4-12. The two ecological pyramids mentioned in the diagram explain the reason as to why a majority of the people in developing countries consume a vegetarian diet, which has corn, rice and wheat instead of meat. For example, as the figure depicts, in the grain to human food chain, ten human can feed on the 20000 kilocalories of grain per day . If a steer consumes the same 20000 kilocalories of grain and then the humans consume the beef, the 2000 kilocalories of food produced from the beef is sufficient for one person only. Hence, shorter food chains provide more food to the top-level consumers.
Converting to vegetarianism is not only good for the health of the individuals, but also for the environment. Also, a vegetarian diet requires less grain production than a non-vegetarian diet. On the other hand, vegetarianism has a potential impact on the environment as it involved plowing lands and forests in order to grow the food. Also, the use of pesticides and fertilizers on the crops adversely affects the health. Shortening the food chain is not always advisable; however, it allows feeding more people with the same amount of food . In my opinion, I prefer vegetarian diet as it is environmentally friendly and does not involve the slaughtering of animals.
4-13: 4-14. Natural systems are primarily dependent on sun and the recycling of nutrients for their sustenance. The term nutrient refers to all ions and molecules present in the living organisms. In the case of ecosystems, the nutrients pass through a cycle called nutrient cycle or biogeochemical cycle, in which the nutrients flow from the environment into the food web and back into the environment. Carbon cycle is one of the most important nutrient cycles as it undergoes changes throughout the cycle. Carbon dioxide is available in the atmosphere in the form of air and surface water, which includes lakes, ponds, rivers and oceans . Plants and other photosynthetic organisms absorb carbon dioxide, during which carbon dioxide enters the organismic phase of the carbon cycle. The organisms convert carbon dioxide into organic food, which passes through the food chain. The next phase is the environmental phase, in which carbon dioxide enters the environment through the process of cellular respiration, which takes place in the grazer and decomposer food chains .
People should care about carbon cycle because, due to industrial revolution, the amount of carbon dioxide increased in the atmosphere due to the excess utilization of fossil fuels and deforestation. In the recent decades, the amount of carbon dioxide increased in the atmosphere by 30 percent, which is very huge. Due to excess atmospheric carbon dioxide, there is an increase in the global temperatures as carbon dioxide traps the heat and sends it back to the earth’s surface . Increase in global temperatures in turn alters the rainfall pattern, agricultural production, which leads to the extinction of several species. Also, increase in global temperature due to excess carbon dioxide melts the glaciers, thereby causing a rise in the sea level.
4-15. Nitrogen cycle is another important nutrient cycle, which involves element nitrogen. Nitrogen is essential to the biological molecules, such as DNA, RNA and amino acids. Since elemental nitrogen is unstable, it takes the form of nitrate or ammonia through the process of nitrate fixation. Leguminous plants contain bacteria in their root nodules, which convert nitrogen into ammonia or ammonium ions . After the production of ammonia, the bacteria present in the soil convert it into nitrite and finally to nitrate. Plants incorporate nitrates to make nucleic and amino acids. Consumers receive the nitrogen from the plants. The decay of animal and plant wastes also produces nitrate, which decomposes to form ammonia. Ammonia again converts into nitrite and nitrate for reuse. Certain amount of ammonia converts into nitrite and then to nitrous oxide through the action of bacteria . Nitrous oxide converts into elemental nitrogen and releases into the atmosphere.
People should care about the nitrogen cycle because they are responsible for altering the cycle in various ways. The excess usage of fertilizers containing nitrogen pollutes the waterways. The disposal of nitrogen waste in the sewage also ends up settling in the waterways. Another reason is the feeding of cattle on feedlots, which are adjacent to waterways. The burning of fossil fuels also releases nitrous oxide and nitrogen into the earth’s atmosphere. Nitrogen alters the pH balance in the ecosystems, especially in aquatic ecosystem causing harm to millions of species . Also, atmospheric nitrogen returns to the earth in the form of rain and snow. Since nitrogen is a stimulant, its presence in the water leads to the growth of dense vegetation and causes difficulties in navigation.
Byrne, K. (2001). Environmental Science. Nelson Thornes.
Chiras, D. D. (2013). Environmental Science, 9th ed. Jones & Bartlett Learning.