Osmosis: How Water Moves

What is Osmosis?

Osmosis is the movement of water molecules through a semi-permeable membrane from an area of high water concentration to a low concentration to balance things out.

• A raisin swells in water because water moves into it to balance the high sugar concentration inside with the lower concentration outside.
• Plants absorb water through their root cells by osmosis, pulling water from the soil into the plant.
• When we drink saltwater, water leaves our body cells (which have more water), shrinking and dehydrating them.

Cells rely on osmosis to keep the right balance of water, which helps them stay healthy and function properly.

Osmosis in Real Life

Osmosis is happening all around us—at home, in nature, and even in our own bodies!

• When you soak a wilted vegetable in water, it becomes crisp again—thanks to osmosis!
• Medical treatments, like IV fluids, depend on osmosis to deliver the right balance of water and nutrients to cells.
• Salt-curing meat or pickling vegetables pulls water out of the food through osmosis, which helps preserve them.
• Fruit in sugar syrup (like in jams) loses water due to osmosis, which helps prevent bacteria from growing.
• Kidneys use osmosis to filter waste and excess water from the blood, balancing salt and pH levels. 

Fun Facts

Here are some interesting facts about osmosis:

• Red blood cells can burst or shrink if osmosis goes wrong.
• Osmosis is used in water purification through a process called reverse osmosis!
• Jellyfish are about 95% water. If they’re placed in water with different salt levels, osmosis causes them to shrink or swell quickly.
• Your tears maintain the correct water balance across your eye tissues using osmosis to keep them healthy and hydrated.

Review

Let’s quickly recap what we learned about osmosis:

• In what direction does water move in osmosis? High Concentration -> Low Concentration
• What type of membrane does osmosis need? Semi-Permeable
• What happens to a cell in a salty solution? Shrink
• Which part of the plant uses osmosis the most? Roots