Investigating Carbon Fixation in Photosynthesis (DP IB Biology: HL)

NOS: Developments in scientific research follow improvements in apparatus: sources of ¹⁴C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation

• The Calvin cycle was named after American biochemist Melvin Calvin for his work in mapping the complete conversion of carbon dioxide to glucose
• The techniques used at the time were novel and showed developments in scientific research
• Calvin developed methods for growing algae in an apparatus he named "the lollipop" due to its shape
• This apparatus enabled Calvin to introduce radioactive carbon dioxide to the algae in order to study photosynthesis
• He also used paper chromatography and production of x-ray chromatograms to enable Calvin to identify compounds using in reactions during photosynthesis
• His approaches and methods were novel at the time and were only possible because of advancements in apparatus and technologies   

• The experiments performed by Calvin show process of using radioactive carbon dioxide and autoradiography in explaining the reactions of the Calvin Cycle:
  • Radioactively labeled carbon-14 (¹⁴C) was introduced to the algae Chlorella in an apparatus called a lollipop (the experiments are sometimes referred to as the “lollipop experiment” due to the shape of the apparatus)
  • Light was shone on the lollipop vessel containing the Chlorella to induce photosynthesis and carbon-14 was incorporated into the algae
  • After varying time periods the algae was killed by heated alcohol which denatures proteins and enzymes within the cells and stops metabolic processes
  • The pathway of the radioactive carbon was mapped and analysed throughout the algae using two-dimensional paper chromatography
  • Chromatography separated out the different carbon compounds that had been made by the algae
  • Any radioactive carbon-14 atoms (that had been incorporated into either intermediates or products of photosynthesis) were identified using autoradiography (x-ray)
  • By comparing the different time periods in which the carbon compounds formed Calvin was able to map the order in which they were generated
• The results of the experiments showed that carbon was converted to carbohydrates during the light-independent reactions of photosynthesis
• Today, the method Calvin used is called “feeding experiments”

Calvin’s lollipop experiments for determining the reactions in the light-independent reaction