Co-Ordination And Control (Plants)

Question 1

What is Long-day plant?

Answer 1

A plant which only flowers when the number of hours of light is above a critical level

Question 2

What is a Short-day plant?

Answer 2

A plant which only flowers when the number of hours of light is below a critical level.

Question 3

What is phytochrome?

Answer 3

A light-sensitive pigment found in small quanties in leaves of flowering plants. It absorbs light and exists in two interchangeable forms.

Question 4

What forms does phytochrome exist?

Answer 4

P660 and P730

Question 5

What causes the conversion between the two forms of phytochrome?

Answer 5

Absorption of light causes the rape conversion

Question 6

What does P660 absorb?

Answer 6

Red light

Question 7

What does P730 absorb?

Answer 7

Far red light

Question 8

What form is physiologically active form and what does it control?

Answer 8

P730. Ur either stimulates or inhibits, depending on the critical length of interrupted darkness.

Question 9

What are the flowering requirements for LDPs?

Answer 9

High concentration of P730 stimulates flowering

Question 10

What are the flowering requirements for SDPs?

Answer 10

Low concentration of P730 stimulated flowering.

Question 11

What is the effect of flowering on LDPs and SDPs during a long day and short night?

Answer 11

• stimulates flowering of LDPs
• inhibits flowering of SDPs
• P730 accumulates during the day but not sufficiently removed during the night.

Question 12

What is the effect of flowering on LDPs and SDPs during a short day and a long night?

Answer 12

• stimulates flowering of SDPs
• inhibits flowering of LDPs
• P730 removed at night and not sufficiently produced during the day

Question 13

What is the effect of flowering on LDPs and SDPs during a long day (interrupted by a short dark period) and short night?

Answer 13

• stimulates flowering of LDPs
• inhibits flowering of SDPs
• the short dark period converts P730 to P660, but when light returns P730 levels increase rapidly.

Question 14

What is the effect of flowering on LDPs and SDPs during a short day and a long night (interrupted by a short light period)?

Answer 14

• stimulates flowering of LDPs
• inhibits flowering of SDPs
• during the night, the period of light allows sufficient P730 to accumulate. H

Question 15

What are the different plant growth substances?

Answer 15

Auxin, cytokinins and gibberellins

Question 16

Where is auxin produces?

Answer 16

Growing shoot tip (apical meristem)

Question 17

Where is cytokinins produced?

Answer 17

Actively dividing tissue

Question 18

Where is gibberellins produced?

Answer 18

Apical/terminal buds/leaves

Question 19

What is the main plant growth effect of auxin?

Answer 19

Stimulate elongation of cells by allowing cell wall as to be stretched more easily.

Question 20

What is the main plant growth effect of cytokinins?

Answer 20

Promote cell divisor by mitosis

Question 21

What is the main plant growth effect of gibberellins?

Answer 21

Stimulate elongation of intermodal regions to increase overall length of stem.

Question 22

Explain the process of phototropism

Answer 22

• auxin is produced in the apical meristem
• they diffuse down the stem to the zone of elongation
• they bind to specific receptors on the cell-surface membrane
• the membrane pumps H+ ions into the cell wall
• the acidication of the cell wall activates agents which loosen the linkages between microfibrils, making them flexible
• the cell wall absorbs water by osmosis, making the cell expand
• the more auxin received in the zone of elongation, the more this effect allows the cells to expand.