Photosynthesis

Nature of science:

Developments in scientific research follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation. (1.8)

• Light-dependent reactions take place in the thylakoid membranes and the space inside them.
• Light-independent reactions take place in the stroma.
• Reduced NADP and ATP are produced in the light-dependent reactions.
• Absorption of light by photosystems generates excited electrons.
• Photolysis of water generates electrons for use in the light-dependent reactions.
• Transfer of excited electrons occurs between carriers in thylakoid membranes.
• Excited electrons from Photosystem II are used to contribute to generate a proton gradient.
• ATP synthase in thylakoids generates ATP using the proton gradient.
• Excited electrons from Photosystem I are used to reduce NADP.
• In the light-independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate.
• Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP.
• Triose phosphate is used to regenerate RuBP and produce carbohydrates.
• Ribulose bisphosphate is reformed using ATP.
• The structure of the chloroplast is adapted to its function in photosynthesis.

Applications and skills:

• Application: Calvin’s experiment to elucidate the carboxylation of RuBP.
• Skill: Annotation of a diagram to indicate the adaptations of a chloroplast to its function.

• The lollipop experiment used to work out the biochemical details of the Calvin cycle shows considerable creativity. To what extent is the creation of an elegant protocol similar to the creation of a work of art?

Utilization:

• The Global Artificial Photosynthesis (GAP) project aims to create an artificial “leaf” within the next decade. An electronic version of the leaf that creates oxygen and hydrogen from water and sunlight has already been invented and will be developed for use in the next decade.

• Syllabus and cross-curricular links:
• Biology
• Topic 2.9 Photosynthesis
• Topic 4.2 Energy flow
• Topic 4.3 Carbon cycling
• Chemistry
• Topic 9.1 Oxidation and reduction

Aims:

• Aim 6: Hill´s method demonstrating electron transfer in chloroplasts by observing DCPIP reduction, immobilization of a culture of an alga such as Scenedesmus in alginate beads and measurement of the rate of photosynthesis by monitoring their effect on hydrogencarbonate indicator are all possible experiments.