An enzyme works like a key to a lock. If it finds the right thing it can work.
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The health effects of drinking contaminated water can range from no physical impact to severe illness or even death. Some of the effects of drinking contaminated water can be immediate, or not noticed for many years. These include gastrointestinal and stomach illnesses like: nausea.
It would be commensalism- a symbiotic relationship where one organism benefits while the other remains unaffected.
Answer;
A bottleneck effect
Explanation;
When only a few individuals survive unfavorable times, thereby losing the majority of genotypes in the next generation, it is called a bottleneck effect.
It occurs when there is a disaster of some sort that reduces a population to a small handful, which rarely represents the actual genetic makeup of the initial population.