HBSE Class 10 Science Important Question Answer 2024-2025

Haryana Board (HBSE) Class 10 Science Important Question Answer 2024-2025. HBSE Class 10 Science Important Questions 2024. BSEH Class 10 Science Case Study Based Questions 2024. Class 10 Science Most important questions for Board Exam 2024. HBSE Class 10 Physics , Chemistry & Biology Important Questions 2024.

HBSE Class 10 Science Important Question Answer 2024-2025


Science (Physics)

1. Which of the following has milky and cloudy crystalline lens in eye ?
(a) Myopia
(b) Cataract
(c) Presbyopia
(d) Hypermetropia
Answer – (b) Cataract

2. The magnetic field inside a long straight solenoid carrying current :
(a) is zero
(b) decreases as we move towards its end
(c) increases as we move towards its end
(d) is the same at all points
Answer – (d) is the same at all points

3. …………. is the commercial unit of electrical energy.
Answer – kilowatt hour (kW h)

4. Draw the symbol of a wire joint.
Answer –

5. A positively charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is :
(a) towards south
(b) towards east
(c) downward
(d) upward
Answer – (d) upward

6. At the time of short circuit, the current in the circuit :
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously
Answer – (c) increases heavily

7. Magnetic field lines of a magnet never …………. each other.
Answer – intersect

8. Name the substance which has the highest refractive index.
Answer – Diamond

9. An electron enters a magnetic field at right angles to it. The direction of force acting on the electron will be :

(a) to the right
(b) to the left
(c) out of the page
(d) into the page
Answer – (d) into the page

10. What happens when live wire and neutral wire of a circuit comes in direct contact ?
(a) boiling
(b) melting
(c) overloading
(d) none of these
Answer – (c) overloading

11. The refractive index of water is …………. .
Answer : 1.33

12. What is type of lens if it has focal length of – 40 cm ?
Answer – Concave

13. Magnetic field is a quantity that has :
(a) magnitude
(b) direction
(c) both of the above
(d) none of these
Answer – (c) both of the above

14. Right hand thumb rule can be used to determine the direction of :
(a) Magnetic field
(b) Force
(c) both of the above
(d) none of these
Answer – (a) Magnetic field

15. Inside a magnet, magnetic field lines move from …..…….. to …………. .
Answer – South to North

16. Define one volt.
Answer – One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.

17. Beams of light are incident through the holes A and B and emerge out of the box through holes C and D respectively as shown in the figure. Which of the following could be inside the box ?

(a) Rectangular glass slab
(b) Convex lens
(c) Concave lens
(d) Prism
Answer – (a) Rectangular glass slab

18. Which of the following represents voltage ?
(a) (work done) ÷ (current × time)
(b) work done × current
(c) (work done × time) ÷ current
(d) work done × current × time
Answer – (a) (work done) ÷ (current × time)

19. …………… is the most important safety device used for protecting the circuits due to short circuiting or overloading of the circuits.
Answer – Fuse

20. Write the lens formula.
Answer : 1/f = 1/v – 1/u

21. Assertion (A) : Light enters the eye through retina.
Reason (R) : Lens system of eye forms image on retina.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (d) A is false but R is true.

22. Assertion (A) : Voltmeter is always connected in parallel across the points between which the potential difference is to be measured.
Reason (R) : Potential difference is measured by ammeter.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (c) A is true but R is false.

23. Assertion (A) : An electric current through a metallic conductor produces a magnetic field around it.
Reason (R) : Direction of magnetic field associated with a current-carrying conductor is given by Left-Hand thumb rule.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (c) A is true but R is false.

24. Assertion (A) : A strong metal with high melting point is used for making bulb filaments.
Reason (R) : Filament of bulb must retain as much of heat generated as possible to emit light.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

25. Assertion (A) : The near point of a hypermetropic eye is more than 25 cm away.
Reason (R) : Hypermetropic eye is corrected using spectacles containing concave lens.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (c) A is true but R is false.

26. On what factors does the resistance of a conductor depend ?
Answer – Resistance of a conductor depend on :
(i) the length of the wire
(ii) the area of the transverse cut (cross section) of the conductor
(iii) the nature of the substance

27. Define 1 dioptre power of a lens.
Answer – When the focal length of a lens is 1 meter, the power of that lens is called 1 diopter.

28. Find the power of a concave lens of focal length 4 m.
Answer – Given, focal length (f) = 4 m
We know that, Power of a lens (P) = 1/f
P = 1/4 = 0.25 Dioptre

29. Explain why the planets do not twinkle.
Answer – The planets are much closer to the earth and are thus seen as extended sources.
If we consider a planet as a collection of a large number of point-sized sources of light, the total variation in the amount of light entering our eye from all the individual point-sized sources will average out to zero, thereby nullifying the twinkling effect.

30. Write the values of near point and far point for a normal human eye.
Answer : Near Point = 25 cm
Far point = infinity

31. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected ?
Answer – The student is suffering from myopia (near sightedness). It can be corrected by using concave lens of suitable power.

32. Explain why is the colour of the clear Sky Blue ?
Answer – The red light has a wavelength about 1.8 times greater than blue light.
Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue colour (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes. So colour of clear sky is blue.

33. Define power of a lens. Write its unit.
Answer – The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power. The SI unit of power of a lens is ‘Dioptre’.

34. Define far point and near point of human eye with normal vision.
Answer – The farthest point up to which the eye can see objects clearly is called the far point of the eye.
The minimum distance, at which objects can be seen most distinctly without strain, is called the near point of the eye.

35. Why does the sky appear dark instead of blue to an astronaut ?
Answer – There is no atmosphere in space. Thus, no scattering of light takes place in space. Thus, the sky appears dark instead of blue to an astronaut.

36. Write laws of refraction of light.
Answer – The incident ray, the refracted ray and the normal to interface of two transparent media at the point of incidence, all lie in the same plane.
The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction.

37. Define Dispersion of light.
Answer – When sunlight (white light) passes through the prism, this light is divided into seven constituent colors.

38. Define Spectrum.
Answer – The sequence of seven colors obtained as a result of the dispersion of white light is called the spectrum.

39. Why does the cord of an electric heater not glow while the heating element does ?
Answer – The resistance of the electric heater cord is negligible, so it doesn’t heat. Whereas due to the high resistance of its heating element, it produces more heat and becomes agitated.

40. State Ohm’s law. What is resistance ?
Answer – According to Ohm’s law, if physical conditions such as temperature remain constant, then the potential difference generated between the ends of a resistor is proportional to the current flowing from it.
The property of a conductor which opposes the current flow in the conductor is called electrical resistance.

41. What is a solenoid? What is the magnetic field inside a long solenoid carrying current.
Answer – A multiple-round coil of the cylinder shape of an insulated copper wire wrapped nearby is called a solenoid. The magnetic field lines within the solenoid are like parallel lines. All the points within a solenoid have the same magnetic field.

42. State right hand thumb rule.
Answer – If we hold the electric current in our right hand in such a way that our thumb points towards the current, our fingers will be wrapped in the direction of the lines of the magnetic field around the conductor.

43. Why is the tungsten used almost exclusively for filament of electric lamps ?
Answer – due to the high melting point and high resistivity of tungsten, it is the only use in the manufacture of electric lamps.

44. Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal ?
Answer – Alloys have high melting point and high resistivity than pure metals. Therefore, conductors of the electric heating devices are made of an alloy rather than pure metal.

45. Why is the series arrangement not used for domestic circuits ?
Answer – In series circuit the voltage is divided among electrical appliances connected, because of which electric components do not work properly.
The electrical circuit breaks down when a device malfunctions in combination in a series, so if a single appliance in the house malfunctions, all the appliances will stop working.
Only one switch works in a series circuit, so different electrical appliances in homes cannot be turned off or on at convenience.

46. How does the resistance of a wire vary with its area of cross-section ?
Answer – Resistance is inversely proportional to the area of cross section of wire. This means resistance increases with decrease in area of cross section and vice versa.

47. Why are copper and aluminium wires usually employed for electricity transmission ?
Answer – Copper and aluminium have low resistivity, are good conductors of electricity due to their low resistance and are relatively cheap and accessible metals.

48. Differentiate between convex lens and concave lens.
Answer –

Convex Lens Concave Lens
1. The convex lens is thicker from the middle and thinner at the edges. 1. Concave lens is thinner in the middle and thicker at the edges.
2. Convex lens is used as a prevention of farsightedness. 2. Concave lens is used as a prevention of nearsightedness.
3. In convex lens, the image of the object becomes real and inverted. 3. In concave lens, the image of object becomes virtual and erect.
4. The focal length of convex lens is positive. 4. The focal length of concave lens is negative.
5. Convex lens converges ray of light at one point. 5. Concave lens diverge rays of light.


49. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series ?
Answer – Advantages of connecting electrical devices in parallel :
(i) Potential difference does not divide among the appliances; thus all electric appliances get equal voltage and work better.
(ii) The other devices continue to work efficiently even in the event of a malfunction of one of the devices connected in the parallel order.
(iii) Separate switch can be attached with each of the electrical appliances so that anyone can be switched off as per requirement keeping other operating.
(iv) The total effective resistance of the circuit becomes lower than the resistance of appliances.

50. Write the sign convention set for reflection by spherical mirrors.
Answer – (i) The object is always placed to the left of the mirror. This implies that the light from the object falls on the mirror from the left-hand side.
(ii) All distances parallel to the principal axis are measured from the pole of the mirror.
(iii) All the distances measured to the right of the origin (along +x axis) are taken as positive.
(iv) All the distances measured to the measured to the left of the origin (along –x axis) are taken as negative.
(v) Distances measured perpendicular to and above the principal axis (along +y axis) are taken as positive.
(vi) Distances measured perpendicular to and below the principal axis (along –y axis) are taken as negative.

51. Draw a well labelled diagram of the human eye.
Answer –

52. Draw a ray diagram of image formed by a concave spherical mirror if object is placed between C and F.
Answer –

53. Draw the magnetic field lines around a bar magnet. Write down the properties of magnetic field lines.
Answer –

Properties of magnetic field lines :
(i) Magnetic field lines emerge from the North Pole and merge into the South Pole.
(ii) Inside the magnet, the direction of the magnetic field is from its south pole to the north pole.
(iii) Magnetic field lines are closed curves.
(iv) Where the magnetic field lines are dense, the magnetic field is strong.
(v) Two magnetic field lines never intersect each other.

54. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series.
Answer –

55. Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
Answer – (i) To get 9 Ω of resistance from three resistors of 6 Ω, two resistors have to be placed in parallel and third resistance in their series.

(ii) To get 4 Ω resistance from three resistors of 6 Ω, two resistors have to be placed in series and the third resistor in their parallel order.

56. An electric iron consumes energy at a rate of 840 W when heating is at the maximum rate and 360 W when the heating is at the minimum. The voltage is 220 V. What are the current and the resistance when heating is maximum ?
Answer – We know that the power input is P = V × I
Thus, the current I = P/V
When heating is at the maximum rate, I = 840W/220V = 3.82 A
The resistance of the electric iron is R = V/I = 220V/3.82A = 57.60 Ω

57. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem ?
Answer : f = – x = – 80 cm, here x is distance of far point.
Given, focal length (f) = – 0.8 m
We know that power of a lens (P) = 1/f
P = 1/(-0.8) = – 1.25 Dioptre
Since the power is negative, the nature of the lens is concave lens.

58. An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of focal length 15.0 cm. Find the distance and the size of the image.
Answer – Height of the object (h) = + 4.0 cm
object-distance (u) = – 25.0 cm
Focal length (f) = – 15.0 cm
Since, 1/v + 1/u = 1/f
1/v = 1/f – 1/u = 1/(-15) – 1/(-25) = -2/75
v = – 37.5 cm
Magnification (m) = h’/h = – v/u
h’ = -h(v/u)
Height/size of image (h’) = -4[(-37.5)/(-25)] = – 6 cm

59. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω ?
Answer – (a) If these four resistors are placed in a series, the maximum resistance will be obtained :
Rs = 4Ω + 8Ω + 12Ω + 24Ω = 48Ω

(b) The above four resistors will be placed in parallel order to get minimum resistance.
1/RP = 1/4 + 1/8 + 1/12 + 1/24 = 12/24 = 1/2
RP = 2Ω

60. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Answer – Distance of image (v) = – 1 m
Distance of object (u) = – 25 cm = – 0.25 m
1/f = 1/v – 1/u = 1/(-1) – 1/(-0.25) = 3
P = 1/f = 1/3 D

61. Name and state the rule to determine the direction of following :
(i) magnetic field produced around a straight conductor carrying current.
Answer – Right Hand Thumb Rule, which states that that if one holds a straight current carrying conductor with right hand such that the thumb points towards the direction of current, then fingers will wrap around the conductor in the direction of field lines of the magnetic field.

(ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.
Answer – Fleming’s Left Hand Rule, which states that if the first finger points in the direction of magnetic field and second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

62. Explain with the help of a labelled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current carrying coil has n turns the field produced at any point is n times as large as that produced by a single turn ?
Answer – At every point of the current carrying circular loop the concentric circles representing the magnetic field around it become larger and larger as we move away from the wire.
At the centre of the loop the field appears as straight line.

If there is a circular coil having n turns, the field produced is n times as large as that produced by a single turn.
It happens because the current in each circular turn has same direction and the field due to turn just adds up.

63. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification.
Answer – Height of the object (h) = + 2.0 cm
Focal length (f) = + 10 cm
object-distance (u) = – 15 cm
Since, 1/v – 1/u = 1/f
1/v = 1/u + 1/f = 1/(-15) + 1/10 = 1/30
v = + 30 cm
The positive sign of v shows that the image is formed at a distance of 30 cm on the other side of the optical centre. The image is real and inverted.
Magnification (m) = h’/h = v/u =
h’ = h(v/u) =
Height of image (h’) = 2 [+30/(-15)] = – 4 cm
Magnification (m) = v/u = 30/(-15) = – 2

64. Draw ray diagram and write nature of image formed by concave mirror when object is placed (i) at C and (ii) between P and F.
Answer – (i) Nature of image: real and inverted.

(ii) Nature of image: virtual and erect.

65. In the circuit diagram given in figure, suppose the resistors R1, R2 and R3 have the values 5 Ω, 10 Ω, 30 Ω, respectively, which have been connected to a battery of 12 V.

Calculate : (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance.
Answer – Use Ohm’s law, I = V/R :
(a) I1 = 12/5 = 2.4 A
I2 = 12/10 = 1.2 A
I3 = 12/30 = 0.4 A

(b) I = I1 + I2 + I3 = 2.4 + 1.2 + 0.4 = 4

(c) 1/RP = 1/5 + 1/10 + 1/30 = 1/3
RP = 3 Ω

66. Define and explain Ohm’s law.
Answer – The potential difference across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same. This is called Ohm’s law.
V ∝ I
V/I = constant = R
V = IR
R is a constant for the given metallic wire at a given temperature and is called its resistance. It is the property of a conductor to resist the flow of charges through it. Its SI unit is ohm, represented by the Greek letter Ω.
It is obvious from eqn. V = IR ⟹ I = V/R that the current through a resistor is inversely proportional to its resistance. If the resistance is doubled the current gets halved.

67. An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to a 6 V battery as shown in figure.

Calculate the following :
(a) Total resistance of the circuit
(b) The current through the circuit
(c) The potential difference across the electric lamp and conductor.
Answer – (a) The resistance of electric lamp, R1 = 20 Ω
The resistance of the conductor connected in series, R2 = 4 Ω
Then the total resistance in the circuit, R = R1 + R2 = 20 Ω + 4 Ω = 24 Ω

(b) The total potential difference across the two terminals of the battery, V = 6 V
Now by Ohm’s law, the current through the circuit is given by, I = V/R = 6/24 = 0.25 A

(c) Applying Ohm’s law to the electric lamp and conductor separately
Potential difference across the electric lamp, V1 = 20 Ω × 0.25 A = 5 V
Potential difference across the conductor, V2 = 4 Ω × 0.25 A = 1 V

68. (a) What is reflection of light? Write down the laws of reflection.
Answer – When light falls on a smooth and polished surface, the light is returned to the same medium by hitting the surface. This phenomenon is called reflection of light.
The following are the two laws of reflection :
(i) The angle of incidence and the angle of reflection are always equal, i.e. ∠i = ∠r
(ii) The incident ray, reflected ray and normal are all in the same plane.

(b) Name the type of mirror used in the following situations and state reason for your answer :
(i) Headlight of a car
Answer – Concave mirror, because it is a converging mirror and is used to obtain a parallel beam of light.

(ii) Rear view mirror of a vehicle
Answer – Convex Mirror, because it is give an erect, virtual and full size diminished image of distant objects with a wider field of view.


Science (Chemistry)

1. Which of the following is produced by thermal decomposition of limestone ?
(a) Graphite
(b) Quick lime
(c) Lime water
(d) Slaked lime
Answer – (b) Quick lime

2. What type of chemical reaction occurs when aqueous solutions of sodium sulphate and barium chloride are mixed ?
(a) Decomposition
(b) Combination
(c) Precipitation
(d) Displacement
Answer – (c) Precipitation

3. Tamarind contains ………… acid.
Answer – Tartaric acid

4. Give an example of a metal which is the best conductor of heat ?
Answer – Silver

5. Which of the following can prevent oxidation ?
(a) Moisture
(b) Dust
(c) Antioxidant
(d) All of these
Answer – (c) Antioxidant

6. What of the following has the highest boiling point ?
(a) Chloroform
(b) Acetic Acid
(c) Methane
(d) Ethanol
Answer – (b) Acetic Acid

7. …………… is a type of medicine used for treatment of indigestion.
Answer – Antacid

8. Name a solvent in which ionic compounds are insoluble.
Answer – Kerosene, petrol, oil

9. What is the colour of product when dilute hydrochloric acid is mixed with copper oxide ?
(a) Red-orange
(b) Green-yellow
(c) Blue-green
(d) Black
Answer – (c) Blue-green

10. What is the number of molecules of water of crystallisation in gypsum ?
(a) 1
(b) 2
(c) 3
(d) 0
Answer – (b) 2

11. Hydrogen gas combines with …………. to form ammonia.
Answer – Nitrogen

12. Name the gases produced on thermal decomposition of lead nitrate.
Answer – Nitrogen Dioxide (NO2), Oxygen (O2)

13. Which of the following is produced by recrystallisation of sodium carbonate ?
(a) Common salt
(b) Bleaching powder
(c) Washing soda
(d) Gypsum
Answer – (c) Washing soda

14. Which is the most ductile metal ?
(a) silver
(b) gold
(c) platinum
(d) copper
Answer – (b) gold

15. Ethanoic acid reacts with ………….. to form ethyl ethanoate.
Answer – Ethanol

16. Name the chemical compound which makes tooth enamel.
Answer – Calcium Hydroxyapatite

17. Which of the following gas prevents rancidity in foods ?
(a) Oxygen
(b) Hydrogen
(c) Nitrogen
(d) Chlorine
Answer – (c) Nitrogen

18. What is common name of NaHCO3 ?
(a) Gypsum
(b) Bleaching Powder
(c) Baking Soda
(d) Washing Soda
Answer – (c) Baking Soda

19. …………. is a non-metal which is conductor of electricity.
Answer – Graphite

20. Why is sodium metal kept in kerosine oil ?
Answer – Sodium is a highly reactive metal which reacts with the oxygen present in the air and catches fire.

21. Assertion (A) : Soap forms scum with hard water.
Reason (R) : Hard water contains salts of calcium and magnesium.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

22. Assertion (A) : Dry copper sulphate crystals are blue in colour.
Reason (R) : Copper sulphate crystals contain water of crystallisation.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (d) A is false but R is true.

23. Assertion (A) : Bags of chips are filled with nitrogen gas.
Reason (R) : Nitrogen gas prevents oxidation of fats.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

24. Assertion (A) : Electrolytic refining is method of obtaining impure metal from pure metal.
Reason (R) : Impure metal is made anode and pure metal is made cathode.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (d) A is false but R is true.

25. Assertion (A) : MnO2 + HCl → MnCl2 + 2H2O + Cl2 is an example of redox reaction.
Reason (R) : In this reaction HCl is reduced to Cl2 and MnO2 is oxidized to MnCl2.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (c) A is true but R is false.

26. What is a balanced chemical equation? Why should chemical equations be balanced ?
Answer – A reaction where atoms of each elements present on left-hand and right-hand side are equal is called as balanced chemical equation. To satisfy the law of conservation of mass, the chemical reaction should be balanced.

27. Why are carbon and its compounds used as fuels for most applications ?
Answer – Optimum ignition temperature and high calorific value.

28. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
Answer – Hydrogen
Fe + H2SO4 → FeSO4 + H2

29. Write the name of following compounds.
Answer – (i) CH3CH2Br : Bromoethane
(ii) CH3COCH3 : Propanone
(iii) CH3CHO : Ethanal
(iv) CH2=CHCH2CH3 : Butene
(v) CH3CH2CH2CH2CH2CH3 : Hexane
(vi) HCHO : Methanal
(vii) CH3CH2CH2OH : Propanol
(viii) CH3CH2COOH : Propanoic Acid

30. Name an alloy. Write its components. Write its one use.
Answer – Stainless steel is an alloy. Iron, Nickel, Chromium are components. Rust resistance materials are formed from alloy.

31. Write three uses of baking soda.
Answer – Uses of baking soda :
(i) For making baking powder.
(ii) In the form of antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
(iii) It is also used in soda-acid fire extinguishers.

32. What is bleaching powder? How is it produced? Write balanced chemical equation for its production.
Answer – CaOCl2 is bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

33. Name two metals with low densities and low melting points.
Answer – Lithium, Sodium, Potassium

34. Write general formula for alkenes and alkanes.
Answer – General formula for alkenes = CnH2n
General formula for alkanes = CnH2n+2

35. What does mean by exothermic and endothermic reactions? Give examples.
Answer : Exothermic Reactions – Chemical reactions in which heat is evolved are called exothermic reactions. Example: combustion of natural gas and respiration
• Endothermic Reactions – Chemical Reactions in which heat is absorbed are called endothermic reactions. Example: Thermal decomposition

36. Define the Mineral, Ore and Gangue.
Answer : Mineral – Naturally occurring elements or compounds in earth’s crust are called minerals.
• Ore – Minerals which contain a very high percentage of a particular metal, and the metal can be profitably extracted from it are called ores.
• Gangue – Gangue is the impurities present in ores mined from earth.

37. Write name of important products from chlor-alkai process. Write one use of each product.
Answer – (i) Chlorine gas.
Use: Water treatment, swimming pool, disinfectants, CFCs, insecticides.
(ii) Hydrogen gas.
Use: Fuel, Margarine, Ammonia for fertilisers
(iii) Sodium Hydroxide.
Use: De-greasing metals, Soaps and detergents, Paper making, artificial fibers

38. What is neutralisation reaction? Give an example.
Answer – When acid reacts with a base, salts and water are formed. e.g. NaOH + HCl → NaCl + H2O

39. What happens when eggshell is placed in a beaker containing concentrated solution of HNO3 ?
Answer – Egg shells contain calcium carbonate. Carbon dioxide gas is released when nitric acid is added to it.
CaCO3 + HNO3 → Ca(NO3)2 + H2O + CO2

40. Write the name and chemical formula of acid found in ant sting. Also give the common method to get relief from the discomfort caused by ant sting.
Answer – Methanoic acid (formic acid) is found in ant sting. The chemical formula is HCOOH. Any available basic salts, for example, baking soda (NaHCO3) can be used to relieve this.

41. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why ?
Answer – The reaction of the acid with the metal depends on the strength of the acid.
As hydrochloric acid is a strong acid. It will give reaction with metal vigorously and evolve hydrogen gas with fizzing sound, while acetic acid is a very weak acid. It will take time to react with the metal and slowly give hydrogen gas.

42. Draw the electron dot structures of following compounds :
(i) Methane, (ii) Methanal, (iii) Ethene
Answer –

43. Draw a labelled diagram of electrolytic refining of copper.
Answer –

44. Write three examples of decomposition reaction.
Answer – (i) 2FeSO4(s) + Heat → Fe2O3(s) + SO2(g) + SO3(g)
(ii) CaCO3 + Heat → CaO(s) + CO2(g)
(iii) 2Pb(NO3)2(s) + Heat → 2PbO(s) + 4NO2(g) + O2(g)
(iv) 2H2O(l) + Electric Current → 2H2(g) + O2(g)
(v) 2AgCl(s) + Sunlight → 2Ag(s) + Cl2(g)
(vi) 2AgBr(s) + Sunlight → 2Ag(s) + Br2(g)

45. Draw electron dot structure of N2 and O2 molecules. 
Answer –

46. Write reactions of ethanol with
(i) Sodium
Answer : 2Na + 2CH3CH2OH → 2CH3CH2O-Na+ + H2

(ii) Hot Conc. H2SO4
Answer : CH3CH2OH + Hot Conc. H2SO4 → CH2=CH2 + H2O

(iii) Acidified K2Cr2O7 with Heat
Answer : CH3CH2OH + Acidified K2Cr2O7 + Heat → CH3COOH

47. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas ?
Answer – Metal reacts with acids to form hydrogen gas. Gas reacts with fatty acids to form hydrogen gas.
For example, when magnesium metal reacts with hydrochloric acid, hydrogen gas and magnesium chloride are formed.
Mg(s) + 2HCl(aq) → MgCl2(s) + H2(g)
Hydrogen gas burns with a pop sound. Therefore, when a burning matchstick or candle is taken near the gas coming out of the pipe in the given reaction, it starts burning with the pop sound. This shows that the gas released is hydrogen.

48. Write two examples of displacement reaction.
Answer – (i) Fe(s) + CuSO4 → FeSO4(aq) + Cu(s)
(ii) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
(iii) Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)

49. Write a balanced chemical equation for a reaction when hydrogen sulphide is burnt in air.
Answer : 2H2S + 3O2 → 2SO2 + 2H2O

50. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube ?
Answer – (a) Solution in test tube which changes red litmus paper blue is acid.
(b) Now, blue litmus paper which is changed to blue by acid is dipped in rest of the two test tubes one by one. Solution which changes the blue litmus paper red is basic solution.
(c) Third one solution in test tube left, which does not change either red litmus blue or blue litmus paper red is identified as distilled water.

51. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below.

(a) What will be the action of gas on ?
(i) dry litmus paper ?
Answer – there is no effect on dry litmus paper. Dry litmus paper does not turns red or blue with acid or base.

(ii) moist litmus paper?
Answer – Gas evolved is sulphur dioxide. Since, sulphur dioxide is a non-metallic oxide and non-metallic oxides are acidic in nature. Thus, moist blue litmus paper turns red.

(b) Write a balanced chemical equation for the reaction taking place.
Answer : S + O2 + ∆ → SO2

52. Differentiate between metals and non-metals on the basis of chemical properties.
Answer –

Metals Non-Metals
1. Metals form basic oxides. 1. Non-metals form acidic or neutral oxides.
2. Metals react with diluted HCI or dilute H2SO4 to release H2 gas, as they displace hydrogen. 2. Non-metals do not react with dilute HCI or dilute H2SO4, because they do not displace hydrogen.
3. Metals are reducing in nature. 3. Non-metals are oxidising in nature.
4. Metals displace hydrogen from water (or steam). 4. Non-metals do not react with water (or steam). Therefore, H2 is not displaced from water.
5. Metals lose electrons to form positive ions. 5. Non-metals gain electrons to form negative ions.
6. Not all metals combine with H2 to form hydrides. 6. All non-metals combine with H2 to form hydrides.


53. Explain the difference between roasting and calcination with examples.
Answer –

Roasting Calcination
1. It occurs in the presence of air. 1. It occurs in the absence of air.
2. It is for Sulphide ores. 2. It is for carbonate, oxide, hydroxide ores.
3. The ore becomes partially or completely oxidized. 3. The ore is not oxidized.
4. In this, the ore is completely melted.

Example: ZnS + O2 → ZnO + SO2

4. In this, the ore is not allowed to melt.

Example: CaCO3 → CaO + CO2


54. What is corrosion? Write its two examples. Name four methods that can be used to prevent to corrosion.
Answer – When metals are kept in contact with the atmosphere, the metal gradually starts to damage due to the presence of gases and moisture present in the atmosphere. This process is called corrosion.
Example : Corrosion on iron, Silver blackening, Formation of a green layer on the surface of copper.
Methods for prevent : Corrosion can be prevented by painting, applying oil, grease, Galvanization (by coating iron objects with zinc), chromium coating, anodization, alloying.

55. What are electrovalent compounds? Explain their properties.
Answer – The compounds formed by the transfer of electrons from a metal to a non-metal are known an electrovalent compounds.
Properties :
(i) Physical Nature – Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.
(ii) Melting and Boiling points – Ionic compounds have high melting and boiling points. This is because a considerable amount of energy is required to break the strong inter-ionic attraction.
(iii) Solubility – Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
(iv) Conduction of Electricity – The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution and conduct electricity.

56. Write names and structures of first five members of homologous series ketone.
Answer – (i) Propanone : CH3COCH3
(ii) Butanone : CH3COCH2CH3
(iii) Pentanone : CH3COCH2CH2CH3
(iv) Hexanone : CH3COCH2CH2CH2CH3
(v) Heptanone : CH3COCH2CH2CH2CH2CH3

57. Explain the mechanism of the cleaning action of soaps.
Answer – Most dirt is oily in nature and as you know, oil does not dissolve in water. The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic end of soap interacts with water while the carbon chain interacts with oil. The soap molecules thus form structures called micelles where one end of the molecules is towards the oil droplet while the ionic-end faces outside.

This forms an emulsion in water. The soap micelle thus helps in pulling out the dirt in water and we can wash our clothes clean.

58. Explain the process of extraction of metals of medium reactivity.
Answer – The metals in the middle of the activity series such as iron, zinc, lead, copper, are moderately reactive. These are usually present as sulphides or carbonates in nature.
It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides.
The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination.
The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows :
Roasting: 2ZnS(s) + 3O2(g) + Heat → 2ZnO(s) + 2SO2(g)
Calcination: ZnCO3(s) + Heat → ZnO(s) + CO2(g)
The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.
For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc.
ZnO(s) + C(s) → Zn(s) + CO(g)
The highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their compounds because they can displace metals of lower reactivity from their compounds.

59. Explain the reactivity of metals with water.
Answer – Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide.
Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) + Heat
The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire.
Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen.
It also starts floating due to the bubbles of hydrogen gas sticking to its surface
Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.
2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g)
Metals such as lead, copper, silver and gold do not react with water at all.

60. Write the name of products of following reactions.
(a) Combustion of ethanol
Answer – Carbon Dioxide, water

(b) Oxidation of ethanol
Answer – Ethanoic acid

(c) Hydrogenation of propene
Answer – Propane

(d) Reaction of sodium with ethanol
Answer – Sodium ethoxide, hydrogen

(e) Reaction of hot and concentrated sulphuric acid with ethanol
Answer – Ethene, water

61. (a) What is hydrogenation? Write its industrial application.
Answer – Saturated hydrocarbons are formed by the addition of unsaturated hydrocarbons and hydrogen in the presence of catalysts such as palladium or nickel, which is called hydrogenation.
Industrial Applications : Vegetable ghee (saturated fat) is made from hydrogenation of unsaturated fats (vegetable oils).

(b) Explain the properties of carbon which lead to formation of large number of carbon compounds.
Answer : Catenation – Carbon has an amazing ability to form bonds with other atoms of carbon itself, this quality is called catenation. Long chains of carbon in these compounds carbon are found arranged in the shape of a chain or ring with different branches of carbon.
Tetravalency – Carbon has four valency, it therefore has the ability to form bonds with four other atoms of carbon or atoms of some other elements.

62. (a) How many structural isomers can you draw for Pentane ?
Answer – Three

(b) Draw structures of following compounds.
(i) Ethanoic acid

(ii) Bromopentane

(iii) Hexanal


Science (Biology)

1. Where does breakdown of glucose into pyruvate takes place in a cell ?
(a) Mitochondria
(b) Nucleus
(c) Cytoplasm
(d) Ribosomes
Answer – (c) Cytoplasm

2. Wilting of leaves in plants is caused by ?
(a) Abscisic Acid
(b) Cytokinins
(c) Auxins
(d) None of these
Answer – (a) Abscisic Acid

3. Ozone molecules are formed from ………… atoms of oxygen.
Answer – Three

4. What is biological magnification ?
Answer – Biological magnification is the increase in the concentration of chemicals in the food chain from one level to another.

5. Which part of brain is main thinking part ?
(a) Fore-brain
(b) Mid-brain
(c) Hind-brain
(d) Cerebellum
Answer – (a) Fore-brain

6. Which chromosome is not found in human females ?
(a) X
(b) Y
(c) Both of these
d) None of these
Answer – (b) Y

7. Growth hormone is secreted by ………… gland.
Answer – Pituitary

8. What is geotropism ?
Answer – This growth of shoots and roots in response to the pull of earth or gravity is called geotropism.

9. Which of the following chromosome is inherited by a girl child from her father ?
(a) X
(b) Y
(c) Both of the above
(d) None of these
Answer – (a) X

10. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as :
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Answer – (c) TtWW

11. Primary consumers come at ……..…. trophic level in a food chain.
Answer – Second

12. Name the hormone that helps the cells to grow longer in shoot tip.
Answer – Auxin

13. Who gave the rules for inheritance ?
(a) Mendel
(b) Darwin
(c) Crick
(d) Newton
Answer – (a) Mendel

14. Which of the following represents F2 ratio for independent inheritance of two separate traits ?
(a) 9 : 6 : 3 : 1
(b) 9 : 3 : 3 : 1
(c) 9 : 3 : 6 : 1
(d) 9 : 1 : 3 : 1
Answer – (b) 9 : 3 : 3 : 1

15. The complete digestion of fats produces …………. and ………….. .
Answer – Fatty acids, Glycerol

16. What are plant hormones?
Answer – Various chemicals that help in coordinating plant growth, development and response to the environment.

17. Which of the following is non-biodegradable ?
(a) Glass
(b) Grass
(c) Paper
(d) None of these
Answer – (a) Glass

18. Which of the following can reproduce by regeneration ?
(a) Hydra
(b) Planaria
(c) Both of the above
(d) None of these
Answer – (c) Both of the above

19. Which hormone regulates the sugar level in the human blood ?
Answer – Insulin

20. Assertion (A) : All papaya plants do not bear fruits.
Reason (R) : Papaya plants have only unisexual flowers.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

21. Assertion (A) : Excretion is the process of breakdown of food.
Reason (R) : Kidneys are part of excretory system.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (d) A is false but R is true.

22. Assertion (A) : Ozone shields the surface of earth from ultraviolet radiation from the sun.
Reason (R) : Ozone is deadly poison in lower levels of atmosphere.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (b) Both A and R are true and R is not the correct explanation of A.

23. Assertion (A) : Sexual reproduction results in more variations than asexual reproduction.
Reason (R) : Germ-cells from two individuals combine during sexual reproduction to form a new individual.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

24. Assertion (A) : When there is no air in the trachea, it is not compressed.
Reason (R) : The trachea is supported by cartilage.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false
(d) A is false but R is true.
Answer – (a) Both A and R are true, and R is the correct explanation of A.

25. What are the problems caused by the non-biodegradable wastes that we generate ?
Answer – (i) Obstruction in drains
(ii) Soil pollution
(iii) Death of herbivores by ingesting substances such as plastic.
(iv) Biomagnification in the human body.

26. What steps are being taken to limit the damage to the ozone layer ?
Answer – (i) Decrease in production of CFC.
(ii) Manufacturing of CFC-free refrigerators.

27. Name four diseases that are sexually transmitted.
Answer – Gonorrhoea, syphilis, warts and HIV-AIDS.

28. Who gave the rules for inheritance of traits? Write the organism studied for his observations.
Answer – Gregor Mendel gave the rules for inheritance of traits. Uncovered the fundamentals of inheritance through his studies on pea plants.

29. What are the methods used by plants to get rid of excretory products ?
Answer – (i) O2 as a product in photosynthesis and CO2 in respiration are expelled through stomata.
(ii) Plants can get rid of excess water by transpiration.
(iii) In plants, dormant leaves are shed from time to time, in which waste products accumulate.
(iv) In plants, other waste products are stored in the form of resins and gums, especially in the old xylem.
(v) Plants excrete some waste materials into the soil around them.
(vi) Many plant waste products are stored in cell vacuoles.

30. Name the source gland of adrenaline hormone. How does our body respond when adrenaline is secreted into the blood ?
Answer – Adrenal Gland is source gland of adrenaline hormone.
Body respond when adrenaline is secreted into the blood :
(i) The heart beats faster.
(ii) The blood to the digestive system and skin is reduced.
(iii) This diverts the blood to our skeletal muscles.
(iv) The breathing rate increases.

31. Explain structure of placenta.
Answer – This is a disc which is embedded in the uterine wall. 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 substances to pass from the mother to the embryo.

32. How is the equal genetic contribution of male and female parents ensured in the progeny ?
Answer – Equal genetic contribution of male and female parents in the progeny is ensured by the equal inheritance of chromosome from each parent. Human possesses 23 pairs of chromosomes, of which 22 pairs are autosomes and 1 pair is the sex chromosomes. During the process of gamete formation meiosis ensure haploid gametes are produced. A haploid sperm fuses with a haploid ovum to produce a diploid zygote. Zygote receives equal amount of genetic material from each parent and thus, retains the diploid nature on fertilization.

34. Write two functions of each, cerebellum and medulla.
Answer : Cerebellum functions – Walking in a straight line, cycling, lifting a pencil
• Medulla functions – Blood pressure, salivation, vomiting

35. What is contraception? Explain different methods of contraception.
Answer – Contraception is a method or device used to prevent pregnancy.
Methods of contraception :
(i) Mechanical barrier – In this method fusion of gamete is blocked. For example, covering the penis with condom prevents sperms to reach ovum. It has no side effects and prevents transmission of sexually transmitted diseases.
(ii) Hormonal Imbalance – Use of pills to create hormonal imbalance can act as contraceptive method. It prevents formation of egg and fertilisation cannot occur. It has side effects.
(iii) Uterine devices – Devices such as the loop or the copper-T are placed in the uterus to prevent pregnancy. Again, they can cause side effects due to irritation of the uterus.
(iv) Surgical method – If the vas deferens in the male is blocked, sperm transfer will be prevented. If the fallopian tube in the female is blocked, the egg will not be able to reach the uterus. In both cases fertilisation will not take place. Surgical methods can be used to create such blocks. While surgical methods are safe in the long run, surgery itself can cause infections and other problems if not performed properly.

36. What could be the reasons for adopting contraceptive methods ?
Answer – Reasons for adopting contraceptive methods :
(i) To increase the gap between two children.
(ii) To prevent unwanted pregnancy.
(iii) To prevent transmission of sexually transmitted diseases.
(v) To control population growth.

37. What are the functions performed by testis in humans ?
Answer – Production of testosterone hormone and Sperm production.

38. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer – (i) Minimize use of non-biodegradable substances.
(ii) Recycling of non-biodegradable materials such as plastics.
(iii) Production of compost, production of biogas from biodegradable waste.
(iv) Reduce the amount of waste by burning it in incinerators.
(v) Putting non-biodegradable and biodegradable materials in separate dustbins.

39. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?
Answer – Yes, the effect of removing organisms at a trophic level will vary at different levels. It is not possible to remove organisms of any trophic level without affecting the ecosystem.

40. Draw a well labelled diagram of cross section of leaf.
Answer –

41. Draw a well labelled diagram of the human heart.
Answer –

42. Draw a labelled diagram of seed germination.
Answer –

43. Draw a labelled diagram of human brain.
Answer –

44. Draw the labelled structure of a neuron.
Answer –

45. What are the changes seen in girls at the time of puberty ?
Answer – Changes in the body parts of girls are as follows :
• Thinning of voice, softening of skin and frequent oily skin
• Sometimes formation of pimples,
• Increase in the size of the breasts and also darken the skin color of the nipples,
• Hair in some new parts of the body such as armpits, middle genital areas of thighs and their color is dark
• Beginning of menstruation and becoming more aware of others, etc.

46. How is oxygen and carbon-dioxide transported in human beings ?
Answer : Transport of oxygen – The oxygen molecule can bind to the haemoglobin molecules easily. Haemoglobin present in the blood takes up the oxygen from the air in the lungs. It carries the oxygen to tissues which are deficient in oxygen before releasing it.
• Transport of carbon dioxide – Similarly, Carbon dioxide is more soluble in water. Therefore, it is mostly transported from body tissues in the dissolved form in our blood plasma to lungs.

47. How do Mendel’s experiments show that traits may be dominant or recessive ?
Answer – Mendel found that F1 is caused by hybridization between pure long pea plant and pure dwarf pea plant. All the plants obtained in the generation were tall.
(T T) × (t t) → (T t), (T t), (T t), (T t)
Long × Short All long (F1 generation)
That is, only one of the two traits appears ancestral trait. This is called dominant traits.
In the second stage, F1 (T t) When self-polling was done in the plants obtained from the generation, it was found that the ratio of long and dwarf plant was 3 : 1. i.e. F2 Tall plants were also dominant in generation, but dwarf plants were also with recessive traits.
(T t) × (T t) + cross breeding → (T T), (T t), (T t), (t t)
That is, the use of Mendel makes it clear that symptoms can be effective or ineffective.

48. How is the sex of the child determined in human beings ?
Answer – In human beings, sex is determined on the basis of specific sex chromosomes. Males have XY chromosomes and females have XX chromosomes. It is clear from this that the female does not have the Y chromosome. When offspring are produced by male-female combination, the female may not be able to produce a male infant at any stage because the male infant must have XY chromosomes.
In fertilization, if the X chromosome of a man is fused with the X chromosome of the woman, then it will form an XX pair. Hence, the child will be in the form of a girl. But when a man’s Y chromosome combines with the female’s chromosome X, XY will be formed. This will lead to the birth of a boy.

49. Explain any five modes of reproduction used by single organisms.
Answer – Modes of reproduction used by single organisms :
(i) Fission – For unicellular organisms, cell division, or fission, leads to the creation of new individuals. Many bacteria and protozoa simply split into two equal halves during cell division such as Amoeba.
(ii) Fragmentation – In multi-cellular organisms with relatively simple body organisation, simple reproductive methods can still work. Spirogyra, for example, simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.
(iii) Regeneration – Many fully differentiated organisms have the ability to give rise to new individual organisms from their body parts. That is, if the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, Hydra and Planaria.
(iv) Budding – Organisms such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.
(v) Vegetative Propagation – There are many plants in which parts like the root, stem and leaves develop into new plants under appropriate conditions. Unlike in most animals, plants can indeed use such a mode for reproduction. This property of vegetative propagation is used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes.
(vi) Spore Formation – Even in many simple multi-cellular organisms, specific reproductive parts can be identified. As on the hyphae of Rhizopus, tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.

50. Explain photosynthesis in plants.
Answer – It is the process by which autotrophs take in substances from the outside and convert them into stored forms of energy. This material is taken in the form of carbon dioxide and water which is converted into carbohydrates in the presence of sunlight and chlorophyll.
6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 (glucose) + 6O2 + 6H2O
The following events occur during this process :
(i) Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
(iii) Reduction of carbon dioxide to carbohydrates.
These steps need not take place one after the other immediately.

51. Explain break-down of glucose by various pathways.
Answer –

The first step is the break-down of glucose, a sixcarbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm.
In yeast during fermentation, pyruvate is converted into ethanol and carbon dioxide. Since this process takes place in the absence of air (oxygen), it is called anaerobic respiration.
Breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration.
When there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken. Here the pyruvate is converted into lactic acid which is also a three-carbon molecule.

52. Explain reproductive parts of flower with diagram.
Answer –

Stamens and pistil are the reproductive parts of a flower which contain the germ-cells. Stamen is the male reproductive part and it produces pollen grains.
Pistil is present in the centre of a flower and is the female reproductive part. It is made of three parts.
The swollen bottom part is the ovary, middle elongated part is the style and the terminal part which may be sticky is the stigma.

53. Explain human female reproductive system with diagram.
Answer –

The female germ-cells or eggs are made in the ovaries. They are also responsible for the production of some hormones. On reaching puberty, one egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube. The two oviducts unite into an elastic bag-like structure known as the uterus.

54. Describe the structure of nephrons with diagram.
Answer –

The basic filtration unit in the kidneys is a cluster of very thin-walled blood capillaries.
Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman’s capsule that collects the filtrate. Each kidney has large numbers of these filtration units called nephrons packed close together. The tubular part of the kidney absorbs selected substances from the urine flowing in it.

55. How are water and minerals transported in plants ?
Answer – Plant transport system to move raw materials from roots is constructed as independently organized conducting tubes.
It is known as xylem which moves water and minerals obtained from the soil.
In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plant.
At the roots, cells in contact with the soil actively take up ions. This creates a difference in the concentration of these ions between the root and the soil.
Water, therefore, moves into the root from the soil to eliminate this difference, creating a column of water that is steadily pushed upwards.
However, this pressure by itself is unlikely to be enough to move water over the heights that is commonly found in plants.
Provided that the plant has an adequate supply of water, the water which is lost through the stomata is replaced by water from the xylem vessels in the leaf.
In fact, evaporation of water molecules from the cells of a leaf creates suction which pulls water from the xylem cells of roots.
The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration. Thus, transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.
The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

56. Write three differences between autotrophic and heterotrophic nutrition.
Answer –

Autotrophic Nutrition Heterotrophic Nutrition
1. The mode of nutrition in which the organism can prepare their own food. 1. The mode of nutrition in which the organism does not prepare their food themselves.
2. In this type of nutritional process, the organism is independent of other organisms for food. 2. In this type, the organism is dependent on other organisms for food as nourishment.
3. This type of nutritional mode involves preparing food using carbon dioxide and water in the presence of sunlight through the process of photosynthesis. 3. No photosynthesis activity occurs.
4. The organism employing this mode of nutrition are known as producers. 4. The organisms employing this mode of nutrition are known as consumers.
5. In this mode of nutrition, simple inorganic substances are converted into complex organic ones. 5. It involves consumption of complex organic compounds and then digested to break down into simpler components.
6. This mode of nutrition is carried out by the plants and some bluegreen algae and bacteria. 6. The heterotrophic mode of nutrition occurs in all animals, fungi, and all other non-photosynthetic organisms.


57. Draw a well labelled diagram of human excretory system.
Answer –

58. Write the difference between arteries and veins.
Answer –

Arteries Veins
1. Carries blood away from the heart. 1. Carries blood towards the heart.
2. Carries oxygenated blood. 2. Carries deoxygenated blood.
3. Its location is deep within the body. 3. Its location is close to the skin.
4. Their colour is red due to the oxygenated blood. 4. Their blood is blue due to the deoxygenated blood.
5. The lumen in arteries is narrow. 5. The lumen in veins is wide.
6. The pressure of blood flowing is high. 6. The pressure of blood flowing is low.



Leave a Comment