2. Pollination
Pollination 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
4. 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.
5. 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.
6. The seed – For example pea seed (pisum sativum)
7. 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)
11. Storing seeds in case of extinction
Hope to store 25% of seeds from plants around the
world by 2020.
12. 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.
13. 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
14. 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
15.
16.
17. 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.
