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.
En anglais

Counting cells that double

Science · Microbiology · ages 18-20
Name ______________________   Date ____________

  1. Which is the typical phase order in a closed batch culture?

    • Exponential, lag, death, stationary
    • Lag, exponential, stationary, death
    • Stationary, death, lag, exponential

  2. During constant exponential population growth, what is generation time?

    • The number of doublings per hour
    • The time for one doubling
    • The time spent adjusting before growth

  3. In binary fission, one parent cell divides into two daughter cells.

    Circle one:   True   False

  4. Why does constant exponential growth give a straight line when logarithmic counts are plotted against linear time?

    • Equal time intervals give equal increases in log count.
    • Equal time intervals give equal increases in raw cell count.
    • A logarithmic count axis makes every growth pattern linear.

  5. A population grows from 120 to 960 cells in 90 minutes at a constant doubling rate, with no cell loss. What is the generation time in minutes?

    Answer: ______________

  6. Which feature distinguishes a chemostat from a closed batch flask?

    • It keeps cells growing after their nutrient supply ends.
    • It makes all strains divide at the same fixed speed.
    • It continuously supplies medium and removes culture.

  7. During exponential growth, strain A doubles every 30 minutes and strain B every 60 minutes. Which has the higher rate in doublings per hour?

    • A: two doublings per hour
    • B: two doublings per hour
    • Both: one doubling per hour

  8. A population doubles every 40 minutes throughout a 2-hour interval, with no cell loss. It starts with 25 cells. How many cells are present at the end?

    Answer: ______________

LightMySky · lightmysky.comW1-mt_ltzgjIBytk-s1

Answer key

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

Counting cells that double W1-mt_ltzgjIBytk-s1

  1. Lag, exponential, stationary, death · Cells adjust during lag, grow exponentially, reach stationarity as growth becomes limited, and later show declining viable counts.
  2. The time for one doubling · Generation time measures the time needed for the population to double.
  3. True · Binary fission produces two daughter cells from one parent. Mutations can occur, so genetic identity is not guaranteed.
  4. Equal time intervals give equal increases in log count. · Constant exponential growth multiplies counts by equal factors in equal times. Logarithms turn these factors into equal increments.
  5. 30 · 120 to 240 to 480 to 960 is three doublings. Generation time is 90/3 = 30 minutes.
  6. It continuously supplies medium and removes culture. · A chemostat has continuous medium inflow and culture outflow. Suitable settings can maintain steady density while cells divide.
  7. A: two doublings per hour · An hour contains two 30-minute intervals but only one 60-minute interval. A has two doublings per hour; B has one.
  8. 200 · Two hours is 120 minutes, giving 120/40 = 3 doublings. Doubling 25 three times gives 200 cells.
Worksheet · LightMySky