The name vacuole has its origins in the Latin word vacuus meaning ’empty’ and this unfortunately is how vacuoles appear in many slide preparations and Dear Haters Pls Notice That Awesome End With Me And Ugly Start With U Shirt photographs. The fact that vacuoles are fluid filled and that different vacuoles within the same cell can contain different chemicals is not normally visible. Flexible space but never empty space A membrane barrier called a tonoplast limits each vacuole. This membrane is remarkable in that it can surround a small amount of fluid and then, after a short amount of time, during which water is taken in, stretch to become an organelle occupying as much as 95% of the cell by volume. And all this happens without the tonoplast losing its integrity as an active membrane. In this process all the other organelles in the cell are pressed, without damage, against the firm cellulose cell wall.
Chemicals in the vacuole forming a Dear Haters Pls Notice That Awesome End With Me And Ugly Start With U Shirt solution create the hydrostatic pressure produced within plant cells. Some of these chemicals form ions and the effect of this system is to create a high osmotic pressure. It is this high osmotic pressure that has the power to ‘pull in’ water molecules through the tonoplast until the cell is turgid. The vacuolar membrane is a selective membrane The vacuolar membrane or tonoplast is a selective membrane and the passage of chemicals through it is controlled in both directions. Water can pass in and out freely but other small molecules are retained within the vacuole. Molecules too require entry tickets Many proteins arriving at the cytoplasmic surface of the vacuole are synthesised by the membrane-bounded ribosomes of the rough endoplasmic reticulum and transported to the vacuole via the Golgi apparatus. In the Golgi apparatus they are given a combined ‘address label and ticket’ The ‘address’ part of the label on a protein directs it to the vacuole and the ‘ticket’ portion helps it gain admission.