16.2 Plant Responses to Abiotic Stress

Question 1

What are examples of abiotic stresses which plants experience?

Answer 1

• lack of water/excess water
• lack of light
• suboptimal temperature
• suboptimal soil pH

Question 2

What is photoperiodism & what changes in a plant is it responsible for?

Answer 2

photoperiodism = plant’s sensitivity to lack of light in environment

responsible for:

• leaf bud dormancy
• timing of flowering
• tuber formation

Question 3

How does abscission help a plant to survive?

Answer 3

during winter, light intensity decreases

cost of glucose (to maintain leaves & produce antifreeze) > glucose produced by photosynthesis

∴ loses leaves to conserve glucose.

leaves regrow when photosynthesis becomes efficient

Question 4

How do plants prevent freezing?

Answer 4

after long periods of no light,

plants actively transport salts ⟶ vacuole + cytoplasm

lowers melting point, preventing freezing.

Question 5

Why can most plants not survive sudden frost despite having anti-freezing measures?

Answer 5

during sudden frost, plants cannot prepare by actively transporting salts into vacuole to lower melting point

∴ water freezes & expands,

increasing turgour pressure & causing cell to burst

Question 6

Describe the mechanism by which stomata close:

Answer 6

1. Roots detect abiotic stress - lack of water
2. ABA (abscissic acid) released ⟶ vascular system
3. Binds to receptor on guard cell
4. Triggers active transport of ions out of guard cell ⟶ surrounding solution
5. Water moves out of guard cell by osmosis, down water potential gradient
6. Guard cells become flaccid & close

Question 7

Why must plants be able to respond to their surroundings?

Answer 7

• Survive in changing conditions
• Avoid abiotic stress
• Maximise photosynthesis
• Avoid herbivory