Exam 2 Notes: Set 4
Exam 2 Notes: Set 4 Bio 1144
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This 3 page Class Notes was uploaded by Murry on Tuesday February 16, 2016. The Class Notes belongs to Bio 1144 at Mississippi State University taught by Thomas Holder in Spring 2015. Since its upload, it has received 54 views. For similar materials see Biology II in Biology at Mississippi State University.
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Date Created: 02/16/16
Exam 2 Notes: Set Four Flowers and the Sexual Cycle • Occurs only in angiosperms (over 300,000 species) • Flowers come in all sizes, shapes, colors, and aromas. • Essential processes of sexual reproduction occur within the flower o Meiosis/Cytokinesis – reduces chromosome number o Syngamy (fertilization) – restores chromosome number with new genetic arrangement • “Ideal” Flower o 4 sets of highly modified leaves in whorls at tip of modified stem o Highly modified leaves originate in the highly modified, yet short term, shoot system. o Pedicel – “stalk;” the modified stem; has 4 sets of modified leaves that arise from the receptacle o Receptacle – enlarged tip of a flower stalk o Sepal – protection of the unopened bud o Calyx – term for collection of all individual sepals o Corolla – collection of petals; attracts pollinators o Calyx and corolla are “sterile” modified leaves (not directly involved in reproduction) o Stamen – consists of filament and anther o Androecium – all stamens; the “male household”; where pollen is produced o Pistil - stigma, style, and ovary make up female part of the plant o Gynoecium – all pistils; the “female household”; where eggs are produced o Androecium and Gynoecium are “fertile” modified leaves • Pedicel: receptacle, 4 sets of modified leaves are 2N (part of sporophyte generation) • Pollen (sperm) and eggs are part of gametophyte generation (1N). • Sexual Cycle: Male Side o Pollen formation within the anther of stamen o Anther – bi-lobed with 2 pollen chambers per lobe (4 chambers total) o Anther contains 2N microspore mother cells o Mother cell undergoes meiosis and produces 4 haploid cells called microspores o Each of the 4 microspores undergoes cell division à unequal division mean cells are of different size; therefore, the division is incomplete o Tube cell pollen grain (2-celled) is the male gametophyte o Each 2N microspore mother cell can produce 4 2- celled pollen grains o Pollen is produced within the anther of stamen(s). Anther containing pollen grains • Sexual Cycle: Pollination o Pollination – transfer of pollen from an anther to a stigma § Self Pollination – transfer between the same flower or within the same plant; provides low genetic variation § Cross Pollination – transfer between plants o Pollen needs agents to help transfer between plants. These include: wind, water, or animals (majority). o Plants will trick or reward animals for collection pollen. A reward could be fruit, nectar, pleasant aroma, etc. Trick would be making plant parts look like female wasps to male wasps. • Sexual Cycle: Female Side o Ovule – future seed; enclosed within ovary of pistil o There are one to millions of ovules per ovary. (Ex: coconut only has 1) o Ovule attached to central axis (support beam) of hollow ovary or to the ovary wall. (Ex: peas attached to pea pod, which is the ovary wall) Flowers attract animals for pollination. o Ovules are always enclosed structures. o Inside the ovule is one large diploid cell called the Megaspore Mother Cell (MMC). o MMC undergoes meiosis and produces 4 haploid megaspores o Only 1 megaspore will become a functional megaspore o The 1 haploid cell will undergo 3 cell divisions to produce a total of 8 cells. These are unequal and incomplete division, so the cells are not completely separated. à 8 nucleate, 7 cell structure which is called the Embryo Sac (the female gametophyte) o Embryo sac develops into seed; highly protected o 3 antipodal cells (1N) – opposite end from micropyle o Micropyle – “little gate;” 2 synergid cells o 1 central cell with 2 large 1N nuclei called Polar Nuclei o 1 egg at micropyle end in between synergids • Sexual Cycle: Syngamy o One haploid egg and one haploid sperm fuse to form a diploid zygote (the fertilized egg). o Tube cell produces pollen tube o Pollen tube delivers sperm to site of the egg o Generative cell divides to produce 2 haploid sperm o Pollen tube enters micropyle and digests nucleus o 2 sperm placed inside tube nucleus o Pollen tube enters one synergid, releases its contents, and the synergid ruptures; tube nucleus degrades and 2 sperm are released into the large central cell o Micropyle closes and the sperm is trapped o Double Fertilization – angiosperms produce a fertilized egg as well as primary endosperm cell (2 sperm fuses with 2 haploid nuclei to form 3N cell) o Primary endosperm cell cannot occur without fertilized egg o Post Fertilization within ovule: growth of embryo and primary endosperm cell o Endosperm becomes endosperm tissue which is nutritive tissue for the embryo o Ovule matures into a seed with a 2N embryo and 2 seed coats, starchy endosperm tissue, and 3 integuments. This is a new sporophyte generation. o Ovary matures and enlarges with sugar and water and becomes a fruit with enclosed seeds. Why does fruit taste good? • Seed Germination o Seeds are dispersed (enclosed in fruit) by wind, water, and animals (most common) o Dormancy must be broken by a combo of external and internal temperatures in order for it to start growing. st o Radicle (1 root) emerges downward and shoot emerges upward. END OF EXAM 2 MATERIAL
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