8. Why do plants transpire water faster under certain environmental conditions?
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General Thoughts
So what is the task you are facing this week? Like the previous labs, you have a situation in which you have to determine which of many possible factors exerts an influence on some general phenommena. In this case it is water loss from the soil and what is going to increase or decrease how quickly plants remove the water. So on what should you be focusing? (Hint - not the soil!) To understand something about the process by which plants draw water from the soil and the structures involved, look up the Valuable Concepts in your text. You will find that the processes involved here are related to those we learned about in Fire and Ice and might make it worthwhile that you review the Osmosis tutorial. We will return to this concept and look at it as part of a larger ecological process when we are involved with the Hogs, Chickens and More scenario.
Water loss is a serious problem faced by plants. When do they lose it? Well plants can be pretty well protected by a thick epidermis and a waxy cuticle. However, they need to exchange gases with the atmosphere just like we do.We learn about this in The Rainbow Connection and Out of the Rainforest. Do you lose water to the atmosphere as you breathe? How does that work? What processes are involved? Well the same is true of plants.
In this lab you can investigate lots of different parameters. You can try to measure water volume directly. Or you can measure the change in pressure that occurs as volume occurs using the appropriate sensor and indirectly measure volume. The pre-lab will give you the opportunity to practice with the latter set-up.
What did you learn from the Logal© simulation in the pre-lab? It will give you a chance to investigate the effect of one parameter on the stomata. How will that affect the passage of water through the plant? from the soil?
| Transpiration | Surface Area | Evaporation |
| Stomata | Temperature-Pressure-Volume | |
| Guard Cells | Xylem |
