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Grade 11 University Biology Plant Reproduction Section 14.1 Pages 582-592 For a very detailed description of the life of plants, see http://www.sebring.k12.oh.us/McKinley_Jr__Sr__High_School/Naples/7th/chap10.pdf Seedless Reproduction Seedless plants include all non-vascular plants and some vascular plants (i.e., ferns) Plants such as ferns and mosses do not produce seeds; rather, they grow from spores The sporophyte stage of these plants produces haploid spores inside spore cases. When the case breaks, the spores are released and moved by either wind or water. The spores may grow into plants that can produce sex cells. (i.e., male and female gametophytes) Non-vascular plants do NOT have vascular bundles (...in other words, they cannot transport water throughout the plant). Instead, water just flows from cell to cell. Moss Life Cycle Starting in the upper left corner of the illustration, the spores (n) are released from the moss capsule. On suitable ground, a spore starts to grow and develops into a small green shoot called a protonema. The protonema grows buds that become the familiar leafy green stems of a moss. This phase of the moss lifecycle is termed the gametophyte. The gametophyte may be male (n) or female (n). Within some leaves of the gametophyte, special structures develop into male and female sex organs. The male part is called the Antheridium (n) and the female part the Archegonium (n) Inside the Antheridium, sperm are produced. They have tails (flagella) so they can swim, in a film of water, to the Archegonium. The sperm are attracted to the Archegonium by chemicals released into the film of water. Once reaching the Archegonium, the sperm swim down the Archegonium’s neck to reach and fertilize the egg The fertilized egg (2n) develops into a structure called the sporophyte. The sporophyte consists of a stem or seta and a capsule in which vast numbers of spores, via meiosis, are produced. During the growth period, the capsule is covered by a thin protective layer (calyptras). When the spores are nearing maturity, the calypra falls off revealing a cap or operculum that keeps the spores from being released. At maturity, the operculum falls off and, usually in dry weather, the spores are shaken out of the capsule and dispersed by the wind. On the ground, the spores begin to produce new gametophytes...and the cycle is repeated. Fern Life Cycle (Vascular Seedless Plants) Fern leaves are fronds that grow from an underground stem called a rhizome. The roots also grow from the rhizome Fern do not flower; rather, they produce spores and grow with a gametophyte intermediate stage. Different from the moss, the fern sporophyte produces its own food from photosynthesis. Spores are produced on the underside of the frond in a structure called a sori (...sometimes mistaken for disease) Once released, the spores fall to the ground. If they land on damp soil, the spore grows into a small, green, heartshaped prothallus (the gametophyte). Male and female reproductive structures form on the prothallus. Using water, the male sperm swims to the egg, and fertilization occurs to produce a zygote The zygote grows into the familiar fern plant. Meiosis occurs to produce spores inside a spore case Once mature, the spores are ejected and fall to the ground...and the cycle is repeated. Sexual Reproduction Cost and Benefits of Sexual Reproduction Populations have a high level of genetic diversity. If environmental conditions change, the chance of some individuals will survive is increased. The products of sexual reproduction are seeds. Seeds can be dispersed far from the parent plant. Thus, seeds may find better growing conditions, inhabit new areas and experience less competition for resources Seeds can remain dormant for long periods and germinate when growing conditions are favourable. This increases the chance of survival. Gymnosperms Gymnosperm means “naked seed.” In other words, seeds are NOT enclosed in an ovary as in the flowering plants; rather, seeds grow on the surface of a modified leaf in a strobilus or cone. Thus, gymnosperms are conifers (e.g., pine, cedar). Conifers produce both male and female cones. In the male cone, haploid cells called microspores are produced by meiosis. Each microspore develops into a pollen grain containing a male gametophyte. In the female cone, meiosis produces megaspores that give rise to egg-producing female gametophytes. Pollination (i.e., transfer of male pollen grains to the female ovule) is wind pollination. Sticky resin and the cone’s shape guide the pollen to the ovule. Once at the ovule, the pollen grain grows a pollen tube. As the tube grows, the haploid nucleus divides by mitosis to produce two haploid sperm nuclei. One sperm fertilizes the egg to produce a diploid zygote. The other sperm degrades....THUS “single fertilization.” Upon fertilization, the ovule develops the seed structures (i.e., seed coat and endosperm) and the zygote develops into the embryo. Female cones remain on the parent plant until the seeds mature. If the seed germinates, it grows into a sporophyte and the cycle is repeated. Alternation of generations is involved in gymnosperm reproduction. They are all heterosporous: the microspores are shed as pollen; whereas, the megaspore germinates in the strobilus to produce the female gametophyte. The archegonia is fertilized by sperm from the male gametophyte and the zygote grows to produce an embryo which is enclosed in a seed coat of tissue from the parent plant. Angiosperms Angiosperms are flowering plants. Most angiosperms are terrestrial...and thus, they lack mobility. Thus, the flower is very important to angiosperm fertilization. Meiosis in the sporophyte generation produces two kinds of spores: (1) microspores which develop into the male gametophyte, and (2) megaspores which develop into the female gametophyte. Both gametophytes are produced in the flower. Monocots have “imperfect flowers” on the same plant. That is, one flower has male parts while a different flower has only female parts. Dicots flowers ON THE SAME PLANT are either male or female. The male part of the plant is the stamen with two parts: (1) anther produces pollen grains, and (2) filament gives support. Meiosis produces pollen grains. The female part is the carpel with three parts: (1) stigma with a sticky surface as a landing site for pollen grains, (2) style is a tube and (3) ovary containing ovules. Meiosis produces four haploid cells...one megaspore and three smaller cells that degenerate. The megaspore undergoes three mitotic divisions to produce eight nuclei consisting of (1) an egg cell, (2) two cells that secrete an attractant the guides the pollen tube, (3) two polar nuclei which will develop into the endosperm after fertilization and (4) three antipodal cells When a pollen grain reaches the stigma, it germinates into a pollen tube. The germ cell divides by mitosis forming two sperm cells. The two sperm cells migrate down the pollen tube and into the female ovule chamber. At this point, Double Fertilization occurs. One sperm cell fuses with the egg forming the diploid zygote. The other sperm cell fuses with the polar nuclei forming the endosperm nucleus. Most angiosperms have two polar nuclei so the endosperm is triploid (3n). The product of sexual reproduction in angiosperms are seeds contained inside a fruit (...a ripened ovary)