Sec 2 Normal (A) CT1.2009 Answer

Here is the marking scheme for your Common Test (Term 1, 2009)Please understand that this is only a guideline. I must read your whole answer in context in order to award the correct marks.

Question 1ai)
- Similar pattern for all 3 gases
- Increase slower/steadily before 1900
- Begin accelerating after 1900
- Sharp increase around year 1950/ very steep curve

Any 3 clear descriptions of the trend/pattern observed in the graphs.
1 mark for only mere description of any graph without stating any trend or pattern.


Question 1aii)
- Increase population (esp. sharp increase around 1950) leads to increase demand for food and land
- More forests are destroyed for food/agricultural and residential purposes
- When more forests are destroyed, CO2 in the atmosphere will increase. Moreover, some forests are destroyed through burning, which will release more CO2.
- Increased wet rice farms and cattle ranches caused by demand from a larger population increases the release of methane
- More fertilisers are used on farms to increase food production. This account for the increase in nitrous oxide in the atmosphere.

5 points @ 1 mark each


Question 1bi)
- Carbon Dioxide [1]
- CO2 remains in the atmosphere a lot longer than most of the other gases
- CO2 is released into the atmosphere on a daily basis e.g. burning of fossil fuel
- Industrialisation and number of motor vehicle on the road is still increasing as more countries become develop
- Deforestation removes trees, which should control the amount of CO2
- Deforestation which involves burning of trees will further increase amount of CO2

1 mark allocated to name of gas
Max 5 points @ 1 mark each; for explanation


Question 1bii)
- Increasing global temperature leading to the melting of glaciers, ice in north and south pole
- Habitat of polar bears (Arctic circle) is being destroyed as the ice melts
- Without suitable habitat for food and reproduction, the polar bear will face extinction
- Global warming will cause more extreme weather condition (e.g. hotter summers, flooding)
- Farmers are unable to cultivate crop during the expected seasons, and harvest is destroyed by the extreme weather
- This harvest usually provide food for the Cambodians for the rest of the year
- This results in food shortage for the Cambodians in year 2002

2 marks for each phenomenon, or max.
Students expected to explain all 3 phenomenon. Total of 6m.


Question 2ai)
- Fertiliser runoff/ pesticide dusting - when farmers use fertilisers/ pesticide excessively, the rain will wash the excess into the river and pollute its water
- Oil Spill - tanker accidents will pollute the sea with oil that its carrying; the action of the wind and waves will spread the oil over a large area of the sea
- Urban waste/ industrial waste/ septic tank - sewage from the urban city/ industries/ household might be discharged/disposed into the river before it has been treated at the sewage treatment plant
- Leakage from the septic tank might also pollute the river water when it's carried by the underground water
- Non-biodegradable substances cannot be broken down even if it goes through sewage treatment. They are then discharged into the sea, polluting the water

2 marks for each way explained. No marks for mere listing.
2 marks X 3 ways (Total 6 marks)


Question 2aii)
- during an oil spill, a layer of oil will spread over the sea; sea birds and mammals who come into contact with the polluted water will dirty their feathers and fur
- the oil will remove air trapped by the feathers and fur, causing these creatures to either freeze to death or drown
- sea creatures who consume the polluted water will also be poisoned
- sunlight will also be blocked by the layer of oil, thus affecting the growth of aquatic plants and planktons beneath
- when the oil is washed ashore, the beaches will also be polluted; this in turn also affect any plants or creatures which are found on the polluted beaches

5 points @ 1 mark each


Question 2bi)
- dust and smoke particles can cause irritations in people's throat and eyes
- in more serious cases, they can also suffer from respiratory problems (such as asthma and bronchitis)
- toxic gases (sulphur dioxide and nitrogen oxides) which pollutes the atmosphere also attack the respiratory system, giving rise to lung and heart diseases
- when exposed to air pollution over a long period of time, the lifespan of these victims can also be shortened
- when workers fall ill and go on medical leave, the workforce will be affected and production drops

4 points at 1 mark each
1 mark for just lifting the answer from the passage

Question 2bii)
- Power stations and manufacturing plants are usually found in the cities. These are major sources of pollution
- As fossil fuel is burnt to generate power and in the process of manufacturing, soot and sulphur dioxide are produced
- The number of motor vehicles on the city road is also much higher than the country side.
- Vehicle emission contains harmful gases such as carbon monoxide and nitrogen oxides into the atmosphere
- Construction of buildings also takes place rapidly in the city area. This activity create huge amount of dust particles and smoke, thus adding to the problem of air pollution

5 points @ 1 mark each