Photosynthesis in Higher Plants — Class 11 MCQs with Answers

Photosynthesis in Higher Plants — important questions & MCQs with answers (Class 11 Biology)

14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.

1. Q1Easy

   Site of photosynthesis in cell:

   A.Nucleus

   B.Mitochondrion

   C.Chloroplast✓ Correct

   D.Ribosome

   Answer: C. Chloroplast

   Explanation: Chloroplasts hold thylakoids for light reactions and stroma for the Calvin cycle; mitochondria generate ATP via respiration, not photosynthesis.

2. Q2Easy

   Photosynthesis converts light energy primarily into which form?

   A.Heat energy

   B.Chemical energy in carbohydrates✓ Correct

   C.Mechanical energy

   D.Electrical energy

   Answer: B. Chemical energy in carbohydrates

   Explanation: Photosynthesis converts light energy primarily into chemical energy stored in C-C and C-H bonds of carbohydrates, not heat, mechanical or electrical forms.

3. Q3Easy

   CO₂ acceptor molecule in the Calvin cycle is:

   A.PGA

   B.PEP

   C.OAA

   D.RuBP (Ribulose-1,5-bisphosphate)✓ Correct

   Answer: D. RuBP (Ribulose-1,5-bisphosphate)

   Explanation: RuBisCO combines CO2 with RuBP (ribulose-1,5-bisphosphate), the Calvin cycle's actual CO2 acceptor; PEP is the C4 pathway's acceptor, not C3's.

4. Q4Easy

   Main pigment of photosynthesis:

   A.Carotenoid

   B.Chlorophyll a✓ Correct

   C.Anthocyanin

   D.Xanthophyll

   Answer: B. Chlorophyll a

   Explanation: Chlorophyll a is the primary pigment absorbing red and blue light at the reaction centre; chlorophyll b and carotenoids only pass energy to it as accessories.

5. Q5Easy

   Who demonstrated that O₂ released in photosynthesis comes from water?

   A.Cornelius van Niel

   B.Joseph Priestley

   C.Engelmann

   D.Ruben and Kamen✓ Correct

   Answer: D. Ruben and Kamen

   Explanation: Ruben and Kamen traced 18O-labelled water to the O2 released, proving photolysis of water is the source; van Niel only inferred this earlier from sulphur bacteria.

6. Q6Easy

   Primary CO₂ acceptor in C₄ plants is:

   A.RuBP

   B.PEP✓ Correct

   C.Pyruvate

   D.OAA

   Answer: B. PEP

   Explanation: In C4 mesophyll cells, PEP carboxylase fixes CO2 onto PEP, not RuBP, to form OAA; RuBP and RuBisCO act later in the bundle sheath cells.

7. Q7Medium

   O₂ released in photosynthesis comes from:

   A.CO₂

   B.Water (photolysis)✓ Correct

   C.Glucose

   D.Air

   Answer: B. Water (photolysis)

   Explanation: Ruben and Kamen's 18O-labelled water experiment showed O2 comes from photolysis of water at PSII, not from CO2 reduction in the Calvin cycle.

8. Q8Medium

   Blackman's law of limiting factors states that the rate of a process is limited by:

   A.Temperature only

   B.The factor in maximum supply

   C.Light intensity only

   D.The factor nearest its minimum value✓ Correct

   Answer: D. The factor nearest its minimum value

   Explanation: Blackman's law of limiting factors says the factor nearest its minimum value, not the one in maximum supply, sets the process rate; more of any other factor will not help.

9. Q9Medium

   First stable product of C₃ pathway:

   A.Glucose

   B.OAA

   C.3-PGA (3-phosphoglycerate)✓ Correct

   D.Pyruvate

   Answer: C. 3-PGA (3-phosphoglycerate)

   Explanation: The Calvin cycle's CO2 fixation by RuBisCO first yields two molecules of 3-PGA, a 3-carbon acid, hence the C3 pathway, distinct from C4's 4-carbon OAA.

10. Q10Medium

    Electron donor to PSII reaction centre after photolysis is:

    A.Ferredoxin

    B.NADPH

    C.Plastocyanin

    D.H₂O✓ Correct

    Answer: D. H₂O

    Explanation: After light splits water at PSII's oxygen-evolving complex, H2O itself donates electrons to the oxidised reaction-centre chlorophyll P680+, refilling it for the next photon.

11. Q11Medium

    At low light intensities, doubling CO₂ concentration would:

    A.Double the rate

    B.Not significantly increase photosynthesis✓ Correct

    C.Halve the rate

    D.Stop photosynthesis

    Answer: B. Not significantly increase photosynthesis

    Explanation: When light is the limiting factor at low intensity, raising CO2 does not proportionally raise photosynthesis; only increasing light, the truly limiting factor, would.

12. Q12Hard

    Light reactions produce:

    A.Starch

    B.Glucose only

    C.CO₂

    D.ATP and NADPH✓ Correct

    Answer: D. ATP and NADPH

    Explanation: Non-cyclic photophosphorylation across PSII and PSI yields ATP and NADPH, which power CO2 fixation in the Calvin cycle; no sugar forms during the light reactions themselves.

13. Q13Hard

    Assertion: Green plants release O₂ in light. Reason: O₂ originates from CO₂ during photosynthesis. Choose the correct option.

    A.Assertion true, Reason false✓ Correct

    B.Both true and Reason correct

    C.Both false

    D.Assertion false, Reason true

    Answer: A. Assertion true, Reason false

    Explanation: O2 released in photosynthesis originates from water split at PSII, not from CO2, so the assertion is true but the reason is false, as Ruben and Kamen's isotope tracing proved.

14. Q14Hard

    First stable product of C₄ pathway:

    A.Pyruvate

    B.3-PGA

    C.OAA (4-carbon)✓ Correct

    D.Glucose

    Answer: C. OAA (4-carbon)

    Explanation: PEP carboxylase fixes CO2 onto PEP in mesophyll cells, forming the 4-carbon oxaloacetate (OAA), the C4 pathway's signature first product, unlike C3's 3-PGA.

Photosynthesis in Higher Plants — FAQs

More Class 11 Biology chapters

• 01The Living World
• 02Biological Classification
• 03Plant Kingdom
• 04Animal Kingdom
• 05Morphology of Flowering Plants
• 06Anatomy of Flowering Plants

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