Experiment 2: (1) The curve of experiment 2 shows that the concentration of cell fluid decreases rapidly when vegetables are just immersed in pure water. The reduction of solution concentration needs to be considered from two aspects: the change of solute and solvent. In pure water, cells absorb water, which leads to the decrease of cell fluid concentration. In addition, there are pesticide residues on the surface of vegetables. Cells will also absorb pesticide molecules, thus increasing the concentration of cytosol. The actual result is that the concentration of cell fluid drops rapidly, which shows that the speed of cell absorbing water is much faster than that of cell absorbing pesticides. With the absorption of water by cells, the concentration of cell fluid gradually decreases. The water absorption capacity of cells decreased, and the water absorption rate gradually slowed down. But in pure water, the concentration of cell fluid is definitely higher than that of pure water. There are two reasons for the increase of BC segment: first, from the perspective of cell structure, plant cells have cell walls, which absorb a lot of water and expand, but the elasticity of the outer cell wall is limited, which prevents cells from continuing to absorb water and water enters and exits the cells to achieve dynamic balance; Secondly, from the perspective of the absorption of pesticides by cells, the absorption of pesticides by cells slowed down until it stopped, but pesticides continued to be absorbed. This also shows the relationship between the absorption of water by cells and pesticides: the absorption of pesticides needs to be dissolved in water, but the two processes are relatively independent.
(2) According to the experimental principle analysis, the absorption principle of pesticides by cells is similar to that of mineral ions, and the best fertilization conditions outside the roots can be obtained according to this principle. Cells can only absorb mineral ions dissolved in water, so the biggest fertilizer effect of external fertilization is to keep the humidity after fertilization and keep the leaves moist for a long time, thus promoting the absorption of ions by cells.
(3) Experimental purpose: To explore the relationship between pesticide absorption and water absorption.
So the answer is:
Experiment 1: 1000 grams of the same fresh vegetable samples were sprayed with the same concentration of water-soluble pesticides, and one group was used as control. One group was washed with pure water 1min, and the other group was soaked with pure water for 30min, with the same water consumption. The results are as follows:
Treatment method: rinse with pure water for 65438±0min, soak in pure water for 30min, and determine pesticide residues in indicator cells. Pesticides mainly remain on the surface of vegetable leaves, and most of them can be washed away by pure water. Pesticide molecules can only be absorbed by plant cells after being dissolved in water, which leads to the increase of pesticide content in plant cells.
Experiment 2: (1) Just immersed in pure water, the cell absorbed more water molecules than pesticide molecules, which was limited by the cell wall. When the cell absorbs a certain amount of water, it becomes saturated, and at this time, the cell can also absorb pesticide molecules, which leads to the increase of BC cell fluid concentration. Pesticides can only be absorbed after they are dissolved in water. Water absorption and pesticide are two relatively independent processes.
(2) In the evening when there is no wind or light wind, or on a cloudy day with high air humidity, the liquid on the leaf surface will remain for a long time, which is beneficial for plant cells to fully absorb nutrients dissolved in water.
(3) Explore the relationship between pesticide absorption and water absorption.