bio 543 IV

•1. Freeze Avoidance

• •2. Supercooling (For organisms that are freeze intolerant= very specialized
• kind of freeze avoidance)

•3. Freeze Tolerance

•Body (and cells) are mostly made of water: 50-70%

• •When ice forms, it can rupture cell membranes
• (crystallization)

• •Also, removes water from cells (dehydrates them) forming
• toxic levels of minerals that are left behind

•For some organisms, enzyme failure

• •When temperature drops below freezing point, nucleation occurs and ice
• crystals form- sort of a chain reaction

• Freezing point
• depends on solute concentration: more solutes, freezing point is lowered (stays
• liquid at lower temperatures

• •Freezing involves a certain amount of “chance”- once
• nucleation (“seeding” occurs, it spreads

• •Thus, staying dry on surface can prevent internal
• freezing (=innoculative freezing)

• •Larger organisms have a greater chance of freezing than
• smaller organisms

• •Hibernate in areas below the frost line or in
• microhabitats that don’t freeze

• •Animals would die if they froze- cell membranes would
• fracture
• •Maintain fluids at an unfrozen state below the freezing
• equilibrium point
• •Involves exclusion of nucleating agents

•Live with their body fluids well below 0°C

• •Takes advantage of concept that fluids can dip well below freezing point without actually
• solidifying

•Water can be supercooled to -40°C as long as it is completely free of contaminants

• •Can also add antifreeze
• compounds-
• commonly glycerol

•Antifreeze peptides-prevent ice crystals from forming

• •Often involves:
• • ice nucleating proteins: controls ice formation so that it occurs outside of
• cells (Extracellular)
• •Cryoprotectants: assures that only a
• limited amount of body water freezes (slows chain reaction)

• •Mobilizes glucose
• when freezing first begins (from liver to bloodstream)- allows ice to form more
• slowly)
• •Intentionally dehydrates- shunts water out of cells into coelomic tissues

• •Freezing needs to
• start at relatively high tissues, before supercooling starts, otherwise freezing will occur too rapidly and
• animal will die

• • ice nucleating proteins: controls ice formation so that it occurs outside of
• cells (Extracellular)

• Cryoprotectants: assures that only a
• limited amount of body water freezes (slows chain reaction

• are predictable and prolonged
• Freeze intolerence (avoidance or supercooling) in places where freezing is unpredictable-can rapidly switch back and forth