Question

Ed Yong is a science journalist who wrote a book on the Human Microbiome called “I Contain Multitudes”. The book

was fascinating because it describes the good role our resident bacteria have on our bodies. In particular, he

mentioned one study that looked at the effect of good bacteria on the health of our intestinal system and how a poor

diet can change the bacterial communities (microbiome) inside the gut. The study wanted to prove that both a poor

diet and bad gut bacteria lead to malnourishment. Researchers collected gut bacteria from healthy children living in

the US and gut bacteria from malnourished children living in the African country of Malawi, where there is a crisis with

hunger and child malnourishment. They transferred both groups of gut bacteria into germ-free mice (mice with no

bacteria in their gut) and weighed the mice 2 weeks after the transfer. The experimental setup looked like this:

1. Group A received no gut bacteria.

2. Group B received bacteria from healthy children.

3. Group C received gut bacteria from malnourished children

ALL 3 GROUPS WERE FED A REGULAR DIET AND WEIGHED AFTER 2 WEEKS.

They found that mice that had bacteria from malnourished children lost weight even when given a good diet. Mice with

bacteria from healthy children did not lose weight. The group went on to identify specific bacteria from the gut of

healthy children so they could try to transfer those bacteria into the mice to see if the mice could revert to gaining

weight.

Based on the scenario above, describe an appropriate

“if/then”

statement for this situation.

What was the dependent variable (i.e. what were the scientists measuring in the mice?) in the main experiment?

Which group of mice is considered the negative control group?

What could be a next step for their investigation?

Answer 1

• If the specific bacteria from the gut of healthy children is tranferred to the group C mice and possitive effect is observed, then the study could pave a way for future studies in eradicating malnourishment.
• Weight of the mice is the dependent variable. A dependent variable is a variable, whose value depends on that of another variable. The other variable being the source of bacteria.
• Group A is the negative control. A negative control does not receive any test or treatment and no response is expected.
• The next step in the investigation will be to measure the weight gained after inoculating the group C mice with the identified specific bacteria from healthy children. Then the biochemical activity of the identified bacteria needs to be investigated that is responsible for the positive effect.