Important Questions for CBSE Class 11 Biology Chapter 13 - Photosynthesis in Higher Plants

Very Short Answer Questions.  (1 Mark)

1. Expand NADP. 

Ans: NADP stands for Nicotinamide adenine dinucleotide phosphate. 

2. Name one plant that carries out photosynthesis at night? 

Ans: Opuntia and chenopodium perform photosynthesis during the night.

3. Name the cell–organelles involved in photorespiration. 

Ans: Mitochondria, chloroplast, and peroxisomes. 

4. Why is photosynthesis important? 

Ans: 

(a) Photosynthesis is the primary source of all food on the planet.

(b) Green plants emit O2 into the atmosphere.

5. Define photosynthesis? 

Ans: Photosynthesis is an endergonic, anabolic, and oxidation-reduction process by which green plants produce food from raw components in sunlight.

6. What is the site for photosynthesis in Opuntia? 

Ans: Stem is the site for photosynthesis in Opuntia.

7. Explain chlorophyll is an essential photosynthetic pigment?

Ans: In a reaction center of the photosystem, chlorophyll–b and other pigments absorb sun energy and transfer it to chlorophyll–a. In the end, it is chlorophyll-a that initiates the photosynthetic process.

8. What is the end product of the light reaction? 

Answer: ATP, NADPH2, and O2.

9. Give examples of photosynthetic microorganisms which also fix atmospheric nitrogen? 

Ans: Anabaena, Notec. 

10. Name two photosynthetic pigments belonging to Carotenoids. 

Ans: Carotene and Xanthophyll. 

11. How many molecules of ATP are required for the synthesis of one molecule of glucose in the C3 and C4 pathways? 

Ans: In the C3 pathway, there are 18 ATP molecules present and in C4 pathway, there are 30 ATP molecules present. 

12. What part of sunlight is most suitable for photosynthesis? 

Ans: Photosynthesis is more effective in the blue and red parts of the light spectrum.

13. Which one of the photosystems can carry on photophosphorylation independently? 

Ans: PS-I. 

14. Name two plants that can carry out photosynthesis at night

Ans: Opuntia, Chenopodium, Bougainvillea.

15. Name the enzyme which is found abundantly in the world. 

Ans: RuBisCO.

16. Name the scientist who Proposed the pathway. 

Ans: Hatch and Slack.

17. Where does carbon fixation occur in the chloroplast. 

Ans: Carbon fixation occurs in the stroma in the chloroplast.

18. Which compound acts as CO, acceptor in the Calvin cycle? 

Ans: Ribulose 1,5 bisphosphate.

19. Name the end products of light reaction. 

Ans: ATP, NADPH, and O2

Short Answer Questions (2 Marks)

1. What is a red Drop? 

Ans: It is the occurrence of a drop in photosynthetic yield beyond the red part of the spectrum. This is also known as the Emerson effect.

2. What are the enzymes that catalyze the dark reaction of carbon fixation located? 

Ans: During the dark process, the stroma contains enzymes that can use ATP and NADPH2 to create carbohydrates. Carbon fixation takes place in the stroma via a succession of enzyme-catalyzed reactions situated outside the thylakoids.

3. What are the two main functions of pigments other than chlorophyll in green leaves? 

Ans: 

(i) Light energy is absorbed and transferred to chlorophyll for photosynthesis.

(ii) To prevent photooxidation of the chlorophyll molecule.

4. Differentiate between respiration and photorespiration.

Ans: Respiration: It takes place in all types of plants C3 and C4 Glucose is the substrate of this kind of reaction.

Photorespiration: It takes place in C3 plants only. In peroxisomes, glycolate is the substrate that is converted into glycine, NH3, and CO2.

5. Explain the role of water in photosynthesis.

Ans: 

(i) Photosynthesis acts as a reactant in the light reaction.

(ii) Water stress induces stomata to close.

(iii) It reduces carbon dioxide availability.

(iv) It lowers leaf surface area.

6. What is the law of limiting factors? 

Ans: According to this law, “if a chemical process is influenced by more than one component that is closest to its minimal value; then the rate will be defined by the factor that is closest to its minimal value; it is the factor that directly influences the process if its quantity is changed.”

7. Compare chlorophyll ‘a’ and chlorophyll ‘b’?

Ans: Chlorophyll a has a methyl group at the third carbon position of the porphyrin head's II pyrrole ring. Whereas chlorophyll b has an aldehyde group at the third carbon position of the II pyrrole ring or porphyrin head.

Chlorophyll a has the greatest absorption at 429 nm (blue) and 660 nm (red) whereas chlorophyll b has the greatest absorption at 453 nm (blue) and 642 nm (red) wavelengths.

Chlorophyll a is very soluble in petroleum and ether whereas chlorophyll b is soluble in methyl alcohol.

Chlorophyll a is blue-green in color whereas chlorophyll b is yellow-green in color.

8. What is kranz anatomy?

Answer: Kranz anatomy is defined as the anatomy in which the vein of the leaf is wrapped by a bundle sheath holding a number of chloroplasts and having bull shape cells in the upper epidermis.

9. Give advantages of C4 cycle over C3 Cycle.

Ans: 

(i) The C4 cycle is more efficient than the C3 cycle.

(ii) C4 plants do not have photorespiration.

(iii) In comparison to C3 plants, the C4 cycle may utilize C02 at relatively low quantities.

(iv) The C4 cycle works in plants that are suited to high light intensity, high temperature, and low water availability; the C3 cycle cannot work under these conditions.

10. Why does the rate of photosynthesis decline in the presence of continuous light? 

Ans: The rate of photosynthesis declines in the presence of continuous light because the breakdown of chlorophyll is caused by an increase in incident light above a certain point. 

11. Why do green plants start evolving carbon dioxide instead of oxygen on a hot sunny day? 

Ans: When the enzyme RuBP carboxylase becomes active on a hot bright day, its affinity COreduces and increases. Photorespiration is causing an increase in the loss of photosynthetically fixed carbon.

12. Fill the space, left blank in the given table to bring the difference between C3 and C4 plants:

Ans: 

(a) Bundle sheath

(b) RuBP

(c) Oxaloacetic acid

(d) 20oC to 250C

13. State two functions of accessory pigments found in thylakoids. 

Ans: 

(a) Light absorption and energy transfer to chlorophyll ‘a'.

(b) Prevent photooxidation of chlorophyll ‘a’.

14. Why do C3 and C4 plants are more expensive than C3 plants. 

Ans: C4 plants are more expensive than C3 plants because they absorb more energy (30 ATPs) to synthesize one glucose molecule than C3 (18 ATPs).

Short Answer Question (3 Marks)

1. Explain -There is no oxygen evolution in bacterial photosynthesis. 

Ans: The raw material for proton delivery in bacterial photosynthesis is H2S rather than H2O As a result, S is produced rather than O2 during the light reaction's splitting.

The reaction is shown below.

$2H_{2}S\rightarrow 2HS^{+}+2H^{+}$

$HS+HS\rightarrow H_{2}S+S$

2. What is the advantage of using chlorella rather than a higher plant? 

Ans: Although photosynthesis in chlorella and higher plants is biochemically similar, Melvin Calvin (1954) chose chlorella for the following reasons:

(i) Chlorella culture is a chloroplast culture because a single chloroplast occupies a substantial volume of each cell.

(ii) Synchronous culture can be easily accomplished in a short period of time.

(iii) Cells are killed quickly when exposed to radioactive carbon dioxide. So, handling chlorella for research is simplified.

3. What is the advantage of having more than one pigment molecule in a photo center? 

Ans: The amount of solar energy captured by the pigment determines the light reaction. The energy captured by a single pigment molecule is insufficient to initiate the initial reaction that may occur in the light. As a result, a variety of pigment molecules protect the chlorophyll molecule from light oxidation.

4. Why are C4 plants preferred in the tropical region? 

Ans: C4 plants use 30 ATP molecules to make one molecule of glucose, which is preferred in tropical regions. Photorespiration is the method used by these plants to avoid losing photosynthetic carbon. Instead of mixing with CO2, RuBP is catabolized to a 3-carbon atom molecule during photorespiration. Photorespiration consumes more than half of the CO2 fixed by photosynthesis. Since no energy-rich chemical is created during this phase, photorespiration acts to undo the activity of photosynthesis. Thus, C4 plants photosynthesize better than C3 plants, and the C4 pathway has an adaptation benefit in tropical regions, hence these plants are favored.

5. Distinguish between photosystem – I and Photosystem – II.

Ans: Photosystem – I: It is a collection of pigment molecules that absorb light with wavelengths of 700 nm or less. The light collected by any pigment molecule in the cluster is transferred to the reaction center, P700. It has a high proportion of chlorophyll a to chlorophyll b.

Photo system-II: It is a collection of pigment molecules that absorb light with wavelengths of 680 nm or less. The light collected by any pigment molecule in the cluster is transferred to the reaction center, P680. It has a high amount of chlorophyll b to chlorophyll a.

6. How does temperature affect photosynthesis? 

Ans: The temperature of the dark reactions is controlled. C4 plants adapt to greater temperatures, and they have a high rate of photosynthesis. C3 has a much lower optimal temperature. Photosynthesis occurs at a higher temperature in tropical plants.

7. The figure shows the effect of light on the rate of photosynthesis Based on the graph, answer the following questions: (i) At which point(s) A, B, or C in the curve, light is a limiting factor? (ii) What could be the limiting factor/s in region A? (iii) What do regions C and D represent on the curve?

Ans: 

(a) In general, light is not a limiting factor.  It becomes a limiting factor for plants growing in the shadow or under tree canopies. Light is a limiting factor in the provided graph at the point where photosynthesis is at its lowest. Region A has the lowest photosynthesis value. As a result, light is a limiting element in this area.

(b) In region A, light is a limiting factor. Water, temperature, and carbon dioxide concentrations could all be limiting factors in this region.

(c) Point D denotes the optimum point and the light intensity at which maximum photosynthesis is seen. Even though the intensity of light decreases after this point, the rate of photosynthesis remains constant.

8. What are the steps that are common to C3 and C4 photosynthesis?

Ans: 

(a) Both C3 and C4 plants undergo photolysis of H2O and photophosphorylation. 

(b) In both cases, the stroma undergoes a dark response. 

(c) Starch is formed in both plants as a result of the Calvin cycle. 

(d) Both types of plants go through carboxylation and regeneration phases during the dark reaction.

9. Two potted plants were kept in an oxygen-free environment in transparent containers, one in total darkness and the other in sunlight. Which one of the two is likely to survive more? Justify your answer by giving the reason.

Ans: The plant that is kept in natural sunlight will live longer. The plant which is kept in the dark is unable to perform photosynthesis, therefore, the container will quickly fill with carbon dioxide. The plant would die if there was insufficient oxygen in the container. The plant that is kept in light, on the other hand, will be able to perform photosynthesis and hence, they would be able to transform carbon dioxide into oxygen. As a result, this plant will live for a longer period of time.

Long Answer Questions (5 Marks)

1. (a) suggest some habitats or natural circumstances in which 

(i) Light intensity 

(ii) CO2 concentration 

(iii) temperature might be a limiting factor in photosynthesis. 

(b) In C4 plants which type of chloroplast is specialized for light reactions and which for dark reactions? 

(c) Why is it an advantage that bundle sheath chloroplast lacks grana?

Ans: Some circumstances are as follows:

(i) In a shaded neighborhood; dawn and twilight in a hot climate.

(ii) Carbon dioxide is typically limiting, but it may be particularly so in a densely packed plant standing under bright, warm conditions.

(iii) On a sunny winter day.

(b) Light reaction in mesophyll chloroplast and bundle sheath chloroplast for dark reaction 

(c) The synthesis of oxygen is linked to grana, because oxygen would compete with CO2 for RuBP carboxylase, stimulating photorespiration. Grana take up a considerable portion of the chloroplast. In their absence from the bundle sheath, there is more stroma, which means more RuBP carboxylase and greater starch storage capacity.

2. Briefly explain the chemiosmotic hypothesis?

Ans: The mechanism of ATP synthesis in chloroplasts was explained by the chemiosmotic hypothesis. ATP generation in photosynthesis is tied to the formation of a proton gradient across a membrane. These are thylakoids membranes. The proton accumulation is toward the membrane's interior (in the lumen).

The mechanisms that happen during electron activation and transit to establish the steps that lead to the formation of a proton gradient. The establishment of a proton gradient is linked to the synthesis of ATP.

3. Explain the process of the biosynthetic phase of photosynthesis occurring in the chloroplast.

Ans: Biosynthetic phase (Dark Reaction): It is the carbon fixation in plants by which carbon - dioxide is converted to carbohydrates during the biosynthetic phase (Dark Reaction). Carbon is fixed in the stroma of chloroplasts via a series of enzyme-catalyzed processes.

C3 pathway: It is referred to as the Calvin cycle. Melvin Calvin traced the pathway of carbon in the dark reaction using autoradiography and 14C and therefore, this pathway is known as the Calvin cycle.

Calvin Cycle Consist of Three Phases:

(i) Carboxylation: Six molecules of Ribulose 1, 5 bisphosphates combine with six molecules of carbon dioxide to produce six molecules of carbon dioxide and six molecules of a short-lived 6C – compound. The process is catalyzed by RuBP – carboxylase (Rubisco). Six molecules of the 6C – compound combines to form 12 molecules of 3-phosphoglyceric acid (PGA), the first stable chemical in this pathway. 

(ii) Reduction: Using ATP and NADPH molecules, 12 molecules of phosphoglyceric acid are transformed into 12 molecules of 1,3 diphosphoglycerate, which is subsequently reduced to phosphoryl acetaldehyde (PGAL). Two molecules of PGAL are diverted for sugar production and then into starch. 

(iii) Regeneration of RuBP – The principal acceptor of carbon dioxide, i.e., RuBP, must be regenerated by converting 10 molecules of PGAL into 6 molecules of 5C – chemical, RuBP, via a series of complicated reactions. Six ATP molecules are required for the formation of six RuBP molecules.

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