Alternative Mechanisms of Carbon Fixation

Question 1

what is the problem with RuBisCo

Answer 1

• Rubisco is a very slow enzyme– 3 per second. - inefficient for enzymes
• Will also bind to O2 if the concentration of CO2 decreases, or O2 increases. -lacks specificity
• When it binds with O2 it creates a useless molecule for the cell

Question 2

what is photorespiration

Answer 2

• The recovery of this molecule is long, takes energy (ATP) and produces CO2
• Producing CO2 is the opposite of Rubisco is supposed to do!

Question 3

break down 02 and RuBP

Answer 3

look at your phone bitch

Question 4

draw the photorespiration and the calvin cycle

Answer 4

look it up

Question 5

what does a waxy cuticle do in plants

Answer 5

provides a barrier between the cells and the environment.

Question 6

what do the stomata small openings do

Answer 6

control the gas exchange with the atmosphere.

Question 7

what do normal plants do during the day

Answer 7

the stomata are open to allow for gas exchange.
- Open during day
- Closed at night (conserve water)
- photosynthesis stops

Question 8

what is the problem for plants on hot days

Answer 8

• In high temperatures, as much as 50% of the plant’s energy could be wasted by photorespiration.
• Buildup of O2 in the cells

Question 9

how to reduce THE RATE OF PHOTORESPIRATION

Answer 9

• C4 photosynthesis (in C4 plants)
• Crassulacean acid metabolism (CAM plants)

Question 10

what are c4 plants

Answer 10

• E.g., sugar cane, corn
• Hot, dry climates
• Unique leaf structure

Question 11

what is the Bundle-sheath

Answer 11

cells that surround a vein
- surrounds a barrier to high concentration oxygen levels

Question 12

what is the Mesophyll cells

Answer 12

located around the bundle-sheath
- surrounds a barrier to high concentration oxygen levels

Question 13

what is the strategy of c4 plants

Answer 13

• Mesophyll acts as a barrier to reduce Rubisco’s exposure to O2
• CO2 is continually pumped from mesophyll to the bundle-sheath cells to enter Calvin cycle
• Keeps [CO2] high so it can outcompete O2 – minimize photorespiration
• Extra ATP is used as compared with C3

Question 14

what is the CAM plants

Answer 14

• Succulents – cacti, pineapples
• Hot, dry, desert climates
• These plants open their stomata at night, and close them during the day (opposite of other plants)
• Helps conserve water, but prevents CO2 from entering leaves during day

Question 15

what is the strategy of the CAM plants

Answer 15

• Keep stomata closed during day – minimize water loss
• Take in CO2 at night and store it for use during day

Question 16

explain C4 vs CAM plants

Answer 16

Same steps:
- CO2 temporarily fixed into a 4-carbon organic acid
- C4: OAA
- CAM: malate
- The organic acid releases CO2 to the Calvin cycle