Kathy Johnson , age 12 Lafayette, Calif for her question:
What is osmosis?
Osmosis is a simple law of nature„ It goes on all by itself, all the time, all over the world. Unless we investigate, we, ,,do not even know that it is happening. But if this law wore repealed, the‘ world as we know it would come to an end. There would be no trees to make oxygen for us to breathe, no grass for the cattle, no corn and no crops. Pretty soon there would be no animals and no people„ Thatts how important osmosis is in our world.
Osmosis concerns the behavior of liquids. Water, as you know, tends to flow downhill. But, under certain conditions, water can be forced to flow uphill. We have plumbing systems to make it flow uphilA l pressure., Plants need water to flow uphill from the ground to their topmost leaves. Instead of a plumbing system of metal pipes, they simply let natures law of osmosis do the job for them.
You can see how it works with a small experiment. You will need a glass dish and a glass tube, some water and a little sugar. Most important you will need a strip of membrane. Membrane is covering tissue in animal and plant bodies. You may peel a strip from a sausage, if you are sure this covering is natural membrane and not plastic.
Tie the membrane over one end of the tube. Dissolve the sugar in a little water and use it to half fill the glass tube. Now pour some plain water into the dish and set the glass tube in it with the membrane under water. In a little while you will find more water in the tube and less in the dish. Osmosis has been at work.
The liquid in the dish is plain water. The liquid in the tube is plain water plus dissolved sugar. The water seeped uphill through the membrane to join the stronger solution. By osmosis, a weaker solution will always seep through a membrane to join a stronger solution on the other side uphill or downhill.
The roots and tiny root hairs of plants wear sleeves of membrane. The cells and veins of plants are lined with membranes. And the plant tissues are filled with rich, sugary, liquid sap. The moisture in the ground contains dissolved chemicals, But this solution is weaker than the rich sap in the plant. In the earth, the sap and the ground water are separated by root membranes. So osmosis gets to work and the ground water seeps into the plant.
Other factors operate to keep moisture circulating through the plant, Water evaporates from leaves and branches in the air. This creates space and a pulling force from above. Water molecules tend to cling together. This, along with osmosis pushing up from below and evaporation pulling up from above keeps an elevator of water flowing upwards through the plant, This is the power which keeps the plant food circulating and provides the pressure for plants to stand up and grow.