Chapter 13.3 - VCE Biology Units 1 and 2

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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.
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