Stoma density and water loss
The hypothesis that plants with big leaves have more stomata and lose more water through transpiration is proven to be false. All plants had almost the same rate of water loss over the 5 days. The small ivy plant had more leaves and the big elephant ear plant had less leaves. Therefore the total number of stomata might have been similar.
Evapo-transpiration is the total loss of water from the surface of the earth into the atmosphere. It consists of the water evaporating from the soil and water bodies and also the transpiration of water that occurs in plants. These processes are part of the water cycle.
Try to repeat the experiment using more varieties of plants, or by using just 1 plant variety (eg. elephant ear plant) but varying the number of leaves.
The experiment can also be repeated by calculating the surface area of the leaves and comparing the difference in results.
Plant transpiration - http://www.juliantrubin.com/encyclopedia/botany/transpiration.html
Stoma - http://en.wikipedia.org/wiki/Stoma
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