Introduction

In plants, water is transported from the roots to the leaves, following a decreasing water potential gradient. Transpiration, or loss of water from the leaves, helps to create a lower osmotic potential in the leaf. The resulting transpirational pull is responsible for the movement of water from the xylem to the mesophyll cells into the air spaces in the leaves. The rate of evaporation of water from the leaf to the outside air depends on the water potential gradient between the leaf and the outside air. Various environmental factors, including those conditions which directly influence the opening and closing of the stomata, will also affect a plant’s transpiration rate.

Objectives

In this Preliminary Activity, you will use a Gas Pressure Sensor to measure transpiration rates under different conditions. The data will be collected by measuring pressure changes as the plant takes up water into the stem.

After completing the Preliminary Activity, you will first use reference sources to find out more about transpiration before you choose and investigate a researchable question dealing with transpiration rate. Some topics to consider in your reference search are:

  • transpiration
  • cohesion-tension theory
  • water potential
  • osmosis
  • stomata
  • water potential gradient
  • xylem
  • mesophyll cell