chapter 9

MARKING SCHEME

ACTIVITY:

The diagrams show an environmental phenomenon.  Name the phenomenon and explain how the phenomenon occurs.

1. Ozone Depletion	Explanation Ozone gas (O3) occurs naturally in the stratosphere layer. This ozone layer shields the surface of the earth from UV radiation. The main cause for ozone depletion is chlorofluorocarbon (CFC) CFC is unreactive, remain unchanged  for over 100 years, and able to reach the stratosphere to affect the ozone layer. Ultraviolet radiation breaks down CFCs, releasing chlorine. Chlorine atoms react with ozone molecules, forming chlorine monoxide and molecular oxygen.      Chlorine + ozone                    Chlorine + oxygen         atom                                   monoxide           chlorine + oxygen                 chlorine + oxygen     monoxide Chlorine monoxide reacts with oxygen atom molecule to reform chlorine atom, releasing molecular oxygen. The chlorine atom is not attended by this process. It keeps reacting and breaking down the ozone molecule. Lastly, the ozone layer will be depleted.
2. Greenhouse Effect	Explanation When sunlight enters the Earth’s atmosphere, some of its solar radiation is reflected back to space while most of the radiation is absorbed by the Earth. Heat in the form of infrared radiation is radiated back into space Much of this heat does not escape from the atmosphere but remains trapped by the greenhouse gases, causing the atmosphere to be warmed. At the same time, the greenhouse gases also radiate infrared rays towards the surface of the Earth. Greenhouse gases in the atmosphere behave a lot like the glass panes of a greenhouse which trap the heat and warm the greenhouse.
3. Acid Rain	Explanation Combustion of fossil fuel (coal, air and gas) in power stations, industries, domestic boilers and internal combustion engines releases large quantities of sulphur dioxide and oxides of nitrogen. Both sulphur dioxide and oxides of nitrogen may be deposited immediately out of the air as ‘dry depositions’ or, Combine with water vapour in the atmosphere to form sulphuric  acid and nitric acid respectively (‘wet depositions’) Then they fall back on Earth as acid rain.

OBJECTIVE QUESTIONS:

1. D

2. A

3. C

4. B

5. A

STRUCTURED QUESTION:

1. (a)(i) Carbon dioxide

         (ii) The burning of fossil fuels such as petrol, coal and natural gas in the industrial areas.

      (b)(i) Greenhouse effect

          (ii) Light rays from the sun are able to penerate the atmosphere and warm the earth.  Some of them will arrive on the earth’s surface and then are reflected as infrared rays.

              The thick carbon dioxide layer will reflect the infrared rays back to earth and increase the earth temperature.

          (iii) 1. Ice block melt and causes a rise in a sea level

                2. The direction of wind changes causes storms

      (c )1. Protection and conservation of the forest

           2. Find alternative sources of energy such as solar energy or development of fuel cell to replace fossil fuels.

2. (a) Coal

(b) The mining industry or factories which use coal as a source of fuel.

(c ) Open burning and large-scale cutting down of trees in the forest.

(d) Photosynthesis

(e)(i) Greenhouse effect

    (ii) * When sunlight enters the earth’s atmosphere, some of its solar radiation is reflected back to space while most of the radiation, absorbed by the earth, warm the land and sea surfaces.

          * Heat energy reflected back into the atmosphere by the earth’s surface is in the form of infrared rays.

                     * This heat energy is reflected back and absorbed by the greenhouse gases, such as carbon dioxide in the atmosphere.

                     * The absorption of this heat energy brings about global warming.

           (f) Changes in  the wind direction and uneven rainfall distribution.  As a result, some places experience prolonged droughts whereas other places experience storms.

               Global warming causes shifting of plant zones on hillsides.  Plants and animals that live on mountain peaks would probably become extinct and are replaced by plant and animal species from the lower zones.

ESSAY QUESTION:

1.(a)(i)- CFC and  aerosols from  air conditioners are  released to the stratosphere                                                                                             1

          - Ultraviolet rays will break the bonds of CFC molecules to release

             chlorine                                                                                                     1                                                                                                                                                                                       

          - Chlorine will combine with ozone to produce chlorine monoxide and oxygen molecules                                                                                    1

     - Chlorine monoxide will combine with free oxygen molecules to produce chlorine and oxygen molecules                                                                1

     - This process will go on as the chlorine continues to destroy other ozone molecules                                                                                                 1

     - The more ozone molecules are destroyed, the thinner the ozone layer will be.                                                                                                      1

                                                                                                                      6m

  

 (ii)  Effects:

-        Causes skin cancer and cataract                                           1

-        Plankton are destroyed and the aquatic ecosystem is disrupted                                                                                1

-        Greenhouse effect                                                                 1

-        Photosynthesis rate decreases as the leaves shrink in size and chlorophyll is reduced.                                                    1