When the plant dries up, when its leaves turn yellow, this means that plant cells do not have enough water. But each cell is enclosed in membrane-membrane. How soaked the roots moisture permeates through the membrane into the cell? And that makes the water move against gravity, from the bottom up, from the roots to the leaves?
Before you get answers to these questions, will deliver preliminary experiments with membrane, reminiscent of a cell membrane.
If two solutions are separated by a dense wall, they certainly do not mix. If no partitions at all, the solutions, in contrast, are mixed in themselves, even if they do not stir. Well, what if a semi-permeable partition?
This will be a subject of experience, and a semi-permeable membrane will serve as a piece of parchment or cellophane (but not polyethylene). To acquire certain properties, it should be kept in water until it softens.
Prepare sugar syrup - saturated solution of sugar, so thick that the sugar no longer dissolves. Faster and more convenient to prepare such a solution in hot water. Pour the syrup to the top in the glass, cover the soaked sheet and tightly tie. Make sure that the film does not have air bubbles. The glass is put in a jar or in a pot of water (water should cover the Cup and leave for a few hours. When you again look at a glass of syrup, you will notice that the film, which he closed, swollen: over the glass as if formed bubble.
To understand what happened, we first need to understand what a semi-permeable membrane. This is the kind of film that retains some molecules and at the same time ignores other. And cellophane, parchment film porous, but the pores in them are so small that sugar molecules they are impenetrable. On both sides of our partition there is water, but on the side where the sugar solution, n a every part of the surface have fewer water molecules. So the water passes through the membrane more molecules, and this leads to the fact that the volume of liquid in the glass is increased and, consequently, a semi-permeable film is inflated. Everything in nature seeks equilibrium, in this case the alignment of solution concentration. And soon the equilibrium is: how many molecules of water enters the glass with syrup, as much from him and out into the outer vessel. Therefore, the bubble is not too large.
Physico-chemical phenomenon, which we have just observed, is called osmosisand pressure, causing the film to buckle - osmotic pressure. To observe osmosis necessarily need septum and two liquid: solution of any substance and pure solvent (here water) or at least a weaker solution.
The membrane of living cells is always a semi-permeable membrane. She holds many molecules of substances dissolved in the water, but the water passes. Therefore, every animal and plant cell is a microscopic osmotic system, and the osmotic pressure plays a very important role in the life of organisms.
Osmosis can be observed in the most simple experiments. With a sharp knife cut a thin slice of lemon and place it on a saucer. Note: juice on the surface is almost there. Sprinkle with a slice of sugar or, even better, powdered sugar and very soon the lemon juice will start up.
A similar experience can be put with strawberries and other berries, putting them in dry jars. Berries sprinkled with sugar, quickly allocate juice.
In all these cases is osmosis. On the surface of the lemon or berries formed a concentrated solution of sugar, and the juice is much less concentrated, tends to dilute this solution, it penetrates the cell membrane and exits - just as in the previous experience of the water from the banks rushed into a glass with syrup.
Our next object cabbage. We, of course, will not sprinkle sugar and salt. Shred the cabbage with a knife, sprinkle with salt and a good RUB - cabbage will also give juice. So what happens when fermented cabbage; cabbage salads certainly are advised to RUB how to stand out juice and cabbage became softer and softer. The reason is the same: osmosis.
Move on to the potatoes. Cut potatoes three dice, preferably of the same size. Prepare three banks. In one pour salted water; in another, a concentrated salt solution, and the third just water from the tap. In each jar dip for potato cube. Hours after two or three carefully consider the cubes. Which was in salted water, any changes you will not find. But the other two have changed, and noticeable. The cube, which lay in a concentrated salt solution, is much reduced, but the one you dropped in the water, became, on the contrary, considerably more.
First, why has not changed the first cube. He was in dilute solution, and the salt concentration was approximately the same as in the potato juice. The cube, which was located in a concentrated solution, was to give water, reducing the concentration of this solution; the water from the potatoes were gone, and the cube cringed. And the last cube, the one that was in the water, began to absorb water and increased in size.
From the potatoes will turn to carrots and make it work as a pump.
Cut the carrot tops and "the crown" insert the glass tube. Carrots, put in a glass of water; perhaps you will easily figure out how to hold the carrot in a vertical position.
In a glass tube to pour half of the solution of salt and do some observations. Soon the water level in the tube will begin to rise and, if the experience is placed correctly, the water will even pour out of the tube. Carrots like pumping water from a glass that causes it to move upwards.
When you pour the carrots growing in the garden, it is about as pumping water from the soil to the tops. In her juice salt concentration higher than in the irrigation water, and by osmosis life-giving moisture to get not only the roots, but all plant tissues.