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15 Cards in this Set
- Front
- Back
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What does the SPOROPHYTE produce, what does the GAMETOPHYTE produce?
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1)Sporophyte
-spores by meiosis 2)gametes (sex cells) for fertilization by mitosis |
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What is the SPOROPHYTE?
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-the diploid stage of the plant
-the vascular plant and the major or dominant generation -makes SPORES in SPORANGIA in SORUS covered by INDUSIUM on the ABAXIAL surface |
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What is a TRI-RADIATE MARK?
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-reflects the fact that the spores are produced in clusters of 4 (TETRADS)
-clear indication that these spores have reulted from MEIOSIS in the sporangium |
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What is a TRILETE SPORE?
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-spores that form in a 3-D cluster
-have a Y shaped mark on each spore wall |
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What is a MONOLETE SPORE?
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-somewhat elongate spore that lie in the tetrad with their long axes parallel
-spores of this type have a single mark |
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Go over the early stages of GAMETOPHYTE developement.
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-the spore absorbs water and cracks open along the TRI-RADIATE mark
-then a tube which quickly becomes separated into a FILAMENT emerges (green b/c has chloroplast) -a filament is formed b/c the first cell divisions are all oriented in one plane -sooner or later, this growth pattern gives way to 2-D growth with the result that a single layered plate of clls is formed -filament can remain a filamentous structure, but it usually becomes a heart shaped or cordate THALLUS -in the notch of the thallus gametophyte is a kind of apical meristem with an apical cell -as the gametophyte grows, the central portion thickens and forms a CUSHION or a kind of midrib if the gametophyte is elongated -this is several cells in thickness and represents a limited 3-D growth -on the underside of the cushion, there is ordinarily a profuse development of rhizoids -very soon, a colorless RHIZOID or absorbing hair is added |
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What are the sex organs found on the gametophyte?
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Antheridia
-produce sperm -commonly appear on the gametophyte before the archegonia -located among the rhizoids in the posterior region of the prothallus -hemispherical and protrude from the surface -when they mature, they open, in the presence of water, by means of a cap cell and release a number of motile sperm -the individual sperm is twisted like a corkscrew, bears many flagella, and swims like a KFC Whoopee ball Archegonia -produces eggs -produced closer to the apical notch -only the protruding necks can be seen pointing towards the posterior of the gametophyte -consists of 2 main regions 1)NECK: contains a single NECK CANAL CELL with 2 nuclei; VENTRAL CANAL CELL is the sister cell of the egg and lies close to the... 2)VENTER:which is embedded in the tissue of the cushion -when mature and when water is present, neck and ventral canal cell break down, releasing chem's that attract sperm and open a passage for sperm to enter -more than one sperm may enter, but only one gets the prize **the antheridia bearing gametophytes remain filamentous or narrowly strap shaped while those with archegonia acquire the typical heart shape** |
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What is an essential feature of the reproduction of all the vascular plants?
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-the zygote is not left to fend for itself but is protected and nurtured for a time by the parent plant during an embryonic stage
-usually takes place in the archegonium which protects and nourishes the embryo until it is able to become a self supporting sporophyte |
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Go over the early stages of EMBRYO & YOUNG SPOROPHYTE developement.
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-very quickly the FOOT develops from the inner half of the embryo, probably as an absorbing organ which draws nutrients from the gametophyte for the embryo
-its cells enlarge and intrude between the surrounding cells of the gametophyte -in the outer half of the embryo, 2 organs appear early: the FIRST LEAF and the PRIMARY ROOT -later the shoot apex arises between the first leaf and the foot -all subsequent leaves are produced by the shoot apex -here there is no period of dormancy, the first leaf and root quickly force their way out of the archegonium and establish the young sporophyte as an independent plant -it quickly outgrows the prothallus at its base, which withers away and disappears |
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What external element is needed for sexual reproduction?
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-water
-triggers antheridia and archegonia to open -sperm need to swim in it |
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What chemical triggers the production of ANTHERIDIA?
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-ANTHERIDOGEN
-produced by older gametophytes |
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What is GEMMAE?
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-special structures on gametophytes that act as vegetative reproductive bodies
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What is APOGAMY?
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-development of a sporophyte from a gametophyte without fertilization
-tissues of the gametophyte can give rise directly and vegetatively to a sporophyte |
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What is APOSPORY?
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-production of gametophytes directly from diploid cells of the sporophytes without spore formation (as in certain ferns and mosses)
-can be either haploid or diploid depending upon the ploidy level of the leaves used |
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Why is an alternation of generations needed?
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-noone knows for sure
-the fact that an increase in the carbohydrate supply, that is the energy supply, can cause the gametophytes literally to convert into sporophytes strongly supports the idea that the impoverished conditions under which the spore usually germinates in contrsat to the more favorable nutritional environment of the zygote has a great deal to do with the different morphology of the products of these 2 cell types |
