9.2 Section Objectives – page 225 Relate the structure of chloroplasts to the events in photosynthesis. Section Objectives: Describe light-dependent reactions. Explain the reactions and products of the light- independent Calvin cycle.
5 Types of Energy 1)Chemical Energy 2)Physical Energy 3)Heat Energy 4)Electrical Energy 5)Light Energy
These 5 types of energy can be in two major forms Potential Energy: The energy is stored Kinetic or Free Energy: The energy is released or converted into one of the 5 types of free energy
Two Types of Reactions Endergonic: Needs energy to take place Example: Exergonic: Releases heat, light etc. Example:
Section 9.2 Summary – pages 225-230 Trapping Energy from Sunlight The process that uses the sun’s energy to make simple sugars is called photosynthesis.
Section 9.2 Summary – pages 225-230 Photosynthesis happens in two phases. 2. The molecules of ATP produced in the light- dependent reactions are then used to fuel the light-independent reactions that produce simple sugars. The general equation for photosynthesis is written as 6CO 2 + 6H 2 O→C 6 H 12 O 6 + 6O 2 Trapping Energy from Sunlight 1. The Light –dependent reactions convert solar energy into chemical energy
Section 9.2 Summary – pages 225-230 The chloroplast and pigments To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight. Although a photosystem contains several kinds of pigments, the most common is chlorophyll. Chlorophyll absorbs most wavelengths of light except green.
Section 9.2 Summary – pages 225-230 Light-Dependent Reactions As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons. These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane.
Section 9.2 Summary – pages 225-230 This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. Electrons are re-energized in a second photosystem and passed down a second electron transport chain. Light-Dependent Reactions
Section 9.2 Summary – pages 225-230 The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used. NADP can combine with two excited electrons and a hydrogen ion (H + ) to become NADPH. NADPH will play an important role in the light- independent reactions. Light-Dependent Reactions
Section 9.2 Summary – pages 225-230 Restoring electrons To replace the lost electrons, molecules of water are split in the first photosystem. This reaction is called photolysis. Sun Chlorophyll 2e - H2OH2O O 2 + 2H + 1 _ 2 H 2 O 2 _ 1 O 2 + 2e -
Section 9.2 Summary – pages 225-230 The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. The electrons are returned to chlorophyll. The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration. Restoring electrons
Light Reactions Takes place on thylakoids Electrons excited from chlorophyll Water is split to donate the electrons. The waste is oxygen. It is released into the air Sunlight is needed to split the water and excite the electrons 2 products go to dark reactions: –1) ATP –2) NADPH (carries electrons and hydrogen) Products goes to Calvin Cycle (Dark reactions) to help make sugar.