/allergies/toxic chemical enters food chain/disorders of liver,kidney,lung,hormonal (iv) Use of unleaded petrol / CNG / Chimneys with filters or precipitators / switching off engines when not in use/use of carpool, public transport,planting more trees/regular check up of vehicles (v) Styrofoam / CFCs / Refrigerants / Freons / Ccl 4 / HFCs / HCFCs./halons/methyl bromide (h) (i) X-rays - water pollutants (ii) Pericardium - parts of artery and vein / blood vessels Lumen - Parts of heart/tissues of heart (iii) Spinal Cord - parts of neuron / nerve cell (iv) Centrosome - parts of plant cell (v) Seminiferous tubules - accessory or reproductive glands of male 60 Question 2 (a) The diagram given below represents a stage during cell division. Study the same and answer the questions that follow: (i) [5] Identify whether it is a plant cell or an animal cell. Give a reason in support of your answer. (ii) Name the stage depicted in the diagram. What is the unique feature observed in this stage? (iii) Name the type of cell division that occurs during: 1. Replacement of old leaves by new ones. 2. Formation of gametes. (iv) What is the stage that comes before the stage shown in the diagram? (v) Draw a neat, labelled diagram of the stage mentioned in (iv) above keeping the chromosome number constant. (b) Mention the exact location of the following: (i) Epididymis (ii) Lacrimal gland (iii) Malleus (iv) Hydathodes (v) Pulmonary semilunar valve [5] 61 Comments of Examiners (a) (i) Most candidates identified the diagram as that of animal cell and were able to support it with a suitable reason. (ii) Majority of the candidates wrote the correct stage of Mitosis. A few candidates were unable to give the pattern of arrangement of Chromosomes. (iii) Most candidates named the type of cell division correctly. (iv) Most candidates wrote the stage that comes before the stage shown in the diagram, correctly. (v) Most candidates drew the correct diagram. A few candidates, however, drew Anaphase and did not keep the chromosome number constant. (b) (i) Majority of the candidates were unable to specify the exact location of Epididymis. (ii) Majority of the candidates, instead of writing upper outer corner of the eye, wrote above the eye. Suggestions for teachers - Simplify the textual explanation so that the students are able to write the answers in simple and short sentences. - Train students to draw labelled diagrams of the phases of mitosis with the required number of Chromosomes. Emphasis must be laid on the nuclear changes during mitosis. - Clearly explain the location of various structure and organs in a plant and human body. - Construct similar questions in Unit Tests and Term Examinations for practice and clarify the possible errors. (iii) Most candidates wrote the exact location of Malleus correctly. (iv) The exact location of Hydathodes was written correctly by most candidates. (v) Many candidates wrote the location of the pulmonary semilunar valve in between right and left ventricle. MARKING SCHEME Question 2 (a) (i) Plant cell/cell wall present, Aster absent, Aster present Animal Centrosome present (ii) Metaphase, Chromosomes are in the equatorial plane. (iii) 1. Mitosis 2. Meosis (iv) Prophase (v) 62 cell,Centrioles / (b) (i) on top of the testis/head, dorsal ride, back, rear of testis (ii) upper sideward portion of orbit/upper outer part of eye/upper lateral region of eye (iii) middle ear / between eardrum and incus. /inner surface of eardrum (iv) Tips / margins of leaves / in leaves. /ends or apex of veins/apex of leaves/Epidermis of leaves (v) In the right ventricle at the base of pulmonary artery. /at the opening of Pulmonary Artery Question 3 (a) Given below are diagrams showing the different stages in the process of fertilisation of an [5] egg in the human female reproductive tract. Study the diagrams and answer the questions: A (i) B C D Arrange the letters given below each diagram in a logical sequence to show the correct order in the process of fertilisation. (ii) Where does fertilisation normally take place? What is Implantation that follows fertilisation? (iii) Mention the chromosome number of the egg and zygote in humans. (iv) Explain the term Gestation . How long does Gestation last in humans? (v) Draw a neat, labelled diagram of a mature human sperm. (b) A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagrams and answer the questions. 63 [5] Pale Yellow Leaf A Green (i) What aspect of photosynthesis is being tested in the above diagram? (ii) Represent the process of photosynthesis in the form of a balanced equation. (iii) Why was the plant kept in the dark before beginning the experiment? (iv) What will be the result of the starch test performed on leaf A shown in the diagram? Give an example of a plant with variegated leaves. (v) Draw a neat labelled diagram of a chloroplast. 64 Comments of Examiners (a) (i) Most candidates arranged the letters given below each diagram in a logical sequence to show the correct order in the process of fertilisation. However, a few candidates were unsure of the sequence of fertilisation. (ii) Majority of the candidate wrote the correct place of fertilisation but, some were unable to explain implantation. (iii) Most candidates mentioned the chromosome number of the egg and zygote in humans correctly. (iv) Explanation of the term Gestation and how long does it last in humans was written correctly by most of the candidates. (v) Most of the candidates drew the correct diagram of a mature human sperm. Some candidates, however, were unable to show a clear differentiation of the three parts. (b) (i) Most candidates answered the aspect of photosynthesis being tested through the diagram, correctly. (ii) Most candidates wrote the balanced equation representing the process of photosynthesis correctly. (iii) Majority of the candidates did not mention that de-starching takes place in leaves and not in the plant. (iv) Majority of the candidates did not mention the parts of leaf which give positive and negative test for starch. (v) Most candidates drew a correct diagram. A few candidates, however, did not draw a double membrane for chloroplast. Suggestions for teachers - While teaching the concept of fertilisation, lay stress on the number of Chromosomes in gametes and Zygote. - Setup experiments to enable students to identify the factors necessary for Photosynthesis. - Make students practise writing a balanced overall chemical equation for Photosynthesis. - Give adequate practise to the students in drawing the diagram of chloroplast with a double membrane - Emphasise the significance of destarching the leaves before beginning any experiment on Photosynthesis. - Guide students to collect a number of samples of plants having variegated leaves. - Clearly explain Implantation and Gestation. - Advise students to read the questions carefully so that they do not miss out on answering certain parts MARKING SCHEME Question 3 (a) (i) D C B A/ C B A D (ii) Oviduct, fixing of the embryo in the wall of uterus or Fallopian tube blastocyst in the wall of uterus 65 (iii) Egg 23, Zygote 46 / 23 pairs (iv) Full term development of the embryo in the uterus, 280 days / 40 weeks/9 months. It is the period between implantation and birth of baby (v) (b) (i) Chlorophyll is necessary for photosynthesis. (ii) 6CO 2 + 12H 2 O Sunlight Chlorophyll C 6 H 12 O 6 + 6H 2 O + 6O 2 (iii) to destarch the leaves. (iv) Green part blue black/blackish/dark blue/indigo (v) Yellow part brown/yellowish brown/golden yellow 66 Question 4 (a) The diagram given below shows the internal structure of a spinal cord depicting a [5] phenomenon. Study the diagram and answer the questions: 3 1 2 (i) Name the phenomenon that is depicted in the diagram. Define the phenomenon. (ii) Give the technical term for the point of contact between the two nerve cells. (iii) Name the parts numbered 1, 2 and 3. (iv) How does the arrangement of neurons in the spinal cord differ from that of the brain? (v) Mention two ways by which the spinal cord is protected in our body. (b) Give appropriate biological or technical terms for the following: (i) Process of maintaining water and salt balance in the blood. (ii) Hormones which regulate the secretion of other endocrine glands. (iii) Movement of molecules of a substance from their higher concentration to lower concentration when they are in direct contact. (iv) The condition in which a pair of chromosomes carry similar alleles of a particular character. (v) The complex consisting of a DNA strand and a core of histones. (vi) The onset of menstruation in a young girl. 67 [5] (vii) Squeezing out of white blood cells from the capillaries into the surrounding tissues. (viii) The fluid which surrounds the foetus. (ix) The relaxation phase of the heart. (x) The difference between the birth rate and the death rate. Comments of Examiners (a) (i) Most candidates named the phenomenon depicted in the diagram and wrote its definition correctly. A few candidates, however, were unsure of the meaning of the word phenomenon and therefore, were unable to give the correct answer. (ii) Majority of the candidates did not know the difference between synapse and synaptic cleft, nerve and neuron. (iii) Most of the candidates answered correctly. Some candidates, however, labelled neuron as nerve. (iv) Many candidates wrote the location of grey and white matter instead of Cytons and Axons. (v) Most candidates wrote two ways by which the spinal cord is protected in our body, correctly. (b) In sub-parts(i)-(x), most of the candidates wrote the appropriate biological or technical terms for the given statements. However, in sub-parts (i), (viii) and (x), some candidates wrote Homeostasis instead of Osmoregulation, Amnion fluid instead of Amniotic fluid and Birth rate/ Death rate instead of Growth Rate of population respectively. Suggestions for teachers - Give sufficient practice to the students in drawing the nervous path way of Reflex action and to label all the parts. - Ensure that the students are able to identify the neuron involved in a Reflex action and the location of Synapse. - Emphasise the arrangement of Cytons and Axons in the Brain and in the Spinal cord. - Insist upon learning the correct spellings of the biological terms with their correct meaning. to - Encourage students biological/technical terms. MARKING SCHEME Question 4 (a) (i) Reflex action, /Simple reflex/Reflex act It is an automatic, [spontaneous, quick] involuntary response to a stimulus. (ii) Synapse (iii) 1. Sensory neuron / afferent fibre/Axon of sensory neuron 68 use 2. Motor neuron / efferent fibre/Axon of motor neuron 3. Grey matter/central canal (iv) Spinal Cord Cytons in the inner grey matter and axons in the outer white matter. /Cytons are inside & Axons are outside Brain Cytons in the outer grey matter and axons in the inner white matter. /Cytons inside, Axons outside (v) Meninges, Cerebrospinal fluid, Vertebral column / backbone. (b) (i) Osmoregulation/Osmotic regulation (ii) Tropic hormones (iii) Diffusion (iv) Homozygous (v) Nucleosome (vi) Menarche (vii) Diapedesis (viii) Amniotic fluid (ix) Diastole (x) Growth rate of population Question 5 (a) The diagram given below is that of a structure present in a human kidney. Study the same and answer the questions that follow: 1 2 (i) Name the structure represented in the diagram. 69 [5] (ii) What is the liquid entering part 1 called? Name two substances present in this liquid that are reabsorbed in the tubule. (iii) What is the fluid that comes to part 2 called? Name the main nitrogenous waste in it. (iv) Mention the three main steps involved in the formation of the fluid mentioned in (iii) above. (vi) Name the substance which may be present in the fluid in part 2 if a person suffers from Diabetes mellitus. (b) Differentiate between the following pairs on the basis of what is indicated in the brackets. (i) Leaf and Liver [form in which glucose is stored] (ii) ATP and AIDS [expand the abbreviations] (iii) Testosterone and Oestrogen [organ which secretes] (iv) Ureter and Urethra [function] (v) Hypotonic solution and Hypertonic solution [condition of a plant cell when placed in them] 70 [5] Comments of Examiners (a) In sub-parts(i)-(v), most of the candidates wrote correct answers to the questions based on the given diagram of a structure present in a human kidney. However, in sub-part (v), a few candidates wrote insulin instead of glucose. (b) In sub-parts(i)-(v), most of the candidates wrote the correct differentiation between the given pairs based on what is indicated in the brackets. However, in subpart (iii), some candidates wrote the names of the structure instead of writing the names of the organs and in sub-part (v), many candidates wrote common words like Swells and Shrinks instead of Turgid and Flaccid respectively. Suggestions for teachers - By drawing a simple and clear diagram of Nephron, explain the significance of each part in Urine formation. - Explain the role of insulin in regulating blood sugar level. - Give to the students, a list of the substances which are present in the urine of normal person and in the urine of a person suffering from Diabetes mellitus. - With the help of experiments, teach the concept of endosmosis and exosmosis using hypotonic and hypertonic solution. - Advise the students to use biological terms Turgid and Flaccid when explaining the condition of the cell. - Give to the students, a list of the biological abbreviations mentioned in the scope of the syllabus. - Advise students to use words from and to when structures are involved in transport of certain substances. - Clearly explain to the students the difference between an organ and a structure. - Stress upon the form in which glucose is stored in Plants and Animals. MARKING SCHEME Question 5 (a) (i) Nephron / Uriniferous tubule / Renal tubule / Kidney tubule (ii) Glomerular filtrate, water / glucose / Sodium Chloride/Na ions/chloride ions/amino acids/ultrafiltrate/Nephric filtrate (iii) Urine, Urea (iv) Ultrafiltration, selective reabsorption, tubular secretion, Glomerular filtration. (v) Glucose / Sugar / Ketones 71 (b) (i) Leaf Starch, Liver Glycogen (ii) ATP Adeosine triphosphate, AIDS Acquired immune deficiency syndrome. (iii) Testosterone testis, Oestrogen Ovary (iv) Ureter conducts urine from the kidney to the urinary bladder/transports urine from Renal pelvis to bladder Urethra expulsion of urine from the urinary bladder/eliminates urine from body/expels urine and semen. (v) Hypotonic Turgid / Turgidity Hypertonic Flaccid / Plasmolysed/Flaccidity Question 6 (a) Given below is a diagram of a human blood smear. Study the diagram and answer the questions that follow: (i) Name the components numbered 1 to 4 . (ii) Mention two structural differences between the parts 1 and 2 . (iii) Name the soluble protein found in part 4 which forms insoluble threads during clotting of blood. (iv) What is the average lifespan of the component numbered 1 ? (v) Component numbered 1 do not have certain organelles but are very efficient in their function. Explain. 72 [5] (b) Give biological explanations for the following: [5] (i) Education is very important for population control. (ii) The placenta is an important structure for the development of a foetus. (iii) All the food chains begin with green plants. (iv) Plants growing in fertilized soil are often found to wilt if the soil is not adequately watered. (v) We should not put sharp objects into our ears. Comments of Examiners (a) In sub-parts(i)-(v), most of the candidates wrote correct answers to the questions based on the given diagram of a human blood smear. However, in subpart (iii), a few candidates named the soluble protein found in part 4 which forms insoluble threads during clotting of blood as Fibrin instead of Fibrinogen. (b) In sub-parts(i)-(v), most of the candidates wrote correct explanations for the given statements. However, in sub-part (iii), a few candidates wrote incorrect explanation for the statement: All the food chains begin with green plants. Similarly, in sub-part (iv), many candidates wrote the explanation in terms of transpiration instead of hypertonic medium and ex-osmosis in response to the statement: Plants growing in fertilized soil are often found to wilt if the soil is not adequately watered. Suggestions for teachers Instruct students practice the diagram of blood cells. Teach the significance of RBCs not having certain organelles. Clearly explain the structural differences between RBCs and WBCs. Ensure that the students have a general awareness regarding population control. - Explain the factors causing wilting of plants. - Advise students to read and understand the statements before answering. - Related to the statements, give biological explanations to the students. MARKING SCHEME Question 6 (a) (i) 1. RBCs / Erythrocytes 2. WBC / Leucocytes/named WBC 3. Platelets / Thrombocytes 4. Plasma (ii) 1. RBC 73 - Biconcave disc like - Nucleus absent - Haemoglobin present 2. WBC - Irregular, amoeboid - Nucleus present - Haemoglobin absent (iii) Fibrinogen (iv) 120 days (v) Absence of nucleus increases the surface area for absorbing more oxygen / more RBCs can be accommodated. Absence of mitochondria means they do not use oxygen for respiration, hence all the transported to tissues. Absence of endoplasmic reticulum increases the flexibility to move through narrow capillaries. (b) (i) Desire for a male child, ignorance regarding the functioning of reproductive system, gender inequality, etc can be eliminated with education and population increase can be checked. /to create awareness for birth control measures/vital for growth of nation/Food, water, environmental pollution, lack of job opportunities can be eliminated /to improve quality of life. (ii) - Transport of oxygen / digested foods / hormones / antibodies from maternal blood to foetal blood/nutrients /glucose etc. - Elimination of nitrogenous wastes / carbon dioxide from foetal blood to maternal blood./urea, uric acid, creatinine - Secretes oestrogen and progesterone - Acts as a barrier to germs. (iii) All animals / organisms depend on green plant for oxygen and directly or indirectly depend for food. (iv) Soil medium becomes hypertonic. Roots lose water by exosmosis/ plasmolysis and the plants wilt. (v) Can damage eardrum / tympanum leading to deafness. 74 Question 7 (a) The diagram below represents a process in plants. [5] The setup was placed in bright sunlight. Answer the following questions: Oil Wate r (i) Name the physiological process depicted in the diagram. Why was oil added to the water? (ii) When placed in bright sunlight for four hours, what do you observe with regard to the initial and final weight of the plant? Give a suitable reason for your answer. (iii) What happens to the level of water when this setup is placed in: 1. Humid conditions? 2. Windy conditions? (iv) Mention any three adaptations found in plants to overcome the process mentioned in (i). (v) Explain the term Guttation . 75 (b) A pea plant which is homozygous for Green pods which are inflated [GGII] is crossed with a homozygous plant for yellow pods which are constricted [ggii]. Answer the following questions: (i) Give the phenotype and genotype of the F 1 generation. Which type of pollination has occurred to produce F 1 generation? (ii) Write the phenotypic ratio of the F 2 generation. (iii) Write the possible combinations of the gametes that can be obtained if two F 1 hybrid plants are crossed. (iv) State Mendel s law of Segregation of Gametes . (v) What is the scientific name of the plant which Mendel used for his experiments on inheritance? Comments of Examiners (a) (i) Most candidates wrote the correct answer. Some candidates, however, wrote Absorption instead of Transpiration. (ii) Majority of the candidates were unable to answer this question as they could not relate bright sunlight to loss in weight of the plant due to increased transpiration. (iii) Most candidates answered correctly about the change in the level of water on placing experimental setup (a process in plants) in Humid conditions and Windy conditions. (iv) Most of the candidates mentioned three adaptations found in plants to overcome the process mentioned in (i) correctly. (v) The term Guttation was explained by most of the candidates correctly. (b) (i) Many candidates wrote the phenotype and genotype ratios of Monohybrid cross. Some candidates overlooked the second part of this question. (ii) Most candidates, instead of writing the phenotypic ratio of F 2 generation, drew the Punnett square and worked out the genotypic ratio. 76 Suggestions for teachers - Advise students to observe the diagrams carefully before answering the questions. - Ensure that the students have understood the rate of transpiration under various climatic conditions. - Teach the various adaptations in plants to overcome excessive transpiration. - Give adequate practice of monohybrid and dihybrid cross and the phenotype and genotype ratios related to F1 and F2 generation. - For better retention, instruct students to write the three laws of inheritance put forth by Mendel. [5] (iii) Majority of the candidates could not write the possible combinations of the gametes that can be obtained if two F 1 hybrid plants are crossed. (iv) Most candidates stated Mendel s law of Segregation of Gametes correctly. (iv) Most of the candidates wrote the correct scientific name of the plant which Mendel used for his experiments on inheritance. However, a few candidates wrote only the generic name. MARKING SCHEME Question 7 (a) (i) Absorption of water by roots, Transpiration by leaves. To prevent evaporation of water. (ii) Weight of the plant reduces. Rate of transpiration is more than the rate of absorption of water. /Final weight is less than initial weight because leaves transpire (iii) 1. Remains same 2. Reduces (iv) Sunken stomata, fewer stomata, narrow leaves, Rolled or folded leaves, loss of leaves, leaves modified to spines, thick cuticle on leaves. /small leaves/needle like leaves/hair on leaves/multiple epidermis. (v) Loss of water (as droplets) from the margins / hydathodes of leaves. /apex, tips of leaves. (b) (i) Phenotype: All have green, inflated pods. Genotype: GgIi, Cross pollination (vii) 9 : 3 : 3 : 1 (viii) GI, Gi, gI, gi (iv) Two members of a pair of factors separate during gamete formation./The two alleles of a trait separate during gamate formation. (v) Pisum Sativum 77 Topics found difficult / confusing by candidates Suggestions for candidates Number of Chromosomes in somatic cells and gametes. Layers of eyeball and their associated structures. Biodegradable and Non-biodegradable substances. Antiseptics and Disinfectants. Greenhouse gases and gases causing depletion of ozone layer. Significance of each step in Starch test of leaf. Blood vessels supplying the organs and the kind of blood they carry. Difference between Plant cell and Animal cell. Internal structure of testis. Structures of the male reproductive system. Exact location of structures and organs. Implantation and Gestation. Factors affecting Photosynthesis. Placement of Cytons and Axons in brain and spinal cord. Nucleosome and Nucleotide. Birth rate, Death rate, Growth rate. Significance of each part of Nephron in Urine formation. Biological abbreviations. Efficiency of RBCs in transporting Oxygen to tissues. Factors affecting Transpiration Monohybrid and Dihybrid Cross. Mendel s Laws of Inheritance. Read the scope and syllabus prescribed for ICSE Biology. Revise the topics repeatedly for better understanding of concepts. Maintain a list of abbreviations related to the syllabus. Learn the keywords/biological terms/ definitions with conceptual clarity. Practise drawing neat and labelled diagrams. Give importance to biological and technical terms. Make the best use of the 15 minutes reading time to understand and assimilate the questions. Make your choice of question as per the rubrics and plan and organize your thoughts. Select the four questions you know the best in Section II. Follow carefully the instructions given for each question. Write the correct question number before answering. Be methodical and organized while answering. Do not separate the subsections of the question. Handwriting must be neat and legible. Do not attempt more questions than asked for in the question paper. 78

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