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Are there more stomata per mm2 on old leaves or young leaves?

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Introduction

Are there more stomata per mm2 on old leaves or young leaves? Planning Equipment Leaves (old and young) Clear nail-varnish Microscope Lamp Forceps Slide Graticule (1cm) Method I will take some old leaves and some young leaves. I aim to use three of each. I think this is a realistic amount to use because it is a slow process. The leaves I will use will be from a cherry laurel bush (prunus laurocerasus). I will know which leaves are young and which are old by their colour and size. Young leaves are small and a lighter green. Old leaves are larger, and a darker green. First, I will clean the leaf, to remove dust and dirt. Then I will paint 1cm2 of clear nail-varnish on the underside of the leaf, because that is where the stomata are. I will paint the nail-varnish to one side of the mid-rib, but not too near the edge. I will then leave it to dry, while I measure the size of the microscope's field of view, on medium power. To do this, I will use the graticule to measure its diameter, then divide this in half to find the radius. Then I will use the radius measurement in the formula ?r2 to work out the area of the field of view. When the nail-varnish is fully dry, I will carefully peel it off with a pair of forceps, and place it on a slide the same way up as it was on the leaf. ...read more.

Middle

It was 0.6mm long. Then I divided this by 2 to find the radius, and used it in the formula ?r2, to calculate the area: ? x 0.32 = 0.283mm2 When the nail varnish was dry, I used a pair of forceps to peel the nail varnish off the leaves. Each time, I peeled a section off, I placed it on a clean slide, and labelled the slide to show whether it was a young leaf or an old leaf. When all the nail-varnish had been peeled off and put on slides, I started to make my observations. I placed a slide under the microscope, focused on the image and counted the stomata I could see. As well as counting the full ones, I also counted the ones that were only partially in the field of view. I counted them slowly and accurately, then wrote down my findings. Then I worked out how many there would be per mm2 for each result. To do this I worked out how much smaller my field of view was in proportion to a mm2: 1 � 0.283 = 3.53 This meant that I had to multiply each of my results by 3.53 to obtain the number of stomata per mm2. I put these results into a table: Old Leaves Young Leaves Number of stomata per mm2 204.9 129.7 190.8 188.7 130.7 159.6 I thought these results looked quite random, so I decided to look at some more leaves. ...read more.

Conclusion

This means that the particular place on the leaf that I looked at could have varied enormously from leaf to leaf. I think my evidence is sufficient to support a firm conclusion, because, despite the fact that I only did 5 of each different age, they still showed that age does not seem to have an effect on the number of stomata per mm2 a leaf has. However, I think that there is a way that I could have provided additional evidence for a conclusion. The best way to discover whether age affects the number of stomata per mm2 that a leaf has would be to look at the same leaf as it matures. I could have left the leaf growing on the tree, and painted the nail-varnish on without taking the leaf off the tree, then taken the dry nail-varnish peel back to the laboratory to observe. I could have marked where I had painted the nail-varnish the last time, and each month, I could have repeated the experiment, comparing it to the last result I had got. This way I would know for sure how age affects the stomata, because I would be looking at the same leaf as it grew in the same conditions, rather that different leaves, growing in slightly different conditions. Also, when I drew a graph of my results, the data would be continuous, allowing me plot a line graph and discover the true relationship between the age of a leaf and the amount of stomata it has. ...read more.

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