Why do you drop a drop of water on the slide for onion mounting in the first volume of the seventh grade of human education (what's the purpose of dropping water) but why do you drop normal saline when you do oral epithelium mounting? Why can't you drop water?

Why do you drop a drop of water on the slide for onion mounting in the first volume of the seventh grade of human education (what's the purpose of dropping water) but why do you drop normal saline when you do oral epithelium mounting? Why can't you drop water?

Why not ask your teacher
The purpose of dripping water is to make the cover glass and the slide closely combined, so as to prevent bubbles from entering and affect the observation effect. Onion epidermal cells are plant cells, which have cell walls to maintain cell morphology, so clean water can be used. Human oral epithelial cells will absorb water and burst due to osmosis. Therefore, normal saline, a solution with the same concentration as that in cells, should be used

Here's a glass of water, an alcohol lamp and a plate of ice. Please design a small experiment to verify: "lowering the temperature can liquefy the gas."

In this way, the alcohol lamp boils the water and makes the water boil. Then put the plate with ice on the steaming water. You can observe that a large number of water droplets are formed at the bottom of the plate
Be careful not to burn your hands

An experiment is designed to show that the freezing point of ice and snow can be reduced by sprinkling salt on ice and snow
Such as the title

Prepare ice water mixture (prove it to be 0 °)
If the room temperature is above 0 ° observe the melting rate
If the melting is accelerated, it can be proved that the freezing point of ice and snow can be reduced by spraying salt on ice and snow
On the contrary, if the room temperature is below 0 ° observe the icing speed
If the ice freezes more slowly or the ice shrinks, it can be proved that the freezing point of ice and snow can be reduced by spraying salt on ice and snow

The reason why the respiration of green plants is not significant under light is that

Photosynthesis can absorb all or part of the carbon dioxide produced by cell respiration, which will interfere with the measurement of carbon dioxide release. At the same time, it will release oxygen, which will interfere with the oxygen absorption. If these two factors cannot be measured, the respiration intensity cannot be measured