Alternation of Generations Life cycle
The alternation of generations life cycle contains two stages diploid (2n) and haploid (n). Meiosis occurs from the sporophyte stage to when the spores are produced. The spores will then go through mitosis to grow into gametophytes. The female and male gametes will then fuse together to form a zygote this process is fertilization. From here the zygote will then reenter the diploid sporophyte stage and the sporangium (capsule) will produce more spores and the process will start again.
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Bryophytes Characteristics
They are called the "non vascular plant" becuse they do not have vascular tissue in their dominant stage (Gametophyte). Secondly they require water for reproduction (swimming sperm) and they use spores in reproduction. The dominant stage for bryophytes is the haploid gametophyte stage. In order for bryophytes to move onto land they had to adapt. These adaptions include:
-dessication: prevent them from drying out (waxy cuticle) -Gas exchange through stomatas -Water conducting systems: xylem for water phloem for photosynthetic products -Protection for embyro (seeds) Byrophytes use the alternation of generations life cycle. They begin their lives as spores. The spores then go through mitosis and develop into protenema. They then go through mitosis again and develop female and male gametophytes. The male gametophyte contains an antheridium and the female has an archegonium. Haploid gametophyte stage is above. Fertilization will begin when the swimming sperm enter the archegonium and form a zygote. The zygote will then develop into a young sporophyte and gametophyte, and eventually the sporophyte will mature. The sporophyte has a sporangium (capsule) containing spores. This part of the life cyle is diploid sporophyte. The cycle then restarts when the plant goes through meiosis and releases spores. The dominant stage is the haploid gametophyte. |
Pteriodophyta
Just like Bryophyta, Pteridophyta use the alternation of generation life cycle as well. Secondly, they also have swimming sperm that swim from the male antheridium to the female archegonium. Spores are also used for reproduction. Pteridophytes don't produce seeds, so they are called "seedless vascular plants." They have roots that absorb nutrients and water then conduct them up the stem to fronds, which are photosynthetic. The dominant life cylce is diploid sporophyte.
The life cycle of Pteridophyta is the alternation of generation life cycle. The dominant stage is the diploid sporophyte. The haploid spore will begin to germinate. The haploid gametophyte begins to develop small root like structure but eventually it matures into a thin heart shape. The archegonium (female) and antheridium (male) are the reproductive structures. The sperm swim from the antheridum to the archegonium where fertilization begins and a diploid zygote develops. From here a young sporophyte begins to develop. Eventually the sporophyte will then develop spores are the underside of their fronds (leaves). The spores are sporangia, and are in clusters called sori. The sporangia will reproduce spores and the cycle will repeat. |
Gymnosperms
The following are gymno sperms: Ginkoes and Cycads, which evolved in Paleozoic Era and conifers. Conifers live in dry areas and flourished when the climate changed in the Mesozoic Era. The dominant life cycle in Gymnosperms is sporophyte. They are seeded vascular plants, which means they have vascular tissue. Have seeds, but they are "naked" and use pollen for the male part of reproduction. Their reproduction process no longer requires water. Another characteristic of Gymnosperms is their leaves are needles, which reduces the amount of water loss. They have cones for reproductionn. The male cone contains pollen and the female cone has the eggs.
The life cycle that is dominant in Gymnosperms is sporophyte. Reproduction takes place inside cones. There is a male cone (pollen grain), which contains pollen and the female cone is seed bearing. In the female cone meiosis will produce haploid (n) cells and this is the female gametophyte stage. During the male gametophyte stage a haploid nuclei will split and form two sperm cells. The life cylce starts when the male cone releases a large amount of pollen. If pollen lands on an ovule of the female cone it will split open and begin growing a pollen tube. The pollen tube has two haploid (n) sperm cells. As soon as the pollen tube has reached the female gametophyte, fertilization begins. However, this process of the pollen tube reaching the female gametophyte could take years. After fertilization a diploid (2n) zygote has been produced. This zygote will then go through mitosis and develop into a seed. The seed contains the old sporophyte generation, the haploid cells surrounding the embryo from the female gametophyte, and finally the embryo is the developing sporophyte. As soon as the seed lands in preferred conditions it will germinate and become the new sporophyte plant. |
Angiosperms
Angiosperm means "covered seed." The angiosperm dominant generation is sporophyte. They also contain vascluar tissue. The angiosperms made a big advancement and that was the evolution of specialized reproductive structures, which in this case is the flower. They protect their embryo through the seed, which contains nutrients for the embryo. They use fruit to spread the angiosperm to new areas. ANgiosperms are split into two classes:
1) Dicots: 2 cotyledons (seed leaves) leaves have a network of veins woody plants, trees, shrubs, are examples 2) Monocots: 1 cotyledon parallel veins grasses, palms, and lilies The life cycle of an angiosperm is dominated by the sporophyte generation. The reproduction takes place inside the flower. The life cycle starts when the diploid (2n) sporophyte produces flowers. The flower contains female reproductive structures (carpel) and male reproductive structures (stamen). Within the Anthers (male reproduction) the cells will go through meiosis and produce four haploid cells also (pollen grains). The pollen grains will be released and land on the stigma (female reproductive). The carpel undergoes meiosis and produces four haploid cells and then these cells go through mitosis and eight haploid cells are produced. These eight haploid cells are the embryo sac, this is in the ovule. One of these contains the egg and is usually at the bottom of the embryo sac. Once fertilization has occurred a diploid (2n) zygote has formed. The zygote goes through mitosis till it becomes a sporophyte seed, which is kept inside fruit. The fruit may be eaten by an animal and the seed will go through their digestive system and eventually end up in the animal's feces. The seed will then germinate and develop into a sporophyte plant. |
Organization of Angiosperms
The body plan of an angiosperm includes roots, stems, leaves, and flowers. The function of the roots is they absorb nutrients and water from the soil. They also keep the plant in place. Secondly, the function of the stems are providing support to the plant, and conducting material up and down the plant. The stems also direct the leaves toward the sun and lastly the growth of the height and width of plants. The leaves are stomata functioning. This means if the stomamta is open the guard cells absorb water, which cause the leaves to be stiff an bean shaped and the stomata to be bigger. When the stomata is closing the guard cells are losing water an the leaves are becoming flaccid and losing their shape. Lastly, the flower (reproductive) is used to attract a pollinator. Its structure contains sepals, petals, carpels (female), and stamen (male).