IMO Practice Test — Organisms and Populations
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
A J-shaped growth curve cannot continue forever in nature because:
Resources are limited (carrying capacity)
Animals stop breeding by choice
Births are banned
There is no death
Explanation: Finite food and space eventually slow growth, bending the curve into an S-shape at K.
Question 2 of 6
Removing all predators from an area can harm the ecosystem because the prey may:
Overpopulate and exhaust resources
Disappear at once
Become predators
Stop eating
Explanation: Without predation, prey numbers can explode beyond carrying capacity and crash, destabilising the system.
Question 3 of 6
An age pyramid with a very broad base (many young) suggests the population will likely:
Grow in the future
Decline at once
Stay forever fixed
Vanish
Explanation: A large young cohort will mature and reproduce, so the population is poised to grow.
Question 4 of 6
Lichens (alga + fungus) are mutualistic because the alga makes food while the fungus:
Provides shelter, water and minerals
Eats the alga
Harms the alga
Does nothing
Explanation: Each partner supplies what the other lacks, so both benefit — true mutualism.
Question 5 of 6
A desert kangaroo rat surviving with very little drinking water shows an adaptation to a key ____ factor.
Abiotic (water scarcity)
Biotic
Predatory
Social
Explanation: Coping with scarce water is an adaptation to an abiotic condition of the desert.
Question 6 of 6
Both competition and parasitism harm at least one partner, but they differ because in competition:
Both organisms are harmed by sharing a resource
One lives inside the other
Both benefit
Neither is affected
Explanation: Competition harms both (−−), whereas parasitism helps one and harms the other (+−).