Brain Grain · braingrain.in
Science — Practice Paper · Set 1
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.Asexual reproduction takes place through budding ina. Amoeba.b. Yeast.c. Plasmodium.d. Leishmania.[1]
2.Food cans are coated with tin and not with zinc becausea. zinc is costlier than tin.b. zinc has a higher melting point than tin.c. zinc is more reactive than tin.d. zinc is less reactive than tin.[1]
3.Which of the following pairs will give displacement reactions?a. NaCl solution and copper metalb. MgCl₂ solution and aluminium metalc. FeSO₄ solution and silver metald. AgNO₃ solution and copper metal.[1]
4.What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.a. Hydrogen gas and iron chloride are produced.b. Chlorine gas and iron hydroxide are produced.c. No reaction takes place.d. Iron salt and water are produced.[1]
5.Which of the following correctly describes the magnetic field near a long straight wire?a. The field consists of straight lines perpendicular to the wire.b. The field consists of straight lines parallel to the wire.c. The field consists of radial lines originating from the wire.d. The field consists of concentric circles centred on the wire.[1]
6.Which of the following lenses would you prefer to use while reading small letters found in a dictionary?a. A convex lens of focal length 50 cm.b. A concave lens of focal length 50 cm.c. A convex lens of focal length 5 cm.d. A concave lens of focal length 5 cm.[1]
7.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 asa. TTWWb. TTwwc. TtWWd. TtWw[1]
8.The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?a. Between the principal focus and the centre of curvatureb. At the centre of curvaturec. Beyond the centre of curvatured. Between the pole of the mirror and its principal focus.[1]
9.At the time of short circuit, the current in the circuita. reduces substantially.b. does not change.c. increases heavily.d. vary continuously.[1]
10.Which of the following are environment-friendly practices?a. Carrying cloth-bags to put purchases in while shoppingb. Switching off unnecessary lights and fansc. Walking to school instead of getting your mother to drop you on her scooterd. All of the above[1]
11.A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R', then the ratio R/R' is –a. 1/25b. 1/5c. 5d. 25[1]
12.The anther containsa. sepals.b. ovules.c. pistil.d. pollen grains.[1]
13.A solution turns red litmus blue, its pH is likely to bea. 1b. 4c. 5d. 10[1]
14.Choose the correct option. The magnetic field inside a long straight solenoid-carrying currenta. 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.[1]
15.Which one of the following materials cannot be used to make a lens?a. Waterb. Glassc. Plasticd. Clay[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.Would you be able to check if water is hard by using a detergent?[2]
17.Why is DNA copying an essential part of the process of reproduction?[2]
18.Calculate the number of electrons constituting one coulomb of charge.[2]
19.You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.[2]
20.What is meant by power of accommodation of the eye?[2]
21.What is ozone and how does it affect any ecosystem?[2]
22.Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.[2]
23.Explain the nature of the covalent bond using the bond formation in CH₃Cl.[2]
24.Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?[2]
25.Which of the following hydrocarbons undergo addition reactions: C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.[2]
26.What is the role of the seminal vesicles and the prostate gland?[2]
27.What chemical process is used for obtaining a metal from its oxide?[2]
28.An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.[2]
29.Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.[2]
30.What is an homologous series? Explain with an example.[2]
31.What happens at the synapse between two neurons?[2]
32.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.[2]
33.What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?[2]
🔑 Show Answer Key — Set 1
- 1. (b) Yeast.
- 2. (c) zinc is more reactive than tin.
- 3. (d) AgNO₃ solution and copper metal.
- 4. (a) Hydrogen gas and iron chloride are produced.
- 5. (d) The field consists of concentric circles centred on the wire.
- 6. (c) A convex lens of focal length 5 cm.
- 7. (c) TtWW
- 8. (d) Between the pole of the mirror and its principal focus.
- 9. (c) increases heavily.
- 10. (d) All of the above
- 11. (d) 25
- 12. (d) pollen grains.
- 13. (d) 10
- 14. (d) is the same at all points.
- 15. (d) Clay
- 16. No. Detergents form lather in both hard and soft water because they do not form insoluble scum with calcium and magnesium ions. Soap, not detergent, is useful for checking hardness by lather formation.
- 17. DNA contains the information for body design and functioning. Copying DNA ensures that this information is passed to the next generation, while small variations in copying create diversity among offspring.
- 18. One coulomb of charge contains about 6.25 × 10¹⁸ electrons.
- 19. Tarnished copper has a green coating of basic copper carbonate. Lemon and tamarind contain acids, which react with and dissolve this basic coating, exposing the shiny copper surface.
- 20. Power of accommodation is the ability of the eye lens to adjust its focal length so that objects at different distances are focused clearly on the retina.
- 21. Ozone is a molecule of three oxygen atoms, O₃. In the upper atmosphere it forms the ozone layer, which absorbs harmful ultraviolet radiation from the Sun and protects living organisms. If ozone is depleted, more UV radiation reaches earth and can damage organisms and ecosystems.
- 22. In a combination reaction, two or more substances combine to form a single new substance, whereas in a decomposition reaction a single substance breaks down into two or more simpler substances. Since decomposition is the exact reverse of combination, decomposition reactions are called the opposite of combination reactions. Combination: CaO + H₂O → Ca(OH)₂ Decomposition: CaCO₃ → CaO + CO₂ (on heating)
- 23. In a covalent bond, atoms share pairs of electrons to complete their outer shells. In CH₃Cl, carbon has four valence electrons and shares one electron each with three hydrogen atoms and one chlorine atom. Thus carbon forms four single covalent bonds; hydrogen attains a duplet and chlorine completes its octet.
- 24. The total current drawn is about 0.73 A.
- 25. Unsaturated hydrocarbons undergo addition reactions. Therefore C₃H₆ and C₂H₂ undergo addition reactions; C₂H₆, C₃H₈ and CH₄ are saturated and usually do not.
- 26. The seminal vesicles and prostate gland add fluids to sperm to form semen. These secretions provide nutrition, make transport easier and create a medium in which sperm can move.
- 27. Reduction is used for obtaining a metal from its oxide. The metal oxide is reduced to the metal by removing oxygen, often with carbon, carbon monoxide or a more reactive metal.
- 28. The image is formed about 8.6 cm behind the mirror. It is virtual, erect and diminished, with size about 2.1 cm.
- 29. The gas is carbon dioxide, so compound A is calcium carbonate. The balanced equation is: CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O. Carbon dioxide extinguishes a burning candle.
- 30. A homologous series is a family of organic compounds with the same functional group and similar chemical properties, in which successive members differ by a –CH₂– unit. Example: alcohols, CH₃OH, C₂H₅OH, C₃H₇OH, etc., all contain the –OH group.
- 31. At a synapse, the electrical impulse at the end of one neuron causes release of chemical neurotransmitters. These chemicals cross the synaptic gap and start a new electrical impulse in the next neuron.
- 32. (i) To get 9 Ω, connect two 6 Ω resistors in parallel and then connect this combination in series with the third 6 Ω resistor. (ii) To get 4 Ω, connect two 6 Ω resistors in series and then connect this 12 Ω combination in parallel with the third 6 Ω resistor.
- 33. Biological magnification is the increase in concentration of non-biodegradable toxic substances at successive trophic levels of a food chain. Yes, levels are different; the concentration is lowest in producers and becomes higher at each higher trophic level, usually maximum in top consumers.
Brain Grain · braingrain.in
Science — Practice Paper · Set 2
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.The autotrophic mode of nutrition requiresa. carbon dioxide and water.b. chlorophyll.c. sunlight.d. all of the above.[1]
2.Which of the following methods is suitable for preventing an iron frying pan from rusting?a. Applying greaseb. Applying paintc. Applying a coating of zincd. All of the above.[1]
3.The kidneys in human beings are a part of the system fora. nutrition.b. respiration.c. excretion.d. transportation.[1]
4.Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –a. 1:2b. 2:1c. 1:4d. 4:1[1]
5.Which of the following is not a part of the female reproductive system in human beings?a. Ovaryb. Uterusc. Vas deferensd. Fallopian tube[1]
6.An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –a. 100 Wb. 75 Wc. 50 Wd. 25 W[1]
7.An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to bea. calciumb. carbonc. silicond. iron.[1]
8.Which of the following constitute a food-chain?a. Grass, wheat and mangob. Grass, goat and humanc. Goat, cow and elephantd. Grass, fish and goat[1]
9.No matter how far you stand from a mirror, your image appears erect. The mirror is likely to bea. only plane.b. only concave.c. only convex.d. either plane or convex.[1]
10.A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to bea. both concave.b. both convex.c. the mirror is concave and the lens is convex.d. the mirror is convex, but the lens is concave.[1]
11.Ethane, with the molecular formula C₂H₆ hasa. 6 covalent bonds.b. 7 covalent bonds.c. 8 covalent bonds.d. 9 covalent bonds.[1]
12.Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO₂(g) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced.i. (a) and (b)ii. (a) and (c)iii. (a), (b) and (c)iv. all[1]
13.Which of the following terms does not represent electrical power in a circuit?a. I²Rb. IR²c. VId. V²/R[1]
14.The human eye forms the image of an object at itsa. cornea.b. iris.c. pupil.d. retina.[1]
15.The brain is responsible fora. thinking.b. regulating the heart beat.c. balancing the body.d. all of the above.[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.How are the lungs designed in human beings to maximise the area for exchange of gases?[2]
17.Outline a project which aims to find the dominant coat colour in dogs.[2]
18.What is the role of saliva in the digestion of food?[2]
19.What are the components of the transport system in human beings? What are the functions of these components?[2]
20.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?[2]
21.Which part of the brain maintains posture and equilibrium of the body?[2]
22.An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.[2]
23.What is the far point and near point of the human eye with normal vision?[2]
24.Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.[2]
25.Use the data in Table 11.2 to answer the following – (a) Which among iron and mercury is a better conductor? (b) Which material is the best conductor?[2]
26.What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.[2]
27.Give reasons (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.[2]
28.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?[2]
29.How does chemical coordination occur in plants?[2]
30.How is the amount of urine produced regulated?[2]
31.Draw a labelled diagram of the longitudinal section of a flower.[2]
32.Draw the electron dot structures for (a) ethanoic acid. (b) H₂S. (c) propanone. (d) F₂.[2]
33.Why should curd and sour substances not be kept in brass and copper vessels?[2]
🔑 Show Answer Key — Set 2
- 1. (d) all of the above.
- 2. (c) Applying a coating of zinc
- 3. (c) excretion.
- 4. (c) 1:4
- 5. (c) Vas deferens
- 6. (d) 25 W
- 7. (a) calcium
- 8. (b) Grass, goat and human
- 9. (d) either plane or convex.
- 10. (a) both concave.
- 11. (b) 7 covalent bonds.
- 12. (i) (a) and (b)
- 13. (b) IR²
- 14. (d) retina.
- 15. (d) all of the above.
- 16. The lungs contain millions of alveoli. Each alveolus has a thin wall and is surrounded by blood capillaries, giving a very large surface area and a short diffusion distance for exchange of oxygen and carbon dioxide.
- 17. Collect data on coat colour of many parent dogs and their puppies over several generations. Record crosses between pure-breeding parents of different colours if possible. If all F₁ offspring show one colour and the other colour reappears in later generations, the F₁ colour is likely dominant. A large sample is needed because dog coat colour can involve more than one gene.
- 18. Saliva moistens food and helps in swallowing. It contains salivary amylase, which begins digestion by breaking starch into simpler sugars.
- 19. The human transport system consists of the heart, blood and blood vessels. The heart pumps blood. Blood transports oxygen, carbon dioxide, nutrients, hormones and wastes. Arteries carry blood away from the heart, veins bring blood back to the heart, and capillaries allow exchange with tissues.
- 20. A concave lens of power -1.25 D is required.
- 21. The cerebellum, a part of the hindbrain, maintains posture and equilibrium of the body.
- 22. The heat developed is 15,000 J.
- 23. For a normal human eye, the far point is infinity and the near point is about 25 cm from the eye.
- 24. Hydrogen gas is produced. Iron reacts with dilute sulphuric acid to form iron(II) sulphate and hydrogen: Fe + H₂SO₄ → FeSO₄ + H₂.
- 25. (a) Iron is a better conductor than mercury because its resistivity is lower. (b) Silver is the best conductor among the materials listed because it has the lowest resistivity.
- 26. On heating, sodium hydrogencarbonate decomposes to give sodium carbonate, carbon dioxide and water: 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O.
- 27. (a) Platinum, gold and silver are lustrous, malleable and resistant to corrosion, so they remain attractive as jewellery. (b) Sodium, potassium and lithium react vigorously with air and water, so they are stored under oil to prevent contact. (c) Aluminium forms a thin protective oxide layer that prevents further corrosion; it is also light and a good conductor of heat. (d) Metals are easier to reduce from oxides than from carbonates or sulphides, so ores are first converted to oxides by calcination or roasting.
- 28. Hydrogen gas is usually liberated. For example, zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen: Zn + H₂SO₄ → ZnSO₄ + H₂. The gas is tested by bringing a burning candle near it; hydrogen burns with a pop sound.
- 29. Chemical coordination in plants occurs through plant hormones. Auxins, gibberellins, cytokinins, abscisic acid and other hormones move from where they are produced to other tissues and regulate growth, cell division, dormancy, wilting, and responses to light, gravity and water.
- 30. The amount of urine depends on how much excess water and dissolved waste must be removed. If the body has plenty of water, less water is reabsorbed and more urine is produced. If water is scarce, more water is reabsorbed in the nephrons, producing less concentrated urine. Hormones also regulate this reabsorption.
- 31. A labelled longitudinal section of a flower should show sepals, petals, anther, filament, stigma, style, ovary and ovule. The stamen consists of anther and filament, and the pistil/carpel consists of stigma, style and ovary.
- 32. (a) Ethanoic acid: CH₃–C(=O)–OH, with two lone pairs on each oxygen. (b) H₂S: H–S–H, with two lone pairs on sulphur. (c) Propanone: CH₃–C(=O)–CH₃, with two lone pairs on oxygen. (d) F₂: F–F, with each fluorine having three lone pairs.
- 33. Curd and sour foods contain acids. Acids react with copper and brass to form soluble metal salts, which can make the food poisonous and unfit to eat. Therefore such substances should not be kept in copper or brass vessels.
Brain Grain · braingrain.in
Science — Practice Paper · Set 3
Class: 10CBSE / NCERTMax Marks: 51
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 15 × 1 = 15
Choose the correct answer. (Answer all questions.)
1.Which of the following groups contain only biodegradable items?a. Grass, flowers and leatherb. Grass, wood and plasticc. Fruit-peels, cake and lime-juiced. Cake, wood and grass[1]
2.Which one of the following types of medicines is used for treating indigestion?a. Antibioticb. Analgesicc. Antacidd. Antiseptic[1]
3.The breakdown of pyruvate to give carbon dioxide, water and energy takes place ina. cytoplasm.b. mitochondria.c. chloroplast.d. nucleus.[1]
4.The least distance of distinct vision for a young adult with normal vision is abouta. 25 m.b. 2.5 cm.c. 25 cm.d. 2.5 m.[1]
5.The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due toa. presbyopia.b. accommodation.c. near-sightedness.d. far-sightedness.[1]
6.Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)a. massb. speedc. velocityd. momentum[1]
7.Fe₂O₃ + 2Al → Al₂O₃ + 2Fe. The above reaction is an example of aa. combination reaction.b. double displacement reaction.c. decomposition reaction.d. displacement reaction.[1]
8.While cooking, if the bottom of the vessel is getting blackened on the outside, it means thata. the food is not cooked completely.b. the fuel is not burning completely.c. the fuel is wet.d. the fuel is burning completely.[1]
9.Where should an object be placed in front of a convex lens to get a real image of the size of the object?a. At the principal focus of the lensb. At twice the focal lengthc. At infinityd. Between the optical centre of the lens and its principal focus.[1]
10.Butanone is a four-carbon compound with the functional groupa. carboxylic acid.b. aldehyde.c. ketone.d. alcohol.[1]
11.The xylem in plants are responsible fora. transport of water.b. transport of food.c. transport of amino acids.d. transport of oxygen.[1]
12.A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field isa. towards southb. towards eastc. downwardd. upward[1]
13.The gap between two neurons is called aa. dendrite.b. synapse.c. axon.d. impulse.[1]
14.10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will bea. 4 mLb. 8 mLc. 12 mLd. 16 mL[1]
15.Which of the following is a plant hormone?a. Insulinb. Thyroxinc. Oestrogend. Cytokinin.[1]
Part II — Short Answer Questions 18 × 2 = 36
Answer briefly. (Answer all questions.)
16.What is the role of decomposers in the ecosystem?[2]
17.What does one mean by exothermic and endothermic reactions? Give examples.[2]
18.How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?[2]
19.How does binary fission differ from multiple fission?[2]
20.When does an electric short circuit occur?[2]
21.An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.[2]
22.What would you observe when zinc is added to a solution of iron(II) sulphate? Write the chemical reaction that takes place.[2]
23.Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.[2]
24.Why do stars twinkle?[2]
25.Why is the conversion of ethanol to ethanoic acid an oxidation reaction?[2]
26.What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?[2]
27.What are the methods used by plants to get rid of excretory products?[2]
28.The magnetic field in a given region is uniform. Draw a diagram to represent it.[2]
29.How is the equal genetic contribution of male and female parents ensured in the progeny?[2]
30.What are the functions performed by the testis in human beings?[2]
31.What do you mean by a precipitation reaction? Explain by giving examples.[2]
32.What is a balanced chemical equation? Why should chemical equations be balanced?[2]
33.How are water and minerals transported in plants?[2]
🔑 Show Answer Key — Set 3
- 1. (a), (c) and (d)
- 2. (c) Antacid
- 3. (b) mitochondria.
- 4. (c) 25 cm.
- 5. (b) accommodation.
- 6. (c) velocity and (d) momentum
- 7. (d) displacement reaction.
- 8. (b) the fuel is not burning completely.
- 9. (b) At twice the focal length
- 10. (c) ketone.
- 11. (a) transport of water.
- 12. (d) upward
- 13. (b) synapse.
- 14. (d) 16 mL
- 15. (d) Cytokinin.
- 16. Decomposers break down dead plants, animals and organic wastes into simpler substances. They recycle nutrients back into the soil and help maintain the flow of matter in the ecosystem.
- 17. Exothermic reactions are reactions in which heat (energy) is released along with the products. Examples: burning of natural gas, CH₄ + 2O₂ → CO₂ + 2H₂O + heat; and respiration. Endothermic reactions are reactions in which heat (energy) is absorbed from the surroundings. Example: the decomposition of calcium carbonate on heating, CaCO₃ → CaO + CO₂, which requires a continuous supply of heat.
- 18. Four 176 Ω resistors are required in parallel.
- 19. In binary fission, one parent cell divides into two daughter cells, as in Amoeba. In multiple fission, one parent cell divides simultaneously into many daughter cells, as in Plasmodium.
- 20. A short circuit occurs when the live wire and neutral wire come into direct contact, or when resistance in a circuit becomes very low. This causes a sudden large current to flow.
- 21. The image is formed 6 cm behind the mirror. It is virtual, erect and diminished.
- 22. Zinc is more reactive than iron, so it displaces iron from iron(II) sulphate. The pale green colour of FeSO₄ fades and iron is deposited. Zn + FeSO₄ → ZnSO₄ + Fe.
- 23. Use the electrical conductivity activity. Place two nails in a cork, connect them to a battery, bulb and switch, and dip them in solutions separately. Dilute HCl or H₂SO₄ makes the bulb glow because it produces ions. Glucose and alcohol solutions do not make the bulb glow because they do not produce H⁺ ions in water. This shows that hydrogen-containing compounds are acidic only if they ionise to give H⁺/H₃O⁺ ions.
- 24. Stars twinkle because their light is refracted by layers of the earth's atmosphere with changing density. This atmospheric refraction causes the apparent position and intensity of starlight to fluctuate.
- 25. Ethanol is converted to ethanoic acid by adding oxygen/removing hydrogen. Since oxidation is gain of oxygen or loss of hydrogen, this conversion is an oxidation reaction.
- 26. In parallel, each device gets the full potential difference of the source and can be switched on or off independently. If one device fails, the others continue to work. Parallel connection also allows each device to draw current according to its own resistance.
- 27. Plants remove wastes by diffusion of gases through stomata and lenticels, by storing wastes in leaves, bark or old xylem that later fall off, by converting wastes into resins and gums, and by excreting some substances into the surrounding soil.
- 28. A uniform magnetic field is represented by straight, parallel and equally spaced magnetic field lines, all pointing in the same direction.
- 29. Gametes contain only one set of chromosomes because they are formed by meiosis. During fertilisation, one male gamete and one female gamete fuse, restoring the normal chromosome number. Thus the zygote receives one set of genes from each parent.
- 30. The testes produce male gametes, sperm, and secrete the male sex hormone testosterone. Testosterone regulates sperm production and the development of male secondary sexual characters.
- 31. A precipitation reaction is a reaction in which two solutions react to form an insoluble solid called a precipitate. For example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq), in which insoluble white barium sulphate is formed as a precipitate. Another example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq), where white silver chloride is precipitated.
- 32. A balanced chemical equation is one in which the number of atoms of each element is equal on both the reactant side and the product side. Chemical equations should be balanced to obey the law of conservation of mass, which states that mass can neither be created nor destroyed in a chemical reaction. Since atoms are neither created nor destroyed, the total mass of the reactants must equal the total mass of the products, which means the number of atoms of each element must be the same on both sides.
- 33. Water and minerals are absorbed by root hairs and move into xylem vessels. They rise through xylem due to root pressure and mainly due to transpiration pull created by evaporation of water from leaves.