Spore is a tiny, specialized structure that is able to grow into an organism. Nearly all kinds of plants, plus certain kinds of algae, bacteria, fungi, and protozoans, form spores. Spores help an organism or its species survive and move from place to place.
Spores vary greatly in size and shape, but most consist of one microscopic cell. Some fungi produce complex, multicelled spores. Spores contain cytoplasm and food. Some spores have a thick wall and can remain dormant (inactive) for several months. These features help such spores withstand harsh weather, chemicals, and other conditions that might otherwise kill the organism. Spores called zoospores have flagella (tails) and can swim. Others may move from place to place on air currents.
Plant spores.
Plants produce spores during one stage of their complex life cycle called alternation of generations (see Alternation of generations ). Plants form spores in a number of ways. Some plants grow a structure called a sporangium in which the spores develop. Examples of sporangia include the capsules that grow upright on moss plants and on the undersides of fern leaves. After the spores mature, they are released by the sporangia and scattered. If the spores are in a favorable environment, they germinate (start to grow). The cytoplasm then breaks through the spore wall and begins to develop. Plants that bear spores in this way usually produce many spores at a time, but only a few of the spores live and germinate.
In some plants, such as ferns and mosses, the spores grow into a new plant called a gametophyte. The gametophyte does not resemble the parent plant. It produces gametes (sex cells). The gametes unite and produce a plant called a sporophyte. The sporophyte resembles the original parent plant. The sporophyte produces spores, and the cycle begins again. See Fern .
Seed plants have a reproductive cycle somewhat like that of ferns and mosses. But their spores are produced as a step in seed formation. The female reproductive organ of a seed plant produces spores called megaspores, and the male reproductive organ produces spores called microspores. Each megaspore stays inside the female reproductive organ and grows into a tiny gametophyte that produces an egg cell. Each microspore grows into a pollen grain, which becomes a gametophyte that produces two sperm cells. After pollination, a sperm cell unites with an egg cell, and a seed begins to develop. See Seed (How seeds develop) .
Algal and fungal spores.
Certain kinds of algae and fungi produce spores that function like seeds. These organisms bear sporangia that contain spores. The mature spores burst out of the sporangia and are widely scattered. The spores that germinate grow directly into a new alga or fungus. See Fungi (How a fungus lives) .
Bacterial spores.
Certain types of bacteria form spores as a means of protection. A bacterial spore is a bacteria cell that has developed a thickened cell wall and has become dormant. Some bacterial spores can withstand boiling water and thus hamper the sterilization of various foods.
Protozoan spores.
Certain protozoans form protective spores by a type of cell division. Most of the protozoans are parasites in animals, and they move from animal to animal as spores. One common spore-forming protozoan causes the disease malaria.
