1. 9.3 Reproduction in
Flowering Plants
Topic 9 Plant Science

2. Reproduction in Flowering Plants
 9.3.1 Draw and label a diagram showing the structure of a
dicotyledonous animal-pollinated flower. (Limit the
diagram to sepal, petal, anther, filament, stigma, style and
ovary).
 9.3.2 Distinguish between pollination, fertilization and
seed dispersal.

3. Reproduction in Flowering Plants
 9.3.3 Draw and label a diagram showing the external and
internal structure of a named dicotyledonous seed.
 The named seed should be non-endospermic.
 The structure in the diagram should be limited to testa,
micropyle, embryo root, embryo shoot and cotyledons.
 9.3.4 Explain the conditions needed for the germination
of a typical seed. (Seeds vary in their light requirements
and, therefore, this factor need not be included).

4. Reproduction in Flowering Plants
 9.3.5 Outline the metabolic processes during germination
of a starchy seed.
 Absorption of water precedes the formation of gibberellin
in the embryo’s cotyledon. This stimulates the production
of amylase, which catalyses the breakdown of starch to
maltose. This subsequently diffuses to the embryo for
energy release and growth. No further details are
expected.

5. Reproduction in Flowering Plants
 9.3.6 Explain how flowering is controlled in long-day and
short-day plants, including the role of phytochrome.
 Limit this to the conversion of Pr (red absorbing) to Pfr
(far-red absorbing) in red or white light, the gradual
reversion of Pfr to Pr in darkness, and the action of Pfr as
a promoter of flowering in long-day plants and an
inhibitor of flowering in short-day plants.

6. Structure of a Flowering Plant
Ref: Biology, Rowland
Ref: IB Biology OSC

7. Pollination
 Pollination is the transfer of pollen (containing male
gametes) from the anther to the stigma.
 Pollen grains are immotile (cannot move on their own).
 Two types of pollination:
 Self pollination (same plant).
 Cross pollination (different plant).
 Pollination must take place before fertilisation can occur.
 Pollination does not mean fertilisation will occur.
 Could be incompatible gametes.

8. Fertilisation
 Once pollination has occurred and the pollen grains have
been transferred to the stigma, the male gamete grows a
pollen tube down the style to the ovary.
 Fertilisation is when the male gamete (inside a pollen
grain) fuses with the female gamete (ovule).
 This occurs in the ovary of the flower.
 The fertilised ovules develop into seeds.
 Ovaries containing fertilised ovules develop into fruits.
 The role of the fruit is Seed dispersal.

9. Seed Dispersal
 Seed dispersal is the spreading of seed away from the
parent plant.
 This can be done by:
 Wind.
 Seeds caught by wind.
 eg: dandelion, sycamore, pine.
 Explosion.
 Seed compartments which violently burst open as they dry out.
 eg: gorse, bloom.
 Animal dispersal:
 Adhesive hairs, spines, hooks which attach to animals.
 Eg: bur fruit.
 Fruit eaten by animal and deposited in faeces.
 Apples, blackberry.

10. Seed Structure
Ref: IB Biology OSC

11. Germination
 Germination is the resumption of growth or development from a
seed.
 For a seed to germinate, certain conditions must be met.
 Water:
 Water must be available to rehydrate the dry tissue of the seed.
 Oxygen:
 Oxygen must be available for aerobic respiration.
 Temperature:
 Suitable temperatures are needed.
 Many of the metabolic events of germination use enzymes.
 These enzymes require optimum temperatures.
 Many seeds only germinate after exposure to cold temps and then
warmer temperatures ie: spring.
 Some need bushfires to stimulate germination.
 Calvarias and the dodo (Rowland p468).

12. Metabolic Events of Germination
 1. The seed absorbs water through the micropyle.
 2. A plant growth hormone, Gibberellin, is produced in
the cotyledons.
 3. Gibberellin stimulates the production of amylase,
which catalyses the digestion of starch into maltose.
 4. Maltose is transported from the cotyledons to the
growth areas of the seedling, the embryo root and the
embryo shoot.
 5. Maltose is converted into glucose, which is either
used for:
 Aerobic cell respiration as a source of energy.
 Synthesis of cellulose or other substances needed for growth.

13. Control of flowering
 Short day plants: flower at a time of year
when days are short
 Long day plants: flower at a time of year
when days are long
 Experiments show it is the length of the
night that is important (the length of
continuous darkness) i.e. short day plants
need a long period of continuous darkness

14. Phytochrome and
photoperiodism
 Pigment called phytochrome measures the
period of darkness.
 Exists as Pr (absorbs red light and is
inactive form) and Pfr (absorbs far red and
is active form)
 Pr is rapidly converted to Pfr when it
absorbs red light during the day
 Pfr is rapidly converted back to Pr when
far red light absorbed.
 Pfr gradually convertes to Pr in darkness

15. Mechanism in short/long day
plants
 Gradual conversion to Pr is how dark
period is timed
 In long day plants, enough Pfr remains
after short nights to stimulate flowering
 In short day plants Pfr inhibits flowering:
at the end of long nights enough Pfr has
been converted to Pr to allow flowering.
 Flowering can be induced by artificially
extending the day in long day plants and
the night in short day plants

17. IBO guide:
 9.3.1 Draw and label a diagram showing the structure of a
dicotyledonous animal-pollinated flower. (Limit the
diagram to sepal, petal, anther, filament, stigma, style and
ovary).
 9.3.2 Distinguish between pollination, fertilization and
seed dispersal.

18. IBO guide:
 9.3.3 Draw and label a diagram showing the external and
internal structure of a named dicotyledonous seed.
 The named seed should be non-endospermic.
 The structure in the diagram should be limited to testa,
micropyle, embryo root, embryo shoot and cotyledons.
 9.3.4 Explain the conditions needed for the germination
of a typical seed. (Seeds vary in their light requirements
and, therefore, this factor need not be included).

19. IBO guide:
 9.3.5 Outline the metabolic processes during germination
of a starchy seed.
 Absorption of water precedes the formation of gibberellin
in the embryo’s cotyledon. This stimulates the production
of amylase, which catalyses the breakdown of starch to
maltose. This subsequently diffuses to the embryo for
energy release and growth. No further details are
expected.

20. IBO guide:
 9.3.6 Explain how flowering is controlled in long-day and
short-day plants, including the role of phytochrome.
 Limit this to the conversion of Pr (red absorbing) to Pfr
(far-red absorbing) in red or white light, the gradual
reversion of Pfr to Pr in darkness, and the action of Pfr as
a promoter of flowering in long-day plants and an
inhibitor of flowering in short-day plants.