Polarised light microscopy in the observation of starch
Polarising microscopes are widely used in the fields of minerals and chemistry, and also in biology and botany. For example, in botany, such as the identification of fibres, chromosomes, spindle filaments, starch grains, cell walls and cytoplasm and tissues contain crystals. Medical applications are the use of polarised light microscope to check the crystals in the joint fluid, test starch we all know can be stained with iodine solution to determine, but the use of polarised light microscope, without the need to stain to determine whether it is starch. This is a starch granule from a potato, just cut a small slice of potato and smear it on a slide, drop a drop of water to make a water-buried slide and you are ready to observe. At low magnification there is no staining just the usual granules.
General starch is white or off-white, insoluble in organic solvents such as ether, ethanol, acetone, and insoluble in cold water. Starch is in the state of granules in the endosperm cells, different sources of starch of different shapes and sizes, the application of microscopic observation can distinguish between different starch or to determine the type of unknown specimens. The shape of starch granules can be roughly divided into three types: round, oval and polygonal. Generally high moisture, less protein content of plant starch granules are larger, more round or oval, such as potato starch; on the contrary, the granules are smaller, polygonal, such as rice starch. Observed under a 400 to 600 times microscope, you can see some starch surface with whorls, similar to the annual rings of trees, potato starch whorls are extremely obvious.
But as long as the polariser is rotated, the world will be different, a cross will appear on the starch grain, this cross has a special name, called the Maltese Cross (MalteseCross), the intersection of the cross is in the umbilicus of the starch grain. This Maltese Cross has a history. Zooming in a little more, you can see the rings on the starch grain, with the umbilicus in the centre.
