VCE Biology Unit 2 Area of Study 01

							   VCE Biology Unit 2
    Area of Study 01
Adaptations of Organisms

          Chapter 13.3
  Living in extreme terrestrial
          environments
  Chapter 13.3 Living in extreme terrestrial
               environments
Desert
• Low rainfall
• High level of evaporation
• Hot (Australia, Sahara) or cold (Central Asia,
  South America, Antarctica)
Antarctica largest desert – 50 mm rain per year,
  14,245,000 km2
Sahara largest ‘hot’ desert 9,000,000 km2
  Chapter 13.3 Living in extreme terrestrial
               environments
Australia has greatest percentage of continent
  as desert/semi-arid (44% and 37%
  respectively)
• High temperature
• High solar radiation
• Low rainfall
  Chapter 13.3 Living in extreme terrestrial
               environments
Animals
  Stress
  – Body temperature
  – H2O
  – Salt balance
  Chapter 13.3 Living in extreme terrestrial
               environments
Survival
• Regulate these factors or tolerate extreme
  fluctuations
 Chapter 13.3 Living in extreme terrestrial
              environments
Temperature regulation assisted by
• Behaviour that increases or decreases heat
  exchange with external environment.
• Circulatory adjustments alter blood flow
  through skin – alters heat exchange
• Increase or decrease production of metabolic
  heat.
• Evaporative cooling through sweating or
  panting (trade off with water loss)
  Chapter 13.3 Living in extreme terrestrial
               environments
Reptiles
• Behaviour changes most important to regulate
  rate of heat exchange

Behavioural Thermoregulation
• e.g. Australian agamid lizard, Shark Bay, WA
 Chapter 13.3 Living in extreme terrestrial
              environments
• Some iguanid lizards maintain body
  temperature at ~38°C for extended periods.
• Desert snakes and tortoises maintain body
  temperature at ~30°C adopt nocturnal
  behaviour during summer
  Chapter 13.3 Living in extreme terrestrial
               environments
Sleep through bad times
Some animals survive harsh conditions by going
  into torpor or hibernation. Torpor (fish, frogs,
  lizards, birds, bats and mice) allow body
  temperature to decrease and become inactive
  or dormant.
  Chapter 13.3 Living in extreme terrestrial
               environments
Frogs burrow into sand during dry season and
  become dormant
Water holding frog burrows deep into sand and
  makes a cocoon from its cast off skin and can
  survive for months.
 Chapter 13.3 Living in extreme terrestrial
              environments
Escaping the cold – hibernation
Do any Australian animals hibernate?
Short beaked echidna goes into torpor
  underground to escape winter/snow in
  southern mountains.
  Chapter 13.3 Living in extreme terrestrial
               environments
Hibernation
• Long term torpor
• Happens at onset of winter
• In den/burrow
• Decrease energy requirements (do not eat)
• Hibernation saves 60% of an animal’s annual
  energy requirement
• Some evidence suggest animals may live longer.
 Chapter 13.3 Living in extreme terrestrial
              environments
Triggers for Hibernation. One of more factors
• Scarcity of food
• Decrease in temperature
• Endocrine response to change in daily light
  cycle.
• Mammals and birds enter hibernation from
  sleep and involve decrease of body
  temperature close to ambient, but never
  below zero
  Chapter 13.3 Living in extreme terrestrial
               environments
Triggers for Hibernation. One of more factors
• Burrows/dens temperature constant
• Metabolism decreased (indicated by decrease in
   O2 consumption – leads to fall in body
   temperature
• Heart rate decreases to around 3 to 10 beats per
   minute
• Respiration decrease
• Slow breathing with long periods of no breathing
 Chapter 13.3 Living in extreme terrestrial
              environments
Plants in arid environments
Adaptations for reducing water loss
• Xenophytes (‘lovers of dryness’)
• Two types
  – Flesh succulent plants (e.g. cacti)
  – Hard-leaved plants called sclerophylls
  Chapter 13.3 Living in extreme terrestrial
               environments
Adaptations for reducing water loss
• Thick waxy cuticle
• Hairs covering leaves
• Few stomata
• Sunken or protected stomata
• Reduced leaf surface area to volume
• Orientation of leaves away from direct rays of
  sun
 Chapter 13.3 Living in extreme terrestrial
              environments
Leaf cuticle and hairs
• Xerophytes have thick waxy cuticle
  impermeable to water
• Hairs reduce leaf temperature and water loss
 Chapter 13.3 Living in extreme terrestrial
              environments
Distribution of Stomata
• Fewer stomata. Number and size varies
  between species.
• Pits surrounded by hairs
• Maybe closed at hottest time of day
• Succulents close stomata at day and open at
  night for uptake of CO2
  Chapter 13.3 Living in extreme terrestrial
               environments
Reduced surface area and leaf orientation
• Surface area low to reduce water loss by
  transpiration
• Some species have needle like leaves (e.g.
  Hakea and cacti)
• Eucalypts’ leaves hang vertically. Stomata and
  photosynthetic cells on both sides of leaves
  (i.e. isobilateral).
  Chapter 13.3 Living in extreme terrestrial
               environments
Coping with salinity on land
• [Salt] can be 1/10 of sea water. Combined
  with high temperatures and low rain fall.
• Creates osmotic stress due to lack of water
  Chapter 13.3 Living in extreme terrestrial
               environments
Halophyte adaptations
• Halophytes (‘lovers of salt’) tolerant to high
  levels of salt and many are succulents
• Regulate water loss and salt accumulation in
  leaves from transpiration of water from roots.