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Date	May 2018	Marks available	3	Reference code	18M.2.SL.TZ2.6
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	Outline	Question number	6	Adapted from	N/A

Question

Although simple in structure, bacteria as a group show a wide range of diversity.

Outline the roles bacteria play in the carbon cycle.

[3]

Describe the evolution of antibiotic resistance in bacteria.

[4]

Explain the process of genetically modifying bacteria.

[8]

Markscheme

a. decomposition of dead organic material «by saprotrophic bacteria»

b. «decomposition» leads to CO₂ formation/regeneration due to respiration

c. «saprotrophic bacteria only» partially decompose dead organic matter in acidic/anaerobic conditions in waterlogged soil

d. results in peat formation in bogs/swamps

e. photosynthetic bacteria/cyanobacteria fix CO₂ in photosynthesis

a. problem results from excessive use of antibiotics by doctors/veterinarians/in livestock
OR
low antibiotic doses taken by patients (not finishing treatment)

b. natural variation exists in any population of bacteria making some resistant to a specific antibiotic

c. variation arises from mutation
OR
antibiotic resistance can be transferred between bacteria by plasmids

d. antibiotic kills all bacteria except those that are resistant

e. resistant bacteria survive, reproduce and pass on resistance to offspring

f. soon population is made of mainly antibiotic resistant bacteria

g. this is an example of natural selection «increasing frequency of characteristics that make individuals better adapted to environment»

a. genetic modification carried out by gene transfer between species

b. genes transferred from one organism to another produce the same protein/amino acid sequence

c. due to universality of genetic code
OR
organisms use same codons of mRNA to code for specific amino acids

d. mRNA for required gene extracted/identified

e. DNA copies of mRNA made using reverse transcriptase

f. PCR used (to amplify DNA to be transferred)

g. genes/DNA transferred from one species to another using a vector

h. plasmid acts as vector to transfer genes to bacteria/E. coli

i. plasmid cut open at specific base sequences using restriction endonuclease
OR
plasmid cut to produce blunt ends then extra cytosine/C nucleotides added
OR
sticky ends made by adding extra guanine/G nucleotides
OR
mention of sticky ends if not gained already

j. cut plasmids mixed with DNA copies stick together (due to complementary base pairing)

k. DNA ligase makes sugar-phosphate bonds to link nucleotides of gene with those of plasmid

l. bacteria that take up plasmid are identified

m. (genetically modified) bacteria will reproduce carrying the transferred gene

n. example – eg: as production of human insulin using E. coli bacteria

Accept any of the points clearly explained in an annotated diagram.

Examiners report

[N/A]

Syllabus sections

Core » Topic 4: Ecology » 4.3 Carbon cycling

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