Osmosis in Animals

If a cell uses up water in its chemical reactions, the cytoplasm becomes more concentrated and more water will immediately be drawn in by means of osmosis from outside the cell membrane. Similarly if the cytoplasm becomes too dilute because water is produced during the chemical reactions taking place, water will leave the cell by osmosis restoring the water balance.

However osmosis can also cause some very serious problems in animal cells. If the solution outside the cell is more dilute than the cells contents, then water will move into the cell by osmosis, causing the cell to swell and in some serious cases even burst.

On the other hand, if the solution outside the cell is more concentrated than the cell contents, then water will move out of the cell by osmosis. The cytoplasm will become too concentrated and the cell will shrivle up. Once you understand homeostasis and maintaining constant internal conditions becomes very clear.

Osmosis in Plants

Plants rely on well-regulated osmosis to support their stems and leaves. Water moves into plant cells by osmosis, makeing the cytoplasm swell and press against the plant cells walls. The pressure builds up until no more water can physically enter the cell, this makes the cell hard and rigid.

This swollen state keeps the leaves of and stems of the plant rigid and firm. So for plants there isn't too much of a problem when the water supply is abundant because the plant will also only draw the water from the ground that it needs. The problem comes when there isn't enough water for the plant.

When the water supply is very sparse water is drawn out of the the plant cells to support other processes in the plant for which water is vital. As this happens the cells of the stems ond leaves become flaccid and the plant begins to droop and wilt. If the water supply does not return then the plant will wilt and die.

动物体内的渗透作用

如果细胞在化学反应中用完了水份，细胞质就会变得更浓，更多的水份将从细胞膜外通过渗透作用马上进入细胞。类似地，如果细胞质因为化学反应中产生水份而变得太稀释，水份会通过渗透作用离开细胞，保持水份平衡。

但是，渗透作用也会引起一些动物体内的严重问题。如果细胞外的溶液比细胞内稀释，那么水份会通过渗透作用进入细胞，导致细胞膨胀，严重的时候甚至爆炸。

另一方面，如果细胞外的溶液比细胞内浓度高，那么水份就会通过渗透作用流出细胞。细胞质会变得太浓，细胞也会萎缩。一旦你理解了内环境，保持持续的内部环境就很清楚了。

植物体内的渗透作用

植物依赖有条理的渗透作用供养枝干和树叶。水份通过渗透作用进入细胞，细胞质膨胀并挤压细胞壁。直到没有更多水份可以完全地进入细胞的时候，压强就建立起来，细胞变得坚硬。

这种膨胀的状态让植物的树叶和树干坚硬牢固。所以对植物来说，当水份供给充足的时候，没有太多的问题，因为植物也只会从地下吸取所需水份。当没有植物所需的水份的时候，问题才会出现。

当水份供给非常稀少的时候，水份会被从植物细胞中抽出，用于其他特别需要水份的过程。这种情况发生之后，枝干和树叶的细胞变得软弱，植物开始下垂枯萎。如果水份供给还没有回来，那么植物会枯萎死亡。