Wednesday, January 26, 2011

Group 2 (Arthur, Denise, Helene, Mitchel, Yi Fan)

Q2. How are xerophytes adapted to survive prolonged drought?

Xerophytes are plants that have adapted to survive prolonged drought. They have adapted by having special ways of storing water and having few or no leaves to reduce transpiration. One example of Xerophytes are cacti. It has no leaves, an extensive radial root systems to collect water efficiently when it rains, waxy skin to keep moisture in, spines for shade and the ability to store water in its stems. These physiological adaptations all helped in the storage of water, allowing xerophytes to survive prolonged drought.

Q5. Why can’t a saltwater fish survive in freshwater aquarium? What are the differences in pH between seawater and freshwater ponds?

A saltwater fish prefers to live in an alkaline aquarium of pH 8.0 and above while a freshwater fish thrives in a lower range or PH level 5.5 to 7.5. Changes in the pH, especially sudden changes, can prove harmful or even fatal to fish . As the pH rises it increases the toxicity of chemicals such as ammonia.

The saltwater fish have a liver that repels salt from their body, while the freshwater fish keeps salt in their body. This process of controlling the amount of salt present is called osmoregulation. The saltwater fish contain a high amount of chemicals in their cells which prevent them from shrinking when they are in high concentration salt water. So when the saltwater fish are exposed to freshwater, they will absorb too much water and some of their cells will burst (cytolysis), while the other cells simply won’t work because the chemicals in their cells are too diluted. The opposite goes for the freshwater fish when they are exposed in saltwater. Their cells will shrink or not function because they are not able to excrete excess salt out of their bodies, which will result in their deaths.

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