4.3 Photosynthesis in Detail

KEY CONCEPT Photosynthesis converts light energy is captured and used to build sugars that store chemical energy.

4.3 Photosynthesis in Detail

4.3 Photosynthesis in Detail

• The equation for the overall process is:

6CO2 + 6H2O C6H12O6 + 6O2

C6H12O6

granum (stack of thylakoids)

thylakoid

sunlight

1 six-carbon sugar

6H2O

6CO2

6O2

chloroplastchloroplast1

2

43

energy

stroma (fluid outside the thylakoids)

4.3 Photosynthesis in Detail

Photosynthesis in plants occurs in chloroplasts.

• Photosynthesis occurs in a series of stages in the chloroplasts.– grana (thylakoids)- photosystem II, photosystem I and

the electron transport chain.– Stroma- Calvin Cycle

chloroplast

stroma

grana (thylakoids)

4.3 Photosynthesis in Detail

The first stage of photosynthesis captures and transfers energy.

• The light-dependent reactions include groups of molecules called photosystems.

4.3 Photosynthesis in Detail

• Photosystem II captures and transfers energy.

1.chlorophyll absorbs energy from sunlight

– energized electrons enter electron transport chain

2.water molecules are split

– oxygen is released as waste

3.hydrogen ions are transported across thylakoid membrane

4.3 Photosynthesis in Detail

• Photosystem I captures energy and produces energy-carrying molecules.

4.chlorophyll absorbs energy from sunlight

5.energized electrons are used to make NADPH

– NADPH is transferred to light-independent reactions

4.3 Photosynthesis in Detail

• The light-dependent reactions produce ATP.

6.hydrogen ions flow through a channel in the thylakoid membrane

7.ATP synthase attached to the channel makes ATP

4.3 Photosynthesis in Detail

4.3 Photosynthesis in Detail

• Light-independent reactions occur in the stroma and use

• CO2 molecules enter the Calvin cycle

The second stage of photosynthesis uses energy from the first stage to make sugars.

4.3 Photosynthesis in Detail

• The light-independent reactions make sugars.

– take place in stroma– needs carbon dioxide from atmosphere– use energy to build a sugar in a cycle of chemical

reactions

4.3 Photosynthesis in Detail

• A molecule of glucose is formed as it stores some of the energy captured from sunlight.

1.carbon dioxide molecules enter the Calvin cycle

2.energy is added and carbon molecules are rearranged

3.a high-energy three-carbon molecule leaves the cycle

4.3 Photosynthesis in Detail

4.two three-carbon molecules bond to form a sugar

– remaining molecules stay in the cycle

• A molecule of glucose is formed as it stores some of the energy captured from sunlight.

4.3 Photosynthesis in Detail

4.3 Photosynthesis in Detail