Bacterial population growth curve
BiologyMicrobiology & VirusesAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Microbiology & Viruses
A bacterial population in a culture flask grows following N = N₀·2^(t/g); a graph of log N against time plots itself and colours the four phases — lag, exponential, stationary and death. Students can change the initial cell number, generation time and nutrient supply, or switch to continuous culture (feeding in fresh medium while draining spent broth) to see the death phase disappear.
Lesson: Growth of microorganisms: batch and continuous culture, generation time
What it shows
In a closed flask a bacterial population follows a characteristic growth curve. After a lag phase, while cells adapt and make new enzymes, they divide at a constant rate, so N = N₀·2ⁿ with n = t/g generations and log N rises in a straight line. As nutrients run out and waste builds up, births balance deaths in the stationary phase, and then deaths exceed births in the death phase. In continuous culture, fresh medium flows in while spent broth is removed, holding the population steady, the principle behind industrial fermentation.
How to use
Set Initial cell number N₀, Generation time g and Lag phase (adaptation), then let the graph of log N against time draw itself and note when each coloured phase begins. Press Reset and repeat with a shorter generation time or more initial nutrient to compare the slope and the height of the plateau. During the stationary phase, press + Nutrient or Continuous culture and check whether the death phase still appears.
Parameters you can change
- Initial cell number N₀ 10–1000 cells
- Generation time g 10–60 minutes
- Initial nutrient (supports up to ×1000 cells) 100–1000 units
- Culture type Batch culture (closed vessel), Continuous culture (feed in nutrient, drain broth)
- Lag phase (adaptation) 0–120 minutes
Questions to explore
- With N₀ = 100 and g = 20 minutes, how many cells are there after two hours of exponential growth?
- Why does a death phase appear in a closed flask but not in continuous culture?
- At which phase would you stop a batch culture to collect the most cells, and why?
Teaching ideas
All guides- Remote Learning with Interactive SimulationsRemote learning with interactive simulations: run a live online lesson by screen share and chat link, set async tasks, and see every answer. Two examples.
- Zones of Inhibition Virtual Lab: Antiseptics and AntibioticsZones of inhibition virtual lab: practise aseptic technique, test chlorhexidine at four strengths, measure clear zones and calculate their area with πr².
