Transport in plants & leaf temperature - Biology investigation 🍂🌡️
Channel: Science and Plants for Schools
Date: 2013-10-03

As an introduction to plant physiology, and before any discussion of transpiration or stomatal structure, function and distribution, students will use infrared thermometers to investigate the surface temperature of leaves. Students will measure the temperature of the upper side of each leaf before and after coating the underside of the leaf with petroleum jelly. 

Before carrying out the practical, the students can plan their investigation and consider the variables in their investigation. Students can then carry out simple analysis on their data to investigate the significance of the difference between the leaf temperature with and without petroleum jelly.

The next question to pose is “What is the cause of this difference?”. Hopefully, the students will make the connection between temperature change and evaporative cooling, and some may recall the role of stomata. Stomatal function and transpiration can then be introduced. Students can use the outcome of the analysis to formulate a hypothesis to explain any observed trends in data (i.e. Evaporation of water from stomata [transpiration] cools the leaf).

Following this, the students outline how they could use the infrared thermometer to investigate differences in the stomatal density in the upper and lower epidermis of leaves. This exercise is a good opportunity for stretch and challenge as some students will need a lot of help to realise that this can be achieved by comparing the effect on leaf surface temperature of applying petroleum jelly to the lower epidermis (where there are lots of stomata) with the effect of applying petroleum jelly to the upper epidermis (where there are fewer, if any stomata).

The students can then be introduced to the procedure for investigating stomatal density on the upper and lower epidermis of the leaves, allowing them to collect data to further test their prediction that the leaf heating effect observed when the stomata are blocked will be greatest when the density of stomata in the epidermis is high.

You may also wish to show your students our animation on Transport in Xylem and Phloem (https://youtu.be/LQ03xIkLLQU).

0:00 Introduction to experiment
0:23 Infrared thermometers
0:38 What happens to leaf temperature when the stomata are blocked?
1:04 Investigation outcome
1:35 Credits

Download full instructions and students' worksheet from our website: http://www.saps.org.uk/secondary/teaching-resources/281-an-investigation-into-leaf-surface-temperature

#saps #scienceexperiment #plants