The application of polarizing microscope in observing starch
Polarizing microscopy is widely used in fields such as minerals and chemistry, as well as in biology and botany. For example, in botany, such as identifying fibers, chromosomes, spindle fibers, starch granules, cell walls, and whether crystals are present in cytoplasm and tissue. The application in medicine is to use a polarizing microscope to examine crystals in joint fluid. We all know that starch can be determined by staining with iodine solution, but using a polarizing microscope can determine whether it is starch without staining. This is the starch granules of potatoes. Just cut a small piece of potato, apply it on a glass slide, and drop a drop of water to make a water embedded glass slide for observation. At low magnification, there is no staining, only ordinary particles.
Generally, starch is white or almost white in color and is insoluble in organic solvents such as ethanol and acetone, as well as in cold water. Starch exists in a granular state in endosperm cells, and the shape and size of starch from different sources vary. Microscopic observation can distinguish different types of starch or determine the type of unknown sample. The shape of starch granules can be roughly divided into three types: circular, elliptical, and polygonal. Plants with high water content and low protein content generally have larger starch particles, which are mostly circular or elliptical in shape, such as potato starch; On the contrary, the particles are smaller and polygonal, such as rice starch. Under a microscope at 400-600 times magnification, it can be observed that some starch surfaces have ring patterns, similar to the growth rings of trees, while potato starch has very obvious ring patterns.
However, as long as the polarizer is rotated, the world will be different. A cross will appear on the starch granules, which has a special name called the Maltese Cross. The intersection of the cross is located at the navel of the starch granules. This Maltese cross has a history. Zoom in a little more and you can see the circular pattern on the starch granules, with the center point being the position of the navel.
