Semipermeable Membrane
A semipermeable membrane is a thin barrier that lets some substances pass through but blocks others.
A fine mesh strainer sits over a bowl. You pour broth through it — liquid drips down, but chunks stay on top. The mesh lets small things pass and blocks big things. A semipermeable membrane works the same way: small particles cross it, large ones cannot.
Explaining semipermeable membrane by grade level
An egg has a thin skin inside its shell. Water can move through this skin, but other things cannot. If you put a bare egg in salty water, water moves out through the skin. The egg gets smaller because water left.
Projects that explore semipermeable membrane
The egg membrane is semipermeable, meaning it allows water molecules to pass through while blocking larger molecules. When you place eggs in different liquids, they swell or shrink depending on how water moves across that membrane.
Semipermeable membranes sort molecules by size. Small water molecules pass through freely, while larger salt molecules cannot. The eggshell membrane works this way — it acts like a filter, letting water pass but blocking the salt. As a result, eggs placed in saltier solutions lose more weight because more water exits through the membrane.