classnotes8 - Osmoregulation and excretion: Basic idea is...

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Osmoregulation and excretion: Basic idea is to keep a balance of salts in your body. Osmosis review: definition - diffusion of water across a semi-permeable membrane. diffusion - movement of a substance from a high concentration to a low concentration. Thus, a simple example: - a beaker with 5% salt on one side, 0% salt on the other, divided by a semi-permeable membrane (in this case salt can’t move across the membrane). - which way does water move? - CONVERT to % water. So we have 100% water on one side, 95% water on the other. Water will move from a high concentration to a low concentration. - lots of confusing terminology - hyperosmotic, hypoosmotic, hypotonic, etc., the only one you need to know is isoosmotic (concentration is the same). Otherwise, keep track of where the concentration of water is higher or lower. A problem for many animals: sometimes the concentration of salt (and therefore water) in the surrounding environment is totally different from that inside the body. Aquatic animals: Types: osmoconformer - animal has the same salt concentration as surrounding water. osmoregulator - animal needs to regulate salt concentration since salt concentration in body is different that in the surrounding environment. Fresh water - problem is water will enter body. Animal must get rid of excess water, or it will “explode”. How? Fish - will eliminate water through kidneys (very dilute urine) - absorbs extra salt ions through the kidneys.
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Many other animals similarly will excrete large amounts of dilute urine. Marine water - opposite problem. Water will leave body because salt concentration outside the body is often higher than inside the body (water goes to more concentrated salt area - the animal would shrivel like a raisin). Fish (most)- will excrete highly concentrated urine, thus keeping water
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This note was uploaded on 07/21/2011 for the course BIO 101 taught by Professor Staff during the Spring '08 term at Northern Virginia Community College.

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classnotes8 - Osmoregulation and excretion: Basic idea is...

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