Introduction

Water is transported in plants, 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 air spaces of 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 affect a plant’s transpiration rate. This experiment will measure
transpiration rates under different conditions of light, humidity, temperature, and air movement.
The data will be collected by measuring pressure changes as the plant takes up water into the
stem.

Objectives