9.3 reproduction in angiospermophytse

9.3 Reproduction in Flowering Plants

Topic 9 Plant Science

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.

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).

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.

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.

Structure of a Flowering Plant

Ref: Biology, Rowland

Ref: IB Biology OSC

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.

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.

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.

Seed Structure

Ref: IB Biology OSC

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).

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.

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

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

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

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.

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).

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.

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.