Chemistry - Energy
1. “The energy for life comes from the sun.”
Outline the role of the photosynthesis process to explain what is meant by this statement. (3 marks) chlorophyll
6CO2(g) + 6H2O(l) + energy C6 H12 O6 (aq) + 6O2(g)
2830 kJ glucose
Photosynthesis is the process in which plants use the sun’s light energy to convert carbon dioxide and water into carbohydrates such as glucose, sucrose, starch and cellulose.
Carbohydrates are high energy compounds because when they react with oxygen, they produce large amounts of energy. Plants make their own food by using the glucose they produces as an energy source for growth, reproduction, repairing damaged tissues... Animals cannot carry out photosynthesis, so they eat the plants to obtain food, hence, energy. For that reason the energy for life comes from the sun.
2. Explain what is meant by thermal pollution and discuss the implications for aquatic life. (3 marks)
Thermal pollution is a discharge into a river or lake of a lot of hot water which is enough to significantly (2°C to 5°C) increase the temperature of water. This abnormal increase in temperature is potentially harmful to aquatic organisms in these ways:
• Stress to organisms due to less dissolved oxygen.
• Increase metabolism which would increase oxygen demand, and this would lead to decreasing oxygen supply.
• Fish eggs don’t hatch.
• Migration and spawning would be set off at the wrong time due to false temperature cues.
• Sudden change in temperature would kill off fish eggs even if the temperature is in the egg’s survival range.
3. Identify the sources of pollution which accompany the combustion of organic compounds and explain how these can be avoided. (6 marks)
Carbon dioxide is produced by power plants and motor vehicles by complete combustion when there is plenty of oxygen supply. It...
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