Thursday, October 23, 2014

Life at Low Temperatures

Ideas

Thoughts

  1. Antifreeze in cars, any resemblance with ecology?
  2. Europe and the US feel the cold, for us in Africa we feel the heat is the problem (for their plants too).

That's Why

  1. That's why the human body gets used to AC.
  2. That's why emotional 'hibernation' can help a person withstand and tolerate strong emotional and psychological shock.

Digest

  • "More than 80% of earth’s biosphere is permanently cold."
  • "Cold is the fiercest and most widespread enemy of life on earth."
  • Temperatures below the optimum are harmful, but there is a wide range of such temperatures that cause no physical damage and over which any effects are fully reversible.
  • Damage at low temperatures that can be lethal:
    • chilling
    • freezing
  • Chilling injury: "Many organisms are damaged by exposure to temperatures that are low but above freezing point"
    • "The fruits of the banana blacken and rot after exposure to chilling temperatures."
  • "Temperatures below 0°C can have lethal physical and chemical consequences even though ice may not be formed."
  • "Water may supercool to temperatures at least as low as −40°C.
  • "Organisms have at least two different metabolic strategies that allow survival through the low temperatures of winter"
    • "A freeze-avoiding strategy uses low-molecular-weight polyhydric alcohols (polyols, such as glycerol) that depress both the freezing and the supercooling point and also ‘thermal hysteresis’ proteins that prevent ice nuclei from forming"
    • "A contrasting ‘freeze-tolerant’ strategy, which also involves the formation of polyols, encourages the formation of extracellular ice, but protects the cell membranes from damage when water is withdrawn from the cells."
  • "The tolerances of organisms to low temperatures are not fixed but are preconditioned by the experience of temperatures in their recent past."
    • acclimation: when it occurs in the laboratory
    • acclimatization: when it occurs naturally
  • "The exposure of an individual for several days to a relatively low temperature can shift its whole temperature response downwards along the temperature scale. Similarly, exposure to a high temperature can shift the temperature response upwards."
  • "Acclimatization may start as the weather becomes colder in the fall, stimulating the conversion of almost the entire glycogen reserve of animals into polyols, but this can be an energetically costly affair: about 16% of the carbohydrate reserve may be consumed in the conversion of the glycogen reserves to polyols."
  • "Dormant stages are typically dehydrated, metabolically slow and tolerant of extremes of temperature."

Questions

  1. What's the difference between acclimation and acclimatization?
  2. How do organisms respond to and survive in cold temperatures?
  3. How can plants be acclimated to cold temperature (tomatoes)?