Plant Nutrition: Photosynthesis, Limiting Factors, Leaf Structure and Mineral Requirements

1. A plant is placed in bright light with plenty of water. Increasing carbon dioxide concentration at first increases the rate of photosynthesis, but later the rate becomes constant.
   What is the best explanation?

A carbon dioxide has denatured the chlorophyll
B another factor has become limiting
C oxygen concentration has become zero
D stomata have stopped diffusion permanently

2. Which word equation correctly represents photosynthesis?

A glucose + oxygen → carbon dioxide + water
B carbon dioxide + water → glucose + oxygen
C glucose + water → carbon dioxide + oxygen
D carbon dioxide + oxygen → glucose + water

3. A variegated leaf is destarched and then exposed to light. After testing with iodine, only the green regions turn blue-black.
   What does this show?

A chlorophyll is needed for starch formation
B oxygen is needed for starch formation
C carbon dioxide is released by chlorophyll
D starch is only made in white areas

4. A plant is kept in darkness for 48 hours before a photosynthesis experiment.
   Why is this done?

A to kill the chloroplasts
B to remove stored starch from the leaves
C to stop respiration permanently
D to increase the amount of chlorophyll

5. Which structure is the main site of photosynthesis in a leaf?

A cuticle
B palisade mesophyll cell
C xylem vessel
D stomatal pore

6. Which row correctly matches a leaf structure with its function?

A waxy cuticle: absorbs carbon dioxide
B palisade mesophyll: absorbs most light for photosynthesis
C xylem: transports sucrose away from leaf
D phloem: transports water to leaf cells

7. A leaf is boiled in water and then heated in ethanol before iodine is added.
   Why is the leaf heated in ethanol?

A to remove starch
B to remove chlorophyll
C to soften the cell wall
D to test for reducing sugar

8. A student places a pondweed in water and counts bubbles produced per minute.
   Which assumption makes this method less reliable?

A each bubble contains the same volume of gas
B oxygen is produced during photosynthesis
C light intensity affects photosynthesis
D carbon dioxide is needed for photosynthesis

9. Which factor is most likely limiting photosynthesis when increasing light intensity no longer increases the rate?

A light intensity
B carbon dioxide concentration or temperature
C chlorophyll has become glucose
D water has become oxygen only

10. A plant is placed in a sealed container with potassium hydroxide, which absorbs carbon dioxide. The plant receives light for several hours.
    What result is expected when the leaf is tested with iodine?

A blue-black because light is present
B brown because carbon dioxide is absent
C purple because protein is present
D brick-red because oxygen is present

11. Which mineral ion is needed to make chlorophyll?

A nitrate
B magnesium
C phosphate
D calcium

12. A plant lacking nitrate ions shows poor growth and yellowing of older leaves.
    Which explanation is most accurate?

A nitrate is needed to make amino acids and proteins
B nitrate is needed to make cellulose cell walls only
C nitrate is needed directly to absorb light
D nitrate is needed to produce oxygen gas

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Which statement about chlorophyll is correct?

A it absorbs light energy for photosynthesis
B it is the gas released during photosynthesis
C it is the sugar made during photosynthesis
D it transports water through xylem

14. A plant is illuminated with green light only. Photosynthesis is slower than in red or blue light.
    Why?

A green light is mostly reflected by chlorophyll
B green light contains no energy
C chlorophyll absorbs only oxygen in green light
D green light destroys carbon dioxide

15. Which tissue transports sucrose from leaves to other parts of the plant?

A xylem
B phloem
C epidermis
D palisade mesophyll

16. A leaf has many air spaces in its spongy mesophyll.
    What is the main advantage?

A they store starch permanently
B they allow faster diffusion of gases
C they prevent all water loss
D they transport mineral ions

17. Which statement correctly describes the role of stomata?

A they allow gas exchange and can affect water loss
B they transport glucose through the plant
C they absorb light energy for photosynthesis
D they carry water from roots to leaves

18. Which condition would produce the fastest rate of photosynthesis?

A low light, low carbon dioxide, low temperature
B high light, high carbon dioxide, suitable temperature
C high light, no carbon dioxide, suitable temperature
D no light, high carbon dioxide, suitable temperature

19. A student tests a leaf for starch but forgets to decolourise it.
    Why is this a problem?

A iodine cannot enter cells
B green chlorophyll may hide the iodine colour change
C starch will turn into glucose
D the leaf will stop containing cellulose

20. Which statement about the products of photosynthesis is correct?

A oxygen is used to make amino acids directly
B glucose may be converted into starch for storage
C carbon dioxide is released as a waste product
D water is made from chlorophyll

21. A plant has a low magnesium supply.
    Which process is most directly reduced first?

A chlorophyll production
B protein digestion
C oxygen diffusion into roots
D starch breakdown by amylase

22. Which row correctly shows raw materials and products of photosynthesis?

A raw materials: glucose and oxygen; products: carbon dioxide and water
B raw materials: carbon dioxide and water; products: glucose and oxygen
C raw materials: starch and oxygen; products: water and protein
D raw materials: chlorophyll and light; products: carbon dioxide and water

23. Which statement best explains why a leaf is thin?

A to reduce the distance for diffusion of gases
B to increase the distance travelled by carbon dioxide
C to prevent light reaching palisade cells
D to stop oxygen from leaving the leaf

24. A leaf has most stomata on the lower epidermis.
    What is the main advantage?

A reduced water loss while still allowing gas exchange
B increased direct sunlight absorption by stomata
C prevention of all oxygen diffusion
D increased transport of sucrose in xylem

25. Which cells contain the most chloroplasts in a typical leaf?

A upper epidermal cells
B palisade mesophyll cells
C xylem vessels
D guard cells only

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. A destarched plant has one leaf partly covered with black paper and is then placed in bright light.
    After testing, only the uncovered part turns blue-black.
    What does this show?

A carbon dioxide is needed for photosynthesis
B light is needed for photosynthesis
C chlorophyll is not needed for photosynthesis
D water is produced during photosynthesis

27. Which graph shape is expected when rate of photosynthesis is plotted against light intensity, while carbon dioxide and temperature are not limiting?

A decreases continuously
B increases then levels off
C remains zero at all light intensities
D increases only after light intensity becomes zero

28. Which substance is used to absorb carbon dioxide in a photosynthesis experiment?

A iodine solution
B Benedict’s solution
C potassium hydroxide
D ethanol

29. Why is a plant destarched before testing whether light is needed for photosynthesis?

A so any starch found after the experiment must have been made during the experiment
B so all chlorophyll is removed before light exposure
C so the leaf cannot respire during the experiment
D so carbon dioxide cannot enter the leaf

30. Which statement about photosynthesis and respiration in plants is correct?

A photosynthesis occurs all the time; respiration only occurs in darkness
B respiration occurs all the time; photosynthesis only occurs when light is available
C both occur only in green leaves during daylight
D neither occurs in roots

31. In bright light, a green plant takes in more carbon dioxide than it releases.
    What does this show?

A respiration has stopped
B photosynthesis is occurring faster than respiration
C the plant is dead
D carbon dioxide is not used in photosynthesis

32. Which environmental factor usually affects enzyme activity in photosynthesis most directly?

A temperature
B colour of the pot
C thickness of the soil
D mass of the beaker

33. A student increases temperature from 20 °C to 35 °C and the rate of photosynthesis increases. Increasing it to 60 °C causes the rate to fall sharply.
    What explains the fall at 60 °C?

A enzymes involved in photosynthesis may denature
B carbon dioxide becomes starch directly
C chloroplasts become xylem
D light intensity becomes zero

34. Which statement about glucose made in photosynthesis is correct?

A it must always remain as glucose in the leaf
B it can be used in respiration, stored as starch, or converted into other substances
C it is only used to make oxygen
D it is immediately excreted through stomata

35. Which feature of the upper epidermis helps light reach photosynthetic cells?

A it is usually transparent
B it contains many xylem vessels
C it contains most of the leaf’s chloroplasts
D it is made of dead hollow tubes

36. Which statement about limiting factors is correct?

A the limiting factor is always light intensity
B the limiting factor is the factor in shortest supply that restricts the rate
C limiting factors only occur in darkness
D limiting factors are not relevant to photosynthesis

37. A pondweed experiment is repeated at different distances from a lamp.
    Which variable is being changed?

A carbon dioxide concentration
B light intensity
C temperature of the plant only
D oxygen concentration inside xylem

38. Why should a heat filter or water bath be used between a lamp and pondweed?

A to keep temperature controlled so light intensity is the main variable
B to remove carbon dioxide from water
C to stop oxygen being produced
D to make chlorophyll dissolve faster

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Which adaptation of palisade mesophyll cells increases photosynthesis?

A many chloroplasts near the upper surface of the leaf
B no cytoplasm so light can pass through
C thick waterproof walls preventing gas exchange
D absence of vacuoles to store water

40. Which statement about guard cells is correct?

A they can change shape to open and close stomata
B they transport sucrose from leaves to roots
C they are dead cells with lignified walls
D they contain no chloroplasts in any plant

41. A student removes a leaf from a plant and immediately tests it with iodine. It turns blue-black.
    Why does this not prove photosynthesis occurred during the experiment?

A the starch may have been made before the experiment
B iodine always turns blue-black in leaves
C all leaves contain protein
D chlorophyll reacts directly with iodine

42. Which molecule formed from glucose contains nitrogen and therefore requires nitrate ions?

A starch
B cellulose
C amino acid
D lipid

43. Which statement about photosynthesis is correct?

A light energy is converted into chemical energy in glucose
B chemical energy in glucose is converted into light energy
C oxygen is converted into carbon dioxide by chloroplasts
D starch is converted into chlorophyll using oxygen

44. A plant is grown with sufficient light, water and carbon dioxide but without magnesium ions.
    What is the likely long-term effect?

A leaves become yellow and photosynthesis decreases
B leaves become darker green and photosynthesis increases
C glucose production increases because magnesium is toxic
D stomata permanently close because magnesium absorbs oxygen

45. Which factor is least likely to limit photosynthesis under normal conditions?

A carbon dioxide concentration
B light intensity
C temperature
D nitrogen gas concentration in air

46. Which statement explains why plants need mineral ions?

A to make substances such as proteins and chlorophyll
B to provide light energy directly
C to replace carbon dioxide in photosynthesis
D to stop all respiration

47. A student tests for starch in a green leaf. Which sequence is correct?

A iodine → ethanol → boiling water → rinse → observe
B boiling water → ethanol → rinse → iodine → observe
C Benedict’s → heat → iodine → ethanol → observe
D ethanol → iodine → boiling water → Benedict’s → observe

48. A leaf is boiled in water before being placed in ethanol.
    Why?

A to kill the leaf and make membranes more permeable
B to remove all glucose from the leaf
C to absorb carbon dioxide
D to turn starch into protein

49. Which statement correctly compares xylem and phloem in relation to plant nutrition?

A xylem transports sucrose; phloem transports water
B xylem transports water and mineral ions; phloem transports sucrose and amino acids
C both transport oxygen only
D both are mainly used to absorb light

50. In a photosynthesis experiment, a plant produces bubbles faster when sodium hydrogencarbonate is added to the water.
    Why?

A it increases carbon dioxide availability
B it removes all oxygen from the water
C it denatures photosynthetic enzymes
D it blocks light from reaching chloroplasts

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1. Answer: B
   A is wrong because carbon dioxide does not denature chlorophyll.
   B is correct because once carbon dioxide is no longer limiting, another factor such as light intensity or temperature limits the rate.
   C is wrong because oxygen concentration does not become zero during photosynthesis.
   D is wrong because stomata do not permanently stop diffusion just because carbon dioxide increases.

2. Answer: B
   A is wrong because it shows respiration, not photosynthesis.
   B is correct because photosynthesis uses carbon dioxide and water to make glucose and oxygen.
   C is wrong because glucose is not a raw material of photosynthesis.
   D is wrong because oxygen is not a raw material; it is a product.

3. Answer: A
   A is correct because only green areas contain chlorophyll, and only those areas made starch.
   B is wrong because the experiment tests chlorophyll, not oxygen requirement.
   C is wrong because chlorophyll does not release carbon dioxide during photosynthesis.
   D is wrong because starch is made in green areas, not white areas.

4. Answer: B
   A is wrong because darkness does not kill chloroplasts.
   B is correct because keeping the plant in darkness uses up stored starch in respiration.
   C is wrong because respiration continues in darkness.
   D is wrong because darkness does not increase chlorophyll.

5. Answer: B
   A is wrong because the cuticle mainly reduces water loss.
   B is correct because palisade mesophyll cells contain many chloroplasts and are the main photosynthetic cells.
   C is wrong because xylem transports water and mineral ions.
   D is wrong because stomata allow gas exchange; they are not the main site of photosynthesis.

6. Answer: B
   A is wrong because the waxy cuticle reduces water loss, not absorbs carbon dioxide.
   B is correct because palisade mesophyll absorbs most light due to many chloroplasts.
   C is wrong because xylem transports water and mineral ions, not sucrose.
   D is wrong because phloem transports sucrose and amino acids, not water.

7. Answer: B
   A is wrong because ethanol removes chlorophyll, not starch.
   B is correct because ethanol decolourises the leaf so the iodine colour change can be seen clearly.
   C is wrong because boiling water softens/kills the leaf first, not ethanol’s main role.
   D is wrong because Benedict’s solution is used for reducing sugar, not ethanol.

8. Answer: A
   A is correct because counting bubbles assumes each bubble has the same volume, which may not be true.
   B is true biologically, but it does not make the method less reliable.
   C is true, but not the weakness in bubble counting.
   D is true, but not the assumption causing unreliability.

9. Answer: B
   A is wrong because light intensity is no longer limiting if increasing it has no effect.
   B is correct because carbon dioxide concentration or temperature may now be limiting.
   C is nonsense because chlorophyll does not become glucose.
   D is wrong because water does not become oxygen only.

10. Answer: B
    A is wrong because light alone is not enough for photosynthesis.
    B is correct because potassium hydroxide absorbs carbon dioxide, so photosynthesis cannot make starch.
    C is wrong because purple is a protein test result, not an iodine result.
    D is wrong because brick-red is a Benedict’s result, not a starch test result.

11. Answer: B
    A is wrong because nitrate is needed to make amino acids and proteins.
    B is correct because magnesium ions are needed to make chlorophyll.
    C is wrong because phosphate is mainly linked with DNA, ATP and membranes.
    D is wrong because calcium is not the key ion for chlorophyll.

12. Answer: A
    A is correct because nitrate ions are needed to make amino acids, which are used to make proteins for growth.
    B is wrong because nitrate is not mainly for cellulose cell walls.
    C is wrong because nitrate does not directly absorb light; chlorophyll does.
    D is wrong because nitrate is not used to produce oxygen gas directly.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

13. Answer: A
    A is correct because chlorophyll absorbs light energy for photosynthesis.
    B is wrong because oxygen is the gas released.
    C is wrong because glucose is the sugar made.
    D is wrong because xylem transports water, not chlorophyll.

14. Answer: A
    A is correct because chlorophyll reflects much green light and absorbs red/blue light better.
    B is wrong because green light still has energy.
    C is wrong because chlorophyll does not absorb oxygen.
    D is wrong because green light does not destroy carbon dioxide.

15. Answer: B
    A is wrong because xylem transports water and mineral ions.
    B is correct because phloem transports sucrose from leaves to other parts of the plant.
    C is wrong because epidermis is a protective tissue.
    D is wrong because palisade mesophyll mainly photosynthesises.

16. Answer: B
    A is wrong because air spaces are not mainly for permanent starch storage.
    B is correct because air spaces allow faster diffusion of gases such as carbon dioxide and oxygen.
    C is wrong because air spaces do not prevent all water loss.
    D is wrong because mineral ions are transported mainly through xylem.

17. Answer: A
    A is correct because stomata allow gas exchange and also affect water loss by transpiration.
    B is wrong because phloem transports glucose/sucrose.
    C is wrong because chlorophyll absorbs light energy.
    D is wrong because xylem carries water from roots to leaves.

18. Answer: B
    A is wrong because all three conditions are low, so photosynthesis will be slow.
    B is correct because high light, high carbon dioxide and suitable temperature give a fast rate.
    C is wrong because no carbon dioxide means photosynthesis cannot proceed properly.
    D is wrong because no light means photosynthesis cannot occur.

19. Answer: B
    A is wrong because iodine can still enter after proper preparation.
    B is correct because green chlorophyll can hide the blue-black iodine colour change.
    C is wrong because forgetting ethanol does not turn starch into glucose.
    D is wrong because cellulose does not disappear.

20. Answer: B
    A is wrong because oxygen is released or used in respiration, not directly used to make amino acids.
    B is correct because glucose may be converted into starch for storage.
    C is wrong because carbon dioxide is a raw material of photosynthesis, not its waste product.
    D is wrong because water is not made from chlorophyll.

21. Answer: A
    A is correct because magnesium is needed for chlorophyll production.
    B is wrong because magnesium deficiency does not directly reduce protein digestion in leaves.
    C is wrong because oxygen diffusion into roots is not the first direct effect.
    D is wrong because starch breakdown by amylase is not the most direct effect.

22. Answer: B
    A is wrong because glucose and oxygen are products of photosynthesis, not raw materials.
    B is correct because carbon dioxide and water are raw materials, while glucose and oxygen are products.
    C is wrong because starch and oxygen are not the raw materials.
    D is wrong because chlorophyll and light are conditions/factors, not raw materials.

23. Answer: A
    A is correct because a thin leaf reduces diffusion distance for gases.
    B is wrong because increasing diffusion distance would slow gas exchange.
    C is wrong because thin leaves help light reach palisade cells.
    D is wrong because oxygen must be able to diffuse out.

24. Answer: A
    A is correct because stomata mainly on the lower surface reduce water loss while still allowing gas exchange.
    B is wrong because stomata do not mainly absorb sunlight.
    C is wrong because oxygen diffusion is not prevented.
    D is wrong because sucrose is transported in phloem, not xylem.

25. Answer: B
    A is wrong because upper epidermal cells usually have few or no chloroplasts.
    B is correct because palisade mesophyll cells contain the most chloroplasts in a typical leaf.
    C is wrong because xylem vessels are dead and contain no chloroplasts.
    D is wrong because guard cells have chloroplasts, but not the most in the leaf.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. Answer: B
    A is wrong because carbon dioxide was not the variable being tested.
    B is correct because only the part exposed to light made starch, proving light is needed.
    C is wrong because the experiment does not show chlorophyll is unnecessary.
    D is wrong because the iodine test shows starch, not water production.

27. Answer: B
    A is wrong because rate does not usually decrease continuously as light increases.
    B is correct because rate increases with light intensity at first, then levels off when another factor becomes limiting.
    C is wrong because photosynthesis does not remain zero at all light intensities.
    D is wrong because photosynthesis does not increase after light becomes zero.

28. Answer: C
    A is wrong because iodine tests for starch.
    B is wrong because Benedict’s tests for reducing sugar.
    C is correct because potassium hydroxide absorbs carbon dioxide.
    D is wrong because ethanol removes chlorophyll.

29. Answer: A
    A is correct because destarching ensures any starch detected was made during the experiment.
    B is wrong because destarching does not remove chlorophyll.
    C is wrong because respiration still occurs.
    D is wrong because destarching does not block carbon dioxide entry.

30. Answer: B
    A is wrong because photosynthesis needs light and does not occur all the time.
    B is correct because respiration occurs all the time, while photosynthesis occurs only when light is available.
    C is wrong because respiration occurs in roots too.
    D is wrong because roots respire, although they usually do not photosynthesise.

31. Answer: B
    A is wrong because respiration has not stopped; plants respire continuously.
    B is correct because net carbon dioxide uptake means photosynthesis is faster than respiration.
    C is wrong because a dead plant would not actively photosynthesise.
    D is wrong because carbon dioxide is used in photosynthesis.

32. Answer: A
    A is correct because temperature affects enzyme activity in photosynthesis.
    B is wrong because pot colour does not directly affect photosynthetic enzyme activity.
    C is wrong because soil thickness is not the direct enzyme factor.
    D is wrong because beaker mass is irrelevant.

33. Answer: A
    A is correct because high temperature may denature enzymes involved in photosynthesis, reducing the rate.
    B is wrong because carbon dioxide does not directly become starch.
    C is nonsense because chloroplasts do not become xylem.
    D is wrong because the light intensity has not become zero.

34. Answer: B
    A is wrong because glucose does not always remain as glucose.
    B is correct because glucose can be used in respiration, stored as starch, or converted into cellulose, lipids or amino acids.
    C is wrong because glucose is not only used to make oxygen.
    D is wrong because glucose is not immediately excreted through stomata.

35. Answer: A
    A is correct because the upper epidermis is usually transparent, allowing light to reach palisade cells.
    B is wrong because xylem vessels are in vascular bundles, not mainly upper epidermis.
    C is wrong because most chloroplasts are in palisade mesophyll cells.
    D is wrong because dead hollow tubes describe xylem vessels.

36. Answer: B
    A is wrong because the limiting factor is not always light.
    B is correct because the limiting factor is the factor in shortest supply that restricts the rate.
    C is wrong because limiting factors can occur in light too.
    D is wrong because limiting factors are central to photosynthesis rate.

37. Answer: B
    A is wrong because carbon dioxide concentration is not directly changed by lamp distance.
    B is correct because changing distance from the lamp changes light intensity.
    C is wrong because temperature might accidentally change, but it is not the intended variable.
    D is wrong because oxygen concentration inside xylem is irrelevant.

38. Answer: A
    A is correct because lamps can heat the water, so a heat filter helps keep temperature controlled while light intensity is tested.
    B is wrong because a heat filter does not remove carbon dioxide.
    C is wrong because it does not stop oxygen production.
    D is wrong because chlorophyll is not meant to dissolve.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.

39. Answer: A
    A is correct because palisade mesophyll cells have many chloroplasts near the upper surface to absorb light efficiently.
    B is wrong because palisade cells have cytoplasm.
    C is wrong because thick waterproof walls would reduce gas exchange.
    D is wrong because palisade cells usually have vacuoles.

40. Answer: A
    A is correct because guard cells change shape to open and close stomata.
    B is wrong because phloem transports sucrose.
    C is wrong because guard cells are living, not dead lignified cells.
    D is wrong because guard cells often contain chloroplasts.

41. Answer: A
    A is correct because the starch may have been produced before the experiment began.
    B is wrong because iodine does not always turn blue-black in leaves.
    C is wrong because protein is tested with Biuret, not iodine.
    D is wrong because chlorophyll does not directly give a blue-black iodine result.

42. Answer: C
    A is wrong because starch contains carbon, hydrogen and oxygen only.
    B is wrong because cellulose contains carbon, hydrogen and oxygen only.
    C is correct because amino acids contain nitrogen and require nitrate ions for their production.
    D is wrong because lipids usually contain carbon, hydrogen and oxygen, not nitrogen.

43. Answer: A
    A is correct because photosynthesis converts light energy into chemical energy stored in glucose.
    B is wrong because that is the reverse idea and does not describe photosynthesis.
    C is wrong because oxygen is not converted into carbon dioxide by chloroplasts in photosynthesis.
    D is wrong because starch is not converted into chlorophyll using oxygen.

44. Answer: A
    A is correct because without magnesium, chlorophyll production decreases, leaves may become yellow and photosynthesis falls.
    B is wrong because lack of magnesium makes leaves less green, not darker green.
    C is wrong because magnesium is needed, not toxic in normal amounts.
    D is wrong because magnesium does not absorb oxygen to control stomata.

45. Answer: D
    A is wrong because carbon dioxide concentration often limits photosynthesis.
    B is wrong because light intensity often limits photosynthesis.
    C is wrong because temperature affects photosynthetic enzyme activity.
    D is correct because plants cannot directly use nitrogen gas from the air for photosynthesis, so it is least likely to limit photosynthesis rate.

46. Answer: A
    A is correct because mineral ions are needed to make substances such as proteins, chlorophyll, DNA and ATP.
    B is wrong because minerals do not provide light energy directly.
    C is wrong because minerals do not replace carbon dioxide in photosynthesis.
    D is wrong because plants always need respiration.

47. Answer: B
    A is wrong because iodine should be added after boiling, ethanol treatment and rinsing.
    B is correct: boiling water → ethanol → rinse → iodine → observe.
    C is wrong because Benedict’s is not used in the starch test.
    D is wrong because ethanol should not come before killing/softening the leaf in boiling water.

48. Answer: A
    A is correct because boiling kills the leaf and makes membranes more permeable so later chemicals can enter.
    B is wrong because boiling does not remove all glucose.
    C is wrong because potassium hydroxide absorbs carbon dioxide, not boiling water.
    D is wrong because boiling does not turn starch into protein.

49. Answer: B
    A is wrong because it reverses xylem and phloem.
    B is correct because xylem transports water and mineral ions, while phloem transports sucrose and amino acids.
    C is wrong because neither transports only oxygen.
    D is wrong because they do not absorb light.

50. Answer: A
    A is correct because sodium hydrogencarbonate increases carbon dioxide availability in the water, increasing photosynthesis.
    B is wrong because it does not remove all oxygen.
    C is wrong because it does not denature enzymes in this context.
    D is wrong because it does not block light from reaching chloroplasts.

Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 11 World Records and 7 Distinctions, Educate A Change.