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← Theoretical 2

Q83 — Gut Microbiome and Lifespan in Drosophila

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Ecology

Researchers investigated the effect of the microbiome on the lifespan of the fruit fly (D. melanogaster). To this end, they disinfected fly eggs and transferred them to a sterile food substrate. The non-disinfected eggs served as a control group (“non-axenic”, figure A). Another cohort of the flies (originating from disinfected eggs) was kept on a sterile substrate for the entire lifespan (“axenic”, figures A and B). The rest of the eggs were separated into three groups. They were treated with bacterial cultures either as embryos right after disinfection (figures B, C, D), at day 2 of adulthood (figure D) or at day 7 of adulthood (figure C). The researchers evaluated the fraction of individuals still alive in each population for 100 days, summarizing their results in the graphs below. The percentage in square brackets shows the difference in average lifespan between two populations.

Four-panel survival-curve figure. Panel A: non-axenic flies survive noticeably longer than axenic flies (30% difference). Panel B: flies exposed to bacteria as embryos survive nearly as well as non-axenic flies, far outliving axenic flies (30% difference). Panel C: flies exposed to bacteria as adults at day 7 survive less well than those exposed as embryos (25% difference). Panel D: flies exposed to bacteria as adults at day 2 survive almost identically to those exposed as embryos (0% difference). Survival curves (fraction alive vs. days) for axenic, non-axenic, and bacteria-exposed Drosophila populations, exposed to bacteria at different developmental stages.

Using the information and the data in the figures above, determine which of the statements are true or which are false.

A. Exposure to bacteria at the earliest stages of development extends the average lifespan of fruit flies.
B. Exposure to bacteria at any stage of development can fully restore the lifespan of fruit flies.
C. The information provided here is sufficient to conclude the possibility that fruit fly lifespan was affected by the egg disinfection technique.
D. The critical period when the presence of bacteria affects the lifespan of fruit flies occurs between day 2 and 7 of adulthood.
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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)