Photosynthesis in Higher Plants — Class 11 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 11 Biology chapter "Photosynthesis in Higher Plants" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 11 Biology chapter "Photosynthesis in Higher Plants" — 8 important questions with detailed answers for CBS…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 11 Biology — Photosynthesis in Higher Plants. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Photosynthesis in Higher Plants — All 8 Questions Solved
Q1. What is photosynthesis?
Photosynthesis is an anabolic process in which light energy is used to synthesize organic compounds from carbon dioxide and water. It occurs primarily in chloroplasts of green plants and can be summarized as:
CO2 + H2O + light energy → (CH2O) + O2
The process has two stages: light-dependent reactions (light reactions) and light-independent reactions (dark reactions or Calvin cycle).
Q2. Where do light reactions occur in the chloroplast?
Light reactions occur in the thylakoid membrane of the chloroplast. The thylakoids are flattened sac-like structures stacked to form grana. Photosystem II and Photosystem I are embedded in the thylakoid membrane, along with electron transport chains and ATP synthase that participate in capturing light energy and producing ATP and NADPH.
Q3. What are the products of light reactions?
The light reactions produce three main products:
1. ATP (adenosine triphosphate) - energy currency
2. NADPH (reduced form of NADP+) - reducing agent/electron donor
3. Oxygen (O2) - released as a byproduct from photolysis of water
Both ATP and NADPH are used in the Calvin cycle (dark reactions) to synthesize glucose.
Q4. Explain the Calvin cycle in brief.
The Calvin cycle is a light-independent reaction occurring in the stroma. It has three stages:
1. Carbon fixation: CO2 combines with RuBP (5-carbon sugar) via enzyme RuBisCO to form 3-PGA (3-carbon compound)
2. Reduction: 3-PGA is reduced to G3P using ATP and NADPH from light reactions
3. Regeneration: G3P molecules regenerate RuBP using ATP
For every 6 molecules of CO2 fixed, one glucose molecule is synthesized.
Q5. What is the difference between C3 and C4 photosynthesis?
C3 photosynthesis (Calvin pathway): CO2 directly combines with RuBP to form 3-carbon compound (3-PGA). Found in most plants (rice, wheat, peas).
C4 photosynthesis: CO2 first combines with PEP (3-carbon) to form oxaloacetate (4-carbon), then converted to malate. Found in tropical plants (maize, sugarcane). C4 is more efficient in hot, dry conditions as it reduces photorespiration.
Q6. What is photorespiration? Why is it considered wasteful?
Photorespiration is the oxidation of RuBP when O2 concentration is high and CO2 is low. It occurs in C3 plants and results in the release of CO2 and consumption of ATP/NADPH without producing glucose.
It is wasteful because:
- No glucose is synthesized
- Organic compounds are oxidized
- Energy (ATP/NADPH) is consumed
C4 and CAM plants minimize photorespiration by maintaining high CO2 concentrations around RuBisCO.
Q7. What are the factors affecting the rate of photosynthesis?
Key factors affecting photosynthesis rate:
1. Light intensity - increases rate until saturation point
2. CO2 concentration - higher CO2 increases rate
3. Temperature - optimal around 25-35°C; affects enzyme activity
4. Chlorophyll concentration - more chlorophyll absorbs more light
5. Water availability - required as raw material and to maintain turgor
6. Mineral nutrients - especially Mg (in chlorophyll) and P (in ATP/NADPH)
At light saturation point, CO2 becomes the limiting factor.
Q8. What is the role of chlorophyll and accessory pigments?
Chlorophyll (a and b) are primary photosynthetic pigments that absorb light (maximum absorption in blue and red regions) and transfer energy to reaction centers of Photosystems.
Accessory pigments (carotenoids and xanthophylls) absorb light in wavelengths not efficiently absorbed by chlorophyll (mainly blue-green region) and transfer energy to chlorophyll.
Together they expand the light-capturing range and maximize light energy utilization in photosynthesis.
Photosynthesis in Higher Plants — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Who demonstrated for the first time that oxygen is evolved from water during photosynthesis, not from carbon dioxide?
- A. T.W. Engelmann
- B. Cornelius van Niel
- C. Joseph Priestley
- D. Jan Ingenhousz
Answer: B. Cornelius van Niel — Cornelius van Niel, working with purple and green sulfur bacteria, was the first to suggest that the oxygen released during photosynthesis comes from water, not carbon dioxide.
MCQ 2. Which of the following pigments is directly involved in the light reactions of photosynthesis as the reaction centre?
- A. Chlorophyll b
- B. Carotenoids
- C. Xanthophylls
- D. Chlorophyll a
Answer: D. Chlorophyll a — Chlorophyll 'a' is the primary photosynthetic pigment and the reaction centre pigment in both Photosystem I and Photosystem II, directly absorbing light energy and initiating electron transfer.
MCQ 3. During non-cyclic photophosphorylation, where do the electrons lost by PSII ultimately go?
- A. To the stroma
- B. To PSI
- C. To the lumen of the thylakoid
- D. To NADP+
Answer: D. To NADP+ — In non-cyclic photophosphorylation (Z-scheme), electrons released from PSII are transferred through an electron transport chain to PSI, and then ultimately used to reduce NADP+ to NADPH.
MCQ 4. In C4 plants, the bundle sheath cells are rich in which enzyme, crucial for the Calvin cycle?
- A. PEP carboxylase
- B. RuBisCO
- C. Malate dehydrogenase
- D. Pyruvate orthophosphate dikinase
Answer: B. RuBisCO — C4 plants exhibit Kranz anatomy where bundle sheath cells contain chloroplasts rich in RuBisCO, enabling the Calvin cycle, while mesophyll cells contain PEP carboxylase.
MCQ 5. How many molecules of ATP and NADPH are required to produce one molecule of glucose in the Calvin cycle?
- A. 12 ATP and 12 NADPH
- B. 18 ATP and 12 NADPH
- C. 18 ATP and 18 NADPH
- D. 6 ATP and 6 NADPH
Answer: B. 18 ATP and 12 NADPH — To fix 6 molecules of CO2 and synthesize one molecule of glucose, the Calvin cycle requires 18 molecules of ATP (3 ATP per CO2) and 12 molecules of NADPH (2 NADPH per CO2).
MCQ 6. Joseph Priestley discovered that plants restore the air that 'breathing animals and burning candles remove'. What was this 'restored air'?
- A. Carbon dioxide
- B. Nitrogen
- C. Oxygen
- D. Water vapor
Answer: C. Oxygen — Joseph Priestley, through his bell jar experiment with a mint plant, concluded that plants restore the air, which we now know as oxygen, essential for respiration and combustion.
MCQ 7. Which of the following wavelengths of light is most effectively absorbed by chlorophyll 'a'?
- A. Green and yellow light
- B. Blue and red light
- C. Orange and yellow light
- D. Violet and green light
Answer: B. Blue and red light — Chlorophyll 'a' shows maximum absorption in the blue-violet region and the red region of the visible light spectrum.
MCQ 8. Photorespiration typically occurs in C3 plants when the stomata close due to high temperature and drought conditions. What is the primary product of photorespiration that is not useful to the plant?
- A. Glucose
- B. ATP
- C. PGA
- D. Phosphoglycolate
Answer: D. Phosphoglycolate — In photorespiration, RuBisCO acts as an oxygenase, binding to O2 instead of CO2, leading to the formation of one molecule of PGA and one molecule of phosphoglycolate. Phosphoglycolate is a wasteful product that needs to be salvaged.
MCQ 9. The light-dependent reactions of photosynthesis occur in which part of the chloroplast?
- A. Stroma
- B. Outer membrane
- C. Thylakoid membranes
- D. Inner membrane
Answer: C. Thylakoid membranes — The thylakoid membranes within the chloroplast contain the photosynthetic pigments and electron transport chain components necessary for the light-dependent reactions.
MCQ 10. What is the main difference between cyclic and non-cyclic photophosphorylation regarding the final electron acceptor?
- A. Cyclic uses water as an electron donor, non-cyclic does not.
- B. Non-cyclic uses NADP+ as a final electron acceptor, cyclic does not.
- C. Cyclic produces NADPH, non-cyclic does not.
- D. Non-cyclic involves only PSI, cyclic involves both PSI and PSII.
Answer: B. Non-cyclic uses NADP+ as a final electron acceptor, cyclic does not. — In non-cyclic photophosphorylation, electrons are ultimately donated to NADP+ to form NADPH. In cyclic photophosphorylation, electrons cycle back to PSI, and no NADPH is produced.
MCQ 11. According to Blackman's Law of Limiting Factors, if all other conditions are optimal for photosynthesis, what would limit the rate of photosynthesis on a cloudy day?
- A. Carbon dioxide concentration
- B. Temperature
- C. Light intensity
- D. Water availability
Answer: C. Light intensity — Blackman's Law states that when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest factor. On a cloudy day, light intensity would be the limiting factor.
MCQ 12. The first stable product of CO2 fixation in the C3 pathway is:
- A. Oxaloacetic acid (OAA)
- B. Phosphoglyceric acid (PGA)
- C. Phosphoenolpyruvate (PEP)
- D. Ribulose-1,5-bisphosphate (RuBP)
Answer: B. Phosphoglyceric acid (PGA) — In the C3 pathway, RuBP combines with CO2 in the presence of RuBisCO to form two molecules of 3-phosphoglyceric acid (PGA), which is a 3-carbon compound, hence the name C3 pathway.
MCQ 13. The primary CO2 acceptor in C4 plants, found in mesophyll cells, is:
- A. RuBP
- B. PEP
- C. PGA
- D. OAA
Answer: B. PEP — In C4 plants, the primary CO2 acceptor is phosphoenolpyruvate (PEP), a 3-carbon compound, which combines with CO2 in mesophyll cells to form oxaloacetic acid (OAA).
MCQ 14. Photosystem II is predominantly located on which part of the thylakoid membrane?
- A. Stroma lamellae
- B. Outer surface of the thylakoid membrane facing the stroma
- C. Inner surface of the thylakoid membrane (lumen side) mainly
- D. Appressed regions of grana thylakoids
Answer: D. Appressed regions of grana thylakoids — Photosystem II is predominantly found in the appressed (stacked) regions of the grana thylakoids, while Photosystem I is found in both appressed and non-appressed regions, as well as stroma lamellae.
MCQ 15. The splitting of water molecules during photosynthesis, which releases oxygen, is called:
- A. Glycolysis
- B. Photolysis
- C. Hydrolysis
- D. Phosphorylation
Answer: B. Photolysis — Photolysis is the process where water molecules are split using light energy, releasing electrons, protons, and oxygen in the lumen of the thylakoid.
MCQ 16. The energy currency of the cell, ATP, is synthesized during photosynthesis through a process called:
- A. Substrate-level phosphorylation
- B. Oxidative phosphorylation
- C. Photophosphorylation
- D. Glycolysis
Answer: C. Photophosphorylation — Photophosphorylation is the process of ATP synthesis from ADP and inorganic phosphate using the energy derived from light during the light-dependent reactions of photosynthesis.
MCQ 17. C4 plants are more efficient in photosynthesis than C3 plants primarily because:
- A. They have more chlorophyll
- B. They lack photorespiration
- C. They grow in cooler climates
- D. They utilize water more efficiently
Answer: B. They lack photorespiration — C4 plants have evolved a mechanism (Kranz anatomy and C4 pathway) that concentrates CO2 around RuBisCO in bundle sheath cells, effectively minimizing photorespiration, which is a wasteful process in C3 plants.
MCQ 18. Where does the Calvin cycle (biosynthetic phase) take place in a plant cell?
- A. Cytoplasm
- B. Mitochondria
- C. Stroma of the chloroplast
- D. Thylakoid lumen
Answer: C. Stroma of the chloroplast — The Calvin cycle (biosynthetic phase or dark reaction) occurs in the stroma of the chloroplast, utilizing the ATP and NADPH produced during the light reactions.
MCQ 19. What is the primary role of accessory pigments like carotenoids and chlorophyll b in photosynthesis?
- A. To directly absorb light and convert it to chemical energy
- B. To provide structural support to the photosynthetic machinery
- C. To protect chlorophyll a from photo-oxidation and broaden the absorption spectrum
- D. To break down water molecules
Answer: C. To protect chlorophyll a from photo-oxidation and broaden the absorption spectrum — Accessory pigments absorb light at different wavelengths and transfer the energy to chlorophyll a, thus broadening the spectrum of light used. They also protect the reaction center from excessive light by dissipating excess energy.
MCQ 20. Which of the following is exclusively produced during cyclic photophosphorylation?
- A. ATP and NADPH
- B. ATP only
- C. NADPH only
- D. Oxygen
Answer: B. ATP only — Cyclic photophosphorylation involves only Photosystem I and recycles electrons, producing only ATP. It does not involve water splitting, hence no oxygen is released, and NADP+ is not reduced to NADPH.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.