Exam 3: Calvin Cycle

Question 1

What products from the light-dependent reactions are used in the Calvin Cycle?

Answer 1

NADPH and ATP

Question 2

Where does the Calvin Cycle take place?

Answer 2

Outside of the thylakoid, in the stroma

Question 3

What are the three steps of the Calvin Cycle?

Answer 3

1. CO2 fixation
2. Reduction
3. Regeneration

Question 4

Step 1: What happens?

Answer 4

CO2 reacts with RuBP, forms 2 molecules of 3PG

Question 5

Step 2: What happens?

Answer 5

3PGA is phosphorylated by ATP and reduced by NADPH to form G3P

Question 6

Step 3: What happens?

Answer 6

G3P from step 2 forms RuBP to keep the cycle going, needs ATP

Question 7

How many times does the calvin cycle turn in order to make 1 G3P?

Answer 7

3 times

Question 8

Step 1: What is the ratio of molecules for the 3 turns of the cycle?

Answer 8

3 RuBP + 3 CO2 –> 6 3PGA

Question 9

Step 2: What is the ratio of molecules for the 3 turns of the cycle?

Answer 9

6 3PGA + 6 ATP + 6 NADPH –> 6 G3P (1 of them is used to make glucose/fructose, the remaining 5 move on to step 3)

Question 10

Step 3: What is the ratio of molecules for the 3 turns of the cycle?

Answer 10

5 G3P + 3 ATP –> 3 RuBP

Question 11

Which enzyme fixes CO2?

Answer 11

Rubisco

Question 12

Which enzyme is the most abundant on Earth?

Answer 12

Rubisco

Question 13

How many polypeptides does rubisco have?

Answer 13

16

Question 14

How many active sites does rubisco have?

Answer 14

8

Question 15

Which two molecules can bind to rubisco?

Answer 15

CO2 and O2

Question 16

Why is rubisco inefficient?

Answer 16

When oxygen binds, only 1 3PG is produced and 2PG is produced which produces CO2 when broken down.

Question 17

How many reactions can rubisco facilitate per second?

Answer 17

3

Question 18

What is the process when O2 binds to rubisco?

Answer 18

Photorespiration

Question 19

Carbon fixation is favored over photorespiration when CO2 concentration is ___ and O2 concentration is ___

Answer 19

High, low

Question 20

What prevents the rapid evaporation of water when it is hit by sunlight?

Answer 20

The leaf surface is coated in cuticle, which is a waxy substance that prevents gas exchange

Question 21

Stomata are normally ___ during the day and ___ during the night

Answer 21

Open, closed

Question 22

In dry conditions, is photorespiration or carbon fixation more likely?

Answer 22

Photorespiration because of the build-up of O2

Question 23

What are C3 plants?

Answer 23

90% of plants, these are 3 carbon plants

Question 24

What are the 2 mechanisms that plants in dry environments use to adapt to conditions?

Answer 24

1. C4 pathway
2. CAM plants

Question 25

How does the C4 pathway work?

Answer 25

Spatially separates carbon fixation from the calvin cycle, fixes CO2 into 4-carbon orgnanic acids

Question 26

Which enzyme facilitates the C4 pathway?

Answer 26

PEP carboxylase

Question 27

Where does PEP carboxylase fix CO2?

Answer 27

Mesophyll cells

Question 28

Where do the 4-carbon organic acids travel to?

Answer 28

Bundle sheath cells

Question 29

What do the 4-carbon organic acid release that initiates the calvin cycle?

Answer 29

a CO2 molecule

Question 30

How do CAM plants work?

Answer 30

Temporally (time) separates carbon fixation and the Calvin cycle. The stomata is only open during the night. This allows the calvin cycle to occur during the night.

Question 31

When is CO2 stored in CAM plants?

Answer 31

during the night

Question 32

During the day, what is released from the organic acids that have CO2 fixed into them?

Answer 32

CO2

Question 33

In which environments is C4 favored?

Answer 33

Warm and dry, where evaporation is favored

Question 34

In which environments is C3 favored?

Answer 34

Normal and cooler

Question 35

What is G3P made into? What is this process called?

Answer 35

Glucose and fructose; gluceogenesis

Question 36

What are glucose and fructose combined into?

Answer 36

Sucrose (disaccharide)

Question 37

When photosynthesis is slow, what is glucose stored as?

Answer 37

Sucrose

Question 38

When photosynthesis is fast/sucrose is high, what is glucose stored as?

Answer 38

Starch

Question 39

When is starch broken down and what for?

Answer 39

at night, to make more sucrose for transport