Sterols are a type of lipid molecule that play a crucial role in the structure and function of cell membranes. They are characterized by a complex ring structure and are found in both plants and animals. One of the most well-known sterols is cholesterol, which is essential for maintaining cell membrane integrity and is also a precursor for the synthesis of steroid hormones. In plants, sterols such as phytosterols help to stabilize cell membranes and can also contribute to the plant's defense mechanisms. These compounds are important for human health as well, as they can help lower cholesterol levels when consumed in the diet. Overall, sterols are vital for various biological processes across different organisms.