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.

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

Results:

Eyepiece graticule calibration calculations:

Upper on medium power:

medium = 13.5μm

13.5 x 100 = 1350 μm

Radius = 1350 ÷ 2 = 675 μm

cm’s = 675 ÷ 10,000 = 0.0675

Area = πr²    = π x 0.0675²= 0.014313881 cm²

Lower on High power:

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:

Calculation of stomatal density as numbers of stomata per cm:

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

Upper:

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)

Lower:

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:

The following results have been based on stomatal densities found in the lower and upper sides of the leaves.

Expected stomatal density =

lower + upper stomatal density

                       2

391.2 + 22034.8

          2

= 11213  If the hypothesis is correct we would expect to find 11213 stomata on the upper side and the lower side of the leaves.

To test if the hypothesis is correct we must use the following formula;

  ² =        (O – E )²   =Σ The sum of.  O = Observed no.   E= Expected no.

                E

       

Total observed number for upper side = 391.2

Total observed number for lower side = 22034.8

Total expected number for upper and lower = 11213

Then calculate   (O – E )²   for each category:

                                  E  

Upper = (391 – 11213)²  = (-10822) ² = 10444.63426 =  10445 (rounded up)

                     11213              11213

Lower = (22034 – 11213) ²  = (10821) ²  =  1044.270409  (rounded up)

                     11213                   11213

Therefore  ² = 10445 + 10443 = 20888

Degrees of freedom must be calculated in order to work out whether there is a significant difference between my observed and expected values.

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

= 2-1 x 2-1

= 1 x 1

= 1

Discussion:

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.