9.5 - Plant Adaptations to Water Availability

Question 1

Define xerophyte and give examples.

Answer 1

Plants with adaptations that enable them to survive in dry habitats with short environmental water supply. Cacti, Marram Grass

Question 2

With regards to leaves, what adaptations do xerophytes have?

Answer 2

Reduced Leaves - Reduces SA:V ratio, minimises transpiration water loss. E.g. thin needles in conifers

Hairy Leaves - e.g. spine of cacti, creates microclimate of humid air, reducing water vapour potential gradient. -

Curled Leaves - Confines stomata to microclimate of still humid air. e.g. Marram grass

Leaf Loss - when water isn’t available, some plants shed leaves to prevent water loss

Question 3

With regards to stomata, what adaptations do xerophytes have?

Answer 3

Sunken Stomata - stomata located in pits, reduce air movement, produces microclimate of humid air

• reduces water vapour potential gradient - e.g. in cacti, marram grass,

Reduced Stomata N^o - reduces water loss by transpiration, but also reduces gas exchange capabilities.

Question 4

What root adaptations do xerophytes have?

Answer 4

• Long tap roots, grow deep into soil to access water
• Widespread shallow roots
  
  • large surface area to absorb any water e.g. cacti roots grow 12-18m
• Marram grass roots - grow vertically down, have a mat of horizontal rhizomes (modified stems) - roots develop from them

Question 5

What other adaptations do xerophytes have?

Answer 5

Thick Waxy Cuticle - 10% of water loss in plants attributed to cuticle by transpiration, thick cuticle prevents and minimises this

Succulents - store water in specialised parenchyma tissue in stems and roots

• they are swollen (thick flesh), store water for times of drought (e.g. Aloe plants)
• Some plants lose leaves and become dormant
• Some die and let new seeds germinate
• Some survive as storage organs (bulbs, tubers)

Question 6

Define hydrophyte and give an example.

Answer 6

Plants adapted to survive in wet habitats, submerged or on surface of water E.g. water lillies

Question 7

What issues do hydrophytes face even though they have an abundant supply of water?

Answer 7

Water-logging air spaces in plants, air spaces must have air

Question 8

What are adaptations of hydrophytes?

Answer 8

Reduced Plant Structure - water provides buoyancy for leaves and flowers

Wide Flat Leaves - e.g. water lilly, spread across surface to capture light small roots - water diffuses directly so no need for sole water uptake via a root

Thin/No Waxy Cuticle - don’t need to conserve water as water lost by transpiration is always replaced

Air Sacs - enables leaves to float

Large Stem/Roots - for underwater plants, maximises area for photosynthesis and oxygen diffusion

Question 9

What are the stomatal adaptations of a hydrophyte?

Answer 9

Always Open Stomata

• on upper surfaces, maximised gas exchange, no risk of loss of turgor as water is always there
• guard cells inactive
• on water surface plants stomata must be on upper surface for gas exchange