5B Rubisco in C3, C4 and CAM photosynthesis

Question 1

whats photorespiration

Answer 1

The process in photosynthesis where RUBISCO is oxygenated and wastes energy produced.

Question 2

whats Carbon fixation

Answer 2

The process in living organisms where inorganic carbon, typically within carbon dioxide, is converted into organic compounds such as glucose. Carbon fixation is a central part of the light-independent stage of photosynthesis.

Question 3

whats inorganic

Answer 3

A compound that does not contain a carbon-hydrogen bond (e.g. Co2).

Question 4

whats organic

Answer 4

A compound containing a carbon-hydrogen bond (e.g. glucose)

Question 5

whats Rubisco

Answer 5

Rubisco is a key enzyme of the light-independent stage of photosynthesis.
Its action varies: sometimes it binds to carbon dioxide and facilitates further reactions in the photosynthesis process, whilst other times it binds to oxygen and initiates a wasteful process called photorespiration.

Question 6

whats the role of Rubisco in photosynthesis

Answer 6

initial changes to carbon dioxide at the beginning of the Calvin cycle
uses 3 × CO₂ molecules and 3 × five-carbon molecules (called RuBP) to produce 6 × three-carbon molecules (called 3-PGA).
6 × 3-PGA are then converted by ATP and NADPH from the light-dependent reactions to make different 6 x three-carbon molecules (called G3P).
One G3P molecule then leaves the cycle to undergo further reactions to contribute to making glucose.
The remaining 5 × G3P are recycled with the help of ATP to regenerate the 3 × RuBP we had at the start of the cycle, and the cycle begins all over again.
Overall, the cycle must turn twice to produce one glucose molecule
i.e. 3 × CO2 goes in twice, to contribute to six-carbon glucose.

Question 7

steps of Rubisco in photsynthesis

Answer 7

1. Carbon fixation – which refers to the conversion of CO₂ and RuBP into 3-PGA. Here, we say that the carbon from the inorganic CO₂ is ‘fixed’ into an organic compound.
   Rubisco is responsible for taking carbon from an inorganic, gaseous form (CO₂) and incorporating it into an organic compound (3-PGA)
2. Reduction – NADPH donates electrons to (aka ‘reduces’) an intermediate three-carbon molecule in the cycle to produce G3P
   A reduction reaction refers to the gain of an electron (in this case, the G3P is gaining the electron from NADPH)
3. Regeneration – the RuBP molecules needed to start the cycle again are reproduced.

Question 8

what is C4 photosynthesis

Answer 8

Carbon Fixation and rest of Calvin Cycle is separated.
Carbon Fixation in mesophyll cells, reduction and regeneration occurs in the bundle-sheath cells.
Additional biochemical pathway compared to C3 (moving from the mesophyll cells to the bundle-sheath cells requires energy).
Advantageous in hot environments .
E.g. corn, sugarcane, switchgrass, several weed species

Question 9

C4 photosynthesis steps

Answer 9

1. Carbon Dioxide enters mesophyll cells and fixed by enzyme PEP carboxylase (only uses carbon dioxide). PEP carboxylase binds the carbon from CO2 to another molecule (PEP) to form oxaloacetate.
2. Oxaloacetate is converted into a different four-carbon molecule (malate) to be transported to the bundle-sheath cells.
   Malate breaks down into Pyruvate and CO2. 3. CO2 enters the Calvin Cycle (same as C3) to form glucose.
3. Pyruvate gets transported back to mesophyll cells to convert into PEP. Cycle restarts

Question 10

whats CAM photsynthesis

Answer 10

CAM = Crassulacean Acid Metabolism
Light-dependent stage the same in C3 and C4
Light independent stage is different (at night instead of in the daytime)
CAM plants open their stomata at night to prevent water loss via evaporation in the daytime.
Requires more ATM than C3 photosynthesis.
E.g. : cacti, pineapples, vanilla, orchids

Question 11

what are the steps of CAM photosynthesis

Answer 11

CO2 is fixed into a four-carbon molecule (oxaloacetate) by PEP carboxylase.
Oxaloacetate is converted into a different four-carbon molecule (can be malate or another organic molecule).
The malate (or other organic molecule) is stored in the vacuole within the mesophyll cell until daytime.
During daytime, malate (or other) is transported from the vacuole to be broken down into CO2. CO2 is free to enter the Calvin Cycle (like C3 and C4 plants)