Question:
Examples of circadian rythm
(A). Seed germination in cereals once favourable conditions are met
(B). Root growth of plants into the soil
(C). Opening and closing of stomata
(D). Photosynthetic activity
Choose the correct answer from the options given below:
Examples of circadian rythm
(A). Seed germination in cereals once favourable conditions are met
(B). Root growth of plants into the soil
(C). Opening and closing of stomata
(D). Photosynthetic activity
Choose the correct answer from the options given below:
(A). Seed germination in cereals once favourable conditions are met
(B). Root growth of plants into the soil
(C). Opening and closing of stomata
(D). Photosynthetic activity
Choose the correct answer from the options given below:
Show Hint
Other classic plant circadian rhythms include the "sleep movements" (nyctinasty) of legume leaves, which fold at night and open during the day.
Updated On: Jul 13, 2026
- (A) and (B) only.
- (B) and (C) only.
- (C) and (D) only.
- (A) only.
Show Solution
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Circadian rhythms are endogenous, self-sustaining biological oscillations with a period of approximately 24 hours.
These rhythms are regulated by an internal molecular clock and persist even in the absence of external light or temperature cues.
Step 2: Detailed Explanation:
- Opening and closing of stomata [C]: Shows a distinct circadian rhythm.
In most plants, stomata open in the morning and close at night. This cycle continues even when plants are kept in continuous darkness.
- Photosynthetic activity [D]: Regulated by the circadian clock, which coordinates the expression of light-harvesting complex genes and Rubisco activity to peak during subjective daylight hours.
- Seed germination in cereals [A]: An irreversible developmental transition triggered by environmental signals (imbibition, temperature), not a repeating 24-hour cycle.
- Root growth into the soil [B]: Directed by directional stimuli (gravitropism and hydrotropism), which is a growth response rather than a circadian rhythm.
Therefore, only stomatal movement and photosynthetic activity are examples of circadian rhythms.
Step 3: Final Answer:
The processes that exhibit circadian rhythms are stomatal movement (C) and photosynthetic activity (D).
Circadian rhythms are endogenous, self-sustaining biological oscillations with a period of approximately 24 hours.
These rhythms are regulated by an internal molecular clock and persist even in the absence of external light or temperature cues.
Step 2: Detailed Explanation:
- Opening and closing of stomata [C]: Shows a distinct circadian rhythm.
In most plants, stomata open in the morning and close at night. This cycle continues even when plants are kept in continuous darkness.
- Photosynthetic activity [D]: Regulated by the circadian clock, which coordinates the expression of light-harvesting complex genes and Rubisco activity to peak during subjective daylight hours.
- Seed germination in cereals [A]: An irreversible developmental transition triggered by environmental signals (imbibition, temperature), not a repeating 24-hour cycle.
- Root growth into the soil [B]: Directed by directional stimuli (gravitropism and hydrotropism), which is a growth response rather than a circadian rhythm.
Therefore, only stomatal movement and photosynthetic activity are examples of circadian rhythms.
Step 3: Final Answer:
The processes that exhibit circadian rhythms are stomatal movement (C) and photosynthetic activity (D).
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