CBSE BOARD QUESTION PAPER DELHI-2017

Transcription

1 CBSE BOARD QUESTION PAPER DELHI-2017 Time: 3 Hours Maximum Marks: 90 General Instructions: (i) T he question paper comprises of two Sections, A and B. You are to attempt both the sections. (ii) All questions are compulsory. (iii) There is no choice in any of the questions. (iv) All questions of Section A and all questions of Section B are to be attempted separately. (v) Question numbers 1 to 3 in Section A are one-mark questions. These are to be answered in one word or in one sentence. (vi) Question numbers 4 to 6 in Section A are two-marks questions. These are to be answered in about 30 words each. (vii) Question numbers 7 to 18 in Section A are three-marks questions. These are to be answered in about 50 words each. (viii) Question numbers 19 to 24 in Section A are five-marks questions. These are to be answered in about 70 words each. (ix) Question numbers 25 to 33 in Section B are multiple choice questions based on practical skills. Each question is a one-mark question. You are to select one most appropriate response out of the four provided to you. (x) Question numbers 34 to 36 in Section B are two-marks questions based on practical skills. These are to be answered in brief. SET I SECTION A Q1. Write the molecular formula of first two members of homologous series having functional group Cl. 1 Q2. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual? 1 Q3. What is an ecosystem? 1 Q4. An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror. 2 Q5. What is sustainable management? Why is reuse considered better in comparison to recycle? 2 Q6. Management of forest and wild life resources is a very challenging task. Why? Give any two reasons. 2 Q7. Two carbon compounds X and Y have the molecular formula C 4 H 8 and C 5 H 12 respectively. Which one of these is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case

2 Q8. Complete the following chemical equations: (i) CH 3 COOC 2 + NaOH (ii) CH 3 COOH + NaOH Conc. HSO 2 4 (iii) C 2 OH + CH 3 COOH 3 Q9. Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column? How does the size of atomic radius vary on moving left to right in a horizontal row? Give reason in support of your answer in the above two cases. 3 Q10. An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reason: Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q. 3 Q11. What happens when: (a) Accidentaly, Planaria gets cut into many pieces? (b) Bryophyllum leaf falls on the wet soil? (c) On maturation sporangia of Rhizopzs bursts? 3 Q12. State the basic requirement for sexual reproduction? Write the importance of such reproductions in nature. 3 Q13. State the changes that take place in the uterus when: (a) Implantation of embryo has occurred. (b) Female gamete/egg is not fertilised. 3 Q14. Distinguish between the acquired traits and the inherited traits in tabular form, giving one example for each. 3 Q15. Explain with the help of an example each, how the following provide evidences in favour of evolution: (a) Homologous organs (b) Analogous organs (c) Fossils 3 Q16. An object 4 cm in height, is placed at 15 cm in front of a concave mirror of focal length 10 cm. At what distance from the mirror should a screen be placed to obtain a sharp image of the object. Calculate the height of the image. 3 Q17. Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens. 3 Q18. You have been selected to talk on ozone layer and its protection in the school assembly on Environment Day. (a) Why should ozone layer be protected to save the environment? (b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment. 3 CBSE Board Question Paper Delhi-2017 n 207

3 Q19. Soaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water? Mention any two problems that arise due to the use of detergents instead of soaps. 5 Q20. (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions. (b) Name the parts of the human female reproductive system where fertilisation occurs. (c) Explain how the developing embryo gets nourishment inside the mother s body. 5 Q21. How do Mendel s experiments show that (a) traits may be dominant or recessive? (b) inheritance of two traits is independent of each other? 5 Q22. Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow, without doing any calculations: S.No. 208 n Science X Object distance u (cm) Image distance v (cm) (a) What is the focal length of the convex lens? Give reason in support of your answer. (b) Write the serial number of that observation which is not correct. How did you arrive at this conclusion? (c) Take an appropriate scale to draw ray diagram for the observation at S. No. 4 and find the approximate value of magnification. 5 Q23. (a) To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror. (b) A concave mirror produces three times magnified image on a screen. If the object is placed 20 cm in front of the mirror, how far is the screen from the object? 5 Q24. (a) Draw a ray diagram to explain the term angle of deviation. (b) Why do the component colours of incident white light split into a spectrum while passing through a glass prism, explain. (c) Draw a labelled ray diagram to show the formation of a rainbow. 5

4 SECTION B Q25. You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube / test tubes would be suitable for the correct test of acetic/ethanoic acid? (a) only A (b) A and B (c) B and C (d) A and D 1 Q26. For demonstrating the preparation of soap in the laboratory which of the following combinations of an oil and a base would be most suitable? (a) Mustard oil and calcium hydroxide (b) Castor oil and calcium hydroxide (c) Turpentine oil and sodium hydroxide (d) Mustard oil and sodium hydroxide 1 Q27. A student took four test tubes P, Q, R and S and filled about 8 ml of distilled water in each. After that he dissolved an equal amount of Na 2 SO 4 in P, K 2 SO 4 in Q, CaSO 4 in R and MgSO 4 in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes: (a) P and Q (b) P and R (c) P, Q and S (d) Q, R and S 1 Q28. A student while observing an embryo of a gram seed listed various parts of the embryo as listed below: Testa, Micropyle, Cotyledon, Tegmen, Plumule, Radicle. On examining the list the teacher commented that only three parts are correct. Select these three correct parts: (a) Cotyledon, Testa, Plumule (b) Cotyledon, Plumule, Radicle (c) Cotyledon, Tegmen, Radicle (d) Cotyledon, Micropyle, Plumule 1 Q29. Select the set of homologous organs from the following: (a) Wings of pigeon and a butterfly (b) Wings of bat and a pigeon (c) Forelimbs of cow, a duck and a lizard, (d) Wings of butterfly and a bat 1 Q30. Three students A, B and C focussed a distant building on a screen with the help of a concave mirror. To determine focal length of the concave mirror they measured the distances as given below: Student A : From mirror to the screen Student B : From building to the screen Student C : From building to the mirror Who measured the focal length correctly: (a) Only A (b) Only B (c) A and B (d) B and C 1 Q31. If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens, the shape of the image of this object on the screen would be: CBSE Board Question Paper Delhi-2017 n 209

5 (a) (b) Q32. In the following diagram the correctly marked angles are: (c) (d) 1 A i r D e (a) A and e (b) i, A and D (c) A, r and e (d) A, r and D 1 Q33. The correct sequencing of angle of incidence, angle of emergence, angle of refraction and lateral displacement shown in the following diagram by digits 1, 2, 3 and 4 is: (a) 2, 4, 1, 3 (b) 2, 1, 4, 3 (c) 1, 2, 4, 3 (d) 2, 1, 3, 4 1 Q34. A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas. 2 Q35. Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Write the first step from where such a type of reproduction begins. Draw first two stages of this reproduction. 2 Q36. A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen. (a) In which direction-toward or away from the lens, does he move the screen to focus the image? (b) How does the size of the image change? (c) How does the intensity of the image change as the flame moves towards the lens? (d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size? n Science X

6 SET II Note: Except for the following questions, all the remaining questions have been asked in Set-I. SECTION A Q1. Write the molecular formula of first two members of homologous series having functional group Br. 1 Q2. How does Planaria reproduce. Is this method sexual or asexual? 1 Q3. Why is forest considered a natural ecosystem? 1 Q4. An object is placed at a distance of 40 cm in front of a convex mirror of radius of curvature 40 cm. List four characteristics of the image formed by the mirror. 2 Q5. Why is sustainable management of natural resources necessary? Why is reuse better as compared to recycle? 2 Q6. Explain how would the involvement of local people be useful for successful management of forests. 2 Q7. Complete the following chemical equations: (i) CH 3 COOH + Na 2 CO 3 (ii) CH 4 + O 2 (iii) C 2 OH + Na 3 Q8. Two carbon compounds X and Y have the molecular formula C 3 H 6 and C 4 H 10 respectively. Which one of the two is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case. 3 Q11. Mention the total number of chromosomes along with the sex chromosomes that are present in a human female and a human male. Explain how in sexually producing organisms the number of chromosomes in the progeny remains the same as that of the parents. 3 Q14. Natural selection and speciation leads to evolution. Justify this statement. 3 Q16. A 3 cm tall object is placed 18 cm in front of a concave mirror of focal length 12 cm. At what distance from the mirror should a screen be placed to see a sharp image of the object on the screen. Also calculate the height of the image formed. 3 Q17. With the help of ciliary muscles the human eye can change its curvature and thus alter the focal length of its lens. State the changes that occur in the curvature and focal length of the eye lens while viewing (a) a distance object, (b) nearby objects. Explain, why a normal eye is not able to see distinctly the objects placed closer than25 cm, without putting any strain on the eye. 3 SET III Note: Except for the following questions, all the remaining questions have been asked in Set-I & Set-II. SECTION A Q1. Write the molecular formula of first two members of homologous series having functional group OH. 1 Q2. How does Plasmodium reproduce. Is this method sexual or asexual? 1 CBSE Board Question Paper Delhi-2017 n 211

7 Q3. Why is a lake considered to be a natural ecosystem? 1 Q4. An object is placed at a distance of 12 cm in front of a concave mirror of radius of curvature 30 cm. List four characteristics of the image formed by the mirror. 2 Q5. How do advantages of exploiting natural resources with short term gains in mind differ from the advantages of managing our resources with a long-term perspective? 2 Q6. What is meant by wildlife? How is it important for us? 2 Q7. Complete the following chemical equations: (i) C 2 OH + O 2 (ii) C 2 OH Conc. H 2 SO K (iii) CH 3 COOH + NaHCO 3 3 Q8. The molecular formula of two carbon compounds are C 4 H 8 and C 3 H 8. Which one of the two is most likely to show addition reaction? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case. 3 Q11. How did Mendel s experiments show that different traits are inherited independently? Explain. 3 Q14. List any four steps involved in sexual reproduction and write its two advantages. 3 Q16. The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a distance of 60 cm from its pole. What is the nature of the mirror? Find its focal length. If the height of the flame is 2.4 cm, find the height of its image. State whether the image formed is erect or inverted. 3 Q17. Write about power of accommodation of human eye. Explain why the image distance in the eye does not change when we change the distance of an object from the eye? 3 qq 212 n Science X

8 SOLUTIONS TO CBSE BOARD QUESTION PAPER DELHI-2017 SET I SECTION A 1. The general formula for the homologous series of functional group Cl is C n H 2n + 1 Cl. The molecular formula two consecutive members of this series are: (i) CH 3 Cl (Chloromethane) (ii) CH 3 CH 2 Cl (Chloroethane) where n is 1 and 2 respectively. 2. Under favourable conditions, spirogyra reproduces by a process known as fragmentation. This is an asexual method of reproduction. 3. An ecosystem is a self sustaining system where biotic and abiotic components of various communities interact with each other. Ponds, forests, grasslands, etc are a few examples of ecosystem. 4. Four properties of the image formed by the given convex mirror are: (i) Image is always erect (ii) Small in size (iii) Virtual (iv) Always forms behind the mirror between focus and pole. 5. Sustainable management is a resource management technique which aims to conserve the resources and use them efficiently to avoid their misuse for individual purposes such that they are conserved for the future. Reuse is better than recycle because of the following reasons: (i) Recycling needs some processes to use the same material again. (ii) Reuse saves energy by using material again without any changes. (iii) Reuse prevents environmental pollution by not creating any waste. (iv) Reuse saves cost as same material is used again without any process. 6. Management of forest and wildlife resources is considered as a challenging task because: (i) There are many stakeholders of forest. They are those people who are directly or indirectly involved in forest. Management of forest and wildlife has to take into account the interests of all these stakeholders which become a challenging task. (ii) Industries would consider the forest as merely a source of raw material for its factories and huge interest-groups lobby the government for access to these raw materials at artificially low rates which further poses a challenge to manage the forest and wildlife resources. 7. Compound X has the molecular formula = C 4 H 8 (C n H 2n, alkene) Compound Y has the molecular formula = C 5 H 12 (C n H 2n + 2, alkane) C 4 H 8 is unsaturated hydrocarbon, i.e. alkene (butene) and C 5 H 12 is a saturated hydrocarbon, i.e. alkane (pentane). Saturated compounds undergo substitution reaction. 213

9 Unsaturated compounds undergo addition reaction at the multiple bonds. For example, 1-butene and 2-butene will add a chlorine molecule (Cl 2 ) to form 1, 2-dichlorobutane and 2, 3-dichlorobutane, respectively. The reaction will be: (i) CH 3 CH 2 CH = CH 2 + Cl 2 CH 3 CH 2 CH(Cl) CH 2 Cl (ii) CH 3 CH = CH CH 3 + Cl 2 CH 3 CH(Cl) CH(Cl) CH 3 8. Complete chemical equations are: (i) CH 3 COOC 2 + NaOH C 2 OH + CH 3 COOH (ii) CH 3 COOH + NaOH CH 3 COONa + H 2 O 2 4 (iii) C 2 OH + CH 3 COOH CH 3 COOC 2 + H 2 O 9. In the Modern Periodic Table, there are 18 vertical columns known as Groups and 7 horizontal rows known as Periods. As we move down the group, the electrostatic attraction between the nucleus and the outermost electron decreases due to increase in the distance between them. This happens because, on moving down the group, a new shell is added. So the valence electrons can be easily lost by the element. As we know, metallic character is characterised by the ease of loss of an electrons, thereby, metallic character increases on moving down the group in the Modern Periodic Table. When we move across a period, the number of electrons in the same shell increases. This leads to greater electrostatic attraction between the nucleus and the outer-most electron. This increased attraction pulls the outer-most electron closer to the nucleus, thereby decreasing the atomic size. 10. Atomic number of element P = 20 Electronic configuration of element P = 2, 8, 8, n Science X Conc. HSO Atomic number of element Q = 17 Electronic configuration of element Q = 2, 8, 7 The position of P in the Modem Periodic Table Period (Number of shells) = 4 Group (Electrons in outer-most shell) = 2 The position of Q in the Modern Periodic Table Period (Number of shells) = 3 Group (Electrons in outer-most shell) = (10 + 7) = 17 When P reacts with Q, it loses the two valence electrons (valency 2). These two valence electrons are accepted by two Q atoms (valency 1). Hence, the formula of the compound formed between P and Q is PQ (a) When Planaria gets cut into many pieces, it will undergo a process known as regeneration due to which each piece will grow into a new Planaria organism. (b) When Bryophyllum leaf falls on the wet soil, the buds that are produced in the notches along the leaf will develop into new plants by the process known as vegetative propagation. (c) When the sporangia of Rhizopus bursts upon maturation, the spores present inside it spread in the open environment Then, with the help of different agents, they are carried to different places and when they land on a favourable surface, they start growing and produce new organism.

10 12. The basic requirements for sexual reproduction to take place are involvement of two parents and fusion of their haploid gametes. In the sexual reproduction, a new Individual is formed by the fusion of two haploid gametes, one from the male parent and the other from the female parent. Since the new individual formed is diploid in nature, the gametes must be formed by meiosis, so that chromosome number can be reduced to half. When fusion of gametes occurs, the two nuclei of these two gametes fuse and the chromosome number is then restored to normal. The zygote, thus formed is diploid in nature. Importance of sexual reproduction: Sexual reproduction involves fusion of male and female gametes coming from both the parents. The fusion of these gametes results in genetic variations in the offsprings. This way sexual reproduction promotes diversity of characters in offsprings by providing genetic variations. These genetic variation, thus lead to evolution of species as well as allow the organisms to become better adapted In the changing environment. 13 (a) When the implantation has occurred in uterus of the mother, the inner lining of the uterus thickens and is richly supplied with the blood vessels to provide nourishment to the growing embryo. (b) If the egg is not fertilised, it lives for about one day. Since, the thickened uterus lining is no more required, it will slowly break down and comes out through the vagina as blood and mucous known as menstruation which lasts for about two to eight days. 14. Acquired Traits Inherited Traits (i) Acquired traits are those that are developed in an individual during his/her lifetime. (ii) They are result of changes in nonreproductive tissues (somatic cells). (i) Inherited traits are the qualities or characteristics present in an individual since birth. (ii) They are a result of changes in the DNA. (iii) They cannot be passed on to the progeny. (iii) They are transmitted to the progeny. e.g. Pierced ear, large muscle size, etc. e.g. Colour of eyes, skin or hair. 15. (a) Homologous organs: These organs are similar in their form (or are embryologically same), but perform the different functions in different organisms. These organs provide strong evidence in the favour of evolution. For example, the bone structure observed in the forelimbs of birds and bats, flippers of dolphins and arms of human beings are similar and have the same pentadactyl plan but they perform different functions. (b) Analogous organs: These organs have different origin and different basic structure but perform same function. For example, wings of birds and wings of bats (bird wings are made of feathers while bat wings are the folds of skin) have different structure but perform the same function of flying. Thus, these organs provide evidence for evolution that they are different in origin but evolve to perform same function to survive in hostile environmental conditions (c) Fossils: They are the impressions of dead organisms and they can tell a great deal about the changes that various species of organisms have gone through. For example, Archaeopteryx is a connecting link between birds and reptiles and it suggests that the present animals have evolved from the existing ones through the process of continuous evolution. Solutions to CBSE Board Question Paper Delhi-2017 n 215

11 16. Using the mirror equation, = 1 M v u f 1 1 v + 1 A D = B C v = 1 B F P 1 10 cm + Α 15 cm v = = 5 N v = 30 cm Thus, to obtain a sharp image of the object the screen should be placed in front of the mirror at a distance of 30 cm from the mirror. Magnification: m = v u = hi h = 30 o 15 m = 2 2 = h i 4 h i = 8 cm The image height will be 8 cm. 17. The defect caused due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens is presbyopia. Presbyopia is the defect of eye in which a person cannot see nearby objects comfortably and distinctly without corrective eye-glasses. A presbyopic eye has its near point greater than 25 cm and it gradually increases as the eye becomes older. The type of lens required by such a person to improve the vision is bifocal lens. A bifocal lens consists of both convex lens and concave lenses. The convex lens used in bifocal lens is used to correct hypermetropia (far-sightedness) and concave lens is used to correct myopia (short-sightedness). 18. (a) Ozone layer is a rich zone of ozone found in upper atmosphere. It helps in shielding the Earth from the harmful UV radiations coming from the Sun. If ozone layer gets depleted, UV radiations can directly reach the Earth s surface and drastically affect the life on Earth. For instance, UV radiations coming from the Sun causes skin cancer. So, it is very important to protect the ozone layer so as to save our environment. (b) The ozone layer can be protected by taking following measures: Some of the ways to help protect and stop the depletion of the ozone layer include not buying products. In aerosol cans, maintaining air-conditioning filters and units. In order to halt the depletion of the ozone layer, countries around the world have banned the use of chlorofluorocarbons and other ozone-depleting substances. These compounds produce chlorine and bromine atoms high in the atmosphere, and these atoms react with ozone, destroying it. By reducing the use of fluorescent lights. By minimising the use of vehicles to limit the emission of harmful gases that cause damage to the ozone layer, we can contribute to its protection. 216 n Science X

12 19. Difference between soap and detergents: Soap Detergents (i) Soaps are sodium salt of long chain carboxylic acids. (i) Detergents are sodium salt of long chain benzene sulphonic acids. (ii) The ionic group in soap is COO Na + (ii) The ionic group in detergents is SO 3 Na + or SO 4 Na + (iii) Soaps are not useful when water is hard. (iii) Detergent can be used for washing purpose even when water is hard. (iv) Soaps are biodegradable. (iv) Some of the detergents are nonbiodegradable. (v) Soaps have relatively weak cleansing (v) Detergents have strong cleansing action. action. The mechanism of the cleansing action of soaps: The dirt present on clothes is organic in nature and insoluble in water. Therefore, it cannot be removed by only washing with water. When soap is dissolved in water, its hydrophobic ends attach themselves to the dirt and remove it from the cloth. Then, the molecules of soap arrange themselves in micelle formation and trap the dirt at the centre of the cluster. These micelles remain suspended in the water. Hence, the dust particles are easily rinsed away by water. Soap molecules Dirty cloth Soap solution Dirt Soaps do not form lather (foam) with hard water: Soaps do not work property when the water is hard. A soap is a sodium or potassium salt of long chain fatty acids. Hard water contains salts of calcium and magnesium. When soap is added to hard water, calcium and magnesium ions present in water displace sodium or potassium ions from the soap molecules forming an insoluble substance called scum. A lot of soap is wasted in the process. Problems that arise due to the use of detergents instead of soap: Detergents being non-biodegradable, they accumulate in the environment causing pollution In soil, the presence of detergents leads to ph changes making soil infertile. The entry of detergents into food chain leads to bio-accumulation in living being and tend towards serious health issues. 20. (a) The organ that produces sperms as well as secretes male hormone is testis. The hormone secreted by it is testosterone. Its Important functions are as follows: It stimulates sperm production. It stimulates the development of secondary sexual characters in males like growth of beard hairs, low pitch voice, etc. Solutions to CBSE Board Question Paper Delhi-2017 n 217

13 It involves in the development, maturation and functioning of the male accessory sex organs like vas deferens and seminal vesicles (b) In human female reproductive system, the process of fertilisation takes place in one of the fallopian tubes. (c) The embryo gets nutrition from the mother s blood with the help of a special tissue called placenta. Placenta is a vascular membranous organ that connects the developing foetus to the uterine wall of the mother. It contains villi on the embryo s side of the tissue. On the mother s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The placenta draws nourishment and oxygen, which it supplies to the foetus, from the maternal circulation. In tum, the placenta receives carbon dioxide and wastes of foetal metabolism and discharges them into the maternal circulation for disposal. 21. (a) Mendel demonstrated that traits can be either dominant or recessive through his monohybrid cross. He crossed true-breeding tall (TT) and dwarf (tt) pea plants. The seeds formed after fertilisation were grown and the plants that were formed represent the first filial or F 1 generation. All the F 1 plants obtained were tall. Then, Mendel self-pollinated the F 1 plants and observed that all plants obtained in the F 2 generation were not tall. Instead, one-fourth of the F 2 plants were short. Parents Pure tall plant (TT) X Pure dwarf plant (tt) P 1 generation (Tt) (Tt) Selfing of F 1 plants (Tt) X (Tt) F 2 generation 218 n Science X (Tt) (Tt) From this experiment, Mendel concluded that the F 1 tall plants were not true breeding; they were carrying traits of both short height and tall height. They appeared tall only because the (Tt) (tt)

14 tallness trait was dominant over the dwarfness trait. This shows that traits may be dominant or recessive. (b) Mendel demonstrated that traits are inherited independently through his dihybrid cross. He considered two traits at a time, seed colour and seed shape in which yellow colour (YY ) and round shape (RR) are dominant over green colour (yy) and wrinkled shape (rr), respectively. RRyy rryy Parents Round green Wrinkled yellow Gametes Ry ry RY Ry ry ry F 1 generation RrYy Round and Yellow RY Ry ry ry RRYY Round yellow RRYy Round yellow RrYY Round yellow RrYy Round yellow RRYy Round yellow RRyy Round green RrYy Round yellow Rryy Round green RrYY Round yellow RrYy Round yellow rryy Wrinkled yellow rryy Wrinkled yellow RrYy Round yellow Rryy Round green rryy Wrinkled yellow rryy Wrinkled green Mendel cross bred the plants and observed that the F 2 progeny of dihybrid cross had a phenotypic ratio of 9 : 3 : 3 : 1 and produced nine plants with round yellow seeds, three plants with round green seeds, three plants with wrinkled yellow seeds and one plant with wrinkled green seeds. In this experiment, he found that round yellow and wrinkled green are parental combinations whereas round green and wrinkled yellow are the new combinations. In a dihybrid cross between two plants having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes (RY, Ry, ry, ry ) are produced. Each of these gametes segregate independently of each other and each has a frequency of 50% of the total gametes produced. From this experiment, he concluded that when two pairs of traits are combined together in a hybrid, one pair of character segregates independent of the other pelf of character. This is known as the law of independent assortment. 22. (a) From S.No.3 we can say that the radius of curvature of the lens is 30 cm because when an object is placed at the centre of curvature of a convex lens its image is formed on the other side of the lens at the same distance from the lens. And, we also know that focal length is half of the radius of curvature. Thus, focal length of the lens is + 15 cm. (b) S.No.6 is not correct as the object distance is between focus and pole, so for such cases the image formed is always virtual but in this case it is written that a real image is formed as the image distance is positive. Solutions to CBSE Board Question Paper Delhi-2017 n 219

15 (c) Approximate value of magnification for object distance 20 cm and image distance + 60 cm is 3. m = v 60 cm Q 4 = 20 P 2F 1 P F 1 O F 2 2F 2 20 cm 15 cm Q 23. (a) Two light rays whose path of refection are priorly know are: (i) The incident ray passes through the centre of curvature: In this case, light after reflecting from the concave mirror moves back in the same path. This happens because light is incident perpendicularly on the mirror surface. C F P (ii) The ray incident obliquely to the principal axis: In this case, the incident ray will be reflected back by the reflecting surface of the concave mirror obliquely and making equal angles with the principal axis. Concave mirror C i r P Concave mirror Let an object a candle is placed between the focus and pole of the concave mirror. Then using above two rays, image of the candle can be located as shown below: R Object C B R Image Q Q F P In this case, the image is formed behind the mirror. This image is virtual, erect and magnified. (b) Here, Magnification, m = 3 (As the image is real) Object distance, u = 20 cm Image distance, v =? 220 n Science X A

16 We know, m = v u v 3 = 20 v = 60 cm The screen is placed in front of the mirror at a distance of 60 cm from the pole of the mirror. Thus, the screen is placed 40 cm (= 60 cm 20 cm) away from the object. 24. (a) The angle between a ray of light incident on a refracting medium and the ray emerging out of the medium after undergoing refraction is called angle of deviation (D).This can be explained with the help of the figure given below: A Incident ray i D e Emergent ray (b) M A Beam of white light N B Prism C P D Coloured spectrum The splitting of a beam of white light in to its seven constituent colours, when it passes through a glass prism, is called the dispersion of light. When a beam of white light enters a prism, rt gets refracted and splits into its seven constituent colours, viz. violet, indigo, blue, green, yellow, orange, and red. This splitting of the light ray occurs because of the different angles of bending for each colour. Hence, each colour while passing through the prism bends at different angles with respect to the incident beam. This gives rise to the formation of the coloured spectrum. (c) The given diagram shows the formation of rainbow in the sky. Solutions to CBSE Board Question Paper Delhi-2017 n 221

17 SECTION B 25. (d) A and D 26. (d) Mustard oil and sodium hydroxide 27. (a) P and Q 28. (b) Cotyledon, Plumule, Radicle 29. (b) Wings of bat and a pigeon 30. (a) Only A 31. (b) 32. (a) A and e 33. (b) 2, 1, 4, The gas liberated is CO 2. On bringing a burning splinter near the mouth of the test tube, the flame extinguishes as CO 2 is a non-supporter of combustion. 35. Fission, e.g. Fission in Amoeba I II III IV 36. (a) He needs to move the screen away from the lens. (b) The size of image will go on increasing. (c) The intensity will remain the same. (d) Till the point 2F 1, i.e. the radius of curvature. 222 n Science X SET II 1. The general formula for the homologous series of functional group Cl is C n H 2n + 1 Br. The two consecutive members of this series are: (i) CH 3 Br (Bromomethane) (ii) CH 3 CH 2 Br (Bromoethane) where n is 1 and 2 respectively. The molecular formula for both of them are CH 3 Br and C 2 Br. 2. Planaria reproduces by a process known as regeneration. It is a type of asexual reproduction in which if Planaria can be cut into any number of pieces, each piece grows into a new orgainsm. 3. Forests are considered as natural ecosystem because of the following reasons: (a) They have species of plants and animals that grow without human intervention. (b) All these species interact with each other and are inter-dependent on each other. (c) These are naturally sustainable. 4. Four properties of the image formed by the given convex mirror are: (i) Image is always erect (ii) Small in size (iii) Virtual (iv) Always forms behind the mirror between focus and pole.

18 5. Natural resources are an integral part of our life. As some resources are exhaustible, non-judicious use of such resources will lead to their depletion and ultimate banishment, which will affect the life on Earth. By sustainable use of these natural resources, we are able to conserve our environment. Hence, sustainable management of resources is very necessary. Reuse is better than recycle because (i) Recycling needs some energy consuming processes to use the same material again. (ii) Reuse saves energy by using material again without any change. (iii) Reuse prevents environmental pollution by not creating any waste. (iv) It also saves cost as same material is used again without any processing. 6. The involvement of local people will be useful for the successful management of forests in the following ways: (i) They should be aware of the fact that diminishing forest cover would disturb the ecological balance. If they show their objection against any such illegal activity that would destroy the forests, it can lead to a massive effect that will help in management of forests more effectively as it happened during Chipko Andolan. (ii) Phenomenon forest fires must be reported immediately to the forest officers. The sooner the action is taken, more the area will be protected. Forest fires purposely caused by local people must not be practiced. 7. Complete the following chemical equations: (i) CH 3 COOH + Na 2 CO 3 2CH 3 COONa + H 2 O + CD 2 Heat (ii) CH 4 + O 2 CO Light 2 + 2H 2 O (iii) C 2 OH + Na 2C 2 O Na + + H 2 8. Compound X has the molecular formula = C 3 H 6 (C n H 2n, alkene) Compound Y has the molecular formula = C 4 H 10 (C n H 2n + 2, alkane) C 3 H 6 is an unsaturated hydrocarbon, i.e. alkene (propene) and C 4 H 10 is a saturated hydrocarbon, i.e. alkane (butane). Saturated compounds undergo substitution reaction. Unsaturated compounds undergo addition reaction at the multiple bonds. For example, propene will add a chlorine molecule (Cl 2 ) to form 1, 2-dichloropropane The reaction will be CH 3 CH = CH 2 + Cl 2 CH 3 CH(Cl) CH 2 Cl 11. The total number of chromosomes present in both human male and female is 46. Out of these, two chromosomes are the sex chromosomes. In human males, the two sex chromosomes present are X and Y, while in human female, both sex chromosomes are X. During sexual reproduction, the new individual is formed by the fusion of gametes from both the parents. These gametes are haploid in nature, i.e. they contain only one set of the chromosomes. They are formed by the meiosis, a type of cell division which reduces chromosome number to half. When these haploid gametes fuse during fertilisation, the two nuclei of these two gametes fuse and the chromosome number is then restored to normal. Hence, the progeny formed has the same number of chromosomes as that of the parents. 14. Natural selection is the phenomenon by which the nature selects those species which possess survival advantage over the other species. According to theory of natural selection, there is Solutions to CBSE Board Question Paper Delhi-2017 n 223

19 struggle for existence within the species of a population for the environmental resources and this struggle leads to survival of certain organisms and elimination of the less competent species. Thus in this competition, some organisms might undergo genetic changes which help them in their survival. The better adapted organisms would, thus survive and pass on their traits to the next generation, gradually leading to evolution. Speciation is a process of formation of new species from the existing one due to reproductive isolation of a part of its population. This reproductive isolation can occur due to geographical isolation of a part of population. With time, the genetic drift Will accumulate different variations in each of the geographically separated sub-populations. Ultimately, all the individuals of these two groups will isolate reproductively, thus, leading to formation and evolution of new species. Thus, we can say that both natural selection and speciation lead to the evolution of species on earth. 16. Using the mirror equation, = 1 M v u f 1 1 v + 1 A D = B C v = 1 B F P 1 12 cm + Α 18 cm v = 3+ 2 = 1 N v = 36 cm Thus, to obtain a sharp image of the object the screen should be placed in front of the mirror at a distance of 36 cm from the mirror. Magnification: m = v u = hi h = 36 o 18 m = 2 2 = h i 3 h i = 6 cm The image height will be 6 cm. 17. (a) When we see distant object, the ciliary muscles relax/expand to decrease the curvature and there by increase the local length of the lens. Hence, the lens becomes thin. This enables us to see the distant object clearly. Thus the focal length of the eye lens increases while seeing distant objects. Light coming from distant object Image 224 n Science X

20 (b) To see the nearby objects clearly, the focal length of the lens should be shorter. For this, the ciliary muscles contract to increase the curvature and thereby decrease the focal length of the lens. Hence, the lens becomes thick. This enables you to see the nearby objects clearly. Light coming from distant object Image A normal eye is not able to see distinctly the objects placed closer than 25 cm, without putting any strain on the eye. This is because the ciliary muscles of eyes are unable to contract beyond a certain limit. If the objects are placed at a distance less than 25 cm from the eye, then the objects appear blurred because light rays coming from the object meet beyond the retina. SET III 1. The general formula of the compounds having OH functional group is C n H 2n + 1 OH. Its two members are: (i) CH 3 OH (Methanol) (ii) CH 3 CH 2 OH (Ethanol) 2. Plasmodium is a single celled organism which reproduces by the process of multiple fission. Multiple fission (i.e. breaking up of a single cell into many daughter cells) is an asexual mode of reproduction. 3. Lake is a natural water body and thus it is considered as natural ecosystem. 4. The four characteristics of the image formed by concave mirror is: (i) Image is formed behind the mirror (ii) Virtual (iii) Enlarged (iv) Erect 5. Exploiting natural resources with short term gains in mind will lead to unwanted and excessive use of resources, that will lead to the depletion of these resources. On the other hand managing our resources with a long term perspective involves judicious use of the resources that can conserve resources for the future. 6. All the living forms, including both plants and animals that live in their natural environment, i.e. forests is wildlife. Wildlife is of great importance for us: (i) It maintains the ecological balance of the nature. (ii) It provides us with many useful resources. 7. Complete chemical equations are: (i) C 2 OH + O 2 CH 3 COOH (ii) C 2 OH Conc. H2SO4 443 K CH 2 = CH 2 (iii) CH 3 COOH + NaHCO 3 CH 3 COONa + H 2 O + CO 2 Solutions to CBSE Board Question Paper Delhi-2017 n 225

21 8. Among C 4 H 8 and C 3 H 8, the compound having molecular formula C 4 H 8 is likely to undergo addition reaction as it is an unsaturated hydrocarbon (general formula: C 2 H 24 ), while C 3 H 8 is a saturated hydrocarbon (general formula: C n H 2n + 2 ) is not likely to show addition reaction. This can be explained as follow: X (i) CH CH CH = CH + X CH CH CH CH X 3 2 (C3H 8) HX (C3H 8) (Substitution reaction) (ii) CH CH CH +X CH CH CH X We can see that in reaction (i), due to the presence of double bond, X 2 (halogen) can undergo addition reaction, while in case of reaction (ii) as no double bond is present so only substitution reaction can take place, and not addition reaction. 11. When gametes are formed during Mendel s experiment with pea plant, the factors that controls the inheritance of characters segregate. This forms the basis of law of segregation. In F 1 generation only one characteristic, which is expressed by the dominant factor can be seen. However the other factor, that is for the recessive character is not lost. It is only suppressed in the presence of dominant character. On selfing F 1 generation, the recessive character can be seen along with the dominant character in the ratio 1 : 3 in the F 2 progeny. This forms the basis of law of independent assortment. Thus, from Mendel s experiment it is explained that different traits are inherited independently. 14. The four main steps involved in sexual reproduction are: (i) In the first stage of sexual reproduction, meiosis process occur and the number of chromosomes reduces from diploid (2n = 46) to haploid (n = 23) for each gamete. (ii) In the second stage, there is transfer of male gametes into the female body. (iii) In the third stage, the two gametes will fuse together after fertilisation, a single male gamete will fuse with a female gamete. i.e. fertilisation process takes place. (iv) After fusion of male and female gametes, they form a zygote, in which the number of chromosomes is restored to diploid (2n = 46). The two main advantages of sexual reproduction are: (i) There are more variations, which leads to better adaptability of the offsprings in the environment. (ii) Promotes the diversity in the characteristics of offspring, because it results by fusion of gametes. 16. Nature of Mirror: Concave mirror Hence, u = 30 cm, v = 60 cm, h o = 2.4 cm, Mirror formula: = 1 v u f = 1 f f = 20 cm 226 n Science X = 1 f 1 20 = 1 f

22 hi Now, = v ho u h i = v h o = u 30 = 4.8 cm m = v = (+) ve u The image is real, inverted and enlarged. 17. The ability of the eye lens to adjust its focal length to see the far away and nearby objects clearly. It occurs by contraction and relaxation of the ciliary muscles. By contraction of ciliary muscles, the eye lens become thick and one can clearly view the nearby objects, as the focal length of eye lens decreases. By relaxation of ciliary muscles, the eye lens become thin and one can clearly view the far away objects, as the focal length of eye lens increases. By the virtue of power of accommodation of human eye lenses, the nearby and far away objects can be distinctly viewed without any change in the image distance with respect to the object distance. Solutions to CBSE Board Question Paper Delhi-2017 n 227