Chapter 11 Trophic Levels I.Teaching Objective: 1.Mater food chain and web in ecosystems 2.Help the students to know Lindeman's law of trophic efficiency IL.Focal Points and Difficulties in the Chapter(教学重点和难点) 1.Focus Lindeman's law oftrophic efficiency Pyramid of Biomass 2.Difficulties Food chain and web II.Methodology Powerpoint presentation will be the main method.Blackboard will be an assistance.Fifteen minutes'discussion will be arranged.Some beautiful diagrams have been prepared for visualization. IV Presentation(课堂讲解，学时分配为2学时左右) Step 1.Warm-up Activity Draw Food chain and web 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(twenty minutes) Can you think of a food chain where there are fewer producers than herbivores? Agree or Argue:Highly productive ecosystems cannot support large numbers of secondary consumers