Which glassware is closed at one end?

The test tube is the only piece of glassware listed that is closed at one end. This design allows it to contain substances without risk of spilling, making it ideal for various laboratory procedures such as mixing, heating, and storing small amounts of liquids or solids. The closed end also helps maintain a controlled environment, preventing contamination and allowing for reactions to occur without exposure to the atmosphere.

In contrast, a flask, graduated cylinder, and beaker typically have an open top, making them suitable for pouring and measuring but not for containing substances in the same way a test tube can. The ability of test tubes to hold and mix samples securely is essential in many experimental setups in bioscience and chemistry.