Experiments to deepen the understanding of efficient diffusion of water through small pores.
Operation method
Diffusion Observation Experiment in Small Holes
Principle
The stomata on the leaf surface are the main channels for carbon dioxide and gaseous water molecules to and from the leaf. Although there are many stomata on the leaf surface, the area is very small, accounting for only 1 to 2 % of the total leaf area, but the rate of water loss through the stomata (i.e., the rate of transpiration) is very fast. In some plants, when the stomata on the leaf surface are fully open, the rate of transpiration is close to the rate of evaporation from a free water surface of the same size as the leaf. Such high efficiency is the result of the edge effect of diffusion through small pores. In any evaporation surface, in the center of the evaporation surface of the gas molecules due to intermolecular interference, the diffusion rate to the atmosphere is slower, in the edge of the evaporation surface of the gas molecules due to less interference and diffusion faster. The smaller the hole, the greater the ratio of perimeter to area, the more significant the edge effect. Therefore, if the same evaporation area, the smaller the hole, the greater the amount of water evaporated per unit area. This is the small area of the stomata can be a large number of important reasons for water loss.
Materials and Instruments
Petroleum ether Wax Move 1. Equipment fabrication For more product details, please visit Aladdin Scientific website.
Bench balance Petri dish Dowling paper Single sided blade Straightedge
(1) Prepare two petri dishes of the same size (diameter 9 cm), two sheets of 11 cm diameter wax-impregnated dowel paper, drill a 3 cm diameter circular hole in the center of one sheet, and drill 225 small circular holes of 0.2 cm diameter on the other sheet, with 225 small circular holes in 15 rows of 15 holes each, so that the total area of holes on the two sheets is the same, but the total perimeter of the holes is different.
(2) will open the holes in the Dowling paper to cover the petri dish mouth, the edge of the paper folded downward, with glue on the petri dish wall, after drying for use.
2. Determination
The two petri dishes were placed on the weighing pan at both ends of the balance, the first weights to adjust the balance, and then use a dropper to suck petroleum ether (or other low-boiling liquid) added to the two petri dishes about 0.5 cm deep, adjust the amount of petroleum ether so that the balance reaches equilibrium. As the petroleum ether diffuses outward through the hole in the paper, after a few minutes, it can be clearly seen that the weight of the small hole side becomes lighter, indicating that the small hole side diffuses faster than the large hole side.