PRACTICE PAPER 1 F O R BOARD EXAM 2025 SUBJECT: SCIENCE CLASS : X (ANSWER KEY) MAX. MARKS: 80 DURATION: 3 HRS General Instruction: 1. This Question Paper has 5 Sections A-E. 2. Section A has 20 MCQs carrying 1 mark each. 3. Section B has 5 questions carrying 02 marks each. 4. Section C has 6 questions carrying 03 marks each. 5. Section D has 4 questions carrying 05 marks each. 6. Section E has 3 case based integrated units of assessment (04 marks each) with sub-parts of the values of 1, 1 and 2 marks each respectively. 7. All Questions are compulsory. However, an internal choice in 2 Qs of 5 marks, 2 Qs of 3 marks and 2 Questions of 2 marks has been provided. An internal choice has been provided in the 2marks questions of Section E 8. Draw neat figures wherever required. Take π =22/7 wherever required if not stated. SECTION – A Questions 1 to 20 carry 1 mark each. 1. Ria added 10 ml of hydrochloric acid and 10 ml of sodium hydroxide solution in two separate beakers labelled I and II respectively. She added aluminium metal strip in both the beakers and made some observations. Which of the following observation is correct? (a) H2 gas is evolved in beaker I but not in beaker II. (b) H2 gas is evolved in beaker II but not in beaker I. (c) H2 gas is not evolved in either of the two beakers. (d) H2 gas is evolved in both the beakers. Ans. (d) H2 gas is evolved in both the beakers. 2Al + 6HCl → 2AlCl3 + 3H2 2Al + 2NaOH + 2H2O → 2NaAlO2 + 3H2(g) 2. Which of the following statement is correct about below diagram? (a) The colour at position marked 5 is similar to the colour of gold metal. (b) The colour at position marked 2 has longer wavelength than 1. (c) The colour at position marked 7 is violet. (d) The colour at position marked 1 in traffic signal indicates that vehicles must go. Ans. (c) The colour at position marked 7 is violet. 3. PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O Which one of the following is the reducing agents? (a) Pb (b) HCl (c) Cl2 (d) PbO2 Ans. (b) HCl acts as reducing agent. 4. Chemical properties of acids are given in a tabular form. Which one of the options is not true? (a) Acid + Metal Salt + Hydrogen gas (b) Acid + Metal carbonate Salt + Carbon dioxide + Water (c) Acid + Base Salt + Water (d) Acid + Metal oxide Salt + Hydrogen gas Ans. (d) Acid + Metal oxide → Salt + Hydrogen gas When a metal reacts with metal oxide, salt and water are formed. 5. The largest gland which is associated with the alimentary canal of human beings is (a) Salivary glands (b) Liver (c) Pancreas (d) Thyroid Ans. (b) Liver 6. The observation(s) that can be observed on the moon is (a) sun appears dark (b) sun appears pure white (c) sky of moon look like that of earth (d) all of them Ans. (b) sun appears pure white 7. If a round seed pea plant is crossed with a wrinkled seed pea plant, then the phenotypic and genotypic ratio will be: Ans. (b) 8. Which of the following is the part of female reproductive system where the egg is fertilized? (a) Uterus (b) Vagina (c) Oviduct (d) Cervix Ans. (c) Oviduct 9. Reciprocal of focal length in metres is known as the (a) focus (b) power (c) power of accommodation (d) far point Ans. (b) power 10. Select the incorrect statement. (a) Silver articles become black due to formation of silver sulphide. (b) Iron forms brown flaky substance called rust on ts surface. of a lens. (c) Copper forms a brown coating due to formation of basic copper carbonate. (d) Corrosion causes damage to car bodies, bridges, iron railings, ships etc. Ans. (c) Copper forms a brown coating due to formation of basic copper carbonate. This is is incorrect statement. Copper forms a green coating due to formation of basic copper carbonate. 11. Meenu found out the pH of aqueous solutions of HCl, CH3COOH, NH4OH and NaOH. Then she arranged these solutions in the order of increasing pH. Which one of the following is correct? (a) HCl < CH3COOH < NH4OH < NaOH (b) CH3COOH < HCl < NH4OH < NaOH (c) HCl < CH3COOH < NaOH < NH4OH (d) NH4OH < NaOH < HCl < CH3COOH Ans. (a) HCl < CH3COOH < NH4OH < NaOH 12. Identify the colour of A. (a) Green (b) Bluish-black (c) Yellow (d) Black Ans. (b) Bluish-black 13. Study the given diagram carefully and identify the part through which information travels as an electrical impulse. (a) A (b) B (c) C (d) D Ans. (c) C 14. Which option correctly tell us about olfactory indicators? (a) Substances whose odour changes only in acidic medium. (b) Substances whose odour changes only in basic medium. (c) Substances whose odour never changes in acidic or in basic medium. (d) Substances whose odour changes in acidic or basic medium. Ans. (b) Substances whose odour changes only in basic medium. 15. When red litmus solution is added to lime water, then its colour is: (a) red (b) green (c) blue (d) yellow Ans. (c) blue Bases turn red litmus blue. 16. When a person uses a convex lens as a simple magnifying glass, the object must be placed at a distance. (a) less than one focal length (b) more than one focal length (c) less than twice the focal length (d) more than twice the focal length Ans. (a) less than one focal length DIRECTION: In the question number 17 and 20, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct option (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A) (b) Both assertion (A) and reason (R) are true and reason (R) is not the correct explanation of assertion (A) (c) Assertion (A) is true but reason (R) is false. (d) Assertion (A) is false but reason (R) is true. Ans: (b) Both assertion (A) and reason (R) are true and reason (R) is not the correct explanation of assertion (A) 17. Assertion (A): Brain is a delicate organ which is protected from injury Reason (R): Only the bony box protects the brain from any shock. Ans. (d) A is false but R is true. 18. Assertion (A): When CO (g) and H2(g) react at 340 atm, CH3OH(l) is formed. Reason (R): Chemical reaction changes the physical and chemical state of substance. Ans. (a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A) 19. Assertion (A): In human beings, there are 23 pairs of chromosomes. Reason (R): All the children inherit an X chromosome from their father whether they are boys or girls. Ans. (c) Assertion (A) is true but reason (R) is false. 20. Assertion (A): The value of f in a concave mirror is taken as –ve and in a convex mirror, it is taken as +ve. Reason (R): All distances measured to the right of the origin are taken as +ve and those measured along the left of the origin are taken as –ve. Ans. (a) Both A and R are true and R is the correct explanation of A. SECTION – B Questions 21 to 26 carry 2 marks each. 21. Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. What type of a chemical reaction is it? Support your answer with a chemical equation and observation. Ans. Thermal decomposition is the type of a chemical reaction. t 2FeSO4(s) hea Fe2O3(s) + SO2(g) + SO4(g) Green coloured salt changes to reddish brown Fe2O3, pungent smelling SO2 and SO3 gases are formed OR Akshaya added zinc granules to four salt solutions add recorded his observations as shown in the table given below: Metal + Salt solution Displacement Reaction (a) Zn + CuSO4 Blue colour to colourless (b) Zn + FeSO4 Pale green to colourless (c) Zn + MgSO4 Yes (d) Zn + Al2(SO4)3 Yes Select the correct observation (s) and give chemical equation(s) of the reaction involved. Ans. Zn + CuSO4 ZnSO4 + Cu Zn + FeSO4 ZnSO4 + Fe Zn + MgSO4 No reaction Zn + Al2(SO3)4 No reaction Hence, the correct observations are (a) and (b). 22. Give reasons (a) Blood circulation in human heart is called double circulation. (b) Small intestine in herbivores is longer than carnivores. Ans. (a) The blood goes through the human heart twice during each cycle, so it is called double blood circulation. (b) Herbivores eating grass, need a longer small intestine to allow the cellulose to be digested whereas for carnivores, meat is easy to digest so they have a shorter small intestine. 23. Draw the structure of a nephron and level the following parts: Glomerulus, Bowman’s capsule, Renal artery. 24. (a) Redraw the diagram given below in your answer book and show the direction of the light ray after reflection from the mirror. (b) A convex lens of focal length 25 cm is placed in contact with concave lens of focal length 50 cm. Calculate. (i) Power of the combination (ii) Focal length of the combination Ans. (a) (b) Focal length of convex lens = 25 cm 1 100 Power of convex lens (P1) = 4.0D f 25 Focal length of concave lens = — 50 cm 1 100 Power of concave lens (P2) = 2.0D f 50 Power of combination, P = P1 + P2 ⇒ P = +4.0 D + (-2.0) D = +2.0D 1 (ii) Focal length of the combination, F 1 0.5m or 50cm P 2.0 OR (a) Why does a pencil appear bent and short when immersed in water? (b) A convex lens produces a real and inverted image 2.0 times magnified at a distance of 20 cm from the lens. Calculate the focal length of the lens. Ans. (a) A pencil appears bent and short when immersed in water due to apparent displacement of a pencil i.e. refraction. The light reaching from the portion of the pencil inside water appears to come from a different direction, compared to the part above water. (b) Magnification (m) = 2.0 (real image) Distance of the image from the lens (v) = 20 cm Distance of the object from the lens (u)= ? Focal length of the lens (f) = ? v 20 m 2.0 u 10cm u u 1 1 1 1 Lens formula, 1 1 3 6 9 v u f f 20 10 60 60 60 20 f 6.67cm 9 3 25. What is a food chain? ‘Flow of energy in a food chain is unidirectional’ Justify the statement. Ans. Food chain is a series of organisms in which one organism eats another organism as food. Flow of energy in a food chain is unidirectional because the energy captured by the autotrophs does not revert back to the solar input and the energy passes to the herbivores does not come back to producers. Sun Producer Herbivore Carnivore Green plants capture 1% of sunlight and convert it into food energy. As per 10 per cent law, only 10% of energy is transferred to the next trophic level. The remaining 90% of energy is used in various life processes by the present trophic level. 26. Male tall pea plant was cross pollinated with female short pea plant, all the plants of progeny were tall plants, when 100 tall plants of F1 generation were self pollinated, short plants also appeared in F2 generation. How many short pea plants were produced? Explain with suitable reason. Ans. A cross between two plants having one pair of contrasting characters is called a monohybrid cross. A cross pollination between tall pea plants (TT) and short pea plants (tt) produced all tall plants progeny. There were no halfway characteristics in this progeny or F, progeny i.e. no medium height or short plants. Only one of the parental traits was expressed. The one that was expressed is a dominant trait. When F, offsprings were allowed to self pollinate, both the traits were expressed. Self pollination of F1 offsprings We can conclude tallness is a dominant trait. TT and Tt both are tall plants but tt is a short plant. SECTION – C Questions 27 to 33 carry 3 marks each. 27. Adi took solid quick lime in a beaker and added water to it. (a) What type of sound would he hear? (b) State the type of reaction it is and write the chemical equation. Ans. (a) He would hear hissing sound. (b) It is exothermic and combination reaction as the beaker becomes warm, it is an exothermic reaction. In this reaction, calcium oxide and water combine to form a single product, calcium hydroxide. Since a single product is formed, it is a combination reaction. CaO(s) + H2O(l) Ca(OH)2(aq) + Heat Quick lime Slaked lime 28. (a) What is the colour of copper nitrate crystals before heating and after heating? Write chemical reaction involved. (b) Identify the gases formed. (c) Write the chemical name and chemical formula of two salts which contain water of crystallisation. Ans. (a) The colour of copper nitrate is blue which on heating gives black copper oxide. 2Cu(NO3)(s) 2CuO(s) + 4NO2(g) + O2(g) Blue Black Brown Colourless Before heating — Blue After heating — Black (b) Brown coloured nitrogen dioxide and colourless O2 gas are formed. (c) Salts which contain water of crystallisation: Chemical name Chemical formula Na CO .10H Sodium carbonate decahydrate 2 3 2O 1 CaSO4. H2O Calcium sulphate hemihydrate 2 29. (a) What will be the resistance between A and B in the given figure? (b) The fuse used for domestic purposes are rated as 1A, 2A, 3A, 5A, 10A etc. Calculate and select the fuse for operating 1 kW power at 220 V line. (c) Why does the cord of an electric heater not glow while the heating element glows? Ans. (a) As it is clear from the figure 5Ω, 10Ω and 10Ω resistors as R1, R2, and R3; are connected in parallel respectively. Now 4 ohm (obtained from parallel combination) and 20 ohm are in series (b) P = 1kW or 1000 W, V = 220V P 1000 P = VI I 4.54 A V 220 ∴ In this case, SA fuse must be used. (c) The cord of an electric heater does not glow as it is made of copper which has low resistance and heat produced is negligible. The heating element of electric heater which is made of nichrome (an alloy) has high resistance and a large amount of heat is produced. Due to the heat, the heating clement glows. 30. What is scattering of light? Why is the colour of the clear sky blue? Explain. Ans. Scattering of light: Phenomenon of deviation of ray of light from its original path when comes in contact with particles of size equivalent to wavelength of light ray. Scattering is inversely proportional to wavelength of light ray. Fine particles present in atmosphere scatter rays of light to greater extent which are smaller in wavelength. Blue colour present in visible light is scattered the most by the molecules present in atmosphere and reach to earth in larger amount so sky appears blue. 31. (a) A coil of many circular turns of insulated copper wire wrapped loosely in the shape of a cylinder is called a solenoid. Draw the pattern of magnetic field around a current carrying solenoid and compare the pattern of the field with the magnetic field around a bar magnet. (b) How can you say that the magnetic field is same at all points inside the solenoid? Ans. (a) The magnetic field lines are exactly identical to those due to a cylindrical bar magnet with one end of solenoid acting as a south pole and its other end as a north pole. (b) The field lines inside the solenoid are in the form of parallel straight lines. The field is uniform inside the solenoid. This indicates that the field is the same at all points inside the solenoid. OR How will the magnetic field produced at a point due to a current carrying circular coil change if we: (a) increase the current flowing through the coil? (b) reverse direction of current through the coil? (c) increase the number of turns in the coil? Ans. Magnetic field (B) at the centre of the circular coil (a) increases if the current is increased as B ∝ I (b) reverses on reversing the current. (c) increases if the number of turns in the coil increases as field is directly proportional to the number of turns. 32. What is biological magnification? Which level of food chain will have the maximum magnification? Will the levels of this magnification be different at different levels of the ecosystem? Ans. The increase in the concentration of harmful chemical substances mainly pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification. The highest trophic level of a food chain mostly human beings will have the maximum amount of pesticides. The concentration of harmful chemicals will be different at different trophic levels as of these chemicals are not degradable, these get accumulated progressively at each trophic level. 33. Draw neat diagram of human brain and label on it the following parts: (a) Midbrain (b) Pituitary gland Ans. SECTION – D Questions 34 to 36 carry 5 marks each. 34. (a) Name an instrument that measures potential difference between two points in a circuit. Define the unit of potential difference in terms of SI unit of charge and work. Draw the circuit symbols for a (i) variable resistor, (ii) a plug key which is closed one. (b) Two electric circuits I and II are shown below (i) Which of the two circuits has more resistance? (ii) Through which circuit more current passes? Give reason. (iii) In which circuit, the potential difference across each resistor is same? (iv) If R1 > R2 > R3, in which circuit more heat will be produced in R1 as compared to other two resistors? Given reason. Ans. (a) Voltmeter Unit of potential difference is volt. One volt: The potential difference between two points in an electrostatic field is said to be 1 volt if one joule of work is done in moving one coulomb of electric charge from one point to another in the same electrostatic field. (i) Variable resistor (ii) a plug key which is closed one (b) (i) Equivalent resistance of a series combination is more that of a their parallel combination. Hence, circuit ‘" has more resistance. (ii) From Ohm’s Law, for the same applied potential difference, current is inversely proportional to equivalent resistance of the combination, i.e. I = 1/R Therefore, in parallel combination, circuit II, has less resistance, hence, more current will pass through it. (iii) In parallel combination (Circuit II), the potential difference across each resistance is equal to the applied potential difference. (iv) More heat will be produced in R, in circuit II as compared to other two resistor (for R1 > R2 > R3 Justification: In series, less current will flow due to increase in resistance of the circuit and potential difference across each resistance is less than that of applied potential. While in parallel combination for the same potential, current is inversely proportional to resistance (I ∝ 1/R) so more current will flow through R, than that in series combination. Hence, from Jule’s law of heating, H = I2Rt heat produced in R, in parallel combination will be more as compared to their series combination. OR Draw magnetic field lines produced around a current carrying straight conductor passing through a cardboard. Name, state and apply the rule to mark the direction of these field lines. How will the strength of the magnetic field change when the point where magnetic field to be determined is moved away from the straight conductor? Give reason to justify your answer. Ans. Right-Hand Thumb Rule. This rule is used to find the direction of magnetic field due to a straight current carrying wire. It states that if we hold the current carrying conductor in the right hand in such a way that the thumb is stretched along the direction of current, then the curly finger around the conductor represents the direction of magnetic field produced by it. Using compass needle, we can determine the strength of magnetic field at various point. If the needle is moved away from the straight wire carrying constant current, the deflection in the needle decreases. It implies that magnetic field strength decreases as the distance increases. 35. Suman heated ethanoic acid with different subtances and wants to find out the results. Let’s help her out. (a) What happens when (i) ethanoic acid reacts with sodium carbonate. (ii) ethanoic acid reacts with sodium bicarbonate. (iii) ethanoic acid reacts with sodium hydroxide. One of the products formed in all the three reactions is common. Name that product. (b) Why ethanoic acid is also known as (i) glacial acetic acid (ii) vinegar? Ans. (a) (i) Ethanoic acid reacts with carbonates and hydrogen carbonates to give rise to salt, carbon dioxide and water. 2CH3COOH + Na2CO3 2CH3COONa + H2O + CO2 (ii) CH3COOH + NaHCO3 CH3COONa + H2O + CO2 (iii) Ethanoic acid reacts with a base such as sodium hydroxide to give a salt and water. CH3COOH + NaOH CH3COONa + H2O The product which is formed in all the three reactions is sodium ethanoate or commonly called sodium acetate. (b) (i) Ethanoic acid is also called glacial acetic acid as the melting point of pure ethanoic acid is 290K and hence it often freezes during winter in cold climates. (i) 5-8% solution of ethanoic acid (commonly known as acetic acid) in water is called vinegar. OR (a) What is homologous series of organic compounds? State any two characteristics of homologous series. (b) Write the preceeding and succeeding homolgue of butane. (c) Write molecular, electron dot structure and structural formula of propene. Ans. (a) A series of compounds in which the same functional group substitutes for hydrogn in a carbon chain is called homologous series. Characteristics of homologous series (i) The molecular formulae of any two successive members of a homologous series differ by — CH2. (i) There is a regular gradation in physical properties of members of a homologous series. (b) Butane is C4H10. The preceeding homologue of butane is propane C3H8. The succeeding homologue of butane is pentane C3H6. (c) Molecular formula of propene is C3H6 Electron dot structure Structural formula 36. (a) List three contraceptive methods that have been developed to prevent pregnancy. State the basic principle involved in these methods. Which one of the techniques is (i) not meant for males? (ii) used to control sexually transmitted diseases? (b) Name two STDs caused by bacteria. Ans. (a) Different contraceptive methods are: Barrier method—Physical barriers like condoms worn over penis by males, diaphragm used by females, cervical cap and copper-T for females. Chemical method—Oral pills used by females. Surgical method—Portion of vas deferens in males (vasectomy) or portion of fallopian tube in females (tubectomy) is cut or ligated. Basic principle involved in all the contraceptive methods is to prevent fertilization of ovum and sperm. (i) use of oral pills is not meant for males. (ii) use of condoms by males also prevents sexually transmitted diseases. (b) Two STDs caused by bacteria are: Gonorrhoea and syphilis OR (a) Draw a longitudinal section of female reproductive part of a flower showing germination of pollen grain. Name and label on it the following: (i) where pollen grains land (ii) which ripens and forms fruit. (iii) which carries male gamete to the embryo sac. (b) Differentiate between pollination and fertilization. (c) Which type of tropism is it?—Growth of pollen tube towards ovule? Ans. (a) (b) Pollination 1. Transfer of pollen grains from anther to stigma. 2. Pollination occurs in higher plants only. 3. It is a physical process. (c) Chemotropism. Fertilization 1. The process of fusion of male gamete and female gamete resulting in the formation of zygote. 2. Fertilization occurs both in males and female. 3. It is a genetic and biochemical process. SECTION – E(Case Study Based Questions) Questions 37 to 39 carry 4 marks each. 37. A rainbow is one of the most spectacular natural light shows observed in the sky. A number of scientist and mathematician including Aristotle, Bacon, Theodoric, Descartes, Newton, Young, Airy and Mie have worked on the explanation of various observations on rainbows. To understand the formation of rainbow one should actually study the refraction, internal reflection, dispersion and total deviation of white light by the spherical water drop. A rainbow is produced when sunlight falls and gets diverted to the eyes of the observer due to a large number of water droplets in the sky on a rainy day. In addition to primary Rainbow there is a secondary rainbow. It occurs in the same manner as the primary rainbow but due to two internal reflections. In nature we can observe only primary and secondary rainbows. Higher order rainbows are never seen since they are weaker than (A) the background sky brightness (B) the light reflected from the outside surface of the drops and (C) the light transmitted through the process with no internal reflections. (a) What is refraction? (b) What is the shape of a rainbow? (c) List two essential conditions for observing a rainbow. OR (c) Why the red colour appears on the top of rainbow? Ans. (a) The phenomenon of change in the direction of propagation of light rays in the second medium when it enters obliquely from one transparent medium to another is called refraction of light. (b) Rainbow is an arc at a constant angle from the shadow of your head. So the shape is an arc along the circumference of a circle. (c) Necessary conditions for the formation of a rainbow. (i) The presence of water droplets in the atmosphere, and (ii) The sun must be at the back of the observer, i.e. the observer must stand with his back towards the sun. OR (c) Red has the longest wavelength among the visible colours. So, it tends to bend the least and the angle between the incident light and our line of sight for red is approximate 42 degrees. As a result, red appears on the top of the rainbow. 38. Anjali read that different metals are found in the earth’s crust which are in impure form. Elements or compounds which occur naturally in the earth’s crust are known as minerals. Minerals from which metals can be extracted profitably are called ores. She also read that: Metals can be separated out in pure form using various techniques leaving behind impurities. The extraction of metals from their ores profitably is called metallurgy. (a) Anjali’s Chemistry teacher explained that during extraction of metals, electrolytic refining is used to obtain pure metals. Name one metal refined by this method. (b) She wants to know which material is used as anode and cathode for refining of copper metal? Suggest her a suitable electrolyte also. In the electrolytic cell, where will she get pure copper after passing electric current? (c) Draw a diagram showing electrolytic refining of copper. OR (c) Observe the figure showing thermite reaction. What is thermite reaction? Where is it used? Ans. (a) Copper is refined by electrolytic refining. (b) Anode — Impure copper Cathode — A thin sheet of pure copper Electrolyte — Acidified solution of copper sulphate We get pure copper at cathode (c) OR A process of reduction of iron (III) oxide (Fe2O3) using aluminium powder as the reducing agent. This is an exothermic reaction. Iron obtained in this reaction is in molten state. Fe2O3(s) + 2 Al(s) 2Fe(l) + Al2O3(s) + Heat Thermite reaction is used to join railway tracks or cracked machine parts. 39. Respiratory disease causes an immense worldwide health burden. It is estimated that 235 million people suffer from asthma, more than 200 million people have chronic obstructive pulmonary disease (COPD), 65 million endure moderate-to-severe COPD, more than 100 million adult population experience sleep disordered breathing, 8.7 million people develop tuberculosis (TB) annually, millions live with pulmonary hypertension and more than 50 million people struggle with occupational lung diseases. At least 2 billion people are exposed to the toxic effects of biomass fuel consumption, 1 billion are exposed to outdoor air pollution and 1 billion are exposed to tobacco smoke. Each year, 4 million people die prematurely from chronic respiratory disease. Infants and young children are particularly susceptible. Nine million children under 5 years of age die annually and lung diseases are the most common causes of these deaths. Pneumonia is the world’s leading killer of young children. Asthma is the most common chronic disease, affecting about 14% of children globally and is still rising. COPD is the fourth leading cause of death worldwide and the numbers are growing. The most common lethal cancer in the world is lung cancer, which kills more than 1.4 million people each year, and the numbers are growing. Respiratory tract infections caused by influenza kill 250000–500000 people and cost 71–167 billion US dollars annually. Respiratory infections are ranked as the greatest single contributor to the overall burden of disease in the world. (a) Write one difference between respiration in plants and respiration in animals. (b) Define cilia. (c) How are lungs designed to maximize exchange of gases? OR (c) ‘While breathing cycle is rhythmic, exchange of gases is a continuous process.’ Justify. Ans. (a) Respiration in Plants: Plants do not have respiratory system. Respiration in animals: Animals have respiratory system. (b) These are the tiny hair like structures on cells in linings of many parts of respiratory system which removes dust, microbes and other harmful effluents from inhaled air. (c) In human being, to maximize the area for exchange of gases, inner surface of lungs has smaller tubes that terminate into balloon like structures called alveoli. The walls of alveoli have extensive network of blood vessels. OR (c) Even though the breathing cycle is rhythmic, the lungs always contain a residual volume of air so that absorption of oxygen and release of carbon dioxide becomes continuous.
