Chapter 7 Capturing Solar Energy Photosynthesis Part I The Pieces of Photosynthesis 7 1 What Is Photosynthesis For most organisms energy is derived from sunlight either directly or indirectly Those organisms that can directly trap sunlight do so by photosynthesis Process by which solar energy is trapped and stored as chemical energy in the bonds of a sugar Englemann s Experiment o Certain bacterial cells will move toward places where oxygen concentration is high o Photosynthesis produces oxygen as a by product Cellular respiration aerobic respiration Photosynthesis and Cellular Respiration are Linked Processes o Photosynthesis o Energy storing pathway storing sugar for long term o Releases oxygen o Requires carbon dioxide reactant o Aerobic Respiration o Energy releasing pathway o Requires oxygen reactant o Releases carbon dioxide Where Atoms End Up in Photosynthesis Leaves and chloroplasts are adaptations for photosynthesis o Chlorophyll containing organelles called chloroplasts are concentrated in leaf cells o Chloroplasts are able to convert energy in sunlight into stored energy of sugars o Both the upper and lower surfaces of a leaf consist of a layer of transparent cells the epidermis leaves o The outer surface of leaves are covered by the cuticle o Transparent waxy and waterproof covering reduces the evaporation of water from o Leaves obtain CO2 for photosynthesis from the air through pores in the epidermis called stomata singular stoma o o Stoma pore lets carbon dioxide in and releases oxygen When water is present in stoma they open When little or no water is in stoma it closes nothing can get in and out AKA guard cells Inside the leaf are layers of cells called the mesophyll o Concentration of chloroplasts o Photosynthesis occurs here o Bundle sheath cells surround the vascular bundles o Form veins in the leaf o Supply water and minerals to the mesophyll o Leaf Anatomy o Chloroplasts are organelles with a double membrane enclosing a fluid called the stroma o Embedded in the stroma are disk shaped membranous sacs called thylakoids o The LIGHT DEPENDENT REACTIONS occur in and adjacent to the membranes of the o The DARK REACTIONS Calvin cycle capture carbon dioxide and produce sugar occur in thylakoids the stroma o Chloroplast Anatomy Phototropism auxin o Describes the process by which plants respond to the light in their environment o Light sensing hormone responsible for the curvature of plant shoots towards light is o Auxin collects primarily on the darker side of the stem and stimulates cell elongation o Cells on the side not directly exposed to light will grow much faster than the opposing side and the stem will curve towards the light source o Growth away from light is called negative phototropism Photosynthesis consists of the light reactions and the Calvin cycle only during the day o Starting with carbon dioxide and water photosynthesis converts sunlight energy into chemical energy stored in bonds of glucose and releases oxygen o The photo part of photosynthesis refers to the capture of sunlight in the thylakoids o The synthesis part of photosynthesis refers to the Calvin cycle DARK REACTIONS which makes sugar from the energy captured in ATP and NADPH in the light reactions 7 2 Light Reactions How Is Light Energy Converted to Chemical Energy Sunlight emits a broad spectrum of radiation called the electromagnetic spectrum o Visible light small slice of EM spectrum o Different wavelengths seen as different colors o Violet 380 nm to red 750 nm o Nm nanometer o Longer wavelengths lower energy o Shorter wavelengths higher energy o ROYGBIV o Shortest wavelength to longest wavelength o Gamma rays violet o X rays o UV radiation o Visible light o Infrared radiation o Microwaves o Radio Waves red Light is composed of individual packets of energy called photons o Each type of photon has fixed amount of energy o Photons having the most energy travel as shortest wavelength blue violet light Color of light you see is the wavelength that is reflected and NOT absorbed o Absorption of wavelengths light is trapped o Reflection of wavelengths light bounces back o Transmission of wavelengths light passes through Light is captured by pigments in chloroplasts o Visible light has wavelengths with energies strong enough to alter biological pigment molecules such as chlorophyll a and b o Chlorophylls a and b are the key light capturing pigment molecules o Chloroplasts also contain accessory pigments o Cannot transfer sunlight energy directly to the photosynthetic pathway but must pass their absorbed energy to chlorophylls a or b o Ex Carotenoids play a role in leaves turning red and orange in the Fall Insects can see detect patterns using UV light Light and Chloroplast Pigments o Yellow green light has virtually no activity for photosynthesis between violet and red Loss of Chlorophyll Reveals Yellow Carotenoid Pigments A Preview of Photosynthesis The Steps of Photosynthesis The LIGHT REACTIONS occur in association with the thylakoid membranes o The thylakoid membranes contain many photosystems PS o Photosystem is an array of chlorophyll and pigments that are bound to and organized by proteins by various proteins during the light reactions o Each PS consists of a cluster of chlorophyll and accessory pigment molecules surrounded o Two photosystems photosystem II PS II and photosystem I PS I work together o Each type of photosystem has a unique electron transport chain ETC associated with it o Each ETC consists of a series of electron carrier molecules embedded in the thylakoid membranes o The overall path of electrons is as follows PS II ETC II PS I ETC I NADP o Photosystem II uses light energy to create a hydrogen ion gradient and split water o Photosystem I uses light energy to produce NADPH an energy molecule The ion gradient generates ATP by a process called chemiosmosis and occurs in 3 steps 1 As the energized electron travels along electron chains some of the energy it liberates is hydrogen used to pump hydrogen ions into the thylakoid space 2 This pumping creates a high concentration of H inside the space relative to the surrounding stroma 3 H flow down concentration gradient through a thylakoid channel protein called ATP synthase synthesis generating ATP from ADP Energy Stored in a Water Gradient Can Be Used to Generate Electricity Oxygen Is a By product of LIGHT Reactions 7 3 The Calvin Cycle DARK RXNS How Is Chemical Energy Stored in Sugar Molecules The Calvin cycle DARK REACTIONS
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