IMO Practice Test — Ecosystem
7 Questions • 15 min • Olympiad level
15:00
Question 1 of 7
Food chains are usually only 4-5 links long mainly because:
So much energy is lost at each level (10% law)
Animals dislike long chains
There is no Sun
Plants are rare
Explanation: With only ~10% passed on each step, little energy remains to support many higher levels.
Question 2 of 7
If all decomposers were removed from an ecosystem, the most direct result would be that:
Dead matter and nutrients would not be recycled
More sunlight would arrive
Plants would grow faster
Energy would cycle
Explanation: Without decomposers, nutrients stay locked in dead bodies and cycling halts, starving producers over time.
Question 3 of 7
The pyramid of energy can never be inverted because:
Energy always decreases from one level to the next
Energy increases upward
Producers have the least energy
Top predators store all energy
Explanation: Since energy is lost at every transfer, higher levels always hold less — an upright pyramid only.
Question 4 of 7
Burning fossil fuels adds extra carbon to the air, disturbing the:
Carbon cycle
Food chain length
Number of trophic levels
Sun's output
Explanation: Releasing stored carbon as CO₂ upsets the balance of the carbon cycle, contributing to climate change.
Question 5 of 7
Protecting forests is important partly because they provide the ecosystem service of:
Releasing oxygen and regulating climate
Making plastic
Producing fossil fuels quickly
Stopping all rain
Explanation: Forests supply oxygen, store carbon and stabilise climate — services vital to human well-being.
Question 6 of 7
A pyramid of numbers can sometimes look inverted (e.g. one big tree supporting many insects), but the pyramid of energy stays upright because it measures:
The actual energy, which always falls up the chain
Only the count of organisms
The size of organisms only
Nothing real
Explanation: Counting individuals can mislead, but tracking energy always shows the unavoidable decrease upward.
Question 7 of 7
Secondary succession (e.g. on an abandoned field) is faster than primary succession because:
Soil is already present
There is no sunlight
There are no seeds anywhere
It needs no producers
Explanation: Because soil and some life already exist, the community re-establishes more quickly.