[Principle]
Stomatal transpiration is the main way for plants to lose water. The stomata are very small, and their total area generally does not exceed 1% of the leaf area. However, the water lost by the leaf through stomata transpiration reaches 50 80% of the free surface equal to the leaf area. Such an amazing amount of transpiration can be explained by the principle of pore diffusion. The amount of water diffused through the pores is proportional to the length of the circumference of the pores, and not proportional to the area of the pores. The phenomenon produced by this test can prove the existence of the small hole edge.
[Steps]
1. How substances diffuse through small pores
Prepare a piece of polyethylene plastic film (food bag can be used), about 5×5cm in size, take the dissecting needle and heat it on a gas lamp, and puncture a small hole in the center of the film. Prepare 1% agar and pour it into a small glass beaker laboratory. If you use a 10ml small scientific beaker, it is easier to observe. When the agar has not completely solidified, place the film carefully on the surface of the agar so that the small hole is in the center of the borosilicate beaker. After the agar has solidified, pour a little colored solution on the film. After 4 to 5 hours, the colored solution can be seen to diffuse into the agar gel through the small holes, forming a colored hemisphere, which shows the way the dye diffuses through the small holes.
2. Cut the card paper into a disc with the same size as the petri dish sterile, and then cut a large square hole in the middle of a piece of card paper. Each side is 3cm long, and the area is 9cm2. Cut several small holes on another card paper, the total area of which is exactly the same as that of the large holes. To do this, cut it into 9 square holes with a length of 1cm on each side, and distribute them evenly on the round cardstock. Then immerse the cardstock in molten paraffin, take it out and place it on the borosilicate petri dish. And seal the edges tightly with paraffin wax. Add the same amount of sprinkling essence (or acetone) to each of the two dishes, place the dishes on both sides of the flat side and adjust the balance with alcohol. After 15 and 30 minutes, due to the high edge effect, the alcohol evaporates faster, so the balance pointer is inclined to the side of the large hole. It can be seen that although the total area of the hole is equal, the alcohol loss ratio through the small hole is large. The hole is much faster. It proves that the edge effect of small holes is larger, because the length of the periphery is larger than that of large holes.
Post time: Dec-17-2021
