Chapter 10 Lecture 1 PDF

Preview

Summary

Chapter 10 lecture 1 notes...

Description

CHAPTER 10: PHOTOSYNTHESIS An Overview of Photosynthesis - Photosynthesis  Uses sunlight to produce carbohydrates  Requires sunlight, CO2 and H2O  Produces O2 as by-product - Overall reaction using glucose as carbohydrate: 6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2 - Photosynthesis is endergonic: Reduces CO2 to sugar - Photosynthesis contrasts with cellular respiration  Cellular respiration is exergonic o Oxidizes sugar to CO2 Photosynthesis: Two Linked Sets of Reactions 1. Light-dependent reactions  Convert light energy into chemical energy (ATP and NADPH)  Produce O2 from H2O 2. Calvin Cycle  Uses ATP and NADPH to produce sugar from CO2 Photosynthesis Occurs in Chloroplasts - Photosynthesis occurs in chloroplasts - Thylakoids- internal membranes of chloroplasts that form flattened, vesicle-like structures stacked in grana - Contain large quantities of pigment chlorophyll - Stroma- fluid-filled space between the thylakoids and the inner membrane of chloroplast How Do Pigments Capture Light Energy? - Electromagnetic radiation is form of energy - Light type of electromagnetic radiation  Acts both wavelike and particle-like o As a wave, light can be characterized by its wavelength: distance between two wave crests o As a particle, light exists in discrete packets called photons The Nature of Light Energy - Each photon has a specific amount of energy and is inversely proportional to its wavelength. Photosynthetic Pigments Absorb Light - Photons may be absorbed, transmitted, or reflected when they strike an object. - Pigments absorb only certain wavelengths of light Different Pigments Absorb Different Wavelengths of Light - There are two major classes of pigment in plants: 1. Chlorophylls (Chlorophyll a and Chlorophyll b)  Absorb red and blue light  Reflect and transmit green light 2. Carotenoids

 Absorb blue and green light  Reflect and transmit yellow, orange, and red light The Structure of Chlorophyll - Chlorophyll a and b  Similar in structure and absorption spectra  Long “tail” of isoprene subunits  “head” consisting of a large ring structure with a magnesium atom in the middle  Light absorbed in head What Is the Role of Carotenoids and Other Accessory Pigments? - Carotenoids and xanthophylls are accessory pigments found in chloroplasts  Absorb light and pass energy on to chlorophyll  Absorb wavelengths of light not absorbed by chlorophyll, so appear yellow, orange, or red.  Extend range of wavelengths that can drive photosynthesis  Protect chlorophylls from damage by stabilizing free radicals Photosystems - Chlorophyll molecules work together in groups  They form a complex called a photosystem - A photosystem consists of two major elements: 1. Antenna complex  Harvests light 2. Reaction Center  Converts energy to chemical energy Electrons Become Excited When Light Is Absorbed - When photon hits antenna complex, energy is absorbed, and an electron excited - The electron becomes excited-raised to a higher energy- “gains energy, wants to get rid of it” The Antenna Complex - Energy from excited electron is passed to another chlorophyll molecule exciting another electron - Energy transferred inside antenna complex from one molecule to next until it reaches reaction center The Reaction Center - At reaction center  Excited electrons transferred to specialized chlorophyll molecule acts as an electron acceptor  Electron acceptor becomes reduced  Electromagnetic energy transformed to chemical energy The Discovery of Photosystems I and II 1. Photosystem I (PS I): absorbs light energy at 700 nm, passes an excited electron to NADP+, reducing it to NADPH 2. Photosystem II (PS II): absorbs light energy at 680 nm, produces ATP, and oxidizes water molecules...