Biology Lab: Comparing The Number Of Stomata

12 Oct



This lab report aim to compare the number of stomata in the upper and lower epidermis of a plant leaf. and how does the number of stomata will affect the rate of Transpiration and the water loss through stomata. Transpiration is the loss of water from a living plant. While, Losing water through stomata is carried out by diffusion, Water diffuses from a region of high water potential gradient to a region of low water potential gradient. However, The rate of transpiration is dependent on the size of the stomatal aperture and the diffusion gradient between the leaf and the atmosphere. so it is an internal factor. This lab will show the number of stomata in the upper and lower epidermis.  


The area with a great stomatal density will have a greater rate of transpiration, The area with low stomatal density will have the lowest rate of transpiration. And there will be more stomata on the lower side of the leaf, The lower epidermis, than on the upper epidermis, because that way the maximum amount of sunlight can enter leaf without many stomata blocking the way. Also, a lower number of stomata would increase the surface area therefore increase the amount of area available for light to hit.  

-Methods & Materials : 


Leaves, Calibrated Slides, Microscope slides and Coverslips, Graph Papers. 


1-Trace the shape of leaf on a graph paper and estimate its surface area by counting the squares within the lines of the traced leaves. 
2-Place a calibrated slide on the microscope table and measure the diameter of the microscope view using the middle mangifigaction. Calculate the surface area of the view. 
3-Peal the lower epidermis of part of the leaf and prepare a wet slide preparation of it.
4-View under the microscope and count the number of stomata present in the view using the middle mangification. 
5-Calculate te number of stomata present in the whole of the lower epidermis of the leaf.
6-Repeat step,3-5 for the upper epidermis. 
7-Recprd your results and analyze them appropriately.
8-draw a valid conclusion according to your results with explanation and compare them with literature information.
9-Evaluate the procedure and results including limitations, weaknesses and errors.
10-Suggest way of improvements to the investigation. 

-Results : 
Table 1: 
Shows The Number Of Stomata In The Upper & Lower Epidermis Of The Leaf.

    36    40    35    39     38       44


*Calculating the average :36+40+35+39+38\5=x. 

Table 2:
Shows The Area Of The Leaf.

Area (cm²)

*Calculating the surface area: 1 square = 1 cm²

The Results showed that the number of the stomata in the upper epidermis is Zero, even after taking 5 different readings. However, the number of the stomata in the lower epidermis had an average of 37 after 5 different readings and each one indicated a different number. Table 1represents the number of stomata in the lower and upper epidermis, and table 2 shows the surface area of the leaf used.

-Discusion :

Table 1 shows the mean number of stomata, at each five different readings, on the upper epidermis, all the five readings were Zero, which shows that there is no stomata in the upper epidermis in the leaf. Which will lower the rate of transpiration of the plant on that area, which is the upper area.  Moreover, the five readings of the lower epidermis were :”36,40,35,39,38″. And by calculating the average the number was “37”. Which indicates that the rate of transpiration in the lower part of the epidermis of the leaf will have a higher rate of transpiration than that the upper part.  

Table 2 show the surface area of the leaf, which is 78.5, it is more than the number os stomata which indicates that there will be more available space for light to hits affecting and increasing the rate of transpiration. Because when more light hits the leaf more will be the the transpiration, Hence, Temperature is on of the factors affecting the transpiration. higher the temperature, higher will be the rate of transpiration. 

-Conclusion : 

The hypothesis and results where very much similar, i predicted that there will be more number of stomta on the lower epidermis than the upper one, and the results shoed that the number of stomata in the upper epidermis was 0, While, the number of stomata in the lower epidermis was 44. This certainly indicates that in the upper epidermis more available spaces are needed for more light to hit the leaf, to increase the rate of transpiration or even for transpiration to occur. However, in the Xerophytic plants the number of stomata in the upper & lower epidermis would certainly differs, because those plants lives in the deserts where the temperatures are very high. So, to adapt those plants will have to open their stomatas at night to take the co2 needed for Photosynthesis    and store it in the form of Malate. 
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