8.3

Question 1

Identify where in the chloroplast the Calvin cycle occurs.

Answer 1

stroma

Question 2

Illustrate how the products of the light reactions are used in the Calvin cycle (i.e. how are ATP and NADPH used in the Calvin cycle).

Answer 2

• Builds sugar from smaller molecules by using energy from ATP & NADPH
• Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phosphate (G3P)
• net synthesis: 1 G3P, cycle must take place 3 times, fixing 3 molecules of CO2

Question 3

Describe carbon fixation and the function of rubisco.

Answer 3

• Catalyzed by rubisco
   RuBP + CO2 = PGA

Question 4

Describe the three phases of the Calvin cycle.

Answer 4

• Carbon fixation
   Catalyzed by rubisco
   RuBP + CO2 -> PGA
• Reduction
   PGA is reduced to G3P
• Regeneration of the CO2 acceptor
   RuBP
   G3P is used to regenerate RuBP

Question 5

Identify the output of the Calvin cycle.

Answer 5

• G3P
   3 carbon sugar
• Used to form sucrose
   Major transport sugar in plants
   Disaccharide made of fructose and glucose
• used to make starch
   insoluble glucose polymer
   stored for later use

Question 6

Explain the energy cycle between the mitochondria and chloroplasts.

Answer 6

chloroplasts produce photosynthesis and mitochondria are responsible for cellular respiration. these two processes are exact opposites of each other yet use products of each other as starting substrates. ex) photosystems use water that is produced by the ETC and the ETC uses the oxygen that is produced from the photosystems. the CC uses CO2 from the CAC while the CAC uses the glucose/pyruvates that the CC produces. in the chloroplast, the CC also uses the ATP & NADPH molecules that the photosystems produced. The ETC also uses electrons from NADH and FADH2 which the CAC produced.

Question 7

Define photorespiration.

Answer 7

Fix CO2 into a 3 carbon compound using rubisco

Question 8

function of carbon fixation in C3 plants.

Answer 8

Most plants are this
Plants that fix carbon using only C3 photosynthesis (Calvin cycle)

Question 9

function of carbon fixation in C4 plants.

Answer 9

2 pathways occur in different cells.
Spatial solution to photorespiration.
corn, sugarcane, sorghum & a number of other grasses.
initially fix carbon using PEP carboxylase in mesophyll cells.
produces 4C molecules (malate) that is transported to bundle-sheath cells.
within the bundle-sheath cells, malate is decarboxylated to produce pyruvate and CO2.
Carbon fixation using CO2 by rubisco via the calvin cycle

Question 10

function of carbon fixation in CAM plants.

Answer 10

crassulacean acid metabolism.
C4 pathway at night and the C3 pathway during the day.
Temporal solution to photorespiration
many succulent (water-storing) plants, cacti, & pineapples use this.
stomata open during the night (opposite of most plants)
fix CO2 using PEP carboxylase during the night and store in a vacuole
when stomata is closed during the day, organic acids are decarboxylated to yield high levels of CO2
increasing levels of CO2 drive Calvin Cycle and minimize photorespiration

Question 11

function of carbon fixation in both C4 and CAM plants.

Answer 11

Use both C3 and C4 pathways.
Add CO2 to PEP to form 4 carbon molecules
use PEP carboxylase