Figure 7.0_1 Chapter 7: Big Ideas An Overview of Photosynthesis The Light Reactions: Converting Solar Energy to Chemical Energy The Calvin Cycle: Reducing CO 2 to Sugar Photosynthesis Reviewed and Extended
Can these organisms hold the key to our future energy needs?
Leaf Cross Section Mesophyll CO 2 O2O2 Vein Leaf Stoma Mesophyll Cell Chloroplast Thylakoid Thylakoid space Stroma Granum Inner and outer membranes Photosynthesis occurs in chloroplasts in plant cells
Leaf Cross Section Mesophyll CO 2 O2O2 Vein Leaf Stoma Mesophyll Cell Chloroplast Veins in the leaf deliver water absorbed by roots. Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf. Stomata are tiny pores in the leaf that allow –carbon dioxide to enter and –oxygen to exit.
Chloroplast = double membrane Thylakoid Thylakoid space Stroma Granum = stack of thylakoids Inner and outer membranes Stroma = thick fluid surrounding thylakoids = site of Calvin cycle!!! Thylakoids = interconnected system of membranous sacs Thylakoid membranes = site of chlorophyll and light reactions!!!
7.4 Photosynthesis is an endergonic, redox process Reduced = gain of electrons; oxidized = loss of electrons –CO 2 becomes reduced to sugar. –Water molecules are oxidized to O 2 Photosynthesis is endergonic: –light energy is captured by chlorophyll molecules to excite electrons –light energy is converted to chemical energy, and –chemical energy is stored in the chemical bonds of sugars. Becomes reduced Becomes oxidized
Light Reactions (in thylakoids) NADP + ADP P H2OH2O Light Chloroplast Photosynthesis occurs in two stages The light reactions occur in the thylakoid membranes. Light energy splits H 2 O to O 2, releasing high energy electrons Movement of electrons used to ATP is generate from ADP and P Electrons end up on NADP + reducing it to NADPH.
Light Reactions (in thylakoids) O2O2 NADPH ATP NADP + ADP P H2OH2O Light Chloroplast Photosynthesis occurs in two stages The light reactions occur in the thylakoid membranes. Light energy splits H 2 O to O 2, releasing high energy electrons Movement of electrons used to ATP is generate from ADP and P Electrons end up on NADP + reducing it to NADPH.
Light Reactions (in thylakoids) Calvin Cycle (in stroma) Sugar O2O2 NADPH ATP NADP + ADP P H2OH2O CO 2 Light Chloroplast Calvin cycle occurs in the stroma of the chloroplast. Cyclic series of reactions that assembles sugar molecules using CO 2 and ATP, NADPH of the light reactions. NADPH provides the electrons for reducing carbon in the Calvin cycle. Carbon fixation = incorporation of C into organic compounds
7.6 Visible radiation drives the light reactions Increasing energy 10 5 nm 10 3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m 650 nm Wavelength (nm) Visible light Gamma rays Micro- waves Radio waves X-rays UVInfrared The shorter the wavelength, the greater the energy.
Pigments = compounds that absorb light Chloroplasts contain 4 major pigments: –Chlorophyll a –absorbs blue-violet and red light and reflects green. –Chlorophyll b –absorbs blue and orange and reflects yellow-green. –Carotenoids –broaden the spectrum of colors that can drive photosynthesis –provide photoprotection What pigments and wavelengths are responsible for photosynthesis? Animation: Light and Pigments
Photosynthesis in Two Acts Photosynthesis Carbon dioxide Water Glucose Oxygen gas Light energy C 6 H 12 O 6 CO 2 H2OH2O O2O2 Act 1 - The Light Reactions GOAL: Transform light energy into chemical energy of ATP and NADPH Harvest electrons from H2O, forming O2 Use these excited electrons to generate ATP Then transfer these electrons to NADP+, forming NAPDH. H 2 O + ADP + P + NADP + O 2 + ATP + NADPH Light energy
7.7 Photosystems capture solar energy Photosystem Light Light-harvesting complexes Reaction-center complex Primary electron acceptor Pigment molecules Pair of chlorophyll a molecules Transfer of energy Thylakoid membrane Photosystem = Pair of chlorophyll a molecules surrounded by pigments and various enzyme Capture solar energy to excite electrons in chlorophyll a
7.7 Two Photosystems Cooperate in the Light Reactions Photosystem II (P680) - oxidizes H 2 O Photosystem I (P700) - reduces NADP + Light Stroma Photosystem II Thylakoid space Thylakoid membrane Primary acceptor P680 P700 Photosystem I Light NADP NADPH Electron transport chain Provides energy for synthesis of ATP by chemiosmosis 2 1 H2OH2O H O2O2 H 2
Cast of Characters, Contd Electron Transport Chain –Complex of proteins that transfer electrons between PSII and PSI –And actively transport H+ from stroma into thylakoid space ATP synthase –Enzyme responsible for ATP synthesis
Light Stroma Photosystem II Thylakoid space Thylakoid membrane Primary acceptor P680 P700 Photosystem I Light NADP NADPH Electron transport chain Provides energy for synthesis of ATP by chemiosmosis 2 1 H2OH2O H O2O2 H Two photosystems connected by an electron transport chain generate ATP and NADPH Electrons are –removed from water, –passed from PS II to PSI and –accepted by NADP +, reducing it to NADPH. Between the two photosystems, the electrons –move down an electron transport chain and –provide energy for the synthesis of ATP.
Figure 7.8B Photosystem I Photosystem II NADPH ATP Mill makes ATP Photon
Figure 7.9 H+H+ ATP synthasePhotosystem I Photosystem II Electron transport chain ATP P ADP NADPH NADP + Light Chloroplast To Calvin Cycle Stroma (low H + concentration) Thylakoid membrane Thylakoid space (high H + concentration) H2OH2O O H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+
Figure 7.9_1 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP synthase Photosystem I Photosystem II Electron transport chain H+H+ H+H+ ATP P ADP NADPH NADP + Light H+H+ To Calvin Cycle H2OH2O O