Chapter 7 Capturing Solar Energy Photosynthesis What happened to the dinosaurs 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 Certain bacterial cells will move toward places YouTube video click me where oxygen concentration is high Photosynthesis produces oxygen as a by product Notice that the bacteria white specks concentrate in 2 separate color regions where oxygen concentration is higher Photosynthesis and Cellular Respiration are Linked Processes Photosynthesis Aerobic Respiration Energy storing Energy releasing pathway pathway Releases Oxygen Requires Oxygen Requires Carbon Releases Carbon Dioxide Dioxide Photosynthesis and Cellular Respiration are Linked Processes Where Atoms End Up Reactants Water splits 12H2O 6CO2 Products 6O2 C6H12O6 6H2O Author Animation Photosynthesis Leaves and chloroplasts are adaptations for photosynthesis Chlorophyll containing organelles called chloroplasts are concentrated in leaf cells Chloroplasts are able to convert energy in sunlight into stored energy of sugars Both the upper and lower surfaces of a leaf consist of a layer of transparent cells the epidermis An Overview of Photosynthetic Structures cuticle upper epidermis mesophyll cells lower epidermis a Leaves stoma outer membrane inner membrane thylakoid stroma stoma chloroplasts bundle sheath cells vascular bundle vein b Internal leaf structure d Chloroplast channel interconnecting thylakoids c Mesophyll cell containing chloroplasts Fig 7 1 Leaves and chloroplasts are adaptations for photosynthesis continued The outer surface of leaves are covered by the cuticle transparent waxy and waterproof covering reduces the evaporation of water from leaves Leaves obtain CO2 for photosynthesis from the air through pores in the epidermis called stomata singular stoma Stomata http youtu be cFX4JrsPaUs Cells swollen Cells flaccid Fig 7 2 Leaves and chloroplasts are adaptations for photosynthesis continued Inside the leaf are layers of cells called the mesophyll concentration of chloroplasts photosynthesis occurs here Bundle sheath cells surround the vascular bundles form veins in the leaf supply water and minerals to the mesophyll Leaf Anatomy Leaves and chloroplasts are adaptations for photosynthesis continued Chloroplasts are organelles with a double membrane enclosing a fluid called the stroma Embedded in the stroma are disk shaped membranous sacs called the thylakoids The LIGHT DEPENDENT REACTIONS occur in and adjacent to the membranes of the thylakoids The DARK REACTIONS Calvin cycle capture carbon dioxide and produce sugar occur in the stroma Anatomy of a Chloroplast two outer membranes elaborate inner membrane system Anatomy of a Chloroplast Stroma fluid within chloroplasts Thylakoid one of the sacs within a chloroplast chlorophyll is built into the thylakoid membranes penny like appearance Granum a stack of thylakoids within a chloroplast stack of pennies appearance Phototropism describes the process by which plants respond to the light in their environment light sensing hormone responsible for thee curvature of plant shoots towards light is auxin auxin collects primarily on the darker side of the stem and stimulates cell elongation 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 growth away from light is called negative phototropism Phototrophism When sunlight is directly overhead the auxin molecules are distributed evenly Cells grow evenly When sunlight shines on the plant at an angle the auxin molecules move to the far dark side of the stem causing those cells to elongate Cell elongation results in the bending of the shoot towards light Phototropism in Tomatoes Timelapse Experimental timelapse video of tomato plants This was taken over a period of several hours one frame was taken every 6 seconds http youtu be Ze8NV7cvW8k http youtu be IIsvRwNRoVw Photosynthesis consists of the light reactions and the Calvin cycle Starting with carbon dioxide and water photosynthesis converts sunlight energy into chemical energy stored in bonds of glucose and oxygen 6 CO2 6 H2O light energy C6H12O6 6 O2 carbon water oxygen dioxide glucose sugar sunlight An Overview of the Relationship Between the Light Reactions and the Calvin Cycle Fig 7 3 Photosynthesis consists of the light reactions and the Calvin cycle continued The photo part of photosynthesis refers to the capture of sunlight in the thylakoids 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 Author Animation Reactions of Photosynthesis 7 2 Light Reactions How Is Light Energy Converted to Chemical Energy Sunlight emits a broad spectrum of radiation called the electromagnetic spectrum Visible light small slice of EM spectrum Different wavelengths seen as different colors Violet 380 nm to red 750 nm Longer wavelengths lower energy Shorter wavelengths higher energy VISIBLE LIGHT ELECTROMAGNETIC SPECTRUM shortest wavelength Gamma rays X rays UV radiation Visible light Infrared radiation Microwaves Radio waves LONGEST wavelength Author Animation Visible Light Light is composed of individual packets of energy called photons Packets of energy Each type of photon has fixed amount of energy 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 Absorption of wavelengths light is trapped Reflection of wavelengths light bounces back Transmission of wavelengths light passes through Light is captured by pigments in chloroplasts Visible light has wavelengths with energies strong enough to alter biological pigment molecules such as chlorophyll a and b Chlorophylls a and b are the key light capturing pigment molecules Chloroplasts also contain accessory pigments cannot transfer sunlight energy directly to the photosynthetic pathway but must pass their absorbed energy to chlorophylls a or b i e carotenoids play a role in leaves turning red and orange in Fall Insects can see detect patterns using UV light Visible light UV light Visible light UV light Visible light UV light Visible
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