9.5 Plant Adaptations to Water Availability

Question 1

When plants open their stomata, they compromise between ____ & ____.

Answer 1

water conservation

gas exchange

Question 2

What are xerophytes?

Answer 2

Plants which are ADAPTED

to surviving in LOW WATER environments

(maintain gas exchange whilst conserving water)

Question 3

What are hydrophytes?

Answer 3

Plants which are ADAPTED

to surviving in VERY WET environments

(maximise gas exchange without worrying about water conservation)

Question 4

What are the adaptations of xerophytes?

Answer 4

• THICK WAXY CUTICLE
• SUNKEN STOMATA
• LESS STOMATA

• (leaf adaptations)
◦ REDUCED/HAIRY/CURLED

• LEAF LOSS

• (root adaptations)
◦ DEEP/WIDESPREAD + SHALLOW

• STORAGE ORGANS

Question 5

Explain why xerophytes have a thick waxy cuticle:

Answer 5

decreases evaporation

∴ decreases water lost by transpiration

(conserving water)

Question 6

Explain why xerophytes have sunken stomata:

Answer 6

stomata located in area of still, humid air

decreases water potential gradient

∴ decreases water lost by transpiration

Question 7

Explain why xerophytes have less stomata:

Answer 7

less openings for steam to leave leaf

reduces water lost by transpiration

(but also reduces gas exchange)

Question 8

Describe + explain the leaf adaptations of xerophytes:

Answer 8

• REDUCED leaves:
◦ less stomata + surface area
- less evaporation

• HAIRY leaves:
◦ traps water droplets close to surface
- decreases water potential gradient

• CURLED leaves:
◦ traps humid air + reduces air exposure
- decreases water potential gradient

(link all back to less water lost by transpiration)

Question 9

How are succulents adapted as xerophytes?

Answer 9

Specialised parenchyma in stems/roots

allows storage of water

Question 10

Explain why xerophytes lose their leaves when water supply is low:

Answer 10

less leaves = less stomata + SA for evaporation

less water lost by transpiration

Question 11

Describe + explain the root adaptations of xerophytes:

Answer 11

• DEEP roots
◦ access water deep underground

• WIDESPREAD, SHALLOW roots
◦ large SA for absorbing rainwater

Question 12

What are the adaptations of hydrophytes?

Answer 12

• THIN/NO WAXY CUTICLE
• MANY ALWAYS OPEN STOMATA ON UPPER EPIDERMIS
• REDUCED SUPPORT
• WIDE, FLAT LEAVES
• SMALL ROOTS
• LARGE SA OF STEMS + ROOTS
• AERENCHYMA

Question 13

Explain why hydrophytes have a thin/no waxy cuticle:

Answer 13

more water lost by evaporation + transpiration out of stomata

(water conservation by reducing transpiration is not an issue)

Question 14

Explain why hydrophytes have many stomata, which are always open, on the upper epidermis:

Answer 14

maximises gas exchange + water lost by transpiration

Question 15

Explain why hydrophytes have reduced supporting structures:

Answer 15

water provides support for plant

no need for adapted stems for support

Question 16

Explain why hydrophytes have wide, flat leaves:

Answer 16

provides large SA:volume

increases water lost by evaporation + transpiration

captures more light

Question 17

Explain why hydrophytes have small/short roots:

Answer 17

water + mineral ions can diffuse directly into plant cells to meet demand

Question 18

Explain why hydrophytes have submerged roots + stems of large surface area:

Answer 18

maximises diffusion of oxygen in water.

Question 19

Explain why hydrophytes have aerenchyma:

Answer 19

increases BUOYANCY

provides LOW RESISTANCE internal pathway for oxygen diffusion into plant

(aerenchyma is tissue containing air sacs, found in stems + roots)

Question 20

What is aerenchyma and in which type of plant is it found in?

Answer 20

tissue containing air sacs,

found in stems + roots of hydrophytes.

Question 21

The adaptations of xerophytes focus on ____

Answer 21

conserving water

Question 22

The adaptations of hydrophytes focus on ____

Answer 22

maximising gas exchange