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Topic 9: Plant Structure Part II

Topic 9: Plant Structure Part II. Biology HL Mrs. Ragsdale. Structure and Function of Flowers. Flowers are typically the site of external sexual organs in plants for reproduction Most flowers have both male/female anatomy Female gametes – contained in ovules located in the ovaries

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Topic 9: Plant Structure Part II

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  1. Topic 9: Plant Structure Part II Biology HL Mrs. Ragsdale

  2. Structure and Function of Flowers • Flowers are typically the site of external sexual organs in plants for reproduction • Most flowers have both male/female anatomy • Female gametes – contained in ovules located in the ovaries • Male gametes – contained in pollen grains produced by the anthers • A fertilized zygote formed by pollen fusing with the ovules http://www.webquest.hawaii.edu/kahihi/sciencedictionary/P/perfectflower.php

  3. Pollination • Transfer of pollen from an anther to a stigma • Since plants themselves do not move, an outside agent is typically required for successful cross pollination to occur • Wind dispersal • Insect/Bee dispersal • Animal dispersal

  4. Pollination • Flower structure typically adapted to method for pollination • Bees – flowers are typically equipped with “landing platforms” and has strategically placed anthers to catch pollen • Birds – sweet nectars for attraction http://www.mrac.ca/story/protecting-against-pests

  5. Wasp Flower • Tricking nature to do its bidding!

  6. After Pollination • Pollen grains germinate on the stigma of the flower • Pollen tube with the male gametes travels down the style to the ovary • Fusion of male and female gametes • Ovaries with fertilized ovules develop into fruits • The fertilized ovules develop into seeds • Ultimate job of a fruit is seed dispersal http://www.motherearthnews.com/organic-gardening/self-pollinating-apples.aspx

  7. Structure of a seed • Testa -Seed Coat protective layer • Micropyle – opening for the pollen • Plumule – (embryo shoot) • Radicle – embryo root • Cotyledon - food storing seed leaf http://www.cmg.colostate.edu/gardennotes/137.html

  8. Structure of a seedling Cotyledons provide energy and nutrients for germination! First foliage leaves are about to open! Bend in the stem protects the leaves as the shoot pushes up through the soil Stem between the cotyledons and the first foliage leaves has grown Branches of the main root increase the surface area for absorption Main root growing downward into the soil

  9. Factors Needed For Seed Germination Must have adequate water, oxygen and temperatures • Water • Dry tissues must be rehydrated • Oxygen • Needed for aerobic cellular respiration • Temperature • Germination involves enzymes! • Extreme high temps and low temps are not conducive to germination

  10. Metabolic Events of Germination • Stage One • Absorption of water – leads to the rehydration of living tissues inside the seed • Stage Two • Gibberellin is a plant hormone that is produced in the cotyledon of the seed. Production begins after rehydration. • Stage Three • Gibberellin stimulates the production of amylase • Amylase catalyses the digestion of starches into maltose

  11. Metabolic Events of Germination • Stage Four • Maltose is transported from food storage to the places that are growing like the embryo root and embryo shoot • Stage Five • Maltose is finally converted into glucose • Glucose is used in aerobic cell respiration OR it is used to synthesize cellulose • Stage Six • The seedling leaves will finally reach light and begin photosynthesis

  12. Auxin and Phototropism • Phototropism – plants grow towards light and will literally bend and contort towards it • Auxin – a plant hormone that acts as a growth promoter • Research has shown that auxin redistributes itself in the shoot tips from the lighter side to the darker. • Additional growth on the shadier side causes the plant to bend towards the light

  13. Auxin Mechanism • Pumps in plasma membrane = auxin efflux carriers • Pumps distributed unevenly • Auxin is able to be redistributed as needed in tissues • Auxin works by binding to auxin receptors in plant cells • Once auxin binds to the receptor, transcription of specific genes is promoted • This affects the growth of the cells

  14. Photoperiodic Control of Flowering • Why do certain plants only bloom at specific times of the year? • Studies show that it’s not the length of day but the length of night that controls flowering • Short-day plants • Long-day plants http://www.flowersgrowing.com/chrysanthemum/

  15. Phytochrome and Photoperiodism • Plants have the ability to sense day and night light/dark with extreme accuracy • Phytochrome is a pigment in the leaves that exists in two interconvertible forms • Pr – absorbs red light with a wavelength of 600nm • Inactive form of phytochrome • Once the red light is absorbed it is rapidly converted into Pfr • Active form of phytochrome • As soon as light disappears Pfr is gradually converted back into Pr

  16. Pfrand Flowering • The reversion of Pfr is most likely what is used as a darkness “timer” • Pfr in short day plants acts an inhibitor to flowering. Once all of the Pfr has been converted to Pr then flowering will begin • In long day plants, Pfr binds to proteins which then trigger genes involved in flowering to switch on

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