Step 2.The students are required to finish reading the whole text before the class and try to understand the major points of the chapter.The students are supposed to underline the difficult words or structures and raise their questions concerning any difficulties their may have in their understanding of the text,the teacher is responsible for helping them resolve the above problems. Discussion organization(ten minutes) Organize a group discussion among students to let them talk about population size regulated by density-dependent factors or by density-independent factors Part V.Assignment: Exercises: 1.Compare two types of population growth:Exponential and Logistic 2.Mechanisms of population regulation:Why are some species rare?What factors regulate population size?