May/June 2026 Paper 22

2026 · 6 questions · 29 parts · 60 marks

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1(a)Cell Structure OrganellesEasy1 mark
The bacterium Escherichia coli is a typical prokaryotic cell. One key feature of a prokaryotic cell is the absence of organelles surrounded by a double membrane. Name one organelle surrounded by a double membrane that is not found in E. coli.

Answer

1(b)(i)Pathogens Communicable DiseaseEasy2 marks
Bacteriophages are viruses that infect bacterial cells. They are specific to a bacterial species or to a strain of a bacterium. Figure 1.1 is a transmission electron micrograph showing a type of bacteriophage, known as a T-phage, attached to the surface of E. coli. T-phages are also visible inside the cell.
Figure 1.1, a transmission electron micrograph of a T-phage bacteriophage attached to the surface of an E. coli cell, with a vertical line marked X at the top and Y at the bottom showing the cell's diameter; a line labelled A points to the phage's rounded head above the cell surface, a line labelled 'protein tail fibre' points to the short fibres just below the head, and a line labelled B points to the outer edge of the E. coli cell where the tail fibres attach.
Structure A of the T-phage in Figure 1.1 contains the nucleic acid core, which is DNA. The DNA is injected into E. coli after the T-phage has attached to structure B, the outer layer of the cell.
Name structure A and structure B, shown on Figure 1.1.
Structure A
Structure B
1(b)(ii)Microscopy MagnificationMedium2 marks
Bacteriophages are viruses that infect bacterial cells. They are specific to a bacterial species or to a strain of a bacterium. Figure 1.1 is a transmission electron micrograph showing a type of bacteriophage, known as a T-phage, attached to the surface of E. coli. T-phages are also visible inside the cell.
Figure 1.1, a transmission electron micrograph of a T-phage bacteriophage attached to the surface of an E. coli cell, with a vertical line marked X at the top and Y at the bottom showing the cell's diameter; a line labelled A points to the phage's rounded head above the cell surface, a line labelled 'protein tail fibre' points to the short fibres just below the head, and a line labelled B points to the outer edge of the E. coli cell where the tail fibres attach.
Structure A of the T-phage in Figure 1.1 contains the nucleic acid core, which is DNA. The DNA is injected into E. coli after the T-phage has attached to structure B, the outer layer of the cell.
The actual diameter of the E. coli cell in Figure 1.1 along the line X–Y is 0.9 µm. Calculate the actual length of the T-phage attached to the surface of E. coli. Give your answer in nanometres (nm) to the nearest whole nm.
1(c)Pathogens Communicable DiseaseMedium2 marks
Suggest why a T-phage can attach to E. coli, but cannot attach to cells of other species of bacteria.

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1(d)(i)Pathogens Communicable DiseaseEasy1 mark
Research has been carried out into the use of bacteriophages as a treatment for infectious diseases (bacteriophage therapy), such as those caused by some strains of E. coli. It has been suggested that bacteriophage therapy may help to solve some of the problems associated with the current treatments for bacterial diseases. Cholera, malaria and tuberculosis (TB) are three common infectious diseases. Explain which of these three diseases is least likely to be treated with bacteriophage therapy.

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1(d)(ii)Antibiotics ResistanceMedium3 marks
Suggest the benefits of using bacteriophage therapy for bacterial diseases.

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