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A2 Biology > Chemical Control Systems In Plants > Flashcards

Chemical Control Systems In Plants Flashcards

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1
Q

What 3 main parts can plant growth be divided into?

A

Cell division
Cell elongation
Cell differentiation

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2
Q

What is tropism?

A

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

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3
Q

What is positive tropism?

A

Towards stimulus

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4
Q

What is negative tropism?

A

Away from stimulus

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5
Q

Synergy

A

Hormones interact together

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6
Q

Antagonism

A

Hormones have opposite effects

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7
Q

Growth factors: auxins

A

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

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8
Q

Growth factors: gibberellins

A

Promote seed germination and growth of stems

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9
Q

Growth factors: cytokinins

A

Promote cell division

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10
Q

Role of gibberellins

A
  • 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
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11
Q

Evidence for gibberellins role in stem elongation

A

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

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12
Q

What are photoreceptors?

A

Structures or pigments sensitive to light of specific wavelengths

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13
Q

Phototropins

A

Group of photoreceptors responsible for triggering phototropism

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14
Q

Where is indoleacetic acid made

A

Shoot apex

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15
Q

Positive phototropism involving IAA

A

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

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16
Q

How does auxin stimulate cell growth?

A

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

17
Q

Apical dominance

A

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

18
Q

Evidence that apical dominance is controlled by auxin

A

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

19
Q

Example of antagonism in this process of apical dominance

A

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

20
Q

Germination and wavelength: red light

A

Stimulates germination

21
Q

Germination and wavelength: far red light

A

Inhibits it

22
Q

Photomorphogenesis

A

Development of structure driven by light

23
Q

Phytochromes

A

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

24
Q

Role of Pr

A

Absorbs red light- there is no response

25
Q

Role of pfr

A

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

26
Q

Short day plants

A

Red light inhibits flowering

In long periods of darkness pfr levels fall to allow flowering

27
Q

Long day plants

A

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

28
Q

Florigen

A

Migrates through vascular system to apical meristem to promote floral initiation

29
Q

Evidence that florigen spreads through grafted plants via plasmodesmata

A
  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
30
Q

Etoliation plants

A

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

31
Q

Pfr as a transcription factor

A

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

A2 Biology (19 decks)

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