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2 Pollination and Fertilisation 2011.ppt - P5 GE Science 2011

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2 Pollination and Fertilisation 2011.ppt - P5 GE Science 2011 Powered By Docstoc
					SEXUAL REPRODUCTION IN
        PLANTS

           Types of flowers
 Self-pollination vs Cross-pollination
 Insect-pollinated vs Wind-pollinated
              Fertilisation



                                         1
                        FLOWERS
                    Unisexual           Bisexual


 Flower with either the male        Flower with both the male and
   part or the female part                  female parts

 male and female      male and female
  flowers can be     flowers are borne
  found on same      on separate trees     e.g. hibiscus, morning
plant (Monoecious                             glory, string bean
                     (Dioecious plant)               plant
       plant)

                    e.g. papaya plant
e.g. maize plant
                     (see next slide)
                                                                2
papaya flowers


                 3
                         maize flowers




Mrs Theresa Teo GE2003                   4
                POLLINATION
• What is pollination?
   – To reproduce sexually, you need to fuse a male sex cell
     (gamete) with a female sex cell (gamete).
   – The male gamete must be brought to the female gamete.
     In animals, there is the mating process.
   – How about for plants? They can’t move from place to
     place!
   – They need an external agent and since it is the male
     gametes which are contained in the pollen grains that
     gets transferred , the process of transferring the pollen
     grains from the male part of the flower to the female
     part is known as pollination.
   – Pollination must occur before fertilisation can occur.
                                                             5
Pollen




         Help! I’m covered
             in pollen!

                             6
               Pollination
• Pollination is the transfer of pollen grains
  from the anther to the stigma of a flower.
  – The pollen grains can be transferred within the
    same flower.

      stigma                           pollen grains
                                       from anther
                Pollination
• Pollination is the transfer of pollen grains
  from the anther to the stigma of a flower.
  – The pollen grains can also be transferred from
    one flower to another.
Self-pollination vs
Cross-pollination




                      9
  Self-Pollination vs Cross Pollination
• SELF-POLLINATION                  • CROSS-POLLINATION
  – Pollen grains falling on the      – Pollen grains falling on the
    stigma of the same flower           stigma of another flower of
    or of a different flower but        the same kind but on a
    of the same plant
                                        different plant
  – less adaptable to changes in
    the environment.                  – offspring has more variety.
  – Analogy : Marrying within            Genetic variation.
    same family
                                      – Offspring inherit traits from
  – If parent plant has a genetic       both parents  can be good,
    disease, it will be passed on
    to offspring.                       but can be a bad thing too!
                                        E.g. genetic defect, disease,
                                        etc.



                                                                10
How does a plant ensure there are
more chances of cross-pollination
      than self-pollination?
 1. Presence of dioecious plants (plant has
    only male or only female parts)
 2. For those with bisexual flowers, the male
    and female parts of the flower mature at
    different times
 3. The male and female parts of a bisexual
    flower may be some distance away or at a
    certain position such that self-pollination
    is difficult.                               11
        Helpers of Pollination
• Pollen cannot move on its own from the anther to
  the stigma.
• Help must be given.
• The insects and the wind help in transferring the
  pollen.
• However, insects and wind are very different
  helpers so insect-pollinated flowers and wind-
  pollinated flowers must look very different from
  each other to facilitate the process.
• How different are they?
                                                      12
Insect-pollinated Flowers vs Wind-pollinated Flowers
1.   Flowers are large, brightly-     Flowers are smaller and scentless
     coloured and scented             with dull coloured petals
2.   Nectar present                   Nectar absent
3. Stamens and stigma hidden          Stamens and stigma hang out of
   inside petals. Filaments not       the flower. Filaments are long
   pendulous. Flowers face            and pendulous. Flowers hang
   upwards                            down for easy shaking
4. Stigma is sticky so that pollen    Stigma is larger with feathery
   grains that land on it cannot be   branches for catching pollen
   easily shaken off                  grains. Not sticky
5.   Pollen grains are large and      Pollen grains are smaller,
     heavy with rough surface for     smoother and light, easily blown
     sticking to insect’s body.       by wind. Larger number of
     Smaller number produced          pollen grains produced     13
    Insect pollinated flower




e.g. Hibiscus
                               14
wind pollination - grass flower




               Mrs Theresa Teo GE2003   15
Grass flower




  Mrs Theresa Teo GE2003   16
             Wind pollination




e.g. Maize, grass




                                17
All about Flowers!
• You can infer the method of pollination and
  what type of pollinator (if animal
  pollinated) by observing the flower!
• Observe the size, shape, colour, presence of
  nectary
• Smell




               http://www.colours.phy.cam.ac.uk/pollination-game/
Sexual
parts
of a
flower




         19
Releasing the pollens




                        20
21
 Fertilization

When all the ovules
have been fertilised,
the petals, stamens,
stigma and style are
no longer needed.
They will usually
wither and fall away,
leaving an ovary in
which the ovules are
developing into
seeds.
                        Mrs Theresa Teo GE2003   22

				
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posted:5/11/2013
language:English
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