Question:
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : ABA helps during water stress
Reason R : ABA has a role in stomatal closing
In light of the above statements, choose the correct answer from the options given below [Question ID = 523][Question Description = 143_30_HOR_AUG22_Q43]
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : ABA helps during water stress
Reason R : ABA has a role in stomatal closing
In light of the above statements, choose the correct answer from the options given below [Question ID = 523][Question Description = 143_30_HOR_AUG22_Q43]
Assertion A : ABA helps during water stress
Reason R : ABA has a role in stomatal closing
In light of the above statements, choose the correct answer from the options given below [Question ID = 523][Question Description = 143_30_HOR_AUG22_Q43]
Show Hint
Think of ABA as the "emergency brake" for a plant. When water is scarce, it pulls the brake (closes stomata) to stop water loss.
Updated On: Aug 7, 2026
- Both A and R are true and R is the correct explanation of A
- Both A and R are true but R is NOT the correct explanation of A
- A is true but R is false
- A is false but R is true
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
Abscisic Acid (ABA) is a vital plant hormone often referred to as the "stress hormone." It plays a fundamental role in mediating the plant's response to environmental stressors, particularly drought, salinity, and cold.
Step 2: Detailed Explanation:
Assertion A is true. During periods of water deficit (water stress), plants synthesize increased amounts of ABA in their roots and leaves. This hormone acts as a signal to trigger physiological changes that help the plant conserve water and survive the drought period. Without ABA, plants would continue to lose water rapidly and wilt under stress.
Reason R is also true and provides the direct mechanism for Assertion A. The most significant function of ABA during drought is the induction of stomatal closure. Stomata are tiny pores on the leaf surface through which transpiration (water loss) and gas exchange occur. When ABA levels rise, it triggers a signaling cascade in the guard cells involving calcium ions and the efflux of potassium and chloride ions. This loss of solutes results in a decrease in turgor pressure within the guard cells, causing them to collapse and close the stomatal pore.
By closing the stomata, ABA drastically reduces the rate of transpiration, thereby preserving the internal water status of the plant. This physiological response is the primary reason why ABA is considered a "helper" or "protector" during water stress. Thus, Reason R explains how Assertion A is achieved.
Step 3: Final Answer:
Both statements are scientifically accurate, and the mechanism described in R is the reason why A occurs.
Abscisic Acid (ABA) is a vital plant hormone often referred to as the "stress hormone." It plays a fundamental role in mediating the plant's response to environmental stressors, particularly drought, salinity, and cold.
Step 2: Detailed Explanation:
Assertion A is true. During periods of water deficit (water stress), plants synthesize increased amounts of ABA in their roots and leaves. This hormone acts as a signal to trigger physiological changes that help the plant conserve water and survive the drought period. Without ABA, plants would continue to lose water rapidly and wilt under stress.
Reason R is also true and provides the direct mechanism for Assertion A. The most significant function of ABA during drought is the induction of stomatal closure. Stomata are tiny pores on the leaf surface through which transpiration (water loss) and gas exchange occur. When ABA levels rise, it triggers a signaling cascade in the guard cells involving calcium ions and the efflux of potassium and chloride ions. This loss of solutes results in a decrease in turgor pressure within the guard cells, causing them to collapse and close the stomatal pore.
By closing the stomata, ABA drastically reduces the rate of transpiration, thereby preserving the internal water status of the plant. This physiological response is the primary reason why ABA is considered a "helper" or "protector" during water stress. Thus, Reason R explains how Assertion A is achieved.
Step 3: Final Answer:
Both statements are scientifically accurate, and the mechanism described in R is the reason why A occurs.
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