IMO Practice Test — Our Environment
6 Questions • 15 min • Olympiad level
15:00
Question 1 of 6
If all the decomposers in an ecosystem suddenly disappeared, the most likely result would be:
Dead matter piles up and nutrients are not recycled
More energy at every level
Faster plant growth
No change at all
Explanation: Without decomposers, dead organisms accumulate and nutrients are not returned to the soil.
Question 2 of 6
In the chain grass (10,000 J) to deer to tiger, the tiger receives about:
100 J
1000 J
10,000 J
5000 J
Explanation: 10% to deer = 1000 J, then 10% to tiger = 100 J (ten per cent law applied twice).
Question 3 of 6
Harmful chemicals like pesticides become most concentrated in the bodies of top carnivores. This happens because:
The chemicals are passed up and build up along the food chain (biomagnification)
Top carnivores eat plants only
The chemicals disappear
Producers store the most
Explanation: Non-degradable chemicals accumulate at each level, becoming most concentrated at the top (biomagnification).
Question 4 of 6
Why is there usually a far smaller number of top carnivores than producers in an ecosystem?
Only a small fraction of energy reaches the top levels
Carnivores never reproduce
Producers eat carnivores
There is no Sun
Explanation: With ~90% energy lost per level, only a little energy reaches the top, supporting fewer organisms.
Question 5 of 6
A 'hole' in the ozone layer is a serious concern mainly because it lets in more:
UV radiation, raising skin-cancer risk
Oxygen
Rain
Sound
Explanation: Less ozone means more harmful UV reaches the surface, increasing health and crop damage.
Question 6 of 6
Using cloth bags and composting kitchen waste at home helps the environment mainly by:
Reducing non-biodegradable waste and recycling nutrients
Increasing plastic use
Depleting ozone
Adding CFCs
Explanation: It cuts plastic waste and returns biodegradable matter to the soil, aiding waste management.