The alternation of generations life cycle in plants
Plants start as a diploid, multicellular, 2n, sporophyte. It then goes through the process of meiosis to create 1n, spores. The spores then goes through mitosis and turns into a haploid gametophyte, 1n. It then goes though mitosis again and gets turned into male and female gametes. The female gamete, egg, goes through fertilization by the male gamete and creates a fertilized zygote. That then can travel by wind and get planted and regrow into a diploid sporophyte.
Bryophyta
The sporangium on top of a mature sporophyte acts like a capsule. It holds a collection of spores that grow into a protonemata that bud and eventually turn into either a male or female gametophyte. Both gametophytes have roots called rhizoids. The male gametophyte has an antheridia that holds sperm that is carried by water to the female reproductive organ. Called the archegonia, that hold the eggs. Once the egg has ben fertilized it's called a zygote that develops into an embryo. which then turns into a sporophyte and then a gametophyte. Then the cycle starts again.
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Flagellated sperm
Lacks vascular tissue Gametophyte is the dominant stage, haploid Don't produce seeds Reproduce using spores They have roots, that absorbs nutrients and conducts it up the stem to the fronds which are photosynthetic. The diploid sporophyte develops haploid spores by meiosis, these spores are in containers called sporangia and grouped together in clusters and called sori. |
pteridophyta
The mature sporophyte contains a sporangium which goes through meiosis and releases spores that grow into young gametophytes. The gametophyte contains three main structures. The rhizoids, act like roots and absorbs nutrients. The antheridia is the male reproductive organ that contains sperm, and the archegonia is the female reproductive organ that contains eggs. When the egg gets fertilized by the sperm it turns into a diploid zygote. It then goes through mitosis and grows a new sporophyte and the cycle then starts again.
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Contain a vascular tissue
- xylem: conducts water from roots to shoots - phloem: conducts the photosynthetic products from roots to shoots. Plants are larger, because they contain a vascular tissue. Flagellated sperm Sporophyte stage is the dominant stage, diploid Fragile gametophyte Spores for reproduction |
Gymnosperms
Contains a seed
- gametophyte reduced and became dependent on sporophyte - asexual spores developed into sexual pollen for air distribution - development of an embryo protectant system Reproduce without water, spread Sporophyte is the dominant stage, diploid Has vascular system Heterospory Pollen= male gametophyte True roots are visible modified leaves, needles, that contain a natural antifreeze A gymnosperm starts off as a sporophyte with male, pollen bearing, and female, seed bearing, cones. The pollen bearing cone contains scales that have microspores, that go through meiosis and turn into pollen. The seed bearing cone contains a megaspore that gets pollinated by the pollen, being carried in the wind by it's air bladder. The pollen sprouts a pollen tube and attaches to the egg inside the mega spore. The fertilized egg turns into a 2n zygote through mitosis, that is called a pine seed. The pine seed gets carried by the wind to a new location, gets planted, grows and starts over again as a sporophyte.
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angiosperms
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"Flowering plants"
- vector pollinated (bees) - don't need to rely on wind or water for reproduction - resulted in parallel evolution between angiosperms and animals Specialized reproductive structures Sporophyte stage more dominant, diploid Have four principle organs: - Leaves: holds the water that is absorbed - Flowers: attracts pollinators - Stems: conducting materials, orienting leaves to the sun, provides structural support, and growth of the plant width and height. - Roots: absorbs water and minerals from the soil, as well as anchor the plant to the ground. Divided into two classes - dicots: 2 cotyledons, leaves with a network of veins, ex. woody plants -monocots: 1 cotyledon, leaves with parallel veins, ex. grasses palms, lilies. 8. Filament- A star like structure of the stamen that supports the anther.
9. Sepal- The outer green part of the flower often encompassing a flower bud. 10. Petal- The parts of the flower that are brightly colored to attract a pollinator. |