Alternation of generations in ferns


All spores the same size homospory or isospory. Each antheridial head contains several antheridia full of sperm. Karogamy produces a diploid zygote, which is a short-lived sporophyte that soon undergoes meiosis to form haploid spores.

For further information, see Double fertilization. True dormancy or innate dormancy is caused by conditions within the seed that prevent germination under normally ideal conditions. In gymnosperms, such as conifers, the food storage tissue is part of the female gametophyte, a haploid tissue.

When it rains, the antheridia release sperm.

How is alternation of generations different in ferns and pines?

Secondary dormancy is caused by conditions after the seed has been dispersed and occurs in some seeds when non-dormant seed is exposed to conditions that are not favorable to germination, very often high temperatures. Alternation of generations occurs in almost all multicellular red and green algae, both freshwater forms such as Cladophora and seaweeds such as Ulva.

Within the seed, there usually is a store of nutrients for the seedling that will grow from the embryo. When the two kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia.

Horsetails species of Equisetum have spores which are all of the same size. A 'female' zygote develops by mitosis into a megasporophyte, which at maturity produces one or more megasporangia. The gametophyte produces gametes often both sperm and eggs on the same prothallus by mitosis.

When fruits do not open and release their seeds in a regular fashion they are called indehiscent, which include these fruits; Achenes, caryopsis, nuts, samaras, and utricles.

Seed dispersal is seen most obviously in fruits; however many seeds aid in their own dispersal. The resulting 2n zygote remains within the archegonium for protection from dessication, and grows by mitosis to form the new, 2n sporophyte generation.

On flowers and fruits of Pyrethrum sp. However, in ferns and their allies there are groups with undifferentiated spores but differentiated gametophytes. Apterous males and oviparae occur in October in England Blackman. Ferns also exhibit alternation of generations, but for them, the 2n sporophyte generation is the dominant generation, and the 1n gametophytes are inconspicuous.

The sporophyte plant consists of an underground, horizontal rhizome from which arise the roots and leaves. Alternation of Generations Sexual reproduction involves the two alternating processes of meiosis and fertilization.


In meiosis, the chromosome number is reduced from the diploid to the haploid number.; In fertilization, the nuclei of two gametes fuse, raising the chromosome number from haploid to diploid. Definition. Alternation of generations is defined as the alternation of multicellular diploid and haploid forms in the organism's life cycle, regardless of whether or not these forms are free-living.

In some species, such as the alga Ulva lactuca, the diploid and haploid forms are indeed both free-living independent organisms, essentially identical in. A general form of alternation of generations looks like this: The forms that the sporophytes, spores, gametophytes and gametes take on vary depending on the type of plant.

In bryophytes (mosses and their ilk), the gametophytes are the bigger generation but in other land plants, sporophytes are bigger. Alternation of generations, also called metagenesis or heterogenesis, in biology, the alternation of a sexual phase and an asexual phase in the life cycle of an organism.

The two phases, or generations, are often morphologically, and sometimes chromosomally, distinct. This alternation of generations is a life cycle that includes both diploid and haploid multicellular stages.

Most of the definition is probably unfamiliar, so let's review the terms before talking.

Alternation of generations in ferns
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SparkNotes: The Life Cycle of Plants: Alternation of Generations