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The purpose of this experiment is to plan design and carry out an experiment to compare the stomatal density of the upper and lower side of a leaf of my choice.

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IT Key Skills In Biology


The purpose of this experiment is to plan design and carry out an experiment to compare the stomatal density of the upper and lower side of a leaf of my choice.

This is relevant to my AS course in Biology as I am currently studying transpiration. This is a process involoving stomata opening and closing to release moisture from the plant. Therefore the amount and distribution of these stomata is very relevant to what I am learning.

Null Hypothesis is that ‘there will be no difference between the stomatal density on the upper and lower sides of the leaf.


  • leaves of a privit or similar plant
  • plain glass slides and cover slides
  • scalpel/sharp knife
  • nail varnish
  • Electron Microscope
  • Small painting brush
  • Forceps


Method for determining stomatal density:

(see attached sheet for source of method)

  • Select a few leaves from a privit or similar plant
  • Cover the upper surface of one of the leaves with a thin layer of nail varnish using a small brush
  • Repeat this on the lower surface of one of the other leaves
  • When varnish is dry peel layer off upper surface of the first leaf. (Use forceps)
  • Place this on a microscope slide with a tiny amount of water and label the slide U (upper surface)
  • Repeat this process with the lower surface of second leaf. (label this slide L)
  • Examine both slides under microscope using high and medium power.
  • Take an area on each leaf to count stomata. Calculate the area of the field of view. ( formula = πr²)
  • From this calaculate the number of stomata per unit area on each side of the leaf.

Method for Eyepiece graticule calibration:

  1. Insert the eyepiece into the microscope
  2. Place stage micrometer on microscope stage
  3. Focus low power objective on stage slide
  4. Adjust stage and eyepiece scales until eyepiece scale lies along the single line of the stage scale.
  • The eyepiece scale is divided into 100 divisions
  • The calibration slide scale is 1mm divided into 100 small divisions therefore each division is equivelant to 10 μm
...read more.


High= 3.5μm

3.5 x 100 = 350 μm

Radius = 350 ÷ 2 = 175 μm

cm’s = 175 ÷ 10,000 = 0.0175cm

*Area = πr²  = π x 0.0175² = 9.6211275024cm²

Tables of stomatal counts:

Side of Leaf

Stomatal Count


UPPER (Medium power)







LOWER (High power)







Calculation of stomatal density as numbers of stomata per cm:

Divide the number of stomata by the area of the field of view


Number of stomata = 5.6

Area of field of view = 0.014313881cm

Stomatal Density = 5.6 ÷ 0.014313881 = 391.2286263 =391.2 (To 1 decimal place)


Number of stomata =21.2

Area of field of view = 0.0009621127502

Stomatal density = 21.2 ÷ 0.0009621127502 = 22034.83947 = 22034.8 (To 1 dp)

Chi Squared Calculations:

...read more.



Degrees of freedom = (number of rows-1) x (number of columns-1)

= 2-1 x 2-1

= 1 x 1

= 1


Based on my results I can conclude that stomatal density is much greater on the lower side of the leaf than the upper side of the leaf.

From my chi squared test I know that the probability that chance alone could produce the deviation is below 1% as the degrees of freedom were equal to 1.

therefore I can reject my null hypothesis and conclude that there is a significant difference between the number of stomata on the upper epidermis and the number on the lower epidermis of a privit leaf.

There could have been errors in the way the experiment was carried out. For example, different people counted the number of stomata and if someone looked in a different field of view or over/under counted the number of stomata this would make errors in the experiment.

...read more.

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