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Bacteria, viruses and pathogens
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Bacteria are prokaryotes with no nucleus. Viruses are not even cells. Both include pathogens.
Bacteria
Bacteria are microscopic single-celled organisms (prokaryotes).
They have a cell wall, cell membrane, cytoplasm and plasmids. They have no nucleus, but contain a circular chromosome of DNA.
Some bacteria can photosynthesise, but most feed off other living or dead organisms.
Examples: *Lactobacillus bulgaricus* (rod-shaped, used to make yoghurt) and *Pneumococcus* (spherical, causes pneumonia).
They have a cell wall, cell membrane, cytoplasm and plasmids. They have no nucleus, but contain a circular chromosome of DNA.
Some bacteria can photosynthesise, but most feed off other living or dead organisms.
Examples: *Lactobacillus bulgaricus* (rod-shaped, used to make yoghurt) and *Pneumococcus* (spherical, causes pneumonia).
Viruses
Viruses are not living organisms. They are small particles, smaller than bacteria.
They are parasitic and can only reproduce inside living cells. They can infect every type of living organism.
They have no cellular structure: just a protein coat around one type of nucleic acid, either DNA or RNA.
Examples: tobacco mosaic virus (stops chloroplasts forming, so tobacco leaves become discoloured), the influenza virus and HIV.
They are parasitic and can only reproduce inside living cells. They can infect every type of living organism.
They have no cellular structure: just a protein coat around one type of nucleic acid, either DNA or RNA.
Examples: tobacco mosaic virus (stops chloroplasts forming, so tobacco leaves become discoloured), the influenza virus and HIV.
Pathogens
A pathogen is an organism that causes disease.
Pathogens may be fungi, bacteria, protoctists or viruses.
Examples: *Pneumococcus* (bacterium), *Plasmodium* (protoctist), influenza and HIV (viruses).
Pathogens may be fungi, bacteria, protoctists or viruses.
Examples: *Pneumococcus* (bacterium), *Plasmodium* (protoctist), influenza and HIV (viruses).
Give two ways a virus is different from a bacterium.
- A bacterium is a cell: it has a cell wall, membrane and cytoplasm.
- A virus has no cellular structure, just a protein coat and DNA or RNA.
- A virus can only reproduce inside a living cell, and it is much smaller.
Answer: Viruses have no cell structure (only a protein coat and nucleic acid), and can only reproduce inside living cells.
Bacteria are single-celled with a cell wall, membrane, cytoplasm, plasmids and a circular chromosome, but no nucleus. Viruses are not living, have a protein coat and DNA or RNA, and reproduce only inside living cells. Pathogens can be fungi, bacteria, protoctists or viruses.
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