Plant Hormones

Question 1

Examples of abiotic stress

Answer 1

Freezing
Drought
Increased soil water salinity
Presence of heavy metals e.g lead, copper

Question 2

Ways plants respond to abiotic stress
E.g response to drought?

Answer 2

• dropping their leaves
• shutting their stomata (so reducing water loss via transpiration)

Others:
Some plants produce an antifreeze chemical in their cells, that decreases the formation of ice crystals that can destroy plant cells if allowed to form within them

Question 3

What is herbivory

Answer 3

Consumption of plants by herbivores

Question 4

Chemical defences to herbivory (& folding in response to it)

Answer 4

Alkaloids
Pheeonones
Tannins

Question 5

What are tannins

Answer 5

Question 6

What are alkaloids

Answer 6

Question 7

What are pheromones

Answer 7

Question 8

What are Nastic movements

Answer 8

Question 9

What are tropisms

Answer 9

Growth movements of a part of a plant in response to a directional stimulus

Question 10

Postive vs negative tropism

Answer 10

Towards vs against stimulus

Question 11

5 types of tropisms table

Answer 11

Question 12

How did darwin investigate phototropism and show that the tip detected light

Answer 12

Question 13

How did scientists investigate tropisms using mica to show that the growth stimulus was a chemical that could travel through gelatin

Answer 13

Question 14

How tropism was investigated (how the tip led to curvature)

Answer 14

Question 15

Phototropism: how they found out it was due to a hormone by replacing the tip with a block

Answer 15

Question 16

What does auxin do

Answer 16

Control growth elongation

Question 17

What does auxin do

Answer 17

Control growth elongation

Question 18

Where is auxin synthesised

Answer 18

The meristems (growing tips of roots & shoots)

Question 19

Where does auxin move after it’s synthesised in the meristems

Answer 19

Passed down the stem to stimulate elongation / growth
Then, activates proteins in cell wall (expansins) which loosen bonds between cellulose microfibrils
Therefore, flexibility increases, so more elongation

Question 20

Phototropism mechanism pic

Answer 20

Question 21

Negative vs positive geotropism

Answer 21

Neg = shoots grow away from gravity
(Auxin accumulates on the lower side of the shoot, therefore grows upwards) This
Pos = roots grow towards gravity
In roots = higher IAA conc, so lower rate of elongation, as IAA accumulates at the lower side, therefore inhibiting cell elongation, so the lower side grows slower, so the root bends dowm

Question 22

Investigating geotropism

Answer 22

Question 23

What do deciduous plants do in very hot & dry conditions

Answer 23

Lose leaves to reduce water loss

Question 24

What do deciduous plants do in winter

Answer 24

Lose leaves as water absorption is difficult due to frozen soils
Leaves shedded due to photosynthesis being limited by low temperatures and reduced light

Question 25

What role does ethene play in leaf loss

Answer 25

Stimulates the breakdown of cell walls in the abscission layer, causing the leaf to drop of

Question 26

What role does auxin / IAA play in leaf loss

Answer 26

Inhibit leaf loss & are produced in young leaves, making the leaves insensitive to ethene temporarily The conc of IAA decreases as leaves age until leaf loss can occur

Question 27

Main hormone that plays a role in stomatal closure?

Answer 27

ABA Abscisic Acid

Question 28

Examples of water stress

Answer 28

High temperature Reduced water supplies

Question 29

What happens in times of water stress

Answer 29

ABA produced by plants to stimulate stomata closing

Question 30

How does ABA work e.g. what does it bind to etc

Answer 30

- guard cells have ABA receptors on their cell surface membrane ABA binds with these receptors, inhibiting the proton pumps & therefore stopping the active transport of H+ out of guard cells - ABA also causes Ca2+ ions to move into the cytoplasm of the guard cells, through the cell surface membrane

Question 31

How do Ca2+ ions act as a chemical messenger to lead to stomatal closure

Answer 31

1. Causes channel proteins to open, that allow negatively charged ions to leave the guard cells -> this stimulates the opening of further channel proteins that allow K+ to leave the guard cells 2. Loss of ions = Increased W.P. Of guard cells, therefore water leaves via osmosis Therefore Guard cells become flaccid: stomata close

Question 32

Role of gibberellins

Answer 32

- Control seed germination - promotes fruit development - promotes activity of amylase Can also play a role in stem elongation

Question 33

When the seed is shed from a parent plant is it active or inactive

Answer 33

- state of dormancy (metabolically inactive): little water And can survive harsh weather

Question 34

What does the seed contain

Answer 34

Endosperm (a starch containing energy store) Embryo (which grows to the new plant when the seed germinates) Aleurone layer (outer, protein rich layer)

Question 35

What does the seed contain

Answer 35

Endosperm (a starch containing energy store) Embryo (which grows to the new plant when the seed germinates) Aleurone layer (outer, protein rich layer)

Question 36

H2O absorbed = germination begins. This stimulates the embryo to produce what hormone

Answer 36

Gibberellins

Question 37

H2O absorbed = germination begins. This stimulates the embryo to produce what hormone

Answer 37

Gibberellins

Question 38

How do gibberellins molecules lead to amylase action

Answer 38

Gibberellins diffuses into the aleurone layer & stimulates the cells to synthesise amylase

Question 39

How does amylase work to transport / give the embryo glucose

Answer 39

Amylase hydrolyses starch Therefore soluble maltose produced Maltose hydrolysed into glucose Glucose transported to embryo

Question 40

What breaks dormancy of the embryo

Answer 40

When the embryo respires the glucose given after amylase action

Question 41

How does apical dominance happen

Answer 41

Question 42

Commercial uses of plant hormones

Answer 42

- control ripening - fruitless seed production - hormone rooting powder - hormonal weed killers

Question 43

Other things specific hormones do Ethene, auxin, cytokinins, gibberellins

Answer 43

Question 44

How does ethene control ripening

Answer 44

Question 45

How do auxins act as hormone root powders

Answer 45

Question 46

How do synthetic auxins act as hormonal weed killers

Answer 46

Question 47

Evidence for gibberellins role in germination and stem elongation

Answer 47

Question 48

How would you investigate diff / conc plant hormone on growth

Answer 48

Use diff hormone Use serial dilutions

Question 49

How to investigate diff conc levels of hormone effect on plant

Answer 49

Question 50

Factors to control when investigating plant hormone action

Answer 50

Volume of water Light intensity Temperature Humidity Ideally = genetically identical plants and cuttings to ensure they response the same way

Question 51

Normal action of IAA in cells (ms answer)

Answer 51

Stimulates cell elongation & division

Question 52

How can herbicides kill plants

Answer 52

By disabling proton pumps in a photosystem -> reducing proton pumping & therefore chemiosmosis -> photophosphorylation stops -> less ATP produced -> less NADP produced -> no Calvin cycle stage -> no TP/hexose sugars made

Question 53

Answer 53