Ib Bio Example Transpiration Lab

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Nicolette Lindberg
11/30/12
IB Biology 2, Period 1
Transpiration Lab
Background Information- Transpiration is the loss of water from a plant. Plants transpire water out of the stomata in their leaves at a different rate in every environment. The amount of transpiration is affected by the environment, how developed the plant is to not lose as much water, the surface area of the leaves, and how affected the plant is by its environment (Von Bargen). For this experiment, the plant we used was (Viola tricolor subsp. Hortensis), or pansies. Problem Question- What is the effect of distance from a wind source on how much water a plant transpires? Manipulated Variable- The manipulated variable in this experiment was the distance of the 5 pansies from the wind source. Each plant was 20 cm farther from the fan than the last, starting at 2o cm distance. This means that the farthest plant was 100 cm away. These distances were selected because we needed a wide range of distances from the fan to measure how much the plants were transpiring with minimal and maximum exposure. Control Group- Alternating each plant in 2 columns, there were also 5 plastic bags filled with the same amount of water that we watered each plant with. These bags were placed alongside the plants at each distance from the fan. This was to measure if this amount of water without having leaves to transpire, would transpire anyway because of the room environment. It was to measure the validity of the experiment and to determine if a conclusion could be drawn. Responding Variable- The responding variable was the amount of water that was transpired. We measured this by measuring the mass of each plant and bag each day in grams. We then compared our new measurements to the original ones we took after the initial watering to decide how much water the plant had lost. Hypothesis- If the plant is closer to the wind source, then the plant will transpire more because the closer to the wind it is, the more dry the air will be which increases the rate of transpiration.

There are proven reasons for plant transpiration to increase or decrease due to the environment. Some factors include the amount of light, the temperature, humidity, the amount of wind, and the amount of soil water. Each factor effects transpiration in a different way. For amount of wind, there is a very strong positive correlation between the amount of wind and transpiration. This means that as the amount of wind increases, so does the amount of transpiration occurring within a plant (Von Bargen). This lead me to believe that the closer a plant was to the wind source, the more dry the air would be, and the more it would transpire. Table 1: Controlled Variables

Controlled Variables| Why it must be controlled| How it was controlled| Type of Plant used| Different plants have differently shaped and designed leaves that may be more adapted to keeping water from transpiring. This would greatly affect the data if one plant was used that was well adapted to not transpiring and another normal garden plant was used.| We only used 5 of the exact same type of plant| Amount of water given to each plant and when it was given| This would throw off all the data. If the initial measurement of each plant had more water than the others, then there would be no way to measure the trends of how much water was lost at each MV level.| We only watered the plants twice throughout the experiment, documenting it both times, and watered all the plants at the same time| Fan used| Different fans blow air at different rates or strength. If we had used 2 different fans, all the data would have been irrelevant because we need a constant wind source to measure the effect on the plants.| We only used one fan throughout the experiment, eliminating risks of different fan settings|

Materials-
* 1 fan
* 1 tray
* 5 pansy plants (Viola tricolor subsp. Hortensis)
* 10 plastic bags
* 50mL graduated cylinder...
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