Plant Evolution

Satisfactory Essays

Plant Evolution

Colette Andrews
Strayer University

SCI 115
Dr. David Davies
November 24, 2012

Plant Evolution has been around for millions of years. In fact, plants were the first species on earth and the first to live on land (“Plant Evolution”, D. Davies, accessed 11/24/12). For 1500 million year’s photosynthetic organisms remained in the sea. This is because, in the absence of a protective ozone layer, the land was bathed in lethal levels of UV radiation. Once atmospheric oxygen levels were high enough the ozone layer formed, meaning that it was possible for living things to venture onto the land (The University of the West Indies. Department of Biological and Chemical Sciences 2003-2012). The seashore
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Poikilohydric organisms have no mechanisms to prevent desiccation: they desiccate, and remain dormant, when their environment dries out, but can rehydrate when water becomes available again. They usually absorb water directly through their body surface. Poikilohydric organisms include some green algae, cyanobacteria (blue-green algae), lichens, and the bryophytes (The University of the West Indies. Department of Biological and Chemical Sciences 2003-2012). Homoiohydric plants can keep their water content constant, and don't equilibrate with the environment.

This is achieved by: * Controlling water loss (waterproofing, cuticle) * Controllable valves in cuticle for photosynthesis (stomata) * Replacing lost water, internal conducting tissue (xylem): vascular plants * 3D structure: minimizes surface area, provides support * Ventilated tissue for enhanced gas exchange (internal intercellular spaces) * All modern land plants - with the exception of the bryophytes - have these features.
There was also competition for light, leading to pressure to increase productivity, which could be achieved by increasing the area available for photosynthesis (evolving leaves) and/or keeping stomata open for longer. This meant that mechanisms for obtaining and transporting water also needed improvement. Thus, evolution was a slow, continuous, linked improvement in water relations and productivity increase Homoiohydric plants can keep their water
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