Describe the relationship between the rise in the concentration of atmospheric carbon dioxide and the enhanced greenhouse effect.

Outline the precautionary principle.

Antibiotic resistance in bacteria is an example of evolution in response to environmental change. Using another example, explain how an environmental change can lead to evolution.

CO₂ is a greenhouse gas;
increases in CO₂ increase/enhance the greenhouse effect;
greenhouse effect is a natural phenomenon but not its increase;
Earth receives short wave radiation from the sun;
reradiated from Earth as longer wave radiation/infra red/heat;
CO₂ /greenhouse gases trap/absorb longer wave radiation/infra red/heat;
global warming happened during same time/period as CO₂ rise;
CO₂ concentration correlated (positively) with global temperature / global temperature increases as CO₂ concentration increases;
(causal) link accepted by most scientists;
no proof that man-made increases in CO₂ have caused global warming;

those proposing something must prove that it causes no harm;
before they start to do it;
objectors do not have to prove that there will be harm;
activities that risk/threaten/may cause harm are banned;
trials/tests must be done first;
precautionary principle is applied when possible consequences are severe;
precautionary principle should be used in the case of global warming;
action should be taken to reduce CO₂ emissions before proved it is the cause;
another example of implementation of the precautionary principle;

natural selection (in correct context);
better-adapted individuals survive/more likely to survive;
more reproduction/genes passed on by better adapted individuals;
name of species; (accept even if remainder of answer is invalid)
description of original/decreasing phenotype;
type of environmental change that led to evolution;
consequence of environmental change
description of new/increasing phenotype;
genetic basis of phenotypes;
reason for new phenotype being better adapted;
detail of reason for adaptedness of new phenotype;

The following has been provided as an example answer.
great tit;
bird that lays its eggs in spring;
global warming/climate change;
more caterpillars (on trees) in early spring;
laying eggs earlier in spring;
time of egg laying is (partly) genetically controlled;
eggs laid early hatch at start of period of greatest food abundance;
more young can be fed/young grow faster/fewer deaths;

Answers to part (a) were varied but mostly were rather weak, with confusion about long wave and short wave radiation and between the greenhouse effect and ozone depletion. Most answers explained the greenhouse effect in general terms and only a few really described the relationship between the rise in atmospheric carbon dioxide and the enhanced greenhouse effect. The best answers explained that the greenhouse effect is a natural phenomenon but that there was been an anthropogenic increase in carbon dioxide concentrations that is positively correlated with global warming. Although not proven, almost all climate scientists accept that there is a causal link.

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Part (b) was also poorly answered on the whole, with much evidence of guesswork rather than secure understanding. The term precautionary principle has been used in different ways and a teacher‟s note was therefore inserted in the current IB Biology programme, to make clear what is expected in answers to IB Biology questions. Teachers are encouraged to follow the guidance in that note.

Part (c) of this question was also poorly answered. Fewer than half of candidates gave an acceptable example of evolution in response to environmental change. Candidates were expected to give a real and well documented example, with the species named and the precise environmental change explained. Resistance to a named pesticide in a named pest species was acceptable for example, but not accounts of how resistance might develop in general. Giraffes were not accepted as an example, as their evolution cannot be tied in to any proven and specific environmental change. The human examples that were seen in candidates' answers were also not accepted.  

Many candidates' answers were vague and confused and in some cases were based on guesswork, in the hope that examiners might not realise. It is of course unacceptable to fabricate examples and evidence in science, whether in an exam or any other situation. Particularly with evolution, any assertion that we make should be based on reliable evidence. Despite these negative comments about the quality of answers, some were excellent with a clear explanation of how the characteristics of a species can change by natural selection when the environment of a species has changed.