Lecture: M/W/F 11-11:50, Copernicus 210; Lab Tues. 2-5 or Thurs. 8-11, Copernicus 321. Office hours: Mon. 3:00-3:50,Wed. 2:00-3:50, Thurs. 11:00-11:50 or Friday 8:00-8:50.

Web address: www.biology.ccsu.edu/Nicholson

Snowday lecture:

Chapter 44 Controlling the Internal Environment

Lecture held during the snow day of Wed., Jan. 28th, 2004.

Environmental factors, particularly climate impacts the global distribution of a species

Each species has a unique tolerance range of environmental conditions which has evolved over time.

The Life box figure of a hypothetical organism with respect to three environmental variables. Each point represents conditions experienced and survived by an organism at a particular place and time. All conditions experience and survived at all places and times defines the life box for the species. If conditions go beyond the life box the organism dies.

Temperature

Most terrestrial organisms maintains some sort of normal activity over a narrow range of temperatures 10ºC - 48ºC.

The lowest natural temperature recorded on Earth = -89ºC at Antarctica, the highest in the shade in Libya at 58ºC. This gives a natural range of 147ºC. One location in Siberia has a range of 105ºC.

The responses of organisms to changes in temperature is complex. The simplest responses involve changes to activity, growth rates and metabolism. At low temperatures, metabolism is undetectable, with higher temperatures the rate increases due to an increase in the amount of kinetic energy supplied to the biochemical reactions. At high temperatures denaturing of the enzymes begin. Death at high temperature can be either due to the permanent denaturing of the enzymes, loss of water, imbalance in metabolism such as osmoregulation in fish, or imbalance in the nervous system.

Cold Biology, extreme cold

When water becomes frozen it changes from a liquid to a solid state. Ice crystals expand by drawing water unto them selves. As water is drawn towards the ice crystal, dehydration can occur in other portions of the cell. Ice is less dense than water and thus expands 10% upon freezing. Ice crystals are sharp, and if they pierce membranes or important organelles will result in cell death.

Therefore cells die when frozen for several reasons:

* Membranes are torn when ice pushes the cells apart.
* Dehydration can occur
* Membranes and organelles are pierced by the sharp shards
* Oxygen starvation can occur because heart and lungs have stopped functioning

To survive freezing an organisms must either

1. Survive ice forming within their cells = Freeze tolerant
2. Ensure that their fluids remain liquid at temperatures below freezing = Freeze avoiding.

The strategy that an organisms uses depends on the structure and physiology that it has developed during its evolutionary history.

Freeze Tolerant

Organisms that are freeze tolerant tend to live in damp or wet environments. They are likely to have ice come in contact with their surfaces during the winter hibernation period. Physical contact with ice will allow ice to enter into the body. The ice crystals will travel across the cell or body wall and enter through body openings such as the mouth or anus. This is known as innoculative freezing.

The first line of defense for these species is to prevent ice from physically touching their bodies. The have structure such as a cuticle, eggshell or cocoon that acts as a barrier to the spread of ice. Their body liquids remain unfrozen during the winter.

Some can withstand the bulk of their body tissues being frozen. It is generally thought that an organism can only survive if ice formation is confined to body cavities and extracellular spaces where the ice crystals cannot pierce any important membranes.

More than 60 species of insects are freeze tolerant. They freeze at -5ºC to -10ºC but will survive colder temperatures than this. These species freeze slowly, giving time for the cells to adjust. Goldenrod flies found in NE take 1-2 days to freeze at -23ºC.

The second line of defense involves producing ice nucleating proteins that trigger ice formation at relatively high temperatures. These are produced in the intracellular fluids, so that ice crystals will form where it is safest. Water will not change states and become frozen unless it has a nucleator. As freezing proceeds, the ice excludes salts, the concentration of which will rise in the unfrozen portion of the cell. The depresses the freezing point of the remaining liquid, preventing further freezing. Approx. 82% of the water in an organism will freeze.

Freezing of wood frogs over the winter takes place by innoculative freezing across the skin in moist habitats. Ice nucleating bacteria is found in the gut, promoting ice formation there instead of its organs. This will also serve to trigger ice formation at relatively warm temperatures (below freezing) if the frog is dry and innoculative freezing cannot occur. Freezing is slow and gentle and take 24 hours at -2.5ºC.