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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.


9/25 A Cross Section Of Anther


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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 &not 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!!!

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