CCEA A Level Biology
CCEA A Level Biology 1.3 Viruses Exam Questions
Free CCEA A Level Biology revision for 1.3 Viruses: what you need to know, common mistakes and exam-style questions with answers. Covers structure of bacteriophages and HIV, reverse transcriptase, replication of phages in bacteria and HIV in helper T-cells.
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About CCEA A Level Biology 1.3 Viruses
Viruses are a short but often examined section in Unit AS 1. CCEA expects you to describe the structure of a bacteriophage, with DNA in a protein coat, and of HIV, an RNA virus with a protein coat, a lipid envelope containing glycoproteins and the enzyme reverse transcriptase. You also need to describe how phages invade and destroy bacteria and how HIV invades helper T-lymphocytes, weakening the immune system. This links to nucleic acids (1.1), cells (1.4), immunity (4.2) and gene technology in A2 2, where phages are used as vectors. Questions usually ask for labelled structures and outline replication steps.
What you need to know
- What viruses are Viruses are not cells: they have no cytoplasm, ribosomes or metabolism of their own and can only replicate inside a host cell, using its enzymes, ribosomes and ATP.
- Bacteriophage structure A bacteriophage has DNA enclosed in a protein coat (capsid), usually with a head, tail and tail fibres used to attach to a bacterium.
- HIV structure HIV has two single strands of RNA and reverse transcriptase inside a protein coat, surrounded by a lipid bilayer envelope with glycoproteins that bind to receptors on host cells.
- Phage replication The phage attaches to a bacterium and injects its DNA. The bacterium's machinery makes new phage DNA and coat proteins, which assemble into new phages. The bacterium bursts (lysis) and releases them.
- HIV replication HIV glycoproteins bind to receptors on helper T-cells and the virus enters. Reverse transcriptase makes viral DNA from viral RNA, which is incorporated into the host DNA. New viruses are made and bud off, taking host membrane as their envelope.
- Effect on the immune system Destruction of helper T-cells reduces activation of B-cells and killer T-cells, so the immune system is weakened and opportunistic infections take hold.
Common mistakes in 1.3 Viruses
- Calling a virus a cell or a microorganism with organelles. Viruses are non-cellular particles that cannot replicate outside a host cell.
- Saying reverse transcriptase makes RNA from DNA. It makes DNA from an RNA template.
- Stating that HIV attacks all white blood cells. It targets helper T-lymphocytes in particular.
- Saying antibiotics can treat viral infections. Antibiotics target bacterial structures and metabolism that viruses do not have.
- Describing the phage as entering the bacterium whole. Only the nucleic acid is injected; the protein coat stays outside.
Try three 1.3 Viruses exam-style questions
1. Describe the structure of HIV. (3 marks)
Show the mark scheme answer
RNA as genetic material; reverse transcriptase enzyme; protein coat or capsid; lipid envelope with glycoproteins.
2. Explain the role of reverse transcriptase in HIV replication. (2 marks)
Show the mark scheme answer
Uses viral RNA as a template to make DNA; this DNA can then be inserted into the host cell's DNA so the cell makes new viral components.
3. Explain why a person infected with HIV is more likely to develop other infections. (3 marks)
Show the mark scheme answer
HIV infects and destroys helper T-cells; fewer helper T-cells to activate B-cells or killer T-cells; reduced antibody and cell-mediated responses so pathogens are not destroyed.
1.3 Viruses FAQs
What does CCEA A Level Biology 1.3 Viruses cover?
It covers the structure of bacteriophages and HIV and how each replicates, including the effect of HIV on helper T-cells.
Which unit is 1.3 Viruses examined in?
It is examined in Unit AS 1: Molecules and Cells, a 1 hour 30 minute written paper of structured questions and an essay.
Which viruses do I need to know for CCEA?
The specification names bacteriophages (DNA viruses) and HIV (an RNA virus with reverse transcriptase). Learn a labelled diagram and the replication steps for each.
