A petri dish is a shallow, flat, cylindrical container made of glass or plastic, commonly used in laboratories for growing cultures of microorganisms. It typically has a lid that covers the dish, helping to prevent contamination. Scientists use petri dishes to observe the growth of bacteria, fungi, and other small organisms in a controlled environment. These dishes are often filled with a nutrient-rich gel called agar, which provides the necessary food for the microorganisms. Petri dishes are essential tools in microbiology, allowing researchers to study the characteristics and behaviors of various species, including their responses to different conditions and treatments.