Angiosperm Life Cycle
The angiosperm life cycle is characterized by alternation of generations, with a dominant sporophyte stage and a reduced gametophyte stage. It involves the production of flowers, which contain the reproductive structures of the plant. The process of double fertilization leads to the formation of seeds within fruits, enabling angiosperms to disperse and reproduce efficiently.
7 Key excerpts on "Angiosperm Life Cycle"
eBook - ePub- Laurie Ann Callihan(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
...When a sperm cell fertilizes an egg cell (haploid cells join to form a diploid cell), they produce a zygote. The zygote will grow into an embryo, which resides within the growing seed. We are accustomed to identifying particular plants according to their adult phase, which is only one phase of the life cycle. Various phyla of plants have their own identifiable life cycles, which include an alternation of generations. Fig. 4–5 Alternation of Generations in Ferns. Mosses and ferns alternate haploid and diploid phases, developing two distinct generations of the plant, each with its own recognizable form. One generation is haploid, the other diploid. The haploid phase is most prominent in mosses; while in ferns, the diploid stage is most prominent. Fig. 4–6 Pine Life Cycle. The adult tree produces both male (pollen) and female (ovulate) cones that form the pollen and ovules that combine to produce a seed. In conifers (such as pines), the sporophyte generation (diploid) is the familiar adult of the species. The process of meiosis produces the haploid gametophytes (male and female) from the male and female cones. The male gametophyte forms the male pollen grain and its attached air bladders, which assist it in being borne by the wind. The pollen contains sperm cells and tube cells, which will fertilize an egg cell of a female scale when they are brought into contact. In angiosperms, the dominant adult generation is also the sporophyte—the flowering plant. (See Fig. 4–7.) Asexual Plant Reproduction Some plants may also reproduce through vegetative propagation —an asexual process. Asexual reproduction occurs through mitosis only (it does not involve gametes), and produces offspring genetically identical to the parent. While sexual reproduction leads to genetic variation and adaptation, asexual reproduction of a plant with a desirable set of genetic traits, preserves these intact in successive generations...
eBook - ePub- Peter Scott(Author)
- 2013(Publication Date)
- Wiley-Interscience(Publisher)
...The formation of separate sex gametophytes is considered to be one of the major steps towards the formation of plants that bear seeds. Figure 1.4 The life cycle of a heterosporous pteridophyte. In a small number of instances species of ferns are heterosporous and this is thought to be a crucial evolutionary step in the formation of the flowering plants. In Figure 1.3 the egg cell and the sperm are the same size, but in heterosporous pteridophytes, the female gamete (macrogametophyte) is much larger than the male gamete (microgametophyte). The habitat range of plants on land was widened considerably with the evolution of plants that produce seeds. The transition from being wholly aquatic to wholly terrestrial is considered complete in such plants. The seed-bearing plants are divided into two divisions, the gymnosperms (Pinophyta) and the angiosperms (flowering plants, Magnoliophyta). The angiosperms form the largest and most diverse plant division. Angiosperms produce reproductive structures in specialized organs called flowers, where the ovary and the ovule are enclosed in other tissues. The gymnosperms do not form a flower and the reproductive structures are in the form of cones, in which the ovule is not enclosed at pollination. On formation of a seed, the embryo is covered by a specialized scale leaf rather than the ovary and this gives rise to the name ’gymnosperm’, which means ’naked seed’. Gymnosperms were widespread in the Jurassic and Cretaceous periods of the Earth’s history but there are now fewer than 800 different species. They occupy a range of different habitats from temperate forests to more arid habitats. Most of the species are trees and shrubs, which are adapted very well to temperate areas of the world, where water availability is limited over extensive periods of the year (due to ground frosts)...
eBook - ePub- Arun K. Pandey, Shruti Kasana(Authors)
- 2021(Publication Date)
- CRC Press(Publisher)
...CHAPTER-19 ORIGIN AND EVOLUTION OF ANGIOSPERMS The flowering plants (angiosperms) constitute the higher group of seed plants with about 3,50,000 species. They are found in far greater range of habitats than any other group of land plants. Angiosperms arose from some unidentified ancestral lineage and diversified rapidly within a short geological time period (Li et al., 2019). To trace the origin of this group has been one of the main emphasis of evolutionary biologist. It has also been popularly called by Charles Darwin as an “abominable mystery”. On July 22, 1879, Charles Darwin famously stated in a letter to Joseph Dalton Hooker that “the rapid development, so far as we can judge, of all the higher plants within recent geological times is an abominable mystery.” Darwin was referring to the apparently abrupt evolutionary origin and subsequent rapid diversification of the angiosperms (Darwin and Seward, 1903). Angiosperms (from Greek word ‘ angeion’ meaning pot or vessel) are the group of plants in which ovules are formed inside the specialized female reproductive organ known as carpel. They are characterized by the presence of flowers, carpels, columellate pollen, non-motile sperm, elongated pollen tubes with callose plugs, double fertilization leading to endosperm production, highly reduced megagametophytes and microgametophytes, an outer integument enclosing the ovule, paracytic stomata, and vessels in the secondary xylem (Doyle, 2008). Due to these characters, the angiosperms rapidly radiated into several, distinct lineages and gradually replaced gymnosperms as the dominant plant life form on the earth. In addition to this, the success of the angiosperms is also attributed to the extensive coevolution with pollinators, herbivores and predators...
eBook - ePub- Donald Kaplan, Chelsea D. Specht(Authors)
- 2022(Publication Date)
- CRC Press(Publisher)
...In the long course of flowering plant evolution, the only part of seed development that seems to have been developmentally conserved (perhaps as a result of developmental constraint) appears to be the development of the embryo itself. All the patterns of megagametophyte ontogeny seem to have permitted a wide range of developmental variability without jeopardizing in any way the basic function of the gametophyte tissue in angiosperm seeds. FIGURE 22.68 Mature embryo sacs in angiosperms. Note the wide range in the number of polar nuclei that join with the sperm nuclei (shown in black) in the initiation of the endosperm. (From Foster and Gifford, 1974; adapted from Maheshwari, 1950.) Since we initially began this life history context in Chapter 4 of this book, in essence we have now come full circle and closed this life-history sequence for flowering plants. For readers who wish to be acquainted with the essentials of seed development and the events associated with the origin and development of the next sporophyte generation, we encourage you to review the fundamentals of these processes in Chapters 4 and 5 of this book. Changes in Floral Morphology in the Post-Fertilization State (Floral vs. Fruit Development) Although we have tended to refer to the fully developed form of the floral organs in the pre-fertilized state as “mature” organs, in fact, such organs are not truly “mature” until they reach the post-fertilization or fruiting stage of development. Thus, the fully developed flower should be seen as an intermediate developmental state of which the fruit or fruiting unit is the true mature state of the particular organ whorl. Depending upon the species, each of the floral organ whorls may or may not undergo later development...
eBook - ePubPlant Systematics
An Integrated Approach, Fourth Edition
- Gurcharan Singh(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Chapter 9 Phylogeny of Angiosperms Angiosperms form the most dominant group of plants with at least 295,383 (Christenhusz and Byng, 2016), a number much greater than all other groups of plants combined. Not only in numbers, angiosperms are also found in a far greater range of habitats than any other group of land plants. The phylogeny of angiosperms has, however, been a much-debated subject, largely because of very poor records of the earliest angiosperms. These earliest angiosperms probably lived in habitats that were not best suited for fossilization. Before trying to evaluate the phylogeny, it would be useful to have an understanding of the major terms and concepts concerning phylogeny in general, and with respect to angiosperms in particular. ORIGIN OF ANGIOSPERMS The origin and early evolution of angiosperms are enigmas that have intrigued botanists for well over a century. They constituted an ‘abominable mystery’ to Darwin. The mystery is slowly being ‘sleuthed’ and at the present pace of ‘Sherlock Holms research’, it may be no more mysterious within the next two decades than for any other major group. With the exception of conifer forest and moss-lichen tundra, angiosperms dominate all major terrestrial vegetation zones, account for the majority of primary production on land, and exhibit bewildering morphological diversity. Unfortunately, much less is known about the origin and early evolution of angiosperms, resulting in several different views regarding their ancestors, the earliest forms and course of evolution. The origin of angiosperms may be conveniently discussed under the following considerations. What are Angiosperms? Angiosperms form a distinct group of seed plants sharing a unique combination of characters. These important characters include carpels enclosing the ovules, pollen grains germinating on the stigma, sieve tubes with companion cells, double fertilization resulting in triploid endosperm, and highly reduced male and female gametophytes...
- Ian Clarke, Helen Lee(Authors)
- 2019(Publication Date)
- Melbourne University Press Digital(Publisher)
...4 Reproduction Reproduction in Flowering Plants may be either sexual or asexual. Sexual reproduction involves the fusion of male and female reproductive cells known as gametes. In asexual reproduction no fusion of gametes takes place and the reproductive entities are vegetative bodies such as corms, tubers, bulbs, cuttings etc. Sexual reproduction may be dealt with in a number of stages: • pollination—the transfer of pollen from anthers to stigma • fertilisation—union of male and female gametes • development of the seed • development of the fruit • germination of the seed. Pollination The transfer of pollen, which carries the male gamete, to the stigma takes place in several ways. Many plants are pollinated by wind including the conifers (pines and their allies), she-oaks and grasses, and many northern hemisphere trees such as birches, alders and oaks. These plants produce large quantities of pollen and release it into the air, and it may float or be blown onto a compatible stigma. The stigmas of wind-pollinated plants are commonly large and feathery, which gives them a better chance of trapping pollen. Insects are the most important pollinators of flowers. They visit to collect nectar or pollen or both, and at the same time incidentally transfer some pollen from one flower to another. Insects locate flowers by odour and then are influenced by colour and shape. It is known that bees preferentially visit yellow or blue flowers whereas moths, which emerge in the evening, are attracted to white or cream flowers, which are more readily seen at that time. Birds, particularly honeyeaters, are important pollinators of flowers with tubular corollas, to which they are attracted by the presence of copious nectar. Pollen catches on the head feathers of the birds as they probe for nectar and then is carried to other flowers. Birds seem to be attracted to red flowers, but they visit other colours if nectar is available...
eBook - ePub- Helen Lee, Ian Clarke(Authors)
- 2014(Publication Date)
- Melbourne University Press Digital(Publisher)
...4 Reproduction Reproduction in the flowering plants may be either sexual or asexual. Sexual reproduction involves the fusion of male and female reproductive cells known as gametes. In asexual reproduction no fusion of gametes takes place and the reproductive entities are vegetative bodies such as corms, tubers, bulbs, cuttings etc. Sexual reproduction may be dealt with in a number of stages: pollination—the transfer of pollen from anthers to stigma fertilisation—union of male and female gametes development of the seed development of the fruit germination of the seed. Pollination The transfer of pollen, which carries the male gamete, to the stigma takes place in several ways. Many plants are pollinated by wind including the conifers (pines and their allies), she-oaks and grasses, and many northern hemisphere trees such as birches, alders and oaks. These plants produce large quantities of pollen and release it into the air and it may float or be blown on to a compatible stigma. The stigmas of wind-pollinated plants are commonly large and feathery, which gives them a better chance of trapping pollen. Insects are the most important pollinators of flowers. They visit to collect nectar or pollen or both, and at the same time incidentally transfer some pollen from one flower to another. Insects locate flowers by odour and then are influenced by colour and shape. It is known that bees preferentially visit yellow or blue flowers whereas moths, which emerge in the evening, are attracted to white or cream flowers, which are more readily seen at that time. Birds, particularly honeyeaters, are important pollinators of flowers with tubular corollas, to which they are attracted by the presence of copious nectar. Pollen catches on the head feathers of the birds as they probe for nectar and then is carried to other flowers. Birds seem to be attracted to red flowers but they visit other colours if nectar is available...
