chapter 16 - plant hormones

Question 1

what are the roles of the hormone auxin?

Answer 1

• promote cell elongation
• abscission(prevent leaf fall)
• maintain apical dominance
• involved in tropisms
• stimulate the release of ethene
• involved in fruit ripening

Question 2

what are the roles of gibberellin?

Answer 2

• causes stem elongation
• stimulate the production of digestive enzymes to release glucose
• stimulate pollen tube growth in fertilisation
• germination

Question 3

what are the roles of ethene?

Answer 3

• causes fruit ripening
• promotes abscission in deciduous trees

Question 4

what are the roles of abscisic acid?

Answer 4

• maintains dormancy of seeds and buds
• stimulates cold protective responses, for example, antifreeze stimulates stomatal closing

Question 5

what is apical dominance and what hormone is involved?

Answer 5

• the hormone involved is auxin
• auxins produced by apical meristems, cells divide by mitosis. The apical bud is removed, auxin moves down the stem by diffusion, the lateral buds are promoted to grow, all the leaves receive sunlight for photosynthesis

Question 6

How does stem elongation work and what hormone is involved?

Answer 6

• the hormone involved is Gibberellin
• the higher the conc. of GA, the longer the internodes, the taller the plant is

Question 7

what is the purpose of stem elongation and apical dominance?

Answer 7

• so the plant is able to better compete for light

Question 8

what are examples of abiotic stresses?

Answer 8

• changes in daylight
• lack of water

Question 9

What is abscission and what is the purpose?

Answer 9

• abscission, stress response to light levels falling
• reduces energy needed to maintain leaves in winter
• fallen leaves insulate roots
• rotten leaves provide minerals in plants

Question 10

What is the process of abscission?

Answer 10

1 - phytochrome detect falling light levels
2 - auxin production falls
3 - ethene levels rise
4 - ethene activates genes to produce digestive enzymes
5 - enzymes digest the cell wall
6 - vascular bundles are sealed and the leaf falls

Question 11

How does the plant respond to a lack of water?

Answer 11

• closes the stomata

Question 12

Explain the process of the stomata closing

Answer 12

1 - roots detect a lack of water and produce ABA
2 - ABA travels to the leaves and binds to the receptors of guard cells
3 - ion channels incur a conformation change and ions leave the guard cells affecting the water potential gradient(more water in the guard cells)
4 - water leaves by osmosis
5 - guard cells become flaccid and close stomata

Question 13

What are the physical defences to herbivory?

Answer 13

• thorns
• spikes
• hairy leaves

Question 14

what are the chemical defences to herbivory and how do they prevent the plant from being eaten?

Answer 14

• Tannins, bitter taste and are toxic to insects
• Alkaloids, bitter taste and are poisonous to animals
• Terpenoids, toxic to insects and fungi
• Pheromones, affect the behaviour of other plants by signalling the potential of herbivory
• volatile organic compounds, same as pheromones but affect other species
• folding response in specifically the mimosa pudica

Question 15

What are tropisms and what are the types?

Answer 15

• Tropisms are plant responses to stimuli
• phototropism, response to light
• geotropism, responses to gravity

Question 16

How does a unilateral light source differ from a light source covering an entire plant?

Answer 16

1 - unilateral light causes auxin to move laterally in shoot tip to the shaded side
2 - higher auxin conc. on the shaded side
3 - High conc. promotes cell elongation on shaded side and so it grows faster
4 - shoot bends towards the light

Question 17

What are the benefits of positive phototropism?

Answer 17

• ensures maximum rate of photosynthesis

Question 18

If a plant is tilted what are the types of geotropism’s displayed by the roots and shoots and what is benefits of this?

Answer 18

• the shoots display negative geotropism and this ensures the shoots grow upwards for more light meaning more photosynthesis
• the roots display positive geotropism and this ensures the roots grow downwards to absorb water and minerals

Question 19

What are the commercial uses of plant hormones?

Answer 19

• Ethene is used in the production of ripe fruit for supermarkets
• Auxin is applied to cut shoots stimulating the production of roots
• Auxin is used as a weedkiller
• Auxin is used in the production of seedless fruits
• Ethene is used to promote fruit dropping
• cytokinins is used to prevent ageing of fruit