9.3 reproduction in angiospermophytse

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9.3 reproduction in angiospermophytse

  1. 1. 9.3 Reproduction in Flowering Plants Topic 9 Plant Science
  2. 2. Reproduction in Flowering Plants  9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower. (Limit the diagram to sepal, petal, anther, filament, stigma, style and ovary).  9.3.2 Distinguish between pollination, fertilization and seed dispersal.
  3. 3. Reproduction in Flowering Plants  9.3.3 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed.  The named seed should be non-endospermic.  The structure in the diagram should be limited to testa, micropyle, embryo root, embryo shoot and cotyledons.  9.3.4 Explain the conditions needed for the germination of a typical seed. (Seeds vary in their light requirements and, therefore, this factor need not be included).
  4. 4. Reproduction in Flowering Plants  9.3.5 Outline the metabolic processes during germination of a starchy seed.  Absorption of water precedes the formation of gibberellin in the embryo’s cotyledon. This stimulates the production of amylase, which catalyses the breakdown of starch to maltose. This subsequently diffuses to the embryo for energy release and growth. No further details are expected.
  5. 5. Reproduction in Flowering Plants  9.3.6 Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.  Limit this to the conversion of Pr (red absorbing) to Pfr (far-red absorbing) in red or white light, the gradual reversion of Pfr to Pr in darkness, and the action of Pfr as a promoter of flowering in long-day plants and an inhibitor of flowering in short-day plants.
  6. 6. Structure of a Flowering Plant Ref: Biology, Rowland Ref: IB Biology OSC
  7. 7. Pollination  Pollination is the transfer of pollen (containing male gametes) from the anther to the stigma.  Pollen grains are immotile (cannot move on their own).  Two types of pollination:  Self pollination (same plant).  Cross pollination (different plant).  Pollination must take place before fertilisation can occur.  Pollination does not mean fertilisation will occur.  Could be incompatible gametes.
  8. 8. Fertilisation  Once pollination has occurred and the pollen grains have been transferred to the stigma, the male gamete grows a pollen tube down the style to the ovary.  Fertilisation is when the male gamete (inside a pollen grain) fuses with the female gamete (ovule).  This occurs in the ovary of the flower.  The fertilised ovules develop into seeds.  Ovaries containing fertilised ovules develop into fruits.  The role of the fruit is Seed dispersal.
  9. 9. Seed Dispersal  Seed dispersal is the spreading of seed away from the parent plant.  This can be done by:  Wind.  Seeds caught by wind.  eg: dandelion, sycamore, pine.  Explosion.  Seed compartments which violently burst open as they dry out.  eg: gorse, bloom.  Animal dispersal:  Adhesive hairs, spines, hooks which attach to animals.  Eg: bur fruit.  Fruit eaten by animal and deposited in faeces.  Apples, blackberry.
  10. 10. Seed Structure Ref: IB Biology OSC
  11. 11. Germination  Germination is the resumption of growth or development from a seed.  For a seed to germinate, certain conditions must be met.  Water:  Water must be available to rehydrate the dry tissue of the seed.  Oxygen:  Oxygen must be available for aerobic respiration.  Temperature:  Suitable temperatures are needed.  Many of the metabolic events of germination use enzymes.  These enzymes require optimum temperatures.  Many seeds only germinate after exposure to cold temps and then warmer temperatures ie: spring.  Some need bushfires to stimulate germination.  Calvarias and the dodo (Rowland p468).
  12. 12. Metabolic Events of Germination  1. The seed absorbs water through the micropyle.  2. A plant growth hormone, Gibberellin, is produced in the cotyledons.  3. Gibberellin stimulates the production of amylase, which catalyses the digestion of starch into maltose.  4. Maltose is transported from the cotyledons to the growth areas of the seedling, the embryo root and the embryo shoot.  5. Maltose is converted into glucose, which is either used for:  Aerobic cell respiration as a source of energy.  Synthesis of cellulose or other substances needed for growth.
  13. 13. Control of flowering  Short day plants: flower at a time of year when days are short  Long day plants: flower at a time of year when days are long  Experiments show it is the length of the night that is important (the length of continuous darkness) i.e. short day plants need a long period of continuous darkness
  14. 14. Phytochrome and photoperiodism  Pigment called phytochrome measures the period of darkness.  Exists as Pr (absorbs red light and is inactive form) and Pfr (absorbs far red and is active form)  Pr is rapidly converted to Pfr when it absorbs red light during the day  Pfr is rapidly converted back to Pr when far red light absorbed.  Pfr gradually convertes to Pr in darkness
  15. 15. Mechanism in short/long day plants  Gradual conversion to Pr is how dark period is timed  In long day plants, enough Pfr remains after short nights to stimulate flowering  In short day plants Pfr inhibits flowering: at the end of long nights enough Pfr has been converted to Pr to allow flowering.  Flowering can be induced by artificially extending the day in long day plants and the night in short day plants
  16. 16. IBO guide:  9.3.1 Draw and label a diagram showing the structure of a dicotyledonous animal-pollinated flower. (Limit the diagram to sepal, petal, anther, filament, stigma, style and ovary).  9.3.2 Distinguish between pollination, fertilization and seed dispersal.
  17. 17. IBO guide:  9.3.3 Draw and label a diagram showing the external and internal structure of a named dicotyledonous seed.  The named seed should be non-endospermic.  The structure in the diagram should be limited to testa, micropyle, embryo root, embryo shoot and cotyledons.  9.3.4 Explain the conditions needed for the germination of a typical seed. (Seeds vary in their light requirements and, therefore, this factor need not be included).
  18. 18. IBO guide:  9.3.5 Outline the metabolic processes during germination of a starchy seed.  Absorption of water precedes the formation of gibberellin in the embryo’s cotyledon. This stimulates the production of amylase, which catalyses the breakdown of starch to maltose. This subsequently diffuses to the embryo for energy release and growth. No further details are expected.
  19. 19. IBO guide:  9.3.6 Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.  Limit this to the conversion of Pr (red absorbing) to Pfr (far-red absorbing) in red or white light, the gradual reversion of Pfr to Pr in darkness, and the action of Pfr as a promoter of flowering in long-day plants and an inhibitor of flowering in short-day plants.

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