What are the functions of the cell wall?

It gives shape and support and prevents the cell bursting by osmosis.

What is the function of the capsule?

It protects the bacterium from phagocytes and drying out, and helps it attach to surfaces.

What is the function of a flagellum?

It rotates to move the bacterium through liquid.

What are pili used for?

Attachment to surfaces and host cells, and joining bacteria for plasmid transfer.

A small circular DNA molecule, separate from the main DNA, carrying extra genes such as antibiotic resistance.

How can a plasmid pass between bacteria?

By conjugation: a copy is transferred through a pilus.

Describe the main DNA of a bacterium.

A single circular molecule, free in the cytoplasm, not enclosed in a nuclear envelope.

What do bacterial ribosomes do?

They synthesise proteins; they are smaller than eukaryotic ribosomes.

Why does penicillin not harm human cells?

It stops bacterial cell walls forming; human cells have no cell wall.

Give two features present in eukaryotic but not prokaryotic cells.

A nucleus and membrane-bound organelles such as mitochondria.

Why does a gene on a plasmid spread faster than one on the main chromosome?

Plasmids pass to other bacteria by conjugation without cell division.

Prokaryotic cellsEdexcel International A Level Biology: Flashcards

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What is a prokaryotic cell?

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What is a prokaryotic cell?: A cell with no nucleus and no membrane-bound organelles, such as a bacterium.
What is the bacterial cell wall made of?: Peptidoglycan.
What are the functions of the cell wall?: It gives shape and support and prevents the cell bursting by osmosis.
What is the function of the capsule?: It protects the bacterium from phagocytes and drying out, and helps it attach to surfaces.
What is the function of a flagellum?: It rotates to move the bacterium through liquid.
What are pili used for?: Attachment to surfaces and host cells, and joining bacteria for plasmid transfer.
What is a plasmid?: A small circular DNA molecule, separate from the main DNA, carrying extra genes such as antibiotic resistance.
How can a plasmid pass between bacteria?: By conjugation: a copy is transferred through a pilus.
Describe the main DNA of a bacterium.: A single circular molecule, free in the cytoplasm, not enclosed in a nuclear envelope.
What do bacterial ribosomes do?: They synthesise proteins; they are smaller than eukaryotic ribosomes.
Why does penicillin not harm human cells?: It stops bacterial cell walls forming; human cells have no cell wall.
Give two features present in eukaryotic but not prokaryotic cells.: A nucleus and membrane-bound organelles such as mitochondria.
Why does a gene on a plasmid spread faster than one on the main chromosome?: Plasmids pass to other bacteria by conjugation without cell division.

Exam questions on Prokaryotic cells

Penicillin-type antibiotics work by preventing the formation of cross-links in the cell wall of growing bacteria. A culture of bacteria growing in a very dilute nutrient solution is treated with such an antibiotic and the cells are seen to burst.
Explain why an antibiotic that prevents cell wall formation does not damage human cells.2 marks
Two strains of a bacterium were compared. Strain S has a capsule and pili; strain R has neither. Both strains have circular DNA in the cytoplasm. When mice were injected with strain S they developed pneumonia and died. When mice were injected with strain R they survived and no bacteria were found in their lungs after a few days. Strain S bacteria were found attached to the lung epithelium of the dead mice.
Explain why the mice injected with strain R survived.2 marks
A hospital laboratory isolates a bacterium that is resistant to the antibiotic ampicillin. The gene for resistance is on a small circular DNA molecule that is separate from the main bacterial chromosome. When this strain was mixed with a non-resistant strain, a thin tube formed between pairs of cells. After several hours some of the previously non-resistant cells were able to grow on agar containing ampicillin.
Explain how the non-resistant bacteria became resistant to ampicillin.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).