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Question 1

Moisture stress

Answer 1

1) Escape water stress: Annual plants, short life cycle so tolerant to no water
2) Water stress avoiders: e.g. succulent cacti
3) Water stress tolerators: e.g. S. lepidophylla ‘resurrection plants’

Question 2

Osmoregulation stress results in accumulation of active substances:

Answer 2

1) Non-structural sugars (carbohydrates)
2) Stress metabolites (accumulate in cytoplasm)
3) Proline (from synthesis of glutamate or hydrolysis of proteins)
4) Heat shock proteins
5) Aquaporins:

Question 3

aquaporins

Answer 3

o high diversity, small, uncharged, water channel proteins
o Have 6 transmembrane domains and NPA signature residues for water translocation
o They modulate cell membrane permeability and are sensitive to water status
o E.g. Nod26-like proteins in root water uptake
o Highly regulated (assembly of subunits in ER, Golgi modifications, vesicle trafficking, endocytosis for polar distribution)

Question 4

EXAMPLE: Poikilohydric xerophytes

ressurection plant

Answer 4

o Lose water rapidly in dry season and survive in state of desiccation
o Shed leaves to lose less water
o Some can survive 250 years of drought
o Most are in south Africa

Question 5

EXAMPLE: Homoiohydric xerophytes

Answer 5

o Soft leaves species which are in semi-desert conditions
o Shed leaves in drought e.g. Lavender
o OR hard leaved species which reduce their transpiring surface area during drought periods, have extensive and deep root system (Araucaria Araucana)

Question 6

EXAMPLE: Succulent xerophytes

Answer 6

o Water-storing species
o Crassulacean acid metabolism (CAM): alternative metabolism to cope with evaporation.
o Shallow rooted, sometimes lack roots or regenerate following dry period
o Some can be buried in ground to stop water output with no leaves (just a stem)
o Reduced leave structures and large stems to store water
o Reduced stomata, thick epidermis, stomata immerged to create local humidity (anatomical adaptations)
o Stomatal hairs to create local humidity
o Thick waxy cuticle = more waterproof, impermeable to water = less evaporation

Question 7

 Water reserves in amphibians

Answer 7

1) Water reserved in bladder or as subcutaneous water (applied/absorbed under skin)
2) Can burrow
3) No definite breeding seasons
4) Nocturnal activity

Question 8

 Lizards

Answer 8

1) Use burrows from other animals
2) Water storage:
o Fatty tissue in tails to hold water
o Accessory lymph spaces along abdominal folds to head region
o More water in blood

Question 9

 Mammals

Answer 9

• Extreme adaptation = water integral to activity = loss of 15-20% water= fatal
  1) 2/3 water by weight
  2) Water loss lower in arid dwellers (live underground)