Plant Responses

Question 1

Apparatus used to nullify the effects of gravity or unidirectional light

Answer 1

Clinostat

Question 2

Mechanical defences against herbivores

Answer 2

• Thorns and prickles
• Thorns housing mutualistic bacteria that cause gangrene in herbivores
• Galls housing mutualistic ants that release chemicals that burn herbivores’ lips/ snouts

Question 3

Function of Abscisic Acid

Answer 3

• Protects plants during stress periods (e.g. drought, winter)
• Promotes leaf senescence
• Closes stomata

Question 4

Auxin response to gravity in roots is…

Answer 4

positive: it moves towards gravity, or downwards.

Question 5

Indolacetic Acid (IAA)

Answer 5

Example of auxin

Question 6

Initial response to infection

Answer 6

cells at site of infection die to create barrier around infection that stops spread of micro-organism

Question 7

phototropism

Answer 7

plant growth towards light

Question 8

Gibberellic Acid

Answer 8

Example of gibberellins

Question 9

Clinostat

Answer 9

Apparatus used to nullify the effects of gravity or unilateral light

Question 10

auxin is produced in…

Answer 10

apical meristem (tips of roots and shoots)

Question 11

plant growth towards gravity

Answer 11

Gravitropism (geotropism)

Question 12

response to night time (closing up of leaves or flowers)

Answer 12

nastic movement

Question 13

If the tip of a plant is removed…

Answer 13

it will grow broader, but not taller (makes a hedge)

Question 14

Auxin response to light in shoots is…

Answer 14

negative: it is destroyed by light, or moves away from light.

Question 15

Functions of auxin

Answer 15

• promotes apical dominance
• cell elongation and enlargement resulting in phototropism in shoots
• inhibition of cell growth resulting in geotropism in roots
• prevents leaf senescence
• delays fruit ripening

Question 16

Example of auxin

Answer 16

Indolacetic Acid (IAA)

Question 17

nastic movement

Answer 17

response to night time (closing up of leaves or flowers)

Question 18

Commercial uses for auxins

Answer 18

• Causing cuttings to root
• induce flowering
• induce fruit setting (creating seedless fruits)
• herbicides (weed killers)

Question 19

Systemic Acquired Resistance

Answer 19

Production of Salicylic Acid at site of infection which travels to rest of plant in inactive form to make rest of plant resistant to infection

Question 20

plant growth towards light

Answer 20

phototropism

Question 21

geotropism

Answer 21

plant growth towards gravity

Question 22

Example of gibberellins

Answer 22

Gibberellic Acid

Question 23

Sequence the events resulting in phototropism

Answer 23

1. Auxins produced in apical meristem.
2. They move away from light to dark side of shoot.
3. Auxins cause cell elongation in cells on dark side.
4. Uneven growth between light and dark sides causes shoot to bend towards the shorter, light side.
5. Plant grows towards the light source.

Question 24

Plants’ first line of defence to prevent infection

Answer 24

• Waxy cuticle
• Lignin
• Sticky gum that seals wounds

Question 25

Sequence the events resulting in geotropism

Answer 25

1. Auxins produced in apical meristem.
2. They move towards gravity, to the lower side of the root.
3. Auxins inhibit cell elongation in cells on lower side.
4. Uneven growth between upper and lowers sides causes root to bend towards the shorter, lower side.
5. Roots grow down, towards gravity.

Question 26

‘Stress’ chemicals produced that make plants unpalatable to herbivores

Answer 26

• tannins
• alkaloids
• essential oils (e.g. menthol in lemons) u
• rushiol (the ‘poison’ in Poison Ivy)
• glycosides in foxgloves

Question 27

Function of gibberellins

Answer 27

• increase internode length
• promotes seed germination
• promotes fruit setting