Question

Given below are two statements:
Statement I - During night, guard cells become flaccid.
Statement II - During day time, guard cells become turgid due to endosmosis.
In light of above statements, choose the most appropriate answer from the option given below.

• A. Both statement I and statement II are correct.
• B. Both statement I and statement II are incorrect.
• C. Statement I is correct and statement II is incorrect.
• D. Statement I is incorrect and statement II is correct.

Hint:

Day: K$^{+}$ in $\rightarrow$ Water in $\rightarrow$ Open stomata
Night: K$^{+}$ out $\rightarrow$ Water out $\rightarrow$ Closed stomata

Answer 1

The Correct Option is A

Concept: Stomatal movement is regulated by changes in turgor pressure of guard cells, which depends on osmotic movement of water.
• During daytime, guard cells actively accumulate $\text{K}^{+}$ ions.
• This increases osmotic concentration, leading to water entry (endosmosis).
• As a result, guard cells become turgid and stomata open.
• During night, ions move out, water exits (exosmosis), and guard cells become flaccid.

Step 1: Analyze Statement I.
At night, stomata close and guard cells lose water, becoming flaccid. Hence, Statement I is correct.

Step 2: Analyze Statement II.
During daytime, guard cells gain water due to endosmosis and become turgid. Hence, Statement II is correct.

Step 3: Conclusion.
Both statements correctly describe stomatal behavior. Final Answer: Option (A)