Pollutants are substances with which organisms have had no prior evolutionary experience, in terms of kinds or amounts, so adaptive mechanisms are not in place that can deal with them. Much of the world_s land, air and water are partially polluted by chemical wastes. Pollutants affect all of the abiotic factors on which plants survive. Each of the abiotic factors necessary for plant survival, which is necessary for our survival is increasingly subjected to pollutants, locally and globally.
____
Pollutants affect cycles in nature which are necessary for our survival. Plants are an integral part of these cycles. All of the world around us is continually involved in cycles of some sort or another. There are three cycles, however, that are responsible for the recycling of those key elements that make up all life: carbon, hydrogen, oxygen, nitrogen (C,H,O,N). Every living organism needs these elements on a continual basis in order to survive. Without them being continually renewed on our planet, life could not exist. The three cycles responsible for providing the continual flow of these elements are: the water cycle, the carbon-oxygen cycle, and the nitrogen cycle.
____
The Water Cycle includes precipitation, evaporation and transpiration. Plants need the water from precipitation. Precipitation is rain, sleet, snow and other forms of moisture that come from the sky. They also, however, contribute to this process through respiration. Water is released during photosynthesis and evaporates into the atmosphere.
____
Plants drive, and are critical to the Carbon-Oxygen cycle. Through photosynthesis and respiration, atmospheric carbon dioxide (CO2) is converted to oxygen (O2). Plant decay creates stored carbon as well. Carbon Dioxide is essential for the growth of food, through the process of photosynthesis. Through this process, oxygen upon which all organisms survive, is released. In photosynthesis, plants take in carbon dioxide and release oxygen. This process gives energy to plants, but gives energy to us as well.
____
Plants are critical to the Nitrogen Cycle as well. Approximately 78% of air is Nitrogen. Nitrogen is important to life because it is a key part of amino and nucleic acids. Also, it is an important part of ATP, the basic energy molecule for living things. Neither plants or animals can obtain nitrogen directly from the atmosphere. Instead, they depend on a process known as nitrogen fixation. Key players in this process are legumes and bacteria are known as nitrogen-fixing bacteria. These organisms convert nitrogen in the soil to ammonia, which can then be taken up by plants.
____
After nitrogen has been fixed, other bacteria convert it into nitrate, in a process known as nitrification. In the first step of this process, Nitrosomonas convert ammonia into nitrite, and in the second step, nitrite is converted into nitrate, by Nitrobacteria. This nitrate is then consumed by plants.
____
The final aspect of the nitrogen cycle is the process of denitrification. This process is performed by a variety of microscopic bacteria, fungi, and other organisms. Nitrates in the soil are broken down by these organisms, and nitrogen is released into the atmosphere. This complete the cycle. Have students diagram and label each of the three cycles in nature.
____
Plant life is critical to all three life cycles. It is absolutely necessary for these cycles to function. However, plants can also causes imbalances in these systems. They absorb water from the ground which is released during transpiration and evaporates, contributing to the water cycle. However, too much growth is blamed on desertification which robs areas of necessary water. They absorb nitrates from the soil and do not replace all they absorb when they decay. Nitrogen is needed as a compound for the growing of plants. But nitrogen-fixed fertilizers are overburdening the environment with nitrogen and upsetting the complex nitrogen cycle. Nitric Oxide is one component of smog.
