Angiosperms and reproduction


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For part of topic 9.3 in the IB curriculum

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Angiosperms and reproduction

  1. 1. REPRODUCTION IN ANGIOSPERMS <ul><li>Topic 9.3 </li></ul><ul><li>Flower structure </li></ul><ul><li>Pollination </li></ul><ul><li>Fertilization </li></ul><ul><li>Germination </li></ul>
  2. 2. Flower structure <ul><li>Flowers are reproductive structures </li></ul><ul><li>They have evolved to send and receive pollen from one flower to another </li></ul><ul><li>This is the process of pollination </li></ul><ul><li>Flowers are developed from a series of modified leaves </li></ul><ul><li>These leaves are arranged in a rings (whorls) </li></ul>
  3. 3. Types of pollination <ul><li>Wind </li></ul><ul><li>Animal </li></ul><ul><li>Water </li></ul>Bumble bee Bombus hortorum on red clover Trifolium pratense Yorkshire fog grass Holcus lanatus
  4. 4. Animal pollination <ul><li>Usually insects </li></ul><ul><li>Also other flying animals </li></ul><ul><li>e.g. hummingbirds or fruit bats </li></ul>Cerambycid beetle pollinating bramble Rubus fruticosus
  5. 5. Flower structure Stigma Style Ovary Petal Sepal Filament Anther
  6. 6. Pollination <ul><li>Pollen grains contain the male gametes of the plant </li></ul><ul><li>They are picked up by a pollinator and transferred to another flower </li></ul><ul><li>Plants tend to specialise in pollinators </li></ul><ul><li>This ensures the pollen is delivered to same species of plant </li></ul>Yellow archangel Lamiastrum galobdolon being pollinated by a bumble bee Bombus hortorum
  7. 7. Pollination <ul><li>Most species of flowering plants are hermaphroditic </li></ul><ul><li>Pollen from a flower could land on the stigma of the same flower or another flower on the same plant = self-pollination </li></ul><ul><ul><li>Less genetic variation in species </li></ul></ul><ul><li>Pollen transferred from the anther on one flower to the stigma of another flower on a different plant = cross-pollination </li></ul>The honey bee Apis melifera on marsh thistle Cirsium palustris
  8. 8. Fertilization <ul><li>Pollination ≠ Fertilization </li></ul><ul><li>The male gamete (the male nucleus ) has to get to the egg cell </li></ul><ul><li>The egg cell lies in an ovule in an ovary at the centre of the plant </li></ul><ul><li>The pollen grain germinates on the stigma </li></ul><ul><li>It grows a pollen tube down the style </li></ul><ul><li>It male nuclei travel down the pollen tube to the ovule </li></ul>
  9. 9. Fertilization Style Stigma Pollen grain Ovule Embryo sac Pollen tube Ovary
  10. 10. Fertilization Egg cell Polar nuclei Embryo sac Micropyle
  11. 11. Fertilization Pollen grains of the daisy Bellis perennis
  12. 13. Fruits and seed dispersal Animal dispersal Strawberry Fragaria vesca Wind dispersal Ragwort Senecio Explosive dispersal Bird’s foot trefoil Lotus corniculatus Animal dispersal Wood avens Geum urbanum
  13. 15. Conditions for seed germination <ul><li>Other seeds require more specific conditions: </li></ul><ul><li>Fire </li></ul><ul><li>Freezing </li></ul><ul><li>Passing through digestive system of a seed dispersing animal </li></ul><ul><li>Washing to remove inhibitors (beans) </li></ul><ul><li>Erosion of the seed coat (Poppy) </li></ul><ul><li>Seeds require a combination of certain conditions to germinate: </li></ul><ul><li>Oxygen for aerobic respiration </li></ul><ul><li>Water to metabolically activate the cells </li></ul><ul><li>Temperature for optimal function of enzymes </li></ul><ul><li>Each seed has its own particular combination of the above three factors </li></ul>
  14. 16. <ul><li>Water is absorbed (imbibition) </li></ul><ul><li>Giberillin (plant growth hormone) is made </li></ul><ul><li>Giberillin causes enzymes to be made (amylase) </li></ul><ul><li>Starch is hydrolysed to maltose which can then be absorbed by the young plant </li></ul><ul><li>Maltose can be further hydrolysed to glucose for cellular respiration or polymerised to form cellulose for the cell walls. </li></ul>