Topic 3 - Coordination And Control In Plants

Question 1

What are plant growth substances

Answer 1

Plant responses that are controlled by hormone-like chemical coordinators

Question 2

What is the apical meristem

Answer 2

The tip of the plant where cell division takes place

Question 3

What is the zone of elongation

Answer 3

The region below the tip where cells enlarge

Question 4

What is the internode of a plant

Answer 4

The region between the nodes, or points at which leaves develop

Question 5

What are the three major plant growth substances

Answer 5

Auxins
Cytokinins
Gibberellins

Question 6

What is the site of production and main plant growth effect of Auxins

Answer 6

The produce in the growing tip of the stem, and stimulate elongation of cells

Question 7

What is the site of production and main plant growth effect of Cytokinins

Answer 7

They produce in actively dividing tissues and promote cell division, especially in combination with auxins

Question 8

What is the site of production and main plant growth effect of Gibberellins

Answer 8

They produce in apical bud and leaves, and stimulate elongation of intermodal regions

Question 9

What is the process of cell enlargement

Answer 9

The cell of the apical meristem absorbs water by osmosis and form permanent vacuoles. As the vacuoles absorb water, the cell increases in size

Question 10

What is the process of auxin action

Answer 10

They are produced in the apical meristem
They diffuse down the shoot towards the zone of elongation
They bind to specific receptors on the membrane of new cells, which causes the membranes pumps to move H ions out into the cell wall
This acidification activates agents which loosen linkages between cellulose microfibrils allowing slippage
The cells absorb water by osmosis and expand the cell
The more auxin that is received, the more the cell can expand

Question 11

When do long-day plants flower

Answer 11

Only if the day length exceeds a critical value

Question 12

When do short-day plants flower

Answer 12

Only if the day length is less than a critical value

Question 13

What is photoperiod measured in

Answer 13

Phytochrome pigments

Question 14

What are the two forms of Phytochrome

Answer 14

P660 and P730

Question 15

What is the difference in red-light absorption of P660 and P730

Answer 15

P730 maximally absorbs Red light of wavelength 730nm, while P660 maximally absorbs far-red light of wavelength 660nm

Question 16

What happens to the Phytochrome forms in darkness

Answer 16

There is a slow conversion of P730 to P660, which means P660 accumulates at night

Question 17

Why does P730 accumulate during the day

Answer 17

Daylight contains more red light than far-red light

Question 18

What is the physically active form of Phytochrome, and why

Answer 18

P730, because it can either stimulate or inhibit flowering

Question 19

What is the Phytochrome response in Long Day, and Short Night, and which plant flowers

Answer 19

P730 accumulates during the long day and is not sufficiently removed during the short night- mostly P730, which results in flowering of Long Day plants

Question 20

What is the Phytochrome response in Short Day, and Long Night, and which plant flowers

Answer 20

P730 is removed during the long night and is not produced sufficiently during the short day - little P730, resulting in flowering of Short Day Plants

Question 21

What is the Phytochrome response of a Short Day, and Long night interrupted by short light period

Answer 21

During the night, the short light period converts P660 to P730 - enabling sufficient P730 to accumulate, resulting in flowering of Long Day plants

Question 22

What is the difference in receptors and effectors

Answer 22

Receptors receive the stimulus
Effectors being about the response

Question 23

What is an example of a receptor in plants, and animals

Answer 23

The Phytochrome system in the leaf detects the photoperiod
The osmoreceptors in the hypothalamus are stimulated by changes in the water potential of the blood

Question 24

What is an example of an effector in plants and animals

Answer 24

A bud may develop into a flower, while cells elongate in the zone of elongation in response to auxin
In animals, muscles contract

Question 25

Why do animals need an additional system to linking receptors fast

Answer 25

They can move from one place to another