Lecture 15.1. Parts of a seeda. Megaspore (1N): the sporangia produce female spore.b. Nucellus/ Megasporangium (2N): the food source of developing embryo.c. Integument (2N): the outermost layer of a seed.d. Micropyle: opening coat. Allow entry of pollen. 2. Three ways seed are adaptive.- embryophytic- dispersal: enable seeds to spread out- dormancy: delay between development & dispersal or between development and sprout. It increase survival rate because seeds can choose when to start growing.3. Homospory vs. Heterospory- Homospory: sporophyte produces single type of spore. (most fern)- Heterospory: seed plants are heterosporous. Sporophyte produces two type of sporangia; male and female; microspore and megaspore. (usually monoecious; different sexes within a single species.)4. Important facts about seed plants- allow for dispersal- allow for dormancy- all heterosporous- dramatic reduction of gametophytic phase- sporophyte is the dominant form5. Seed plants life cyclea. Male sporangiaMicrospore mother cell –(meiosis)-> microspore –(mitosis)-> pollen grain: - gametophyte.- multicellular.- disperse to female gametophyte (air, water, animal).- sperm develop by mitosis inside male gametophyte.b. Female sporangiaOvules (2N) in the cone develop after fertilization. Megaspore mother cell –(meiosis)-> 4 haploid megaspores (1N); only one of them is going to survive-> functional megaspore) –(mitosis)->female gametophyte (1N); protected by diploid tissue.- Further reduction in gametophytic phaseA. GymnospermsB. Angiosperms6. Gymnosperms (Naked seeds)- The most recent diverse group- Small portion of the life cycle, the seed is not wrapped by sporophytic tissue.A. Pollen tube- The structure that grows from the pollen grain mitotically. It allows delivery of sperms to the egg cell to inside of the megasporangium.B. Why aren’t seed plants dependent on water?- Pollen grain is non-motile sperm, so it cannot swim. Moreover, it has a pollen tube to make a pathway for sperm reaching the eggcell. It provides more variety and broader environment.C. Examplea. Cycad- Ancient lineage- Extreme slow growers- Resemble palm trees (not closed related at all)- Cones (not flower): huge in female- Motile sperms (unlike pain): it swim down fluid in pollen tube.- Largest sperm (~30nm)b. Ginkgos- Only one extended species: Ginkgo Biloba- No more wide species, but cultivated.- Dioecious: male (small cone) and female (fruit-like structure: noxious smell) individuals on separate plants- Sperm swim through pollen tube.c. Gneyophyte- Have a lot of traits in common with angiosperms- Only gymnosperm that has tracheid cells: completely analogous (homoplasious) to the angiospemrs (convergent evolution)(1) Gnetum(2) Welwitschia- Desert- Stem is cup shaped- Two leaves- Longest leaf (~3M)- Dioecious(3) Ephedra (Morman tea/ Indian Tea)- Resemble horsetails- Psuedoephedrine: heart medicationd. Conifers- Common- Big tree- Sequoia sempervirens: the tallest tree.- Have cones for seeds7. Angiosperms (flowers and fruit): attract pollinatorA. Flower partsB. Types of fruits a. Apple: single carpel with interior seeds; seed->ovuleb. Tomato: True berry with fused carpels: 2 carpels used to 4 -> eudiocotsc. Peas and beans (legume): the bean pod is ovary, and the circle beans are ovules. Each seed has a sugary coat.d. Peach (stone Fruit): Drupe fruit: hard pit; There is seed inside pit.e. Backberry: Many ovaries; many carpels: unlike tomato, each ovary forms each berries. Unfussed ovary. f. Pineapples (compound or multiple fruits): many flowers form on the single stem, and fused into one fruit.C. Few very important change (gymnosperm -> Angiosperm)a. Megaspore only go through three mitotic division. 1-> 2 -> 4 -> 8- In mother cell –(meiosis)-> 1 functional megaspore; ovule(1N) –(3 mitosis)-> 8 cell; 2 synergids(1N each), 1 egg (1N), 3 antipodal cell (1N each), 2 polar nuclei (1N each).b. Double fertilization (only in angiosperm)- Pollen grain travel through pollen tube. Generative cell mitotically divided two. When the tube arrive, 1 synergid cell degenerate. One generative cell fusses with 1 egg cell (zygote; 2N). The other fusses with 2 polar nuclei (endosperm; 3N)- Angiosperms differ from gymnosperms- Reduced cell number in female gametophyte: further reduction in the importance of the gametophyte.- Speed of pollen tube growth: much faster- Double fertilization: triploid endosperms, zygotes-
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