Their external layers are composed of proteins which in part play a role in the resistance behaviour of spores to varied chemical and environmental assaults. Upon pollination, the microspores and megaspores unite to form seeds, while the ovary develops into fruit.Endospores are metabolically dormant, multi-layered cellular structures formed by Gram-positive bacteria belonging to the genera Bacillus, Clostridium and related organisms. The male microspores are contained within pollen and the female megaspores are produced within the flower ovary. In angiosperms, the flower produces both male microspores and female megaspores. In flowering plants (angiosperms) and nonflowering seed-bearing plants, the gametophyte generation is totally dependent upon the dominant sporophtye generation for survival. The fern leaf or frond represents the mature diploid sporophyte, while the sporangia on the underside of the fronds produce spores that develop into the haploid gametophyte. In vascular plants that do not produce seeds, such as ferns, the sporophtye and gametophyte generations are independent.
The gametophyte phase consists of green mossy vegetation, while the sporophtye phase (nonsexual phase) consists of elongated stalks with spores enclosed within sporangia located at the tip of the stalks. The primary phase of the plant life cycle for non-vascular plants, such as mosses, is the gametophyte generation (sexual phase). Spores are produced within sporangia and are released into the environment. Plants without seeds, such as ferns and mosses, develop from spores. Like algae and fungi, plants also exhibit alternation of generations. Credit: Matt Meadows/Photolibrary/Getty Images This fern leaf has sori or fruit dots, which contain clusters of sporangia. Dormancy allows fungi to survive under stressful conditions. Germination after periods of dormancy in some fungi can be triggered by factors including temperature, moisture levels, and the numbers of other spores in an area. Sometimes environmental conditions are such that it is necessary that fungal spores go dormant.
Alternation of generations is common among fungi. Once in the air, the spores are carried by the wind to other locations. The spores can be actively ejected from reproductive structures (ballistospores) or can be released without being actively ejected (statismospores). Most fungi rely on the wind to disperse spores to areas where they can germinate successfully. Sexual spores include ascospores, basidiospores, and zygospores. Other asexual spores, such as conidia, are produced on filamentous structures called hyphae. Asexual spores, such as sporangiospores, are produced and held within structures called sporangia. They come in a variety of colors, shapes, and sizes depending on the species. Fungal spores can be single-celled or multicelluar. Most spores generated by fungi serve two main purposes: reproduction through dispersal and survival via dormancy. Credit: Steve Gschmeissner/Science Photo Library/Getty Images These are the reproductive cells of the fungus. This is a colored scanning electron micrograph (SEM) of puffball fungus spores. The sporophyte produces haploid spores via meiosis. In the diploid phase, the zygote develops into a diploid structure called a sporophyte. The fusion of these gametes forms a zygote. In the haploid phase, a structure called a gametophyte produces male and female gametes. This type of life cycle is called alternation of generations and it consists of a haploid phase and a diploid phase. Some algae have a life cycle that alternates between distinct periods of asexual and sexual reproduction. At such time, the zygospore will undergo meiosis to produce haploid spores. The zygospore will remain dormant until conditions become favorable once again. These sex cells fuse to become a diploid zygospore. During times when conditions are unfavorable for development, the algae undergo sexual reproduction to produce gametes. The spores are haploid and are produced by mitosis. When conditions are favorable, the mature algae divide and produce spores that develop into new individuals. Some algae can reproduce either asexually or sexually. These spores may be non-motile (aplanospores) or they may be motile (zoospores) and move from one place to another using flagella. Dartmouth Electron Microscope Facility, Dartmouth College (Public Domain Image)Īlgae produce spores as a means of asexual reproduction. These algae are also capable of sexual reproduction. Chlamydomanas reinhardtii is a a type of green algae that reproduces asexually by producing zoospores and aplanospores.