Chapter 16 - Plant Responses

Question 1

What is abiotic stress?

Answer 1

Non-living environmental factor that could harm a plant (e.g. mineral deficiency, drought, etc.)

Question 2

what are auxins responsible for?

Answer 2

tropsims, leaf fall (abscission) prevention, stimulating ethene production, cell elongation, and maintaining apical dominance.

Question 3

what do giberrellins do?

Answer 3

• Cause food stores to become mobile during germination
• stem elongation
• causes pollen tube growth for fertilisation

Question 4

what does ethene do?

Answer 4

• ripens fruits

- promotes leaf fall (abscission)

Question 5

What does ABA (abscisic acid) do?

Answer 5

• maintains seed dormancy
• stimulates stomatal closure
• initiates protective responses against cold (antifreeze)

Question 6

What is geotropism?

Answer 6

the tropism response to gravity - shoots are negative, roots are positive

Question 7

What is phototropism?

Answer 7

the tropism response to unilateral light - shoots are positive, roots are negative

Question 8

What is thigmotropism?

Answer 8

the tropsim response to pressure

Question 9

What is hydrotropism?

Answer 9

the tropism response to water

Question 10

What are the commercial uses of giberellins?

Answer 10

delay ripening of fruit

Question 11

What are the commercial uses of auxins?

Answer 11

• producing seedless fruit

- weedkiller

Question 12

What are the commercial uses of ethene?

Answer 12

ripening fruit quickly

Question 13

What are the commercial uses of cytokines?

Answer 13

prevent the ageing of ripened fruit

Question 14

What is Abscission?

Answer 14

leaf drop, as a result of ethene responding to an abscission zone, which uses enzymes to weaken the cell walls - caused by long periods of darkness.

Question 15

How do plants prevent themselves from freezing?

Answer 15

• Certain chemicals (

Question 16

What is a tropism?

Answer 16

A directional growth response of plants

Question 17

Why do shoots so positive phototropism?

Answer 17

• auxin diffuses to the shaded side of the shoot tip
• as it does this, it stimulates H+ ions to move into cell wall via active transport
• Disruption to H-bonds makes cell more permeable
• Cells on shaded side elongate due to higher turgor pressure
• shoot elongates on shaded side, causing plant to bend towards the light.

Question 18

How do hormones stimulate stomata to close?

Answer 18

• ABA binds to comp. receptors on guard cell membrane, causing Ca2+ ion channels on tonoplast to open - Ca2+ ions diffuse from vacuole.
• positive feedback causes other channels to open
• solute gradient increases, so water potential outside of cell decreases
• water diffuses out by osmosis
• guard cells get flaccid and close.

Question 19

What is apical dominance?

Answer 19

Occurs during growth of apical shoot, where lateral shoots do not grow (caused by action of auxins, ABA and cytokinins.