Study Guide for Reproduction of Plants
The sexual reproduction of plants is a process. Four different steps are involved in this process. Understanding the sexual reproduction of plants allows you to better understand how they sprout and grow, as well as how to best care for them.
Alternation of Generations
All plants have a life cycle that gets each plant through the haploid and diploid generations. The sporophyte, a multicellular diploid plant structure, creates spores through asexual (meiotic) division. The gamephyte, a multicellular haploid plant structure, is created from the spore and causes haploid gametes. The fluctuation between the haploid and diploid stages that plants go through is referred to as alternation of generations.
The type of plant determines how alternation of generations occurs. Bryophytes (liverworts and mosses) need a moist environment to survive and are nonvascularized. They go through both the diploid and haploid stages and they progress through their lifecycle. The main part of the plant is comprised on the gametophyte and attached to the gametophyte is a much smaller diploid sporophyte. The dominant stage in this plant's life is the haploid stage. A diploid zygote is them produced when the mature gametophyte produces both female and male gametes. This zygote then becomes a diploid sporophyte that extends from the gametophyte and, through meiosis, creates haploid spores. Once the spores experience germination, new gametophyte plants are produced and the cycle continues.
Tracheophytes contain vascular tissue and the two of the major classes include flowering plants (angiosperms) and conifers (gymnosperms). Unlike bryophytes, tracheophytes protect their embryos with seeds that encase them. The diploid stage is the dominant stage in this plant's life cycle. Without the parent plant, the gametophytes cannot exist and they are very small. The sporophytes reproductive structures (flowers in angiosperms and cones in gymnosperms) produce megaspores (female) and microspores (male), two different types of haploid spores. Heterospory is the sexually differentiated spores phenomenon. These spores cause gametophytes that are similarly sexual differentiated, and in turn create gametes. Fertilization occurs when a female gamete and a male gamete join to create a zygote. The resulting embryo (with a seed coating) will eventually turn into a new sporophyte.
When a diploid zygote is created through the meeting of haploid gametes, an embryo develops. This process is known as fertilization. With angiosperm and gymnosperm fertilization, the gametes meet by the male gametes that are covered with pollen grains are carried away by insects or wind to the reproductive organs of females. Once fertilization is complete, the embryo will be encased in a seed.
Many plants can create clones of themselves, through asexual reproduction, which can then become independent plants. This process is known as vegetative propagation, or in some cases, vegetative reproduction. This process can occur though fragmentation in which a whole new plant can grow from a severed plant. Other modes of this process include the production of specialized structures like runners, tubers, and bulbs. Tubers include plants such as potatoes. Runners include plants such as strawberry plants. Bulbs include plants such as tulips and onions.
This process is an artificial type of vegetative propagation. It is done when tissue regeneration and artificial means join two parts of young plants together. A plant's bud or twig (scion) is cut from a plant and is then joined to a rooted plant (stock) of a variety or species that is related. The scion will eventually become a total shoot system. Grafting allows horticulturists to combine two plant's best features into a single plant. Sometimes the independent characteristics stay the same and sometimes they are altered.
Archegonium: Terrestrial plant's female sex organ where the production of egg cells happens.
Cross-pollination: The process that the majority of angiosperms experience in which a plant's male gametes fertilize another plant's eggs when carried by pollen grains.
Endosperm: This is a substance that is created during angiosperm reproduction from a triploid nucleus. It nourishes an embryo that is developing inside a seed.
Fusion Nucleus: This is diploid product that is created when two polar nuclei, within the angiosperm ovule, are joined together.
Meiosis: Cell division that occurs in cells that have half the chromosomes that their parent cells do.