Chapter 16 - Plant responses

Question 1

What is tropism?

Answer 1

A plants response to abiotic factors

Question 2

What are some roles of auxin?

Answer 2

Control of cell elongation, preventing abscission, apical dominance and stimulates ethene release

Question 3

What are some roles of gibberellins?

Answer 3

Causes stem elongation, stimulates pollen growth and triggers mobilisation of food stores in germination

Question 4

What are some roles of ethene?

Answer 4

Causes fruit ripening and promotes abscission (in deciduous trees)

Question 5

What are some roles of ABA?

Answer 5

Maintains dormancy, stimulates protective responses and stimulates stomatal closing

Question 6

What is the process of seed germination?

Answer 6

• Absorbed water activates the embryo and gibberellins are produced
• Digestive enzymes are stimulated to break down food stores
• Food stores used to produce ATP so the plant can break through the seed coat

Question 7

Experimental evidence of gibberellins role in germination:

Answer 7

• Biosynthesis inhibitors stop germination, if gibberellins reapplied, germination continues
• Mutant seeds without gibberellins don’t germinate unless external gibberellins are applied

Question 8

What is apical dominance?

Answer 8

The apical bud on the tip of the plant stem has dominance over other lateral buds on the stem, if apical bud is removed, the lateral buds have a higher yield of auxin than before which allows them to grow more

Question 9

What is effected by high concentrations of auxin?

Answer 9

• Lateral shoots become suppressed to growth, leading to apical dominance
• Inhibitory of root growth

Question 10

What is effected by low concentrations of auxin?

Answer 10

Promoted root growth (unless apical bud is removed)

Question 11

What effect do gibberellins have on plant stems?

Answer 11

Allow stems to grow at increased rates in darkness and stem elongation by increasing the length of internodes

Question 12

What effect does auxin have on plant stems?

Answer 12

Auxin effects the growth of the apical shoot and the direction of growth

Question 13

What is synergism?

Answer 13

When multiple plant hormones act together to create a greater response

Question 14

What is antagonism?

Answer 14

The balance between two hormones that have opposite effects

Question 15

What is the process of abscission?

Answer 15

• As light levels decrease, auxin concentration decrease
• Lower auxin conc. produce ethene that initiates gene switching in abscission zone
• Vascular bundles sealed off and fatty acid is deposited in cells of the separation layer (protective layer)
• Low temperature and strong winds finish the process (strain breaks off the leaf)

Question 16

How do plants prevent themselves from freezing?

Answer 16

Roots store salt, sugar and antifreeze proteins which prevent the cells from becoming frigid in colder temperatures

Question 17

How are the stomata controlled by the plant?

Answer 17

• ABA controls stomata under abiotic stress
• Root cells detect low water availability and release ABA
• ABA is transported to the leaves, causing guard cells to become turgor and close over the stomata, preventing water loss

Question 18

What are the three main responses to herbivory?

Answer 18

Physical, chemical and pheromones

Question 19

What are the chemical responses of herbivory?

Answer 19

Tannins -
Alkaloids -
Terpenoids -

Question 20

What are pheromones?

Answer 20

Chemicals made by an organism which affects the social behaviour of other members within the species or be used to defend the organism

Question 21

What is phototrpism?

Answer 21

A plants response to light (eg. by bending towards it)

Question 22

What is photoperiodism?

Answer 22

• A plants sensitivity to a lack of light, triggering change
• Plants have light sensitive pigments called phytocrhromes (Pr and Pfr) which alter depending on light levels

Question 23

What is thigmotropism?

Answer 23

A plants physical response to touch (eg. leaves curling up)

Question 24

What is geotropism?

Answer 24

A plants physical response to gravity (eg. roots growing downwards)

Question 25

Where is auxin produced?

Answer 25

In the tips of roots and shoots

Question 26

What happens to plant shoots that are kept in the dark?

Answer 26

Plants rapidly grow upwards to be able to reach light for photosynthesis (gibberellins allow for stem elongation of the internodes)

Question 27

What happens to plant shoots that are kept in unilateral light?

Answer 27

Auxins allow the shoot to grow in the direction of the light via geotropism, phototropism and cell elongation

Question 28

How can fruit ripening be controlled?

Answer 28

Gibberellins can be used to delay fruit ripening and ageing, allowing a larger size and different shapes of fruit

Question 29

What effect do hormone rooting powders have?

Answer 29

Artificial auxins when applied to cut shoots will stimulate the production of new roots (allows for easier propagation of new plants from cuttings)

Question 30

What if the effect of hormonal weedkillers?

Answer 30

Synthetic auxins that once absorbed effect the metabolism of plants, rapidly increasing their growth rate so it’s unsustainable, causing the plant to die

Question 31

What are some other uses of plant hormones?

Answer 31

Auxins - used in the production of seedless fruit
Ethene - used to promote fruit dropping
Cytokines - used to prevent the ageing of ripened fruit and control tissue development
Gibberellins - can be used to delay ripening and ageing in fruit (to improve size and shape of fruits/ speed up malting process)

Question 32

What is the role of ABA in germination?

Answer 32

Contradicts gibberellins to control when seeds germinate (imbalances hormones)

Question 33

What are VOC’s?

Answer 33

Pheromones that act between themselves and other organisms (usually insects)

Question 34

What are benefits to using hormonal weedkillers?

Answer 34

They are simple and cheap to produce, have very low toxicity to animals and are selective