Diatoms reproduce asexually, via binary fission, and also sexually, through meiosis and fertilization. Diatoms are capable of switching back and forth from sexual to asexual reproduction and also forming an inactive phase when necessary.
Diatoms reproduce mainly through binary fission. In binary fission, a single cell splits into two daughter cells. The daughter cells are genetic copies of the parent cell and, typically, are each capable of growing to the same size as the parent cell. Diatoms, however, exhibit shrinking fission. In shrinking fission, one of the two daughter cells is always smaller than the parent cell, leading to a constant decrease in size along one line of daughter cells. Once diatoms become too small, they begin reproducing sexually.
The parent cell undergoes meiosis to form eggs or motile sperm. Male cells release sperm which locate and fertilize female egg cells to form an auxospore, the diatom's zygote. The auxospore eventually grows to become the beginning of a new lineage of diatoms, and the diatom goes back to asexual reproduction. This ability to utilize multiple reproductive strategies ensures that diatoms never become too small and sexual reproduction introduces genetic variability.
Diatoms are a type of algae, present in large quantities in phytoplankton, and important producers in the ecosystem. They are single-celled organisms that form colonies of various shapes and sizes.