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Photosynthesis in Higher Plants — NEET Biology MCQs with Solutions
Free NEET Biology Photosynthesis in Higher Plants MCQs with step-by-step solutions covering Early Experiments, Site & Pigments, Light Reaction & Photophosphorylation, Chemiosmosis, C3 Pathway (Calvin Cycle), C4 Pathway & Photorespiration, Factors Affecting Photosynthesis. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Early Experiments, Site & Pigments · easy · theory
The most abundant photosynthetic pigment, absorbing chiefly blue and red light and reflecting green, is:
A. Chlorophyll b
B. Xanthophyll
C. Chlorophyll a ✓ Correct
D. Carotene
Solution: Chlorophyll a is the chief pigment (reaction centre); accessory pigments (chl b, carotenoids) widen the absorbed spectrum.
Q2 — Early Experiments, Site & Pigments · easy · theory
Photosynthesis in higher plants takes place in the:
A. Chloroplast (mesophyll) ✓ Correct
B. Cell wall
C. Mitochondrion
D. Nucleus
Solution: The chloroplast is the site: light reactions occur in the thylakoid (grana) and the Calvin cycle in the stroma.
Q3 — Light Reaction & Photophosphorylation · easy · theory
The splitting of water (photolysis) that releases O₂, protons and electrons is associated with:
A. Photosystem II ✓ Correct
B. The Calvin cycle
C. Photosystem I
D. Glycolysis
Solution: Water splitting occurs on the inner thylakoid side associated with PS II, replenishing its electrons.
Q4 — Light Reaction & Photophosphorylation · easy · theory
The products of the light reaction that are used in the dark reaction are:
A. ATP and NADH
B. Glucose and O₂
C. CO₂ and water
D. ATP and NADPH ✓ Correct
Solution: The light reaction produces assimilatory power (ATP + NADPH) used to fix CO₂ in the Calvin cycle.
Q5 — Chemiosmosis · easy · theory
ATP synthesis in the chloroplast is driven by a proton gradient across the ______ membrane:
A. Nuclear
B. Mitochondrial inner
C. Thylakoid ✓ Correct
D. Outer chloroplast
Solution: Protons accumulate in the thylakoid lumen; their flow back through ATP synthase makes ATP — chemiosmosis.
Q6 — Chemiosmosis · easy · theory
During the light reaction, protons accumulate in the ______ of the thylakoid:
A. Lumen (inner space) ✓ Correct
B. Cytosol
C. Intermembrane space of mitochondria
D. Stroma
Solution: Water splitting (in the lumen) and electron transport pump protons into the lumen, creating a gradient.
Q7 — C3 Pathway (Calvin Cycle) · easy · theory
The primary CO₂ acceptor in the Calvin (C3) cycle is:
A. RuBP (ribulose-1,5-bisphosphate) ✓ Correct
B. PEP
C. OAA
D. Pyruvate
Solution: RuBP (5-C) accepts CO₂; the first stable product is 3-PGA (a 3-carbon acid) — hence "C3".
Q8 — C3 Pathway (Calvin Cycle) · easy · theory
The first stable product of carbon fixation in the C3 pathway is:
A. Glucose
B. Oxaloacetic acid
C. Malic acid
D. 3-phosphoglyceric acid (3-PGA) ✓ Correct
Solution: CO₂ + RuBP → 2 molecules of 3-PGA (3-carbon), catalysed by RuBisCO.
Q9 — C4 Pathway & Photorespiration · easy · theory
The primary CO₂ acceptor in C4 plants (mesophyll cells) is ______, and the first product is ______:
A. PEP; oxaloacetic acid (OAA) ✓ Correct
B. PEP; malate only
C. RuBP; 3-PGA
D. RuBP; OAA
Solution: C4 plants fix CO₂ first via PEP carboxylase into OAA (4-carbon) in mesophyll cells.
Q10 — C4 Pathway & Photorespiration · easy · theory
C4 plants (e.g. maize, sugarcane) possess a special leaf anatomy called:
A. Isobilateral anatomy
B. Radial anatomy
C. Kranz anatomy ✓ Correct
D. Dorsiventral anatomy
Solution: Kranz ("wreath") anatomy features chloroplast-rich bundle sheath cells around the veins.
Q11 — Factors Affecting Photosynthesis · easy · theory
Blackman's law of limiting factors states that when several factors affect a process, its rate is limited by the factor that is:
A. At its maximum
B. Nearest to its minimum value ✓ Correct
C. Constant
D. Unrelated to the rate
Solution: The pace of the process is set by the most limiting (scarcest) factor at that time.
Q12 — Factors Affecting Photosynthesis · easy · theory
Which is NOT an external factor affecting photosynthesis?
A. Temperature
B. CO₂ concentration
C. Light
D. Number of chloroplasts (internal) ✓ Correct
Solution: External factors: light, CO₂, temperature, water. Internal factors include chlorophyll amount, leaf age, chloroplast number.
Q13 — Early Experiments, Site & Pigments · hard · theory
Carotenoids (accessory pigments) are important because they:
A. Release oxygen
B. Are the main reaction-centre pigment
C. Fix carbon dioxide
D. Absorb light at wavelengths chlorophyll cannot and protect chlorophyll from photo-oxidation ✓ Correct
Solution: Carotenoids extend the absorption range and protect chlorophyll from photo-oxidative damage.
Q14 — Early Experiments, Site & Pigments · hard · theory
An action spectrum superimposed on the absorption spectrum of chlorophyll a shows that photosynthesis is highest in blue and red because:
A. These wavelengths are absorbed most by chlorophyll and drive the reaction ✓ Correct
B. Chlorophyll absorbs all colours equally
C. Photosynthesis needs UV light
D. Green is absorbed most
Solution: The close match between action and absorption spectra confirms chlorophyll a as the primary light-harvesting pigment.
Q15 — Light Reaction & Photophosphorylation · hard · theory
The reaction-centre chlorophyll of PS I and PS II absorb maximally at, respectively:
A. P700 and P680 ✓ Correct
B. P700 and P700
C. P680 and P680
D. P680 and P700
Solution: PS I peaks at 700 nm (P700) and PS II at 680 nm (P680) — hence their names.
Q16 — Light Reaction & Photophosphorylation · hard · theory
Cyclic photophosphorylation also occurs when only wavelengths beyond ______ are available (only PS I functional):
A. 680 nm ✓ Correct
B. 400 nm
C. 550 nm
D. 300 nm
Solution: Beyond 680 nm only PS I works, so electron flow is cyclic, producing only ATP (the "red drop"/enhancement context).
Q17 — Chemiosmosis · hard · theory
In the chloroplast, NADPH and ATP are released into the ______, where the Calvin cycle occurs:
A. Stroma ✓ Correct
B. Cytosol
C. Thylakoid lumen
D. Intermembrane space
Solution: ATP synthase's catalytic site faces the stroma, so ATP (and NADPH) are made available in the stroma for carbon fixation.
Q18 — Chemiosmosis · hard · theory
Three factors set up the transmembrane proton gradient in the thylakoid: water splitting in the lumen, proton transport across the membrane by the electron carriers, and:
A. Uptake of CO₂
B. Removal of protons from the stroma by NADP⁺ reduction ✓ Correct
C. Photolysis in the stroma
D. Glucose oxidation
Solution: NADP⁺ reductase on the stromal side takes up stromal protons to make NADPH, deepening the gradient.
Q19 — C3 Pathway (Calvin Cycle) · hard · theory
The three phases of the Calvin cycle are, in order:
A. Regeneration → carboxylation → reduction
B. Carboxylation → reduction → regeneration (of RuBP) ✓ Correct
C. Reduction → regeneration → carboxylation
D. Carboxylation → regeneration → reduction
Solution: Carboxylation (CO₂ + RuBP), reduction (3-PGA → G3P using ATP/NADPH), and regeneration of RuBP.
Q20 — C3 Pathway (Calvin Cycle) · hard · theory
To synthesise one glucose molecule, the Calvin cycle must turn ______ times, fixing ______ CO₂:
A. 6; 6 ✓ Correct
B. 1; 6
C. 12; 12
D. 3; 3
Solution: Six turns fix six CO₂ molecules, consuming 18 ATP and 12 NADPH to produce one hexose.
Q21 — C4 Pathway & Photorespiration · hard · theory
C4 plants have negligible photorespiration because:
A. They do not use the Calvin cycle
B. They fix CO₂ only at night
C. The bundle sheath maintains a high CO₂ concentration around RuBisCO ✓ Correct
D. They lack RuBisCO
Solution: By pumping CO₂ into bundle sheath cells, C4 plants keep RuBisCO carboxylating, suppressing its oxygenase activity.
Q22 — C4 Pathway & Photorespiration · hard · theory
Photorespiration is considered a wasteful process because it:
A. Fixes additional CO₂
B. Increases glucose yield
C. Produces extra ATP
D. Consumes O₂ and releases CO₂ without producing ATP or NADPH (or sugar) ✓ Correct
Solution: Unlike normal respiration, photorespiration yields no ATP/NADPH and results in a net loss of previously fixed carbon.
Q23 — Factors Affecting Photosynthesis · hard · theory
Very high light intensity can DECREASE the photosynthetic rate due to:
A. Excess CO₂
B. Photo-oxidation (breakdown) of chlorophyll ✓ Correct
C. Increased water
D. Low temperature
Solution: Excessive light causes photo-oxidative damage (photoinhibition) to the pigments and photosynthetic apparatus.
Q24 — Factors Affecting Photosynthesis · hard · theory
The temperature response of photosynthesis differs between C3 and C4 plants in that:
A. Both have identical optima
B. Temperature has no effect on C4
C. C4 plants have a higher temperature optimum than C3 plants ✓ Correct
D. C3 plants tolerate higher temperatures
Solution: C4 plants are adapted to warmer, high-light environments and photosynthesise optimally at higher temperatures than C3 plants.
Q25 — Early Experiments, Site & Pigments · medium · theory
Engelmann's experiment, using a filamentous alga and aerobic bacteria, identified the ______ regions of the spectrum as most effective for photosynthesis:
A. Blue and red ✓ Correct
B. Green and yellow
C. Only green
D. Ultraviolet
Solution: Bacteria accumulated where blue and red light fell — the action spectrum peaks matching chlorophyll absorption.
Q26 — Early Experiments, Site & Pigments · medium · theory
Half-leaf experiments and Ruben's isotope studies established that the O₂ released in photosynthesis comes from:
A. Carbon dioxide
B. Glucose
C. The atmosphere directly
D. Water ✓ Correct
Solution: Using H₂¹⁸O, the released ¹⁸O₂ was traced to water — O₂ comes from the photolysis of water, not CO₂.
Q27 — Light Reaction & Photophosphorylation · medium · theory
In NON-cyclic photophosphorylation, electrons flow from ______ and both ATP and NADPH are produced:
A. PS II → PS I (Z-scheme), with water as the electron source ✓ Correct
B. CO₂ → glucose
C. NADPH → water
D. PS I → PS II
Solution: The Z-scheme: PS II → electron carriers → PS I → NADP⁺; water donates electrons and NADPH is formed.
Q28 — Light Reaction & Photophosphorylation · medium · theory
CYCLIC photophosphorylation involves only ______ and produces ______ (no NADPH, no O₂):
A. PS II; O₂
B. PS II; NADPH only
C. Both photosystems; glucose
D. PS I; ATP only ✓ Correct
Solution: In cyclic flow, electrons return to PS I; only ATP is made, with no water splitting or NADPH.
Q29 — Chemiosmosis · medium · theory
The enzyme that uses the proton-motive force to phosphorylate ADP is:
A. NADP reductase
B. RuBisCO
C. Cytochrome oxidase
D. ATP synthase (CF0–CF1) ✓ Correct
Solution: ATP synthase has a channel (CF0) letting protons cross and a catalytic head (CF1) that makes ATP.
Q30 — Chemiosmosis · medium · theory
Protons move from the thylakoid lumen back to the stroma through ATP synthase because:
A. They are pumped uphill
B. Of active transport
C. The stroma is more acidic
D. They flow down their electrochemical (concentration) gradient ✓ Correct
Solution: The high-H⁺ lumen releases protons to the low-H⁺ stroma; this diffusion powers ATP synthesis.