Chapter 5: Plant Responses

Question 1

Outline three chemical defences in plants

Answer 1

• Alkaloids
• Tannins
• Pheromones

Question 2

What is abiotic stress? Give two examples

Answer 2

Stress from the abiotic factors in the environment - eg. Drought, day length

Question 3

How do Pheromones protect the plant from herbivory?

Answer 3

Signalling chemicals that will produce a response in other organisms

Question 4

How does Auxin work in the shoot of a plant?

Answer 4

• Avoids light
• Promotes cell elongation by activating proteins in the cell walls (expansins) to loosen bonds between cellulose microfibrils
• Shoot grows towards the light

Question 5

True or False: Plants are negatively phototropic

Answer 5

False

Question 6

How do plants prevent from freezing?

Answer 6

• Abscisic acid is released which stimulates the cold responses
• Sugars may act as anti-freeze protecting
• Cell sap and cytoplasm decrease their freezing point

Question 7

Suggest one commercial use of the plant hormone Gibberellins

Answer 7

• To delay ripening

Question 8

Why do deciduous plants lose their leaves in the winter?

Answer 8

The cold weakens the cell walls so abscission takes place to conserve ATP in the rest of the plant as the leaves require too much ATP

Question 9

Outline two functions of Abscisic acid in plants

Answer 9

• Stimulates cold protective responses
• Inhibits seed germination

Question 10

Suggest one commercial use for the plant hormone Cytokinins

Answer 10

• To prevent ripened fruit from aging

Question 11

How do Alkaloids protect the plant from herbivory?

Answer 11

They can contain nicotine, caffeine and poison

Question 12

Outline two functions of the plant hormone Ethene

Answer 12

• Fruit ripening
• Promotes production of cellulose which promotes leaf abscission

Question 13

Suggest and explain one commercial use of the plant hormone Ethene

Answer 13

• Ripen fruit: Ethene promotes fruit ripening and abscission of fruit/leaves

Question 14

How is the stomata controlled during water stress?

Answer 14

• Roots produce abscisic acid which bind to the guard cells
• Leads to the turgor decreasing and stomata closing

Question 15

How will root growth be affected if the tip is removed?

Answer 15

Auxin is synthesised in the tip and it inhibits cell elongation in the roots - roots will keep growing

Question 16

What are two limitations of the investigation were we investigate the effect of auxin on root growth?

Answer 16

• Despite being the same species, plants will have genetic differences eg. sensitivities to auxin
• Evenness of growth can be hard to determine - human error

Question 17

Outline two functions of Gibberellins in plants

Answer 17

• Stimulates cell division - cell elongation
• Promotes seed germination

Question 18

What is it known as when shoot grow in the opposite direction of gravity?

Answer 18

Negative geotropism

Question 19

Outline two functions of the plant hormone Cytokinins

Answer 19

• Promote bud growth
• Side shoot formation

Question 20

Outline three functions of the plant hormone Auxin

Answer 20

• Stimulates growth in shoots and inhibits growth in roots
• Promotes apical dominance
• Inhibits leaf abscission

Question 21

Suggest and explain three commercial uses of the plant hormone Auxin

Answer 21

• Selective weed killers: High concentrations cause the plant to grow too quickly, damaging tissues, exposing the plant to pathogens
• Rooting powders: Low concentrations can be used to stimulate growth from cuttings to produce new roots
• Producing seedless fruits

Question 22

Outline three physical defences in plants

Answer 22

• Thorns
• Spiny leaves
• Stings

Question 23

How do Tannins protect the plant from herbivory?

Answer 23

Bitter taste