Transpiration is the evaporation of water from plant tissues into the atmosphere. There are several factors that affect the rate of transpiration, temperature, humidity, wind speed, and atmospheric CO₂ levels. Temperature is the measure of hotness or coolness of air. If the temperature is high, transpiration rates will increase as the surrounding air is drying the leaf surfaces. In kind, if temperatures are low, transpiration rates will decrease. Humidity is the amount of water vapor in the atmosphere. When the atmosphere has a high humidity, the air is more saturated with water. Water diffuses from areas of high concentration to areas of lower concentration, so when humidity is high, transpiration rates will slow. If humidity reaches 100%, transpiration will cease. When wind speeds are high, leaf surfaces become dry and transpiration rates will increase. When wind speeds are low, transpiration rates will decrease. Stomata are the openings in leaf surfaces where gas exchange takes place. The amount of CO₂ concentration in the atmosphere affects the rate at which stomata will open. When CO₂ concentrations are high in the surrounding air stomata will not open; therefore, gas exchange cannot take place.

What if your students could actually see the results of plant transpiration as it happens? In a traditional lab, transpiration experiments were too difficult to do in a reasonable amount of time. In this science lab, one instantly sees changes in transpiration when a leaf is placed in a sunny window or into the breeze from a fan. Compare the transpiration of high and low surface area leaves, desert dwelling cacti and tropical vegetation. 

In the lab our group attempted to measure the rate of transpiration in certain tree species.

Required Materials

Procedures

Inside the lab

Assembly of apparatus (by teacher)

 Mounting of specimen

The following steps are to be completed under water.