Question

What is the working principle of a potometer?

• A. Amount of water absorbed is the same as the amount of water transpired
• B. Amount of water absorbed is double the amount of water transpired
• C. Amount of water absorbed is 2.63 times the amount of water transpired
• D. Amount of water absorbed is 0.56 times the amount of water transpired

Hint:

Remember that a potometer does not measure transpiration directly.
Instead, it measures water absorption.
Because almost all absorbed water is transpired, the absorption rate serves as an accurate proxy for the transpiration rate.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A potometer (such as Ganong's or Farmer's potometer) is a scientific instrument used to measure the rate of transpiration in plants.
Transpiration is the loss of water vapor from the plant's aerial parts, primarily through the stomata of leaves.

Step 3: Detailed Explanation:
The physical construction of a potometer measures the rate of water absorption by a cut plant shoot.
The working principle relies on a key physiological assumption:
- More than \(98%\) of the water absorbed by plant roots is lost to the atmosphere through transpiration.
- Only a tiny fraction (\(1\--2%\)) is retained by the cell for photosynthesis and metabolic activities.
- Because the volume of water used for cellular growth is negligible, the amount of water absorbed by the plant is virtually the same as the amount of water transpired.
- By measuring the movement of an air bubble in a graduated capillary tube over time, the potometer measures the rate of water absorption.
- Under this working principle, this absorption rate is assumed to equal the rate of transpiration.
Therefore, the working principle assumes that water absorption is equal to water transpiration.

Step 4: Final Answer:
The working principle of a potometer is that the amount of water absorbed is the same as the amount of water transpired, matching Option (A).