Transpiration of A Pine Needle Lab

GCSE Science

How Different Conditions Affect the Transpiration Rates of Pines

Steven Chen, Patrick Huang, Andy Zhang, and Jerry Zhang

AP Biology

Period 1-2

Mr. Resch

September 30th, 2009

Abstract

We attempted to find the effect of different conditions on the transpiration rate of pines. We measured the amount of water transpired per gram of pine needle under windy, humid, constant light and dark conditions by placing a pine in a sealed Ziploc bag under each condition for a day. The transpiration rates for darkness, control, constant light, humidity and wind were 17.78, 6.91, 2.92, 0.382, 1.92 grams of water transpired per gram of needle respectively. We concluded that plants transpire the most under dark and normal conditions and that wind, humidity and daylight inhibit the transpiration rates of plants.

Introduction

[Transpiration is] in botany, the loss of water by evaporation in terrestrial plants. Some evaporation occurs directly through the exposed walls of surface cells, but the greatest amount takes place through the stomata, or intercellular spaces (Columbia Universtiy Press, 2004). The amount of water that plants transpire varies greatly geographically and over time. Because of that, there are a number of factors that determine transpiration rates (Burba and Pidwirny, 2007). Some conditions that affect the rate of transpiration include light intensity, humidity, temperature and wind (Transpiration Article).

We decided to test whether light intensity, humidity and wind would affect the transpiration rate of a pine. The conditions were chosen because we knew light initiated photosynthesis, humidity augmented the water moisture in the air and wind decreased the water moisture (Burba and Pidwirny, 2007). All of these factors would in turn affect the transpiration rate. We chose a pine because the density of the stomata on each needle is the same and the mass of needles is easy to measure (Hultine and Marshall, 2001). Therefore, we were able to calculate the transpiration rates as a ratio between water loss and the mass of the needles. We tested the hypothesis that different conditions would cause varied rates of transpiration. Our prediction was that wind and constant light would cause a plant to transpire more whereas a plant in constant darkness and a plant kept in humid conditions would transpire less than the control group.

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 ...

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Materials and Methods

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.