2. 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.
3. TH E G E N E R A L S TR U C TU R E
O F A F L O WE R
• FLOWER = a modified shoot which is the
reproductive structure of angiosperms.
4. Petal
Anther
Stamen
Stigma
Filament
Style
Ovary
Ovul
Sepal
Th e S tru c tu re s O f
F lo w e r
5. • Each part of the flower serves a certain
function :
– the pedicel supports the flower in the best
position for pollination;
– The petals are usually big & brightly
coloured to attract insects @ birds for
pollination;
– The sepals protect the flower when it is still
a bud.
6. • The male structure = stamen
(consists of a filament & an
anther).
• The anther functions in
producing pollen grains & is
supported by the filament.
• The male gametes are found in
the pollen grain.
7. • The female structure = pistil
(consists of stigma, style & ovary).
• Inside the ovary, one @ more
ovules can be found.
• The female gametes @ egg cell is
found in the ovule.
• Pollen grain are received by the
stigma.
8. THE FORMATION OF POLLEN
GRAINS
• Are formed in the anther.
• Each anther contains 4 chambers called
pollen sacs in which pollen grains are
formed.
• The tapetum provides nourishment to
the developing pollen grains.
10. • Each pollen sac contains many
diploid pollen mother cells
meiosis a tetrad of 4
haploid cell separate &
become the pollen grain.
• The haploid nucleus divides
by mitosis to produce a
generative nucleus & a tube
nucleus.
• Pollen grain is a microspore &
not a gamete.
• Male gamete are form when
the generative nucleus
divides.
13. THE FORMATION OF EMBRYO SAC
• Embryo sac = a structure containing the egg
cell found in the ovule.
• Initially, the ovule contains similar diploid
cells, nucellus one of the cells enlarges to
become the embryo sac mother cell.
• Embryo sac mother cell meiosis 4
haploid cells, 3 disintegrate.
14. • The remaining cell (which represents the
young embryo sac) will undergo mitosis thrice
to produce 8 nuclei.
• 2 of the nuclei will move to the middle of the
embryo sac polar nuclei.
• Other 6 nuclei are enveloped with cytoplasm
& become cells 3 antipodal cells, 2
synergids, 1 egg cell mature embryo
(megaspore containing the female gamete)
15. • Only the egg cell & the 2 polar nuclei are
important in fertilisation the other will
disintegrate.
• The ovule becomes enveloped by 2
layers of integuments, leaving a small
opening (micropyle) connected to the
ovary by funicle. megaspore (embryo
sac containing the female gamete).
18. THE FORMATION 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
produce 2 male nuclei.
19. 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
a diploid zygote develops into embryo
which consist of the radicle, plumule, & 1 @ 2
cotyledons.
• The other male nucleus fuses with the 2 polar
nuclei to form a triploid nucleus (3n)
endosperm (store food for the developing
embryo).
20. • The ovary becomes a fruit pericarp & the
ovules become seeds.
• The outer integument becomes the seed coat
@ testa (to protect the seed)
• The inner integument becomes tegmen, a
thin membrane underneath the testa.
• All parts of the flower wither away.
21. PERI CARP M ODE OF FRUI T
DI SPERSAL
F l e s h y, Eat e n b y an i mal s
s uccul e nt ; s e e d s ar e t h e n
ed i bl e d i s c ar d e d , f ar f r o m
Ho o k / s p i n e s S t i tchkes ptar efnutr. o f
o
p as s i n g an i mal s
W n g - s h ap e d ; d r y
i Eas i l y c ar r i e d b y
& l i gh t ; wi n d .
f e at h e r y h ai r s
Fi b r ou s t i s s u e Car r i e d b y wat e r .
wi t h man y ai r
Un e ve s p ac e s n g o f
n d r yi Se e d s d i s pe rs e d by
f r u i t wal l e x p l o s i ve me c h an i s m
c au s i n g s u d d e n
22. D o u b le F e r t ilis a t io n In F lo w e r in g
P la n t s
23. THE IMPORTANCE OF DOUBLE
FERTILISATION FOR THE SURVIVAL OF
FLOWERING PLANTS
• Double fertilisation is important for two
reasons :
• By formation of the 3n nucleus endosperm,
the parent plants provide an important nutrient
store for the developing plant.
• It is ensure that the nutritive tissue formed is
not wasted because it will be used by the growing
embryo the endosperm only develops if the
ovum has been fertilised.
24. • The provision of food for the embryo is
important for the survival of flowering plants.
• The presence of food enables the embryo to
live for a long period of time even when
conditions are unfavourable 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 by the embryo to build
tissues for germination.
25. DON’T FORGET
TO DO
CHECKPOINT 4.5
(page 147).
PLEASE MAKE A
REVISION!!!
