Part 1 — Historical Experiments, Chloroplast, Pigments (Q1–25)

Part 1 — Historical Experiments, Chloroplast, Pigments (Q1–25)

Q1.

Joseph Priestley’s experiment with a candle and a mouse in a closed jar demonstrated:
A. Plants release CO₂
B. Plants release O₂ ✅
C. Plants absorb O₂
D. Plants release nitrogen

Explanation:

• A. Plants do not release CO₂ in light; they absorb it.
• B. (Correct) Priestley showed that plants restore “something” (O₂) that keeps a candle burning and mouse alive.
• C. Not correct, O₂ is absorbed only in respiration.
• D. Nitrogen not involved in his experiment.

Q2.

Jan Ingenhousz proved that:
A. Green parts release O₂ only in presence of sunlight ✅
B. Plants take CO₂ from soil
C. Plants respire only at night
D. Plants produce starch in darkness

Explanation:

• A. (Correct) Ingenhousz demonstrated O₂ is released only in sunlight and by green parts.
• B. Plants absorb CO₂ from air, not soil.
• C. Respiration is continuous.
• D. Starch synthesis requires light.

Q3.

Julius von Sachs showed that:
A. Glucose is final product
B. Starch is produced during photosynthesis ✅
C. Oxygen is produced by roots
D. Carbohydrates are absorbed from soil

Explanation:

• A. Glucose is produced but Sachs proved starch presence.
• B. (Correct) Sachs demonstrated starch formation in green leaves as evidence of photosynthesis.
• C. O₂ is released by leaves.
• D. Not correct, plants synthesize carbohydrates.

Q4.

Which scientist demonstrated action spectrum of photosynthesis using filamentous algae?
A. Julius von Sachs
B. Engelmann ✅
C. Blackman
D. Priestley

Explanation:

• A/D. Different experiments.
• B. (Correct) Engelmann used a prism + Cladophora algae and aerobic bacteria → action spectrum.
• C. Blackman studied limiting factors.

Q5.

Engelmann’s experiment demonstrated:
A. CO₂ fixation in roots
B. O₂ release is highest at red and blue light ✅
C. Photosynthesis requires water only
D. Plants absorb green light efficiently

Explanation:

• A. Incorrect.
• B. (Correct) Aerobic bacteria clustered near regions of red and blue light → action spectrum.
• C. Requires CO₂, light, chlorophyll, water.
• D. Green light least absorbed.

Q6.

Blackman’s Law of Limiting Factors states that:
A. Photosynthesis depends on temperature only
B. Rate of photosynthesis is controlled by the factor in least supply ✅
C. Light intensity always limits rate
D. CO₂ is never a limiting factor

Explanation:

• A/C/D. Oversimplifications.
• B. (Correct) When multiple factors affect, the slowest/least available factor limits rate.

Q7.

Cornelius van Niel proposed the general equation of photosynthesis and proved:
A. O₂ comes from CO₂
B. O₂ comes from water ✅
C. O₂ comes from soil
D. O₂ comes from chlorophyll

Explanation:

• A. Previously assumed but incorrect.
• B. (Correct) Van Niel studied photosynthetic bacteria → O₂ evolved from H₂O, not CO₂.
• C/D. Not correct.

Q8.

Chloroplast is bounded by:
A. Single membrane
B. Double membrane ✅
C. Triple membrane
D. Protein coat

Explanation:

• A. Mitochondria/chloroplast are double-membraned.
• B. (Correct) Chloroplast has outer and inner envelope membranes.
• C/D. Not true.

Q9.

The site of light reactions in chloroplast is:
A. Stroma
B. Thylakoid membranes ✅
C. Outer membrane
D. Matrix

Explanation:

• A. Stroma hosts dark reactions (Calvin cycle).
• B. (Correct) Thylakoid membranes house PS I & PS II, ETC, ATP synthase.
• C/D. Not sites of light reaction.

Q10.

The site of dark reactions (Calvin cycle) is:
A. Thylakoid lumen
B. Stroma ✅
C. Intermembrane space
D. Grana

Explanation:

• A. Proton accumulation site.
• B. (Correct) Stroma contains enzymes for Calvin cycle.
• C/D. Not the site.

Q11.

Grana are stacks of:
A. Starch granules
B. Thylakoids ✅
C. Cristae
D. Rubisco

Explanation:

• A. Starch is stored separately.
• B. (Correct) Grana are stacks of thylakoids.
• C. Cristae are in mitochondria.
• D. Rubisco is stromal enzyme.

Q12.

Which pigment acts as the primary reaction center in photosynthesis?
A. Chlorophyll b
B. Chlorophyll a ✅
C. Carotenoids
D. Xanthophylls

Explanation:

• A/C/D. Accessory pigments.
• B. (Correct) Chlorophyll a at PS I (P700) and PS II (P680) is the reaction center.

Q13.

Which pigment is essential but accessory to chlorophyll a?
A. Chlorophyll b ✅
B. Hemoglobin
C. Bilirubin
D. Ferredoxin

Explanation:

• A. (Correct) Chlorophyll b broadens absorption spectrum.
• B/C/D. Not photosynthetic pigments.

Q14.

Which pigment protects chlorophyll from photo-oxidation?
A. Carotenoids ✅
B. Chlorophyll b
C. Anthocyanin
D. Xanthophyll

Explanation:

• A. (Correct) Carotenoids act as accessory pigments + photoprotection.
• B. Accessory role, but not protection.
• C. Anthocyanins color petals, not photosynthesis.
• D. Xanthophyll is a type of carotenoid, also protective, but carotenoids is the broader correct term.

Q15.

Which is the absorption peak of chlorophyll a?
A. 450 nm (blue) and 680 nm (red) ✅
B. 600 nm and 700 nm
C. 400 nm and 520 nm
D. 500 nm and 600 nm

Explanation:

• A. (Correct) Chl a absorbs strongly in blue (~430–450 nm) and red (~660–680 nm).
• B-D. Not correct absorption peaks.

Q16.

Which pigment is absent in higher plants but present in cyanobacteria and red algae?
A. Chlorophyll b
B. Phycobilins ✅
C. Carotenoids
D. Xanthophyll

Explanation:

• A/C/D. Present in higher plants.
• B. (Correct) Phycobilins (phycoerythrin, phycocyanin) are accessory pigments in cyanobacteria, red algae.

Q17.

Action spectrum differs from absorption spectrum because:
A. Action spectrum shows pigments only
B. Action spectrum shows actual photosynthetic activity ✅
C. Absorption spectrum shows O₂ release
D. Absorption spectrum shows ATP formation

Explanation:

• A/D. Not true.
• B. (Correct) Absorption = pigments absorbing light; Action = rate of photosynthesis under different wavelengths.
• C. O₂ release used in Engelmann’s experiment, not definition.

Q18.

In Engelmann’s experiment, which organisms aligned at regions of high O₂?
A. Yeast
B. Aerobic bacteria ✅
C. Cyanobacteria
D. Protozoa

Explanation:

• A/C/D. Not used.
• B. (Correct) Aerobic bacteria clustered near red/blue light zones where O₂ was released.

Q19.

Accessory pigments in photosynthesis:
A. Absorb all wavelengths
B. Transfer excitation energy to chlorophyll a ✅
C. Release oxygen
D. Are present in roots

Explanation:

• A. Not all wavelengths.
• B. (Correct) Accessory pigments broaden spectrum, transfer energy to Chl a.
• C. Only Chl a at reaction center evolves O₂.
• D. Roots lack pigments.

Q20.

Which pigment is golden yellow and found in all higher plants?
A. Carotenoids ✅
B. Anthocyanin
C. Chlorophyll b
D. Phycobilins

Explanation:

• A. (Correct) Carotenoids (carotenes + xanthophylls) are golden yellow.
• B. Anthocyanin gives red/blue coloration.
• C. Green pigment.
• D. Found in algae.

Q21.

Stroma lamellae differ from grana lamellae because they:
A. Lack PS II ✅
B. Lack PSI
C. Lack pigments
D. Lack ATP synthase

Explanation:

• A. (Correct) Stroma lamellae have only PSI and ATP synthase; no PS II.
• B. PSI is present.
• C/D. They contain pigments and ATP synthase.

Q22.

Which is the universal pigment of photosynthesis?
A. Chlorophyll a ✅
B. Chlorophyll b
C. Carotenoids
D. Phycobilins

Explanation:

• A. (Correct) Chl a is essential in all oxygenic photosynthesis.
• B-D. Accessory pigments, absent in some groups.

Q23.

Why are green leaves not black despite absorbing much light?
A. They reflect green wavelengths ✅
B. They absorb only red light
C. They lack pigments
D. They scatter all light

Explanation:

• A. (Correct) Leaves reflect green wavelengths → appear green.
• B. They absorb blue + red strongly too.
• C/D. Not correct.

Q24.

Which structure in chloroplast is directly involved in ATP synthesis?
A. Stroma
B. Thylakoid membrane (CF₀–CF₁ ATP synthase) ✅
C. Outer membrane
D. Granule

Explanation:

• A. Stroma hosts Calvin cycle.
• B. (Correct) ATP is produced via chemiosmosis across thylakoid membrane.
• C/D. Not involved.

Q25.

The first step of photosynthesis that converts light energy into chemical energy occurs in:
A. Stroma
B. Photosystems (reaction centers) ✅
C. Mitochondria
D. Nucleus

Explanation:

• A. Stroma = dark reaction.
• B. (Correct) PS II and PS I in thylakoid membranes capture photons, excite electrons → start photochemistry.
• C/D. Not sites of photosynthesis.

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