The purpose of each concentration of alcohol,

The purpose of each concentration of alcohol,

The application of different concentrations of alcohol in high school biology experiment is listed as follows. (1) 50% alcohol 1.1 function: wash off floating color. 1.2 principle: Sudan III is a weak acid dye, which is easily soluble in 50% alcohol. 1.3 application: fat identification experiment. In this experiment, after the peanut cotyledon slice is dyed with Sudan III, (2) 95% alcohol 2.1 function: ① dissociation; ② extraction of DNA with less impurity. 2.2 principle: ① dissociation principle: 15% hydrochloric acid and 95% alcohol 1:1 mixture, (2) the principle of extracting DNA with less impurity: DNA is insoluble in alcohol, especially 95% volume fraction of frozen alcohol, 2.3 Application: ① observe the mitosis of plant cells; ② rough extraction and identification of DNA; (3) 75% alcohol 3.1 function: disinfection and sterilization. 3.2 principle: 75% alcohol can smoothly penetrate into the cell, absorb the water of bacterial protein, make it dehydrate, denatured and coagulate, and lose its function, In order to achieve the purpose of disinfection and sterilization, when alcohol with a concentration higher than 75% by volume contacts with bacteria, it may cause the surface of bacteria to solidify rapidly and form a film, which prevents the alcohol from permeating into the bacteria. At an appropriate time, the cells in the film may break through the film and revive, If the concentration of alcohol is lower than 75%, it can not penetrate into the bacteria and kill the bacteria completely. If 75% alcohol is used, the protein of bacteria can be coagulated and the film can not be formed, It is worth noting that the germicidal power of 75% alcohol solution is not absolutely strong, and it has no effect on spores. 3.3 application: learn the cultivation technology of microorganisms. At the beginning of inoculation, wash hands with soap, and then wipe hands with 75% alcohol cotton ball, 4.2 principle: all kinds of pigments in chloroplast are organic substances, which can be dissolved in organic solvents. The solubility of pigments in absolute alcohol is relatively high, and the alcohol is non-toxic and easy to operate. 4.3 application: extraction and separation of pigments in chloroplast. (5) industrial alcohol (generally 95% alcohol by volume) 5.1 function: combustion heating. 5.2 principle: alcohol is an organic substance rich in energy, and combustion can produce a lot of heat. 5.3 application: all kinds of experiments that must be heated are included here, For example, the identification of reducing sugar in biological tissues, the comparison of catalase and Fe3 + catalytic efficiency, the exploration of the role of amylase on starch and sucrose, the rough extraction and identification of DNA, the effect of temperature on enzyme activity, the study of basic techniques of microbial culture, the isolation of self nitrogen fixing bacteria and other experiments