TEACHER’S NOTES
3.
Investigating metabolism in microorganisms
(a)
Enviromental control of metabolism
(ii)
Patterns of growth
Links to prior/prerequisite knowledge
Students will already be familiar with growth and multiplication by mitos is.
New content areas
 Bacterial growth represented in graphical form.
 Growth of the bacterial cells follows a number of phases. These phases are
called the lag (or latent or initial) phase, exponential (or log) phase,
stationary phase and final (or death or senescent) phase.
Background information
 The graph below shows a typical bacterial growth curve of the number of
viable bacteria in the culture medium in relation to time. You can see that
the growth of the bacterial cells follows a number of phases. These phases
are called the lag (or latent or initial) phase, exponential (or log) phase,
stationary phase and final (or death or senescent) phase.
These bacterial cells do not continue to grow indefinitely despite being
placed initially in medium containing all the factors needed for growth.
The lag phase begins with the bacterial cells being introduced (inoculated)
into the new culture medium. During the lag phase there is little or no
increase in bacterial cell numbers, although the cells may increase in size.
During this phase, the bacterial cells are adapting to their new growth
METABOLISM IN MICROORGANISMS (H, BIOLOGY)
© Learning and Teaching Scotland 2011
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TEACHER’S NOTES
conditions, for example by producing enzymes to process the nutrients
present in the growth medium.
During the exponential phase the bacterial cells double at a constant rate. The
actual time that the bacteria take to double depends on the culture medium
and the temperature. The time taken for the numbers of bacterial cells to
double is called the doubling rate. It is the exponential phase that is the most
suitable phase for carrying out experiments to find out growth rates and to
investigate the factors that affect growth.
In the stationary phase there is no increase in the number of viable bacterial
cells. The number of new cells being produced is equivalent to the number of
bacterial cells that are dying. During this phase there is no further increase in
bacterial cell growth because the available nutrients are starting to be used
up. Also, conditions such as pH may have altered to such an extent that they
are now inhibiting the growth of the bacteria.
During the death phase the bacterial cells die due to starvation and/or adverse
environmental conditions.
SAPS growth rate activity pdf
Identification of key concepts
 Draw the general shape of a bacterial growth curve .
 Name the phases observed in the growth curve.
 Describe the events that occur in each phase of the growth curve.
Identification of particular areas of difficulty
 Related problem-solving type tasks such as graph drawing, cell count
calculations.
Links to websites, animations, PowerPoints, audio or video files etc
http://www.ryancshaw.com/Files/micro/Animations/BacterialGrowth/PLAY_
bacterial_growth.html
http://www.youtube.com/watch?v=SuvGpMevLPU
Other useful information to stimulate interest
http://www.ltscotland.org.uk/Images/microbiologyhunit 1_tcm4-134104.pdf
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METABOLISM IN MICROORGANISMS (H, BIOLOGY)
© Learning and Teaching Scotland 2011