Question

e this experiment follows a modified procedure designed to demonstrate only the lag and log phases by using an indirect method foe measuring growth. The indirect method is based on atisie at intervals during the incubation period. Such a procedure does not lend itself to a regular laboratory curve will be plotted usin appears cloudier as the bacteria increase in number by cell division. A tube of bacte- r can measure the n liquid culture, the medium amount of light passing through the tube, or conversely the amount of light absorbed. These measurements hat optical density (OD) are not direct measurements of bacterial numbers, but an indirect measurement of e includes both living and dead cells. You will determine gen with the indirect spectrophotometric me ple extrapolation from the log phase. Select two points on the absorbance scale (y-axis). sent a doubling of turbidity. Using a ruler, extrapolat eration time of cultures growing under variable conditions thod by using data on the growth curve. Indirect determination is made by sim- such as 0.2 and 0.4, that repre- e by drawing a line between each of the selected absorbencies on the y-axis and the growth curve. Then draw perpendicular lines from these endpoints on the plotted line of the growth curve to their respective time intervals on the x-axis. With this information, determine the generation (GT, also called dou- bling time) as follows: GT- t(A at 0.4) - (A at 0.2) e.g. GT-90 minutes-60 minutes = 30 minutes Based on what you know about bacterial growth, formulate hypotheses (Scientific, H, and H,) for what you expect to occur at the different treatments over time. Write the hypotheses in the space provided and explain your reasoning for Scientific Mitosis and the Cell Cycle

Answer 1

What is growth curve?

The growth of bacteria has been studied extensively since they are easy to grow in the lab. It has been determined that in a closed system or batch culture (no food added, no wastes removed) bacteria will grow in a predictable pattern, resulting in a growth curve. The phases of growth can be visualized in a graph by plotting time and cell count in the x and y axis. It is composed of four distinct phases of growth: the lag phase, the exponential or log phase, the stationary phase, and the death or decline phase as shown in the graph below.

2 Log phase: 3 Stationary phase: 4 Death or exponential increase in number of living bacterial cells plateau in number of living bacterial cells, rate of cell division and death roughly equa decline phase: exponential decrease in number of living bacterial cells 0 1 Lag phase: no increase in number of living bacterial cells Time

What is the principle behind the indirect analysis?

The amount of transmitted light through turbid broth decreases with subsequent increase in the absorbance value.

the generation doubling time can be calculated as shown below:

The exactly doubled points from the absorbance readings were taken and, the points were extrapolated to meet the respective time axis.
Generation Time =   (Time in minutes to obtain the absorbance 0.4) – (Time in minutes to obtain the absorbance 0.2)

= 90-60

= 30 minutes

Hypothesis₀:

Consider, increasing the temperature. Temperature changes affects the growth curve drastically, as shown in the below example. The graph is growth curve of Pseudomonas sp. at different temperatures.

13.5 4 -15 C 12.5 11.5 10.5 9.5 8.5 7.5 0 2 4 6 810 121411820 22 24 Time (h)

the doubling time is 2.2, 2.5, and 5.5 hours at 4^oC, 15^oC, and 25^oC respectively. We can clearly see the doubling time has increased with increase in the temperature.

Hypothesis₁:

When the pressure is increased, also impacts the growth curve.

0.6 8 atm 0.5- Ambient pressure 0.4 0.3 0.2 0.1 -10 0 10 20 30 40 50 60 70 Time(hrs)

Similar to the previous condition, we can see the lag in the growth phase due to alteration in the optimum pressure conditions.