During photosynthesis, the light-independent reactions occur in which compartment of the chloroplast?
Answer: A
The Calvin cycle (light-independent reactions) takes place in the stroma of chloroplasts, where CO2 is fixed and glucose is synthesized.
Q.62Easy
Which element is essential for the synthesis of chlorophyll and is present at the center of the chlorophyll molecule?
Answer: B
Magnesium is the central atom in the porphyrin ring of chlorophyll molecules, making it essential for photosynthetic light absorption.
Q.63Easy
Which of the following hormones primarily promotes stomatal closure in response to water stress?
Answer: B
Abscisic acid is the stress hormone that promotes stomatal closure during drought by reducing guard cell turgor pressure, thereby reducing water loss.
Q.64Easy
In phloem transport, the source is typically the:
Answer: B
The source in phloem transport is any photosynthetically active tissue, primarily mature leaves, which produce and load photosynthates into sieve tubes.
Q.65Easy
Which of the following is the primary pigment involved in capturing light energy during photosynthesis?
Answer: A
Chlorophyll a is the primary pigment that directly participates in the photochemical reactions of both PSI and PSII, while other pigments act as accessory pigments.
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Q.66Easy
The rate of transpiration is LEAST affected by which of the following factors?
Answer: B
Soil pH has minimal direct effect on transpiration rate. Primary factors affecting transpiration are light, humidity, temperature, and wind velocity.
Q.67Easy
In C4 photosynthesis, the primary CO2 acceptor molecule is:
Answer: B
In C4 plants, CO2 first combines with PEP (3-carbon molecule) to form oxaloacetate (4-carbon), which is why it's called C4 photosynthesis.
Q.68Easy
Which hormone is primarily responsible for closing stomata under water stress conditions?
Answer: B
ABA accumulates in guard cells during water stress and causes stomatal closure by reducing turgor pressure in guard cells.
Q.69Easy
A student observes that a plant kept in a completely dark room still shows some gas exchange. This can be attributed to:
Answer: B
In darkness, photosynthesis stops, but aerobic respiration continues, consuming O2 and releasing CO2, resulting in measurable gas exchange.
Q.70Easy
During photosynthesis, the splitting of water molecules occurs in which compartment of the chloroplast?
Answer: B
Water photolysis (photosystem II) occurs in the thylakoid lumen where oxygen is released as a byproduct.
Q.71Easy
In the Calvin cycle, which enzyme catalyzes the fixation of CO2?
Answer: A
RuBisCO is the most abundant enzyme on Earth and catalyzes the carboxylation of RuBP with CO2 in the dark reactions.
Q.72Easy
The Q10 value for enzyme-catalyzed reactions is typically:
Answer: B
Q10 of 2.0-3.0 indicates that enzyme activity doubles or triples with every 10°C increase in temperature, typical for biological systems.
Q.73Easy
The grana in chloroplasts are composed of:
Answer: A
Grana are stacks of thylakoids arranged vertically, while stroma lamellae are unstacked thylakoids connecting different grana.
Q.74Easy
The phenomenon where plants lose water in liquid form through hydathodes is called:
Answer: B
Guttation occurs when root pressure forces water out through hydathodes (water pores) as liquid water droplets, typically at night.
Q.75Easy
Which of the following enzyme complexes in the thylakoid membrane is responsible for water splitting and oxygen evolution?
Answer: B
Photosystem II contains the oxygen-evolving complex (OEC) with a manganese cluster that catalyzes water splitting, releasing O2, H+, and electrons.
Q.76Easy
A desert plant maintains stomata closure during the day and opens them at night, fixing CO2 into malic acid. This adaptation is characteristic of which photosynthetic pathway?
Answer: C
CAM (Crassulacean Acid Metabolism) plants fix CO2 at night into malate and release it during the day for photosynthesis, reducing water loss in arid environments.
Q.77Easy
Stomatal opening is primarily regulated by the accumulation of which osmotically active solute in guard cells?
Answer: C
K+ accumulation in guard cells lowers the water potential, causing water influx and turgor increase, leading to stomatal opening. This is the primary mechanism.
Q.78Easy
Which of the following correctly describes the role of carotenoids in photosynthesis?
Answer: B
Carotenoids absorb light energy in blue and green regions, transfer it to chlorophyll, and provide photoprotection by quenching singlet oxygen and excess excitation energy.
Q.79Easy
The photoperiodic response in plants (flowering) is primarily detected by which photoreceptor?
Answer: C
Phytochrome exists in two interconvertible forms (Pr and Pfr) and acts as a red/far-red light sensor, measuring day length for photoperiodic flowering responses.
Q.80Easy
A variegated plant leaf shows white and green patches. Which organelle dysfunction is responsible for white patches?
Answer: B
White patches result from chloroplasts lacking chlorophyll or being non-functional, typically due to mutations in chloroplast DNA (maternal inheritance). Green patches have functional chloroplasts.
