Alternation of Generations Life Cycle
Plants under go a life cycle called alternation of generations. This means plants go through both a haploid and diploid stage were as in animals we are always diploid other then our sperm and egg. The Alternation of generation life cycle is shown to the right. Starting at the top the haploid spore undergoes mitosis and grows into a portonemia, which are either female or male and both are haploid. Once fully grown they are called gametophyte and have small roots called rhizoids. The eggs are produced in the archegonium of the female and the sperm are produced in the antheridium of the male. With the help of water the sperm gets onto the female plant and swims down the archegonium to the egg where fertilization occurs. The sperm and egg fuse to make a diploid zygote. The zygote grow into a long stalk with a spore capsule on the end, this stalk is called the sporophyte. The capsule at the end of the sporophyte releases the spores contained inside to land elsewhere and grow into more plants. All plants use this life cycle, but some plants have a dominant gametophyte stage and others have a dominant sporophyte stage.
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Characteristics
Bryophyta- Mosses & liverworts, non-vascular, no true roots, swimming sperm, spore reproduction and a dominant gametophyte stage.
Pteridophyta-Ferns, vascular including the xylem & phloem, small roots, swimming sperm, spore reproduction and a dominant sporophyte stage.
Gymnosperm-meaning "naked seed", conifers, vascular, large roots, wind born sperm 'pollen', seed reproduction with pollen cones & ovulate cones and a dominant sporophyte stage.
Angiosperm-meaning "covered seed", the flowering plants, vascular, large roots, sperm moved by vectors, seed reproduction with stamen & carpel and a dominant sporophyte stage.
Pteridophyta-Ferns, vascular including the xylem & phloem, small roots, swimming sperm, spore reproduction and a dominant sporophyte stage.
Gymnosperm-meaning "naked seed", conifers, vascular, large roots, wind born sperm 'pollen', seed reproduction with pollen cones & ovulate cones and a dominant sporophyte stage.
Angiosperm-meaning "covered seed", the flowering plants, vascular, large roots, sperm moved by vectors, seed reproduction with stamen & carpel and a dominant sporophyte stage.
Life Cycles
Bryophytes use spores for reproduction. They also use swimming sperm that can only be transferred to the female with the help of water, so in really dry conditions they have no way of reproducing. Pteridophytas have a special gametophyte stage called a prothallus that makes the female and male gametes. They still use swimming sperm and spores for reproduction. Gymnosperms use seed instead of spores to spread to new places. Their sperm is now in whats called pollen which floats with the wind to get to the egg. This makes a lot of the fertilization by chance. Gymnosperms use cones that make male and female gametes, a pollen cone that makes the sperm and pollen and a ovulate cone that makes the eggs and where fertilization occurs. Angiosperms use pollen for fertilization not by wind but with the help of pollinators or vectors. This method makes pollination more exact and not by chance. Angiosperm have a stamen to produce male gametes and a carpel to produce female gametes. They also have bright flashy pedals to attracted pollinators. Most of these flowering plants, after fertilization, grow a fruit containing seeds that is eating by an animal and is pooped out elsewhere for a new plant to grow. |
The Angiosperm
The stamen is the male reproductive structure and makes sperm and pollen. It includes the filament, the stem structure, and the anther, that holds the pollen. I the middle is the female reproductive structure the carpel that makes eggs, houses the zygote and turns into fruit after fertilization. They have bright colorful pedals to attracted pollinators. The sepals under the pedals are used for support and protection as the flower blooms.
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