Posted by Quinny on .
A fully illuminated plant was placed in an atmosphere containing CO2 composed of radioactive carbon. Then the atmosphere surrounding the plant was exchanged for air containing no radioactive carbon, and the plant was placed in total darkness. When the atmosphere surrounding the plant was sampled for radioactive carbon dioxide at various times after the plant was placed in total darkness, the following data were obtained.
Time (hr.) 1 2 3 4
CPM (counts/min.) 40 86 126 159
Which one of the following is the most likely interpretation?
1 Plants cannot respire in the dark.
2 Respiration was occurring in the dark.
3 Respiration, but not anaerobic glucose breakdown occurs in the dark.
4 Fermentation and glucose breakdown were occurring in the dark.
5 The interpretation provided in choices 2 and 4 are equally valid.