Chapter 16 Reproduction in Plants Lesson 3 - Fertilization & post fertilization changes


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Chapter 16 Reproduction in Plants Lesson 3 - Fertilization & post fertilization changes

  1. 1. Fertilization & Post-Fertilization Changes
  2. 3. ***Fertilization <ul><li>After pollination, pollen grain germinates in response to sugary fluid secreted by the mature stigma </li></ul><ul><li>From each pollen grain, a pollen tube grows out </li></ul>
  3. 4. ***Fertilization (continued) <ul><li>The cytoplasm and 2 nuclei ( vegetative + generative nuclei ) pass into the pollen tube </li></ul><ul><li>The growth of the pollen tube is controlled by the vegetative nucleus </li></ul><ul><li>Enzymes are secreted to digest the tissue of the stigma and style as the tube grows </li></ul><ul><li>The pollen tube penetrates right through the style as it grows and enters the ovule through the micropyle (opening in the ovule wall) </li></ul>
  4. 5. vegetative
  5. 6. ***Fertilization <ul><li>Along the way, the generative nucleus divides to form 2 male gametes (vegetative nuclei degenerates) </li></ul><ul><li>Within the ovule the tip of the pollen tube absorbs sap and bursts releasing 2 male gametes </li></ul><ul><li>One male gamete + ovum  zygote (fertilization!) </li></ul><ul><li>One male gamete + definitive nucleus  endosperm nucleus </li></ul>Double fertilisation
  6. 8. Post-fertilization changes <ul><li>The zygote develops into the embryo of the seed with cotyledons, developing shoot ( plumule ) + developing root ( radicle ) </li></ul><ul><li>The endosperm nucleus divides and gives rise to the endosperm </li></ul><ul><li>In some seeds the endosperm is completely absorbed by the embryo which stores the food materials in the cotyledons </li></ul><ul><li>A fruit is formed from the ovary and the ovules </li></ul><ul><li>The ovary walls ripens to form the pericarp (hard/dry OR fleshy and succulent) </li></ul><ul><li>The ovules becomes the seeds </li></ul><ul><li>Fruit chambers = loculi </li></ul>Refer to table 20.2 page 322
  7. 12. Endospermic vs Non-endospermic seeds
  8. 13. Terms to familiarise <ul><li>Monocotyledonous vs dicotyledonous </li></ul><ul><li>Endospermic vs non-endospermic seeds </li></ul>
  9. 14. Endospermic vs non-endospermic seeds <ul><li>Endospermic seeds </li></ul><ul><li>The endosperm is present in the mature seed and serves as food storage organ </li></ul><ul><li>Testa and endosperm are the two covering layers of the embryo </li></ul><ul><li>Non-endospermic seeds </li></ul><ul><li>The cotyledons serve as sole food storage organs as in the case of pea ( Pisum sativum ) </li></ul><ul><li>During embryo development the cotyledons absorb the food reserves from the endosperm </li></ul><ul><li>The endosperm is almost degraded in the mature seed and the embryo is enclosed by the testa </li></ul>
  10. 15. Endospermic vs non-endospermic seeds (ENDOSPERMIC SEED) (NON-ENDOSPERMIC SEED)
  11. 16. Testa ( ) endosperm
  12. 17. Structures of a seed the scar on seeds marking its point of attachment to the funicle
  13. 18. Structure of seeds (dicotyledons) 1 2 3 5 4 6 7
  14. 19. Structure of seeds (dicotyledons)
  15. 20. Germination
  16. 21. Conditions for germination <ul><li>Sufficient water </li></ul><ul><li>Suitable temperature </li></ul><ul><li>Adequate O 2 supply </li></ul>
  17. 22. Dormancy <ul><li>Period in which seeds of plants will not germinate even though environmental conditions are favourable </li></ul><ul><li>May be days, weeks or even years (depending on species) </li></ul><ul><li>Seeds usually dry ( lack of water ) </li></ul><ul><li>Respire anaerobically as vital activities are much reduced ( lack O 2 ) </li></ul><ul><li>Allow seeds to survive unfavourable seasons e.g. winter /drought ( unfavourable temperature ) </li></ul>
  18. 23. Changes during germination <ul><li>The absorption of water by the seed </li></ul><ul><li>Seed swells </li></ul><ul><li>1) testa becomes more permeable to O 2 and CO 2 </li></ul><ul><li>2) and may rupture the testa </li></ul>
  19. 24. Roles of enzymes in germination <ul><li>With water absorption, cotyledons produce enzymes to digest stored food so that growing embryo can use it </li></ul><ul><li>In endospermic seeds, the enzymes flow into the endosperm to digest the food stored there </li></ul><ul><li>In non-endospermic seeds, the digestion of the stored food occurs within the cotyledons </li></ul><ul><li>Digested food are transported to growing regions of the embryo e.g. plumule and radicle </li></ul>
  20. 25. Enzyme digestion
  21. 27. Utilization of food substances for growth during germination <ul><li>Carbohydrates and fats used in tissue respiration </li></ul><ul><li>Some carbohydrates+ fats used for formation of cell walls + cell membranes </li></ul><ul><li>a.a. assimiliated in building of new protoplasm </li></ul>
  22. 28. Types of germination <ul><li>Epigeal germination </li></ul><ul><li>– cotyledons are carried above the ground </li></ul><ul><li>e.g. sword bean seed </li></ul><ul><li>Hypogeal germination </li></ul><ul><li>– cotyledons remain below the surface of the soil </li></ul><ul><li>e.g. maize </li></ul>
  23. 29. Parts of a germinating seed 1 2 3 4 5 6
  24. 30. Parts of a germinating seed
  25. 31. Stages in the germination of sword bean seed (epigeal germination) <ul><li>Radicle grows rapidly and pushes against testa at micropyle. The testa splits as the radicle emerges and grows downwards. Lateral roots develop . Root hairs formed behind the tips of the radicle and lateral roots help to absorb H 2 O and mineral salts </li></ul><ul><li>Meanwhile, the stem below the cotyledons elongates , pulling the cotyledons above the ground and leaving the testa behind in the soil . At first the cotyledons are hook-like with the cotyledons bent over and still closed together to protect the delicate plumule </li></ul><ul><li>Soon the stem straightens, the cotyledons turn green and spread out , exposing the first foliage leaves with the bud between them . The bud will grow into a future shoot . The foliage leaves expand , turn green and carry out photosynthesis . The seedling is now a self-supporting plant </li></ul>
  26. 32. Germination of a dicotyledon Epigeal germination
  27. 33. Hypogeal germination
  28. 34. Dispersal of fruits
  29. 35. <ul><li>By wind e.g. angsana </li></ul><ul><li>By animals e.g. tomatoes </li></ul><ul><li>By water e.g. coconut </li></ul><ul><li>Explosive mechanism e.g. rubber fruits </li></ul>Dispersal of fruits and seeds
  30. 36. Wind dispersal <ul><li>What do you think will be the factors that will aid dispersal by wind? </li></ul><ul><li>small and light (able to float in air and blown about by wind) </li></ul><ul><li>large flattened wing-like structures OR parachute of fine-hairs </li></ul><ul><li> enlarges surface area </li></ul><ul><li> increases buoyancy in air </li></ul>