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SUMMATIVE ASSESMENT-II CLASS 10YEAR: 2013 SET: 2SCIENCE -BOARD PAPERQUESTIONS ALONGSIDE ANSWERS ACCORDING TO MARKING SCHEME. SECTION-A1] The atomic numbers of three elements X , Y, Z are 3, 11, 17 respectively. State giving reason which two elements will show similar chemical properties.Ans:X and Y ; both have one valence electron/group/valency.2] Why is DNA copying necessary during reproduction ?Ans: To maintain the same body design as that of parents.3] Name any two items which can be easily recycled but are generally thrown in the dustbin by us?Ans: Envelopes, tin cans, plastic bottles, plastic container, polythene bags.(or any other)4] List two advantages of growing grapes or banana plants through vegetative propagation.Ans: (i) These plants do not produce viable seeds so these plants can be propagated.(ii) It is a cheaper,easier and more rapid method of propagation in plants.5] “ A convex lens of focal length ‘f’ can form a magnified erect as well as inverted image.” Justify this statement stating the position of the object with respect to the lens in each case for obtaining these images.Ans: Convex lens of focal length f forms magnified, erect image when object is between optical centre and focus (u<f). the same lens forms magnified and inverted image when object is between f and 2f.6] Why is sustainable management of natural resources necessary ? which one out of reuse and recycle would you suggest to practice and why ?Ans: a) To meet current basic human needs. b) To preserve the resources for the needs of future generations. Reuse approach is suggested as it does not involve consumption of energy and is also environment friendly.7] Write the harmful effects of using plastic bags, on the environment. Suggest alternatives to plastic bags.Ans: Harmful effects:Being non-biodegredable it adds to the bulk of waste materials.During recycling, harmful gases are released which pollute the environment.Alternatives: Jute bags/ cloth bags/ paper bags ( any two )8] What is meant by isomers ? “ We cannot have isomers of first three members of alkane series “. Give reason to justify this statement. Draw the structures of two isomers of pentane.Ans: Isomers: Compounds having the same molecular formula but different structural formula / structure.Only one arrangement of atoms is possible. Isomers of pentane :- n-pentane isopentane neopentane9]A carboxylic acid C2H4O2 reacts with an alcohol in the presence of sulphuric acid to form a compound ‘X’.The alcohol on oxidation with alkaline KMnO4 followed by acidification gives the same carboxylic acid,C2H4O2 . Write the name and structure of (i) carboxylic acid, (ii) alcohol and (iii) the compound ‘X’.Ans: (i) Ethanoic acid: CH3COOH (ii) Ethanol : CH3CH2OH (iii) ‘X’ is Ethyl ethanoate : CH3COOC2H510] The atomic number of an element is 17. Predict (a) its valency, (b) whether it is a metal or non metal, (c) its relative size with respect to other members of the group, justify your answer in each case.Ans: Atomic no. 17= 2, 8, 7. Valency of the element = 8-7=1It is a non metal; since it has seven electrons in its outermost shell/ it belongs to 17th group. Its size is larger than F ( the element above it), while its size is smaller than the elements below it, in its group.11] The electronic configuration of an element ‘X’ is 2, 8, 8, 2. To which (a) period & (b) group of the modern periodic table does ‘X’ belong ? State its valency. Justify your answer in each case.Ans: (a) IV period, since ‘X’ has 4 shells. (b) II group, since it has 2 valence electrons. (c) Its valency is 2, since it has 2 valence electrons.12] Explain the process of regeneration in Planaria.Ans: If planaria is cut into many pieces, these piecs grow into separate individuals by the process of regeneration; which is carried out by specialised cells; these cells proliferate & make large number of cells; from this mass of cells different cells undergo changes to become various cell types & tissues. These changes take place in an organised sequence to form the new organisms.13] List any 4 methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of the family?Ans: (i) mechanical method/condom (ii) chemical / pills / drugs (iii) surgical methods (iv) copper-T / loopMaintains the health of women.Parents can give more time and attention to the children.More resources for family.14] A blue colour flower plant denoted by BB is crossbred with a white colour flower plant denoted by ww.State the colour of flower we would expect in their F1 progeny.Write the percentage of plants bearing white flower in F2 generation when the flowers of F1 plants were selfed.State the expected ratio of the genotype BB and Bw in the F2 progeny.Ans: (a) F1– blue (b) 25% (c) BB:Bb 1:215] Explain with the help of suitable examples why certain traits cannot be passed on to the next generation. What are such traits called?Ans: The traits like cutting of tail in mice and loss of weight in beetles are not passed on to the next generation. Because these traits donnot affect DNA/Gametes (which carry parental characteristics to offsprings). These traits are called accquired traits.16] A student focussed the image of an object on a white screen using a converging lens. He noted down the positions of the object, screen and the lens on a scale as given below: Position of object = 10.0 cm Position of lens = 50.0 cm Position of screen = 90.0 cm Find the focal length of the converging lens.Find the position of the image if the object is shifted towards the lens at a position of 30.0 cmState the nature of the image formed if the object is further shifted towards the lens.Ans: (i) u = (50 – 10) cm = 40 cm ; v = (90 – 50) cm = 40 cm u=v, so image is formed at 2f 2f=40 cm f=20 cm (ii) u= (50 – 30) cm = 20 cmTherefore, object is at the focus of the lens so the image is formed at infinity.When object is further shifted towards the lens, then object is between focus and optical centre so the image is erect, virtual and magnified.17] Name the type of mirror used (i) by dentists and (ii) in solar furnaces. Give two reasons why such mirrors are used in each case.Ans: (i) Concave mirror.Reason: Forms magnified, erect image of the object placed within its focal length. Hence minute details can be studied. (ii) Concave mirror. Reason: Converges parallel rays coming from the sun at the focus of the mirror, producing a high temperature at that point in a short time.18] When and where do we see a rainbow ? How is a rainbow formed ? Draw a labelled diagram to illustrate the formation of a rainbow.Ans: After a rain shower rainbow is seen in the sky opposite to the direction of the sun. Water droplets in atmosphere act like small prism causing refraction, dispersion and internal reflection of sunlight forming a spectrum in the sky.19] State in brief two ways in which non-biodegradable substances would affect the environment. List two methods of safe disposal of the non-biodegradable waste.Ans: (1) Non-biodegredable solid waste may block water drains that causeflooding of area and provide breeding sites for the mosquitoes. (2) Excessive use of weedicides and chemical fertilizers reduces the natural bacterial population of soil and cause water pollution.Non biodegredable waste can be disposed off by incineration (burning at high temperature) / land filling / pyrolysis (anaerobic burning of solid waste).20] List the sign conventions that are followed in case of refraction of light through spherical lenses. Draw a diagram and apply these conventions in determining the nature and focal length of a spherical lens which forms a four times magnified real image of an object placed 20 cm from the lens.Ans: Sign conventions ( optical centre is taken as the origin)The object is always placed to the left of the lens.All distances parralel to the principal axis are measured from the optical centre of the lens.All the distances measured to the right of the origin (optical centre) are taken as positive while those measured to the left of the origin are taken as negative.Distances measured perpendicular to and above the principal axis are taken as positive.Distances measured perpendicular to and below the principal axis are taken as negative.m=-4 (four times magnified image)u=-20 cmV= +80 cm1/f = 1/v – 1/uf = uv/u-vf= (-20 cm) (80 cm)/ (-20-80) cm = +16 cm+ sign of ‘f’ means lens is convex and its focal length is 16 cm.21](a) A student cannot see clearly a chart hanging on a wall placed at a distance of 3 m from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustratethis defect. List its two possible causes. (b) Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length. (c) An eye donation camp is being organized by social workers in your locality. How and why would yo help in this cause ?Ans: (a) Myopia / shortsightedness / nearsightedness. Diagram : refer page no. : 189 fig 11.2 (b) of NCERT textbook. (b)Diagram : refer page no. : 189 fig 11.2 (c) of NCERT textbook. (c) Motivation / creating awareness by any means.22] An organic compound ‘x’ on heating with conc.H2SO4 forms a compound ‘Y’ which on addition of one molecule of hydrogen in the presence of nickel forms a compound ‘Z’. One molecule of compound ‘Z’ on combustion with forms two molecules of carbon dioxide and three molecules of water. Identify giving reasons the compounds ‘X’, ‘Y’, ‘Z’ . Write the chemical equations for all the chemical reactions involved.Ans: Since one molecule of Z gives 2 molecules carbon dioxide and three molecules of water on combustion, it means Z has 2 carbon atoms and its molecular formula is C2H6. The compoun Z is obtained by addition of one molecule of hydrogen to compound Y, therefore the formula of Y should be C2H4. The compound Y is obtained by heating compoun X with conc. H2SO4 which shows that it is an alcohol. So the compound X is C2H5OH.Refer NCERT text book for the equations.23] What is pollination ? How does it occur in plants ? How does pollination leads to fertilization ? Explain.Ans: Pollination : Transfer of pollen from anther to stigma.Two ways of pollination :Pollen of one flower to stigma of same flower without the help of any agency.Pollen from a flower to stigma of other flower belonging to the same species by agents like wind, water or animals.Process of fertilisation: Four steps =>Landing of pollen grain on stigma of a flower.Formation of pollen tube carrying male gamete.Pollen tube enters into embryosac.Fusion of male germ cell with the female germ cell to form zygote (fertilisation).24] Write the 2 causes of human population explosion. Explain with the help of suitable examples how this explosion can be checked.Ans: The causes are:Increase in birth rate .Decline in death rate .Increased longevity . (any two)Example:Encouraging small family norms through educational awareness and explaining the benefits of small families.Making general public aware through diverse media about adopting contraceptive methods and their use.SECTION-B25] A sharp image of a distant object is obtained on a screen using a convex lens. In order to determine the focal length of the lens, we need to measure the distance between the Ans:Lens and the image screen.26]A student focussed the image of a distant object using a device X on a white screen S as shown in the figure. if the distance of the screen from the device is 30 cm, select the correct statement about device X.Ans: The device X is a concave mirror of focal length 15 cm.27] Select the correct diagram for the location of an image formed by a convex lens when the object is placed between F and 2F.Ans: The image will be formed beyond 2F2.28] The diagrams showing correct path of the ray after refraction from the convex lens are.Ans: If the ray is passing through F1 it should go parallel to the principal axis after refraction. If the ray passes through the optic centre it would go staight without any deviation after refraction.29] A student traces the path of a ray of light through a rectangular glass slab for four different angles of incidence. He very cautiously measures the angle i, angle r and the angle e. on analysing his measurements , he is likely to draw the following conclusion.Ans:angle i = angle e> angle r30] For tracing the path of a ray of light through a rectangular glass slab, the range of angle of incidence should be betweenAns: 30 and 6031] For tracing a ray of light through a glass prism, the most appropriate distance between the two pins must be Ans: 7 to 10 cm; 3 to 5 cm; 2 to 4 cm.32] For the refraction of a ray of light through a glass prism, the path of a ray of light is shown below.. The angle of incidence, the angle of emergence and the angle of deviation respectively have been represented byAns:Refer page.no 192 fig no. :11.4 of NCERT textbook.33] Study the different conclusions drawn by the studets on the basis of their observations of fresh available specimens of plants and animals :Potato and sweet potato are homologus organs.Wings of insects and wings of birds are analogus organs.Wings of insects and wings of bats are homologus organs.Thorns of citrus and tendrils of cucurbita are homologus organs.The correct conclusions are Ans:II & IV.34] You have a basket of vegetables which contains carrot, potato, tomato, inger, radish, sweet potato. Select two vegetables to represent the correct homologus structures.Ans:Carrot and radish.35] In the following diagram, the structure of embryo of a dicot seed is shown. In this the parts I, II and III are sequentially.Ans:Plumule, Cotyledon, Radicle.36] Following diagrams were drawn by 5 different students I,II,III,IV and V on having seen prepared slides of budding in yeast.The students who have drawn the diagram correctly areAns:Every daughter cell should have a nucleus. The daughter cells having nucleus are the correct slides for budding in yeast.37] Slides of binary fission in amoeba and budding in yeast were given for observations to agroup of students. Some of the observations reported by the group are given below :Cytokinesis were observed in the yeast cell.A chain of buds were observed due to reproduction in amoeba.Single cell of amoeba and single cell of yeast were undergoing binary fission and budding respectively.Elongated nucleus was dividing to form two daughter nuclei in amoeba.The correctly reported conclusions are Ans:III & IV38] On the basis of study of saponification reactions, a group of students noted down the following comments in their notebooks :The nature of the reaction mixture is basic.In saponification reactions, heat is evolved.Saponification reaction is not a neutralisation reaction.Soap is nothing but a salt of fatty acids.Ans:I, II & IV39] In the preparation of a soap, a small amount of sodium chloride is added to the mixture of fat and sodium hydroxide. The role of common salt is to Ans: Favour the precipitation of soap.40] A student takes about 6 mililitres of distilled water in 4 test tubes markes P, Q , R and S. He dissolves sodium sulphate in P, potassium sulphate in Q , calcium sulphate in R and magnesium sulphate in S. After that he adds equal amount of soap solution in each test tube. On shaking these test tubes, he would observe a good amount of lather in the test tubes markedAns: P & Q.41] A student takes sodium hydrogen carbonate powder in a test tube and pours 4-5 drops of acetic acid over it. He would observeAns:Bubbles of a colourless and odourless gas.42] Select the correct observation about dilute solution of acetic acid.Ans:It smells like vinegar and turns blue litmus red.********************************************************** ................
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