Placing a gummy bear into plain water versus salt water is a demonstration of a fundamental biological process. This experiment reveals a dramatic difference in how the candy reacts to its environment, providing a visible lesson in how water moves. The core question is why the gummy bear behaves so differently when the only change is the addition of salt to the liquid. The answer lies in the physics of water movement and the unique structure of the gummy bear itself.
What Makes a Gummy Bear React
The structure of a gummy bear is defined by gelatin, which is a protein derived from collagen. This gelatin forms a polymer network, creating a flexible, mesh-like matrix that gives the candy its characteristic chewiness. This internal network is initially embedded with high concentrations of sugar and a small amount of water.
The gelatin matrix functions like a semi-permeable barrier, allowing small molecules, like water, to pass through its pores. However, the larger sugar molecules trapped within the candy cannot easily escape. The high concentration of dissolved substances, or solutes, inside the bear sets the stage for water movement.
Observing the Reaction in Plain Water and Salt Water
When a gummy bear is submerged in plain water, the physical change is dramatic. The bear rapidly increases in size, often doubling its volume and mass over several hours. This swelling occurs because the water is drawn into the gelatin matrix, causing the polymer chains to expand, and the resulting texture is soft and easily deformed.
The observation is different when the same candy is placed in a highly concentrated saltwater solution. In this scenario, the gummy bear undergoes minimal swelling and may even shrink slightly, becoming firmer than its original state. The presence of salt actively prevents the massive water absorption seen in the plain water test.
Understanding the Science of Osmosis
The differing results observed in the two liquids are explained by the process of osmosis. Osmosis is defined as the movement of water molecules across a semi-permeable membrane, like the gelatin network. Water moves from an area where its concentration is higher to an area where its concentration is lower. This movement occurs because the system attempts to balance the concentration of dissolved substances (solutes) on both sides of the barrier.
In the case of the plain water, the liquid outside the bear has a much higher concentration of water molecules and a lower concentration of solutes (a hypotonic solution). Since the gummy bear’s interior has a high concentration of sugar, water rushes inward to dilute the internal sugars and equalize the solute balance, causing the bear to swell extensively. This influx of water is driven by the concentration gradient.
Conversely, the saltwater solution contains a very high concentration of salt, making it a hypertonic solution. The salt binds up many of the water molecules on the outside, lowering the free water concentration in the liquid surrounding the bear. This means the water concentration inside the gummy bear’s gelatin matrix is now higher than the water concentration outside. Water moves out of the bear into the surrounding salt water, leading to little or no swelling and sometimes a slight reduction in size.
Osmosis Beyond the Kitchen Counter
The simple movement of water demonstrated by the gummy bear experiment is a process that governs many functions in the natural world. For instance, plant roots absorb water from the soil using osmosis, as the water concentration in the soil is typically higher than the concentration within the root cells. This mechanism allows plants to hydrate and maintain their structure.
In the human body, osmosis helps the kidneys regulate the water balance in the blood, ensuring that waste is removed while water is reabsorbed. The principle is also used in food preservation, where high concentrations of salt or sugar are used to cure meats or make jams. The highly concentrated brine or syrup draws water out of the food and any microbial cells, preventing spoilage by dehydration.