10.3

Question 1

Light independent reactions: Calvin cycle

Answer 1

Biochemical pathways that allows for carbon fixation:
Uses ATP as energy source
Uses NADPH as source of protons and electrons
Converts inorganic CO2 into organic carbohydrates
Also called C3 photosynthesis

Question 2

Calvin cycle occurs in the

Answer 2

Stroma if the chloroplast

Question 3

Calvin cycle has 3 phases

Answer 3

1. Carbon fixation
2. Reduction
3. Regeneration of RuBP

Question 4

Carbon fixation

Answer 4

Key step: RuBP +CO2-> 2PGA
-uses enzyme ribulose bisphospgage carboxylase/oxygenate or rubisco

Question 5

Reduction

Answer 5

PGA is reduced to G3P

Question 6

Regeneration of RuBP

Answer 6

G3P used to regenerate RuBP

Question 7

3 turns of Calvin cycle

Answer 7

Incorporates enough carbon to produce a new G3P

Question 8

6 turns of Calvin cycle

Answer 8

Incorporates enough carbon for 1 glucose molecule

Question 9

Glucose production

Answer 9

-glucose is not a direct product of the Calvin cycle
-2 molecules of G3P leave Calvin cycle
-each G3P contains 3 carbons (from 6 O2 molecules)
-2 G3P used to produce 1 glucose in reactions in the cytoplasm
-new glucose may be converted to sucrose or starch

Question 10

Rubisco has 2 enzymatic activities

Answer 10

Carboxylation and oxidation

Question 11

Carboxylation

Answer 11

-leads to carbon fixation
-addition of CO2 to RuBP
-favored under normal conditions

Question 12

Oxidation

Answer 12

-leads to photorespiration
-addition of O2 to RuBP leads to CO2 release
-favored in hot and dry conditions

Question 13

Climate influences photorespiartion

Answer 13

-Under normal conditions at 25°C, 20# of fixed carbon is lost to photorespiration
-the loss becomes greater as temp increases under hot, arid conditions

Question 14

C4 and CAM pathways minimize photorespiration

Answer 14

Add CO2 to PEP to form a 4 carbon molecule
-use PEP carboxylase instead of rubisco
-has greater affinity for CO2 and no oxidase activity
C4 plants use a spatial solution
CAM plants use a time based solution

Question 15

C4 plants

Answer 15

Corn, sugarcane, sorghum, many other grasses
• Initially fix carbon using PEP carboxylase in mesophyll cells
Malate is transported to bundle-sheath cells
Within bundle-sheath cells, malate is decarboxylated to produce pyruvate and
СО2
*Carbon fixation by rubisco and Calvin Cycle
• Pyruvate returns to mesophyll cells to reform PEP
• C pathway has a cost
• requires 12 additional ATP compared to Calvin cycle in order to make 1 glucose

Question 16

CAM pathway

Answer 16

Many succulent plants such cacti, pineapples
• Stomata open during night (cool temp) and close during day (hot temp)
• Reverse of most plants
• Fix CO, using PEP carboxylase during the night and store in vacuole
• When stomata close during the day, CO, is released from vacuoles
• High levels of CO, drive the Calvin cycle and minimize photorespiration