ASCP Medical Laboratory Technician (MLT) Practice Exam

Starch stains blue black with iodine due to the formation of a complex between the starch molecules and iodine. When iodine interacts with the helical structure of amylose, a component of starch, it gets lodged inside the helix, producing a characteristic blue-black color. This reaction is widely used in laboratory settings as a qualitative test to confirm the presence of starch in a sample.

This reaction is crucial in various applications, including in biology and histology, where staining is a key method for visualizing structures. Understanding this staining reaction can help differentiate starch from other carbohydrates that do not exhibit the same color change when treated with iodine, thus providing a diagnostic tool in laboratory practice.