31/1/2 2022 Class 10 Science Question Paper Solution
SECTION A
1.) (a) What is ozone ? How is it formed in the upper layers of the Earth’s atmosphere ? How does ozone affect our ecosystem?
Ans:
- Ozone is a molecule formed by three atoms of oxygen.
- UV radiations split some molecular oxygen (O2) into free oxygen atoms (O + O). These atoms then combine with molecular oxygen to form ozone.
- Ozone layer shields the surface of the earth from damaging UV radiation of the sun. / Depletion of ozone layer causes harmful effects on the organism.
OR
(b) (i) List two human-made ecosystems.
Ans: Aquarium, crop field, gardens, etc. (any two)
(ii) “We do not clean a pond in the same manner as we do in an aquarium.” Give reason to justify this statement.
Ans: A pond is a natural ecosystem. It has decomposers whereas an aquarium is an artificial ecosystem and does not contain decomposers. Therefore it needs regular cleaning for proper functioning.
2.) (a) (i) Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
Ans:
- Fleming’s left-hand rule
- Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
(ii) An alpha particle while passing through a magnetic field gets projected towards north. In which direction will an electron project when it passes through the same magnetic field?
Ans: South
Or
(b) (i) What is a solenoid?
Ans: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder
(ii) Draw the pattern of magnetic field lines of the magnetic field produced by a solenoid through which a steady current flows.
Ans:
3.) (a) What is variation? List two main reasons that may lead to variation in a population.
Ans:
- The differences in the traits shown by the individuals of a species.
- Two reasons : i) Inaccurate / Error in DNA copying ii) Sexual reproduction
OR
(b) (i) In a cross between violet flowered plants and white flowered plants, state the characteristics of the plants obtained in the F1 progeny.
Ans: F1 Progeny : Violet flowered plants
(ii) If the plants of F1 progeny are self-pollinated, then what would be observed in the plants of F2 progeny?
Ans: F2 Progeny : Violet as well as white flowered plants
(iii) If 100 plants are produced in F2 progeny, then how many plants will show the recessive trait?
Ans: 25 plants
4.) (a) Which of the following flowers will have higher possibility of self-pollination?
Mustard, Papaya, Watermelon, Hibiscus
Ans: Mustard and Hibiscus
(b) List the two reproductive parts of a bisexual flower.
Ans: Stamens and Pistil / Carpel
5.) (a) Name the process shown below and define it:
Ans:
- Regeneration
- It is a process in which each cut or broken up pieces of an individual grows into a new individual through specialised cells.
(b) Name the types of cells present in the organisms which exhibit this process.
Ans:
- Specialized cells
6.) What is a Dobereiner triad? Why can’t the following three elements form such a triad ?
N (14); P (31); As (75)
(Atomic masses are given in parenthesis)
Ans:
- When three elements with similar properties are arranged in order of their increasing atomic masses, the atomic mass of the middle element is roughly the average of the atomic masses of the other two elements.
- The atomic mass of phosphorus is not the average of the atomic masses of nitrogen and arsenic. /
Average of atomic mass of N and As = 14 + 75 / 2 = 44.5
But atomic mass of phosphorus is 31
So N, P and As cannot be classified as Dobereiner’s Triad
7.) The molecular formulae of two alkynes, A and B are CxH2 and C3Hy respectively.
(a) Find the values of x and y.
Ans:
- x is 2
- y is 4
(b) Write the names of A and B.
Ans:
- A is Ethyne
- B is Propyne
SECTION—B
8.) (a) Name the group of organisms which form in the first trophic level of all food chains. Why are they called so?
Ans: Producers, as they can manufacture food by the process of photosynthesis.
(b) Why are the human beings most adversely affected by bio-magnification?
Ans: When non-degradable harmful chemicals (pesticides / DDT, etc.) enter a food chain, they get progressively accumulated at each trophic level. Human beings occupy the top level in any food chain, therefore the maximum concentration of these chemicals get accumulated in their bodies.
(c) State one ill-effect of the absence of decomposers from a natural ecosystem.
Ans: ill-effects of absence of decomposers from natural ecosystem :
(i) Earth would be covered with dead bodies & foul smell
(ii) Recycling of minerals will not take place
(iii) Soil will not get replenished
(iv) Ecosystem will get disrupted
9.) (a) (i) Define Electric Power and write its SI unit.
Ans: The rate at which electric energy is dissipated or consumed in an electric circuit.
S.I. unit—watt / V.A / joule per second
(ii) Two bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to an electric mains of 220 V. Find the current drawn by the bulbs from the mains.
Ans:
- Current drawn by first bulb
- Current drawn by second bulb
(b) (i) State Joule’s law of heating. Express it mathematically when an appliance of resistance R is connected to a source of voltage V and the current I flows through the appliance for a time t.
Ans:
This law states that heat produced in a resistor is—
- directly proportional to the square of current for a given resistance / (H a I 2 )
- directly proportional to the resistance for a given current / (H a R)
- directly proportional to the time for which the current flows through the resistor / (H a t)
- H = V I t
(ii) A 5 resistor is connected across a battery of 6 volts. Calculate the energy that dissipates as heat in 10 s.
Ans:
10.) (a) Calculate the resistance of a metal wire of length 2 m and area of cross-section 1·55 × 10-6 m2 . (Resistivity of the metal is 2·8 10-8 Ω m
Ans: Given : Length of the wire = 2 m
(b) Why are alloys preferred over pure metals to make the heating elements of electrical heating devices?
Ans: Alloys used for heating element have generally high melting point / high resistivity / Do not get oxidised at high temperature.
11.) A cross was made between green-stemmed tomato plants denoted by (GG) and purple-stemmed tomato plants denoted as (gg) to obtain F1 progeny.
(a) What colour of the stem would you expect in their F1 progeny and why?
Ans: Green; It is the dominant trait
(b) Give the percentage of purple-stemmed plants if F1 plants are allowed to self-pollinate to produce F2 progeny.
Ans: Purple stemmed plants in F2 progeny are 25%
(c) Write the ratio between GG and gg plants in the F2 progeny?
Ans: GG : gg
1:1
12.) (a) Draw two different possible structures of a saturated hydrocarbon having four carbon atoms in its molecule. What are these two structures of the hydrocarbon having same molecular formula called ? Write the molecular formula and the common name of this compound. Also write the molecular formula of its alkyne.
Ans:
- Isomers
- C4H10
- Butane
- C4H6
OR
(b) (i) Write the molecular formula of benzene and draw its structure.
Ans:
- C6H6
(ii) Write the number of single and double covalent bonds present in a molecule of benzene.
Ans:
- Single bond 9
- Double bond 3
(iii) Which compounds are called alkynes?
Ans: Hydrocarbons containing triple bond
13.) (a) List two advantages of adopting the atomic number of an element as the basis of classification of elements in the Modern Periodic Table.
Ans:
- Atomic number is more fundamental property and it decides the
properties of an element. - Atomic number increases by one in going from one element to
the next, so arrangement of elements becomes more systematic. - Prediction of properties of elements could be made with more
precision when the elements are arranged in increasing order of
their atomic numbers.
(b) Write the electronic configurations of the elements X (atomic
number 13) and Y (atomic number 20).
Ans:
Electronic configuration of X – 2, 8, 3
Electronic configuration of Y – 2, 8, 8, 2
SECTION C
14.) A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.
(a) Draw a diagram to show this pattern of iron filings.
Ans:
(b) What does this pattern of iron filings demonstrate?
Ans:
- Iron filings experience a force due to which they arrange
themselves along the direction of force experienced . - Force is maximum at poles.
(c) (i) How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other?
Ans:
- By placing a compass needle on magnetic field lines, direction of north pole will give direction of magnetic field.
- If they cross or intersect , it means that at the point of intersection the compass needle would point into two directions, which is not possible. / If they cross or intersect, it means that at the point of intersection there will be direction of two resultant fields which is not possible.
OR
ii) How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet.
Ans:
- Take a small bar magnet, place it in the centre of the drawing sheet fixed on a drawing board and mark its boundary.
- Place a small compass needle near the north pole of the magnet, south pole of the compass needle points towards the north pole.
- Mark the position of two ends of the needle. Now move the needle to a new position such that the south pole of needle occupies the position previously occupied by the north pole and again mark the new position of the north pole. In this way proceed step by step till you reach the south pole of the magnet. Join the points marked to get a field line. Similarly draw one more field line on the other side of the magnet.
15.) The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.
(a) Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size?
Ans:
- XY
- Y is shorter than X
(b) If the gametes always have half the number of chromosomes, then
how is the original number of chromosomes restored in the
organism?
Ans: Fusion of egg with sperm ( female gamete with male gamete )
results in formation of zygote which restores the original number of
chromosomes. /
Egg (n) + Sperm (n) = Zygote (2 n)
(c) (i) Name two animals whose sex is not genetically determined. Explain the process of their sex determination.
Ans:
- Reptiles & Snails
- In reptiles, the temperature at which fertilised eggs are kept determines whether the animal developing in the eggs would be a male or a female. In snails, they can change their sex during their life time.
OR
(ii) With the help of a flowchart only, show how sex is genetically determined in human beings.
Ans: