Gummy bears, a popular chewy candy, demonstrate a fundamental scientific principle when placed in different liquids. While they swell in fresh water, a phenomenon occurs when these candies are submerged in salt water: they shrink. This change in size provides a simple example of how water moves in and out of certain materials, a process central to many biological systems.
What Are Gummy Bears Made Of?
Gummy bears derive their texture and shape from a few primary ingredients: gelatin, sugar, and water. Gelatin, a protein derived from animal collagen, forms a matrix that traps water and sugar molecules within the candy. This gelatin matrix acts as a semi-permeable structure, allowing small molecules like water to pass through, but restricting the movement of larger molecules, such as sugars. This property of gelatin is fundamental to understanding how gummy bears interact with different solutions.
The Science of Osmosis
The shrinking of a gummy bear in salt water is explained by osmosis. Osmosis is the passive movement of water molecules across a semi-permeable membrane. Water moves from an area where its concentration is higher (meaning fewer dissolved substances or solutes) to an area where its concentration is lower (meaning more dissolved substances). This movement continues until the concentration of water molecules becomes balanced on both sides of the membrane. This spontaneous flow of water does not require external energy.
Why Gummy Bears Shrink in Salt Water
When a gummy bear is placed in salt water, the salt water acts as a hypertonic solution relative to the gummy bear’s interior. A hypertonic solution has a higher concentration of solutes (in this case, salt) and a lower concentration of water molecules compared to the inside of the gummy bear. Because the gelatin matrix of the gummy bear is semi-permeable, water molecules inside the gummy bear move out through this membrane and into the salt water. The net outflow of water causes the gummy bear to lose its internal water content, resulting in a reduction in its size and mass.
Osmosis Beyond Gummy Bears
The principle of osmosis is not limited to candy experiments; it is a widespread phenomenon observed in various biological and everyday contexts. Plants absorb water from the soil through their roots via osmosis, as the water potential in the soil is higher than inside the root cells. If a plant is not watered, its cells can lose water through osmosis, leading to wilting.
Osmosis also plays a role in the human body, such as in the kidneys, where it helps regulate water balance and filter waste products from the blood. These examples illustrate how the movement of water across membranes is fundamental to life processes and daily observations.