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Placentation is the formation, type and structure, or modes of arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo , and in some instances to remove waste from the embryo.
Placentation has also evolved in some reptiles. [9] The mammalian placenta evolved more than 100 million years ago and was a critical factor in the explosive diversification of placental mammals. [10] Although all mammalian placentas have the same functions, there are important differences in structure and function in different groups of mammals.
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The form of the human placenta is generally classified as a discoid placenta. Within this, the cotyledons are the approximately 15-25 separations of the decidua basalis of the placenta, separated by placental septa. [3]
Roman numerals: for example the word "six" in the clue might be used to indicate the letters VI; The name of a chemical element may be used to signify its symbol; e.g., W for tungsten; The days of the week; e.g., TH for Thursday; Country codes; e.g., "Switzerland" can indicate the letters CH; ICAO spelling alphabet: where Mike signifies M and ...
An ovary with free central placentation, on the other hand, consists of a single compartment without septae and the ovules are attached to a central column that arises directly from the floral apex (axis). In some cases a single ovule is attached to the bottom or top of the locule (basal or apical placentation, respectively).
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A fruit is the mature, ripened ovary of a flower following double fertilization in an angiosperm.Because gymnosperms do not have an ovary but reproduce through fertilization of unprotected ovules, they produce naked seeds that do not have a surrounding fruit, this meaning that juniper and yew "berries" are not fruits, but modified cones.