This document summarizes the sexual reproduction process in flowering plants. It begins with an overview of the plant lifecycle and the structure and function of floral parts. It then describes microsporogenesis and microgametogenesis, where pollen is produced from microspores containing male gametes. Megaspore development and megagametogenesis are also outlined, where the ovule contains female gametophytes with egg cells. Fertilization occurs when pollen is transferred to the stigma, and the seeds that develop contain embryos to germinate into new plants.

1. Sexual Reproduction of the
Flowering Plant

2. Review the plant life cycle
1
4
2
pollen is
transferred
3
After fertilization
flower withers
seeds disperse
and germinate
into new plant
seeds develop
in ovary
4

3. Structure of the flower

4. Carpel
Petal
Anther
Filament
Stamen
Stigma
Style
Ovary
OvuleSepal
Structure of the flower

5. Function of floral parts
 Sepal : To protect the
flower (and to prevent it
from drying out
 Petals : To attract
insects to the flower for
pollination

6. Function of floral parts
 Stamen : To produce
the pollen grains in the
anthers. (Each pollen
grain produces two
male gametes, one of
which can fertilise an
egg cell)

7. Function of floral parts -Stamen
Anther
• Produces pollen
Filament
• Holds the anther in place

8. Function of floral parts
 Carpel : To produce
the ovules (Each ovule
contains an egg cell
inside an embryo sac)

9. Function of floral parts - Carpel
Stigma
• Where pollen lands after
pollination
Style
• Pollen travels down this
Ovary
• Contains ovules

10. Angiosperm anther
Dithecous - anther is bilobed
with each lobe having two theca
A longitudinal groove runs
lengthwise separating the theca.
10

11. Structure of an Anther
11

12. .S. OF AN ANTHER
12

13. T.S. of an anther
 Usually the anther is Dithecous - bilobed nature
 Anther - Two microsporangia in each lobe develop into
pollen sacs.
 Microsporangium: microsporangium is surrounded by four
wall layers -- the epidermis, endothecium, middle layers
and the tapetum.
 The outer three wall layers perform are for protection and help
in dehiscence of anther to release the pollen.
 The innermost wall layer is the tapetum. It nourishes the
developing pollen grains. Cells of the tapetum possess dense
cytoplasm and generally have more than one nucleus.
Nucleus divides – without cytoplasmic division- polyploidy
13

14. MICROSPOROGENESIS
Cells
of
sporange
ous
tissue
Four
cells
Haploid
Stay
together
Tetrad
cells
separates
Meiosis
Micro-
sporogen
esis
Anthers
mature,
Dehydrat
ion
14

15. 15
Structure of a Pollen grain
 The pollen grains represent the male
gametophytes.
 Sizes, shapes, colours, designs-
according to different species
 Very resistant because of the
presence of sporopollenin(Tough
Protein)
 Cryopreservation(-196 0
C ) used in
crop breeding
 Pollen food nutritional value –
performance of athletes and race
horses
 Pollen Allergy-asthma, bronchitis eg
Parthenium(notorious invasive Sp)
 Viability of pollen grains depends on
temperature and humidity. Viable from
few mins to several months according
to species.

16. 16
The cytoplasm of pollen grain is surrounded by a plasma membrane.
A mature pollen grain – ( inside intine and exine )
During development from microspore mitosis – 2 cells
vegetative cell / tube cell --bigger, has abundant -food reserve and
a large irregularly shaped nucleus.
generative Cell -- small , spindle shaped with dense cytoplasm & a
nucleus. It floats in the cytoplasm of the vegetative cell.
60 % angiosperms, pollen grains are shed at 2-celled stage.
In others generative cell divides mitotically - the two male gametes
before pollen grains are shed (3-celled stage).

17. Stages of microspore maturing into a
pollen grain

18. Stigma
Style
Ovary

19. TYPES OF PLACETATION-attachment of ovules to placenta

20. Cells in the
nucellus
near
micropylar
region.
Four cells
Haploid
3 near
micropyle
degenerrate
1 functional
megaspore
Meiosis
Mega-
sporogenesis
Functional megaspore enlarges,
mitotic division 2 nuclei – move
opposite poles – 2 mitoic
division- 4 nuclei at each pole
Wall formation only after this
stage
Chalaza end – 3 form antipodals
Micropylar end – 3 form egg
apparatus
Remaining 2 nucei Polar nuclei
in large central cell.
20

21. 21
Megaspore
mother
cells MMC
Deploid

22. 22

23. 23
Megasporangium / Ovule (Anatropus)