Applications of Polarizing Microscopes in the Observation of Starch
Polarized microscopes are widely used in fields such as minerals and chemistry, as well as in biology and botany. For example, in botany, identification of fibers, chromosomes, spindle fibers, starch granules, cell walls, and the presence of crystals in cytoplasm and tissues. The medical application is to use a polarizing microscope to examine crystals in joint fluid, and we all know that iodine staining can be used to determine starch. However, with a polarizing microscope, it is possible to 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, just ordinary particles.
Generally, starch appears white or off white and is insoluble in organic solvents such as ether, ethanol, acetone, and cold water. Starch exists in
granular form in endosperm cells, and starch from different sources has different shapes and sizes. Microscopic observation can distinguish different starches 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 granules, mostly round or oval in shape, such as potato starch; On the contrary, the particles are smaller and polygonal, such as rice starch. Under a microscope at a magnification of 400-600 times, some starch surfaces can be observed to have ring patterns, similar to tree rings. Potato starch has very obvious ring patterns.
However, as long as the polarizer is rotated, the world is different. A cross will appear on the starch granules, which has a special name called the Maltese Cross. The intersection of the cross is at the navel of the starch granules. This Maltese Cross has a history. If you zoom in a little more, you can see the circular pattern on the starch granules, with the center point being the position of the navel.
