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2.5 gather and process information from secondary sources to identify and describe relevant modern technologies not available to the above people that would have assisted them in their investigations

gather and process information from secondary sources to identify and describe relevant modern technologies not available to the above people that would have assisted them in their investigations

Sample information

Pure sources of gases

If pure sources of gas were available then as they are today, plants could be grown in pure atmospheres of CO2(g), O2(g), or N2(g) to determine which components of the atmosphere support photosynthesis. Plants grown in an atmosphere of pure oxygen or nitrogen would not survive while those in carbon dioxide would produce sufficient oxygen by photosynthesis to respire and survive, thus proving that carbon dioxide is the gas required for photosynthesis.

Geiger counters

Geiger counters or scintillation counters and a supply of radioactively labeled CO2(g), H2O(l) or O2(g) would have allowed the early experimenters to trace the movement of these substances in the plant. Using Geiger counters it is possible to follow, for example, the movement of water from the shoots to the leaves. Traces of radioactivity would be found in the leaves and in the atmosphere around the plant as some water would be transpired but other water molecules would be incorporated into glucose by photosynthesis. Using radioactive 14CO2(g) Calvin described the processes of the Calvin Cycle of photosynthesis in 1962.

Autoradiography

Autoradiography could have been used to determine the location of the radioactively labeled substances. The cells or tissues, washed clean of any radioactive material that was not taken up, are fixed and preserved on glass slides. The slides are covered with a layer of photographic emulsion and kept in the dark. As the radioactive substance decays, it exposes the photographic emulsion and when developed, the sites of radioactivity can be examined under a microscope. This technique would have revealed chloroplasts as the site of photosynthesis.

Oxygen electrodes and dataloggers

These can be used to monitor long-term changes in gases entering and leaving plants.