This set of Cell Biology Questions and Answers for Experienced people focuses on “Chloroplast Function – CO2 Fixation and Carbohydrate Synthesis in C4 Plants”.
1. Who discovered C4 cycle?
a) Hatch and Slack
b) Kolliker
c) Robert Brown
d) Rudolph Markus
View Answer
Explanation: Hatch and Slack discovered the C4 pathway in the year 1966. It is also called a Hatch – Slack pathway. The pathway produces four carbon sugar molecules.
2. What is the enzyme used in the conversion of pyruvate to phosphoenolpyruvate?
a) Pyruvate monophosphate dikinase
b) Pyruvate orthophosphate dikinase
c) Pyruvate monophosphate reductase
d) Pyruvate orthophosphate reductase
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Explanation: This reaction is the first step in the Hatch – Slack pathway. The enzyme pyruvate orthophosphate dikinase is used to convert pyruvate to phosphoenolpyruvate along with ATP.
3. Which of the following leaf anatomy is a characterization of C4 plants?
a) Piezo anatomy
b) Norman anatomy
c) Kranz anatomy
d) Richard anatomy
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Explanation: Kranz has the meaning “wreath” in German anatomy. There are two rings surrounding the vascular bundle. The inner ring is made of bundle sheath while the outer ring is made up of mesophyll cells.
4. Which of the following is an example of C4 plants?
a) Sugarcane
b) Wheat
c) Rice
d) Cactus
View Answer
Explanation: The plants that produce four carbon sugar molecules by taking atmospheric CO2 is known as C4 plants. These plants undergo Hatch – Slack pathway.
5. What is the final product of the C4 cycle?
a) Aspartate
b) Malate
c) Oxalate
d) Acetate
View Answer
Explanation: Malate is formed as a final product of the C4 pathway. Malate in the final step regenerates the pyruvate and fixes CO2.
6. Where does the C4 pathway take place?
a) Bundle sheath
b) Xylem
c) Mesophylls
d) Phloem
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Explanation: The C4 pathway takes place in the mesophyll cells of the plant system. They are dark reaction and does not require light to take place. The Calvin cycle on the other hand takes place on the bundle sheath.
7. The C4 plants grow in the cold climate places.
a) True
b) False
View Answer
Explanation: C4 plants suppress photorespiration and thus require high light, high temperature and low carbon-dioxide conditions. Thus only a handful of C4 plants are found in cold climates. Most of them are found in temperate regions.
8. The total carbon dioxide fixation done by the C4 plants is _________
a) 3%
b) 13%
c) 23%
d) 33%
View Answer
Explanation: They are more efficient than C3 plants in the carbon dioxide fixation in the atmosphere. They usually grow in higher temperature regions where the activity of the enzyme RuBisCO is high.
9. Which enzyme plays the role of a catalyst in CO2 fixation in C4 plants?
a) Carbonic mutase
b) Carbonic reductase
c) Carbonic anhydrase
d) Carbonic dehydrogenase
View Answer
Explanation: Carbonic anhydrase is an enzyme, which plays the role of catalyst in the first CO2 fixation step of C4 pathway. It helps the CO2 molecule to bind to the active site of RuBisCO.
10. What is the chemical formula for oxaloacetic acid?
a) C4H3O5
b) C4H4O5
c) C4H4O6
d) C3H4O5
View Answer
Explanation: The oxaloacetic acid is formed when phosphoenolpyruvate reacts with CO2. This is the first product of the pathway which is a four carbon compound.
11. C4 pathway uses 5 ATP molecules and 4 NADPH molecules as the energy source.
a) True
b) False
View Answer
Explanation: The C4 pathway uses 5 ATP and 2 NADPH molecules as its energy source. This is higher than the energy requirement in Calvin cycle but C4 can be effective under hot and less water content.
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