Fast me
question 15
how many half-lives does it take for a radioactive substance to decay until only one quarter of the original substance remains?
a
one
b
two
c
three
d
four

In kelp forests, seaweeds known as giant kelp provide shelter and food for an entire ecosystem. Sea urchins are powerful primary consumers in kelp forests. ... In the kelp forest, sea otters are secondary consumers that hunt sea urchins. Tertiary consumers eat the secondary consumers and are at the fourth trophic level.