Photosynthesis and Respiration Lecture Notes PDF

10/4/2024 Photosynthesis & Respiration Photosynthesis Chloroplast and Respiration...

10/4/2024 Photosynthesis & Respiration Photosynthesis Chloroplast and Respiration Mitochondrion 1 2 Autotrophs vs. heterotrophs ⚫ Autotroph – self-feeder; Major points from this lecture: uses CO2 as main source of 1. Briefly describe the photosynthesis process carbon. including all reactants, products, the light ⚫ Greek auto- meaning self reaction and Calvin Cycle. ⚫ Photosynthesis 2. What are the factors that affect photosynthesis? How do these factors affect ⚫ Heterotroph – can’t the ability of the plant to make food? manufacture own food; consumes other organisms as carbon source. ⚫ Greek heteros meaning other 3 4 The Carbon Cycle Plant Cell Cells with chloroplasts http://www.windows2universe.org/earth/climate/carbon_cycle.html 5 6 1  10/4/2024 What is Photosynthesis? Photosynthesis reactants light (photons) products 6CO2 + 6H20 C6H12O6 + 6O2 ⚫ Process of converting light energy to ⚫ Light Dependent chemical energy in the form of reduced ⚫ Light Reaction carbon compounds (carbohydrates) ▪ Energy (ATP) ⚫ Light Independent McMahon et al. (2011) ⚫ Calvin Cycle ▪ Sugars 7 8 Photosynthesis Light Reaction light (photons) 6CO2 + 6H20 C6H12O6 + 6O2 ⚫ Chlorophyll absorbs solar energy 1. Excites electrons in the reaction centers ⚫ Light Dependent ⚫ Electron transport chain ⚫ Light Reaction Far-red light ▪ Energy (ATP) ⚫ Light Independent ⚫ Calvin Cycle ▪ Sugars Red light 9 10 Light Reaction Light Reaction ⚫ Chlorophyll absorbs solar energy ⚫ Chlorophyll absorbs solar energy 1. Excites electrons in the reaction centers 1. Excites electrons in the reaction centers ⚫ Electron transport chain ⚫ Electron transport chain 2. H+ and O2 from H2O 2. H+ and O2 from H2O 3. Final electron acceptor ⚫ NADPH 4. H+ gradient ⚫ ATP 11 12 2  10/4/2024 Who is Calvin? Photosynthesis Calvin Cycle ⚫ Inputs light (photons) 6CO2 + 6H20 C6H12O6 + 6O2 ⚫ Carbon fixation – RuBP, CO2 ⚫ Reduction – ATP, NADPH ⚫ Light Dependent ⚫ Outputs ⚫ Light Reaction ▪ Energy (ATP) ⚫ Sugar ⚫ RuBP ⚫ Light Independent ⚫ Regeneration ⚫ Calvin Cycle ▪ Sugars 13 14 Factors affecting rate of Photosynthesis photosynthesis light (photons) ⚫ Two important concepts to remember: 6CO2 + 6H20 C6H12O6 + 6O2 ⚫ Reduced carbon compounds are shuffled around ⚫ Light quality (wavelength) to generate the compound required for a specific ⚫ Light intensity purpose. ⚫ CO2 concentration ⚫ Temperature ⚫ Phosphorylated compounds are often involved in ⚫ Water availability metabolism because phosphorylated versions of ⚫ Plant development and source-sink relationships the sugars are more reactive than the non- phosphorylated forms. ⚫ Plant photosynthetic mechanism 15 16 Factors affecting rate of Factors affecting rate of photosynthesis photosynthesis ⚫ Light quality (wavelength) ⚫ Light intensity ⚫ Plant pigments ⚫ Photosynthetic photon flux (PPF) – intensity of ▪ Chlorophyll a photosynthetically active light, expressed as ▪ Chlorophyll b micromoles of photons per m2 per second (µmol/m2/s). ▪ Carotenoids ⚫ Affects plant growth by influencing rate of ⚫ Absorption mostly from red and blue portions of photosynthetic activity. spectrum ▪ Plants are sun-loving, shade-loving, intermediate ⚫ Artificial light 17 18 3  10/4/2024 Factors affecting rate of Factors affecting rate of photosynthesis photosynthesis ⚫ Carbon dioxide concentration ⚫ Temperature ⚫ Increasing CO2 concentration increases rate of ⚫ General rule: if light is not limiting, photosynthetic rate photosynthesis. doubles for each 10oC (18oF) increase in temperature ⚫ Commercial application – greenhouse-grown crops for many plant species, up to a point. such as carnations, orchids, roses. ⚫ Tropical plants vs. temperate plants ⚫ In the field, practices that improve CO2 availability: ⚫ Very high temperatures – stomates close to conserve ▪ Alter crop density water, reduced photosynthetic rate. ▪ Apply organic matter to soil ▪ Use of wind machines 19 20 Factors affecting rate of Factors affecting rate of photosynthesis photosynthesis ⚫ Water availability ⚫ Plant development and source-sink relationships ⚫ Drought leads to closing of stomates; drop in photosynthesis. Growth of the plant affects rate of photosynthesis, both in single leaves and in the total leaf canopy. ⚫ Water needed in light reaction in photosynthesis. ⚫ Source, e.g., mature leaf – carbohydrate synthesized light (photons) is in excess of what leaf needs; excess transported to 6CO2 + 6H20 ------------------→ C6H12O6 + 6O2 other parts of plant (sinks). ⚫ Sink, e.g., juvenile leaf – needs carbohydrates for ⚫ Too much water – anaerobic conditions around roots, growth. eventually causing a reduction in photosynthesis. ⚫ Other sinks – roots, fruits, seeds 21 22 Factors affecting rate of photosynthesis Major points from this lecture: ⚫ Photosynthetic mechanisms 1. How does photosynthesis differ among C3, C4 ⚫ C3 – about 90% of plant species; sufficient rainfall; and CAM plants? Under what conditions will moderate light intensity and temperature C3, C4, or CAM be the best photosynthetic ⚫ Examples: rice, wheat, potatoes mechanism? Why? ⚫ C4 – warmer and drier conditions ⚫ Examples: corn, sorghum, sugarcane 2. Briefly describe the events that occur during cellular respiration. ⚫ CAM (crassulacean acid metabolism) – warmer and drier conditions, deserts ⚫ Examples: desert plants, some orchids, some bromeliads such as pineapple, jade plant 23 24 4  10/4/2024 Photosynthetic mechanisms Photosynthetic mechanisms ⚫ C3 – CO2 that enters leaf is used to generate 3-carbon phosphoglycerate (PGA). 25 26 Photosynthetic mechanisms Photosynthetic mechanisms ⚫ C4 – CO2 attached to a 3-carbon organic acid, making a 4-carbon organic acid (oxaloacetic acid, OAA). Ligustrum leaf cross-section Zea leaf cross-section ⚫ Anatomy of C3 and C4 (Kranz) leaves: In a C3 leaf the palisade mesophyll cells typically form a layer in the upper part of the leaf; the corresponding mesophyll cells in a C4 leaf are usually arranged in a ring around the bundle sheath. http://www.biog1445.org/demo/03/c3vsc4.html 27 28 Photosynthetic mechanisms Photosynthetic mechanisms ⚫ C3 vs. C4 Calvin Cycle Calvin Cycle Calvin Cycle 29 30 5  10/4/2024 Photorespiration (C3 plants) C4 Plants ⚫ Hot, sunny day ⚫ Stomates close ⚫ Mesophyll ⚫ CO2 levels drop ⚫ CO2 bound to phosphoenol pyruvate (PEP) ⚫ O2 levels increase ▪ Add O2 to RuBP ⚫ Results ⚫ Bundle Sheath ⚫ Hydrogen peroxide (H2O2) ▪ Toxin ⚫ Calvin Cycle ⚫ CO2 ⚫ High CO2 concentration ⚫ Minimize excess energy ▪ ATP ⚫ Prevents photorespiration ▪ NADPH ⚫ Salvage oxygenated RuBP 31 32 Photosynthetic mechanisms Photosynthetic mechanism ⚫ CAM (Crassulacean acid metabolism) ⚫ C4 vs. CAM ⚫ As in C4 plants, CO2 attaches to a 3-carbon organic acid to form oxaloacetic acid (OAA) ⚫ Happens at night; stomates can open without too much water loss. ⚫ CO2 released from OAA and follows normal pathway (C3) in the daytime. 33 34 Respiration https://ripe.illinois.edu/ C6H12O6 + 6O2 + 36ADP + 36PO43- 6CO2 + 6H2O + 36ATP Realizing Increased Photosynthetic Efficiency (RIPE) is an international research project that is engineering crops to be more ⚫ Oxidation of food to yield energy for cellular productive by improving photosynthesis, the natural process all plants activities. use to convert sunlight into energy and yields. By equipping farmers with higher-yielding crops, we can ensure that everyone has access to enough food to lead a healthy, productive life. ⚫ 3 Steps Institutions: USA, Great Britain, and Australia; in the US,includes University of Illinois, University of California at Berkeley, USDA ⚫ Glycolysis ⚫ Krebs Cycle ⚫ Electron transport 35 36 6  10/4/2024 Respiration Respiration ⚫ 1st step: Glycolysis ⚫ 2nd step: Krebs Cycle, Pyruvate (PA) Tricarboxylic acid ⚫ 6C glucose to 3C pyruvate (PA) Acetyl-CoA cycle (TCA), or Citric ⚫ occurs in cytoplasm acid cycle ⚫ complete oxidation of PA to CO2 ⚫ occurs in mitochondria 37 38 Number of ATP molecules produced Respiration from one glucose molecule ⚫ 3rd step: Electron transport system ⚫ series of cyclic reactions ⚫ occurs in cristae (inner walls of mitochondria) 39 40 ⚫ Light compensation point – light intensity at which Anaerobic Respiration photosynthesis and respiration rates are equal. (or Fermentation) ⚫ Anaerobic – oxygen is deficient ⚫ Input ⚫ Pyruvate (PA) ⚫ Output ⚫ Ethanol (plants) or lactic acid (animals) ⚫ CO2 ⚫ NAD+ Light Intensity increasing 41 42 7