Posts tagged life cycle.

Reproductive Cycles of 3 Main Fungi Phylums

Zygomycota

Fungi of the phylum Zygomycota are almost entirely terrestrial and live on dead plant and animal material. Zygotes are able to reproduce both asexually and sexually. In the zygote asexual reproductive cycle, spores germinate into hyphae and and produce haploid spores from sporangium.
Sexual reproduction of zygotes requires the conjugation of plus and minus hyphal strands. The temporary uniting of the plus and minus strands during which the strands exchange genetic material causes each strand to produce a gametangium. The nuclei of the plus and minus strands then fuse in fertilization, creating a diploid zygospore. The zygospore undergoes meiosis to produce four haploid nuclei, out of which only one is functional and the other three degenerate. The zygospore is able to withstand harsh conditions and germinates into hyphae, thus beginning the asexual stage.

Ascomycota

Ascomycota, also known as sac fungi, have both sexual and asexual reproductive stages. In the asexual stage, conidia form on the fungi’s conidiophores, special aerial hyphae. Spores then form on the conidia and are dispersed away from the parent by the wind.
Ascomycota sexually reproduce by first fusing the hyphae of different mating strains. Mitotic nuclear division leads to multiple nuclei in the ascogonium and anthoridium (male and female gametangia, respectively), then the nuclei are transferred to the ascogonium. The haploid nuclei from two different strains are now in the ascogonium, which divides cytokinetically with walls between the nuclei, thus creating dikaryotic cells. These dikaryotic cells divide via mitosis and the dikaryotic and sterile hyphae form cuplike structures called ascocarps containing special cells called asci, or sacs. The fusing of two nuclei in the ascus forms a zygote, which undergoes meiosis to form four haploid ascospores. Each ascospore undergoes mitosis to form two ascospores, thus forming eight ascospores in total. The spores are then released and germinate into new hyphae.

Basidiomycota

Basidiomycota form mushrooms as their fruiting bodies, called basidiocarps, to reproduce. Fungi in phylum Basidiomycota reproduce sexually. Different mating strains meet underground and the cells fuse, however, the nuclei join together without fusing. Dikaryotic hyphae then form and grow into basidiocarps. A basidiocarp is a structure consisting of a stalk, which supports a cap with gills on the underside. The basidiocarp gills give rise to stalks called basidia. Haploid nuclei fuse at the tips of the basidium. each basidium then undergoes meiosis and forms four basidiospores, which are released into the environment and germinate into new hyphae.

#life cycle  #Fungi  #Zygomycota  #Ascomycota  #Basidiomycota  #text  
∆  May 22, 2011
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The life cycle of a conifer consists of a distinct diplioid sporophyte generation and reduced haploid gametophyte generation that is retained within the cells of the sporophyte. The adult sporophyte bears two types of cones – pollen-bearing cones as well as ovulate cones. The pollen-bearing cones have scales in which are many microspore mother cells. The microspores undergo meiosis to develop four haploid daughter cells, which mature into pollen grains. The ovulate cone has scales each containing a megaspore mother cell, which undergoes meiosis to form four haploid megaspores, of which only one is functional and the other three degenerate. Pollination occurs when the pollen grain enters the micropyle. The pollen grain then germinates and develops a pollen tube and releases two sperm that travel through the tube to the megaspore. One of the sperm degenerates after the other unites with an egg. The sporophyte embryo then develops inside of the megaspore and the scale containing the megaspore with the developed embryo is released from the mature sporophte and carried by the wind to another location where, if conditions allow, the embryo will develop into an adult sporophyte.

The life cycle of a conifer consists of a distinct diplioid sporophyte generation and reduced haploid gametophyte generation that is retained within the cells of the sporophyte. The adult sporophyte bears two types of cones – pollen-bearing cones as well as ovulate cones. The pollen-bearing cones have scales in which are many microspore mother cells. The microspores undergo meiosis to develop four haploid daughter cells, which mature into pollen grains. The ovulate cone has scales each containing a megaspore mother cell, which undergoes meiosis to form four haploid megaspores, of which only one is functional and the other three degenerate. Pollination occurs when the pollen grain enters the micropyle. The pollen grain then germinates and develops a pollen tube and releases two sperm that travel through the tube to the megaspore. One of the sperm degenerates after the other unites with an egg. The sporophyte embryo then develops inside of the megaspore and the scale containing the megaspore with the developed embryo is released from the mature sporophte and carried by the wind to another location where, if conditions allow, the embryo will develop into an adult sporophyte.

#gymnosperm  #conifer  #life cycle  #Plantae  
∆  May 21, 2011
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The fern has both a diplid sporotphyte and haploid gametophyte generations in its life cycle. The adult sporophyte has sporangium on the undersides of its leaf fronds. These diploid sporangium undergo meiosis to form haploid spores, which are released from the sporophyte when mature. The spores then undergo mitosis and become independent gametophytes. The gametophyte of a fern has rhizoids to absorb nutrients from the soil, antheridium in which the sperm are housed, and archenonium with one egg in each one. Fertilisation occurs when the sperm from the antheridium come into contact with the egg in the archegonium. The nuclei of the sperm and egg fuse to form a diploid zygote. The zygote then undergoes mitosis to form a sporophyte, which lives off the gametophyte until it reaches maturity. At maturity, the adult sporophtye develops sporangium on the underside of its leaf fronds and thus begins the cycle anew.

The fern has both a diplid sporotphyte and haploid gametophyte generations in its life cycle. The adult sporophyte has sporangium on the undersides of its leaf fronds. These diploid sporangium undergo meiosis to form haploid spores, which are released from the sporophyte when mature. The spores then undergo mitosis and become independent gametophytes. The gametophyte of a fern has rhizoids to absorb nutrients from the soil, antheridium in which the sperm are housed, and archenonium with one egg in each one. Fertilisation occurs when the sperm from the antheridium come into contact with the egg in the archegonium. The nuclei of the sperm and egg fuse to form a diploid zygote. The zygote then undergoes mitosis to form a sporophyte, which lives off the gametophyte until it reaches maturity. At maturity, the adult sporophtye develops sporangium on the underside of its leaf fronds and thus begins the cycle anew.

#fern  #life cycle  #Plantae  
∆  May 21, 2011
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