Discussion
Which of the following best explains why lichens are used as pollution indicators?
Answer: D
Correct answer: They absorb directly and lack a cuticle
Lichens have no roots and no waxy cuticle, so they take up water and nutrients - and any pollutants present - directly across their whole surface from the atmosphere. Nothing intervenes between the air and the living tissue.
They are therefore sensitive to sulphur dioxide at concentrations that leave higher plants unharmed, and because they are long-lived and slow-growing they integrate exposure over years. The result is the lichen desert around industrial centres and a well-established scale relating the species present to ambient sulphur dioxide.
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