Photosynthesis: Chapter 7 (PDF)

Photosynthesis Chapter 7 An Introduction to Photosynthesis Autotrophs (“self-feeders”) make their own food through the process of photosynthesis. Heterotrophs are consumers that feed on plants or animals or decompose organic material. Photosynthesis uses solar energy to convert car...

Photosynthesis Chapter 7 An Introduction to Photosynthesis Autotrophs (“self-feeders”) make their own food through the process of photosynthesis. Heterotrophs are consumers that feed on plants or animals or decompose organic material. Photosynthesis uses solar energy to convert carbon dioxide & water to sugar and other organic molecules.  Light + 6 CO2 + 6 H 2O C6H12O6 + 6 O2 energy Carbon dioxide Wate Oxygen gas r Glucose Photosynthesis occurs in chloroplasts in plant cells Chloroplasts are surrounded by a double membrane and contain stacks of thylakoids and a thick fluid called stroma. Chlorophyll is a light-absorbing pigment in the chloroplasts that converts solar energy to chemical energy. Leaf Cross Section Leaf Vei Mesophyll n CO2 O2 Mesophyll Cell Stoma Chloroplast  Mesophyll Cell Chloroplast Inner and outer membranes Granum Thylakoid Thylakoid space Stroma  Scientists traced the process of photosynthesis using isotopes 6 CO2 + 12 H2O → C6H12O6 + 6 H2O + 6 O2 Photosynthesis is a redox process Photosynthesis, like respiration, is a redox (oxidation-reduction) process. In photosynthesis, H2O is oxidized and CO2 is reduced. Photosynthesis occurs in two stages, which are linked by ATP and NADPH The light reactions occur in the thylakoids, producing ATP and NADPH for the Calvin cycle, which takes place in the stroma. During the Calvin cycle, CO2 is incorporated into organic compounds in a process called carbon fixation.  H2O Light NADP+ ADP + P Light Reactions (in thylakoids) Chloroplast O2  H2O Light NADP+ ADP + P Light Reactions (in thylakoids) AT P− − NADPH Chloroplast O2  H2O CO2 Light NADP+ ADP + P Calvin Light Cycle Reactions (in stroma) (in thylakoids) AT P − − NADPH Chloroplast O2 Sugar  Visible radiation absorbed by pigments drives the light reactions Sunlight is a type of energy called electromagnetic energy or radiation. Certain wavelengths of visible light are absorbed by chlorophyll and other pigments.  Light Reflected light Chloroplast Thylakoid Absorbed Transmitte light d light 10−5 nm 10−3 nm 1 nm 103 nm 106 nm 1m 103 m Gamma X-rays UV Infrared Micro- Radio rays waves waves Visible light 380 400 500 600 700 750 Wavelength (nm) Shorter wavelength Longer wavelength Higher energy Lower energy  Photosystems capture solar energy Thylakoid membranes contain photosystems, each consisting of light-harvesting complexes and a reaction-center complex. A primary electron acceptor receives photoexcited electrons from reaction-center chlorophyll a. Animation: Light and Pigments © 2018 Pearson Education, Inc.  Two photosystems connected by an electron transport chain convert light energy to the chemical energy of ATP and NADPH Electrons shuttle from photosystem II to photosystem I, providing energy to make ATP, and then reduce NADP+ to NADPH. Photosystem II regains electrons as water is split and O2 released.  − AT P − − − − NADPH − − − n Photo Electron transport chain ramp − n Photo Photosystem II Photosystem I  The light reactions take place within the thylakoid membranes In photophosphorylation, the electron transport + chain pumps H into the thylakoid space. The concentration gradient drives H+ back through ATP synthase, powering the synthesis of ATP. Light Electron Light H+ + + Photosystem transport chain Photosystem NADP + H – – II I NADPH H+ – – – H+ – H+ H+ H+ H+ H2O H+ H+ 1O 2 + To 2 2 + H + H Calvin H+ Cycle H+ H+  ATP and NADPH power sugar synthesis in the Calvin cycle The steps of the Calvin cycle include carbon fixation, reduction, release of G3P, and regeneration of RuBP. Using carbon from CO2, electrons from NADPH, and energy from ATP, the cycle constructs G3P, which is used to build glucose and other organic molecules.  Input https://www.youtube.com/watch?v=0UzMaoaXKaM 3 CO2 1 Carbon fixation. Rubisco 3 P P 6 P RuBP 6 ATP 3 4 RegenerationADP 6 ADP + P Calvin of RuBP. 3 AT − − Cycle P 6 NADPH 6 NADP+ 5 P 6 P G3P G3P 2 Reduction. 3 Release of one molecule of G3P. 1 P G3P Glucose and other Output compounds Photosynthesis: A Recap The photosynthetic equation: Provides the carbon to produce organic The organic compound compounds during the ultimately produced Calvin Cycle during the Calvin Cycle light 6 H 2O 6 CO2 6 O2 C6H12O6 Split during the Produced as a light reactions Excites byproduct of the to replace electrons splitting of electrons lost during the water during the from light light reactions Photosystem II reactions 24