Photosynthesis in higher plants Sample paper

Q1. Consider the following statements regarding photosynthesis: A. ATP formation during photosynthesis is termed photophosphorylation. B. Kranz anatomy pertains to leaf. C. Reduction of NADP⁺ to NADPH occurs during the Calvin cycle. D. In a chlorophyll molecule, magnesium is present in the phytol tail Of the above statements,

• 1) A and B are correct.
• 2) A and C are correct.
• 3) C and D are correct.
• 4) B and C are correct.
• 5) A and D are correct.

Solution

ATP and NADPH are formed during the light reaction phase (photophosphorylation), which is used during the dark reactions for the fixation of CO₂ and the synthesis of sugars. Kranz anatomy is a specialised anatomy of the leaves of C₄ plants where the vascular bundle is surrounded by bundle sheath cells, which in turn are surrounded by mesophyll cells.

Q2. Which range of wavelength (in nm) is called photosynthetically active radiation (PAR)?

• 1) 400-700
• 2) 760-10,000
• 3) 390-430
• 4) 100-390

Solution

400-700 nm is the range of visible light in the electromagnetic spectrum. Plants respond to and use only visible light for photosynthesis. 680 nm and 700 nm light wavelengths are the most important for photosynthesis.

Q3. When CO₂ is added to PEP, the first stable product synthesised is

• 1) Pyruvate
• 2) Glyceraldehyde-3-phosphate
• 3) Phosphoglycerate
• 4) Oxaloacetate

Solution

Oxaloacetate is the first stable product formed through the fixation of CO₂ in C₄ plants. In the C₄ pathway, PEP, the primary CO₂ acceptor, is present in the mesophyll cell. PEP by CO₂ in the presence of the enzyme PEPCase is converted to oxaloacetic acid which is further converted to malic acid or aspartic acid and transported to the bundle sheath cells where the Calvin cycle takes place.

Q4. Blue and red light roughly resemble the absorption spectrum of

• 1) Chlorophyll a
• 2) Accessory pigments
• 3) Chlorophyll a and b
• 4) Chlorophyll b

Solution

Blue and red light roughly resemble the absorption spectrum of chlorophyll a and b.

Q5. Which is the primary CO₂ acceptor in C₄ plants?

Solution

The primary CO₂ acceptor in C₄ plants is the 3-carbon molecule phosphoenol pyruvate (PEP).

Q6. How many turns does the Calvin cycle take for the generation of one molecule of glucose?  

• 1) 8  
• 2) 2  
• 3) 6  
• 4) 4  

Solution

Each turn of the Calvin cycle generates one molecule of carbon. Because a glucose molecule is a 6-carbon compound, the cycle goes about 6 times for the synthesis of one molecule of glucose.  

Q7. A photosynthesising plant is releasing ¹⁸O more than the normal amounts; thus, the plant must be supplied with  

• 1) C₆H₁₂O₆ with ¹⁸O  
• 2) O₃  
• 3) CO₂­ with ¹⁸O  
• 4) H₂O with ¹⁸O

Solution

Ruben, Hassid and Kamen, using an isotope of oxygen (¹⁸O) in water, found that oxygen evolved during photosynthesis comes from water.  

Q8. The total amount of incident light absorbed by leaves of plants is

• 1) 80%
• 2) 100%
• 3) 10%
• 4) 50%

Solution

Of the total light incident on the leaf, about 80% is absorbed, 10% is reflected and 10% is transmitted.

Q9. Describe the experiment performed by T. W. Engelmann to determine the first action spectrum of photosynthesis.

Solution

Engelmann used a prism to split light into its spectral components, and then illuminated a green alga, Cladophora, placed in a suspension of aerobic bacteria. The bacteria were used to detect the sites of oxygen evolution. He observed that bacteria mainly accumulated in the region of blue and red light of the split spectrum, thus giving the first action spectrum of photosynthesis.

Q10. The correct sequence of cell organelles during photo respiration is  

• 1) Chloroplast – Mitochondria – Peroxisomes  
• 2) Chloroplast – Rough endoplasmic reticulum – Dictyosomes  
• 3) Chloroplast – Golgi bodies – Mitochondria  
• 4) Chloroplast – Vacuole – Peroxisome  

Solution

The first stage of photorespiration involves the formation of glycolate in the chloroplasts. Further reactions of the glycolate pathway occur in the mitochondria and peroxisomes, and eventually, a compound is formed which is returned to the chloroplasts, where the process began.  

Q11. Give the equation for photolysis of water and give the fate of each of the products so formed.

Solution

2H₂O ————› 4H⁺ + O₂ + 4e⁻ The products so formed are H⁺/protons – These are used for the reduction of NADP to NADPH. Oxygen – It is liberated in the air and replenishes oxygen in the environment. Electrons – These are used to replace electrons lost by PS II.

Q12. The hydrogen donor for purple and green sulphur bacteria is  

• 1) HCl  
• 2) H₂S  
• 3) H₂O  
• 4) H₂SO₄  

Solution

H₂S serves as a hydrogen donor in purple and green sulphur bacteria. The oxidation product thus released is either sulphur or sulphate instead of oxygen.  

Q13. C₅₅H₇₂O₅N₄Mg is the chemical formula for which photosynthetic pigment?  

• 1) Carotene  
• 2) Xanthophyll  
• 3) Chlorophyll b  
• 4) Chlorophyll a  

Solution

The chemical formula of chlorophyll a is C₅₅H₇₂O₅N₄Mg, while that of chlorophyll b is C₅₅H₇₀O₆N₄Mg.  

Q14. Who demonstrated the importance of sunlight for the process of photosynthesis?  

• 1) Robert Hill  
• 2) Engelmann  
• 3) Jan Ingenhousz  
• 4) Joseph Priestley  

Solution

Jan Ingenhousz conducted the experiment with the same setup as that used by Joseph Priestley to determine the importance of air for photosynthesis; however, instead of placing the setup in light, he placed it in dark. He observed that the plant could not help keep the candle burning.  

Q15. What do ATP and NADPH stand for?

Solution

ATP – Adenosine triphosphate NADPH – Nicotinamide adenine dinucleotide phosphate

Q16. How is oxygen produced during photosynthesis?

Solution

During non-cyclic photophosphorylation, PS I passes its electron to NADP⁺ for the production of NADPH + H⁺. This lost electron of PS I is obtained from PS II, which in turn obtains its electron from the splitting of water. When the water molecule is split to provide an electron to PS II, it produces protons as well as oxygen which is released out as a molecule of oxygen.

Q17. The creation of proton gradient across the thylakoid membrane is a result of  

• 1) Decrease in pH in the stroma  
• 2) Accumulation of protons in the stroma  
• 3) Decrease in proton number in the stroma  
• 4) Increase in pH in the lumen  

Solution

The proton gradient is generated due to the accumulation of protons on the inner side of the lumen and a decrease in pH on the lumen side of the thylakoid membrane.  

Q18. What are pigments? Name the types of pigments found in the leaf of a green plant?

Solution

Pigments are substances which can absorb light. The four major pigments found in the leaves of green plants are Chlorophyll a Chlorophyll b Xanthophylls Carotenoids   

Q19. On an average, the light duration for a plant is

• 1) 10-12 hrs/day
• 2) 4-5 hrs/day
• 3) 12-14 hrs/day
• 4) 8-10 hrs/day

Solution

On an average, the light duration for a plant is 10-12 hrs/day.

Q20. Structurally, chlorophyll a and b are different as  

• 1) Chl a has an aldehyde group and Chl b has a methyl group.  
• 2) Chl a has a carboxyl group and Chl b has an aldehyde group.  
• 3) Chl a has a methyl group and Chl b has an aldehyde group.  
• 4) Chl a has an ethyl group and Chl b has an aldehyde group.  

Solution

Chl a has a methyl group (-CH₃) and Chl b has an aldehyde group (-CHO) in its structure.  

Q21. Which light range is most effective in photosynthesis?  

• 1) Red  
• 2) Violet  
• 3) Blue  
• 4) Green  

Solution

Red light is more effective in photosynthesis because both the photosystems (PS I and PS II) absorb light of wavelengths in the red region (680 and 700 nm, respectively). Furthermore, blue light is absorbed by carotenoids, which pass the energy to the chlorophyll, whereas the light in the red region is absorbed by chlorophyll.  

Q22. The active component of photosystem I is composed of

• 1) Chlorophyll a with absorption peak at 680 nm
• 2) Chlorophyll a and h with absorption peak at 700 nm
• 3) Chlorophyll a with absorption peak at 700 nm
• 4) Chlorophyll h with absorption peak at 680 nm

Solution

The chlorophyll a reaction centre for PS I has an absorption maxima peak at 700 nm.

Q23. Which pigment acts directly to convert light energy to chemical energy?

• 1) Carotenoid
• 2) Chlorophyll a
• 3) Chlorophyll b
• 4) Xanthophyll

Solution

Chlorophyll a is the reaction centre for photosynthesis and directly converts light energy to chemical energy.

Q24. A reduction in the quantity of oxygen evolution during photosynthesis may be observed at  

• 1) Light with wave length more than 680 nm  
• 2) Light with wave length 560 nm  
• 3) Light with wave length less than 680 nm  
• 4) Light with wave length less than 360 nm  

Solution

The photosynthetically active radiation (PAR) is the radiation range in which photosynthesis can occur. PAR ranges from 400 to 700 nm. Wavelengths below 360 nm do not fall under PAR, and hence, photosynthesis cannot occur, thus resulting in reduction in the quantity of oxygen evolved during photosynthesis.  

Q25. Which one does not occur in cyclic photophosphorylation?

• 1) Oxygen is not given off
• 2) NADPH formation
• 3) Water is not consumed
• 4) Only photosystem I is involved

Solution

NADPH formation does not take place in cyclic photophosphorylation. In this pathway, only a single molecule of ATP is synthesised.

Q26. Which one of the following is wrong in relation to photorespiration?

• 1) It is characteristic of C₃ plants.
• 2) It is characteristic of C₄ plants.
• 3) It occurs in daytime only.
• 4) It occurs in chloroplast.

Solution

RuBisCO has both carboxylase and oxygenase activity. When the concentration of CO₂ is high, it shows carboxylase activity leading to the Calvin cycle, and when the concentration of O₂ is high, it shows oxygenase activity leading to photorespiration. Photorespiration does not occur in C₄ plants; this is because they have a mechanism for increasing the concentration of CO₂ at the site of the RuBisCO enzyme.

Q27. Which cyclic process is involved in dark reactions? Give the balanced equation for the same.

Solution

Calvin cycle: 6CO₂ + 18ATP + 12NADPH ———› Glucose + 18ADP + 12 NADP + 18P_i  

Q28. What is common between chloroplasts, chromoplasts and leucoplasts?  

• 1) Possession of thylakoids and grana  
• 2) Storage of starch, proteins and lipids  
• 3) Ability to multiply by a fission-like process  
• 4) Presence of pigments  

Solution

Chloroplast, chromoplast and leucoplast are plastids and have the ability to multiply by a fission-like process before they are fully mature.  

Q29. Electrons from an excited chlorophyll molecule of photosystem II are accepted first by  

• 1) quinone  
• 2) Cytochrome-b              
• 3) ferredoxin  
• 4) cytochrome-f     

Solution

Quinine is the first electron acceptor for electrons given out by photosystem II.

Q30. Stomata of CAM plants

• 1) Open during the day and close at night
• 2) Open during the night and close during the day
• 3) Never open
• 4) Are always open

Solution

The CAM cycle is an adaptation in succulent plants. In plants with the CAM cycle, the stomata remain close during the day and open during the night. This helps in preventing loss of water due to transpiration.

Q31. Describe Jan Ingenhousz experiment to determine the importance of sunlight for photosynthesis.

Solution

Jan Ingenhousz used an aquatic plant for his experiment. He observed that small bubbles were released in the presence of sunlight, while no bubbles were released in the dark. These bubbles when tested were of oxygen, which was released during photosynthesis. Thus, his experiment suggested that sunlight was important for photosynthesis.

Q32. Energy released during the movement of electrons through the photosystems in photosynthesis is used to drive protons across the membrane against the concentration gradient. As a result, the protons accumulate in  

• 1) Intrathylakoid space  
• 2) Thylakoid lumen  
• 3) Stroma  
• 4) Stroma lamella  

Solution

Splitting of water and transport of electrons through the series of electron acceptors result in the pumping of protons in the thylakoid lumen which results in the generation of a proton gradient across the thylakoid lumen.  

Q33. T. W. Engelmann used which organism in his experiments for determining the role of red and blue light in photosynthesis?

• 1) Green algae
• 2) Red algae
• 3) Blue algae
• 4) Blue-green algae

Solution

T. W. Engelmann used the green alga Cladophora in his experiments for determining the role of red and blue light in photosynthesis.

Q34. In PS-II, the first known electron acceptor is  

• 1) Cytochrome  
• 2) Pheophytin  
• 3) FRS  
• 4) PQ  

Solution

Pheophytin is the primary electron acceptor for PS II. It picks up the electron given out by P₆₈₀ and passes it to the next electron acceptor plastoquinone, which further passes it to the cytochrome complex.  

Q35. Chloroplast dimorphism is a characteristic feature of

• 1) All plants
• 2) Only in algae
• 3) Plants with the Calvin cycle
• 4) C₄ plants

Solution

C₄ plants are different from C₃ and CAM plants in the sense that they possess two types of chloroplasts, found in two different cell types. The chloroplasts found in mesophyll cells possess grana, while those found in bundle sheath cells are agranal.

Q36. The amount of which of the following factors does not affect the rate of photosynthesis?

• 1) Chlorophyll
• 2) Light
• 3) Air pollutants
• 4) CO₂

Solution

Chlorophyll is important for photosynthesis. However, the amount of chlorophyll does not determine the rate of photosynthesis.

Q37. Name the site for the following in C₄ plants: PEP regeneration Calvin cycle

Solution

Mesophyll cells Bundle sheath cells

Q38. Who proposed the law of limiting factor?  

• 1) Wilstatter  
• 2) Blackman  
• 3) Liebig  
• 4) Arnon  

Solution

Blackman proposed the law of limiting factor. According to this law, ‘When a chemical process is affected by more than one factor, its rate will be determined by the factor which is nearest to its minimal value: It is the factor which directly affects the process if its quantity is changed’.  

Q39. The light reaction phase is also known as?

Solution

Photochemical phase

Q40. Which law comes into effect when more than one factor affects the rate of photosynthesis in a plant? Give one example.

Solution

Blackman’s law of limiting factors. Example: No photosynthesis can take place in a plant if the temperature is not optimal, even if the CO₂ concentration, chlorophyll amount and light intensity are in optimal amounts.

Q41. For every CO₂ molecule entering the Calvin cycle, the number of ATP and NADPH required is  

• 1) 3 ATP + 2 NADPH  
• 2) 2 ATP + 2 NADPH  
• 3) 2 ATP + 3 NADPH  
• 4) 3 ATP + 3 NADPH  

Solution

For every molecule of CO₂ entering the Calvin cycle, 3 molecules of ATP and 2 molecules of NADPH are used. To meet the difference in the number of ATP and NADPH used in the Calvin cycle is probably why cyclic photophosphorylation takes place, as it releases only one molecule of ATP, whereas non-cyclic photophosphorylation releases one molecule of ATP and NADPH each.  

Q42. Which hormone(s) is/are responsible for an increase in the rate of photosynthesis?  

• 1) Auxin  
• 2) Gibberellin  
• 3) Cytokinin  
• 4) Both cytokinin and gibberellin  

Solution

Hormones affect the rate of photosynthesis. Cytokinin and gibberellin increase the rate of photosynthesis, whereas abscisic acid reduces the rate of photosynthesis.  

Q43. RuBisCO is the most abundant enzyme in the world and present in very high concentration in chloroplasts. It is required in very high concentration for     photosynthesis because it  

• 1) Is degraded very rapidly  
• 2) Is a very slow-acting enzyme  
• 3) Also acts as an oxygenase  
• 4) Catalyses a reversible reaction  

Solution

RuBisCO is a very slow-acting enzyme as it can capture only a few molecules of CO₂ for fixation; thus, it is produced in large amounts in plants to carry out optimum levels of photosynthesis.  

Q44. Flowers and fruits are brightly coloured so that they become attractive. This helps in the process of pollination. Which pigment in flowers and fruits imparts these colours?  

• 1) Chlorophyll a  
• 2) Chlorophyll d  
• 3) Carotenoid  
• 4) Chlorophyll b  

Solution

Carotenoids are responsible for the bright colour in fruits and flowers which makes them attractive for pollination.  

Q45. Which elements are essential for photophosphorylation?  

• 1) K and Cl  
• 2) Zn and I  
• 3) Mg and P  
• 4) Mn and Cl  

Solution

Mn and Cl are useful for light reactions as they are important for the process of splitting of water.  

Q46. Consider the following statements regarding photosynthesis:     A. ATP formation during photosynthesis is termed photophorylation.     B. Kranz anatomy pertains to leaf.     C. Reduction of NADP⁺ to NADPH occurs during the Calvin cycle.     D. In a chlorophyll molecule, magnesium is present in the phytol tail.     Of the above statements,  

• 1) A and B are correct.  
• 2) A and D are correct.  
• 3) A and C are correct.  
• 4) B and C are correct.  
• 5) C and D are correct.  

Solution

Photophosphorylation is the process by which green plants use light energy for the generation of energy-rich molecules such as ATP and NADPH.     Kranz anatomy is a special type of anatomy found in the leaves of C₄ plants.  

Q47. The membrane system of chloroplast is responsible for the synthesis of which two molecules?

Solution

ATP and NADPH

Q48. The carbon in CO₂ is radioactively labelled. The product in which this radioactive carbon can be found in C₃ plants is

• 1) RuBP
• 2) PEP
• 3) PGAL
• 4) PGA

Solution

The first stable compound formed from fixation of CO₂ in C₃ plants is 3-PGA. RuBP uses CO₂ to undergo carboxylation to form 2 molecules of 3-PGA with the reaction being catalysed by the enzyme RuBisCO.

Q49. Aquatic plants giving out oxygen in the gaseous form was demonstrated by

• 1) T. W. Engelmann
• 2) Priestley
• 3) Jan Ingenhousz
• 4) Julius von Sachs

Solution

Jan Ingenhousz kept aquatic green plants in sunlight and found bubbles coming out of the plant. These bubbles were not formed in the dark. On further testing, he found that these bubbles were oxygen.

Q50. The point at which the amount of CO₂ fixed in photosynthesis is equal to the CO₂ evolved in respiration and photorespiration is called

• 1) Concentration point
• 2) Compensation point
• 3) Balance point
• 4) Optimal point

Solution

When the levels of CO₂ is reduced, there comes a point in photosynthesis that the plant stops absorbing CO₂ from the atmosphere, and the amount of CO₂ fixed in the plant is equal to the amount of CO₂ produced by the plant as a result of respiration and photorespiration. This point is called the compensation point or threshold value.

Q51. Give details for the following experiments:   Importance of sunlight for photosynthesis   Hydrogen for photosynthesis   Give the overall equation for photosynthesis.  

Solution

Details for the experiments : a. Jan Ingenhousz showed that sunlight is important for the process of photosynthesis. In his experiment, he used aquatic plants. He observed that the plant produced small bubbles around its green parts in the presence of sunlight; whereas, the plant did not produce any bubbles in the dark. Later, he found that these bubbles were of oxygen. Because photosynthesis is the only process by which plants produce oxygen, he could conclude that plants produce oxygen only in the presence of sunlight and thus photosynthesis only occurs when sunlight is present.

b. Cornelius van Niel showed that hydrogen is important for photosynthesis as it is used to reduce carbon dioxide to carbohydrates. Green plants use water as a hydrogen donor which is oxidised to O₂. He based his experiments on purple and green sulphur bacteria which used H₂S as a hydrogen donor, and the oxidation product so formed in them is sulphur or sulphate depending on the organism. Thus, based on these observations, he inferred that oxygen released during photosynthesis is from water and not carbon dioxide.

Q52. Cornelius van Niel demonstrated that photosynthesis is essentially a light-dependent reaction. He based his study on which organism?

• 1) Blue-green algae
• 2) E. coli
• 3) Purple and green bacteria
• 4) Aquatic plants

Solution

Cornelius van Niel based his study on purple and green bacteria and demonstrated that photosynthesis is essentially a light-dependent reaction.

Q53. Why is photorespiration called a wasteful process?

Solution

In photorespiration, there is no synthesis of ATP or NADPH; thus, it is called a wasteful pathway.

Q54. The first stable compound in C₃ plants is

• 1) OAA
• 2) PGA
• 3) PEP
• 4) RuBP

Solution

3-Phosphoglycerate is the first stable compound which is formed in the C₃ cycle in the carboxylation stage. The reaction uses CO₂ and RuBP, a five-carbon compound, with the reaction being catalysed by RuBP carboxylase.

Q55. What are accessory pigments of chlorophyll? State their functions.

Solution

Accessory pigments are pigments other than chlorophyll a which help in the absorption of light. They help perform the following functions: Widen the range of light absorbed in the chloroplast. Absorb light and transfer the energy to chlorophyll a, which is the reaction centre for photosynthesis. Protect chlorophyll a from photo-oxidation.

Q56. In the leaves of C₄ plants, malic acid formation during CO₂ fixation occurs in the cells of  

• 1) Mesophyll  
• 2) Phloem  
• 3) Bundle sheath  
• 4) Epidermis  

Solution

In C₄ plants, mesophyll cells lack RuBisCO enzyme and thus cannot carry out the Calvin cycle. The primary CO₂ acceptor is PEP which is converted to oxaloacetic acid (OAA). OAA is then converted to a 3-carbon compound like malic acid, which is transported to the bundle sheath cells, where it undergoes decarboxylation, and the CO₂ released enters the Calvin cycle.  

Q57. In photorespiration, the cell organelles involved are  

• 1) Chloroplast only  
• 2) Chloroplast and mitochondrion  
• 3) Chloroplast, mitochondrion and peroxisome  
• 4) Chloroplast, mitochondrion and ribosome  

Solution

Chloroplast, mitochondrion and peroxisome are the three cell organelles which are involved in photorespiration. Their sequence of involvement is Chloroplast-peroxisome-mitochondrion.  

Q58. Internally, the chloroplast is divided into two parts – the membrane system and the fluid portion called stroma. Labour is equally divided between the two parts with each responsible for a particular function of photosynthesis leading to the formation of sugars. Which part(s) is/are involved in the synthesis of ATP and NADPH?  

• 1) Membrane system  
• 2) Stroma  
• 3) Neither membrane system nor stroma  
• 4) Both membrane system and stroma  

Solution

The membrane system of the chloroplast is responsible for the trapping of light energy and synthesis of ATP and NADPH. The stroma carries out enzymatic reactions which incorporate CO₂ in plants leading to the synthesis of sugars which later forms starch.  

Q59. Who showed that oxygen evolved during photosynthesis comes from water and not carbon dioxide? How did he/she infer that?

Solution

Cornelius van Niel showed that oxygen evolved in photosynthesis is from water and not carbon dioxide. He conducted experiments on purple and green sulphur bacteria, in which H₂S is the hydrogen donor and not H₂O. In the presence of H₂S, sulphur or sulphate is released as the oxidation product depending on the organism. Whereas in green plants, H₂O is used as a hydrogen donor and oxygen is given out as an oxidation product. Hence, van Niel inferred that oxygen is released from water and not carbon dioxide.

Q60. Which of the following shows maximum photosynthesis in green light?

• 1) Brown algae
• 2) Red algae
• 3) Azadirachta indica
• 4) Sunflower

Solution

Red algae show maximum photosynthesis in green light, while brown algae show maximum photosynthesis in blue light. Most higher plants show maximum photosynthesis in blue and red light.

Q61. Differentiate between PS I and PS II.

Solution

Photosystem I Photosystem II It has absorption maxima at 700 nm. It has absorption maxima at 680 nm. It operates in both cyclic and non-cyclic photophosphorylation. It operates only in non-cyclic photophosphorylation.  

Q62. Give a detailed description of the Calvin cycle.

Solution

The Calvin cycle occurs in the stroma of the chloroplast. It uses ATP and NADPH, produced during the light reactions, to synthesise sugars by fixing CO₂. The Calvin cycle has three main stages: Carboxylation: It is the first phase of the Calvin cycle. It involves the carboxylation of ribulose bisphosphate by using CO₂. The reaction is catalysed by the enzyme RuBP carboxylase-oxygenase.

It results in the formation of 3-phosphoglyceric acid, the first stable compound of the dark reactions. Reduction: It is a series of reactions which lead to the formation of glucose. It uses two molecules of ATP and two molecules of NADPH for phosphorylation and reduction, respectively, per molecule of CO₂­ fixed. Regeneration: This stage involves the regeneration of RuBP. It requires one molecule of ATP for phosphorylation to form one molecule of RuBP.

Q63. Which part of the ATPase enzyme forms a transmembrane channel in the thylakoid membrane which carries out facilitated diffusion of protons across the membrane?  

• 1) Both F₀ and F₁  
• 2) C₁  
• 3) F₁  
• 4) F₀  

Solution

The ATPase enzyme consists of two parts – F₀ and F₁. F₀ is embedded in the thylakoid membrane and forms a transmembrane channel which carries out facilitated diffusion of protons across the membrane. F₁ protrudes to the outer side of the membrane to face the stroma and carries out synthesis of ATP molecules.  

Q64. Chlorophyll in chloroplasts is located in

• 1) Pyrenoid
• 2) Grana
• 3) Stroma
• 4) Both grana and stroma

Solution

Grana are structures present in the chloroplast made of stacks of flattened discs called thylakoids. Thylakoids contain the photosystems within which photosynthetic pigments are present.

Q65. Shade-loving plants which require low light intensity for optimum photosynthesis are called

• 1) Heliophytes
• 2) Succulents
• 3) Sciophytes
• 4) Halophytes

Solution

Sciophytes are shade-loving plants and require low light intensity for optimum photosynthesis.

Q66. Which of the following statements is not true with respect to RuBisCO in C₃ plants?  

• 1) Located in stroma of chloroplast  
• 2) 16% of total cellular protein  
• 3) Bifunctional enzyme  
• 4) It was initially known as carboxydismutase  

Solution

RuBisCO accounts for 16% of the total chloroplast proteins and not total cellular proteins.  

Q67. Read the following four statements A, B, C and D, and select the right option having both correct statements.     Statements:     (A) Z scheme of light reaction occurs in the presence of PS I only.     (B) Only PS I is functional in cyclic photophosphorylation.     (C) Cyclic photophosphorylation results in the synthesis of ATP and NADPH₂.     (D) Stroma lamellae lack PS II as well as NADP.  

• 1) B and D  
• 2) A and B  
• 3) C and D  
• 4) B and C  

Solution

In cyclic photophosphorylation, only PS I is present, and the electron given out by PS I returns to the same PS I. PS II and NADP are present in the thylakoid lamellae.

Q68. The compensation point of CO₂ for C₃ plants is  

• 1) 25-75 ppm  
• 2) 25-50 ppm  
• 3) 50-100 ppm  
• 4) 25-100 ppm  

Solution

The compensation point for CO₂ is the point where the plant does not absorb any CO₂ from the surrounding as the levels of CO₂ used in photosynthesis is equal to the amount of CO₂ released by respiration and photorespiration. In C₃ plants, this value of the compensation point for CO₂ is 25-100 ppm.  

Q69. Jan Ingenhousz determined the importance of which factor for photosynthesis?

• 1) Chlorophyll
• 2) Air
• 3) Light
• 4) Water

Solution

Jan Ingenhousz modified Joseph Priestley’s experiment and demonstrated that sunlight is important for the process of photosynthesis.

Q70. When does Blackman’s law of limiting factors come into effect?

Solution

When there are several or more than one factor which affect any biochemical or chemical process.

Q71. The dark reaction in photosynthesis is called so because

• 1) It does not depend on light energy.
• 2) It occurs more rapidly at night.
• 3) It cannot occur during day light.
• 4) It can occur in dark also.

Solution

Dark reactions are called so because they do not depend on light energy, but they depend on the products formed by the light reactions.

Q72. Which of the following statements is true with regard to the light reaction of the photosynthetic mechanism in plants?

• 1) Photosystems I and II are both involved in non-cyclic photophosphorylation.
• 2) Both ATP and NADPH₂ are formed during cyclic photophosphorylation.
• 3) 0₂ is evolved during cyclic photophosphorylation.
• 4) Magnesium and sodium ions are associated with photolysis of water molecules.
• 5) Chlorophyll a occurs with peak absorption at 680 nm in photosystem I and at 700 nm in photosystem II.

Solution

In non-cyclic photophosphorylation, the electrons are passed from PS II to PS I, and PS II gains its lost electron from the splitting of water. Because the same electron does not return to PS II, it is called non-cyclic photophosphorylation.

Q73. What acts as the hydrogen donor in photosynthesis in higher plants?

• 1) Water
• 2) All of the above
• 3) Carbohydrate
• 4) Hydrogen sulphide

Solution

In higher plants, water is the hydrogen donor in photosynthesis.

Q74. Select the incorrectly matched pair with regard to the C₄ cycle.  

• 1) Primary CO₂ fixation product – PGA  
• 2) Primary CO₂ acceptor – PEP  
• 3) C₄ plant – Maize  
• 4) Site of initial carboxylation – Mesophyll cells  
• 5) Location of enzyme RuBisCO – Bundle sheath cells  

Solution

The primary CO₂ fixation product in C₄ plants is oxaloacetic acid, which is converted to malic acid or aspartic acid that is transported to the bundle sheath cells where the acid is decarboxylated and the CO₂ thus released enters the Calvin cycle.  

Q75. Ferredoxin is a constituent of  

• 1) PS I  
• 2) PS II  
• 3) P₆₈₀  
• 4) Hills reaction  

Solution

Ferredoxin is a soluble protein which acts as an electron carrier and forms a constituent of PS I. Ferredoxin passes electrons to reductase complex which helps in reducing NADP⁺ to NADPH.  

Q76. Define photolysis of water.

Solution

It is the process by which water is split into H⁺, oxygen and electrons in the presence of light by photosystem II.

Q77. A process which makes an important difference between C₃ and C₄ plants is  

• 1) Glycolysis  
• 2) Photorespiration  
• 3) Photosynthesis  
• 4) Transpiration  

Solution

Photorespiration is a process which occurs due to the oxygenase activity of RuBisCO. When the concentration of O₂ is high as compared to CO₂, RuBisCO shows oxygenase activity. C₄ plants have a mechanism by which they can maintain the high concentration of CO₂ at the enzyme site; thus, photorespiration does not occur in C₄ plants.  

Q78. Formation of ATP in photosynthesis and respiration is an oxidation process which uses the energy from

• 1) Electrons
• 2) Cytochromes
• 3) Carbon dioxide
• 4) Ferredoxin

Solution

A high-energy electron is ejected from a molecule, which is passed downhill through multiple electron acceptors. The energy given out by this high-energy electron is used up for the formation of ATP during photosynthesis and respiration.

Q79. NADPH is generated through  

• 1) PS I  
• 2) Glycolysis  
• 3) PS II  
• 4) Aerobic respiration  

Solution

NADPH is generated through PS II in non-cyclic photophosphorylation.  

Q80. Energy required for ATP synthesis in PS II comes from  

• 1) Reduction in glucose  
• 2) Oxidation of glucose  
• 3) Electron gradient  
• 4) Proton gradient  

Solution

The proton gradient is formed due to accumulation of protons on the lumen side of the thylakoid. Also, the transport of electrons through the photosystem moves protons from the stroma to the lumen side, decreasing the proton concentration in the stroma and increasing it on the lumen side. This results in the generation of a proton gradient across the thylakoid membrane. The ATPase enzyme breaks down this proton gradient and uses its energy for the synthesis of ATP molecules.  

Q81. Which one of the following statements about the events of non-cyclic photophosphorylation is incorrect?

• 1) ATP and NADPH are produced.
• 2) 0₂ is released.
• 3) Photolysis of water occurs.
• 4) Only one photosystem participates.

Solution

In non-cyclic photophosphorylation, both PS I and PS II participate.

Q82. Light saturation point for shade plants is at how much percent of full sunlight?  

• 1) 100%  
• 2) 50%  
• 3) 90%  
• 4) 10%  

Solution

The light intensity at which a plant reaches the maximum photosynthesis rate is known as the light saturation point. This is about 10% of full sunlight for shade plants, 50-70% of full sunlight for C₃ sun plants and up to 200% for C₄ sunplants_.  

Q83. A photosystem is composed of

• 1) Reaction centre and light-harvesting complex
• 2) Reaction centre
• 3) Light-harvesting complex
• 4) Granum

Solution

A photosystem is composed of both a reaction centre as well as a light-harvesting complex which are involved in trapping light and synthesising energy-rich molecules like ATP and NADPH.

Q84. Give two examples of C₄ plants.

Solution

Maize and sorghum

Q85. Describe the process of photorespiration.

Solution

Photorespiration occurs in C₃ plants due to the oxygenase activity of RuBisCO. O₂ binds to the enzyme and RuBP instead of being converted to two molecules of phosphoglyceric acid is converted to one molecule of phosphoglycerate and one molecule of phosphoglycolate by binding to O₂. In this process, there is no synthesis of sugars or ATP.

ATP is utilised in this process with the release of CO₂. Because there is no synthesis of sugars, ATP or NADPH, the pathway is also called a wasteful process.

Q86. The Calvin cycle is

• 1) Oxidation
• 2) Oxidative carboxylation
• 3) Reductive carboxylation
• 4) Reduction

Solution

The Calvin cycle is a reductive carboxylation process as it involves the carboxylation of RuBP to 3-PGA and the further reduction of 3-PGA by a series of steps which leads to the synthesis of sugars.

Q87. Which one of the following occurs in both cyclic and non-cyclic photophosphorylation?

• 1) Involvement of both photosystems
• 2) Formation of ATP
• 3) Formation of NADPH and ATP
• 4) Evolution of O₂

Solution

In cyclic photophosphorylation, only a molecule of ATP is released, while in non-cyclic photophorylation, both ATP and NADPH are released.

Q88. In which photophosphorylation process both ATP and NADPH are produced and in which only ATP is produced? 

Solution

In non-cyclic photophosphorylation, both ATP and NADPH are produced. In cyclic photophosphorylation, only ATP is produced. 

Q89. Where does non-cyclic photophosphorylation occur? Describe the process and explain why it is called so.

Solution

It occurs in the lamella of grana. The process of non-cyclic photophosphorylation occurs as follows: It begins with the absorption of light by P₆₈₀ in PS II. The molecule gets excited and gives out an energy-rich electron which jumps into an orbit farther away from the atomic nucleus. These electrons are picked up by primary electron acceptors, which pass them into an electron transport system consisting of cytochromes. The electrons are then passed on to PS I. Simultaneously, light of wavelength 700 nm is absorbed by PS I and electrons are released by it. These electrons are then transferred to another electron acceptor, from where it is transferred to NADP⁺. NADP⁺ is then reduced (NADPH + H⁺) by electrons and protons from the photolysis of water. Both ATP and NADPH are formed during this electron flow. Because the electrons given out by PS II do not return to PS II but are replaced by those from water, the process is called non-cyclic photophosphorylation.

Q90. Why does photorespiration not occur in C₄ plants?

Solution

C₄ plants have a mechanism to increase the concentration of CO₂ at the site where RuBisCO is present, thus photorespiration does not occur.

Q91. Consider the following statements: (a) The portion of the spectrum between 500 nm and 800 nm is also referred to as photosynthetically active radiation (PAR).   (b) Magnesium, calcium and chloride ions play prominent roles in the photolysis of water.   (c) In cyclic photophosphorylation, oxygen is not released (as there is no photolysis of water) and NADPH is also not produced. Of these statements given above,

• 1) (a) is true, but (b) and (c) are false.
• 2) (a) and (b) are true, but (c) is false.
• 3) (a) and (b) are false, but (c) is true.
• 4) (a) and (c) are true, but (b) is false.

Solution

During cyclic photophosphorylation, only a single molecule of ATP is synthesised and there is no photolysis of water, no release of O₂ and no synthesis of NADPH.

Q92. Which technique is used to separate leaf pigments?

Solution

Paper chromatography

Q93. Which of the following is formed during photorespiration?  

• 1) Oxaloacetate  
• 2) Phosphoglycolate  
• 3) ATP  
• 4) Sugar  
• 5) NADPH  

Solution

Phosphoglycolate is a 2-carbon compound which is formed as a result of photorespiration. RuBisCO catalyses the oxygenation reaction of RuBP to form PGA and phosphoglycolate, when the concentration of O₂ is high and that of CO₂ is low in the cell.  

Q94. Quantasomes were discovered by  

• 1) Pelletier and Caventou  
• 2) Park and Biggins  
• 3) Blackman  
• 4) Hatch and Slack  

Solution

Quantasomes were identified by Park in 1962 and then by Biggins in 1964.  

Q95. Why do chloroplasts align themselves along the walls of mesophyll cells?

Solution

Chloroplasts align themselves along the walls of mesophyll cells to obtain optimum quantity of the incident light.

Q96. Which of the following statements is true with regard to the light reaction of photosynthesis?

• 1) In PS I, the reaction centre chlorophyll a has an absorption maxima at 680 nm and is called P 680.
• 2) Photosystems I and II are involved in the Z scheme.
• 3) Lamellae of the grana have PS I and PS II, and stroma lamellae membranes have PS II only.
• 4) In PS II, the reaction centre chlorophyll a has an absorption peak at 700 nm and is called P 700.
• 5) The splitting of the water molecule is associated with PS I.

Solution

The Z scheme of photophosphorylation involves both PS I and PS II with the electrons moving from PS II to PS I and from water to PS II.

Q97. What is the biosynthetic phase also known as? Why is it called so? What products does it require and what is the end-product of the process?

Solution

The biosynthetic phase is also called the dark reaction. It is called so because it does not require the presence of light for its commencement; that is, it is light-independent. The products necessary for the biosynthetic phase are ATP and NADPH, which are obtained from the light reactions. The final product of the biosynthetic phase is sugar (glucose).

Q98. Bacteria which live in regions such as hot springs can perform photosynthesis even at

• 1) 35°C
• 2) 12°C
• 3) 48°C
• 4) 70°C

Solution

Bacteria which live in or near hot springs can perform photosynthesis even at 70°C.

Q99. How is the yield of greenhouse crops such as tomato and bell pepper increased through photosynthesis?

Solution

The yield in greenhouse crops of tomato and bell pepper is increased by growing them in a carbon dioxide-rich environment.

Q100. Who described the first action spectrum for photosynthesis?  

• 1) Julius von Sachs  
• 2) Cornelius van Niel  
• 3) Joseph Priestley  
• 4) T. W. Engelmann  

Solution

T. W. Engelmann described the first action spectrum of photosynthesis in his experiments with Cladophora and aerobic bacteria illuminated with independent spectral components of light which are split using a prism.  

Q101. Chloroplasts are externally covered by  

• 1) Cutaneous membrane  
• 2) Peritoneum  
• 3) Chloroplast envelope  
• 4) Chloroplast lamina  

Solution

Chloroplasts are externally covered by a double membranous structure called the chloroplast envelope. Each membrane is a unit membrane like the plasma membrane.  

Q102. What happens to the electrons as it moves along the electron transport chain?

Solution

The electrons lose energy as they move downhill. The electron transport chain gives some amount of energy to each cytochrome which it moves to.

Q103. With the help of a diagram explain the light-harvesting complex (LHC).

Solution

LHC is a group of pigment molecules which are associated with each other and help carry out photosynthesis. LHC is made of hundreds of pigment molecules except for only one chlorophyll a molecule forming a light-harvesting system also called antennae. The single chlorophyll a molecule forms the reaction centre, while the other pigments serve as accessory molecules and make photosynthesis more effective by absorbing light of different wavelengths.

Q104. The Calvin cycle leads to reduction of

• 1) CO₂
• 2) RUMP
• 3) RUBP
• 4) 0₂

Solution

CO₂ in the Calvin cycle is used for the carboxylation of RuBP in the carboxylation phase; this results in the formation of two 3-PGA which is further reduced in the cycle for the formation of sugars.

Q105. Which of the following is an inhibitor of non-cyclic photophosphorylation?  

• 1) Only DCMU  
• 2) Only diquat  
• 3) Only CMU  
• 4) DCMU, CMU and diquat, all inhibit non-cyclic photophosphorylation  

Solution

DCMU, CMU and diquat are herbicides and inhibit plant growth by blocking non-cyclic photophosphorylation.  

Q106. How does water affect the rate of photosynthesis?

Solution

Water affects the rate of photosynthesis indirectly. Water stress causes the stomata to close, thus reducing the availability of CO₂. It also causes the leaves to wilt, reducing the surface area for photosynthesis.

Q107. What are the absorption maxima for the reaction centres of PS I and PS II?

Solution

The PS I reaction centre has an absorption maxima of 700 nm, and the PS II reaction centre has an absorption maxima of 680 nm. 

Q108. In the C₄ pathway, the CO₂ fixation in mesophyll cells is carried out by the enzyme  

• 1) RuBisCO  
• 2) PEP carboxylase  
• 3) Pyruvate decarboxylase  
• 4) Pyruvate dehydrogenase  

Solution

Mesophyll cells lack the enzyme RuBisCO, which carries out the Calvin cycle. PEP carboxylase is the enzyme which is found in mesophyll cells, and it catalyses the reaction of CO₂ fixation by phosphoenol pyruvate.  

Q109. The reaction which is responsible for the primary fixation of CO₂ is catalysed by

• 1) RuBP carboxylase
• 2) RuBP carboxylase and PEP carboxylase
• 3) PGA synthase
• 4) PEP carboxylase

Solution

RuBP carboxylase is responsible for the fixation of CO₂ in C₃ plants, while PEP carboxylase fixes CO₂ in C₄ plants. RuBP carboxylase uses ribulose-1, 5- bisphosphate as the CO₂ acceptor for the carboxylation reaction, while PEP carboxylase uses phosphoenol pyruvate as a CO₂ acceptor for carboxylation.

Q110. During the Calvin cycle, the total number of CO₂, ATP and NADPH molecules utilised and glucose, ADP and NADP molecules generated is  

• 1) 67  
• 2) 61  
• 3) 36  
• 4) 31  

Solution

The total number of ATP, NADPH and CO₂ utilised and ADP, NADP and glucose generated is 67.     6CO₂ + 18ATP + 12 NADPH + 12H₂O ———> C₆H₁₂O₆ + 18ADP + 18 P_i + 12NADP⁺ + 6H⁺  

Q111. The scientist awarded the Noble Prize in 1960 for tracing the path of carbon in plants is  

• 1) Hatch  
• 2) Ruben  
• 3) Calvin  
• 4) Blackman  
• 5) Huber  

Solution

Melvin Calvin was awarded the Nobel Prize in 1960 for tracing the path of carbon in plants. This pathway is known as the Calvin cycle or C₃ cycle. He used the radioisotope of carbon ¹⁴C for tracing the path of carbon in algal photosynthesis.  

Q112. Which metal ion is a constituent of chlorophyll?

• 1) Magnesium
• 2) Zinc
• 3) Copper
• 4) Iron

Solution

Magnesium is an important component of chlorophyll. It is held within the tetrapyrrole ring by two covalent and two coordinate bonds. Magnesium in chlorophyll helps in absorption of light energy and excitation of electrons.

Q113. The chemiosmotic theory for photophosphorylation was given by  

• 1) Anderson  
• 2) Arnon  
• 3) P. Mitchell  
• 4) Arnold  

Solution

Chemiosmotic theory was proposed by P. Mitchell in 1961; the theory suggested that most of the ATP synthesis which occurs in respiring cells comes from an electrochemical gradient formed across the mitochondrial or chloroplast membrane.  

Q114. At high temperature, plants cannot perform photosynthesis as

• 1) Rate of water absorbed by roots is reduced
• 2) Temperature is not optimum for the activity of most enzymes
• 3) Stomata close
• 4) Chlorophyll shuts down

Solution

Most plant enzymes have their optimum temperature at 30°C. When the temperature rises, most enzymes cannot function and photosynthesis stops.

Q115. Which one of the following is essential for photolysis of water?  

• 1) Manganese  
• 2) Copper  
• 3) Boron  
• 4) Zinc  

Solution

Photolysis of water requires the presence of manganese, chloride and calcium ions.  

Q116. ATP can be formed in the photosynthesising plant cells by

• 1) C₄ cycle
• 2) Photophosphorylation
• 3) C₃ cycle
• 4) CAM pathway

Solution

Photosynthesising plant cells produce ATP by the process of photophosphorylation by using light energy, ADP and inorganic phosphate.

Q117. Solarisation is the process of  

• 1) Utilisation of sunlight  
• 2) Formation of chlorophyll molecules  
• 3) Effect of low level sunlight on photosynthesis  
• 4) Destruction of chlorophyll molecules  

Solution

Solarisation is the phenomenon where the rate of photosynthesis is reduced when light intensity increases beyond the saturation point. Solarisation is caused by two reasons, one is photo-inhibition which is caused by closure of stomata and the second is due to photo-oxidation, where photosynthetic pigments are oxidised, rendering them inactive.  

Q118. Which of the following statements with regard to photosynthesis is/are correct? (a) In C₄ plants, the primary CO₂ acceptor is PEP. (b) In the photosynthetic process, PS II absorbs energy at or just below 680 nm. (c) The pigment which is present in PS I is P₆₈₃.

• 1) (a) and (c) only
• 2) (c) only
• 3) (b) and (c) only
• 4) (a) and (b) only
• 5) (a) only

Solution

P₇₀₀ is the pigment which is present in PS I and not P₆₈₃.

Q119. In the C₃, cycle for the fixation of every CO₂ molecule, the reduction and regeneration steps require  

• 1) 2 ATP and 3 NADPH₂  
• 2) 3 ATP and 3 NADPH₂  
• 3) 3 ATP and 1 NADPH₂  
• 4) 2 ATP and 2 NADPH₂  
• 5) 3 ATP and 2 NADPH₂  

Solution

For every molecule of CO₂ entering the Calvin cycle, 3 molecules of ATP and 2 molecules of NADPH are used. Probably to meet the difference in the number of ATP and NADPH used in the Calvin cycle is why cyclic photophosphorylation occurs, as it releases only one molecule of ATP, whereas non-cyclic photophosphorylation releases one molecule of ATP and NADPH each.  

Q120. Kranz anatomy is one of the characteristics of the leaves of  

• 1) Potato  
• 2) Wheat  
• 3) Sugarcane  
• 4) Mustard  

Solution

Kranz anatomy is a special type of leaf anatomy seen in C₄ plants. In these plants, the vascular bundles are surrounded by concentric rings of bundle sheath cells which in turn are surrounded by mesophyll cells. Sugarcane being a C₄ plant shows Kranz anatomy in its leaves.  

Q121. Define photosynthesis.

Solution

Photosynthesis is a physicochemical process by which green plants and certain other organisms use light energy for synthesising organic compounds.

Q122. The primary CO₂ acceptor in C₃ plants is

• 1) PEP
• 2) RuBP
• 3) Oxaloacetate
• 4) Phosphoglyceraldehyde

Solution

RuBP, a 5-carbon compound, is the primary CO₂ acceptor in C₃ plants. RuBP with the help of CO₂ undergoes carboxylation to form two molecules of 3- phosphoglycerate, a 3-carbon compound.

Q123. Which is the first acceptor molecule in the Calvin cycle?

Solution

Ribulose bisphosphate (RuBP), a five-carbon ketose sugar

Q124. Melvin Calvin was professor of  

• 1) Biochemistry  
• 2) Botany  
• 3) Chemistry  
• 4) Plant physiology  

Solution

Melvin Calvin was a professor of chemistry who along with Benson and Bassham determined the series of reactions which constitutes the C₃ cycle or Calvin cycle using radioactive carbon ¹⁴C.  

Q125. Describe the half-leaf experiment on photosynthesis.

Solution

A potted plant is kept in the dark for 48-72 hours for destarching. A part of a leaf is enclosed in a test tube containing some KOH solution, and the other half is kept out exposed to air. It is made sure that the leaf does not break off from the plant body while the experiment is going on. The setup is then kept in sunlight for some time. Later, the leaf is tested for the presence of starch. The starch test shows that the exposed part of the leaf tests positive for starch, while the part in the test tube tests negative for starch. This shows that carbon dioxide is necessary for photosynthesis.

Q126. Which chlorophyll molecule does not have a phytol tail?  

• 1) Chl c  
• 2) Chl d  
• 3) Chl b  
• 4) Chl a  

Solution

Chlorophyll c is an accessory pigment and forms part of the antennae system. It is different from the rest of the chlorophyll molecules as it lacks a phytol tail. It is generally found in some marine algae (e.g. diatoms).  

Q127. The light reaction of photosynthesis occurs in  

• 1) Grana  
• 2) Endoplasmic reticulum  
• 3) Cytoplasm  
• 4) Stroma  

Solution

The granum is the site for light reactions as it contains light-harvesting complexes, and the stroma is the site for dark reactions as it contains all the necessary enzymes required for the fixation of CO₂ and the synthesis of sugars.  

Q128. The Calvin cycle proceeds in three stages:     1. Reduction, during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH.     2. Regeneration, during which the carbon dioxide acceptor ribulose-1, 5-bisphosphate is formed.     3. Carboxylation, during which carbon dioxide combines with rubulose-1, 5-biphosphate.     Identify the correct sequence.  

• 1) 3-2-1  
• 2) 3-1-2  
• 3) 1-2-3  
• 4) 1-3-2  
• 5) 2-1-3  

Solution

The Calvin cycle is divided into three phases. The first phase is carboxylation where RuBP is converted to two 3-carbon compounds. The next phase is reduction where ATP and NADPH are used for the synthesis of sugars. The final phase is regeneration where RuBP is regenerated for continuity of the cycle.  

Q129. Differentiate between cyclic and non-cyclic photophosphorylation.

Solution

Cyclic photophosphorylation Non-cyclic photo-phosphorylation The electrons given out by PS I (P₇₀₀) return to the same P₇₀₀. The electrons given out by PS II (P₆₈₀) do not return to it, but they are replaced by electrons from water. It involves only PS I. It involves both PS I and PS II. There is no formation of NADPH or photolysis of water. It involves formation of NADPH and photolysis of water. No oxygen is liberated. Oxygen is liberated.  

Q130. The enzyme which is not found in a C₃ plant is

• 1) PEP carboxylase
• 2) RuBP carboxylase
• 3) NADP reductase
• 4) ATP synthetase

Solution

PEP carboxylase is an enzyme found in mesophyll cells of C₄ plants. It is responsible for the fixation of phosphoenol pyruvate (PEP) and CO₂. PEP is the primary CO₂ acceptor which is found only is C₄ plants and not in C₃ plants; thus, PEP carboxylase is absent in C₃ plants.

Q131. How are molecules of the C₄ cycle exchanged between the mesophyll and bundle sheath cells?

Solution

The molecules of the C₄ pathway are exchanged through the plasmodesmata, which are pore-like channels that connect the mesophyll and bundle sheath cells.

Q132. Differentiate between grana and stroma of chloroplast.

Solution

Grana Stroma Grana are made of stacks of thylakoids. Stroma is the fluid present in the chloroplast. Light reactions occur here. Dark reactions occur here.  

Q133. Thylakoids occur inside

• 1) Chloroplast
• 2) Golgi apparatus
• 3) Mitochondria
• 4) Endoplasmic reticulum

Solution

Thylakoids are disc-shaped structures present in the chloroplast. They stack up to form the grana. Thylakoids are the sites for oxygenic photosynthesis in eukaryotic plants and algae.

Q134. Which is the first stage of Calvin cycle? Give details about it.

Solution

The first stage of the Calvin cycle is carboxylation. It involves the fixation of CO₂ into a stable organic intermediate. CO₂ is used for the carboxylation of ribulose bisphosphate, a five-carbon ketose sugar, to form two molecules of 3-PGA. This reaction is catalysed by the enzyme ribulose bisphosphate carboxylase-oxygenase. 

Q135. Blackman’s law of limiting factors was opposed by which of the following individuals?

• 1) Harder
• 2) Hoover
• 3) All of the above
• 4) Boysen-Jensen

Solution

Boysen-Jensen, Hoover and Harder all opposed Blackman’s law of limiting factors stating that the rate of photosynthesis because of a limiting factor declines gradually in the form of a curve and does not decline suddenly.

Q136. Read the following four statements (A-D). (A) Both photophosphorylation and oxidative phosphorylation involve the uphill transport of protons across the membrane. (B) In dicot stems, a new cambium originates from the cells of the pericycle at the time of secondary growth. (C) Stamens in Dowers of Gloriosa and Petunia are polyandrous. (D) Symbiotic nitrogen fixers occur in free-living state also in soil. How many of the above statements are right?

• 1) Two
• 2) Four
• 3) Three
• 4) One

Solution

Statements B and D are true, while A and C are false.

Q137. Bulk fixation of carbon through photosynthesis takes place in  

• 1) Tropical plants  
• 2) Oceans  
• 3) Rain forests  
• 4) Crop plants  

Solution

Oceans cover a large portion of the earth. The ocean is home to a large amount of organisms which include both producers and consumers. In oceans, microscopic organisms (e.g. cyanobacteria and dinoflagellates) along with multicellular producers (e.g. sea weed and sea grass) account for most of the CO₂ fixation on Earth.  

Q138. Photosynthetically active radiation (PAR) represents which of the following range of wavelength?  

• 1) 500-600 nm  
• 2) 400-700 nm  
• 3) 450-950 nm  
• 4) 340-450 nm  

Solution

400-700 nm wavelength of the electromagnetic spectrum belongs to the visible light region which is the main and only source of light for photosynthesis.  

Q139. Which of the following statements regarding the C₄ pathway is false?  

• 1) The enzyme responsible for CO₂ fixation is PEPCase.  
• 2) The primary CO₂ acceptor is phosphoenol pyruvate.  
• 3) The mesophyll cells lack RuBisCO enzyme.  
• 4) The bundle sheath cells contain the enzyme PEPCase.  
• 5) The C₄ acid OAA is formed in the mesophyll cells.  

Solution

The bundle sheath cells do not contain the enzyme PEPCase. Instead, the bundle sheath cells contain the enzyme RuBisCO; thus, the Calvin cycle occurs in them by CO₂ released due to the decarboxylation of malic acid or aspartic acid.  

Q140. The Calvin cycle occurs in plants following which pathway?

Solution

The Calvin cycle occurs in all photosynthetic plants irrespective of whether they have the C₃ or C₄ pathway.

Q141. Which is the final electron acceptor in the Z scheme electron transport chain?

Solution

NADP⁺ is the final electron acceptor in the Z scheme electron transport chain.

Q142. The first action spectrum of photosynthesis was described by

• 1) T. W. Engelmann
• 2) Jan Ingenhousz
• 3) Priestley
• 4) Julius von Sachs

Solution

The first action spectrum of photosynthesis was described by T. W. Engelmann.

Q143. Differentiate between mesophyll and bundle sheath cells of C₄ plants with respect to photosynthesis.

Solution

Mesophyll cells Bundle sheath cells Chloroplasts have grana. Chloroplasts lack grana. CO₂ acceptor is phosphoenol pyruvate. The CO₂ acceptor is ribulose bisphosphate. CO₂ acceptor molecule is present in the cytoplasm. CO₂ acceptor molecule is present in the stroma of chloroplasts.  

Q144. At what concentration of full sunlight does saturation of light take place for photosynthesis?

Solution

10% of full sunlight is the saturation limit for photosynthesis.

Q145. At which phase of the dark reaction is glucose formed?

Solution

Glucose is formed during the reduction phase of the Calvin cycle.

Q146. What do you observe when you plot a graph for light intensity versus the rate of photosynthesis?

Solution

A linear graph with a plateau is observed where the rate of photosynthesis increases up to a certain point. If light intensity is increased further, then the rate of photosynthesis does not increase but remains constant.

Q147. In the half-leaf experiment of photosynthesis, KOH solution is used because  

• 1) It helps in CO₂ fixation.  
• 2) It provides O₂ to the leaf.  
• 3) It provides moisture to the leaf.  
• 4) It absorbs CO₂.  

Solution

KOH is a strong alkali and CO_­2 is an acidic oxide; thus, the two react in an acid base reaction which results in the absorption of CO₂ from the air.  KOH + CO₂  ———> KHCO₃ + K₂CO₃ +H₂O  

Q148. Which enzyme catalyses the carboxylation of ribulose bisphosphate using CO₂?

Solution

Ribulose bisphosphate carboxylase-oxygenase (RuBisCO)

Q149. Which pigment forms a bright blue or blue-green colour band on a chromatogram for pigments of green leaf?

Solution

Chlorophyll a

Q150. What is the first stable compound formed from CO₂ fixation in C₄ plants?

Solution

Oxaloacetic acid

Q151. Why is the lumen of the thylakoids more acidic in nature?

Solution

The splitting of water releases H⁺ ions/protons which accumulate in the lumen of the thylakoids, making it more acidic in nature.

Q152. What is the anatomical structure of the leaves of C_­4­ plants known as?

Solution

Kranz anatomy

Q153. Light reactions include which all processes?

Solution

Light reactions include: Absorption of light Splitting of water molecule Release of oxygen Formation of high-energy chemical intermediates, ATP and NADPH

Q154. The movement of electrons from chlorophyll molecule to NADP occurs in

• 1) Photosystem I and photosystem II
• 2) Cyclic photophosphorylation
• 3) Photorespiration
• 4) Non-cyclic photophosphorylation

Solution

In non-cyclic photophosphorylation, electrons are passed on from PS II to PS I and then finally to NADP, through a series of electron acceptors, for the synthesis of NADPH.

Q155. The first stable product in C₄ plant is

• 1) Ribulose 1, 5 diphosphate
• 2) Malic acid
• 3) Oxaloacetic acid
• 4) Phosphoenol pyruvate

Solution

In C₄ plants, CO₂ fixation occurs in mesophyll cells. Phosphoenol pyruvate is the primary electron acceptor for CO₂­ which is carboxylated to form oxaloacetic acid (OAA) in the presence of the enzyme PEP carboxylase. OAA is then converted to malic acid or aspartic acid, which is then transported to the bundle sheath cells.

Q156. Which pigments constitute the accessory pigments in the thylakoid?

Solution

Accessory pigments include Chlorophyll b Xanthophylls Carotenoids

Q157. Factors affecting the rate of photosynthesis are grouped under which two categories?

Solution

External factors and internal factors

Q158. The type of CO₂ fixation seen in many succulent plant species is  

• 1) C₂ pathway  
• 2) C₃ pathway  
• 3) C₄ pathway  
• 4) CAM pathway  

Solution

Succulent plants are those that live in arid climates or regions with water scarcity. To preserve water in them, they have adapted to the CAM pathway where their stomata remain closed during the day and open at night to prevent the loss of water due to transpiration.  

Q159. In coniferous plants, photosynthesis can take place at a temperature as low as

• 1) −5°C
• 2) −12°C
• 3) −35°C
• 4) 0°C

Solution

In coniferous plants, photosynthesis can even take place at −35°C.

Q160. In higher plants, the shape of the chloroplast is

• 1) Girdle-shaped
• 2) Cup-shaped
• 3) Discoid
• 4) Reticulate

Solution

Discoid-shaped chloroplast is found in higher plants, whereas cup-shaped chloroplast is found in the green algae Chlamydomonas. Ulothrix has girdle-shaped chloroplasts and Chlorophyceae have reticulate chloroplasts.

Q161. State Blackman’s law of limiting factors.

Solution

If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. It is the factor which directly affects the process if its quantity is changed.

Q162. Name the organisms used in the experiments for photosynthesis performed by a) Joseph Priestley b) Cornelius van Niel c) Engelmann d) Jan Ingenhousz

Solution

Mouse and mint plant Purple and green sulphur bacteria Green algae Cladophora Aquatic plant

Q163. What determines the binding of CO_{2 ­}or O₂ to RuBisCO?

Solution

The relative concentration of CO₂ and O₂ in the cell determines whether CO₂ or O₂ will bind to the active site of the enzyme RuBisCO.

Q164. What is Kranz anatomy? Describe bundle sheath cells.

Solution

When large bundle sheath cells surround the vascular bundle, the leaf is said to have Kranz anatomy. Bundle sheath cells are specific to C₄ plants and are characterised by having a large number of chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces.

Q165. Non-cyclic photophosphorylation results in the production of  

• 1) ATP  
• 2) ADP  
• 3) NADPH  
• 4) ATP and NADPH  

Solution

Non-cyclic photophosphorylation results in the production of ATP, NADPH and O₂. O₂ thus produced is released in the atmosphere while ATP and NADPH are used during the dark reaction for the synthesis of sugars.  

Q166. In Priestley’s experiment for photosynthesis, the mouse died in the setup which did not contain the mint plant because of

• 1) Lack of oxygen
• 2) All the given options are true
• 3) Rise in temperature due to the burning candle
• 4) Starvation

Solution

The mouse and burning candle both use up oxygen from the air in the jar for respiration and combustion, respectively; thus, the mouse dies due to suffocation as no more oxygen is available.

Q167. Oxygen in air was discovered by

• 1) Julius von Sachs
• 2) Priestley
• 3) Jan Ingenhousz
• 4) T. W. Engelmann

Solution

Joseph Priestley discovered oxygen in 1774.

Q168. Which radioactive isotope was used by Melvin Calvin to determine the first stable compound of CO₂ fixation in photosynthesis?

Solution

¹⁴C

Q169. How did Melvin Calvin find the first stable compound formed in the biosynthetic phase?

Solution

Calvin used ¹⁴C, a radioactive isotope of carbon, in CO₂ which he supplied to the green photosynthetic algae which he used for his studies. The algae used up the CO₂ for fixation in photosynthesis. He observed that the first compound formed after some time with the presence of the radioactive ¹⁴C was 3-phosphoglycerate, suggesting it as the first stable compound of CO₂ fixation.

Q170. The number of thylakoids in a granum is  

• 1) 100-150  
• 2) 5-10  
• 3) 150-200  
• 4) 2-100  

Solution

The number of thylakoids in a granum can vary from 2 to 100.  

Q206. Name the two sets of reactions which take place in the chloroplast.

Solution

The two sets of reactions which take place in the chloroplast are Light reactions Dark reactions

Q172. List the internal and external factors which affect the rate of photosynthesis.

Solution

Internal factors: Number, size, orientation and age of leaves, chlorophyll content, chloroplast amount and internal CO₂ concentration External factors: CO₂ concentration, temperature, light and water 

Q173.   Who conducted this experiment? Based on the experiment, which factor was shown to be important for green plants? What did he conclude from the experiment?

Solution

Joseph Priestley. The experiment showed the importance of air for green plants. Priestley concluded that green plants restore to the air whatever burning candles and breathing animals remove.

Q174. What happens to the electron which is passed on through the cyclic photophosphorylation process?

Solution

The electron is released from PS I and, after moving through a series electron acceptors, it goes back to PS I.

Q175. Define biosynthetic phase.

Solution

The process by which ATP and NADPH produced during the light reactions of photosynthesis are used to synthesise sugars is called the biosynthetic phase.

Q176. Define phosphorylation.

Solution

The process by which ATP is synthesised in the cells is called phosphorylation.

Q177. Consider a plant which lacks chlorophyll a but has chlorophyll b; will it carry out photosynthesis? What is the role of chlorophyll b and other accessory pigments?

Solution

No. The plant cannot carry out photosynthesis without chlorophyll a because it is the reaction centre for photosynthesis. Chlorophyll b and other accessory pigments absorb light at other wavelengths and pass it to the reaction centre for efficient photosynthesis.

Q178. The splitting of water occurs in which part of the chloroplast? What is its significance?

Solution

Splitting of water takes place near PS II, located in the inner side of the thylakoid membrane. Splitting of water releases oxygen in the atmosphere and generates a proton gradient across the thylakoid membrane. 

Q179. In which region of the visible light spectrum does most photosynthesis take place?

Solution

Most photosynthesis corresponds to the blue and red regions of the visible spectrum.

Q180. How can a C₄ plant leaf section be distinguished from that of a C₃ plant leaf section?

Solution

A section of the leaf from a C₄ plant shows Kranz anatomy, which is observed by the presence of bundle sheath cells around the vascular bundles; this is not observed in the section of a C₃ plant leaf.

Q181. Differentiate between C₃ and C₄ plants on the basis of anatomy.

Solution

C₃ plants C₄ plants Kranz anatomy is absent in leaves. Leaf shows the presence of Kranz anatomy, with bundle sheath cells arranged around the vascular bundle. Chloroplasts are of a single type with the presence of grana. Chloroplast is dimorphic. Chloroplasts of mesophyll cells have grana and those of bundle sheath cells do not.  

Q182. Who first showed that only green parts of plants could release oxygen?

Solution

Jan Ingenhousz

Q183. State the effect of CO₂ concentration on C₃ and C₄ plants under the following conditions: Low light and high CO₂ concentration High light intensities Saturation CO₂ concentration

Solution

Both C₃ and C₄ plants do not respond to low light and high CO₂ concentration. Both C₃ and C₄ plants respond to high light and high CO₂ concentration by an increase in the rate of photosynthesis. Saturation concentration of CO₂ for C₃ plants: Above 450 μlL⁻¹ C₄ plants: At 360 μlL⁻¹

Q184. What is the saturation limit for CO₂ in C₃ and C₄ plants?

Solution

The saturation values for CO₂ are C₄ plants: At about 360 μlL⁻¹ C₃ plants: Above 450 μlL⁻¹

Q185. What governs the internal factors affecting the rate of photosynthesis?

Solution

Genetic predisposition and growth of the plant determine the internal factors which affect the plant.

Q186. What is the first stable compound formed in the Calvin cycle?

Solution

3-Phosphoglyceric acid

Q187. Internally, the chloroplast consists of which fluid?

Solution

Stroma

Q188. How does an increase in light intensity affect the rate of photosynthesis?

Solution

When there is an increase in the incident light beyond a point, it causes the breakdown of chlorophyll, thus decreasing photosynthesis.

Q189. For the production of one molecule of glucose by Calvin cycle, how many molecules of CO₂ need to be fixed?

Solution

Six molecules of CO₂ are fixed for the production of one molecule of glucose by the Calvin cycle.

Q190. Why is that leaves kept in dark frequently become yellow or pale green in colour? Which chloroplast pigment is more stable?

Solution

In the dark, there is no production of chlorophyll. Chlorophyll present in the leaf is degraded, thus making the leaf pale green or yellow. Carotenoid is a more stable pigment.

Q191. Photorespiration does not take place in C₄ plants. Explain.

Solution

Photorespiration occurs due to the oxygenase activity of RuBisCO. When the concentration of O₂ is high, RuBisCO binds to oxygen and carries out photorespiration. C₄ plants have a mechanism of maintaining high CO₂ concentration at the enzyme site, thus photorespiration does not occur.

Q192. Why are leaves of a plant present on the shaded side more dark green as compared to those present on the sunny side?

Solution

Leaves on the shaded side are more green as compared to those present on the sunny side because they have more chlorophyll. Chlorophyll is responsible for the green colour of leaves. Because the leaves are on the shaded side, they need more chlorophyll to trap more light to carry out photosynthesis.

Q193. What is the possible reason for the occurrence of cyclic photophosphorylation?

Solution

For the fixation of one molecule of CO₂, 3 ATP and 2 NADPH molecules are required; thus, in order to meet this difference in the number of ATP and NADPH molecules, cyclic photophosphorylation occurs.

Q194. Name a technique used for the separation of photosynthetic pigments. Which pigments are separated? How do you distinguish pigments from each other?

Solution

Chromatography is used for the separation of photosynthetic pigments. The pigments separated by this technique are Chlorophyll a Chlorophyll b Xanthophylls Carotenoids Each of the separated pigments appears with a different colour and thus can be easily differentiated. Chlorophyll a – Bright or blue green Chlorophyll b – Yellow green Xanthophylls – Yellow Carotenoids – Yellow to yellow orange

Q195. Explain the experiment conducted by Joseph Priestley. Give its conclusions.

Solution

Joseph Priestley conducted an experiment to determine the importance of air for the growth of green plants. He conducted a series of experiments in which he placed a burning candle and a mouse in a bell jar, such that no air could leave or enter the jar. He observed that in this set, the mouse died of suffocation. In the next set, he placed a mint plant along with the mouse and burning candle in the jar. Here, the mouse did not suffocate and lived, and the candle kept on burning. Based on these sets of the experiment, Priestley concluded that Animals which breathe air or a burning candle damaged the air in some way. Green plants restore to the air whatever the burning candle or breathing animals remove.

Q196. Julius von Sachs provided evidence for which facts based on his experiment on green plants?

Solution

He found that the green parts of the plant make glucose, and glucose is usually stored in the form of starch.

Q197. Why is chlorophyll a the chief photosynthetic pigment?

Solution

Chloroplast a is the chief photosynthetic pigment as it shows higher rates of photosynthesis.

Q198. Expand RuBP. Give its role in photosynthesis.

Solution

Ribulose bisphosphate It acts as the first acceptor molecule of CO₂ and forms the first stable compound of the biosynthetic phase.

Q199. What is an LHC? Where is it present?

Solution

LHC is Light Harvesting Complex. It is present in both photosystem I and photosystem II.

Q200. List the internal and external factors which affect the rate of photosynthesis, and give details on three external factors.

Solution

Factors affecting the rate of photosynthesis are classified under two categories: Internal factors: Leaf size, number of leaves, shape of leaves, amount of chloroplast, mesophyll cell content, chlorophyll and internal concentration of CO₂ External factors: CO₂ concentration, sunlight, temperature and availability of water External factors which affect the rate of photosynthesis: Light: At low light intensities, there is a linear relationship between incident light and CO₂ fixation rates. At high light intensities, the rate of photosynthesis does not increase but other factors become limiting.

Light saturation occurs at 10% of full sunlight. Light is usually not a limiting factor, but when light intensity increases beyond a point, it causes break down of chlorophyll and decrease in photosynthesis. Temperature: Temperature mainly affects the dark reaction of photosynthesis. C₄ plants respond to higher temperatures and show higher rates of photosynthesis. C₃ plants, on the other hand, have a much lower temperature optimum.

The temperature dependency of plants for the rate of photosynthesis also depends on the habitat which the plant is living and the group of plants to which it belongs. Water: Water affects the rate of photosynthesis indirectly. Water stress causes the stomata to close in order to reduce transpiration. Closed stomata lead to decrease concentration of CO₂ in the cells, thus resulting in decrease in photosynthesis. Water stress also causes the leaves to wilt, thus reducing the surface area for photosynthesis.

Q201. Give a detailed account of the Hatch and Slack pathway.

Solution

The Hatch and Slack pathway is a cyclic pathway for CO₂ fixation. The primary CO₂ acceptor is a 3-carbon compound phosphoenol pyruvate (PEP) which is present in mesophyll cells. PEP in the mesophyll cells is converted to oxaloacetic acid (OAA), which is then further converted into a 4-carbon compound such as malic acid or aspartic acid, which is then transported to the bundle sheath cells. In the bundle sheath cells, it is again broken down into a 3-carbon compound with the release of CO₂.

The CO₂ released enters the Calvin cycle in the bundle sheath cells, while the 3-carbon compound is transported back to the mesophyll cells. In the mesophyll cells, the 3-carbon compound is converted back to PEP, thus completing the cycle.  

Q202. Name the different stages of the Calvin cycle.

Solution

The Calvin cycle comprises three stages: Carboxylation Reduction Regeneration

Q203. What did Priestley hypothesise following his experiment with a plant, mouse and burning candle inside a bell jar?

Solution

Plants restore to the air whatever breathing animals and burning candles remove.

Q204. Why does the Calvin cycle not occur in mesophyll cells?

Solution

Mesophyll cells lack the enzyme RuBisCO and thus cannot carry out the Calvin cycle.