2014-2015学年高中英语 Unit 4 Exploring plants Backgrounds f or Unit 4 Exploring plants教案 新人教版选修9

Section 1 Backgrounds for Unit 4 Exploring plants1. Importance of PlantsPlants form the basic food staple for all life forms. They a re the major source of food and oxygen on earth, since no animal can supply these necessary components without plants. The cattle we eat as beef, feed on grasses and the fish we eat, consume algae and are therefore dependent on plants for well being. Other important uses of plants include, providing shelter for animals, providing materials for clothing (cotton fibers), paper products, medicines and other chemicals, producing coal from once living plant materi al, reducing wind speed and noise levels, and reducing soil erosion and water runoff. 2. The life cycle of a plantThe life cycle of a plant varies depending on the individual species. There are, however, certain requirements for life that most plants need. The growth of a plant is dependent upon light, water, oxygen, car bon dioxide, minerals in the soil, temperature and microbes in the soil. Light, water, and carbon dioxide are needed for photosynthesis which produces food for the plant. Oxygen is needed when it is dark, because the plant then needs oxygen to maintain itself.