Investigating Rate of Transpiration

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The aim of this experiment was to investigate the effect of temperature rise on the rate of transpiration of a plant (hibiscus) by measuring the plant’s water uptake in a period of time.

Transpiration is the process by which plants loses water to the atmosphere from their leaves. Water in the plant is lost to the atmosphere by evaporation. Evaporation of water can occur at any temperature. In the presence of sunlight, water in the plants evaporates into the intercellular air spaces and diffuses out through the stomata into the atmosphere. The diffusion of water from the plant into the air lowered the water potential in the outermost cell (mesophyll). The differences of water potential with the adjacent cell will cause water to move from the adjacent cell into the mesophyll cell which then established a water potential gradient in the plant. The water potential gradient will cause water to flow from the xylem along a chain of cells to the outermost mesophyll cell. Since, the experiment was dealing with rising the temperature of the plant’s surrounding air, water in the plant will have a greater tendency to evaporate and diffuses out into the atmosphere. Transpiration rate of the plant therefore should be increasing with temperature (to a certain extent).

There are several factors which can affect the rate at which plants loses water from the leaves (transpiration). These factors can either be internal (e.g. no. of stomata, distribution of stomata, etc) or external factors (e.g. temperature, humidity, etc). For this particular experiment, the temperature surrounding the hibiscus plant was raise by placing a table lamp near it. A simple potometer (figure 1) where the distance travelled by an air bubble was used to measure the rate of water uptake from the plant.

Figure 1
The distance (in cm) travelled by the air bubble at a period of time (in h) was taken to be the transpiration rate for the plant....
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