Although moss and hornwort sporophytes can photosynthesise, they require additional photosynthate from the gametophyte to sustain growth and spore development and depend on it for supply of water, mineral nutrients and nitrogen. In other species, the size and shape of the sporophyte and gametophyte is nearly indistinguishable. The gametophyte is reduced and dependent on the sporophyte. An explorer found a plant that had roots, stems, and leaves. The sporophyte is dependent on the gametophyte. A sperm cell swims through a film of moisture to fertilize the egg. The sporophyte is large, and the gametophyte is small and independent.
In isomorphic or homologous type both the alternating generations are morphologically similar, while in heteromophic or heterologous type of alternation of generations both the generations of life cycle are morphologically dissimilar. Life cycle of the common jellyfish Aurelia. If conditions are right, a spore will germinate and grow into a rather inconspicuous plant body called a. This question has been hotly debated, and there is still disagreement about the exact answer. The reproductive organ of angiosperms is the sporangium. Diagram showing the alternation of generations between a diploid sporophyte bottom and a haploid gametophyte top Alternation of generations also known as metagenesis is the type of that occurs in those and in the and the that have distinct sexual haploid and asexual diploid stages.
Why, then, is sexual reproduction so common? A fruits B sepals C petals D anthers E ovaries The pollen tube releases two sperm cells into the embryo sac. The reproductive structures of the sporophyte cones in gymnosperms and flowers in angiosperms , produce two different kinds of haploid spores: microspores male and megaspores female. These plants belong to the phylum Cycadophyte Ginkgophyte. C Only gymnosperms can contain male and female sporangia on the same plant. The way in which the alternation of generations occurs in plants depends on the type of plant. This phenomenon of alternation between gametophyte n and sporophyte 2n in the life cycle of a plant is called alternation of generations Hofmeister, 1851.
Despite all this, few multicellular organisms are completely asexual. No haploid spores capable of dividing are produced, so they do not have a haploid gametophyte alternating with a diploid sporophyte. A researcher has developed two stains for use with seed plants. Differences in the Sporophyte and Gametophyte During the alternation of generations in some species, there is an unequal distribution in size or dominance of either the sporophyte or the gametophyte. The opportunity to increase information content at low cost was advantageous because it permitted new adaptations to be encoded. Like other species of , C. Crane 1997 The origin and early evolution of plants on land.
Later the seed is shed, germinates and grows into a mature tree. The larger sessile megagametes are eggs ova , and smaller motile are sperm spermatozoa, spermatozoids. This spore will undergo successive rounds of mitosis to form a new multicellular individual, the gametophyte. Karogamy produces a diploid zygote, which is a short-lived sporophyte that soon undergoes meiosis to form haploid spores. Absolutely no cheating is acceptable.
The very best evidence for the hypothesis is the derived traits shared by charophytes a taxon of green algae and plants. A The sperm of some gymnosperms have flagella. The pollen tube releases two sperm cells into the embryo sac. Thus, the sporophyte individual remains a 2n organism. Three phyla of bryophytes exist today: liverworts, hornworts, and mosses. In , and , the sporophyte is less well developed than the gametophyte and is largely dependent on it.
Horsetails species of have spores which are all of the same size. Drag the labels onto the diagram below. As an illustration, consider a monoicous moss. A They produced separate male and female gametophytes. D The sperm of gymnosperms do not require water or mobility for fertilization. Mammals do not alternate generations C.
Beyond these basic elements, however, there can be a lot of variation in sexual life cycles. Select the correct statement describing the life cycle of angiosperms. Alternation of generations has several distinct features, and these features can be slightly modified between species. Both mosses and ferns have swimming sperm that require moisture to reach an egg. Gametophyte This represents the next generation in the alternation of generations, as the haploid spore is created. The chloroplasts of plants and green algae all have both chlorophyll a and b.