Granules

Granule is a small particle or grain, a discrete unit produced by growth, aggregation, or secretion. The term is used across many disciplines and covers a wide range of materials, from submicrometer particles to millimeter-scale clumps.

In biology and medicine, granules are often membrane-bound vesicles or dense inclusions within cells. Secretory granules store hormones and enzymes in endocrine and exocrine cells and release them on demand. Pigment granules, such as melanosomes, contribute to coloration in skin and hair. Other cell components, including glycogen, lipid droplets and mineral granules, are frequently described as granules based on their granular appearance.

In plants, starch granules form within plastids like chloroplasts and amyloplasts and serve as carbohydrate reserves. Protein granules or storage granules also occur in seeds and other tissues.

In geology, materials science, and agriculture, granules describe small, discrete particles used as products or inputs. Examples include fertilizer granules, sugar granules, and coffee granules. The properties of granules—size distribution, surface texture, and moisture sensitivity—affect handling, flow, and reactivity.

In astronomy, granules are convection cells on the solar surface, called solar granules, typically about 1,000 kilometers across and lasting several minutes.