An Investigation into the Effects of a Single Factor on the Rate of Transpiration of 2 Different Species of Plant

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Antony Georgiou                       Candidate Number: 0067                      Centre Number: 30645

An Investigation into the Effects of a Single Factor on the Rate of Transpiration of 2 Different Species of Plant.

The aim of this investigation is to determine and compare how variation of a named factor affects the transpiration rates of 2 different species of plant.

    The process of transpiration is the process in which water vapour is lost from within the plant and goes into the atmosphere. It occurs only when stomata are open on the leaves of the plant which allows the water vapour to pass through going to the lower water potential outside the leaf.(1)

     The actual rate of the transpiration can be effected by many different factors including light intensity, wind speed, temperature and humidity of air surrounding plant. In this investigation I am going to look into how one of these factors affects the rate of transpiration of 2 different species of plant.

Factor (variant) = wind speed

Plants = holly and privet

     To get a fair investigation then the other factors must be kept as constants i.e. they must remain the same throughout the experiment whilst taking results as if they are not the results may be inaccurate and inconsistent in respect to what they should be.

     I think that as wind speed increases the rate of transpiration will increase, this is because the wind intensity will be getting rid of the vapour lost from the plant quicker and therefore the water potential outside the plant is kept very low (the higher the speed the more vapour will be moved). The wind intensity will have the same effect on all plants however it will change the rate of transpiration of different species in dramatically different ways. This is due to stomata density of the leaves as a xerophyte (holly) where water is sparse, will have a considerable amount less than that of a mesophyte (privet), where water is more readily available. I chose privet and holly as these are very diverse plants and I suspect they would have considerably different stomata densities and holly also has an extremely thick waxy cuticle layer which would also reduce transpiration. A way of finding out stomata density is by doing a clear nail varnish peel on the underside of the leaf and counting in respect to area the amount of stomata present.

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     I have decided that the most suitable method to measure rate of transpiration would be using a potometer to take the volume of water taken up a branch of each of the two plants which would indicate the rate at which the plant is transpiring. And to measure the wind speed an anemometer which will measure the wind speed.(3)

     I predict that the graph of transpiration rates of the 2 different species of plant at different wind speeds would look like this:

The reason I think the graph would look like this ...

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