Laboratory work 4: Effect of saliva and gastric juice on nutrients
The aim is to see that salivary enzyme splits starch and that enzyme action depends on temperature and environment. Four test tubes prepared by the teacher are used: all receive diluted starch solution. Tube 1 gets no saliva (control); tube 2 gets saliva and is kept in a cold (ice) vessel; tube 3 gets saliva and a few drops of mild acid; tube 4 gets saliva only and is kept in warm (about 37 °C) water. After 20–30 minutes the teacher adds a drop or two of iodine solution to each tube: where starch is present a blue-violet colour appears. Tubes 1, 2 and 3 turn blue (starch not split) while tube 4 does not change or is weak (starch split). Conclusion: salivary enzyme is active at warm temperature and neutral environment; it does not work in the cold or in acid. Safety: only the teacher handles acid, iodine and the water bath; a student gives saliva into a clean container, does not touch others’ saliva and never puts solutions in the mouth; wash hands with soap after work.
Results table: tube – condition – colour with iodine – conclusion. In each row write whether starch is present. Explain why the colour disappeared only in tube 4.