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A microsporangium (pl. microsporangia) is a sporangium that produces microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants , spike mosses and the aquatic fern genus Azolla .
Four chambers (pollen sacs) lined with nutritive tapetal cells are visible by the time the microspores are produced. After meiosis, the haploid microspores undergo several changes: The microspore divides by mitosis producing two cells. The first of the cells (the generative cell) is small and is formed inside the second larger cell (the tube cell).
It can be composed of a single cell or can be multicellular. Virtually all plants , fungi , and many other groups form sporangia at some point in their life cycle . Sporangia can produce spores by mitosis , but in land plants and many fungi, sporangia produce genetically distinct haploid spores by meiosis .
Outline of human anatomy; Cell types. by origin; This is a list of cells in humans derived from the three embryonic germ layers – ectoderm, mesoderm, and endoderm.
The Human Cell Atlas project, which started in 2016, had as one of its goals to "catalog all cell types (for example, immune cells or brain cells) and sub-types in the human body". [13] By 2018, the Human Cell Atlas description based the project on the assumption that "our characterization of the hundreds of types and subtypes of cells in the ...
In human embryogenesis, the theca cells form a corpus luteum after a Graafian follicle has expelled its secondary oocyte arrested in second meiosis. Thecal shape is also important in graptolite and pterobranch taxonomy. In dinoflagellates that are armoured their covering is made up of thecal plates.
During pollination, this generative cell divides and gives rise to sperm cells. The female counterpart to the antheridium in cryptogams is the archegonium, and in flowering plants is the gynoecium. An antheridium typically consists of sterile cells and spermatogenous tissue. The sterile cells may form a central support structure or surround the ...
The main difference between spores and seeds as dispersal units is that spores are unicellular, the first cell of a gametophyte, while seeds contain within them a developing embryo (the multicellular sporophyte of the next generation), produced by the fusion of the male gamete of the pollen tube with the female gamete formed by the ...