Microbial Growth: Generation Time, Growth Curves and Continuous Culture · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Counting cells that double

Science · Microbiology · ages 18-20
Name ______________________   Date ____________
  1. Which order do flask phases run in?

    • Log, lag, death, stationary
    • Lag, log, stationary, death
    • Stationary, death, lag, log
  2. What is generation time?

    • Doublings per hour
    • The time per doubling
    • The lag before growth
  3. Binary fission splits one cell into two matching daughters.

    Circle one:   True   False

  4. Why does the log phase look straight only on a log axis?

    • Each generation multiplies by a fixed factor
    • Cells pause on plain paper
    • The ink spreads evenly
  5. A culture rises from 100 to 800 in 6 hours. Type the generation time in hours.

    Answer: ______________

  6. What does a chemostat control that a closed flask cannot?

    • Faster mutations on demand
    • Growth without any medium
    • Steady growth by matched feeding and outflow
  7. Strain A doubles every 30 minutes and strain B every 60 minutes. Which grows faster and why?

    • B, since longer time means more cells
    • A, since it doubles twice as often
    • Both tie after one hour
  8. A culture doubles every 40 minutes. Starting from 25 cells, how many are there after 2 hours?

    Answer: ______________

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Counting cells that double W1-mt_ltzgjIBytk-s1

  1. Lag, log, stationary, death · Lag, then log doubling, then stationary, then death.
  2. The time per doubling · Generation time is the time one doubling takes.
  3. True · Each doubling makes two identical cells from one.
  4. Each generation multiplies by a fixed factor · Constant factor growth plots curved on plain axes and straight on log axes.
  5. 2 · That is three doublings, and 6 hours divided by 3 is 2.
  6. Steady growth by matched feeding and outflow · Matched inflow and outflow hold cells in one steady phase.
  7. A, since it doubles twice as often · Shorter generation time means more doublings per time.
  8. 200 · Two hours holds three doublings: 25 to 50 to 100 to 200.
Worksheet · LightMySky