5B- rubisco C3 C4 CAM

Question 1

RUBSICO?

Answer 1

key enzyme in L-I stage
- binds to CO2 and facilitates further reactions in photosyn. process - might bind to O2
- Rubisco can be summarised as binding CO2
and fixing the carbon into the organic 3-PGA, thus initiating the Calvin cycle

Question 2

summarised steps of L-I

Answer 2

1 Carbon fixation – which refers to the conversion of CO2 and RuBP into 3-PGA. the carbon from the inorganic CO2 is ‘fixed’ into an organic compound. Rubisco responsible for taking carbon from inorganic, gaseous form (CO2) and incorporating into organic compound (3-PGA).

2 Reduction – NADPH donates electrons to (aka ‘reduces’) an intermediate three-carbon molecule in the cycle to produce G3P .

3 Regeneration – the RuBP molecules needed to start the cycle again are reproduced

Question 3

rubisco limitations

Answer 3

-When Rubisco binds to O2 instead, a different reaction called photorespiration occurs.
-process of photorespiration is wasteful and unwanted in plants.
-Less photosynthesis means less glucose is produced, which, combined with wasted energy used in the photorespiration pathway, negatively impacts a plant’s ability to grow, survive, and reproduce.

Question 4

why does rubisco bind to O2?

Answer 4

Substrate concentration – more CO2 concentration than O2, to facilitate- stomata in leaves open allow CO2 to enter, and O2 ad water vapour simultaneously diffuse out of plant. But, when require water, close stomata and cause O2 production in L-D to build up in cell.
Temperature- regular or low temperatures, Rubisco’s affinity for CO2 is far greater than that for O2. At higher temperatures, the affinity for O2 is higher, leading to Rubisco binding oxygen more often.

Question 5

photorespirationesis

Answer 5

- a wasteful process in plants initiated by Rubisco that limits photosyn.
-occurs more in hot and dry weather, Rubisco has greater affinity for O2 and conditions have caused stomata close

Question 6

C4 PLANTS

Answer 6

-plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycleover space.
-additional biochemical pathway when compared to C3
-mesophyll cells constantly pumping a source of CO2
(in the form of malate) into the bundle-sheath cells, there is always a higher concentration of CO2 present for Rubisco rather than O2.

Question 7

C4 PLANTS LIMIATIONS

Answer 7

-ATP is required to convert pyruvate to PEP for the initial carbon fixation. due to this C4 plants use more energy to undertake photosynthesis than C3 plants.

Question 8

C4 advantage

Answer 8

• in hot environments where C3 plants suffer from increased photorespiration.
• benefits of reduced photorespiration typically outweigh the cost of using ATP in C4 photosynthesis.

Question 9

C4 plant examples

Answer 9

• corn, sugarcane, switchgrass, and several weed species

Question 10

CAM PLANTS (crassulacean acid metabolism,)

Answer 10

-plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over time- separate the steps over time.
AT NIGHT:
-open up their stomata to bring in CO2
-CO2 is fixed into a four-carbon molecule (oxaloacetate) by the enzymePEP carboxylase
-Oxaloacetate is then converted to a different four-carbon molecule (can be malate or another organic molecule).
-The malate (or other) molecule is stored inside vacuoles within the mesophyll cell UNTIL DAYTIME

Question 11

CAM PLANTS PT 2

Answer 11

-DURING DAY-do not open their stomata to prevent water loss- very resistant to water loss
-can still photosynthesise during the day
as the malate (or other) molecule is transported out of the vacuole and broken down to release CO.
- The CO2 is free to enter Calvin cycle same fashion as in C3 and C4 plants, leading to glucose production.

Question 12

CAM advantage

Answer 12

• controlled release of molecules out of vacuoles ensures a high concentration of CO2 is maintained near Rubisco, maximising photosynthesis and minimising photorespiration
  -Water is also conserved in CAM plants as their stomata only open at night when typically cooler and more humid. - reduce water loss
  -CAM plants are very prominent in very hot dry areas like deserts.

Question 13

CAM EXAMPLES

Answer 13

all cacti, pineapples, vanilla, and orchids

Question 14

c3 plants

Answer 14

-stomata is open in the day
-susceptiable to photorespiration initiation
- best adapted to moderate, or cool and wet environments
- most plants include wheat, rice and all trees