Plant Responses

Question 1

What are the functions of Auxins? (6)

Answer 1

• Control cell elongation
• Prevent abscission
• Maintain apical dominance
• Involved in tropisms
• Stimulate the release of ethene
• Involved in fruit ripening

Question 2

What are the functions of Gibberellin? (3)

Answer 2

• Cause stem elongation
• Trigger the mobilisation of food stores at germination
• Stimulate pollen tube growth in fertilisation

Question 3

What are the functions of ethene? (2)

Answer 3

• Causes fruit ripening

- Promotes abscission in deciduous trees

Question 4

What are the functions of ABA (Abscisic Acid)? (3)

Answer 4

• Maintains dormancy of seeds and buds
• Stimulates cold protective responses e.g. antifreeze production
• Stimulates stomatal closing

Question 5

How do seeds germinate? (4)

Answer 5

1) Seeds absorb water
2) Embryo is activated and begins to produce gibberellins
3) Gibberellins stimulate the the production of enzymes (proteases and amylases)that break down food stores in the seed
4) It uses the food stores to produce ATP for building materials to grow and break out of the seed coat

Question 6

Where are the food stores in seeds? (2)

Answer 6

• In Cotyledons in dicot seeds

- In the Endosperm in monocot seeds

Question 7

How is ABA involved with seed germination? (2)

Answer 7

• Acts antagonistically to gibberellins

- Relative levels of gibberellins and ABA decide when the seed will germinate

Question 8

How do Auxins affect apical shoot growth? (7)

Answer 8

1) Auxins are synthesised in meristem cells
2) They diffuse away from the tip and bind to receptor cells
3) Vacuoles form and low pH develops
4) Low pH of cell walls keep them flexible, allowing cells to expand as they absorb water
5) Vacuoles get bigger and cell walls stretch
6) Large central vacuole forms and auxins are destroyed by enzymes
7) Cell walls become rigid and no further cell elongation is possible

Question 9

What is the effect of high concentrations of auxin? (3)

Answer 9

• Supress the growth of lateral shoots b y inhibiting the lateral shoots
• Further down the plant, there is less auxins so there is more lateral growth
• Inhibit root growth

Question 10

What is the effect of low concentrations of auxin? (3)

Answer 10

• Promote root growth - the more auxins that reach the roots, the more they grow
• Auxins produces at root tips and and reaches roots in low concentrations from the growing shoots
• If apical shoot is removed, reduces amount of auxin that reaches the root - root growth slows and stops

Question 11

How do gibberellins affect stem elongation?

Answer 11

Affect the length of the internodes (regions between leaves on a stem)

Question 12

What is meant by synergism?

Answer 12

When hormones compliment each other and giving off a greater response than they would on their own

Question 13

What is meant by antagonism?

Answer 13

When hormones have opposite effects and the balance between them will determine the plant’s response

Question 14

What is meant by tropism?

Answer 14

A growth respone by a plant in response to a unidirectional stimulus

Question 15

What are some examples of abiotic stresses? (5)

Answer 15

• Change in day length
• Temperature
• Water availability
• Wind
• Salinity

Question 16

Why are plants sensitive to seasons? (3)

Answer 16

• Drop in temperature
• Less light during the day
• Less daylight hours

Question 17

How do trees leaves fall (abscission) in the winter? (8)

Answer 17

• Falling light levels mean falling concentrations of auxin
• Plant responds to falling auxin by producing ethene
• At the base of a leaf there is the abscission zone where there are two cell layers sensitive to ethene
• Ethene initiates genes switching and so produces new enzymes
• Those enzymes digest the cell walls in the outer layer of the abscission zone
• Vascular bundles are sealed off and fatty material is deposited on the stem side of the separation layer
• Cells in separation layer respond to hormonal cues and cause strain on the outer layer by retaining water and swelling
• Leaf falls off eventually due to being weakened and abiotic factors and a waterproof scar is left behind

Question 18

How do plants prevent freezing? (3)

Answer 18

• Cytoplasm and sap in vacuoles contain solutes that lower the freezing point
• Some plants produce sugars, polysaccharides, amino acids and proteins that act as antifreeze to prevent freezing or prevent damage for if it does freeze
• Produce chemicals that make them hardy and frost resistant

Question 19

How does plants use their stomata to respond to water availability and heat? (

Answer 19

• Open the stomata when too hot to cool the plant

- Close when less water available to conserve water