Photosynthesis

+ water + energy glucose + oxygencarbondioxide

6CO2 6H2O C6H12O6 6O2light

energy + ++

Reactants Products

Review: Light reactions

• Convert solar energy to chemical energy

– ATP

– NADPH

• What can we do now?

energy

electron donator

build stuff !!

photosynthesis

ATP

The second phase of photosynthesis is called the Calvin Cycle (Light-Independent phase)

LIGHT-DEPENDENT PHASE (Requires Sunlight)

LIGHT-INDEPENDENT PHASE (Does Not Require Sunlight)

REMEMBER: This is when the chemical energy produced in the first phase is combine with Carbon Dioxide to create sugar.

LIGHT-INDEPENDENT REACTIONS/ Calvin Cycle

SUGAR ASSEMBLY- SECOND PHASE

The light-INDEPENDENT reactions (or Calvin cycle) use the chemical energy produced in the light-dependent reactions (ATP and NADPH) and carbon dioxide to

create sugar.

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The Calvin CycleThe Calvin Cycle

STROMA

(Fluid interior)

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

Carbon Dioxide enters the plant leaf through openings called stomata.

THE CALVIN CYCLEAt the beginning of the Calvin Cycle, six CO2 molecules

bond with six 5-carbon sugar called RuBP (Ribulose Biphosphate) to form an six unstable 6-carbon sugar.

(An enzyme called Rubisco is responsible for joining these molecules.)

C C C C CCO

O

CARBON DIOXIDE

RuBP

C C C C C

C C C C C C

UNSTABLE 6-CARBON SUGAR

THE CALVIN CYCLEThis step is called Carbon Fixation, because a carbon is “fixed” onto the RuBP.

C C C C CCO

O

CARBON DIOXIDE

RuBP

C C C C C

C C C C C C

UNSTABLE 6-CARBON SUGAR

(CO2)

(RuPB)

THE CALVIN CYCLE

6 carbon sugar

THE CALVIN CYCLE

C C C C C C

UNSTABLE 6-CARBON SUGAR

C C C

C C C

The unstable 6-carbon sugars immediately split to form twelve stable 3-carbon molecules.

These molecules are called PGA’s (phosphoglycerate)

PGAs

(CO2)

(PGA)

(RuPB)

THE CALVIN CYCLE

6 Carbon sugar

3 Carbon molecules

THE CALVIN CYCLE12 NADPH and 12 ATP (from the light dependent

reactions) then give their energy to turn the 3-carbon PGA molecules into PGALs (3-carbon

sugars called glyceride tri-phosphate with higher energy bonds).

C C C

C C C

C C C

C C C2 PGAL molecules

NADPHATPADP + NADP+

ADP, P, and NADP+ are released and then return to the thylakoid membrane

to be re-energized.

(CO2)

ATP

ADP +

NADPH

NADP+

(PGAL)

(PGA)

(RuPB)

THE CALVIN CYCLE

6 carbon sugar

3 carbon molecules

(CO2)

ATP

ADP +

NADPH

NADP+

(PGAL)

(PGA)

(RuPB)6 carbon sugar

3 carbon molecules

(2 PGAL)

(Sugar)

2 PGALs are transferred out of the chloroplast to the cytoplasm of the cell where they are combined to make a

six-carbon glucose.

(CO2)

ATP

ADP +

ADP +

(Sugar)

NADPH

NADP+

(PGAL)

(PGAL)

ATP

(RuPB)6 carbon sugar

3 carbon molecules

The ten remaining PGAL molecules each with 3-carbon atoms, reorganize using 6 ATP molecules to make 6 molecules of RuBP (the 5-carbon sugar) to start the

cycle all over again.

Question 3 A molecule of adenosine that has two

phosphate groups bonded to it is ______.

A. AMP

B. ADP

C. ATP

D. ACP

The answer is B. ADP is adenosine diphosphate.

Adenosine

Adenosine

P P P

P

P

P P

Adenosine triphosphate (ATP)

Adenosine diphosphate (ADP)

Question 4 What is the function of the protein molecule

shown in this diagram?

ATP

ADP

ADP

Protein P Energy

This protein molecule has a specific binding site for ATP. In order to access the energy stored ATP, the protein molecule binds the ATP and uncouples one phosphate group. This action releases energy that is then available to the cell.

ATP

ADP

ADP

ProteinP Energy

The function accomplished by the light-dependent reactions is ________.

Question 6

D. conversion of sugar to PGAL

C. carbon fixation

B. sugar production

A. energy production

The answer is A. The light-dependent reactions transfer energy from the sun to chlorophyll, and pass energized electrons to proteins embedded in the thylakoid membrane for storage in ATP and NADPH molecules.

Sun

Chlorophyll passes energy down through the electron transport chain.

for the use in light-independent reactions

bonds P to ADP

forming ATPoxygen

released

splitsH2O

H+

NADP+

NADPH

Light energy transfers to chlorophyll.

Energized electrons provide energy that

The first step in the Calvin cycle is the ________.

Question 7

D. Bonding of carbon dioxide to RuBP

C. Splitting of six-carbon sugar into two three-carbon molecules

B. production of PGAL

A. replenishing of RuBP

The answer is D. The carbon atom from CO2 bonds with a five-carbon sugar to form an unstable six-carbon sugar. This molecule then splits to form two three-carbon molecules.

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Photosynthesis Photosynthesis OverviewOverview

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