GAMSAT Section III – “Microbial Growth Curves”

ACER has designed GAMSAT Section III to test the logical reasoning ability of a candidate, with respect to Basic Sciences. As per the domain of Basic Sciences, Biology constitutes a key area of study for every medical practitioner. Keeping that in mind, ACER has engineered innovative aptitude questions in GAMSAT Biology which totally surpass the traditional concept-based approach. They have included background passages dealing with charts, graphs, diagrams and even tabular data on specific topics, which need to be collated and linked with the following multiple choice questions (MCQs). One such important topic for GAMSAT Section III questions is Microbial Growth curve.

Generally, Human body gets infected with microbial invasions through various routes; via – air, water and food. Once inside our body, the microbial cells multiply or replicate at an amazing rate. For example, typical bacteria can double in number in minutes. Their growth cycle or growth phase is so interesting to study that ACER has often included the Bacterial Growth Curve in multiple occasions of GAMSAT. Let us try to understand the uniqueness of Bacterial Growth Curves along with a GAMSAT standard question.

Qs: From a study done on the effect of pH on pathogen growth and commensal growth in drinking water, we get the following graph-

Human Stomach has a higher concentration of commensal microorganisms than pathogens. What could be the most probable pH of gastric (stomach) juices?

The Multiple alternatives are:

(A) 3.0-5.0

(B) 6.0-8.0

(C) 4.0-6.0

(D) 7.0-9.0

Now, to answer the question, we have to refer to the graph. In the graph, the growth of commensals is maximum at the pH range of 3-5. Again, the optimum pH for the growth of pathogens is in between 6-8. But, in the pH ranges of 4-6 and 7-9, the percentage of growth rate for any of the two classes of microorganisms is not high enough. Therefore, option C and D gets discarded from the consideration. Since the stomach environment strongly favours the commensals against the pathogens, hence, gastric juices will have a similar pH to that of the optimum growth pH for commensals. This makes option A the correct alternative for the question.

We have seen how a bacterial growth curve could act as an excellent background passage for GAMSAT Section III questions. Similarly, more questions could be formulated on Bacterial Growth curves, as Bacterial growth is influenced by multiple parameters like temperatures, substrate concentration and others. GAMSAT aspirants should look into this topic and practice requisite exercise questions to develop fluid understanding and problem solving skills for Microbial Growth. Remember, this practice could enhance your GAMSAT preparation for the coming GAMSAT 2010.