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Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. [ 2 ]
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores . Generally speaking, the megaspore, or large spore, germinates into a female gametophyte , which produces egg cells .
Microspores: Produced sexually through meiosis, and give rise to a male gametophyte: Pollen in seed plants In plants, microspores, and in some cases megaspores, are formed from all four products of meiosis. Megaspores (macrospores) Produced sexually through meiosis, and give rise to a female gametophyte: Ovule in seed plants
Spores of two distinct sizes (heterospory or anisospory): larger megaspores and smaller microspores. When the two kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia. A megaspore often (but not always) develops at the expense of the other three cells resulting from meiosis, which abort.
A science fair or engineering fair is an event hosted by a school that offers students the opportunity to experience the practices of science and engineering for themselves. In the United States, the Next Generation Science Standards makes experiencing the practices of science and engineering one of the three pillars of science education.
Aside from the ever-present threat of poachers, Javan rhinos face other threats. Because there are so few left, there is a lack of genetic diversity in the herd, and only about two males for every ...
[7]: 18 These plants produce both microspores and megaspores, which give rise to gametophytes that are functionally male or female, respectively. Most heterosporous plants there are two kinds of sporangia, termed microsporangia and megasporangia.
The Program on Reproductive Health and the Environment at UCSF offers additional tips to help minimize exposure to toxic chemicals, like those sometimes found in microplastics.