DP IB Biology: HL

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First teaching 2014

Last exams 2024

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8.3.4 Investigating Carbon Fixation in Photosynthesis

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Investigating Carbon Fixation in Photosynthesis

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-experiments-for-photosynthesis

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

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Cara Head

Author: Cara Head

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding