1 Most cases of COPD, and therefore emphysema, are caused by cigarette smoking. 2  Emphysema is rarely caused by a congenital condition known as Î±1-antitrypsin deficiency, for which there is a lab test. 3  Shortness of breath and cough are the main symptoms of emphysema.
Most plants, most algae, and cyanobacteria perform photosynthesis; such organisms are called photoautotrophs. Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth's atmosphere, and supplies all of the organic compounds and most of the energy necessary for life on Earth.
The three types of photosynthesis are C3, C4 and CAM photosynthesis. The definition of photosynthesis and the general equation can be found under Overview of Photosynthesis. Plants perform photosynthesis because it generates the food and energy they need for growth and cellular respiration. It is important to note that not all plants photosynthesize. Some are parasites and simply attach themselves to other plants and feed from them.