A tomato plant was placed under a sealed bell jar and
exposed to light. Carbon dioxide containing radioac-
tive carbon was introduced into the bell jar as shown
in the following diagram. After an hour, the inlet
valve was closed. Later, the entire plant was removed
from the soil and cleaned by rinsing it in water,
A Geiger counter indicated radioactivity in the roots.
These roots were then dried and chopped into very
small pieces. The chopped roots were sprinkled into
an aquarium containing a very hungry goldfish that
was not radioactive.
Four days later, the fish was removed from the
aquarium and a tissue section of the fish was tested
with the Geiger counter. The counter indicated an
above-normal level of radioactivity in the fish tissues.
34. Which cycle is primarily being studied by means
of this investigation?
Radioactive CO2
Inlet valve
Light
Tomato plant
(1) oxygen
(3) nitrogen
(4) water
12 carbon