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a. Describe the appearance of a bacterial plasmid - VCE - SSCE Biology - Question 4 - 2006 - Paper 1
Question 4
a. Describe the appearance of a bacterial plasmid. A bacterial plasmid was modified in the laboratory so that it contained a gene for an enzyme which provided resis... show full transcript
Worked Solution & Example Answer:a. Describe the appearance of a bacterial plasmid - VCE - SSCE Biology - Question 4 - 2006 - Paper 1
Step 1
a. Describe the appearance of a bacterial plasmid.
Answer
A bacterial plasmid is typically a small, circular piece of DNA that is distinct from the chromosomal DNA. It appears as a loop and does not participate in the usual processes of cell division. Plasmids can carry genes that provide advantages, such as antibiotic resistance. Under the microscope, plasmids may not be easily visible without specific staining techniques.
Step 2
Step 3
c. i. What result would you expect on plate B with respect to the growth of the bacteria?
Answer
On plate B, I would expect no growth of the bacteria because this plate is presumed to contain bacteria that are not exposed to the plasmid, and thus they would not have the resistance to the antibiotic present.
Step 4
c. ii. Explain your answer to c.i.
Answer
The reason for the expected lack of growth on plate B is that the bacteria are sensitive to the antibiotic tetracycline, and since they do not possess the plasmid that provides resistance, they will be unable to survive in the presence of the antibiotic.
Step 5
d. Explain why there is a difference in the way the bacteria have grown on plates A and C.
Answer
The difference in bacterial growth on plates A and C can be attributed to the presence of tetracycline. On plate A, the bacteria are likely not exposed to any antibiotic, allowing them to grow freely. However, on plate C, only those bacteria that have taken up the plasmid which provides resistance to tetracycline will be able to grow. Therefore, any bacterial cells that did not take up the plasmid will die in the presence of the antibiotic.