Infiltration

Biological terminology

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Osmosis refers to the separation of two solutions with different concentrations Semipermeable membrane (a membrane that allows solvent molecules to pass, but does not allow solute molecules to pass), water The phenomenon that molecules or other solvent molecules enter the solution of high concentration from the solution of low concentration through the semipermeable membrane. Or the phenomenon that water molecules move from the side with high water potential to the side with low water potential through the semipermeable membrane.

Chinese name: Infiltration
Foreign name: Osmosis
Properties: Biological terminology

Definition: The phenomenon that two solutions of different concentrations are separated by a semipermeable membrane (a membrane that allows solvent molecules to pass through, but does not allow solute molecules to pass through), and water molecules or other solvent molecules enter the solution of high concentration from the solution of low concentration through the semipermeable membrane

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one principle
two Experiment description
three Water absorption and loss of plants

principle

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Infiltration

Water molecules pass through systems with high water potential Semipermeable membrane The phenomenon of moving towards the system with low water potential is called infiltration（ osmosis )。 so Infiltration phenomenon There are two conditions of occurrence: first, there is a semi permeable membrane; 2、 There are two sides of semi permeable membrane Amount and concentration of substance Poor.^[1]

plant cell Of vacuole The full aqueous solution is called Cytosol , we can Tonoplast 、 cytoplasm and cell membrane be called Protoplast , which is equivalent to semi permeable membrane. Infiltration occurs between cells, or when cells are immersed in solution or water, as long as the concentration of solution on both sides of the protoplast layer is different. actually, Biomembrane Not an ideal semipermeable membrane, it is Selective permeable membrane , both water molecules and some solutes are allowed to pass through, but usually solvent molecules pass through much more than solute molecules, so infiltration can occur. Plant cells due to cell wall The cell wall has a protective and supportive effect, which can generate pressure to gradually equalize the water potential inside and outside the cell, and the cell meets dynamic equilibrium 。 Therefore, plant cells generally do not break when placed in water. Animal cell as red blood cell When it is put into water, it will break due to water absorption.

Experiment description

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Schematic Diagram of Infiltration

hold Broad bean The seed coat (or animal bladder membrane) is tightly attached to the funnel, and sucrose solution is injected, and then the whole device is immersed into the Beaker The liquid level inside and outside the funnel is equal. Because the broad bean seed coat is close to Semipermeable membrane (semipermeable membrane) (i.e. a membrane that allows water molecules to pass through but cannot be penetrated by sucrose molecules), so the whole device becomes a permeation system. In an osmotic system, the direction of water movement depends on the water potential of solutions on both sides of the semipermeable membrane. The water of the solution with high water potential flows to the solution with low water potential. In fact, the water molecules on both sides of the semipermeable membrane can pass freely, but the water potential of clear water is high, and the water potential of sucrose solution is low. The water molecules from clear water to sucrose solution are sucrose There are many water molecules from the solution to the clear water, so in appearance, the clear water in the beaker flows into the funnel glass tube The internal liquid level rises, Hydrostatic pressure It also began to increase. As the water gradually enters the glass tube, the more the liquid level rises, the greater the hydrostatic pressure is, which presses the water from the glass tube to the beaker Movement speed The faster, the faster the water in and out of the membrane. Finally, the liquid level will no longer rise and stay still, which is essentially the same speed of water in and out dynamic equilibrium 。

Water absorption and loss of plants

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Plant cells lose water and undergo plasmolysis

There are two ways for plants to absorb water: Imbibition (no vacuoles are formed) and osmosis (after vacuoles are formed).^[2]

Imbibition（ imbibition ）The process of hydrophilic gel adsorbing water molecules and making them expand. Nonliving physical process 。 plant tissue It contains many such substances as cellulose Pectin substance , starch and protein They have strong Hydrophilicity When not saturated with water, there is a strong Water absorption capacity 。 The most obvious example is air dried seeds, because they store a lot of protein or starch. The tendency of protein to combine with water is greater than that of starch, therefore, peas and beans Seed imbibition is very obvious. The imbibited object expands due to the adsorption of water molecules, and its pressure is very large. For example, if the dry seeds are filled with rock cracks, the imbibition pressure generated by its water absorption can cause rock fracture.

No swelling effect vacuole Of plant cell Ways of absorbing water, such as growing point Cells and stem of Seed cell The principle is that there are a lot of hydrophilic substances in the cell, which can absorb a lot of water from the outside, Living cell 、 Dead cell Can absorb water through swelling.

Osmotic action is the way that mature plant cells with vacuoles absorb water. The principle is: Protoplast have Selectivity There is a concentration difference between the solution inside and outside the protoplasm layer, so water molecules can solution concentration The low side diffuses through the protoplast layer to the side with high solution concentration. Solution osmotic pressure The height of Amount of substance The more solute molecular substances in the solution, osmotic pressure The higher it is, the lower it is. When comparing the osmotic pressure of the two solutions, take the amount of solute molecules in the two solutions as the standard for comparison. If the solute molecules are the same mass fraction Compare. The cell that can absorb water through osmosis must be a Living cell 。

A mature plant cell It is an infiltration system. Verify that water is absorbed by osmosis or water loss The best example of Plasmolysis and Plasmolysis restoration Experiment. Excessive fertilization at one time“ Burn seedlings ”, due to Soil solution A sudden increase in the concentration of, resulting in difficulty or inability of root cells to absorb water. Saline alkali land One of the reasons why most crops can not grow normally is that the concentration of soil solution is too high. Preserved fish, meat, etc. are not easy to deteriorate due to high concentration Salt solution Make cells and other microorganisms lose water and die.

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