Photosynthesis Handouts (PPT) PDF - 19/11/2022

19/11/2022 Photosynthesis: Capturing Light Energy  Of all organisms, only plants, algae, and certain prokaryotes are capable of absorbing and converting light energy...

19/11/2022 Photosynthesis: Capturing Light Energy  Of all organisms, only plants, algae, and certain prokaryotes are capable of absorbing and converting light energy from the sun to chemical energy through the process of photosynthesis. Light  The end products of photosynthesis are carbohydrates (formed from the  Electromagnetic Spectrum- a continuous simple raw materials water and carbon range of radiation. dioxide) and oxygen (O2).  All radiation in this spectrum travels as waves.  A wavelength is the distance from one wave peak to the next. Light  Light is composed of small particles, or packets, of energy called photons. Electromagnetic radiation from the sun includes ultraviolet radiation and visible light of varying colors and wavelengths. 1  19/11/2022 – Reflect light, which include the colors we see Light Reflected Light The color of the light seen is the color not Chloroplast absorbed. Absorbed Granum light Transmitted light Figure 10.7 Chloroplasts: The Sites of Photosynthesis  Chloroplasts in Plants – Are the organelles in which photosynthesis occurs – Contain thylakoids and grana, embedded in the stroma.  The leaves of plants Mesophyll – Are the major sites of photosynthesis Chloroplast 5 µm Outer membrane Thylakoid Thylakoid Intermembrane Stroma Granum space space Inner membrane 1 µm Chloroplast  Chlorophyll lies mainly inside the chloroplast which is found in the mesophyll layer of the leaf. Chlorophyll is found in the thylakoid membrane. 2  19/11/2022 Thylakoid Membrane Chlorophyll  Thylakoid membranes contain several  chlorophyll a, the pigment that kinds of pigments. initiates the light-dependent reactions  Chlorophyll, the main pigment of of photosynthesis. photosynthesis, absorbs light primarily in the blue and red regions of the  Chlorophyll b is an accessory visible spectrum. pigment that also participates in  Green light is not appreciably photosynthesis. absorbed by chlorophyll. Chlorophyll – The green pigment that Photosynthesis  is directly involved in light trapping and energy conversion process  A process in which CO2 and H2O are  Chloroplast – Are oblong brought together chemically to form a membranous, close bags containing carbohydrate; many thin, flat disks called thylakoids  The energy for the process is radiant  Thylakoids –Stacked up in many energy (from sunlight). groups called grana  Stroma – Regions between grana Overall Reaction of Photosynthesis CO2 + H2O  CH2O + O2 + H2O Carbon Water Light carbohydrates Oxygen Water Dioxide Energy 3  19/11/2022 Two stages of Light phase (energy- Photosynthesis conversion stage) Takes place in the grana.  Light phase (energy-conversion stage)  Light energy is converted into  Light Independent (CO2-conversion chemical energy. stage)  a. Photosystem I (PS I)= P700 Light phase (energy-conversion stage) 2 phase: i. cyclic ii. non cyclic ADP + P  ATP  b. Photosystem II (PS II)= P680 2 NADP + 2 ATP + 2P + 2H2O  2 NADPH2 + 2ATP + O2 Closer look of the photosystems  A mechanical analogy for the light reactions e– ATP e– e– NADPH e– e– e– Mill makes ATP e– Photosystem II Photosystem I Figure 10.14 4  19/11/2022 Products: ATP and NADPH Oxygen produced by photosynthesis On sunny days, the oxygen released by aquatic plants is sometimes visible as bubbles in the water. This plant (Elodea) is actively carrying on photosynthesis. Light Independent phase (CO2-conversion stage)  Occur outside the grana, that is the stroma.  CO2, ATP, and NADPH2 are converted to simple sugar. Light Independent phase (CO2-conversion stage)  Carbon fixation occurs in the stroma through a sequence of 13 reactions known as the Calvin cycle. Light Independent Phase (CO2-conversion stage) CO2 + H2O  CH2O + O2 + H2O Carbon Water Light Carbohydrates Oxygen Water Dioxide Energy 5  19/11/2022 The 13 reactions of the Calvin cycle are divided into three phases:  CO2 uptake  Carbon reduction, and  RuBP regeneration Calvin Cycle: summary 2 pathways, depending on type of plants:  Calvin-Benson Cycle (C3 pathway) -PGA (3 carbon compound)  Hatch-Slack Cycle (C4 and CAM (crassulacean acid metabolism) pathways) -Oxaloacetic Acid as the starting material C3 Plants C4 Plants  3 carbons  Four-carbon oxaloacetate  Such as in Basswood, bluegrass and  Such as in Corn beans 6  19/11/2022 Sugarcane Pineapple C4 CAM CO2 CO2 Night Organic acid 1 CO2 incorporated Organic acid into four-carbon Bundle- organic acids sheath cell (carbon fixation) Mesophyll cell A typical CAM plant CAM plants fix CO2 at night CALVIN 2 Organic acids CALVIN Day Prickly pear cactus CYCLE release CO2 to CYCLE Calvin cycle (Opuntia) Sugar Sugar A review of Photosynthesis Light reaction Calvin cycle H2O CO2 Light NADP+ ADP +P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP G3P NADPH Starch (storage) Amino acids Fatty acids Chloroplast O2 Sucrose (export) Light reactions: Calvin cycle reactions: Are carried out by molecules in the Take place in the stroma thylakoid membranes Use ATP and NADPH to convert Convert light energy to the chemical CO2 to the sugar G3P energy of ATP and NADPH Return ADP, inorganic phosphate, and Split H2O and release O2 to the NADP+ to the light reactions Figure 10.21 atmosphere 7  19/11/2022 Organic compounds produced by photosynthesis – Provide the energy and building material for ecosystems 8