Equipment: Test tubes, stoppers, test tube racks, measuring cylinders, spatulas, incubator, 50 ml beakers, filter paper. Chemicals: Methylene blue solution (1%, Löffler method), UHT milk (whole milk), various types of yogurt, and yogurt ferment. Methylene blue is a widely used vital dye in microscopy for staining living material. Löffler's methylene blue solution is a solution in water used to stain bacteria, fungi, and blood parasites.

Fill four test tubes with 15 ml of milk each. Add 20 drops of methylene blue solution to each test tube, stopper, and shake vigorously. Add two spatulas of different types of yogurt or yogurt ferment to three of the tubes, close the tubes, and shake vigorously again. Label the test tubes. Incubate all four tubes overnight at 30-40 °C in an incubator.

This warms the jars and prepares them perfectly for the lactic acid bacteria in the yogurt. If I were to pour the warm milk-yogurt mixture into cold jars, the bacteria wouldn't feel as comfortable due to the coldness of the jars, causing them to become less active or even die off completely. The next day, I'll examine the results.

a) Examine the test tubes. Briefly describe the changes you observed in the four experiments. ________________________________________________________________________________________________________________________________________________________________________________________________________________ b) Draw a sketch of your experimental results. ________________________________________________________________________________________________________________________________________________________________________________________________________________

a) The formation of yogurt from milk occurs through a specific process. Name this process and briefly explain it. Include details of the bacteria involved. _______________________________________________________________________________________________________________________________________________________ ______________________ b) How can the different tastes of milk and white natural yogurt be explained? _______________________________________________________________________________________________________________________________