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Plant Science

Plant Science. Topic 9. Reproduction in Angiospermophytes. Topic 9.3. Assessment Statements. Variety in Flowers. Reproductive structure of angiosperms Smallest Flower Largest Flower. Flower Structure and Function. Flower Structure and Function. Meiosis occurs in:

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Plant Science

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  1. Plant Science Topic 9

  2. Reproduction in Angiospermophytes Topic 9.3

  3. Assessment Statements

  4. Variety in Flowers • Reproductive structure of angiosperms • Smallest Flower • Largest Flower

  5. Flower Structure and Function

  6. Flower Structure and Function • Meiosis occurs in: • Carpel/Pistil = Female part of the flower • Stamen = Male part of the flower • Flower Variety: • Complete flowers contain all four basic flower parts • Sepals, petals, stamen, carpel • Incomplete flowers lack at least one of these parts • Staminate flowers have only stamen, not carpels • Carpellate flowers have only carpels

  7. Flower Structure and Function Staminate Carpellate

  8. Pollination and Fertilization • Alternation of Generations • Generations are named according to the reproductive cells made • Life Cycles of Plants: • Gametophyte generation: haploid • Gametes produced by mitosis • Sporophyte generation: diploid • Spores produced by meiosis • Flowering Plant  sporophyte generation • Grew from zygote, new cells made through mitosis • Flowers gametophytes are made through haploid spores • Sperm in pollen • Eggs in ovary

  9. Pollination • Pollination: • Pollen (containing make sex cells) is places on the female stigma • First step towards fertlization • Pollen Vectors • Wind • Insects • Fossil evidence that angiosperms and insects coevolved • Birds • Water • Animals • Attractive Flowers • Red flowers are conspicuous to birds • Yellow and orange flowers are noticed by bees • Heavily scented flowers are easily found by nocturnal animals • Plants that rely on wind have inconspicuous, odorless flowers

  10. Pollination • Two types of pollination • Self-pollination • Pollen from anther of the same plant falls onto its own stigma • Form of inbreeding • Results in less genetic variation within a species • Cross-pollination • Pollen is carried from the anther of one plant to the stigma of a different plant • Increases variation  offspring with better fitness • Problem: female stigma may not receive male pollen due to distance travelled

  11. Fertilization • Fertilization • Male and female sex cells unite to form a diploid zygote • Process: • Pollen germinates to produce a pollen tube • The pollen tube grows down the style of the carpel • Within the growing pollen tube is the nucleus that will produce the sperm • The pollen tube completes its growth by entering an opening at the bottom of the ovary • The sperm moves from the tube to combine with the egg of the ovule to form a zygote • Zygote develops with the surrounding tissue into the seed • As seed develops, the ovary around the ovule matures into a fruit • Fruit encloses and helps to protect the seed

  12. The Seed • Seed: • Means by which an embryo can be dispersed to distant locations • Protective structure

  13. The Seed • Maturation • Involves dehydration until H2O content is 10-15% of its weight • Dormancy period • Very low metabolism, no growth or development • Variable for different seeds • Adaptation to overcome hard environmental conditions • Germination • Development of the seed into functional plant • Conditions • Water is needed to rehydrate the dried seed tissues • Oxygen is needed to allow aerobic respiration to produce ATP • An appropriate temperature for the seed is necessary • Enzyme action

  14. The Seed • Germination continued • Conditions • Testa must be disrupted/scarified before water uptake can occur, or • Fire or smoke is needed • Emerging seedling is fragile • Exposed to harsh weather, parasites, predators, many other hazards

  15. Seed Metabolism during Germination • Seed absorbs water • Gibberellin, aka gibberellic acid, is released after the uptake of water • Gibberellin is a growth substance (plant growth hormone) and it triggers the production of the enzyme amylase • Amylase causes the hydrolysis of a starch into maltose. • The starch is present in the seed’s endosperm or food reserve • Maltose is pivotal compound • Used to produce a number of different compounds, depending on seeds needs • Meristematic regions

  16. Seed Metabolism during Germination • Maltose is then further hydrolyzed into glucose that can be used for cellular respiration or may be converted into cellulose by condensation reactions • The cellulose is necessary to produce the cell walls of new cells being produced

  17. Control of Flowering in Angiosperms • Light • Required for photosynthesis • Controls many aspects of plant growth and development • Plants are able to detect presence of light, its direction, wavelength, and intensity • Photoperiodism • Plants response to light involving the relative lengths

  18. Control of Flowering in Angiosperms * Actually length of night controls flowering process in plants

  19. Control of Flowering in Angiosperms • Control by Light • Blue-green pigments  phytochrome • Inactive = Pr • Active = Pfr • Red light (660nm)  inactive phytochromePr converted to Pfr  able to absorb far red light (730nm)  converted back to Pr • In darkness, the conversion back to Pr is much slower • Controlling factor for flowering • Long-day • Remaining Pfr at the end of short night stimulates the plant to flower • Acts as a promoter • Short-day • Remaining Pfr appears to act as an inhibitor • Pfrhas been converted to Pr to allow flowering to occur

  20. Control of Flowering in Angiosperms

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