The Working Cell: Energy From Sunlight Chapter 8 Photo Credit: ©Stone Copyright Pearson Prentice Hall

The Photosynthesis Equation The equation for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 Light Copyright Pearson Prentice Hall

Where does photosynthesis occur? In plants, photosynthesis takes place inside chloroplasts. Function – convert solar energy into chemical energy Chloroplast Plant cells Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Inside a Chloroplast thylakoids—saclike membranes inside the chloroplasts. Structure – thylakoid membranes are stacked; they contain pigments such as chlorophyll Single thylakoid Chloroplast Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Inside a Chloroplast A stack of thylakoids is called a granum. Granum Chloroplast Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Inside a Chloroplast The fluid that fills the chloroplast and surrounds the thylakoids is called the Stroma Stroma Chloroplast Copyright Pearson Prentice Hall

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 7

Light- dependent reactions H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin cycle Calvin Cycle The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. O2 Sugars Copyright Pearson Prentice Hall

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. Photosynthesis requires light and chlorophyll. In the graph above, notice how chlorophyll a absorbs light mostly in the blue-violet and red regions of the visible spectrum, whereas chlorophyll b absorbs light in the blue and red regions of the visible spectrum. Copyright Pearson Prentice Hall

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 10

H+ concentration is at equilibrium Inside Thylakoid H+ H+ H-O-H H-O-H H+ H+ H-O-H H-O-H H+ concentration is at equilibrium H+ H-O-H H-O-H H-O-H H-O-H H+ H+ H+ Outside Thylakoid (Stroma) 11

1. Start of Light Reaction- Light is absorbed by clorophyll. Inside Thylakoid 1. Start of Light Reaction- Light is absorbed by clorophyll. H+ H+ H+ H+ H+ H+ H+ H-O-H H+ H+ H+ H+ Outside Thylakoid (Stroma) 12

Oxygen, more Hydrogen Ions are made AND 2 ELECTRONS ARE RELEASED Inside Thylakoid 2. Light energy is taken by Clorophyll and WATER SPLITTING ENZYME TO split water. H+ H+ H+ H+ H+ H+ H+ H-O-H H+ H+ Oxygen, more Hydrogen Ions are made AND 2 ELECTRONS ARE RELEASED O2 H+ H+ H+ H+ H+ H+ Outside Thylakoid (Stroma) 13

At each electron acceptor, H+ are pumped into the Thylakoid. Inside Thylakoid 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+ H+ H+ H+ H+ H+ H+ H+ H+ At each electron acceptor, H+ are pumped into the Thylakoid. Outside Thylakoid (Stroma) 14

4. At this point the electrons have no more energy. Inside Thylakoid 4. At this point the electrons have no more energy. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ More light is absorbed so the electrons can continue down the ETC. Outside Thylakoid (Stroma) 15

5. A Concentration Gradient has been created. Inside Thylakoid 5. A Concentration Gradient has been created. High Concentration H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Low Concentration H+ The H+ ions flow through the ATP SYNTHASE. Outside Thylakoid (Stroma) 16

This is facilitated diffusion. Inside Thylakoid 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+ H+ H+ H+ H+ H+ H+ A P P A P H+ H+ This is facilitated diffusion. Energy from H+ movement used to make ATP Outside Thylakoid (Stroma) 17

A molecule called NADP+ bonds with an H+ to remove the electrons. Inside Thylakoid 7. The last step is to remove the electrons so the ETC can continue to function. A molecule called NADP+ bonds with an H+ to remove the electrons. H+ H+ H+ H+ H+ NADP+ NADPH H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ Outside Thylakoid (Stroma) 18

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 19

The Carbon Cycle 21