4. Usefulness of lichens as
bio-indicators
• They are found almost everywhere
and at all seasons
• They absorb nutrients and pollutants
from the air, often to high
concentrations
• Different species show different
sensitivities and accumulation abilities
• They are symbiotic organisms. The
fungus cannot survive if the algae is
killed by pollution
11. (a) What can you conclude from the results
about the level of pollution in the stream?
Give your reasons. [3 marks]
The level of pollution is
decreasing / the stream has
become cleaner. [1]
The species that live in cleaner
water have increased or specific
examples. [1]
The species that live in polluted
water have decreased or specific
examples.[1]
12. (b) Nona said that these samples should be taken at the same time
each year but Rhys said it doesn’t matter. State who you think is right,
giving a reason. [1 mark]
(c) State one other non-biological factor that could be measured and
used as an indicator of the level of pollution in the stream. [1 mark]
(b) (Nona because) water conditions such as temperature must
be the same to be a valid comparison. [1]
(c) Oxygen/pH/heavy metals/nitrate/phosphate/pesticide
(Any 1) [1]
