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.

    動(dòng)物體內(nèi)的滲透作用

    如果細(xì)胞在化學(xué)反應(yīng)中用完了水份，細(xì)胞質(zhì)就會(huì)變得更濃，更多的水份將從細(xì)胞膜外通過滲透作用馬上進(jìn)入細(xì)胞。類似地，如果細(xì)胞質(zhì)因?yàn)榛瘜W(xué)反應(yīng)中產(chǎn)生水份而變得太稀釋，水份會(huì)通過滲透作用離開細(xì)胞，保持水份平衡。

    但是，滲透作用也會(huì)引起一些動(dòng)物體內(nèi)的嚴(yán)重問題。如果細(xì)胞外的溶液比細(xì)胞內(nèi)稀釋，那么水份會(huì)通過滲透作用進(jìn)入細(xì)胞，導(dǎo)致細(xì)胞膨脹，嚴(yán)重的時(shí)候甚至爆炸。

    另一方面，如果細(xì)胞外的溶液比細(xì)胞內(nèi)濃度高，那么水份就會(huì)通過滲透作用流出細(xì)胞。細(xì)胞質(zhì)會(huì)變得太濃，細(xì)胞也會(huì)萎縮。一旦你理解了內(nèi)環(huán)境，保持持續(xù)的內(nèi)部環(huán)境就很清楚了。

    植物體內(nèi)的滲透作用

    植物依賴有條理的滲透作用供養(yǎng)枝干和樹葉。水份通過滲透作用進(jìn)入細(xì)胞，細(xì)胞質(zhì)膨脹并擠壓細(xì)胞壁。直到?jīng)]有更多水份可以完全地進(jìn)入細(xì)胞的時(shí)候，壓強(qiáng)就建立起來，細(xì)胞變得堅(jiān)硬。

    這種膨脹的狀態(tài)讓植物的樹葉和樹干堅(jiān)硬牢固。所以對(duì)植物來說，當(dāng)水份供給充足的時(shí)候，沒有太多的問題，因?yàn)橹参镆仓粫?huì)從地下吸取所需水份。當(dāng)沒有植物所需的水份的時(shí)候，問題才會(huì)出現(xiàn)。

    當(dāng)水份供給非常稀少的時(shí)候，水份會(huì)被從植物細(xì)胞中抽出，用于其他特別需要水份的過程。這種情況發(fā)生之后，枝干和樹葉的細(xì)胞變得軟弱，植物開始下垂枯萎。如果水份供給還沒有回來，那么植物會(huì)枯萎死亡。