Greenhouses are made almost completely of glass for two reasons. First, glass allows the maximum amount of sunlight into the building. Plants need the sunlight for photosynthesis. Second, glass prevents heat produced in the greenhouse from escaping. Clear plastic can also serve these same two functions. When materials like glass and plastic let sunlight, but not heat, pass through them, this is known as the greenhouse effect, which is a form of solar heating. How does the greenhouse effect work? This Activity will model how a greenhouse effect can occur. This free selection also includes the Table of Contents, Introduction, Safety in the Classroom Practices, Standards Organizational Matrix, and Index.