There are a lot of changes in the current world. Today, many things have changed from the ancient world. Time, climate, and other factors have led to changes in the earliest possible of everything in the world today. Like the evolution of animals that led to the extinction of some and the adaptability of the surviving animals, for instance; man, plants were not always land organisms. Plants originated from a single aquatic green algae known as chlorophyte over 400 million years ago or during the Silurian period (Lewis, & McCourt, 2004). This paper is divided into four other sectors that will enable a clear understanding of the evolution of plants from the green algae. The chapters begin with a brief description of the evolution of the land plants from the algae. The next section will focus on describing alteration of generations, followed by the life cycles of both bryophytes and pteridophytes which will enable understanding the ancestral and derived features of non-vascular and vascular plants about the mechanism to adapt to land. The final chapter tackles the role of peat moss as a carbon sink.
Background
Over 400 million years ago, the first colonists or territorial organisms that have some of the characteristics of the modern plants were populated the earth in the form of the green algae. The scientists claim that this period saw the evolution of plants began with the liverworts, mosses and hornworts which are non-vascular commonly known as bryophytes being the first land plants (Lewis, & McCourt, 2004). Since they were non-vascular, they could not grow independent of water and did not have the rigidity required to survive independently on the land hence their preference in wetlands. These features are discussed further later in the paper. The challenges faced by the bryophytes in their new environment led to further diversification thus between 425 to 300 million years ago vascular plants evolved in the form of lycophytes, and pterophytes. Pterophytes mainly ferns which are seedless vascular plants were the first and most diversified second only to the gymnosperms and angiosperms which are the flowering plants that are more developed to live on land. Since the bryophytes to the current plants, there have been many changes as plants diversify to suit their independence and the environment.
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Alternation Generation
The concept refers to the diversification of plants reproduction and life cycle. The life cycles of different plants help understand the concept in that it demonstrates the alternation between multicellular haploid life stages and the diploid life stages of any plant since the start of the evolution (Lewis, & McCourt, 2004). Alternation generation depicts the diploid forms commonly known as sporophytes that produce the haploid spores that divide and develop into gametophytes. The concept is better understood after describing the life cycles of both the bryophytes and pteridophytes.
Bryophytes (Mosses)
Since they are regarded as the earliest evolution, they are non-vascular and submerged in water. Their lack of vascularity makes them weak to live entirely on land thus do not have the ability grow tall. They absorb water by diffusion as they lack the structural support, for example, the water-conducting cells (Lewis, & McCourt, 2004). They depict the first transition from water to land; hence they have marginal adaptations to survive entirely on land. The body is the gametophyte generation that is haploid. They do not have true roots, leaves or stems as the gametophyte is the plant body and is also responsible reproduction.
The life cycle of a moss begins when the gametophyte generates the gametes, the egg and sperms which are produced separately from the archegonia and the antheridia respectively. Since the male and female gametophyte is haploid or produces either the male or female gamete, the sperm moves via water to the female archegonia thus fertilization taking place in the archegonia. The fertilized egg becomes a diploid zygote which via mitosis begins to develop into the embryo. The embryo matures to form the sporophyte or the diploid plant body and via meiosis in the sporangium of the mature sporophyte which produces haploid spores (Lewis, & McCourt, 2004). The haploid spores are dispersed with each spore via mitosis creates a haploid multicellular gametophyte, and the prominent haploid will produce a gamete and continue the same cycle (Lewis, & McCourt, 2004). The change from a haploid to diploid genes depict the cell division that is identical to modern plants hence the bryophytes are at the base of the plant evolution.
Pteridophytes
Unlike the bryophytes, the pteridophytes are seen as the first true land plants in that they are vascular and have the key structures required for photosynthesis, have leaves, stems, and roots. Ferns being the dominant plants in under the pteridophytes, are seedless vascular plants and do not rely on the gametophytes for their survival like the mosses do but they are also not as independent as the seed plants. The gametophytes have a short life as it is only important in the development of the gametes and fertilization.
Any individual fern either produces a male or female gamete with the antheridia producing a sperm whereas the archegonia produce the egg. The single gametophyte produces both antheridia and archegonia meaning that can function both as a male and as a female (Haufler, 2017). The dominant sporophyte generation produces the spores via meiosis while the free-living gametophyte generation forms the egg and sperm. The fern life cycle begins with diploid sporophytes. When mature the underside of the fern leaves produces sporangia which through meiosis forms the haploid spores. The spores are then dispersed from the sporangia which are carried by the winds once they find moist habitats they germinate and yield multicellular but microscopic gametophytes. The gametophytes are short lived and once mature they produce egg-forming archegonia and antheridia. With the presence of water, multi-flagellated sperm swim from the mature antheridia move to the egg and fertilization takes place (Haufler, 2017). The diploid zygotes produced following fertilization divide via mitosis and differentiated into mature sporophytes completing the cycle.
Roles of Peat Moss in Carbon Sinks
Recent studies demonstrate that peat moss are important as they help in carbon sinks. The studies claim that the peat bogs soak vast volumes of carbon dioxide from the air which is approximately 455 billion tonnes of the carbon. The main inhibit of using moss is that most of the carbon dioxide is lost when the plants rot before the moss can suck it all from the atmosphere. The peat moss has illustrated to be suck carbon during photosynthesis and shows that they can help in enhancing climate change by providing better carbon sinks in the wetlands (Trail, 2013). The sphagnum peat moss also helps in soil conservation which also contribute to enabling the soil to suck in more carbon components from the atmosphere.
References
Haufler, C., (2017). Pteridophytes. Biology Reference . Retrieved May 19, 2017, from, http://www.biologyreference.com/Po-Re/Pteridophytes.html
Lewis L. A., & McCourt, R. M., (2004). Green algae and the origin of land plants. Am J Bot . 2004, 91 (10): 1535-1556. 10.3732/ajb.91.10.1535.
Trail, J. V. (2013, January 25). The truth about peat moss. The ecologist.org . Retrieved May 19, 2017, from, http://www.theecologist.org/blogs_and_comments/commentators/other_comments/1780209/the_truth_about_peat_moss.html
