DO'S AND DON'TS FOR BOARD

SCIENCE -ANSWER SCHEME PREBOARD 1

                                                ANSWER KEY

CLASS X

SUMMATIVE ASSESSMENT II

SCIENCE

Code No. 086

1. Bio magnification- concentration of harmful chemicals will be maximum at fourth trophic level- bird. 1

2. The screen has to be moved away from the mirror. 1

3. Al2(SO4)3 1

4. Seminal vesicles are a pair of thin walled muscular sac which secretes fluid for nourishment of

 Sperms. Prostate glands-nourishment and transportation of sperm. 1+1

5. Sustainable management of natural resources is necessary so that it lasts for a longer period and future generations

can benefit from it.

Any example for alternative sources of energy. 1+1

6. Those compounds which have same molecular formula but different structural formulae are called Isomers.

 Catenation, tetravalency. 1 + 1

7. Reduce, recycle, reuse. Explain giving examples. 2

8.a) (i)Increasing order atomic mass as physical properties and similarities in chemical properties of Elements.

(ii)The formulae and nature of hydrides and oxides formed by elements was treated as basic chemical properties for its

classification.

b. Periodic law.

c. It is because it resembles both with alkali metals as well as halogens. 1+1+1

9. A. Saturated hydrocarbons- single bond- general formula CnH2n+2, Alkane

 Unsaturated hydrocarbons- double or triple bond- Alkene-CnH2n, Alkyne-CnH2n-2 ½+½

 B. Hexanal 1

 C. CH3 – CH2OH CH2= CH2+H2O 1

10. A. (a) Sodium or potassium. (b) Phosphorus (c) Carbon (d) helium 1

 B. (i) Atomic size decreases from left to right because one proton and one electron is being added therefore force of

attraction between valence electron and nucleus increases. 1

(ii) Number of shells keep on increasing therefore distance between nucleus and valence electron increases, hence

atomic size increases down the group. 1

11. DNA- deoxy riboneuclic acid ½

Hot conc

H2SO4DNA copying is called DNA replication. In this process one copy each of replicated DNA will be passed to daughter cells.

1

Variations may be introduced during DNA copying. This inbuilt tendency for variation during reproduction form the basis

of evolution. 1 1/2

12. Bacteria and fungi break down the dead and waste products of organisms. They breakdown the complex organic

substances into simple inorganic substances that go into the soil and used by the plants.

Any two advantages 2

13. Diagram 1 ½

 A. Fallopian tube or oviduct B. Uterus C. ovary ½ + ½+ ½

14.Definition ½+½+ ½

 Example for each ½ +½+ ½

15 . a)Snell’s law and other law- 2

 b)( i) bending is more in A – refracted ray bends towards normal when it moves from rarer to denser medium

1/2

(ii) Speed of light is more in rarer medium, that is in A ½

16. it is the ratio of height of image to height of object 1

1/v ---1/u = 1/f ½

m =3 , v/u =3 , v=3u ½

ie 1/3u -1/u = 1/20 ½

 u= 13.33 cm ½

17a)image can be obtained on a screen –real ½

image can not be obtained on a screen –virtual ½

 Image is of the same size as the object -real ½

 Image is not of the same size as the object –virtual ½

b) They have a wider view as they are curved upwards hence it has got larger area – 1

18. a) hypermetropia or far sightedness ½ b) This defect arises because – i) focal length of the eye lens is long & ii) The eye ball has become too small –

1 1 marks ( only 2nd diagram is required)

Corrected by using a convex lens of appropriate power ½

19. 1. It brings in the resistivity wherever required (survival)

 2. It is responsible for acclimatization in varied environmental conditions (adjustment)

 3. It also makes on species different from the other (diversity) 1+1+1

20. Diagram 2

 Labeling 1

 Process of fertilization (Page 135 NCERT Text book) 2

OR

Explanation and examples- Methods of asexual mode of reproduction(Page No.131 &132 NCERT book.) 3

Fragmentation ,regeneration – explanation with proper diagram 1+1

21. A.Mendel took pea plants with two different characteristics such as a tall plant with round seeds and short plant with

wrinkled seeds

F1 progeny are all tall with round seeds. Thus tallness and round seeds are dominant traits.

F2 Progeny are tall plants with round seeds and some short plants with wrinkled seeds.

But some F2progeny showed new mixtures like tall having wrinkled seeds and short having round seeds

Therefore tall and short trait and round and wrinkled seed trait are independently inherited. 3

B. Definition 1 Evolution can not be equated to progress from lower forms to higher form. It seems to have given rise to more

complex body designs even while the simpler body designs continue to flourish. Eg. human being s have not evolved

from chimpanzees but both have common ancestor 1

22.A) i) CH3COOH+NaOH                          CH3COONa + H2O 1

            ii) R – C=C-R+H2 1

 I I

 R R

 sunlight

iii) CH4 + Cl2 CH3Cl+HCl 1

 B) Structure of ethanoic acid and butanone ½ + ½

 C) Esters are pleasant fruit-smelling compounds. They are formed by the reaction of carboxylic acids and alcohols. They

are used in making perfumes.(any other use) ½ + ½

OR

A) Soap is a sodium or potassium salt of fatty acid. It does not give lather in hard water because hard water contain Ca2+

and Mg2+ ions react with soap to form calcium and magnesium salts of fatty acids which are insoluble in water. 1+1

B) Cleansing action of soap- page 75 NCERT text book 2

C) A soap micelle is not formed in other solvents like ethanol. It is because soap molecule will not ionize in ethanol and no

micelle formation can take place. 1

23..A 4

Sl No. Device Position of Object Position of Image Nature of Image

1 Concave mirror Beyond C Between F &C (1/2) Real and inverted

(1/2)

2 Convex mirror At infinity (1/2) Behind the mirror Virtual and

erect(1/2)

3 Concave lens For any position Between focus and

optical centre (1/2)

Virtual and

erect(1/2)

4 Convex lens Between f and 2f

(1/2) Away from 2f Real &inverted

(1/2)

B. Any ray diagram 1

24. A.rainbow ½

 B.prism ½

Ni H H

 | |

R - C - C - R

 | |

 R R 2

C. rainbow is always forming opposite to sun - 1

D. any one moral value - 1

MCQ

25. (C)

26. (B)

27. (A)

28. (B)

29. (D)

30. (C)

31. (D)

32. (C)

33. (D)

34. (B)

35. (A)

36. (C)

37. (A)

38. (C)

39. (D)

40. (B)

41. (C)

ANSWER SCHEME OF PREBOARD 1 -SCIENCE

 ANSWER KEY 

MARKING SCHEME

1) Dioptre (1)

2) Chlorofluro carbons (1)

3) Alkaline potassium permanganate

And Acidified potassium dichromate (½ + ½ )

4) h=+2 cm, u=-30cm f=-15cm

U = -30 cm

Screen should be placed at 30 cm in front of the mirror to obtain sharp image

 (2)

5) (a) Ability of eye to adjust its focal length to see hereby and distant objects

clearly (b) Focal length of eye lens decreases (1)

6) Food Chain Food Web

1) Sequential process of one Network of food chains with intercrosses

organism consuming the and linkages

other

2) Each Organism at a tropic Each organism at a tropic level receives

level receives food from one food from more than one group

group of organisms of organisms.

 (1 + 1)

7) For irrigation and generating electricity (1)

(1) Social problems - displacement of people without

proper rehabilitation and compensation ( ½ )

Economic problem - huge input without much benefits ( ½)

8) Structural Formula,

 1 – butyne (1)

 2 – butyne (1)

yes, both are isomers (½ )

Reason ( ½ )

9) (a) ethene being an unsaturated hydrocarbon add bromine and change to

colourless 1,2 – dibromoethane, (1)

but ethane is saturated hydrocarbon and no addition reaction with bromine (1)

(b) Reaction (1)10) Transparent ---- Light can pass through easily

eg: air, water ( ½ + ½ )

Opaque ---- does not allow light to pass through

eg: wood, stone etc ( ½ + ½ )

Transluscent ----- light passes only partially

eg: cloud, waxpaper ( ½ + ½ )

11) Grafting – brief description (1)

Cutting - brief description (1)

Layering - brief description (1)

12) Diagram – with labeling ,

Stigma, style, ovary, anthev, filament, petal, sepal (1 ½ + 1½ )

13) (a) Electronic Configurations,

Oxygen – 2, 6

Magnesium – 2,8,2 ( ½ + ½ )

(b) O2- --- 2,8

Mg2+ -- 2,8

O2- larger in size (1)

Reason.... (1)

14) [1] To increase the magnification of image (1)

 [2] To increase the sharpness of image (1)

 [3] To erect the final image (1)

15) [1] Temperature changes and rainfall failures (1)

 [2] Loss of immunity in humans (1)

 [3] Destruction of aquatic life and vegetation (1)

( Any other points also)

16) Definition (1)

 ray diagram (1)

Reason – lights of different colours travel with different speed in glass(1)

17) Sun as the only source of energy which the plants use for photosynthesis and

thereby to store food (1)

Flow of energy from sun into the biosphere (1)

Release of energy in the form of heat (1)

18) Atomic Number Electronic Group Period Configuration

 A 5 2,3 13 2 (½ + ½ )

 B 7 2,5 15 2 ( ½ + ½)

 C 10 2,8 18 2 ( ½ + ½)

19) [1] Essential for ecological balance

 [2] Maintain biodiversity

 [3] Prevention of flood or any other points (1 + 1 + 1 )

20) Each ray diagram with nature of image ( 1 + 1 + 1 + 1 + 1 )

 OR

 Explanation (3) Diagram (2)

21) [a] HIV (1)

 [b] Sexual contact, blood transfusion (1 + 1)

 [c] destroys white blood cells, reduce the immunity ( ½ + ½ )

 [d] use of condom,

 Using sterilized syringes ( Any one) (1)

 Or

 Diagram (3) Label (2)

22) [a] CH3-COOH ( ethanoic acid) (1)

 Conc. H2SO4

[b] CH3-COOH + C2H5OH → CH3-COOC2H5 + H2O (1)

[c] Ethyl ethanoate (1)

[d] Esterification (1)

[e] Saponication (1)

OR

[a] (i) nCH2=CH2 → ( −CH2 −CH2 −) (1)

(ii) CH3-COOH + NaHCO3 → CH3-COONa +H2O + CO2 (1)

[b] Presence of Ca2+ ions and Mg 2+ ions (1)

Formation of insoluble calcium and magnesium salts with soap (1)

Soap get wasted simply as it do not lather with soap (1)23) a. 2 points of difference (1+1)

 b. F1 generation is the generation of hybrids derived from a cross

 between two genetically different homozygous individuals.

 F2 generation is the generation produced as a result of

 interbreeding between the individuals of F1 generation. (1 + 1)

 c. Variations are difference found in structure, function, behaviors

 and genetic make up of different individuals of same parentage, variety,

 race and species. (1)

 or

 a) When the pollen of a flower falls on the stigma of the same flower the process

Is called as self pollination. If the pollen falls on the stigma of a different flower

The process is called as cross pollination. (1+1)

b) The transfer of pollen from anther to stigma is called pollination.

 The fusion of male and female gamete is called fertilization. (1+1)

 Pappaya, cucumber, water melon. (1)

24) Correct reasons (1+1+1+1+1)

 OR

Myopia, Correction using spectacles with concave lens. 1+1

 Ray Diagrams (1 ½ +1 ½)

 SECTION B

25. (a)

26.( c)

27. (a)

28. (c)

29.( c)

30. (a)

31.( a)

32.( b)33.(d)

34. (d)

35.( a)