31/1/2 2016 Class 10 Science Question Paper Solution
(1) Name the following compounds:
(a) CH3 – CH2 – OH;
(b) CH3 – C = O
Ans: (a) Ethanol
(b) Ethanal
(2) What is DNA?
Ans: It is the carrier of hereditary information from parents to the next generation.
(3) List two biotic components of a biosphere.
Ans: Producers, consumers, decomposers OR Plants, animals, micro-organisms
(4) A ray of light is incident on a convex mirror as shown. Redraw the diagram and complete the path of this ray after reflection from the mirror. Mark angle of incidence and angle of reflection on it.
Ans:
(5) Explain giving example where active involvement of local people lead to efficient management of forest.
Ans:
- In West Bengal the Sal forests had been very badly degraded.
- A forest officer involved villagers in protection of Sal forest and gave them employment in silviculture and harvesting operations.
- Villagers were allowed to collect firewood and fodder on a nominal payment.
- Within a period of 10 years the previously worthless forests became valuable.
(6) List four advantages of properly managed watershed management.
Ans:
Advantages of watershed management –
(i) Mitigates drought and floods
(ii) Increase the life of the dams and reservoirs downstream
(iii) Increases the biomass production and thereby the income of the watershed community.
(iv) Helps in maintaining ecological balance by scientific conservation of soil and water. Or any other
(7) What is an oxidising agent? What happens when an oxidising agent is added to propanol? Explain with the help of a chemical equation.
Ans:
- It is a substance which can give oxygen to other substances.
- Propanol is oxidised to Propanoic acid.
(8) What are covalent compounds? Why are they different from ionic compounds? List their three characteristic properties.
Ans:
- Covalent compounds are those compounds which are formed by sharing of electrons between two atoms / which contain covalent bonds.
- Covalent compounds are different from ionic compounds because the ionic compounds are formed by the transference of electrons.
- Three characteristics of covalent compounds:
(i) Generally have low melting and boiling points.
(ii) Generally insoluble or less soluble in water but soluble in organic solvents.
(iii) Do not conduct electricity. (Or any other characteristic)
(9) An element ‘M’ with electronic configuration (2, 8, 2) combines separately with (NO3)–, (SO4)2- and (PO4)3- radicals. Write the formula of the three compounds so formed. To which group and period of the Modern Periodic Table does the elements ‘M’ belong? Will ‘M’ form covalent or ionic compounds? Give reason to justify your answer.
Ans:
- The electronic configuration (2, 8, 2) of the element ‘M’ suggests that it belongs to group 2 and period 3 of the Modern Periodic Table and its valency is 2.
- The chemical formula of the compounds are –
M (NO3)2/Mg (NO3)2; MSO4/MgSO4; M3 (PO4)2/MG3 (PO4)2.
‘M’ will form ionic compound by losing two electrons.
(10) Name any two elements of group one and write their electronic configurations. What similarity do you observe in their electronic configurations? Write the formula of oxide of any of the aforesaid element.
Ans:
- Two elements of group 1 are Na, K / sodium, potassium Electronic configurations Na = 2,8,1; K = 2,8,8,1
- Similarity: Both have one valence electron / One electron in outermost shell
- Oxide – NaO/K2O
(11) What are the functions of testis in the human male reproductive system? Why are these located outside the abdominal cavity? Who is responsible for bringing about changes in appearance seen in boys at the time of puberty?
Ans:
Functions of testis –
(i) Produce sperms
(ii) Produces male hormone/testosterone
- These are located outside the human body, as sperms need lower temperature than the normal body temperature to mature. 1
- Testosterone
(12) Suggest three contraceptive methods to control the size of human population which is essential for the health and prosperity of a country. State the basic principle involved in each.
Ans:
Three methods of contraception –
(i) Barrier method or mechanical method/ Condom/ Diaphragm, to prevent the meeting of sperms and ova.
(ii) Chemical method/ Oral pills, Changes the hormonal balance of the female partner so that the eggs are not released.
(iii) Surgical method – to block the vasdeferens in males/ vasectomy or the fallopian tube (oviduct) in females/ tubectomy, to prevent the transfer of sperms or egg and hence no fertilization takes place.
(iv) UCDs/ Loop or the copper-T placed in the uterus, to prevent pregnancy
(13) What is multiple fission? How does it occur in an organism? Explain briefly. Name one organism which exhibits this type of reproduction.
Ans:
Multiple fission:- The process of reproduction in which many individuals are formed or produced from the parent cell.
In this process, the nucleus divides repeatedly to produce large number of nuclei. Each nucleus gathers a bit of cytoplasm around itself, develops a membrane around each structure. Many daughter cells develop which on liberation grow into adult organism.
Plasmodium exhibits this type of fission.
(14) How did Mendel interpret his result to show that traits may be dominant or recessive? Describe briefly.
Ans:
Mendel conducted breeding experiments on Pea plants.
- He selected pure bred tall and dwarf plants.
- He cross-pollinated these plants.
- In the F1 generation obtained only tall plants. Tallness is the dominant trait.
- Then, he produced F2 generation by selfing of hybrids / F1
- He found that 3/4th of the plants were tall and 1/4th were dwarf.
- The trait which remains hidden in F1 generation plants is the recessive traits.
(15) List three distinguishing features, in tabular form, between acquired traits and the inherited traits.
Ans:
Acquired traits |
Inherited traits |
Do not bring changes in the DNA of germ sells | Bring changes in the DNA of germ cells. |
Cannot direct evolution | Can direct evolution |
Cannot be passed to the progeny
|
Can be passed on to the progeny |
(16) What is meant by scattering of light? The sky appears blue and the sun appears reddish at sunrise and sunset. Explain these phenomena with reason.
Ans:
- Scattering of light – Phenomenon of spreading of light (diffused reflection) by minute particles in a medium.
- The sky appears blue because the blue colour of sunlight scatters much more strongly than the red colour by particles in atmosphere/ air due to its shorter wave length.
- At sun-rise and sun-set most of the blue light and shorter wavelengths are scattered away by the particles in the atmosphere as the light from the sun near the horizon passes through thick layers of air and larger distance. The light that reaches us is of longer wavelength (red colour) giving a reddish appearance.
(17) Draw the following diagram, in which a ray of light is incident on a concave/convex mirror, on your answer sheet. Show the path of this ray, after reflection, in each case.
Ans:
(18) Give reason to justify the following:
(a) The existence of decomposers is essential in a biosphere.
(b) Flow of energy in a food chain is unidirectional.
Ans:
(a) The existence of decomposers is essential in a biosphere because they breakdown complex organic substances into simple inorganic substances that can be absorbed by the plants. Thus, decomposers
- replenish the soil naturally
- helps in removing the biodegradable waste.
(b) In a food chain the energy moves progressively through the various trophic levels, it is no longer available to the previous level (autotrophs) and the energy captured by the autotrophs does not go back to the solar input. Hence, the flow of energy is unidirectional
(19) (a) Write the functions of the following parts in human female reproductive system :
(i) Ovary
(ii) Oviduct
(iii) Uterus
(b) Describe the structure and function of placenta.
Ans:
(a) (i) Ovary –
(i) Production of female hormone
(ii) Production of female gamete
(ii) Oviduct –
(i) Transfer of female gamete from the ovary
(ii) Site of fertilization
(iii) Uterus –
(i) Implantation of the zygote
(ii) Nourishment of the developing embryo/ placenta formation
(b) Structure of Placenta – it is a disc like structure embedded in the uterine wall connected to the embryo. It has villi on the embryo’s side of the tissue and on the mother side, it has blood spaces, which surround the villi.
Function of Placenta – it provides a large surface area for nutrients/ glucose and oxygen to pass from the mother’s side to the embryo and waste substances from the embryo’s side to mother’s blood
(20) What is meant by speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Give reason to justify your answer.
Ans:
- Speciation:- The process of formation of a new species from a pre-existing one.
- Four factors: Genetic drift Mutation / Drastic change in the genes or DNA Natural selection Geographical isolation
- Geographical isolation cannot be a major factor in the speciation of a self- pollinating plant species.
- Reason:- Physical barrier cannot be created in self-pollinating plants.
(21) (a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbon.
(b) Name the products formed when ethane burns in air. Write the balanced chemical equation for the reaction showing the types of energies liberated.
(c) Why is reaction between methane and chlorine in the presence of sunlight considered a substitution reaction?
Ans:
Pass the vapours of the given samples of saturated and unsaturated hydrocarbons into bromine water taken in two separate test tubes. The one which discharges the colour of bromine water is that of unsaturated hydrocarbon and the other represents saturated hydrocarbon. (or any other test) 2 On burning ethane in air, the products obtained are carbon dioxide and water, along with heat and light.
2C2H6 (g) + 7 O2 (g) → 4CO2 (g) + 6 H2O (I) + Heat + Light
It is considered a substitution reaction because the hydrogen atoms of methane (CH4) are replaced by chlorine atoms one by one.
(22) (a) Draw a ray diagram to show the formation of image by a concave lens when an object is placed in front of it.
(b) In the above diagram mark the object-distance (u) and the image-distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the concave lens in this case.
(c) Find the nature and power of a lens which forms a real and inverted image of magnification –1 at a distance of 40 cm from its optical centre.
Ans:
(a)
(b) Relation:
1/f = 1/v – 1/u
(c) As, m = -1
Hence, the lens is convex
∵ m = v/u ∵ v = -u
Thus, object is at 2f
2f = 40 cm
∵ f = 20cm = 0.2 m
p = 1/f = 1/0.2 = + SD (convex lens)
(23) (a) Define the following terms in the context of spherical mirrors:
(i) Pole
(ii) Centre of curvature
(iii) Principal axis
(iv) Principal focus
(b) Draw ray diagrams to show the principal focus of a
(i) Concave mirror
(ii) Convex mirror
(c) Consider the following diagram in which M is a mirror and P is an object and Q is its magnified image formed by the mirror.
State the type of the mirror M and one characteristic property of the image Q.
Ans:
(a) (i) Pole – Centre of the reflecting surface of the mirror.
(ii) Centre of curvature – The centre of the hollow sphere of which the reflecting surface of mirror forms a part.
(iii) Principal axis – Straight-line passing through the pole and the centre of curvature of a spherical mirror.
(iv) Principal focus – Incident rays parallel to principal axis, after reflection, either converge to or appear to diverge from a fixed point on the principal axis called principal focus of the spherical mirror.
(b)
(c) Convex mirror
Image formed is virtual.
(24) (a) Write the function of each of the following parts of human eye : cornea; iris; crystalline lens; ciliary muscles
(b) Millions of people of the developing countries of world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission how would you contribute in this noble cause?
(i) State the objective of organising such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programme.
Ans:
(a) · Cornea – Refracts the rays of light falling on the eye
- Iris – Controls the size of the pupil
- Crystalline lens – Focuses the image of the object on the retina
- Ciliary muscles – Holds the eye lens and adjusts its focal length
(b) (i) Objectives – To make people aware and realize their duties towards society.
(ii) One person can give sight to two people ½ Our eyes can live even after our death
(iii) Concern for others/ Responsible behavior/Group work/or any other
(25) Which of the following is a correct set of homologous organs?
(a) Forelimbs of frog, bird and lizard
(b) Spine of cactus and thorn of bougainvillea
(c) Wings of bat and wings of butterfly
(d) Wings of a bird and wings of a bat
Ans: (a) Forelimbs of frog, bird and lizard
(26) A student has to perform the experiment “To identify the different parts of an embryo of a dicot seed.” Select from the following an appropriate group of seeds:
(a) pea, gram, wheat
(b) red kidney bean, maize, gram
(c) maize, wheat, red kidney bean
(d) red kidney bean, pea, gram
Ans: (d) red kidney bean, pea, gram
(27) Study the following figure in which a student has marked the angle of incidence (∠i), angle of refraction (∠r), angle of emergence (∠e), angle of prism (∠A) and the angle of deviation (∠D). The correctly marked angles are:
(a) ∠A and ∠i
(b) ∠A, ∠i and ∠r
(c) ∠A, ∠i, ∠e and ∠D
(d) ∠A, ∠i, ∠r and ∠D
Ans: (a) ∠A and ∠i
(28) Select from the following the best experimental set-up for tracing the path of a ray of light passing through a rectangular glass slab :
(a) P
(b) Q
(c) R
(d) S
Ans: (d) S
(29) A student obtained a sharp image of a candle flame placed at the distant end of the laboratory table on a screen using a concave mirror to determine its focal length. The teacher suggested him to focus a distant building about 1 km far from the laboratory, for getting more correct value of the focal length. In order to focus the distant building on the same screen the student should slightly move the :
(a) Mirror away from the screen
(b) Screen away from the mirror
(c) Screen towards the mirror
(d) Screen towards the building
Ans: (c) Screen towards the mirror
(30) To determine the approximate focal length of the given convex lens by focussing a distant object (say, a sign board), you try to focus the image of the object on a screen. The image you obtain on the screen is always :
(a) Erect and laterally inverted
(b) Erect and diminished
(c) Inverted and diminished
(d) Virtual, inverted and diminished
Solution: (c) Inverted and diminished
(31) A student takes four test tubes marked P, Q, R and S of 25 mL capacity and fill 10 mL of distilled water in each. He dissolves one spoon full of four different salts in each as – KCl in P, NaCl in Q, CaCl2 in R and MgCl2 in S. He then adds about 2 mL of a sample of soap solution to each of the above test tubes. On shaking the contents of each of the test tubes, he is likely to observe a good amount of lather (foam) in the test tubes marked:
(a) P and Q
(b) R and S
(c) P, Q and R
(d) P, Q and S
Ans: (a) P and Q
(32) Which of the following sets of materials can be used for conducting a saponification reaction for the preparation of soap?
(a) Ca(OH)2 and neem oil
(b) NaOH and neem oil
(c) NaOH and mineral oil
(d) Ca(OH)2 and mineral oil
Ans: (b) NaOH and neem oil
(33) Consider the following comments about saponification reactions :
(I) Heat is evolved in these reactions
(II) For quick precipitation of soap sodium chloride is added to the reaction mixture
(III) Saponification reactions are special kind of neutralisation reactions
(IV) Soaps are basic salts of long chain fatty acids
The correct comments are:
(a) I, II and III
(b) II, III and IV
(c) I, II and IV
(d) Only I and IV
Ans: (c) I, II and IV
(34) A student focuses the image of a well illuminated distant object on a screen using a convex lens. After that he gradually moves the object towards the lens and each time focuses its image on the screen by adjusting the lens.
(i) In which direction-towards the screen or away from the screen, does he move the lens?
(ii) What happens to the size of the image-does it decrease or increase?
(iii) What happens to the image on the screen when he moves the object very close to the lens?
Ans:
(i) Lens towards the screen/ screen away from the lens (Note: one mark to be awarded for any other answer)
(ii) Increase ½
(iii) No image on the screen
(35) What do you observe when you drop a few drops of acetic acid to a test tube containing:
(i) phenolphthalein
(ii) distilled water
(iii) universal indicator
(iv) sodium hydrogen carbonate powder
Ans: (i) No change / or remains colourless
(ii) No change
(iii) Turns pink/orange
(iv) Evolution of a colourless/ odorless gas with brisk effervescence
(36) Draw a labelled diagram to show that particular stage of binary fission in amoeba in which its nucleus elongates and divide into two and a constriction appears in its cell membrane.
Ans: