Transcript Environmental Interactions

Interactions with the
environment
• Organisms can exist within a range of
environmental conditions
• A change in the environment outside that
range causes stress
• Organisms must respond to stress to survive:
• Resist/ tolerate the change
• Regulate internal environment (maintain
homeostasis)/ adapt physiology
• Avoid change (migrate)
Examples of Environmental
Effects
• Temperature changes
– too cold
• membrane fluidity ceases,
• ice forms in cells rupturing membranes
• enzymes work too slowly
– too hot
• enzymes denature
• dessication occurs
– osmotic changes (salinity changes)
• water gain/ loss
Higher Biology
• Xerophytes – plants which live in arid
climates
• Hydrophytes – plants which live in water
• Mesophytes – plants which live between
these two extremes
•Xerophytic Adaptations to arid environments
Higher
Biology
•Thick waxy cuticle
•Sunken stomata
•Reversed stomatal rhythm
•Hairs
•Rolled Leaves
•TRAP MOIST AIR
•Spines/ needles as leaves, photosynthetic stems
•Storing water
•Extensive root system – maximum water uptake
•Rapid life cycle
•Collapsible stems
CAN DESSICATE WITHOUT DAMAGE
Animals in arid environments
Resistance
• The ability to prevent the external environment
from changing the internal conditions
• e.g. Limpets on seashore form a seal (scrape)
between themselves and the rock to resist
dessication
• e.g. Dog Whelk (Nucella lapis) close shell to
resist dessication
Tolerance
The ability to survive internal changes caused by
environmental fluctuation
e.g. Nucella lapis shell closure causes large
temperature change.
Tolerated – enzymes are not denatured by high
temperatures
e.g Nucella lapis shell closure leads to low
oxygen
Tolerated - anaerobic processes are used
RESIST/TOLERATE – short term solution
survive not thrive
Adaptation
• Alter physiology to allow survival
– e.g. reduced oxygen - pH falls (lactic acid)
– Horseshoe crab reduction in pH causes an increase
in affinity of oxygen carrying pigment (haemocyanin)
for oxygen
– e.g. Rising to altitude – low oxygen
– DPG secreted into blood to increase haemoglobin
affinity for oxygen
– Saturate at the lower oxygen levels found at altitude
• Get more oxygen out of the air!
• Long term solution
Regulation
• Evolve physiological mechanisms which
maintain a constant internal environment –
despite external changes
– e.g. Kangaroo rat – long loop of Henle (16X urine)
maintains electrolyte balance without loss of water
– e.g. Humans sweat for thermoregulation
• Long term solutions
Avoidance
• Barnacle Goose
– Migrate from Arctic Regions to Scotland to avoid cold
temperatures/ lack of food
• African Plains
– Herbivores migrate to follow rains (avoid dessication)
• Lungfish
– Buries in mud to prevent dessication
Life History – Variations allow survival
• Life History
– Growth & Development
– Reproduction
Reproduction
r-selected
K-selected
Development
rapid
slow
Competition
poor competitor
good competitor
Mortality
High
Constant,
Not density dep.
Density dep.
Adult size
small
large
Numbers of
offspring
many, small
few and large
Generation time
short
long
Evidence for r & K
• Dandelions (Taraxacum officinale):
•Character
– 4 genetic lines
A
BA
– Disturbed habitat
– (unpredictable)
•Time
of 1st flowering
– Undisturbed habitat
– (predictable)
73%
13%
C
DD
14%
0%
•1st year
2nd year
17%
11%
8%
64%
•Flowers per plant
•0.24 – 35.4
0.04- 27.7
•Seeds per flower
•~100
~200
•Mean weight of seed
•0.32mg
0.44mg
•Total numbers of seeds
•4-5 X D
Reproduction – K strategists
• K strategists –
– invest energy in adult, reproduce late
– need certainty of resource supply/ environment
– subject to intense competition/predation early in
life
– population size limited by carrying capacity
– populate climactic sera (final stable stage of
succession), habitats
Reproduction – r strategists
P
O
P
U
L
A
T
I
O
N
• r strategists
– invest energy in prolific reproduction
– can capitalise on unexpected and short term
resource gluts
– long term assurance not required
– colonisers of new habitats (succession), low cost
of reproduction, low competition
TIME
Growth & Development
• Many species separate growth from
development
– Enter a variety of stages in life cycle (often called
instars)
– e.g. Egg – Caterpillar – Chrysalis – Butterfly
• This allows times when organisms can pause to
survive adverse conditions
– DORMANCY
Dormancy
• Survival strategy to endure adverse condition
– Predictive – pre-programmed (genetic) to coincide
with seasonal environmental change
– Consequential – in response to unpredictable
environmental change
• Reduction in metabolic activity avoids food
shortage
Dormancy
• Resting Spores, buds – bacteria, fungi, plants, simple
animals. Protective structures
• e.g. Pasteurisation cause bacteria to spore, seeds,
• Diapause – insects. Suspension of growth/development
at a stage in life cycle
• e.g. Butterflies & moths can “overwinter” as a chrysalis
• Hibernation – winter “sleep” reduced metabolic rate, live
off fat stores
• e.g. Bears
• Aestivation – “hibernation” during long dry/hot spells
• e.g. Lungfish
Response to external change
• Animals can respond in two ways to external
environmental change:
– conform – change internally to match external
change
• restricted distribution (short term survival strategies can
extend range)
– regulate – maintain internal conditions
• more widespread distribution
• requires energy (especially thermoregulation in cold
climates)
•Perfect Osmoconformer
•Perfect Osmoregulater
•Both hyper & hypo
osmoregulation
•Hyperosmoregulation
in dilute media
Homeostasis
• Evolution of mechanisms to maintain a constant internal environment
• Mechanisms exist to maintain:
– temperature
– pH
– osmotic potential (water)
– ion balance
• Scholar details some examples (Higher standard)
• Organisms with diverse homeostatic mechanisms generally need to eat
much more (e.g. reptiles (poikilotherms) eat less than mammals
(endotherms)
• Homeostasis costs energy, but facilitates an organism to exploit a wider
variety of environments and so access more energy sources.
Surviving Change
• Organisms need to maintain their internal
environment within tolerable limits
• Ecosystems are subject to change and may lead
to changes within the internal milieu
• Organisms need to cope with ecosystem change
to survive
• Factors which change
• Temperature – daily (diurnal) change, seashore,
seasonal, microclimate (slope aspect)
• Salinity – estuary, seashore, evaporative water loss in
small water course
• pH – typically pH 3-9 range of pH living organisms
tolerate. pH changes ionisation of nutrients altering
solubility (acid rain leaches aluminium)
Strategies for survival
• 3 Strategies are adopted to survive:
– Migration – leave to avoid changes
– Resist/ Tolerate – anatomical/ physiological
adaptations to prevent environmental change altering
the internal environment causing harm
– Regulate/ Adapt – physiological processes to
regulate the internal environment to prevent change
(Homeostasis)
Migration
• Geese fly south for winter
• African plains animals follow rains
• Monarch butterfly fly NORTH in spring,
SOUTH in winter
Resistance/ Tolerance
• Resistance – physically preventing internal environmental
change despite external change – longer term survival
possible
• Tolerance – physiological adaptations to survive changes
– short term only
• e.g. Limpets would dry out when uncovered at low tide
• - evolution of shell reduces desiccation
• - close shell to prevent desiccation (resistance)
• e.g. Limpets suffer high temperatures when exposed on
seashore/ shell closed
• - enzymes are not denatured by high temperatures (tolerate)
• e.g. Limpets suffer hypoxia when shell closed
• - use anaerobic respiration (tolerate)
Other Examples of Tolerance
• Temperature
– Cold – Polar bear – hollow fibre fur/ black
skin to reduce heat loss
– Heat – Thermus aquaticus bacteria have
enzymes not denatured at 95°C
Plants- Water Loss
Plants - water loss
• Xerophytes – live in arid climates
– Water lost through open stomata
– Stomata need to open for p-synth.
• Resist water loss
– Enhanced waxy cuticle/ slimy
– Fewer stomata
– Spines not leaves (reduced SA)
– Rolled leaves
– Hairy leaves
– Pitted stomata
• Tolerate water loss
– Succulent tissues
Regulation/ Adaptation
• Physiological processes which reduce impact of
environmental fluctuations
• Maintain homeostasis
• Often energy requiring
• e.g. Osmoregulation
– e.g. amoeba
• - Water pump excludes osmotically absorbed water, rate
of pump increases with rate of ingress of water
– e.g. freshwater fish
• - produces dilute urine short loop of Henle (kidney)
– e.g. kangaroo rat
• - long loop of Henle reabsorbs much water from
Plants – water loss
• Reversed stomatal rhythm