This document summarizes the process of sexual reproduction in flowering plants. It describes the male and female structures in flowers, including the formation of pollen grains and embryo sacs. The key stages discussed are pollination, fertilization, and double fertilization. Double fertilization is important because it ensures the nutritive endosperm tissue forms to provide food for the developing embryo, allowing seeds to survive unfavorable conditions until germination.

1. CHAPTER 4 :
REPRODUCTION & GROWTH
4.5 – SEXUAL REPRODUCTION IN FLOWERING PLANTS

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.

9. A Cross Section Of Anther

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.

11. Th e
F o r m a t io n
O f P o lle n

12. POLLEN GRAINS

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).

16. The Formation Of Embryo
Sac

17. T h e F o r m a t io n O f

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!!!