Photosynthesis: Calvin-Benson Cycle

Question 1

Predominant pathway of autotrophic CO2 fixation

Answer 1

calvin-benson cycle

Question 2

Number of steps/biochemical reactions in the Calvin-Benson Cycle

Answer 2

thirteen

Question 3

Three major steps in Calvin-Benson Cycle

Answer 3

1. carboxylation of RuBP → 2 molecules of 3-PGA
2. reduction of 3-PGA → G3P
3. regeneration of RuBP from G3P

or each co2 molecule that reacts with one RuBP, two molecules of 3-PGA f

Question 4

An enzyme that catalyzes carboxylation and oxygenation of RuBP.

Answer 4

RubiSCO

Question 5

Plants that form 3-PGA as the 1st stable compound.

Answer 5

C3 plants

Question 6

Types of RubiSCO

Answer 6

I, II, III, IV

Question 7

• Type/s of RubiSCO having catalytic function.
• Type/s of RubiSCO with lost RubisCO activity.
• Type of RubiSCO that harbors small subunits, consisting of eight large and eight small subunits; found in most autotrophic organisms; most abundant protein

Answer 7

types I, II, III
type IV
type I

Question 8

Reduction is a two-step reaction that converts the 6 molecules of ___ from the carboxylation stage into 6 molecules of ___.

Answer 8

3‐PGA to G3P

Question 9

What is regenerated in the “regeneration” phase of Calvin-Benson Cycle?

Answer 9

RuBP

Question 10

What modulates the levels of stromal enzymes encoded in nuclear and chloroplast genomes?

Answer 10

light

Question 11

Light‐linked ___ regulates the Calvin–Benson Cycle.

Answer 11

posttranslational modifications of enzymes

Question 12

• Accumulation of stromal enzymes = ↓ catalytic effect
• Posttranslational modifications of enzymes = rapid catalytic effect

Answer 12

true

Question 13

Two mechanisms that alter the protein structure of enzymes for their catalytic rates.

Answer 13

1. rubiSCO activase
2. ferredoxin–thioredoxin system (FTS)

Question 14

An ATP-dependent enzyme that modulates RubiSCO activity.

Answer 14

rubiSCO activase

Question 15

Rubisco activity has a fast capacity for CO2 fixation.

Answer 15

false; 1–12 CO2 fixations per second

Question 16

RubiSCO is an “automatic” catalyst. True or False?

Answer 16

false; it must first be activated.

Question 17

An inhibitor, together with other sugar phosphates, that is removed by RubiSCO activase to kickstart RubiSCO catalytic activity.

Answer 17

CAP1

Question 18

A mechanism that regulates enzymes by redox transitions.

Answer 18

ferredoxin–thioredoxin system

Question 19

Ferredoxin–thioredoxin system uses ___ to regulate Fructose 1,6-bisphosphatase, etc.

Answer 19

ferredoxin

Question 20

The oxygenase activity of rubisco causes partial loss of the carbon fixed by the Calvin–Benson cycle and yields ____, an inhibitor of two chloroplast enzymes: triose phosphate isomerase & phosphofructokinase.

Answer 20

2-phosphoglycolate

Question 21

2-phosphoglycolate is metabolized through the process of ___.

Answer 21

photorespiration

Question 22

Where does photorespiration occur?

Answer 22

mitochondria, peroxisome, chloroplast

Question 23

Why do C3 plants close their stomata during dry and hot climate?

Answer 23

open stomata lead to water loss and dehydration; however, it also increases oxygen production and inhibits gas exchange.

Question 24

When the concentration of O2 is relatively high compared to the CO2
concentration, photorespiration becomes a serious problem.

Answer 24

true

Question 25

Photorespiration is also known as ___.

Answer 25

C2 pathway

Question 26

How many molecule/s of O2 is needed to produce 1 molecule of CO2?

Answer 26

two

Question 27

For every 2 molecules of glycine that enters the mitochondrion, 1 molecule each of serine, CO2, and ammonia are produced, and 1NAD+ is reduced to NADH. True or False?

Answer 27

true

Question 28

C2 pathway interacts with:
1. Nitrogen metabolism at multiple levels
2. Cell redox homeostasis
3. C1 metabolism
4. Expression of transcription factors

Answer 28

true

Question 29

Two types of carbon-concentrating mechanisms that land plants use for
increasing the concentration of CO2
at the RubiSCO carboxylation site.

Answer 29

C4 pathway
Crassulacean Acid Metabolism

Question 30

C4 cycle separates ____; while
CAM separates ____.

Answer 30

spatially
temporally

Question 31

C3 plants produce ____; while
CAM plants produce ____.

Answer 31

3-PGA
OAA (oxaloacetic acid)

Question 32

Two concentric cylinders of cells in C4 plants’ leaves.

Answer 32

mesophyll cells: outer cylinder
bundle-sheath cells: inner cylinder

Question 33

Anatomy unique to plants that use C4 pathway which provides spatial separation of carbon fixations in two types of cells and photosynthetic reactions.

Answer 33

kranz anatomy

Question 34

C4 pathway requires more energy. True or False?

Answer 34

true; C3 pathway consumes 3 ATP : 2
NADPH : 1 CO2 vs. C4 pathway, 5 ATP : 2 NADPH : 1 CO2

Question 35

CAM also utilizes PEP carboxylase. True or False?

Answer 35

true

Question 36

Difference of CAM with C4 pathway:
▪ Stomata are closed during the day, open during night.
▪ Carry out light reaction & CO2
fixation at different TIME of the day ~ temporal separation.

Answer 36

true