Where do bacteria grow on nutrient agar?

• A. In liquid culture
• B. In colonies on nutrient agar
• C. On metal surfaces
• D. In the air

Answer: (B)

On nutrient agar, bacteria grow as colonies, which are discrete, visible clusters that originate from a single cell or a small group of cells. The solid agar provides nutrients and moisture, so when plates are incubated, bacteria multiply at specific spots and form these colonies. This is different from growth in liquid culture, where bacteria spread throughout the liquid and the culture becomes cloudy rather than showing separate colonies. Growth on metal surfaces or in the air isn’t the way nutrient agar supports growth—the plate must be the solid medium that the bacteria can colonize.