A Levels Biology (9700)•9700/12/M/J/18

Explanation
Potometer measures water uptake volume per time as transpiration proxy
Steps:
- Identify potometer function: measures rate of water absorption by plant shoot, indicating transpiration.
- Note measurement method: volume of water entering capillary tube over time, via meniscus or bubble displacement adjusted by tube area.
- Calculate rate: volume = distance × cross-sectional area; rate = volume / time.
- Determine units: volume in cm³, time in min, so cm³ min⁻¹.
Why B is correct:
- Transpiration rate is the volume of water vapor lost per unit time, and potometer quantifies this via water uptake volume per time (cm³ min⁻¹).
Why the others are wrong:
- A: Measures linear speed of meniscus (cm min⁻¹), not volume-based rate.
- C: Represents area change per time (cm² min⁻¹), unrelated to water volume.
- D: Indicates acceleration (cm min⁻²), not a steady rate.
Final answer: B
Topic: Transport mechanisms
Practice more A Levels Biology (9700) questions on mMCQ.me