In IB Biology HL D1.3.4, mutations can arise from replication errors, repair errors or chromosome damage. Mutagens include chemicals, ionizing radiation and ultraviolet radiation.
Tobacco smoke contains a number of mutagens that are known to induce lung tumours in rodents, including NNK, a nitrosamine. The graph shows the relationship between NNK and lung tumour incidence in male rats. NNK was administered by subcutaneous injection for 20 weeks. Data points on the graph show percentage incidence of lung cancer in treatment groups of between 20 and 80 rats.
Graph removed for copyright reasons
State the relationship between the dose of NNK and lung tumour incidence.
positive correlation
OR
lung tumour incidence increases as dose increases/OWTTE
Explain the effects of mutagens such as NNK.
a. NNK/mutagens alter «base» sequence of DNA/alter genes/create new alleles
b. increases rate/frequency/incidence of mutations
c. in oncogenes/in genes that control cell division/mitosis
d. tumors/cancers «develop/grow» if cell division/mitosis is uncontrolled
Rates of lung cancer in smokers are high. Discuss whether it can be concluded from the evidence in the two graphs that NNK causes lung cancer in smokers.
Nicotine addiction is the reason that people continue to smoke. Nicotine replacement therapy (NRT) is often used to help people quit smoking. Concerns about the safety of NRT led to a study where mice were given nicotine in drinking water and NNK was administered by subcutaneous injection. The table shows the effect of nicotine consumption on NNK-induced lung tumours in the mice.
Table removed for copyright reasons
a. first graph/data/research shows that NNK induces lung tumors/causes cancer
b. second graph shows that smokers have absorbed NNK «from smoke»/shows that there is NNK in the blood of smokers
c. results are for rats not humans
d. injection of NNK and not inhalation of tobacco smoke
e. dosage of NNK much larger than amounts likely in smokers
f. other chemicals in smoke could cause lung cancer «in addition to those caused by NNK»/no proof that NNK is the only cause
Describe the results when the mice were injected with NNK.
| a | all/ 100 % «of mice/in treatment group 3/in treatment groups 3 to 6 » had tumours |
| b | tumours per mouse «significantly» increased «by NNK» |
| c | no/little difference when nicotine was added «to mice with NNK» |
Evaluate the hypothesis that nicotine is not a mutagen.
hypothesis supported (relevant treatment groups indicated with T numbers)
a. «by itself» nicotine did not increase percentage «of mice» with tumours «T1 versus T2» OR percentage with tumours went down from 31 to 26 with nicotine «T1 versus T2» OR
second treatment group does not have a higher percentage than first group
b. «by itself» nicotine did not increase the number of tumours per mouse «T1 + T2» OR second treatment group does not have more tumours per mouse than first group
c. in mice given NNK nicotine did not increase tumours «significantly» «T3 versus T4/5/6» OR
100% of mice already had tumours with NNK only «T3»
OR
no significant difference/more tumours per mouse in 5th treatment group than 4th /6th even though nicotine was given for a shorter time/for only 2 weeks «T5 versus T4/6»
d. if nicotine was mutagenic there would have been more tumours
hypothesis not supported
e. mice and humans may react to/metabolize nicotine differently/OWTTE
f. nicotine from tobacco smoke may have different effects «from ingested nicotine»
3 max