experimental technique - controlled experiment-number of stomata

Stephen's hypothesis looks as if it is correct. More water was lost from the the bottom surface than the top indicating a greater density of holes on the bottom surface.

The variables are:

temperature of the air;
total surface area of the leaves;
length of stem;
amount of water in the test tube;
density of stomata on the top and the bottom surfaces.

All variables were controlled except for one, the density of the stomata on each surface. In other words both test tubes had exactly the same conditions except that one had the top surface blocked while the other had the bottom surface blocked. A third cutting that has no vaseline applied to its surface should also be included. This way we can compare the water loss from all three cuttings. We assume that the third cutting should lose as much water as the sum of the other two, since both of its surfaces are uncovered.

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The top surface losses 33.3% of the water that the bottom surface losses. We can conclude that it has 33.3% of the stomata of the bottom surface. Hence

33.33/100 X 200 = 67 stomata

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Experimental technique Controlled experiments Density of stomata
Leaves have tiny holes called stomata through which gases are exchanged and water escapes. Stephen wanted to compare the density of these tiny holes on both the top and the bottom surfaces of the leaf of a particular gum tree. Stephen put forward his hypothesis. "I think the top surface of the gum tree leaf will have less holes than the bottom surface. During a hot day a great number of holes on the top surface will cause severe water loss." Stephen set out to test his hypothesis.
He set up the experiment as shown on the right. He took two identical cuttings from the same tree and placed them in test tubes filled with the same amount of water. To the water surface of each test tube he applied oil to stop any evaporation of water from the surface. He applied vaseline gel(an oil based substance that blocks the stomata and prevents water from escaping) to the top surface of all the leaves of the first cutting. He then applied the vaseline gel to the bottom surface of the leaves of the second cutting. He placed both test tubes in the same room next to a window that provided a steady breeze. Observe the outcome on the right. Is his hypothesis accurate? What are the variables of this experiment? Did Stephen control all but one of the variables? Solution
	An independent variable in this experiment is The dependent variable in this experiment is
Stephen measured the water loss every hour and plotted his results on a graph (shown on the right). Assuming that the bottom surface has 200 stomata calculate the number of stomata on the top surface. Solution
Continue with another experiment