Oswal Practice Papers CBSE Class 10 Science Solutions (Practice Paper - 10)

Section-A

Explanation :

As the image is focused on the screen, then the image formed is real. And real images are inverted.

2. (a) Homozygous

Explanation :

According to Mendel’s law of dominance, when there is a heterozygote (an organism with two different alleles for a trait), one allele will dominate and mask the presence of the other allele. Only the dominant allele will be expressed and contribute to the physical characteristics (phenotype). The recessive allele remains hidden but can still be passed on to offspring in the same way as the dominant allele. The recessive trait will only be visible in offspring who inherit two copies of this recessive allele.

3. (b) Real and inverted

Explanation :

The image formed on the retina of the human eye is real and inverted. On retina, the image is converted into electrical impulses and sent to the brain. The brain flips that image into a virtual and erect image.

4. (b) Baking soda

Explanation :

Baking soda: It is sodium bicarbonate (NaHCO₃) in anhydrous form without any water of crystallisation.

Blue Vitriol: It is hydrated salt of copper sulphate containing 5 molecules of water of crystallisation (CuSO₄. 5H₂O).

Washing soda: It is hydrated salt of sodium carbonate containing 10 molecules of water of crystallisation (Na₂CO₃. 10H₂O)

Gypsum: It is hydrated salt of calcium sulphate containing 2 molecules of water of crystallisation (CaSO_4.2 H₂O).

5. (a) A-(iii), B-(ii), C-(i)

Explanation :

A – Stigma. The top part of the carpel is called stigma. Stigma is for receiving the pollen grains from the anther of stamen during pollination.

B – Pollen tube. When a pollen grain falls on the stigma, it bursts open and grows a pollen tube downward through the style towards the female gamete in the ovary. A male gamete moves down the pollen tube.

C – Female gamete (ovum). It is a special reproductive female sex cell which combines with the male gamete to form a zygote.

6. (c) Vegetative propagation

Explanation :

Vegetative propagation is a method of plant reproduction that involves using vegetative parts of a plant, such as stems, roots, or leaves, to create new individuals that are genetically identical to the parent plant. This method ensures that the desired characteristics of the parent plant, including
fruit quality and traits, are preserved in the new plants. This method avoids the genetic variation that can occur through sexual reproduction, which involves the combination of genetic material from two different parent plants and may result in offspring with different traits.

7. (a) live wire

Explanation :

An electric fuse is connected with live wire because it gets blown up when an excess current tries to pass through it to save the electrical appliances by restricting the flow of that current.

8. (d) genes

Explanation :

Characters are transmitted from parents to offspring through genes. Genes are the heredity units of the body in living organisms. Chromosomes in the nucleus of a cell contain information for the inheritance of features from parents in the form of DNA (Deoxyribonucleic acid).

This DNA contains genes.

9. (b) IR²

Explanation :

We know that,

P = VI …(i)

Where, P = Power

V = Potential difference

I = Current

V = IR …(ii)

On substituting equation (ii) in equation (i), we get

P = I²R …(iii)

Again, from Ohm’s law

$$\text{I}=\frac{\text{V}}{\text{R}}\space\text{...(iv)}$$

On substituting equation (iv) in equation (i), we get,

$$\text{P} =\frac{\text{V}^{2}}{\text{R}}$$

Hence, option (b) IR² does not represent power.

10. (d) Iron is essential for synthesis of Thyroxine.

Explanation :

Iodine, not iron, is required to synthesise of Thyroxine. It controls the glucose, protein,and fat metabolism of the body. The thyroid gland produces Thyroxine, which is also known as thyroid hormone.

11. (c) Potential difference (V) decreases

Explanation :

If the temperature of the entire system increases when the current flows through a metallic wire, the power (VI) is dissipated in the form of heat. Hence the potential difference (V) decreases.

12. (c) From receptors to the CNS

Explanation :

Afferent neurons, also known as sensory neurons, are responsible for transmitting nerve impulses from sensory receptors in the peripheral nervous system to the central nervous system (CNS). These neurons carry sensory information, such as touch, temperature, pain, and other stimuli, from various parts of the body to the CNS for processing and interpretation.

13. (d) (i) and (iv)

Explanation :

Good thermal conductivity and a high melting point of aluminium are the properties that makes it suitable for making cooking utensils.

14. (c) Vertically downwards

Explanation :

Force on conductor is calculated using Fleming’s left hand rule.

15. (c) Growth hormones under the influence of the enzymes coded by a gene.

Explanation :

The height of a plant is regulated by a complex interplay of genetic factors, growth hormones, and enzyme activity.

Genes play a crucial role in determining the production and activity of growth hormones in plants. Specific genes code for enzymes that are involved in the synthesis, metabolism, and signaling pathways of growth hormones. These enzymes control the production, transportation, and breakdown of growth hormones within the plant.

While DNA carries the genetic information that influences the production of growth hormones, it is not directly influenced by growth hormones itself (option a). Genes regulate the production of proteins, including the enzymes involved in growth hormone metabolism, rather than directly regulating the proteins themselves (option b). Option d suggests that growth hormones act directly under the influence of a gene, but it is the enzymes coded by genes that mediate the effects of growth hormones.

16. (a) Maximum in situation (A)

Explanation :

As both the coils are in the same plane the induced current is found to be highest when the direction of the coil is at the right angle to the magnetic field.

17. (a) Both A and R are true and R is the correct explanation of A.

Explanation :

Insulin is a hormone released by the β-cells of the pancreas. It maintains the blood glucose level in the body, by its proper utilisation. So, lack of insulin causes accumulation of glucose in the blood and hence a disease called diabetes mellitus is caused.

18. (c) A is true, but R is false.

Explanation :

Ohm’s law states that the electric current flowing through a metallic wire is directly
proportional to the potential difference across its two ends. The expression is written as :

V = IR

Here, R (resistance of the wire) is a constant value, then only the statement will be valid.

$$\text{V}\propto\text{I only if}\space\frac{\text{V}}{\text{I}}=\text{constant}$$

19. (a) Both A and R are true and R is the correct explanation of A

Explanation :

Lumen of the Fallopian tube is lined by ciliated epithelium as cilia have a rhythmic waving and beating motion that helps substances to travel from one place to another.

20. (c) A is true but R is false

Explanation :

Hydrogen peroxide is a highly reactive metal that can react with light or heat to produce water. It decomposes into water and oxygen in the presence of sunlight. To prevent this reaction with light and heat it is stored in coloured bottles so that light cannot pass through it.

Section-B

21. Ozone layer absorbs most of the harmful ultraviolet radiations from the sun to the earth. It is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. Chlorofluorocarbons are the synthetic chemicals responsible for the drop of amount of ozone in the atmosphere.

The use of these chemicals can be reduced by:

Replacement of chloroflurocarbons with hydrochlorofluorocarbons because it breaks down more quickly.
Safe disposal of old appliances such as refrigerators and freezers.

22. (i) The ability of a lens to converge the rays of light falling on it is called the power of the lens.

(ii) (a) The focal length of a concave lens is negative, so its power is negative.

(b) The focal length of a convex lens is positive, so its power is positive.

23.

Two vital functions of kidneys are:

(1) They help in the removal of waste products that are harmful to the body. It is called excretion.

(2) They maintain the proper level of salt and water concentration in the body. It is called
osmoregulation.

24. (i) Between the carbon atoms in each layer covalent bond is found and Van Der Waal’s forces are found between the layers of carbon atoms in graphite.

(ii) Graphite is soft which makes it suitable for use as a dry lubricant. Between the carbon atoms in each layer covalent bond is found and weak Van Der Waals forces are found between the layers of carbon atoms in graphite. So, the layers can slide over one another making it a relatively soft substance.

25. (i) The possible genotype of the guinea pigs is Bb x Bb.

(ii) Black colour is dominant and white colour is recessive.

(iii) This is an example of a monohybrid cross and its phenotypic ratio is 3:1.

The sex chromosome in human female is homomorphic i.e., they contain the same chromosome XX.

During meiosis process at the time of gamete formation all egg cells will get one copy of X chromosome,hence all the gametes formed in human females have an X-chromosome.

26. Some of the characteristics of chemical reactions are:

Formation of a precipitate
Change in colour
Change in temperature
Change in the state.
Evolution of a gas

Section-C

27. Resistance of combination of three bulbs in parallel,

$$\text{R}_{eq}=\frac{\text{V}}{\text{I}}=\frac{4.5}{3}=1.5Ω$$

If R is the resistance of each wire, then

$$\frac{1}{\text{R}_{eq}}=\frac{1}{\text{R}} + \frac{1}{\text{R}} +\frac{1}{\text{R}}\\\Rarr\space \frac{1}{\text{R}_{eq}}=\frac{3}{\text{R}}$$

⇒ R = 3R_eq

⇒ R = 3 × 1.5 = 4.5 Ω

Current in each bulb,

$$\text{I} =\frac{\text{V}}{\text{R}}=\frac{4.5 \text{V}}{4.5Ω}=1\text{A}$$

(i) When bulb B₁ gets fused, the currents in B₂ and B₃ remain same I₂ = I₃ = 1 A, as the voltage across them remains the same so, their glow remains unaffected.

(ii) When bulb B₂ gets fused, the current in B₂ becomes zero and currents in B₁ and B₃ remains 1 A.

Total current I = I₁ + I₂ + I₃

= 1 + 0 + 1 = 2 A

Current in ammeter A₁ = 1 A

Current in ammeter A₂ = 0

Current in ammeter A₃ = 1 A

Current in ammeter A = 2 A

(iii) When all the bulbs are connected in the circuit:

$$\text{Power dissipated, P = }\frac{\text{V}^{2}}{\text{R}_{eq}}$$

$$\Rarr\space\text{P} =\frac{(4.5)^{2}}{1.5}= 13.5\space\text{W}$$

28. Consider the formation of the image A′B′ of an object AB by a concave mirror. As shown in given figure, the right angled triangles ABP and A′B′P are similar hence

$$\frac{\text{A}'\text{B}'}{\text{AB}}=\frac{\text{PB'}}{\text{PB}}$$

As per sign convention followed, PB = – u, PB′ = – v, AB = size of the object = + h and A′B′ = size of the image = – h′.

Hence, we have

$$\frac{-h'}{h}=\frac{-v}{-u}\\\text{or}\space\frac{h'}{h}=\frac{-v}{u}$$

Thus, by definition of magnification of image, we have

$$\text{Magnification, m =}\frac{h'}{h}=-\frac{v}{u}.$$

29. (i) The series of metals in which metals are arranged in decreasing order of their reactivity is called activity series of metals. The increasing order of reactivity will be:

Au < Cu < Fe < Mg.

(ii) (a) When zinc pieces are put into blue colour copper sulphate solution. Zinc displaces copper from copper sulphate solution. In this process, blue copper sulphur solution turns into colourless.

$$\underset{\text{Blue}}{\text{Zn(s)} + \text{CuSO}_{4}(aq)}\xrightarrow{}\\\underset{\text{Colourless }}{\text{ZnSO}_{4}(aq) + \text{Cu(s)}}$$

(b) When some silver pieces are put into green coloured ferrous sulphate solution, there will be no reaction because Ag is less reactive than iron.

$$\text{Ag(s) + FeSO}_{4}(aq)\xrightarrow{}\\\text{ No reaction}$$

The reaction will not take place because Ag is less reactive than iron.

30. Mendel’s experiment show that:

(i) When a cross was made between a tall pea plant with round seeds and a short pea plant wrinkled seeds, the F₁ progeny plants are all tall with round seeds. This indicates that tall and round seeds are the dominant traits.

(ii) When the F₁ plants are self-pollinated and the F₂ progeny show that some progencies tall with round seeds and some progenies were short plants with wrinkled seeds, which are the traits visible in the F₂ generation.

(iii) There were also some progenies with new combinations like tall plants with wrinkled seed short plants with round seeds.

(i) Bar diagram shows the proportion of females in the population over a decade.

(ii) 1:1 should be the sex ratio or the male-to-female ratio at a given point of time.

(iii) Female foeticide is the main reason for this trend showing deviation from the expected sex ratio.

(iv) Banning sex tests of unborn babies; increasing awareness and education will help to stop such trends.

31. (i) Food chain: The series of organisms taking part at various trophic levels for the flow of energy is called a food chain.

(ii) Food web: The food web represents many interlinked food chains as each organism is generally eaten by two or more other kinds of organisms. It cannot be represented by a straight line.

(iii) Biological magnification: The accumulation of harmful chemicals at each trophic level with the help of various biotic and abiotic factors is called biological magnification.

32. (i) An alloy is a homogeneous mixture of a metal with a metal or a non-metal. Amalgam is an alloy of a metal with mercury.

The alloy used for welding electric wires together is Solder. Its constituents are lead and Tin.

(ii) (a) Brass: Brass alloy is made of zinc (Zn) and copper (Cu).

(b) Stainless steel: It contains chromium (12.14%), molybdenum (0.21 %), nickel (less than 2%), and carbon (about 0.11%).

(c) Bronze: It is an alloy consisting primarily of copper, commonly with about 12% tin and often with the addition of other metals (such as aluminium, manganese, nickel or zinc) and sometimes non-metals or metalloids such as arsenic, phosphorus or silicon.

33. (i) Carbon dioxide gas is released.

(ii) Colour changes from purple to colourless

(iii) White precipitate of barium sulphate is formed

Section-D

34. Amoeba follows holozoic nutrition.

It involves the following steps:

Ingestion – Amoeba engulfs the food by using its temporary finger-like projections called pseudopodia. This process is called ingestion.
Digestion – The food which is taken inside the amoeba forms a food vacuole. Many enzymes are secreted into the food vacuole and the complex food molecule is converted into a simple and diffusible form.
Absorption and assimilation – The digested food is absorbed by the cell by the diffusion process.
Egestion – The undigested residue which remains in the vacuole is expelled.

(i) Though bile juice secreted by liver has no enzymes in it is still essential for digestion because:

It makes the medium alkaline in the small intestine so that intestinal juice can perform its functions because the food from stomach which enters the small intestine is acidic in nature.
It emulsifies fats so that enzymes like lipase can act upon fats to convert them into fatty acids and glycerol.

(ii) Breathing process occurs by inhalation and exhalation.

Inhalation: It is the process by which oxygen is taken in through nostrils. During inhalation process, the ribs move upwards and outwards due to contraction of intercostal muscles. The
diaphragm is lowered so that the volume of thoracic cavity increases. As a result air is forced inside the lungs through nostrils.
Exhalation: It is the process by which carbon dioxide is exhaled out from lungs through nostrils. During this process the ribs moves inwards and diaphragm comes back to its original position. The volume of thoracic cavity decreases so air is forced out through the lungs.

35. (i) (a) Carbon dioxide gas is evolved.

(b) Carbon dioxide gas is a non-supporter of combustion so when a burning splinter is brought near this gas, it gets extinguished.

(d) Lime water will turn milky.

$$\text{Ca(OH)}_{2} +\text{CO}_{2}\xrightarrow{}\\\text{CaCO}_{3} +\text{H}_{2}\text{O}$$

(e) When this gas is passed through lime water for a longer period, the milky lime water disappears.

$$\text{CO}_{2} + \text{CaCO}_{3} +\text{H}_{2}\text{O}\xrightarrow{}\\\text{Ca(HCO}_{3})_{2}$$

(ii) (a) Hydrogen ion concentration of an aqueous solution is inversely proportional to its pH.

(b) The solution is neutral.

(d) Tooth enamel gets corroded slowly when pH in the mouth is below 5.5. Acid is produced in mouth due to the degradation of food which is partially hydrolysed by saliva. But if excess acid is produced, it causes tooth decay. It can be prevented by using tooth paste which is generally basic.

(e) H⁺ ions exist in water as H₃O⁺ ions.

(i) The colour produced will be green. Its pH is 7.

(ii) It indicates that the solution is acidic in nature. The pH of 1M HCl is zero.

(iii) The pH of solution ‘A’ is lesser than 7. Carbonates salts react with acids (A) to liberate CO₂ gas.

(iv) The pH of solution ‘B’ is lesser than 7 because ‘B’ is an alkali as it liberates NH₃ gas.

(v) By adding few drops of alkali to pure water, it’s pH increases; and by adding a few drops of an acid decreases the pH of pure water.

36. (i) Case I: Image formed is magnified and erect when the object is placed between the optical centre and focus on a convex lens.

Case II: Image formed is magnified and inverted when the object is placed between F and 2F of a convex lens.

(ii) Given: u = – 20 cm, f = – 10 cm.

Using lens formula,

$$\frac{1}{f} =\frac{1}{v}-\frac{1}{u}\\\Rarr\space\frac{1}{v} =\frac{1}{f} +\frac{1}{u}\\\Rarr\space\frac{1}{v}=-\frac{1}{10}-\frac{1}{20}\\\Rarr\space\frac{1}{v}=\frac{-2-1}{20}=\frac{-3}{20}\\\Rarr\space v=\frac{\normalsize-20}{3}\text{cm}$$

(i) The following rays of light are usually used to locate the images formed by a spherical mirror : The incident ray passing through the centre of curvature: In this case, light after reflecting from the spherical mirror moves back along the same path.

The ray incident obliquely to the principal axis: In this case, the incident ray will be reflected back by the reflecting surface of the spherical mirror obliquely, making equal angles with the principal axis.

When the object is placed between the pole and the focus of the concave mirror, an image is formed behind the mirror and is virtual, erect and magnified.

(ii) Given, Magnification, m = – 3 (As the image is real), Object distance, u = – 20 cm

$$\text{We have,}\space m =-\frac{v}{u}\\\Rarr\space -3=-\bigg(\frac{v}{-20}\bigg)$$

⇒ v = – 60 cm

The image is located at 60 cm in front of the mirror.

Thus, the screen is at 40 cm from the object.

Section-E

37. (a) The balanced chemical equation for given reaction is;

$$\text{3Fe(s) + 4H}_{2}\text{O(g)}\xrightarrow{}\\\text{Fe}_{3}\text{O}_{4}(s) + 4\text{H}_{2}\text{(g)}$$

(b) Law of Conservation of Mass is demonstrated in the above equation.

$$\underset{\text{Barium chloride}}{3 \text{BaCl}_{2}}_{(\text{aq})} +\underset{\text{Aluminium sulphate}}{\text{Al}_{2}(\text{SO}_{4})_{3_{(aq)}}}\xrightarrow{}\\\underset{\text{Aluminium chloride}}{2\text{AlCl}_{3}\text{(aq)}} + \underset{\text{Barium sulphate}}{3\text{BaSO}_{4(s)}}\darr$$

38. (a) It shows that the amount of carbon dioxide affects the process and outcome of photosynthesis.

(b) Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis.

(c) The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink.

No, both the leaves show the presence of a different amount of starch in the given activity.

39. (i) Given that V = 200V; R = 1500Ω.

Therefore, current I = 200 V/1500 Ω = 0.13 A.

(ii) Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc.

(iii) Tungsten

(iv) Nichrome is an alloy of Ni, Cr, Mn, and Fe.