Q) Explain the following as limiting factors of photosynthesis: (i) carbon dioxide (ii) light
Main points | |
Key idea: | What is limiting factor |
· When a rx is affected by several factors, its rate is determined by the factor which is at its min value · i.e. rate of rx changes when value of factor changes | |
Key idea: | Role of CO2 in photosynthesis |
· CO2 required for dark reaction of photosyn · Increase in CO2 level, increases rate of CO2 fixation, where CO2 combines with ribulose bisphosphate (RuBP), to form glycerate-3-phosphate · Result : more triose phosphates to regenerate RuBP and to synthesize biomolecules (e.g. starch) · Ref to atmospheric level of CO2 is ~ 0.04%, it is a major limiting factor of photosyn | |
Key idea: | Role of light in photosynthesis |
· Required for light dep rx of photosyn at thylakoid membr, chloroplasts in plant cells · Increase in light intensity of red and blue-violet wavelengths, increase excitation + subsequent displacement of e of pri pigments (at rx centres of photosys) · More e flow throu ETC + ref to NADP+ as final e acceptors · Result : more ATP + NADPH produced · With more ATP + NADPH, dark reaction of photosyn also proceed at a faster rate | |
Key idea: | Comparison between CO2 and light intensity |
· Unlike CO2, light intensity is often not limiting during bright daylight hours · However, it affects opening of stomata throu which CO2 enters plant, affects rate of photosyn indirectly | |
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) | |
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