BRAINCAKEGram-Staining
Gram staining is a differential staining technique that divides bacteria into two groups according to the structure of their cell wall. It was developed by Hans Christian Gram in 1884 and is still one of the first tests used to identify bacteria.
The method has four main steps, applied to a heat-fixed smear of bacteria on a slide:
1. Flood with crystal violet (the primary stain). All cells turn purple.
2. Add iodine, which forms a large crystal violet-iodine complex inside the cells.
3. Rinse with alcohol (or acetone), the decolouriser.
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Key terms in this lesson
- peptidoglycan
- A polymer of sugars cross-linked by short chains of amino acids that forms the cell wall of bacteria, giving it strength and shape.
More in Prokaryotic Cells
- Cell Surface Membrane
- Plasmids
- Nucleoid
- 70S Ribosomes
- Antibiotics
- Alternative Classification of Bacteria
- Viruses
- The Structure of Viruses
All 31 lessons in Prokaryotic Cells · All Edexcel AS-level Biology topics