2014年托福阅读模拟练习4.docx

The Evolutionary Origin of Plants Paragraph 1 The evolutionary history of plants has been marked 1a series of adaptations. The ancestors of plants were photosynthetic single-anisms that gave rise to plants presumably lacked true roots, stems, leaves, plex reproductive structures such as flowers. All of these features appeared later in the evolutionary history of plants. Of today's different groups of algae, green algae are probably the most similar to ancestral plants. This supposition stems from the close ic (natural evolutionary) relationship between the two groups. parisons have shown that green algae are plants' closest living relatives. In addition, othef lines of evidence support the hypothesis that land plants evolved from ancestral green algae used the same type of chlorophyll and accessory pigments in photosynthesis as do land plants. This would not be true of red and brown algae. Green algae store food as starch, as do land plants and have cell walls made of cellulose, similar position to those of land plants. Again, the good storage and cell wall molecules of red and brown algae are different. Paragraph 2 Today green algae live mainly in freshwater, suggesting that their early evolutionary history may have occurred in freshwater habitats. If so, the green algae would have been subjected to environmental pressures that resulted in adaptations that enhanced their poten