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Date November 2021 Marks available 7 Reference code 21N.2.SL.TZ0.4
Level Standard Level Paper Paper 2 Time zone Time zone 0
Command term Explain Question number 4 Adapted from N/A

Question

Identify four factors that make the use of the insecticide DDT controversial.

[4]
a.

Explain how human activities continue to affect stratospheric ozone.

[7]
b.

To what extent is the use of solid domestic waste (SDW) as an energy source beneficial to a society?

[9]
c.

Markscheme

DDT

  1. is a very effective/affordable insecticide;
  2. can help in the management of insect borne diseases/malaria/zika;
  3. can help in the control of agricultural pests, improving harvests;
  4. is a persistent (organic) pollutant / causes soil degradation/aquatic pollution;
  5. has negative effects on human health;
  6. bioaccumulates in the bodies of organisms;
  7. biomagnifies in food chains;
  8. causes impact on non-target species/death of birds of prey/top carnivores;
  9. reduces biodiversity;
a.

Introductory explanations:

  1. ozone depleting substances (ODSs)/CFCs disrupt (the dynamic equilibrium of) ozone formation;
  2. ODSs are halogenated organic gases such as chlorofluorocarbons (CFCs) / halons;
  3. ....used as cooling agents (old refrigerators, air-conditioning units) / aerosol propellants (spray cans) / blowing agents (insulating foams) / fire-extinguishers / cleaning solvents (electronic equipment) / pesticides;

    Activities that lead to increase/restoration of ozone:
  4. pollution management may be achieved by reducing the manufacture and release of ozone-depleting substances;
  5. methods for this reduction include recycling refrigerants/developing alternatives to gas-blown plastics/ halogenated pesticides/propellants and aerosols/developing non-propellant alternatives;
  6. the Montreal Protocol (on Substances that Deplete the Ozone Layer (1987)) (and subsequent updates) is an international agreement for the reduction of use of ODSs;
  7. this is considered to be a very successful international agreement;
  8. national governments complying with the agreement made national laws and regulations to decrease the consumption/production of ODSs;

    Mechanisms that lead to reduction/destruction of ozone:
  9. UV light breaks apart the ODSs/CFCs and releases a halogen atom;
  10. halogen atom breaks an ozone molecule apart and combines with an oxygen atom;
  11. oxygen atoms combine with the oxygen from the halogen and release the halogen to start the process again;
  12. .… the halogen is considered a catalyst / why the reaction is cyclical;

    Explanations of “continuing” effect on ozone:
  13. ODSs/CFCs have a very long lifetime in the atmosphere / there is a time lag from removal of ODSs to the end of ozone destruction;
  14. halogen atoms are removed very slowly from stratosphere; (Cl by a chemical reaction with methane forming hydrochloric acid)
  15. an illegal market for ozone-depleting substances persists and requires consistent monitoring;
  16. some countries are still not complying with international agreements on bans;
  17. HCFCs may have lower ozone depleting potential, but still destroy ozone (not phased out before 2020);
  18. increasing GCC/GHGs affect polar weather conditions (increasing temperature difference between troposphere and cooler stratosphere), thus affecting the distribution of ozone (positively in 2019, negatively in 2020); (Note that this should be the only link with GCC accepted)

Notes: Award [5 max] if there are no explanations of “continuing” effect on ozone.
Accept CFCs as alternative to ODSs.

b.

Refer to paper 2 markbands, available under “your tests”  tab > supplemental materials

The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria given in each of the markbands (although “ESS terminology” has been conflated with “Understanding concepts”). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.

Answers may include:

c.

Examiners report

Majority were able to identify one or two controversial aspects of DDT although few gained full credit.

a.

Majority were able to link stratospheric ozone and ozone depleting substances like CFC but frequently answers were confused with aspects of greenhouse gases and global warming.

b.

Majority of answers were completely valid but rarely did they explore the question with sufficient breadth.

c.

Syllabus sections

Topic 6: Atmospheric systems and societies » 6.2 Stratospheric ozone
Topic 6: Atmospheric systems and societies

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