Chemical Control Systems In Plants

Question 1

What 3 main parts can plant growth be divided into?

Answer 1

Cell division
Cell elongation
Cell differentiation

Question 2

What is tropism?

Answer 2

The movement of part of a plant in response to and directed by an external stimulus

Question 3

What is positive tropism?

Answer 3

Towards stimulus

Question 4

What is negative tropism?

Answer 4

Away from stimulus

Question 5

Synergy

Answer 5

Hormones interact together

Question 6

Antagonism

Answer 6

Hormones have opposite effects

Question 7

Growth factors: auxins

Answer 7

Promote cell elongation, inhibit the growth of side shoots, inhibit lead abscission

Question 8

Growth factors: gibberellins

Answer 8

Promote seed germination and growth of stems

Question 9

Growth factors: cytokinins

Answer 9

Promote cell division

Question 10

Role of gibberellins

Answer 10

• seed absorbs water and swells
• embryo secretes G which diffuses into the aleurone layer
• G stimulates aleurone layer to produce amylase which diffuses into endosperm and breaks down food store for embryo

Question 11

Evidence for gibberellins role in stem elongation

Answer 11

When G is applied artificially to dwarf plants they can stimulate stem elongation

Question 12

What are photoreceptors?

Answer 12

Structures or pigments sensitive to light of specific wavelengths

Question 13

Phototropins

Answer 13

Group of photoreceptors responsible for triggering phototropism

Question 14

Where is indoleacetic acid made

Answer 14

Shoot apex

Question 15

Positive phototropism involving IAA

Answer 15

Photoreceptors detect light
Auxin diffuses to shaded side of stem
Cells elongate by loosening structure of cell walls involving hydrogen ions
Positive phototropism as cells ok shaded side bend

Question 16

How does auxin stimulate cell growth?

Answer 16

Bind to specific receptor sites on the cell-surface membrane

Activates the active pumping of hydrogen ions into cell wall spaces

Alters the hydrogen concentration which means low pH of cell walls for the enzymes that break bonds between adjacent Celulose microfibrils also mean cells are flexible

Absorb water by osmosis means turgor pressure and cell walls stretch leading to cell elongation

Auxins destroyed by enzymes

Question 17

Apical dominance

Answer 17

The growth of the main central stem of a plant which reduces production of lateral shoots

Question 18

Evidence that apical dominance is controlled by auxin

Answer 18

When the shoot apex is pruned (the apical bud) lateral branches grow higher up the plant

Question 19

Example of antagonism in this process of apical dominance

Answer 19

Cytokinins made in roots and travel upwards to promote lateral growth whereas auxin travels downwards inhibiting lateral growth

Question 20

Germination and wavelength: red light

Answer 20

Stimulates germination

Question 21

Germination and wavelength: far red light

Answer 21

Inhibits it

Question 22

Photomorphogenesis

Answer 22

Development of structure driven by light

Question 23

Phytochromes

Answer 23

Pigments that control photomorphogenesis which has 2 Interconvertible forms pfr and pr

Question 24

Role of Pr

Answer 24

Absorbs red light- there is no response

Question 25

Role of pfr

Answer 25

Absorbs far red light= response- in darkness pfr is converted into Pr slowly

Question 26

Short day plants

Answer 26

Red light inhibits flowering | In long periods of darkness pfr levels fall to allow flowering

Question 27

Long day plants

Answer 27

High levels of pfr stimulate flowering Short nights means little pfr converted to Pr Flower growth

Question 28

Florigen

Answer 28

Migrates through vascular system to apical meristem to promote floral initiation

Question 29

Evidence that florigen spreads through grafted plants via plasmodesmata

Answer 29

1. Graft and keep under long days and short nights 2. Leaf is induced by long nights and short days 3. If the leaf on the end of the chain is subjected to long nights all plants will flower

Question 30

Etoliation plants

Answer 30

Kept in the dark: Grow rapidly to reach light Use food reserves Grow tall with no chlorophyll

Question 31

Pfr as a transcription factor

Answer 31

When Pr is converted into pfr in light it moves into nucleus Binds to nuclear protein phytochrome interacting factor 3 (PIF3) which is a transcription factor PIF3 only activates gene transcription and forms mRNA when it is bound to pfr