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.
Photosynthesis is the process used by plants, algae and certain bacteria to harness energy from sunlight into chemical energy. There are two types of photosynthetic processes: oxygenic photosynthesis and anoxygenic photosynthesis. Oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria. During oxygenic photosynthesis, light energy transfers electrons from water (H 2 O) to carbon dioxide (CO 2), which produces carbohydrates. In this transfer, the CO 2 is reduced, or receives electrons, and the water becomes oxidized, or loses electrons. Ultimately, oxygen is produced along with carbohydrates. Oxygenic photosynthesis functions as a counterbalance to respiration; it takes in the carbon dioxide produced by all breathing organisms and reintroduces oxygen into the atmosphere.