Chapter 29 Plant Diversity I

Chapter 29 Plant Diversity I - Chapter 29 Plant Diversity I...

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Chapter 29 Plant Diversity I: How Plants Colonized Land Lecture Outline Overview: The Greening of Earth For the first 3 billion years of Earth’s history, the land was lifeless. Thin coatings of cyanobacteria existed on land about 1.2 billion years ago. About 500 million years ago, plants, fungi, and animals joined them. More than 290,000 species of plants inhabit Earth today. Most plants live in terrestrial environments, including deserts, grasslands, and forests. o Some species, such as sea grasses, have returned to aquatic habitats. The presence of plants has enabled other organisms to survive on land. o Plant roots have created habitats for other organisms by stabilizing landscapes. o Plants are the source of oxygen and the ultimate provider of food for land animals. Concept 29.1 Land plants evolved from green algae Researchers have identified a lineage of green algae called charophyceans as the closest relatives of land plants. Many key characteristics of land plants also appear in a variety of algal clades. Plants are multicellular, eukaryotic, photosynthetic autotrophs. o But red, brown, and some green algae also fit this description. Plants have cell walls made of cellulose. o So do green algae, dinoflagellates, and brown algae. Plants have chloroplasts with chlorophyll a and b. o So do green algae, euglenids, and a few dinoflagellates. Land plants share four key features only with the charophyceans. o The plasma membranes of land plants and charophyceans possess rosette cellulose-synthesizing complexes that synthesize the cellulose microfibrils of the cell wall. These complexes contrast with the linear arrays of cellulose-producing proteins in noncharophycean algae. Also, the cell walls of plants and charophyceans contain a higher percentage of cellulose than the cell walls of noncharophycean algae. o A second feature that unites charophyceans and land plants is the presence of peroxisome enzymes to help minimize the loss of organic products as a result of photorespiration. Peroxisomes of other algae lack these enzymes. o In those land plants that have flagellated sperm cells, the structure of the sperm resembles the sperm of charophyceans.
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o Finally, certain details of cell division are common only to land plants and the most complex charophycean algae. These include the formation of a phragmoplast, an alignment of cytoskeletal elements and Golgi-derived vesicles, during the synthesis of new cross-walls during cytokinesis. Over the past decade, researchers involved in an international initiative called “Deep Green” have conducted a large-scale study of the major transitions in plant evolution. These researchers have analyzed genes from a wide range of plant and algal
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Chapter 29 Plant Diversity I - Chapter 29 Plant Diversity I...

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