Materials and Methods
This experiment occurred on the lab benches in the biology classroom of Mr. Resch. We first got plastic Ziploc bags which we filled halfway with water from the sink. We then zipped up the plastic bags and labeled each bag with its corresponding experimental condition. Next we used scissors and cut out pine twigs at an angle between 30° and 60°(π/3 or π/6 radians). We placed the pine into a Ziploc bag filled with water, making sure that no water got out and then we securely fastened the Ziploc bag with an elastic band making sure the needles were outside the bag and the tip of the stem was touching the water. We repeated these steps four more times until we had five bags with pines inside them.
We placed each of the bags in their corresponding environments. The wind environment consisted of a fan that was the size of an medium sized computer monitor blowing on the plant. The darkness environment consisted of placing the plant in a dark cabinet where light could not impregnate. The daylight environment consisted of placing the plant underneath an artificial light. The humidity environment was located in a humid tank in the green house. The control environment was placed underneath the window where it would be affected by the changes in daylight.
The following day we removed the pines from their respective bags making sure no water escaped and then we removed the elastic bands. Next we massed the bags with the water and then we massed the pine needles of the corresponding plant at our lab bench where we originally massed the bags and water.
Results
Table 1. Rate of transpiration of pine twigs. Pine twigs were placed in different environments and the amount of grams of water transpired per gram of needles was measured.
Figure 1. Rate of transpiration of pine twigs in different environments. Pine twigs were placed in constant daylight, constant night, windy, humid, and normal (constant) environments.
Discussion
Our experiment was designed to discover the effect different conditions such as daylight, wind, humidity, and darkness have on the transpiration rate of pines. Our hypothesis stated that the groups under the daylight and wind conditions would experience the highest transpiration rates while the groups under the darkness and humidity groups would experience the lowest transpiration rates. Since plants open their stomata for photosynthesis, which occurs in the presence of sunlight, we expected the darkness to cause the pine to transpire less. However, our results proved otherwise. Our results showed that the group under darkness had the highest transpiration rate with a 17.78 grams of water transpired per gram of needle followed by the control group with 6.91, the wind group with 2.92, the daylight group with 1.92, and finally the humidity group with 0.382. We noticed that after we left our bags in their conditions, our control and darkness bags leaked. Our bag under the darkness condition had experienced the most amount of water loss, which explains the high transpiration rate it acquired. Our control group had also lost a great amount of water as we found a hole in the bag later on. Because water loss plays a great factor in the transpiration rate of pines, the transpiration rates of the control group and the darkness group is higher than it actually should have been.
Transpiration rate increases due to the openings of the stomata. Light is a big factor in transpiration because when light intensity increases, plants undergo photosynthesis, causing the stomata of plant cells to open. So when the pine was placed in a condition that provided more daylight, the light caused the time period the stomata were open to increase, thus increasing the transpiration rate as well. This also means that when the pine was placed in a condition that only contained darkness, the amount of light would decrease, causing the stomata to remain closed and decreasing the transpiration rate. However, as humidity increases, the surrounding air of the pine becomes more saturated, causing transpiration to decrease. Increasing air movement around the pine would cause the water that transpires from the leaf to saturate in the surrounding air, therefore lowering the humidity and replacing the saturated air with more dry air. Therefore, placing the pine in a condition with wind would increase the transpiration rate (Burba and Pidwirny, 2007).
Our results supported the idea that when the pine is placed under the condition of darkness, its transpiration would increase the most. If the transpiration rate in dark conditions is high, then the plant placed in humid conditions should have also had a very high transpiration rate instead of the low transpiration rate indicated by our results. Darkness and humidity have similar effects on the pine as they both cause the closing of the stomata, so if darkness has the highest transpiration rate, then humidity should also have a high transpiration rate. However, we know that our bag under the humidity condition did not have a hole so it can be stated that the bag affected by darkness did not really have that high of a transpiration rate, but was indeed affected by a leak.
We only had one pine for each condition and therefore we did not have enough samples to have confidence in our conclusion. Considering we only tested pines, we cannot conclude that these conditions apply to all plants as well.
Conclusion
The control twig that was subjected to normal condition transpired more grams of water per gram of needle than all the other twigs except the darkness twig. This means constant daylight, high humidity, and wind decrease the transpiration rate of a plant while darkness increases it, disproving our hypothesis. This information is most likely incorrect because some of our bags leaked water, making our results invalid.
Works Cited
Burba, George, and Michael Pidwirny. "Transpiration." The Encyclopedia of Earth. The
Encyclopedia of Earth, 4 Oct. 2006. Web. 29 Sept. 2009.
Hultine, Kevin R., and John D. Marshall. "Transpiration: Free Encyclopedia Articles at
Questia.com Online Library." Questia Online Library. Oxford University Press,
20 Sept. 2000. Web. 29 Sept. 2009.
"Transpiration." Questia. Columbia University Press, 2004. Web. 29 Sept. 2009.
"Transpiration." Web. 29 Sept. 2009.