Conditions required for bacterial growthSpec 4.10
In short
Bacteria grow and divide quickly when they have a supply of nutrients, a suitable temperature, the correct oxygen level, a suitable pH and enough water. These conditions are provided in the laboratory using sterile nutrient broth or agar. Bacteria reproduce by binary fission, so a population can multiply rapidly when conditions are right.
Bacteria are prokaryotes that reproduce asexually by binary fission. In ideal conditions some species can divide every 20 to 30 minutes. For growth to happen, several conditions must be met.
| Condition | Why it is needed | In the laboratory |
|---|---|---|
| Nutrients | A carbon source (for example glucose) for respiration and making organic molecules; a nitrogen source for amino acids and nucleotides; mineral ions and sometimes vitamins | Nutrient agar or nutrient broth |
| Temperature | Enzymes have an optimum temperature. Too cold: slow growth. Too hot: enzymes denature | Incubate at a suitable temperature; in school laboratories usually 25 °C and never above 30 °C, to reduce the risk of growing human pathogens (which grow best near 37 °C) |
| Oxygen | Aerobic bacteria need oxygen for aerobic respiration. Anaerobic bacteria are inhibited or killed by oxygen | Plates are incubated with lids on, taped in only a few places, so that oxygen can enter |
| pH | Enzymes work best in a narrow pH range; most bacteria grow best near neutral pH | Buffers or media at a suitable pH |
| Water | Metabolic reactions take place in solution | Agar gel or broth is mostly water |
Providing the conditions safely
- Culture media and equipment are sterilised before use (for example in an autoclave, at 121 °C), so that unwanted microorganisms do not compete with the bacteria being grown.
- Cultures are grown at temperatures that make human pathogens unlikely to grow, and plates are not opened after incubation.
- At the end, cultures are sterilised before disposal.
Do not just list "warmth". Say the bacteria need a suitable temperature because enzymes have an optimum, and name nutrients (carbon and nitrogen sources).
Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026