The Sexual Life Cycle of Plants:
There are various types of reproductive techniques in the Kingdom Plantae (Plants).
Mosses, Ferns, Conifers, and Flowering Plants all have different Life Cycles.
Mosses: Mosses are the most primitive plant life.
Mosses absorb water through pores, not roots. Most mosses don't have true roots, stems, or seeds. Mosses have free-swimming sperm that depend on rainfall to fertilize the egg.
Life Cycle:
Spores are released instead of seeds. In the moss life cycle, the released spores germinate and form a structure that eventually becomes either the male or female moss that we usually recognize. After a rain, the male sperm are washed into the female egg and a `zygote' is formed. The zygote is an early form of the structure that will eventually form more spores, and will repeat the life cycle.
Ferns
Ferns are the first form of plant life that developed a `vascular system.' Vascular systems help move water and sugar throughout the plant in an organized fashion. Ferns, like mosses, lack seeds. They use spores instead. Ferns also lack true roots. They use stem-like structures instead. Ferns have free-swimming sperm that depend on rainfall to fertilize the egg.
Life Cycle:
Certain tissues in the fern sexually divide. This forms spores. The spores are released and they germinate. They eventually grow rhizomes, which are the stem-like `roots' that anchor the plant. At this point in the cycle, the fern is vaguely heart-shaped. Both male and female portions of the plant create sperm and eggs, respectively. After a rain, the sperm are transported to the egg and a `zygote' is formed. The zygote is composed of one sperm and one egg. The zygote matures into the leafy plant that we usually recognize when we think of a fern. The next generation of spores will develop in the leaflets of this fern.
Numbers of chromosomes on certain fern families: 1
Diphasium, 46
Diplazium, 82, 123 depending on species
Dryopteris, 82, 123
Isoetes, 33, 44 1
Ophioglossum, 960, 1100
Polypodium, 72, 111, 148
Polystichum, 82, 164
Psilotum, 208
Selaginella, 20, 36
Ophioglossum reticulatum 1260 !!
Conifers :
Conifers are more advanced than ferns or mosses. They can quickly and efficiently
transport water and nutrients between their various tissues.
Conifers use a waxy coating to prevent their needle-like leaves from drying out.
Conifers use `cones' during their reproduction. The female cones bear the embryo, or
egg, and the male cones bear the pollen, or sperm.
Life Cycle:
Sexual cell division takes place in the male and female cones. Pollen grains form in the male cones. In the female cones, different processes eventually form the ovule. Wind blows the pollen into the female cones, and pollination occurs. Over the course of the next year or more, the pollen will slowly approach the egg cell itself. When the sperm finally reaches the egg, fertilization occurs. The embryo that will follow develops inside a naked seed and, when the time is right, it is released. The seed will germinate and eventually form a new tree.
Flowering Plants (Angiosperms):
Flowering plants are the most advanced form of plant life. Instead of cones, Angiosperms use flowers to reproduce. Rather than using a naked seed, flowering plants' seeds are encased in fruit.
Life Cycle:
(The life cycle of Angiosperms is very complex. The example below is only one example of Angiosperm reproduction.)
A flower develops on the mature plant. Pollen grains form on the male portion of the flower. Each pollen grain divides again, and two sperm are formed. Meanwhile, one embryo sac forms inside the female portion of the plant. Wind eventually blows pollen onto the female portion of the flower the sperm reaches the embryo. Once there, one of the sperm fertilizes an egg and forms an embryo. The other sperm combines with other parts of the sac and forms a nutritious food supply. This food will help the embryo grow. This process is unique to flowering plants. Both a seed coat and a fruit will cover the embryo. Eventually the seed and fruit fall off and take root elsewhere.
Number of chromosomes in certain flowering plants:
Brassica, 18, 20 1
Chrysanthemum, 18, 36, 56, 138, 198 1
Clematis, 16
Helianthus, 34 2
Phaseolus, 22
Primula, 16, 22, 36
Ranunculus, 16, 32, 48
Rumex, 20, 40, 60
Salix, 40, 63
Sedium, 20, 44, 54, 68
Petunia, 14
