Question 23M.3.HL.TZ1.2
| Date | May 2023 | Marks available | [Maximum mark: 4] | Reference code | 23M.3.HL.TZ1.2 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Describe, Explain, Outline | Question number | 2 | Adapted from | N/A |
Between 1860 and 1862, Pasteur carried out a series of experiments focusing on the development of microbes. The illustrations show Pasteur’s diagrams and procedure for one experiment.
[Source: Kgerow16, 2015. Louis Pasteur Experiment. [online] Available at: https://commons.wikimedia.org/wiki/File:Louis_
Pasteur_Experiment.svg [Accessed 8 March 2022]. Public domain.]
Outline the reason for boiling the broth in Stage 1.
[1]
to kill all microbes/bacteria in the flask;
to sterilize the broth/flasks;
This question was answered correctly by almost all candidates.
Describe how Pasteur included a control in his experiment.
[1]
kept a flask in similar conditions with no broken neck;
Unfortunately, many candidates confused the control for an experiment with variables that need to be kept constant. Others listed the differences in the flasks without indicating which was the control.
Explain Pasteur’s conclusions from his observations at Stage 3 of this experiment.
[2]
- observed microbe growth only in the flask without a neck
OR
microbes can’t enter through curved/swan necked flask; - microbes do not arise by spontaneous generation
OR
microbes/bacteria travel in the air;
Many were able to get one mark out of two, usually for indicating that only the flask without a neck had microbial growth.
