12.3 Reproduction in Flowering Plants - PowerPoint PPT Presentation

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12.3 Reproduction in Flowering Plants

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12.3 Reproduction in Flowering Plants Vegetative structures: stems, roots and leaves Reproductive structures: flowers Vegetative Propagation: reproduction of ... – PowerPoint PPT presentation

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Title: 12.3 Reproduction in Flowering Plants


1
12.3 Reproduction in Flowering Plants

2
  • Vegetative structures
  • stems, roots and leaves
  • Reproductive structures
  • flowers
  • Vegetative Propagation
  • reproduction of vegetative structures

3
  • Sexual reproduction
  • introduce variation through meiosis by
  • 1. Independent assortment chromosomes
  • during metaphase
  • 2. Recombination of genes by
  • crossing over between homologous
  • chromosomes at prophase I

4
Structures of a typical flower
Angiosperms reproduce sexually by producing
flowers
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Microsporogenesis and Megasporogenesis
9
  • Development of the pollen grain-
  • pollen mother cells (2n)
  • ?? meiosis
  • ?? tetrad (4) haploid (n) cells
  • ?? microspores (pollen grains)
  • ?? mitosis
  • ?? generative nucleus tube nucleus
  • ?? mitosis ??
  • 2 male nuclei tube nucleus

10
Scheme of Microsporogenesis
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12
  • Development of the ovule
  • nucellus
  • ?? megaspore mother cell (2n)
  • ?? meiosis
  • ?? 4 megaspores (n)
  • ?? 3 degenerated, 1
  • ?? embryo sac ?? mitosis 3 times
  • ?? 8 nuclei (3 antipodal cells,
  • 2 polar nuclei, 2 synergids with 1 egg cell)

13
SCHEME OF MEGASPOROGENESIS-
14
  • Pollination the transfer of pollen grains from
    anthers to the stigmas
  • external agents are needed
  • (1) by insect
  • (2) by wind

15
  • 12.4.1 Fertilization
  • Development in Flowering Plants
  • pollen grains send out pollen tubes which grows
  • down the style ovary, towards the micropyle
  • pollen grains are attracted by sugars in stigma
  • and secrete enzymes to digest a pathway
    through
  • the style

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17
  • Double Fertilization
  • male gamete goes into the ovule and fertilizes
    with the egg cell
  • the other male gamete fuses with the polar nuclei
    to form the triploid endosperm

18
12.4.2 Methods of Preventing Inbreeding
19
12.4.2 Methods of Preventing Inbreeding
  • Self-pollination the transfer of pollen from the
  • anther to the stigma of the same flower,
  • or of another flower of the same plant
  • Cross-pollination the transfer of pollen to a
    flower
  • on a different plant of the same species
  • If pollen lands on the stigma of a plant of a
    different species, it usually dies.
  • Since cross-pollination results in a great
  • variability of more adaptable offspring,
  • many plants prefer cross-pollination

20
Methods to prevent self-pollination
Method Explanation
a) Dichogamy   i) protandry ii) protogyny anthers stigmas mature at different times to minimize self-pollination Androecium ripens first Gynoecium ripens first



21
Methods to prevent self-pollination
Method Explanation
a) Dichogamy   i) protandry ii) protogyny anthers stigmas mature at different times to minimize self-pollination Androecium ripens first Gynoecium ripens first
b) Heterostyly thrum-eyed anthers high up stigmas low down pin-eyed stigmas high up anthers low down


22
Methods to prevent self-pollination
Method Explanation
a) Dichogamy   i) protandry ii) protogyny anthers stigmas mature at different times to minimize self-pollination Androecium ripens first Gynoecium ripens first
b) Heterostyly thrum-eyed anthers high up stigmas low down pin-eyed stigmas high up anthers low down
c) Incompatibility produce chemical in stigma to prevent germination of their own pollens

23
Methods to prevent self-pollination
Method Explanation
a) Dichogamy   i) protandry ii) protogyny anthers stigmas mature at different times to minimize self-pollination Androecium ripens first Gynoecium ripens first
b) Heterostyly thrum-eyed anthers high up stigmas low down pin-eyed stigmas high up anthers low down
c) Incompatibility produce chemical in stigma to prevent germination of their own pollens
d) Unisexual flowers only male or female flowers on a plant, monoecious (one plant) or dioecious (2 plants)
24
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