8.5-8.6: the calvin cycle and photorespiration

The ATP needed in the Calvin cycle comes from ____

both cyclic and noncyclic photophosphorylation

The Calvin cycle is also known as ______ photosynthesis because the first intermediate of the cycle contains three carbon atoms.

C-3

In the Calvin cycle CO₂ is attached to an organic molecule (RuBP) which contains _____ carbon atoms

5

In the process of carbon ______ , carbon dioxide is incorporated into a molecule of ribulose biphosphate forming an unstable 6 carbon intermediate that immediately splits into two 3-carbon molecules.

fixation

What is the name of the enzyme that incorporates CO₂ into organic matter during the Calvin cycle?

Rubisco

Photophosphorylation produces _______ , which stores chemical energy that can be used for the Calvin cycle. Carbon fixation also requires reducing power, which is provided by _______ produced by photosystem I.

ATP/NADH; NADPH

Why is the Calvin cycle also known as C₃ photosynthesis?

Because the first molecule in the cycle has 3 carbon atoms.

The abbreviation, RuBP, stands for ______ 1,5-bisphosphate.

ribulose

Which of the following happens to the molecule formed by the addition of carbon dioxide to ribulose bisphosphate?

• It is the starting point for cellular respiration.

• It is immediately split into two more stable three carbon molecules (PGA).

• It is used to reduce three molecules of NADPH.

• It is immediately stored within the chloroplast for conditions exclusive of photosynthesis.

It is immediately split into two more stable three carbon molecules (PGA).

In the Calvin cycle, ______ molecules of CO₂ are bound to the same number of RuBP molecules to produce 12 molecules of 3PG.

6

What is the function of the enzyme rubisco?

It catalyzes the addition of carbon dioxide to RuBP.

Typically, it is considered that the net gain of the Calvin cycle is(are) ______ molecule(s) of G3P.

2

How many molecules of G3P are needed to make one molecule of glucose?

2

Consider the net equation that describes the Calvin cycle. How many NADPH are needed to synthesize the two net G3P molecules that can be used to make a glucose molecule?

12

How many molecules of CO₂ need to be bound to molecules of RuBP to produce 12 molecules of PGA in the Calvin cycle?

6

_______ molecules of G3P made during the Calvin cycle can be used to make one molecule of ______

2; glucose

Which of the following are phases of the Calvin cycle?

• ATP investment

• Regeneration of ribulose bisphosphate

• Reduction and carbohydrate production

• Carbon fixation

• Polymerization of glucose

• Regeneration of ribulose bisphosphate

• Reduction and carbohydrate production

• Carbon fixation

When you take into account the net equation of the Calvin cycle, how many ATP molecules are needed to synthesize two G3P molecules?

18

Sequence the phases of the Calvin cycle from first (on top) to last.

1. carbon fixation

2. reduction and carbohydrate production

3. regeneration of ribulose biphosphate

The G3P produced during the Calvin cycle is transported into the cytoplasm where it is usually converted into _____ 6-phosphate and _____ 1-phosphate

fructose; glucose

During times of intensive photosynthesis, chloroplast can store glucose in the form of ______

starch grains

The Calvin cycle begins with _____

carbon fixation using Rubisco

After it is transported into the cytoplasm, the G3P made during photosynthesis is usually used to synthesize fructose 6-phosphate and glucose 1-phosphate, which can be used to form _______

sucrose

Glyceraldehyde 3-phosphate formed during the Calvin cycle is an important compound in which of the following stages of cell respiration?

• Krebs cycle

• Electron transport chain

• Glycolysis

Glycolysis

What molecule is released during photorespiration?

Carbon dioxide

When intensive photosynthesis results in the accumulation of G3P in the stroma, the G3P is used to make glucose 1-P which is then used to make _____ grains

starch

Photorespiration has which of the following effects on photosynthesis?

• It reduces the yield of photosynthesis.

• It has no effect on the yield of photosynthesis.

• It increases the yield of photosynthesis.

It reduces the yield of photosynthesis.

In hot, arid conditions, specialized openings in the leaf called _____ close to conserve water, cutting off the supply of carbon dioxide entering the leaf.

stomata

Which of these statements about the relationship between photosynthesis and cell respiration are true?

• The products of cell respiration are the reactants of photosynthesis.

• Photosynthesis and respiration use similar (evolutionarily related) proteins for electron transport and ATP synthesis.

• The products of photosynthesis inhibit cell respiration.

• The products of photosynthesis are the same as the products of cell respiration.

• The products of photosynthesis are the reactants of cell respiration.

• The reactants of photosynthesis are the same as the reactants of cell respiration.

• The products of cell respiration are the reactants of photosynthesis.

• Photosynthesis and respiration use similar (evolutionarily related) proteins for electron transport and ATP synthesis.

• The products of photosynthesis are the reactants of cell respiration.

Plants that only fix carbon using the Calvin cycle are also known as ____ plants

C3

C₃ plants use rubisco to fix carbon dioxide, while other plants can also use ______ carboxylase to add carbon dioxide to a 3-carbon molecule to form a 4-carbon molecule.

PEP

The enzyme rubisco has more than one activity. Because of this, most plants also perform ______ , which consumes oxygen and liberates carbon dioxide. This process can lower the net benefit from photosynthesis.

photorespiration

photorespiration is considered “wasteful” because ____ and _____

• it reduces the yield of photosynthesis

• reduces the ability of a plant to make carbohydrates

Why do hot and dry conditions favor photorespiration?

Because plants close their stomata in hot and dry conditions, inhibiting CO₂ uptake and increasing O₂

A C₃ plant _____

can only fix carbon using the Calvin cycle

Both PEP carboxylase and rubisco can fix carbon dioxide. However, PEP carboxylase:

does not bind to oxygen

What is the name of the enzyme that catalyzes the addition of CO₂ to a molecule of phosphoenolpyruvate?

• CAM

• Rubisco

• PEP carboxylase

PEP carboxylase

Which of the following is a difference between C₄ and CAM plants?

• C₄ plants use C₃ photosynthesis in different cells, while CAM plants use C₃ photosynthesis at certain times.

• CAM plants can also generate ATP from photophosphorylation at night, while C₄ plants cannot.

• C₄ plants also use C₃ photosynthesis, while CAM plants do not use C₃ photosynthesis.

C₄ plants use C₃ photosynthesis in different cells, while CAM plants use C₃ photosynthesis at certain times.

Which statement accurately describes the effect of photorespiration for a C3 plant in tropical climate?

• While photorespiration is quite "wasteful" in a temperate climate, it has little effect on C3 plants in a tropical climate.

• Photorespiration can completely negate the efficiency of photosynthesis.

• The plant can lose up to 75% of its fixed carbon.

• The plant can lose 25-50% of its fixed carbon.

The plant can lose 25-50% of its fixed carbon.

In which type of plant does carbon dioxide capture occur in one cell, and decarboxylation occur in an adjacent cell?

C₄ plants

Corn, sugar cane and sorghum are all ______ plants

C₄ plants

Do C₄ and CAM plants also use C₃ photosynthesis?

yes

In hot and dry conditions, the process of ______ can reduce the efficiency of photosynthesis by 25-50%.

photorespiration

Which of the following accurately describes C₄ photosynthesis?

• PEP is synthesized in the bundle-sheath cells at night, while the Calvin cycle occurs in those same cells during the day.

• PEP is synthesized in the mesophyll cells at night, while the Calvin cycle occurs in those same cells during the day.

• PEP is synthesized in the mesophyll cells, while the Calvin cycle occurs in the bundle-sheath cells.

• PEP is synthesized in the bundle-sheath cells, while the Calvin cycle occurs in the mesophyll cells.

PEP is synthesized in the mesophyll cells, while the Calvin cycle occurs in the bundle-sheath cells.

The C₄ pathway has a cost to plants, because the conversion of _____ to PEP requires the expenditure of ATP.

pyruvate

In which type of plant does carbon dioxide capture occur at night, and decarboxylation occur during the day?

CAM plants

How do CAM plants avoid water loss?

CAM plants close their stomata during the day and open them at night.

Why does CO₂ enter CAM plants at nighttime?

Because the stomata of CAM plants are only open at night

Where does the Calvin cycle occur in a C₄ plant?

In the bundle-sheath cells

Compared to the C₃ pathway, the C₄ pathway has an additional cost to a plant, because ATP is required to ______

convert pyruvate to PEP

plants that use ____ photosynthesis avoid water loss by closing their stomata during the day and opening them at night.

CAM

How are the C₃ and the C₄ pathways separated in CAM plants?

The C₄ pathway occurs at night, while the C₃ pathway occurs during the day.

______ plants only uptake CO₂ at night because they close their _____ during the day

CAM; stomata