Question

In plants, active absorption usually does NOT occur when ____.

• A. stomata are open
• B. stomata are closed
• C. transpiration stops
• D. it is night time

Hint:

High Transpiration (Open Stomata) $\rightarrow$ Passive Absorption dominates.
Low Transpiration (Closed Stomata/Night) $\rightarrow$ Active Absorption becomes noticeable (e.g., causing guttation).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Water absorption in plants occurs through active absorption (requiring metabolic energy) and passive absorption (driven by the transpiration pull).

Step 2: Key Formula or Approach:
Relate the occurrence and dominance of active versus passive absorption to the rate of transpiration and the corresponding state of the stomata.

Step 3: Detailed Explanation:
When stomata are open, the transpiration rate is high, creating a strong transpiration pull.
This pull drives passive water absorption, which is highly efficient and accounts for the vast majority of water uptake, largely dominating over active absorption.
Active absorption only becomes noticeable and prominent when transpiration is very low or absent, such as when stomata are closed or during the night.
Therefore, active absorption usually does not occur (or is negligible) when stomata are open because passive absorption is overwhelming it.

Step 4: Final Answer:
Active absorption is minimal when stomata are open, making option (A) correct.