How to determine the high or low osmotic pressure in high school biology

The determination of osmotic pressure in high school biology experiments can be achieved through five methods: observing changes in cell morphology, comparing differences in solution concentration, measuring with an osmotic pressure gauge, analyzing solute types and quantities, and referencing standard osmotic pressure values.

1. Cell morphology observation:

Place the cells in the test solution under a microscope for observation. Cell expansion and rupture indicate that the osmotic pressure of the solution is lower than that of the intracellular fluid, while cell shrinkage indicates that the osmotic pressure of the solution is higher than that of the intracellular fluid. Animal cells often use red blood cells as observation objects, while plant cells can be judged by the phenomenon of cytoplasmic wall separation. This method is intuitive and simple, but attention should be paid to the impact of cell type differences on the results.

2. Concentration comparison method:

judges the osmotic pressure by comparing the solute molar concentration of two solutions, and the higher the concentration, the greater the osmotic pressure. For electrolyte solutions, ionization factors need to be considered, such as the actual particle concentration of 1mol/L NaCl solution being 2mol/L. Different concentration gradient solutions can be prepared for comparative testing in the experiment, and this method is suitable for simple solution systems with known components.

3. Instrumental measurement method:

uses an osmotic pressure gauge to directly measure the osmotic pressure value of a solution. Common instruments include a freezing point osmotic pressure gauge and a vapor pressure osmotic pressure gauge. The freezing point osmometer calculates the osmotic pressure by measuring the degree of decrease in the freezing point of a solution, with an accuracy of ± 2mOsm/kg. This method has accurate and reliable data and is suitable for precise laboratory measurements, but the equipment cost is relatively high.

4. Solute characteristic analysis:

The osmotic pressure is proportional to the number of solute particles, and the ionization degree and molecular weight of the solute need to be considered. At the same mass concentration, small molecule substances have a higher osmotic pressure than large molecule substances; Electrolytes have higher osmotic pressure than non electrolytes. The osmotic pressure of 5% glucose solution is about 278mOsm/L, while that of 0.9% saline solution is about 308mOsm/L.

5. Standard value comparison method:

Refer to the osmotic pressure standard value of common solutions for judgment, such as the normal range of human plasma osmotic pressure being 280-310mOsm/L. In the experiment, the test solution can be compared with a standard solution such as 0.9% physiological saline, and the high or low can be determined by observing the phenomenon of semi permeable membrane permeation. This method needs to pay attention to the influence of temperature on osmotic pressure.

It is recommended to prioritize the use of a combination of cell morphology observation and concentration comparison in daily experiments, which can ensure accuracy in judgment and facilitate operation. When using plant cells for observation, pay attention to selecting easily peelable materials such as onion skin. For animal cell experiments, it is recommended to use physiological saline as a control. For precise measurement requirements, a professional osmotic pressure gauge should be selected, and a constant temperature environment should be maintained during operation. To understand the concept of osmotic pressure, one needs to master Van Gogh's law, which states that osmotic pressure is proportional to solute particle concentration and absolute temperature, and is independent of solute nature. After the experiment, the composition, concentration, temperature and other parameters of the solution should be recorded in a timely manner to facilitate result analysis and repeated verification.