If the vacuoles lose water, the plant cells become floppy rather than rigid, severe wilting can kill the plant. To reduce the possibility of wilting most plants have a layer of wax covering the surface of the leaf. This layer of wax is called the cuticle. All the plant cells use osmosis to keep their cells turgid (swollen up with water) to give physical structure to a plant cells body.
This picture shows how water is absorbed by a plant.
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Osmosis in humans.
The kidney is made up of a very large number of tubules. Each tubule is divided into regions where different processes occur.
• Filtration is brought about by blood pressure. Because the walls of the kidney tubule are partially permeable only small molecules such as water, glucose, urea and ions are filtered.
• Reabsorption of the filtered glucose and ions from the filtrate into the blood is by active transport.
• Most of the urea is not reabsorbed.
This diagram below shows how urea is made and when osmosis is used.
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Osmosis in animals.
Cell membranes behave very like visking tubing. They will let some substances pass through them, but not others. They are selectively permeable membranes.
There is always cytoplasm on one side of any cell membrane. Cytoplasm is a solution of proteins and other substances in water. There is usually a solution on the other side of the membrane too. Inside large animals, cells are surrounded by tissue fluid. In the soil, the roots of plants are often surrounded by a film of water. Single-celled organisms such as amoeba are also surrounded by water. So, cell membranes often separate two different solutions - the cytoplasm and the solution around the cell. If the solutions are of different concentrations, then osmosis will occur. .
The picture below illustrates an animal cell in pure water. The cytoplasm inside the cell is a fairly concentrated solution. The proteins and many other substances dissolved in it are too large to get through the cell membrane.