In addition to morphology,bacteria are classified by mode of nutrition or serology, which detects characteristic chemicals such as peptidoglycan. Bacterial filaments can rarely be seen by eye with a normal microscope but often can be seen as black hairlike extensions on aquatic organisms such as attached algae. Nevertheless, most bacteria are very small, between 0.2 and 5 um long, and often appear only as dots when viewed under the highest power of the light microscope. Consequently, their ability to perform chemical transformations has become the standard method for identification and classification. Although this functional classification requires time-consuming procedures, it should be familiar to limnologists who are already acquainted with the functional role of higher organisms.