Plants Reproductive Organs and Functions
The general life cycle of plants:
The mature, multicellular organism is a diploid sporophyte. Later, some cells undergo meiosis to produce haploid gametes which are then released. Gametes fuse and form the zygote which develops by mitosis to become the multicellular diploid sporophyte.
In some plants, the dominant part of the life cycle is a multicellular, haploid gametophyte ( all cells have a haploid chromosome number). Mitosis releases individual cells that can act like gametes (gamete are produced by mitosis).
The different types of life cycles:
I. Haplontic life cycle
A. Show life cycle of the green alga Chara
i. Chara is a multicellular green alga related to higher plants because it has both chlorophyll a and b and produce plant starch. Its dominant stage is a multicellular haploid stage which produces gametes that eventually fuse to form unicellular zygotes. Each zygote then undergoes meiosis to become haploid, after which it undergoes mitosis to become the multicellular organism.
II. Haplodiplontic life cycle
A. Show life cycle of a moss (use figure 3 at the end of the document as reference)
i. A moss has a multicellular haploid (gametophyte) stage that produces gametes. These gametes fuse to produce a zygote that undergoes mitosis to produce a multicellular sporophyte. Within a part of the sporophyte called the capsule, cells undergo meiosis to produce meiospores. These spores are eventually released and germinate by dividing mitotically to become a multicellular gametophyte.
III. Diplontic life cycle
A. Type of life cycle found in flowering plants (and in most animals). The organism is in the diploid stage ( all cells are diploid in chromosome number) except for mature, haploid sex cells which are called gametes.
5. The flower
I. The four major whorls
A. Sepals
B. Petals
C. Stamen with Anther and Filament
D. Carpels- with Stigma, Style, Ovary and Ovule
II. Types of flowers based on the presence of the whorls
A. Complete
B. Incomplete
III. Types of flowers based on the presence of reproductive whorls
A. Perfect / Bisexual
B. Imperfect / Unisexual
i. Staminate flower
ii. Carpellate flower
Development in flowering plants
I. Gametophyte - Development through gametogenesis (use figure 6 to illustrate
gametogenesis in flowering plants)
A. Male gametophyte - The microsporangium in the anther contains numerous microsporocytes. Each microsporocyte will undergo meiosis to produce four haploid microspores each microspore develops into a pollen grain (containing two sperm nuclei and one tube nucleus)
B. Female gametophyte - The megasporangium in the ovule contains megasporocytes. One megasporocyte will undergo meiosis to produce four haploid megaspores three megaspores degenerate remaining megaspore divides mitotically three times, an embryo sac with eight haploid nuclei membranes partition to make the embryo sac multicellular
II. Pollination
A. Transfer of pollen grain from the anther to the stigma
B. May be animal-aided or wind-aided
III. Double fertilization
A. Inside a pollen grain there is a tube cell and generative cell generative cell divides to produce two sperm cells while the tube cell becomes pollen tube pollen tube elongates along the style and penetrates the ovule in the ovary via the micropyle (an opening) pollen tube discharges the sperm cells into the embryo sac inside the ovule one sperm unites with the egg to form the zygote while the other sperm fuses with the polar nuclei to become the endosperm, which serves as food of the early embryo
IV. Embryo development (embryogenesis)
A. Zygote divides mitotically to produce the proembryo and suspensor, which anchors the proembryo and transfers nutrients from the parent plant to it cotyledons appear on the proembryo (monocots have only one cotyledon whereas dicots have two) proembryo elongates into an embryo.
V. Maturation of ovary and ovule
A. Ovary matures into fruit while the ovule becomes the seed. The seed may become dormant for some time.
VI. Seed germination
A. Transformation of seed to seedling
B. Seed undergoes imbibition to break dormancy nutrients stored in the endosperm or cotyledons are digested and transferred to the growing regions of the embryo to primary meristems (protoderm, ground meristem, procambium) develop to radicle emerges to plumule breaks through the soil surface
i. Epigeal germination occurs when the cotyledon emerges above ground, thereby exposing the hypocotyl of the plumule.
ii. Hypogeal germination occurs when the cotyledon remains below ground, thereby concealing the hypocotyl.
VII. Seedling growth to mature plant
A. Primary meristems differentiate to become the different plant tissues
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