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PollinationPollination is the process by which pollen (containing

male sex cells) is placed on the female stigma.

Birds, water and animals other than insects are all

vectors of pollination.

Two types:

Self-pollination

Cross-pollination

Fertilization

Starter – Put the following statements in the

correct order to describe fertilization.

A. Within the pollen tube is the nucleus that will produce the sperm.

B. Pollen germinates to produce pollen tube

C. The sperm moves from the tube to combine with the egg of the ovule to form

a zygote.

D. Pollen tube grows down the style of the carpel.

E. The pollen tube completes its growth by entering an opening at the bottom of

the ovary.

Fertilization Once pollination has occurred, next step is fertilization.

Male and female sex cells unite to form a diploid zygote.

Female sex cells are present within the ovules of the flower. Ovules are present within the

ovary of the carpel.

1. Pollen germinates to produce pollen tube

2. Pollen tube grows down the style of the carpel.

3. Within the pollen tube is the nucleus that will produce the sperm.

4. The pollen tube completes its growth by entering an opening at the bottom of the ovary.

5. The sperm moves from the tube to combine with the egg of the ovule to form a zygote.

Once the zygote is formed, it develops the surrounding tissue into the seed. As the seed is

developing, the ovary around the ovule matures into a fruit. The fruit encloses and helps to

protect the seed.

The seed – For example pea seed (pisum sativum)

Conditions needed for Germination

Germination is the process by which a seed emerges from a period of

dormancy and starts to sprout

For germination to occur, a seed requires a combination of:

Oxygen: For aerobic respiration (need ATP in order to grow)

Water: To metabolically activate the cells

Temperature: For the optimal function of enzymes

In addition, particular seed species may require other specialised conditions, such as:

• Fire • Light or darkness • Freezing • Prior animal

digestion •Erosion of the seed coat • Washing (to remove inhibitors)

Unusual germination – Jack Pines

Artic Poppy – (Papiver radicatum)

Seed Germination

Storing seeds in case of extinction

Hope to store 25% of seeds from plants around the

world by 2020.

Metabolic Processes during germination of a seed

Begins with absorption of water.

1. Gibberellin released after water uptake.

2. Gibberellin is a growth substance (plant growth hormone) and triggers the

production of amylase.

3. Amylase hydrolyses starch into maltose. Starch is present in the seeds

endosperm.

4. Maltose is then further hydrolysed into glucose that can be used for cellular

respiration or cellulose (condensation).

5. Cellulose is necessary to produce the cell walls of new cells being produced.

Control of flowering in angiosperms Light is an important factor

Plants detect the presence of light, its direction, wavelength, and even

intensity.

Photoperiodism is the plant’s response to light involving the relative lengths

of day and night

In order to survive plants must flower when pollinators are available and

when necessary resources are plentiful.

Plant type Flowering and light Examples

Long-day plants Bloom when days are longest and

nights are shortest

Radishes, spinach, and lettuce

Short-day plants Bloom in spring, late summer,

and autumn when days are

shorter

Poinsettias, chrysanthemums,

and asters

Day-neutral plants Flower without regard to day

length

Roses, dandelions, and tomatoes

How is the flowering process controlled?

Plants actually depend on the amount of uninterrupted darkness to flower

Control by light is brought about by a special blue/green pigment called

phytochrome

Inactive Pr

Active Pfr

Red light (660nm) cause inactive form to become active

In Far Red light (730nm) the active form reverts back quickly to the inactive

form.

In darkness the active form slowly converts back to the inactive form

Mechanism behind flowering

The search for the substance that causes the development of meristematic

tissue into flowers was focused on the identification of 'florigen', the

flowering hormone.

Phytochrome Fr is the biologically active form of phytochrome but it is

florigen. Most research indicates that phytochrome cannot move from the leaf

cells to the meristem tissue.