This teacher's guide presents teaching suggestions and presentation materials about the importance of biodiversity, examines why it is threatened, and suggests ways of conserving it. The lesson is divided into seven parts and suggests allowing two or more class periods for completion. Student handouts include: (1) "Test Yourself: How Much Do You Know about Biodiversity?"; (2) "Facts about Biodiversity"; (3) "Collecting Species Data in Costa Rica"; and (4) "Answers to 'How Much Do You Know about Biodiversity?'" Transparency masters are titled: (1) "Species Remaining to be Described"; (2) "Wetland Loss in Selected Industrialized Countries, 1950-80"; (3) "Trends in Deforestation and Population Growth, 1850-1980"; and (4) "Tropical Areas with Rich Floral Diversity." (EH)