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The Working Cell: Energy From Sunlight

Chapter 8

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The Photosynthesis Equation

•The Photosynthesis Equation• The equation for photosynthesis is:

6CO2 + 6H2O C6H12O6 + 6O2

Light

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Where does photosynthesis occur?

• In plants, photosynthesis takes place inside chloroplasts.

• Function – convert solar energy into chemical energy

Plant cells

Chloroplast

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Inside a Chloroplast

Chloroplast

Singlethylakoid

• thylakoids—saclike membranes inside the chloroplasts.

• Structure – thylakoid membranes are stacked; they contain pigments such as chlorophyll

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Inside a Chloroplast

• A stack of thylakoids is called a granum.

Granum

Chloroplast

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Inside a Chloroplast• The fluid that fills the chloroplast and surrounds the

thylakoids is called the Stroma

Stroma

Chloroplast

Photosynthesis Occurs in Two Steps

• The Light Reaction– Uses sunlight & H2O to make ATP and

NADPH and releases O2

• The Calvin Cycle– Light-independent reaction

– Uses ATP, CO2 and NADPH to produce high energy sugars

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Light

H2O

O2

CO2

Sugars

NADP+

ADP + P

Calvin Cycle

Light- dependent reactions

Calvin cycle

How do chloroplasts harvest light energy?

• Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum.

• Chlorophyll does not absorb light well in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green.

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The Light Reaction

• Takes place in the Thylakoid membrane– Also called the Electron Transport Chain.– Requires:

• Light• Water• NADP+ and H+

– Produces:• ATP

• Oxygen (O2)

• NADPH

Outside Thylakoid (Stroma)

Inside Thylakoid

H-O-H

H-O-H

H-O-H

H-O-H

H-O-HH-O-H

H+

H-O-H

H-O-H

H+H+

H+

H+

H+H+

H+ concentration is at equilibrium

H+

Outside Thylakoid (Stroma)

Inside Thylakoid

H-O-HH-O-H

H+H+H+

H+H+

H+H+

H+

1. Start of Light Reaction- Light is absorbed by clorophyll.

H+H+

H+

Outside Thylakoid (Stroma)

Inside Thylakoid

H-O-HH-O-H

H+H+

H+

H+H+

H+H+

H+

2. Light energy is taken by Clorophyll and WATER SPLITTING ENZYME TO split water.

H+H+

H+

H+H+

H+ H+ Oxygen, more Hydrogen Ions are made AND 2 ELECTRONS ARE RELEASED

O2

Outside Thylakoid (Stroma)

Inside Thylakoid

H+ H+H+

H+H+

H+H+

H+

3. The electrons will then move into the ETC. They go to each ELECTRON ACCEPTOR in the chain.

H+H+

H+

H+H+

H+ H+

At each electron acceptor, H+ are pumped into the Thylakoid.

Outside Thylakoid (Stroma)

Inside Thylakoid

H+ H+H+

H+H+

H+

H+

H+

4. At this point the electrons have no more energy.

H+H+

H+H+

H+

H+

H+

More light is absorbed so the electrons can continue down the ETC.

Outside Thylakoid (Stroma)

Inside Thylakoid

H+

H+

H+

H+

H+H+

H+

H+

5. A Concentration Gradient has been created.

H+

H+

H+H+

H+

H+

H+

The H+ ions flow through the ATP SYNTHASE.

High Concentration

Low Concentration

Outside Thylakoid (Stroma)

Inside Thylakoid

H+

H+

H+

H+

H+H+

H+

H+

6. As the H+ ions flow through the ATP Synthase, the ATP Synthase takes ADP and turns it into ATP.

H+

H+

H+H+

H+

H+

H+

This is facilitated diffusion.

A P PP P PA P P P

Energy from H+ movement used to make ATP

Outside Thylakoid (Stroma)

Inside Thylakoid

H+H+

H+

H+

H+

H+

H+

7. The last step is to remove the electrons so the ETC can continue to function.

H+ H+

H+

H+

H+

H+

A molecule called NADP+ bonds with an H+ to remove the electrons.

NADP+H+H+

NADPH

The Calvin Cycle

• Takes place in the Stroma– Also called the “Dark Reaction”– Requires:

• NADPH and ATP from light reaction

• CO2

– Produces:• ADP + P• NADP+• 3C sugar (G3P) glucose, fatty acids, or cellulose

The Carbon Cycle