Impact of metals and non-metals on living systems and the environment
Francine Taylor-Campbell, Contributor

Hands clasped and eyes closed, this Spot Valley High School student takes time out to pray. - Claudine Housen/Staff Photographer

MAIN POINTS

Water is made available for mankind through the water cycle in which there is a continual exchange of water between the surface of the earth and the atmosphere. The essential processes in the cycle are evaporation, condensation, transpiration, precipitation and runoff.

Nitrogen is made available to living systems through the process of fixation. This can occur in three ways; atmospheric fixation, industrial fixation and biological fixation.

The carbon cycle maintains the concentration of carbon dioxide in the air. This gas is taken in by plants and converted to organic compounds through the process of photosynthesis and is released by plants and animals through respiration.

NON-METALS AND LIVING SYSTEMS

1. Carbon dioxide and water are important elements in the process of photosynthesis. 6CO2(g) + 6H2O(l) ===== C6H12O6(aq) + 6O2(g)

sunlight / chlorophyll

2. Oxygen is important to the process of respiration in which food is burnt to produce energy. C6H12O6(aq) + 6O2(g) ==== 6CO2(g) + 6H2O(l) + energy

3. Nitrogen and sulphur are important in protein synthesis, which is essential for growth and development of tissues.

4. Phosphorus is an important plant nutrient and helps to build strong bones and teeth.

5. Water, containing the elements hydrogen and oxygen, is a universal solvent, which is essential for many processes and reactions in living cells.

NON-METALS AND THE ENVIRONMENT

1. Ions of nitrogen, phosphorus and sulphur (NO3-, PO43- and SO42-) from untreated sewage, detergents and fertilisers can affect water bodies by causing nutrient enrichment which can lead to oxygen depletion and death of aquatic organisms.

2. Organic waste from sewage can affect aquatic organisms by depleting their oxygen supply.

3. Insecticides and herbicides can become toxic to animals and can become concentrated up the food chain.

4. 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.

5. Chlorofluorocarbons (CFC's) from aerosols can break down the ozone layer thereby allowing harmful UV-radiation to reach earth, which can lead to skin cancers.

METALS AND LIVING SYSTEMS

1. Magnesium and iron are important constituents of chlorophyll in green plants. Iron forms part of the haemoglobin molecule found in red blood cells.

2. Calcium is essential for the formation of healthy teeth and bones.

3. Ions of sodium and potassium are needed for the transmission of nerve impulses.

4. Zinc, copper, manganese and cobalt are examples of trace elements needed by plants and animals for their proper growth and development.

METALS AND THE ENVIRONMENT

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.

Our next series of lessons will focus on past paper questions on metals and non-metals

Francine Taylor-Campbell is an independent contributor.