concept 8.3 ap bio: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar

What is the main function of the Calvin cycle?

The Calvin cycle uses ATP and NADPH to reduce CO2 to sugar, gaining electrons and producing glucose (C6H12O6).

How is the Calvin cycle similar to the citric acid cycle?

Both cycles regenerate their starting material after molecules enter and leave the cycle.

What type of process is the Calvin cycle?

The Calvin cycle is anabolic, meaning it builds larger molecules (sugar) from smaller ones using energy.

How many times must the Calvin cycle occur to make one G3P molecule

The cycle must occur three times, fixing three CO2 molecules to create one G3P molecule.

How many CO2 molecules are needed to make one glucose molecule (C6H12O6)?

Six CO2 molecules are needed to make one glucose molecule, requiring the Calvin cycle to run six times.

What are the three phases of the Calvin cycle?

The three phases are carbon fixation, reduction, and regeneration of the CO2 acceptor (RuBP).

What happens during phase 1 of the Calvin cycle (Carbon Fixation)?

CO2 is incorporated into RuBP using the enzyme rubisco, forming a 6-carbon intermediate that splits into two 3-carbon molecules.

What happens during phase 2 of the Calvin cycle (Reduction)?

3-phosphoglycerate is phosphorylated by ATP and reduced by NADPH to form G3P (glyceraldehyde 3-phosphate).

What happens during phase 3 of the Calvin cycle (Regeneration)?

G3P molecules are rearranged to regenerate RuBP, which is required for the next cycle to begin.

How many ATP and NADPH molecules are consumed for the net synthesis of one G3P molecule?

The Calvin cycle consumes 9 ATP and 6 NADPH molecules for the net synthesis of one G3P molecule.

What is the final product of the Calvin cycle?

The final product of the Calvin cycle is G3P (glyceraldehyde 3-phosphate), which can be used to make glucose and other sugars.

What is the role of rubisco in the Calvin cycle?

Rubisco is the enzyme that catalyzes the incorporation of CO2 into RuBP during the first step of the Calvin cycle.

Where does the Calvin cycle take place in the plant cell?

The Calvin cycle takes place in the stroma of the chloroplast.

What is the importance of G3P in the Calvin cycle?

G3P is the sugar produced by the Calvin cycle and can be used to form glucose, sucrose, and other carbohydrates.

How do C3 plants cope with dehydration and photorespiration?

C3 plants close their stomata on hot, dry days to conserve water, but this also limits CO2 intake and can lead to photorespiration, which reduces photosynthetic efficiency.

What is photorespiration and why is it considered wasteful?

Photorespiration occurs when rubisco adds O2 instead of CO2, producing a 2-carbon compound. It consumes ATP and O2 but produces no sugar or ATP, reducing photosynthesis efficiency.

How do C4 plants minimize photorespiration?

C4 plants incorporate CO2 into a 4-carbon compound in mesophyll cells, which is then transferred to bundle-sheath cells where CO2 is released for use in the Calvin cycle.

What is the difference between spatial and temporal separation in C4 and CAM plants?

In C4 plants, spatial separation occurs with different types of cells for the initial CO2 fixation and Calvin cycle. In CAM plants, temporal separation occurs with CO2 fixation at night and the Calvin cycle during the day.

How do CAM plants fix carbon?

CAM plants open their stomata at night to fix CO2 into organic acids, which release CO2 during the day for use in the Calvin cycle.

Why is photosynthesis important for life on Earth?

Photosynthesis converts solar energy into chemical energy stored in organic molecules, which provides energy for plants and oxygen for the atmosphere, supporting life on Earth.

What is the Calvin cycle and what does it do?

The Calvin cycle is a series of biochemical reactions in the stroma of chloroplasts that uses ATP and NADPH to convert CO2 into sugar, specifically a 3-carbon sugar called G3P (glyceraldehyde 3-phosphate).

How does the Calvin cycle differ from the citric acid cycle?

The Calvin cycle is anabolic, building sugar molecules from smaller components, while the citric acid cycle is catabolic, breaking down acetyl CoA to produce ATP.

What role do ATP and NADPH play in the Calvin cycle?

ATP provides energy, while NADPH provides reducing power (electrons) for the reduction of CO2 to sugar.

What are the three phases of the Calvin cycle?

• Carbon Fixation – CO2 is incorporated into RuBP.

• Reduction – 3-PGA is reduced to G3P.

• Regeneration of RuBP – G3P is rearranged to regenerate RuBP.

What happens in the carbon fixation phase?

CO2 is attached to the 5-carbon sugar RuBP by the enzyme rubisco, forming an unstable 6-carbon intermediate that immediately splits into two molecules of 3-PGA.

What happens during the reduction phase of the Calvin cycle?

ATP adds a phosphate group to 3-PGA, and NADPH reduces it, forming G3P, which is a 3-carbon sugar.

How is RuBP regenerated in the Calvin cycle?

The carbon skeletons of five G3P molecules are rearranged, using ATP, to regenerate three molecules of RuBP, preparing the cycle to accept more CO2.

What happens to G3P after the Calvin cycle?

G3P can be used to make glucose (from two G3Ps), sucrose, or other carbohydrates. It is also involved in building starch and other organic compounds.

What is photorespiration, and why does it happen?

Photorespiration occurs when rubisco adds O2 instead of CO2, leading to the production of a 2-carbon compound. This happens when CO2 levels are low and O2 levels are high, which can reduce the efficiency of the Calvin cycle.

What are C3 plants, and what is their problem during hot, dry conditions?

C3 plants fix carbon directly via rubisco, but when stomata close to conserve water, CO2 levels drop, reducing the efficiency of photosynthesis and causing photorespiration.

How do C4 plants minimize photorespiration?

C4 plants fix CO2 into a 4-carbon compound in mesophyll cells. This compound is then transported to bundle-sheath cells where CO2 is released for the Calvin cycle, maintaining high CO2 concentrations.

What is the strategy used by CAM plants to reduce water loss and photorespiration?

CAM plants open their stomata at night to take in CO2, storing it as organic acids. During the day, they close their stomata and use the stored CO2 for the Calvin cycle.

Why is photosynthesis important for both plants and humans?

Photosynthesis converts solar energy into chemical energy stored in sugars, which provides energy for plants and oxygen for humans and other organisms.

How do plants store excess sugar from photosynthesis?

Plants store excess sugar as starch in the chloroplasts and other plant structures like roots, tubers, and fruits.

What is the overall equation for photosynthesis?

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.

How do C4 and CAM plants adapt to hot, dry climates?

C4 plants separate carbon fixation and the Calvin cycle in different cells, while CAM plants separate these processes by time (fixing CO2 at night and using it during the day).