Flowers and Sexual Reproduction

1. Sexual reproduction in plants
A flower is a leafy shoot
containing the sexual organs of
a flowering plant.
It is adapted for sexual
reproduction.
It is a modified terminal bud
typically composed of four sets
of modified leaves.

2. Insect-pollinated flower

3. Floral structures

4. Diagram of an insect-pollinated flower
Petal
Stigma
Sepal
Anther
Nectar
Ovule
Ovary
Style
Filament

6. Wind-pollinated flower

7. Diagram of a wind-pollinated flower
Bract
Anther
Filament
Ovary
Stigma

8. Functions of parts of the flower
 sepals
 petals
 Anthers
 filament
 Stigma
 style
 ovaries
 Protects the flower during the bud stage
 Attracts insect pollinators by colour and
scent
 produce and release pollen grains
 positions the anther for effective pickup
of pollen by the pollinating agent
 collects the pollen from the pollinating
agent
 positions the stigma for pollen collection
 site of fertilisation, protects the
developing seeds, aids in seed dispersal

9.  In a form of a table,
compare the
different structural
adaptations of
insect-pollinated
and wind-pollinated
flowers. [6]
. . . . thinking
of you!

10. structural adaptations of insect-pollinated
and wind-pollinated flowers
Insect-pollinated flowers Wind-pollinated flowers
 Petals large & brightly
coloured to attract insects
 Stigma located inside the
flower where the insects have
to brush past it
 Anthers inside the flower
where the insects have to
brush past them
 Stigma usually small & sticky
so that pollen grains can
attach from insect body
 Flower often strongly scented
 Large sticky or spiky pollen
grains which stick to insects
 Petals small or absent, if
present, not brightly coloured
 Stigma exposed to catch
pollen grains blowing in the
wind
 Anthers exposed outside the
flower so that wind can easily
blow the pollen grains away
 Stigma large & feathery to
catch pollen grains blowing
in the wind
 Flowers have no scent
 Light & smooth pollen that
can be blown in the wind

11. Pollination the transfer
of pollen
grains from
the male part
of the plant
(anther of
stamen) to
the female
part of the
plant
(stigma).

12. Agents of pollination
 . . . the means that
moves the pollen
grains from the
anther to the
stigma.
 Agents of
pollination include:
wind; insects; birds;
water & rodents.

13. Photomicrograph of pollen grains:
Note the spikes that attach pollen grains to insect’s body.

14. What happens after pollination?
 pollen grains germinates
forming pollen tube
 the pollen tube grows down
style digesting the style tissue
 the e pollen tube enters ovule
through micropyle
 male nucleus moves into ovule
 male nucleus (male gamete)
fuses with the ovum or egg cell
(female gamete) i.e.
fertilisation occurs
 ovule becomes seed
 ovule wall becomes seed coat or
testa
 ovary becomes fruit
 stigma and the style weathers
and dry up

15. Seed and fruit dispersal
 This is spread of seeds &
fruits some distance away
from the parent plant
 Dispersal allow seeds to
spread out to colonise new
areas so that the new plants
do not compete with parent
plant for light, water and
mineral salts
 means of seeds & fruits are:
 animals
 wind
 water
 self dispersal

16. Seed and fruit dispersal by Wind
Sycamore seed
Dandelion seeds
 Wind dispersed seeds
such as sycamore &
dandelion:
 are light so that they can
easily be blown by wind
 have wing –like outgrowth
or feathery hair
projections which increase
the surface area so that the
seeds can ‘float’ in air for
some time so they are
carried over long distance
from the parent plant

17. Seed and fruit dispersal by Animals
 Animal dispersed seeds
includes: tomato & burr grass.
 Tomato fruits:
 they are fleshy (succulent),
brightly coloured & scented
to attract animals
 Have tough seed coat to
protect the seeds from being
digested in the animals' gut
 Burr grass:
 Are covered with stiff, hooked
spines which catch onto the
animals’ fur to be carried long
distance before dropping off

18. Advantages of seed dispersal
 There is less
competition, with
parent plant & among
seedlings for same
resources such as;
light, water , nutrients
& space
 Dispersal allow plants
to colonise new areas
since plants are
stationary i.e. don’t
move from place to
place

19. External structure of a Seed

20. Internal structure of a Seed
plumule
radicle
micropyle
cotyledon
testa (seed coat)

22.  Testa; protects the
embryo from physical
damage & attack from
pathogens
 Micropyle; a hole in the
testa that allow water &
oxygen to enter into the
seed
 Cotyledons; stores
nutrients (starch, protein
& lipids) required during
germination
 Plumule; grows into
shoot after germination
 Radicle; grows into root
after germination

23. Conditions for seed germination
 Seed germination is the
process in which a plant
emerges from a seed & begins
grow
 Conditions needed for seeds
germination are:
 Suitable temperature; for
enzymes to work effectively
 Oxygen; for aerobic respiration
to provide energy to growing
embryo
 Water; for chemical reactions
to occur in solution, dissolve
nutrients for transportation,
activate enzymes & soak testa

24. Design & carry
out an
experiment to
investigate the
conditions
necessary for
germination of
mung bean
seeds.

25. I am willing to
answer questions
on sexual
reproduction in
plants.
Thank you folks!
You are such a
wonderful group
of students.