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The gymnosperms (/ ˈ dʒ ɪ m n ə ˌ s p ɜːr m z,-n oʊ-/ ⓘ nə-spurmz, -noh-; lit. ' revealed seeds ') are a group of woody, perennial seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae [2] The term gymnosperm comes from the ...
Early land plants had sporophytes that produced identical spores (isosporous or homosporous) but the ancestors of the gymnosperms evolved complex heterosporous life cycles in which the spores producing male and female gametophytes were of different sizes, the female megaspores tending to be larger, and fewer in number, than the male microspores ...
The life cycle of a dioecious flowering plant (angiosperm), the willow, has been outlined in some detail in an earlier section (A complex life cycle). The life cycle of a gymnosperm is similar. However, flowering plants have in addition a phenomenon called ' double fertilization '.
Angiosperm life cycle. All multicellular plants have a life cycle comprising two generations or phases. The gametophyte phase has a single set of chromosomes (denoted 1n) and produces gametes (sperm and eggs). The sporophyte phase has paired chromosomes (denoted 2n) and produces spores.
Ginkgoales are a gymnosperm order containing only one extant species: Ginkgo biloba, the ginkgo tree. [1] The order has a long fossil record extending back to the Early Permian around 300 million years ago from fossils found worldwide. The order was a common component of Permian and Triassic flora before the super dominance of conifers.
Cheetahs can go from 0 to 97 km/h (0 to 60 mph) in less than 3 seconds. [109] There are indirect ways to measure how fast a cheetah can run. One case is known of a cheetah that overtook a young male pronghorn. Cheetahs can overtake a running antelope with a 140 m (150 yd) head start.
Gnetophyta (/ n ɛ ˈ t ɒ f ɪ t ə, ˈ n ɛ t oʊ f aɪ t ə /) is a division of plants (alternatively considered the subclass Gnetidae or order Gnetales), grouped within the gymnosperms (which also includes conifers, cycads, and ginkgos), that consists of some 70 species across the three relict genera: Gnetum (family Gnetaceae), Welwitschia (family Welwitschiaceae), and Ephedra (family ...
Thus, in flowering plants, the two fundamental aspects of sexual reproduction are cross-fertilization (outcrossing) and meiosis and these appear to be maintained respectively by the advantages of genetic complementation and recombinational repair of germline DNA.