Plant Responses

Question 0

Ethene (commercially)

Answer 0

• promotes ripening

- pick unripe food & exported - ethene added at destination to ripen

Question 1

Gibberellin (commercially)

Answer 1

• promotes growth = larger+ sweeter grapes
• cause some citrus fruits to stay on the plant longer = bigger fruits
• longer stems = more sugar in sugar canes
• in beer stimulates barley grains to germinate = the fermentation of alcohol

Question 2

Auxins (commercially)

Answer 2

• prevents abscission - allowed to ripen
• seedless fruits
• stimulate root growth - vegetative propagation
• synthetic versions can be used as selective herbicides - kill broad leaved plants not grass like crops

Question 3

Leaf abscission (why?)

Answer 3

• leaves lost in winter
• reduce water loss
• prevent frost damage & fungal infections
• as not photosynthesising

Question 4

Leaf abscission (how?)

Answer 4

• drop in auxin production
• increased sensitivity to ethene
• increased production of ethene
• abscission layer at base of stalk grows
• layer hydrolyses and breaks off at the petiole
• another protective layer is formed

Question 5

Gibberellin

Answer 5

• can cause rapid growth of stems
• causes stems to get longer at the internodes
• dwarf varieties dont have the gene for GA - good more energy for seeds/crop less growth

Question 6

Internode

Answer 6

• lengths of stem between leaf stalks

Question 7

Evidence auxin concentration stops growth of side shoots

Answer 7

• if you cut the tips off 2 shoots & apply IAA to 1 - that 1 will show apical dominance
• the other side shoots will grow
• if plant is upside down - side shoots grow

Question 8

Evidence for apical dominance

Answer 8

• cut off the tip = growth of lateral buds as no apex

Question 9

Apical dominance

Answer 9

• the inhibition of the growth of lateral buds by the presence of an active apical meristem

Question 10

Phototropism (stages)

Answer 10

• phototropins become phosphorylated from light = sideways gradient
• sideways movement of auxin
• more auxin on shady side
• more auxin = more cell elongation
• grows towards the light

Question 11

How does auxin cause cell elongation

Answer 11

• build up of h+ ions
• activates an enzyme that breaks down the cell wall
• water enters by osmosis
• as shown in phototropism

Question 12

Apical meristem

Answer 12

• the region near the tip of a plant shoot where cells are constantly dividing

Question 13

Phototropins

Answer 13

• acts as a receptor for blue light
• are phosphorylated by blue light
• cause a gradient for phototropism

Question 14

Geotropism

Answer 14

• directional growth response to gravity

Question 15

Phototropism

Answer 15

Directional growth in response to light

Question 16

Tropisms

Answer 16

• a directional growth response in response to a stimuli

Question 17

Nastic movements

Answer 17

• a relatively rapid response of a plant to a stimulus - no direction
• ie petals closing down
• normally from changes in the turgor of specialised cells
• ie venus fly trap