Liverwort Prothallus

A prothallium, or prothallus; from Latin pro = forwards and Greek θαλλος (thallos) = twig; is a pteridophyte, i.e. spore-bearing plant, (almost exclusively ferns) in gametophyte stage in the alternation of generations cycle. It forms from a spore that has fallen from the sporophyte stage and germinated. It is a short-lived and inconspicuous heart-shaped structure typically 2-5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male). Appearance varies quite a lot between species. Some are green and conduct photosynthesis while others are colorless and nourish themselves underground as saprotrophs. Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. ... Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ... Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of about 20,000 species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ... // Overview A gametophyte is the haploidor possibly diploid structure or phase of life of a sexually-reproducing plant. ... Sporic or diplohaplontic life cycle. ... Spores produced in a sporic life cycle. ... In plants that undergo alternation of generations, a sporophyte is the structure, or phase of life, that contains a total complement of chromosomes: The sporophyte produces spores, in a process called meiosis. ... Sunflower seedlings, just three days after germination Germination is the process where growth emerges from a resting stage. ... Rhizoids, in fungi, are small branching hyphae that grow downwards from the stolons that anchor the fungus. ... An archegonium (pl: archegonia) (from the Greek arche = beginning and gonos = born) is a multicellular structure or organ of the gametophyte phase of certain plants producing and containing the ovum or female gamete. ... Diagram of antheridium anatomy An antheridium (plural: antheridia) is a structure or organ of the gametophyte phase of certain plants producing and containing the spermatids or male gametes. ... The leaf is the primary site of photosynthesis in plants. ... A Saprotroph (or saprobe) is an organism that obtains its nutrients from non-living organic matter, usually dead and decaying plant or animal matter, by absorbing soluble organic compounds. ...

Alternation of Generations

Spore-bearing plants, like all plants, go through a life-cycle of alternation of generations. The fully grown sporophyte, what the layman refers to as the fern, produces genetically unique spores in the sori by meiosis. The haploid spores fall from the sporophyte and germinate by mitosis, given the right conditions, into the gametophyte stage, the prothallus. The prothallus then develops independently for several weeks; it grows sex organs and produces ova and flagellated sperm. After rainfall, the sperm are able to swim to the ova for fertilization to form a diploid sporophyte cell. This cell divides by mitosis and grows out of the gametophyte into a new fern, which will produce new spores that will grow into new prothallia etc., thus completing the life cycle of the organism. Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ... Sporic or diplohaplontic life cycle. ... In plants that undergo alternation of generations, a sporophyte is the structure, or phase of life, that contains a total complement of chromosomes: The sporophyte produces spores, in a process called meiosis. ... Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of about 20,000 species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ... Spores produced in a sporic life cycle. ... For the article on the figure of speech, see meiosis (figure of speech). ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... Light micrograph of a newt kidney cell in early anaphase of mitosis. ... // Overview A gametophyte is the haploidor possibly diploid structure or phase of life of a sexually-reproducing plant. ... A human ovum An ovum (from Latin, loosely, egg or egg cell) is a female sex cell or gamete. ... The signifier sperm can refer to: (mass noun, from Greek sperma = seed) a substance which consists of spermatozoa and which is a component of semen (mass noun) semen itself (informally, count noun with plural sperm or sperms) a single spermatozoon (= sperm cell) sperma ceti (Latin ceti, genitive of cetus = whale... Categories: Biology stubs ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... In plants that undergo alternation of generations, a sporophyte is the structure, or phase of life, that contains a total complement of chromosomes: The sporophyte produces spores, in a process called meiosis. ... // Overview A gametophyte is the haploidor possibly diploid structure or phase of life of a sexually-reproducing plant. ... In biology and ecology, an organism (in Greek organon = instrument) is a living complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole. ...

Advantages of Alternation of Generations

There are two important evolutionary advantages to the alternation of generations plant life-cycle. Firstly, by forming a haploid gametophyte, there is only one allele for any genetic trait. Thus, all alleles will be expressed because no allele may be masked by a dominant counterpart (there is no counterpart). The benefit of this is that any mutation that causes a lethal, or harmful, trait expression cannot be masked and will cause the gametophyte to die; thus, the trait cannot be passed on to future generations, preserving the strength of the gene pool. Also, crossing-over during meiosis in the formation of spores, and sexual reproduction in the gametophytes, allows for genetic diversity, which also inhibits harmful recessive genes from "surfacing" and being expressed. Sporic or diplohaplontic life cycle. ... An allele is any one of a number of viable DNA codings of the same gene (sometimes the term refers to a non-gene sequence) occupying a given locus (position) on a chromosome. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... In genetics, dominant allele refers to a genetic feature that hides the recessive allele. ... For the article on the figure of speech, see meiosis (figure of speech). ... For the article on the figure of speech, see meiosis (figure of speech). ... Sexual reproduction is a type of reproduction that results in increasing genetic diversity of the offspring. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ...

External links

• Liverwort Sporophyte
• Fern Life-Cycle