Exam 1: Recycling nutrients
Although ecosystems receive an inexhaustible influx of solar energy, all chemical elements are available only in limited amounts. Life therefore depends on the recycling of essential chemical elements such as carbon and nitrogen (remember the elements carbon and nitrogen are not created or destroyed, they are just cycled from one type of molecule to another). Micro-organisms play an important role in the process of decay, releasing compounds of these elements from the bodies of dead organisms.
The Carbon cycle
Carbon dioxide is added to the air by the respiration of animals, respiration of plants and respiration of microorganisms (decomposers such as bacteria and fungi) and by the combustion of fossil fuels. Photosynthesis takes place on such a great scale that it re-uses almost as much carbon dioxide as is released into the atmosphere from respiration on a daily basis. The production of carbohydrates, proteins and fats contributes to plant growth and subsequently to animal growth (through consumption and assimilation) involving complex food webs.
The dead remains of plants and animals are then acted upon by saprophytes in the soil. Here, fungi and bacteria secrete digestive enzymes on to the dead organic material and absorb the breakdown products of digestion through their cell membranes. These micro-organisms use the absorbed glucose for respiration (to release energy) which ultimately releases gaseous CO2 (as a waste product of respiration) back to the atmosphere.
In past times, large quantities of dead organisms accumulated in anaerobic conditions where they were prevented from being decaying by saprophytes. In time they formed coal, oil and other fossil fuels. The burning of these fuels returns more CO2 to the atmosphere and has resulted in a rise in CO2 in the atmosphere, particularly over the last 50 years.
Although ecosystems receive an inexhaustible influx of solar energy, all chemical elements are available only in limited amounts. Life therefore depends on the recycling of essential chemical elements such as carbon and nitrogen (remember the elements carbon and nitrogen are not created or destroyed, they are just cycled from one type of molecule to another). Micro-organisms play an important role in the process of decay, releasing compounds of these elements from the bodies of dead organisms.
The Carbon cycle
Carbon dioxide is added to the air by the respiration of animals, respiration of plants and respiration of microorganisms (decomposers such as bacteria and fungi) and by the combustion of fossil fuels. Photosynthesis takes place on such a great scale that it re-uses almost as much carbon dioxide as is released into the atmosphere from respiration on a daily basis. The production of carbohydrates, proteins and fats contributes to plant growth and subsequently to animal growth (through consumption and assimilation) involving complex food webs.
The dead remains of plants and animals are then acted upon by saprophytes in the soil. Here, fungi and bacteria secrete digestive enzymes on to the dead organic material and absorb the breakdown products of digestion through their cell membranes. These micro-organisms use the absorbed glucose for respiration (to release energy) which ultimately releases gaseous CO2 (as a waste product of respiration) back to the atmosphere.
In past times, large quantities of dead organisms accumulated in anaerobic conditions where they were prevented from being decaying by saprophytes. In time they formed coal, oil and other fossil fuels. The burning of these fuels returns more CO2 to the atmosphere and has resulted in a rise in CO2 in the atmosphere, particularly over the last 50 years.