In human resources the irritation threshold is the

The right answer is a point at which a person notices something and becomes annoyed.  

In science, a threshold effect refers to the appearance of a phenomenon from a certain value of a variable.

In psychology, irritability is a trait of a character indicating a propensity for angry reactions.

So the threshold of irritability designates the appearance of an angry reaction from a determined intensity of stimulation (below this value, there is no reaction).

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.

lysosome is this part of the cell is surrounded by a very thick outer membrane to protect the rest of the cell from its strong enzymes.