When most of us hear the word tissue, we think of something we reach for when we have a runny nose. But in biology, a tissue is a group of cells that act together to carry out a specific function.

Your body has four basic types of tissues:

• Muscle tissue provides movement. Types include voluntary muscles, like those in the arms and legs, and involuntary muscles, such as those that move food through the digestive system.
• Nervous tissue carries messages throughout the body and includes the brain, spinal cord, and nerves.
• Connective tissue supports other tissues and binds them together. Examples include ligaments, tendons, bones, and fat.
• Epithelial tissue creates protective barriers and includes the skin and the linings of internal passageways.

Together, these different tissues form organs. For example, the stomach contains all four basic types of tissues.

For many people, the word pathway may bring to mind stepping stones in a garden or a trail through a forest. But when biologists talk about a pathway, they’re referring to a series of actions among molecules in a cell that leads to a certain product or change within that cell. Pathways maintain balance during walking, control how the eyes’ pupils respond to light, and affect skin’s reaction to changing temperature. They control our bodies’ responses to the world, and errors in them can lead to disease.

In everyday use, most people understand translation to mean converting words from one language to another. But when biologists talk about translation, they mean the process of making proteins based on the genetic information encoded in messenger RNA (mRNA). Proteins are essential for virtually every process in our bodies, from transporting oxygen to defending against infection, so translation is vital for keeping us alive and healthy.