Asexual Reproduction
Asexual reproduction occurs when a plant, animal or protozoa reproduces without the involvement of another similar organism. A single parent creates a genetically identical copy, or clone, of itself without fertilization and the mixing of genes with another individual. Asexual reproduction is most often found in simple, single-celled life forms such as bacteria or archae. Such organisms lack a cellular nucleus containing genetic material and are called prokaryotes. All prokaryotes reproduce asexually. Other plants, protists and fungi reproduce both sexually and asexually.
Budding
Budding is a biological mechanism for asexual reproduction practiced by sponges, hydras, flatworms, bryozoans and tunicates. The budding process begins when a small clump of cells grows into a bud on or inside the parent organism. With external budding, the new individual forms an exact copy of the parent, then detaches to live independently. Sometimes the buds remain attached to the parent to form a clump of organisms. Internal buds form capsules that are released to grow into adult organisms.
Regeneration
Regeneration, or fragmentation, is a type of asexual reproduction. A complete, fully developed, mature organism develops from a fragment of the parent. Each distinct piece develops into an offspring genetically identical to the parent. Some plants, such as liverworts, evolved specific structures, called gemmae, for intentional regenerational reproduction. Other animals, such as flatworms and segmented annelid earthworms grow new individuals from accidental fragmentation caused by predator attacks or environmental hazards.
Examples
Planarian flatworm regeneration has been studied for more than 100 years. Surgical manipulation and microscopic observation have revealed how the worms generate new tissue by a cell proliferation process called blastema formation. Starfish and many kinds of echinoderms reproduce by regeneration. Hydras are one of the few multi-cellular organisms employing budding as a primary form of reproduction. Many types of fungi, including yeast, mushrooms and mold, reproduce by budding. Most species of plants have the ability to propagate by budding.