<急問>什麼是isotonic solution等等..

你好~
Q:什麼是isotonic solution,hypotonic solution,hypertonic solution?
A:你還記得把細胞放到不同的solution的test嗎? 不同的solution有不同的water potential(水勢) (例如:純水有最高的water potential,為0, sucrose solution 因為加了糖,所以water potential 會下降,即為負數 <0.

當細胞浸在純水之中,其純水即為hypotonic solution ,因為這時細胞外圍的water potential 比細胞內高,所以水就會穿過differentially permeable membrane進入細胞By Osmosis.

而hypertonic solution 正正是跟hypotonic solution 相反.
當細胞浸在非純水之中(Eg.Sucrose solution),其液體即為hypertonic solution .這時細胞外圍的water potential 比細胞內低,所以水就會穿過differentially permeable membrane離開細胞By Osmosis.

最後,若果細胞中的water potential跟周圍的液體的water potential相同的話,其solution即為isotonic solution .這時沒有水分子的net movement,但要注時並不是代表水不會從細胞進入/離開,而是沒有net movement!

另外要注時的是動物細胞＆植物細胞在不同的solution中會有不同的表現!
Animal cells in Hypotonic solution:水會繼續進入細胞中,然後腫脹,最後爆裂.
Plant cells in Hypotonic solution:堅硬的cell wall防止細胞爆裂,水最終停止進入細胞,這時我們可稱細胞是膨脹的.

Animal cells in Hypertonic solution: 細胞會萎縮,變成皺褶的.
Plant cells in Hypertonic solution: 細胞變成質壁分離(Plasmolysis,詳細資料可於網上搜尋),這時我們可稱細胞為軟縮的.

Animal cells and Plant cells in Isotonic solution: 細胞維持原狀,容量不變.

An isotonic soultion is a solution having the same water potential as its surrounding medium.
Suppose there is a dialysis tubing which contains a 0.04% common salt solution. When immersed in a beaker of 0.04% common salt solution, there will not be any net influx or efflux of water. The rTOeason is that the solution in the beaker is ISOTONIC to the solution in the dialysis tubing. No osmotic gradient is present and hence there will not be osmosis across the semi-permeable membrane of the tubing.
On the other hand, if the 0.04% common salt solution is placed in a beaker of water, the water, having higher water water potential as the salt solution, is said to be hypotonic to the salt solution. Similarly, if the surrounding medium, say a 1% common salt solution, has lower water potential, then it is said to be hypertonic to the solution inside the dialysis tubing.
Osmosis is an important concept in Biology since organisms require a balance of water in their bodies for proper functioning. Hypotonic, isotonic or hypertonic are just terms to describe the conditions of solutions so that people will easily understand if osmosis occurs and in what direction.

An additional example: human blood has an approximate water potential as that of 0.04% common salt solution (check it out to see if my memory is incorrect or not on the Internet). So, human blood is said to be isotonic to the salt solution.