Plasmolysis

Under plasmolysis is understood in the biology shrinkage of protoplasts of a plant cell, wherein the plasma membrane detaches from the cell wall. To achieve this, one must suspend the cell a plasmolyticum. This is a hypertonic solution, ie a solution that contains abundant salt or sugar components and therefore has more dissolved particles than the cell sap of the vacuole. In this case, flows on osmotically water from the vacuole through the membranes ( tonoplast, plasmalemma ) into the surrounding, more concentrated medium, so that the vacuole becomes smaller and the material adhering to the vacuole plasma tube together with the plasmalemma separates from the cell wall. At low wall adhesion of the plasma detachment roundish ( Konvexplasmolyse ) occurs in strong wall adhesion form bizarre shapes in which the plasma is drawn out into thin threads ( Hechtsche threads ) ( Konkavplasmolyse ). This process is reversible, that is on the deplasmolysis reversible (provided that the cell is increased by an excessive plasmolysis no damage).

The state in which the protoplast just released from the cell wall - the cell no longer turgid, but still not plasmolysiert properly - called Grenzplasmolyse. This is the case in an isotonic medium.

Cause - the osmosis as a driving force of plasmolysis

Located outside of cells or tissues other highly concentrated salt solution or other highly concentrated substance so dissolves after a short time the protoplast from the cell wall. The vacuoles becomes smaller, until the protoplast in the extreme case, completely released from the cell wall and, finally, is present as a spherical structure.

Cause: The concentration of dissolved solids in the water is higher ( hypertonic ) compared to the inner region of the cell. Such imbalances are similar (if possible) automatically in nature. Thus, water diffuses out of the cell plasma and the vacuole. The driving force behind this taking place here is the concentration equalization osmosis.

The balance is now about primarily by the diffusion of water through the cell membrane. This is all possible because biological membranes are permeable mainly to water but not to solutes. This is known as a semi-permeable membrane ( semi- permeable ) or selectively permeable (actual condition because: only permeable to certain substances ). Taking place diffusion of water through a selectively permeable membrane is also called osmosis.

The hypotonic (ie fewer dissolved particles contained ) solution in the cell loses water because the water particles diffuse into the solution hypertonic ( more concentrated ) to the outside. With the decrease of the dissolved water particles shrink the vacuole and cytoplasm inside the cell.

It follows that the addition of a hypertonic solution to the cell ( in the plasmolysis ) increased in reality, the salt concentration within the cell, which thus adapts to the external medium in the concentration ( and this is indeed additionally diluted by the flowing out of the cell water ) The process is reversible; specifies one cell in pure water, diffuses back into the cell where it is diluted the solution: deplasmolysis.

If both solutions, the external medium and cell interior, the same concentration of a solute, so it is isotonic solutions. However, also takes place in these osmosis, as the osmosis is an ongoing process. However, unlike in hypertonic and hypotonic solutions is the water discharge of the cell is equal to the absorption of water. Thus, it is a constant steady state (also called dynamic balance ) between the isotonic solutions of the cell and the external medium.

Physical approach:

At particle level, the process could be described as follows: The salt ions ( eg Na and Cl- ) form a hydration shell around. This means that the polar water molecules arrange themselves according to the ions and thus immobilized. Thereby, the probability that a molecule of water from the salt ( hypertonic ) solution diffuses through the membrane is less than the other way around. In the less concentrated solution (at the plasmolysis: in the vacuole ), the water molecules are thus more mobile. Therefore, they easily diffuse out through the membrane to the other side out of the vacuole.