Reproduction in PlantsCarissa Fletcher

Draw and label a diagram showingthe structure of a dicotyledonous

animal-pollinated flower.

Distinguish between pollination,fertilization and seed dispersal.

Pollination is the transfer pollen from the anther to the stigmas.

• Fertilisation after the stigma is pollinated, the pollen grain germinates in a response to a sugary fluid secreted by the mature stigma (mainly sucrose).

• From each pollen grain, a pollen tube grows out that attempts to travel to the ovary by creating a path through the female tissue.

• The vegetative (or tube) and generative nuclei of the pollen grain pass into its respective pollen tube.

http://www.biologyjunction.com/images/doublefertilazation.jpg

Seed dispersal the movement of seeds away from the parent plant.

http://www.field-studies-council.org/breathingplaces/food_for_us.htm

Draw and label a diagram showingthe external and internal structure of

a Corn - dicotyledonous seed.

1. Fertilisation takes place 2. The zygote divides rapidly by

mitosis and develops into an embryo,

3. Differentiation into a young shoot (plumule), a young root, (radical) and seed leaves (cotyledons).

4. The primary endosperm nucleus also divides mitotically to give a mass of cells.

Explain the conditions needed for thegermination of a typical seed.

- The water content of seeds at between 5%-10% is very low and is the major factor in preventing them from germinating.

- As a rule the addition of water in the presence of Oxygen and a favourable temperature (5-40OC) is enough to break the dormancy.

- Light intensity is necessary for the germination of certain seeds.

- A sustained period of cold is needed to make some seeds in temperate climates germinate.

- Some will not germinate unless there has been the intense heat of a flash fire.

- A physical abrasion or partial digestion in the intestines of an animal may also be needed before a seed will germinate.

Stages in germination

1. Seed takes up water rapidly – rupturing the testa

2. Water activates enzymes in the seed which hydrolyse insoluble storage material into soluble substances.

3. Proteins to amino acids, starches into sugars and lipids into fatty acids and glycerol.

4. Products are transported to the growing points of the embryos for respiration and the growth of cell walls.

5. The amino acids are used in the formation of new enzymes and proteins.

http://www.youtube.com/watch?v=TJQyL-7KRmw

Economically important seeds

Peanuts

Soya beans

Caster oil seeds

Walnuts

Coconuts

Sunflower seeds

Explain how flowering is controlledin long-day and short-day plants,including the role of phytochrome.

Many plant processes are influenced by light. Just like the photoreceptors used in photosynthesis.

A pigment called PHYTOCHROME can induce a plant light -response.

Phytochrome

Phytochrome 660 absorbs red light at 660nm

Phytochrome 730 absorbs light in the far red region of the spectrum.

http://plantphys.info/plant_physiology/phytochrome.shtml

Photoperiodism

One major influence on the timing of flowering is the length of the day or photoperiod. The effects of the photoperiod on flowering differ from species to species.

The main categories are;

1. Long-day plants – these only flower when the period of daylight exceeds a critical length. (or a short period of darkness) E.g. radish

2. Short-day plants – These only flower when the period of daylight is shorter than a critical maximum length. (or a long period of darkness) E.g. Poinsetia

The role of phytochrome in flowering

Long day plants known to flower after short exposure to red light, the red light is absorbed by phytochrome 660nm which converts to P730nm and induces flowering.

Short day plants absorb light at P730 which is converted to P660nm. This is a much slower process, and needs a long dark period.

Figure 4. Photoperiod and Flowering - Left side: Short day plants flower with uninterrupted long nights. Right side: Long-day plants flower with short nights or interrupted long nights

http://www.cmg.colostate.edu/gardennotes/142.html

Light regulated plant development