Metals and non-metals in living systems and the environment
Magnesium and iron are important constituents of chlorophyll in green plants. Iron forms part of the haemoglobin molecule found in red blood cells.
Calcium is essential for the formation of healthy teeth and bones.
Ions of sodium and potassium are needed for the transmission of nerve impulses.
Zinc, copper, manganese and cobalt are examples of trace elements needed by plants and animals for their proper growth and development.
Heavy metals such as lead and mercury are toxic to living organisms, causing brain damage and death. These metals can accumulate in the environment and concentrate in consumers in the food chain, where they become more toxic. Other metals such as tin, cadmium, copper and zinc can affect aquatic animals and are suspected cancer-causing agents.
Ions of nitrogen, phosphorus and sulphur (NO3-, PO43- and SO42-) from untreated sewage, detergents and fertilizers can affect water bodies by causing nutrient enrichment (eutrophication), which can lead to oxygen depletion and death of aquatic organisms.
Insecticides and herbicides can become toxic to animals and can become concentrated up the food chain.
Oxides of nitrogen, sulphur and carbon from the combustion of fuels can dissolve in rainwater, forming acid rain, which is harmful to plants and animals and can corrode buildings.
Chlorofluorocarbons (CFCs) from aerosols can break down the ozone layer, thereby allowing harmful UV radiation to reach earth, which can lead to skin cancers.
Increase in levels of carbon dioxide in the atmosphere has led to an increase in the absorption of infrared radiation (heat) when the ground is heated up by the sun. This is the greenhouse effect. As more heat is trapped by increased carbon dioxide, temperatures rise, which can cause environmental catastrophes such as droughts, hurricanes and melting polar ice caps.
QUESTIONS:
1. What are the effects and causes of acid rain? Acid rain results from the reaction of acidic oxides released as gases with water vapour and falls as acid rain. This damages buildings and metal surfaces. Water bodies such as streams can become acidified, which affects living organisms in these ecosystems. Acid rain can also affect the respiratory systems of humans, resulting in an increase in respiratory illnesses.
2. How do CFCs affect us? Chlorofluorocarbons are substances usually used because of their unreactivity and stability. When CFCs enter the upper atmosphere, they break down and cause the breakdown of the ozone layer which protects life on earth from harmful ultraviolet (UV) radiation. This results in increased heating of the earth’s surface, increased incidences of sunburns and skin cancers.
3. Identify a named metal and suggest its importance or impact on the environment. Iron is a metal which is present in the haemoglobin molecule. This substance is a necessary part of red blood cells which binds to oxygen and helps in its transport around the body.
4. What strategies can be used to reduce the impact of global warming? Since global warming is made worse by increased levels of carbon dioxide, one way to reduce global warming is to reduce the production of carbon dioxide. This includes reducing the use of fossil fuels and replacing this with alternative fuels such as wind, solar and hydroelectricity. Reducing deforestation and replanting trees will aid in reducing the carbon dioxide levels. The possibility of electric cars in the future and those that use fuel cells would also be another useful strategy.