response to temperature

8/3/2019 Response to Temperature

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Response to Temperature

Ectotherms

Low temperature: freezing and ice crystal formation inside cells

High temperature: risk of thermal denaturation of proteins (limit

about 45C; there are exceptions such as thermophilic bacteria)

Q10 Effect

Chemical reaction rates are highly temperature-dependent

Reaction rates determined at two temperatures (10C apart)

Q10 = Rate (T)

Rate (T-10)

For most physiological processes, Q10 is 2-3


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What are the strategies used by ectotherms in hot

environments?

1. Behaviour: avoidance (seek out microclimates)


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Freeze avoidance: many species of fish, amphibians, reptiles

Freeze tolerance: a few amphibians and reptiles

Freeze Avoidance

Objective is to promote conditions where cellular water can be

cooled to below 0C before ice crystal formation occurs

Supercooling involves:

Making antifreeze bind microscopic ice crystals

Make cryprotectants glycerol, sugars, and proteins which

lower the freezing point

Freeze Tolerance

Accept that you will freeze yet not die very complex

Promote ice crystal formation outside of cells

Produce ice nucleating proteins

When freezing occurs outside of cells this leads to dehydration of

cells and hypoxia because oxygen is no longer delivered to cells


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6/12

A Wood Frogs Life

Summer: spend in the woods, eating and growing

Autumn: hide in insulated spots on forest floor

Winter: freeze when hibernation site falls to about -2C; survive

frozen to -10C

Spring: thaw and revive, move to woodland ponds

Mating and egg laying: within one week in early spring


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Eggs and tadpoles: develop fast before temporary ponds dry out;

metamorphosis in early summer

Frozen Frog Data

Ice content: up to 70%

Protected: Tb -10C vs. Air -40C

Body ice: forms around organs, between cells. Blood and lymph

frozen

Life interrupted: heart, lungs, brain

Organs shrink

Freezing directional

To Survive Freezing

Add ice nucleating proteins to blood

Alter metabolism to synthesize cryoprotectants polyols, sugars

Avoid cellular dehydration with cryoprotectants

Some Ectotherms Function as Heterotherms Flying insects:


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Preparation for flight involves increasing core temperature by

contract of antagonistic thoracic flight muscles (like shivering)

In flight, redistribute blood to abdomen to cool down

Pythons:

Shiver to warm their eggs

Tuna and Billfish

Tuna may be 10C warmer than their environment

If the tuna is 10C warmer and the Q10 is 3, then power

output increases by 3-fold.


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Generate and retain heat to raise the temperature of the brain,

muscle, and eyes 10C above their surroundings

Countercurrent arrangement of blood vessels transfer heat from

warm veins (from the muscles) to cool arteries


10/12

Heater Organ

Modified eye muscle with a high mitochondria content, high

hydrolysis of ATP and a countercurrent exchanger

Plants: Temperature Interactions

Readings

Pages 845-851

Issues

High temperatures destabilize membranes and denature proteins

Low temperatures affect membrane and protein function and there

is the risk of cell damage by ice crystal formation

Cannot use the behavioural adaptations common to animals

Influence of Low Temperatures on Plants: Arctic &

Alpine Regions

Adaptations

Dwarfed features and grow close to ground for heat absorption


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High amounts of red pigments absorb increased solar energy

Large storage organs below ground

Photosynthetic enzyme adaptation

Dormancy in seeds (temperature dependent)

Lower freezing point (cell sap)

Accommodate ice crystal formation

Influence of High Temperatures on Plants

Problem are loss of water (transpiration) and they absorb heat

Adaptations

Small dissected leaves increase convective heat loss

White leaves increase reflection

Alter leaf angle to absorb less solar radiation

Hairs or spines to reflect solar radiation

Adopt succulent growth form to reduce transpiration and have heat

tolerant enzymes

Heterothermic Plants

Arum lilies, skunk cabbage, philodendrons


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Inflorescences (flower clusters) heat up

Increased metabolic energy from metabolizing stored food

Role in attracting flies and beetles involved in pollination

response to temperature

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