IB Biology HL A2.3 Viruses questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceMedium1 mark

Bacteriophage lambda is undergoing its lytic cycle in bacterial cells. The table shows mean measurements at successive times after infection, all normalized per initially infected bacterium.

Time after infection / min	Phage DNA copies per initially infected bacterium	Assembled phages inside bacteria	Free infectious phages
0	1	0	0
10	28	0	0
20	28	20	0
30	28	0	18

Which interval is most consistent with release of assembled phages from the bacteria?

Show answer and explanation

Answer: B. From 20 to 30 min, assembled phages inside bacteria fall from 20 to 0 while free infectious phages rise from 0 to 18. This indicates release; the phage DNA copy number remains unchanged during this interval.

A: selects the earlier increase in phage DNA, which indicates replication rather than release.
C: identifies the interval when assembled particles appear inside bacteria, indicating assembly before release.
D: assigns replication to an interval when the phage DNA copy number is unchanged.

Remember: distinguish replication, assembly and release by tracking what changes inside and outside the host cell.

Question 2

Paper 2Medium4 marks

A culture of Escherichia coli containing bacteriophage lambda was monitored. At 40 min, the culture conditions were changed. Figure 1 shows the measured concentrations of intact bacterial cells and free lambda particles.

(a)

Using Figure 1, identify the viral cycle most consistent with each interval, 0–40 min and 40–80 min. Support each choice with one feature of the graph.

[2]

(b)

Explain how lambda DNA is maintained during the first interval, and state two ways in which the bacterial host supports phage production during the second interval.

[2]

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