[생명과학/실험] osmotic activity in cells / 세포에서의 삼투 현상

Date 

2011. 3. 29

Subject

to learn osmosis and diffusion, and observe cells in solutions of different concentration 

Abstract

  Osmosis is a kind of diffusion which occurs with semi-permeable membrane. If there are a semi-permeable membrane between two different concentration solutions, the solvent moves from low concentration solution to high concentration solution for concentration equilibrium; it is osmosis.

  As the movement of solvent, pressure is generated and it presses the membrane from high concentration to law concentration; it is osmotic pressure.

  When cells are placed in certain solution, the shapes of the cells can be changed.

(표와 그림)

  Animal cells, which do not have cell wall, are burst when they are in hypotonic environment while plant cells, which have cell wall, are taut. When cells are in hypertonic environment, animal cells are shriveled and plant cells are plasmolyzed. 

Materials

Procedure

A. Lable four clean microscope slide with wax pencil.

- Slide "A onion" : solution 1

- Slide "B onion" and "C onion" : solution 2 and 3 (You do not know which solution is DW)

- Slide "D onion" : solution 4

1. Remove several desiccated scales (leaves) of an onion, and cut out a small section from some of the inner purplish leaves.

2. Make a very thin slice of onion. (epidermis)

3. Mount this section on slide A with several drops of solution A. (saline)

4. Place a cover slip over the section and observe the epidermis through the microscope.

5. Repeat steps from 2 to 4 with solution B, C and D, and record your observations.

B. Use RBC instead of onion`s epidermis and follow the upper steps.

※ Paler layer of RBC is required.

Results

RCB with solution A

RCB with solution B

RCB with solution C

RCB with solution D

plant cell with solution A

plant cell with solution B

plant cell with solution C

plant cell with solution D

Discussion

1. Based on the demonstration and your microscopic investigation, which of solution 2 and 3 is distilled water? What of the four solutions is hypotonic to the red blood cells and plant cells? Explain about other case, hypertonic and isotonic.

  DW is a kind of isotonic solution, so cells are lysed or turgid in dW. The cells are turgid in solution B and shriveled or plasmolyzed in solution C. According to the result, solution B is dW and solution C is hypertonic solution.

2. Based on your result, list the four solutions in low concentration order.

  Solution A is isotonic solution, solution B is hypotonic solution, solution C and D is hypertonic solution. The concentration of solution D is higher than the one of solution C because cells are more shriveled of plasmolyzed in solution D. Therefore, these solutions have the concentraion order like this : B, A, C, D.

3. Explain the common points and differences between diffusion and osmosis in point of aiming of two physical process, energy need and net movement of solvent and solute.

  Diffusion is the movement that molecules spread from high concentration to low concentration. Generally, these "molecules" are solute. Osmosis occurs with semi-permeable membrane between two different concentration solutions. The solvent of the low concentration solution move to the high concentration solution across the semi-permeable membrane by osmosis.

  These two phenomena do not require any energy to move molecules because these are occurs for concentration equilibrium: it is the common point of two. But, in diffusion, the net movement is the movement of solute from high concentration to low concentration, and the net movement in osmosis is that solvent is move from low concentration (high solvent concentration) to high concentration (low solvent concentration) : it is the difference of two.

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