bio 5B Flashcards
Rubisco in C3, C3, and CAM photosynthesis
what is rubisco and its functions
an enzyme that works in the light-independent stage and functions to bind to carbon dioxide (inorganic compound) and convert it into 3-PGA (organic compound) and facilitate further reactions in photosynthesis as well being able to bind to oxygen and initiate photorespiration (Wasteful)
what is rubisco’s role in the Calvin cycle in C3 plants
- uses 3x CO2 molecules and 3x five-carbon molecules (RuBP) to produce 6x 3-PGA
- the 3-PGA are then converted by the ATP and NADPH into 6x G3P
- 1x G3P leaves the cycle to undergo further reactions to form glucose (2 G3P are needed to make it) whilst the rest continue to cycle and are used for regeneration
what is the first chemical process in the Calvin cycle in C3 plants
carbon fixation refers to CO2 and RuBP being converted into 3-PGA
what is the second chemical process in the Calvin Cycle in C3 plants
reduction refers to NADPH donating electrons to 3-PGA to produce G3P
what is the last chemical process in the Calvin cycle in C3 plants
regeneration refers to ATP being used to convert 5x G3P into 3RuBP to restart the cycle
what are some limitations of Rubisco
- Rubisco has an affinity to Oxygen and this is detrimental to plants as, without the Rubisco-Co2 pairing, photosynthesis is unable to occur. instead, photorespiration happens (wasteful). with lower levels of photosynthesis, less glucose results in less energy and this impacts the plant’s ability to grow, survive, and reproduce.
influences as to whether or not Rubisco binds to CO2 or O2
temperature: at low or regular temperatures, Rubisco has a higher affinity to bind to CO2 rather than O2 whereas at high temperatures, Rubisco has a higher affinity to bind to O2 due to the stomata closing to prevent water loss (but also prevents oxygen from entering the atmosphere and instead stay in the cells)
substrate concentration: the more substrate present, the greater the chance it will bind to Rubisco. exposure to high concentrations of CO2 maximises photosynthesis (and vice versa)
what occurs in the Calvin cycle of the C4 photosynthesis
initial carbon fixation occurs in the mesophyll cells whilst the rest of the Calvin cycle occurs in specialized cells (bundle-sheath cells)
what is the process of the Calvin cycle in C4 plants
i. atmospheric CO2 enters the mesophyll cells and is fixed to the enzyme PEP carboxylase (responsible for initial carbon fixation in C4 and has no affinity to O2)
ii. PEP carboxylase adds the carbon from CO2 to a three-carbon molecule (PEP) to create a four-carbon molecule (OXALOACETATE)
iii. oxaloacetate is converted to malate (capable of being transported into the bundle-sheath cells)
iv. once in the bundle-sheath cells, the malate breaks down back into CO2 and it enters the Calvin cycle (same way as C3 photosynthesis)
v. pyruvate is formed as a product from the breakdown of malate and is transported back to the mesophyll cells and converted into PEP with the help of ATP
what are advantages of C4 photosynthesis
- the concentration of CO2 inside the bundle-sheath cells is higher compared to that of O2 meaning photosynthesis is more likely to occur
- C4 is advantageous in hot environments (when the stomata is closed to conserve water and O2 is in the cells in high concentrations)
what are disadvantages of C4 photosynthesis
ATP is required to convert pyruvate into PEP for the initial carbon fixation
what occurs in the Calvin cycle of the CAM photosynthesis
photorespiration is minimised by separating initial carbon fixation with the remainder of the Calvin cycle over time
what is the process of the Calvin cycle in CAM plants
AT NIGHT
i. the CAM plant opens up their stomata at night to bring in CO2 from the atmosphere
ii. the CO2 is fixed to oxaloacetate by the enzyme PEP carboxylase
iii. oxaloacetate is then converted to another 4-carbon molecule (either malate or another)
iv. malate is then stored inside the vacuole within mesophyll cells until the daytime
IN DAYTIME
- CAM plants do not open up their stomata to prevent water loss
v. the 4-carbon molecule is then transported from the vacuole and broken back down into CO2
vi. the CO2 is then able to enter the Calvin cycle and create glucose
what are advantages of CAM photosynthesis
- the controlled release of molecules out of the vacuole ensure a high concentration of CO2 is maintained near Rubisco to maximise photosynthesis over photorespiration
- water is conserved as the stomata only opens at night when it is cooler and more humid
what are disadvantages of CAM photosynthesis
- the process requires more energy than C3 to cycle PEP
