高中英语 Unit 4 Exploring plants Backgrounds f or Unit

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 f or Unit 4 Exploring plants
1.Importance of Plants
Plants 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 p lants. Th e cattle we eat as beef, feed on grasses and the fish we eat, consume algae and are therefore dependen t 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 level s, and reducing soil erosion and water runoff.
2. The life cycle of a plant
The 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 bo n 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.
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