Culturing Microorganisms [Biology only]

Growing bacteria

• Bacteria multiply by binary fission, simple cell division, as often as once every 20 minutes with enough nutrients and a suitable temperature
• They are grown in a nutrient broth solution or as colonies on an agar gel plate
• Population after a time: number of divisions $=$ time $\div$ mean division time; population $=$ starting number $\times 2^{\text{divisions}}$
• Worked example: one bacterium dividing every 20 minutes for 3 hours. Time is 180 minutes, so $180 \div 20 = 9$ divisions, and $2^9 = 512$ bacteria
• (HT) Give large answers in standard form: after 24 hours there are 72 divisions, $2^{72} \approx 4.7 \times 10^{21}$