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4.5 SEXUAL REPRODUCTION IN FLOWERING PLANTS
CHAPTER 4 :
REPRODUCTION & GROWTH
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LEARNING OUTCOMES Identify male & female structure in a flower; Describe the formation of pollen grains; Describe the formation of the embryo sac in the ovule; Describe the formation of pollen tube; Describe the formation of zygote; Describe the formation of triploid nucleus; Conceptualise double fertilisation;
Relate the structure of a fruit to the flower parts; Explain the importance of double fertilisation for the
survival of flowering plants.
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THE GENER L STRUCTURE OF
FLOWER
FLOWER = a modified shoot which is thereproductive structure of angiosperms.
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The Structures Of Flower
Anther
Filament
Stamen
Style
Stigma
Petal
Sepal
Ovary
Ovul
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Each part of the flower serves a certainfunction :
the pedicel supports the flower in the best positionfor pollination;
The petals are usually big & brightly coloured toattract insects @ birds for pollination;
The sepals protect the flower when it is still a bud.
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The male structure = stamen (consists of a filament & an anther ).
The anther functions in producingpollen grains & is supported by thefilament.
The male gametes are found in thepollen grain.
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The female structure = pistil (consists ofstigma, style & ovary ).
Inside the ovary, one @ more ovules can be found.
The female gametes @ egg cell is foundin the ovule.
Pollen grain are received by the stigma.
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THE FORM TION OF POLLEN GR INS Are formed in the anther.
Each anther contains 4 chambers called pollen sacs in which pollen grains areformed.
The tapetum provides nourishment to thedeveloping pollen grains.
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Each pollen sac contains manydiploid pollen mother cells meiosis a tetrad of 4 haploid
cell separate & become thepollen grain.
The haploid nucleus divides bymitosis to produce a generativenucleus & a tube nucleus .
Pollen grain is a microspore ¬ a gamete.
Male gamete are form when thegenerative nucleus divides.
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The ormation Of Pollen
Grains
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POLLEN GRAINS
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THE FORMATION OF EMBRYO SAC
Embryo sac = a structure containing the egg cellfound in the ovule.
Initially, the ovule contains similar diploid cells,nucellus one of the cells enlarges to become theembryo sac mother cell.
Embryo sac mother cell meiosis 4 haploid cells,3 disintegrate.
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Only the egg cell & the 2 polar nuclei areimportant in fertilisation the other will
disintegrate.
The ovule becomes enveloped by 2 layers ofinteguments , leaving a small opening(micropyle ) connected to the ovary byfunicle . megaspore (embryo sac containing
the female gamete).
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The Formation Of Embryo Sac
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The Formation Of Embryo Sac
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THE FORM TION OF POLLEN TUBE POLLINATION = the transfer of pollen from the
stamens to the stigma Self-pollination / cross pollination
The stigma secretes a sugary liquid which stimulates
germination. The pollen germinates a pollen tube is produces
through the tissues of the style into an ovule.
The generative nucleus divides by mitosis to produce2 male nuclei .
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FERTILISATION When the pollen tube arrives at the embryo sac, the
tube nucleus disintegrates .
1 of the male nuclei fuses with egg cell to form adiploid zygote develops into embryo which consistof the radicle, plumule , & 1 @ 2 cotyledons .
The other male nucleus fuses with the 2 polar nuclei
to form a triploid nucleus (3n) endosperm (storefood for the developing embryo).
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PERICARP MODE OF FRUIT
DISPERSAL
Fleshy, succulent;edible
Eaten by animals seeds arethen discarded, far from the
parent.Hook / spines Sticks to fur of passing
animalsWing-shaped; dry &light; feathery hairs
Easily carried by wind.
Fibrous tissue withmany air spaces Carried by water.
Uneven drying of fruitwall causing sudden
rupture
Seeds dispersed by explosivemechanism
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The provision of food for the embryo is important forthe survival of flowering plants.
The presence of food enables the embryo to live for along period of time even when conditions areunfavourable such as dry & cold conditions.
When favourable the food in the endosperm will be broken down into simple molecules such as sugar,
amino acids, glycerol & fatty acids absorbed bythe embryo to build tissues for germination.
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DONT FORGET
TO DO CHECKPOINT 4.5
(page 147).PLEASE MAKE A
REVISION!!!