3.3.6 adaptations of plants to availability of water

Question 1

hydrophyte

Answer 1

plant adapted to living in water or where ground’s very wet

Question 2

xerophyte

Answer 2

plant adapted to living in dry conditions

Question 3

what 2 things must plants living on land be adapted to

Answer 3

• reduce loss of water (via stomata - esp. in day)
• replace lost water

Question 4

structural/behavioural adaptations of most terrestrial plants to reduce water loss

Answer 4

• waxy cuticle on leaf = reduce water loss due to evaporation through epidermis
• stomata often found on under-surface of leaf = reduces evaporation from direct sunlight/heat
• most stomata closed at night (no light for photosynthesis)
• deciduous plants lose leaves in winter when ground may be frozen & temps. too low for photosynthesis

Question 5

characteristics of environment of marram grass (ammophila)

Answer 5

• sand dunes
• conditions harsh as any water in sand drains quickly
• sand may be too salty
• leaves often exposed to very windy conditions

Question 6

what are marram grass & cacti examples of

Answer 6

an xerophyte

Question 7

adaptations of marram grass

Answer 7

• leaf rolled longitudinally so air trapped inside & becomes humid = reduces water loss –> can roll more tightly when very dry conditions
• thick waxy cuticle on outer side of rolled leaf (upper epidermis) = reduces evaporation
• stomata on inner side of rolled leaf (lower epidermis) = protected by enclosed air spaces
• stomata in pits in lower epidermis which is folded & covered by trichome hairs = reduce air movement & thus, loss of water vapour
• spongy mesophyll very dense w/ few air spaces = less SA for evaporation

Question 8

adaptations of cacti

Answer 8

• succulents = store water in stems which become fleshy & swollen
  –> stem often ribbed/fluted = expand when water available
• leaves reduced to spines = reduces SA meaning less water lost by transpiration
• stem is green for photosynthesis
• roots widespread = take advantage of any rain fall

Question 9

other xerophytic adaptations/features (not found in marram grass & cacti)

Answer 9

• closing stomata when water availability low = reduce water loss & reduce need for water
• some plants have low water potential inside leaf cells –> achieved by maintaining high salt conc. in cells
  –> low water potential = reduces evaporation from cell surfaces as water potential gradient between cells & leaf air spaces reduced
• very long tap root = reach deep/underground water

Question 10

example of hydrophyte

Answer 10

water lillies

Question 11

adaptations of water lily

Answer 11

• many large air spaces in leaf = keeps leaves afloat so in air & can absorb sunlight
• stomata on upper epidermis = exposed to air allowing gaseous exchange
• leaf stem has many large air spaces = helps buoyancy & allows oxygen to diffuse quickly into roots for aerobic respiration

Question 12

what are hydathodes

Answer 12

= many plants contain specialised structures at tips/margins of leaves to support transpiration
- can release water droplets which may evaporate from leaf surface

–> transpiration won’t occur in environments with very high humidity = transpiration stream stops & mineral ions aren’t transported to the leaves