Honors Biology: Photosynthesis

Important Root Words Root Word Meaning Photo Chloro -phyll Stome Xantho Light Green Leaf Mouth Yellow

All Organisms Need Energy All organisms require energy to live. There are two main ways to obtain this necessary energy: Cells use energy trapped in chemical bonds. When these bonds are broken, energy is released for cellular activities. When cells use several linked chemical pathways to create the energy needed, this is called a biochemical pathway. HETEROTROPHS AUTOTROPHS

Cells use Energy Cells find energy by breaking bonds in a very special molecule called . . . ADENOSINE TRIPHOSPHATE (ATP) ADP (adenosine diphosphate) is another important molecule involved with cellular energy

Storage and Release of Chemical Energy Energy is stored (in a “high energy” bond) when a phosphate group is added to ADP Energy is released from ATP when a phosphate group is removed (the “high energy” bond is broken)… Note: This same system works between NADPH and NADP+

Visible Light Light travels as waves of energy Reflection, Transmission, Absorption

Pigments in plants Pigments: proteins that trap light energy from the sun, photosynthesis depends on this absorption of light to begin Why do pigments appear as different colors? EXAMPLES: Chlorophyll : Appears green A: Traps Red Light B: Traps Blue Light Accessory Pigments: Trap green/yellow Carotene: Appears orange Xanthophyll: Appears yellow The least important color for photosynthesis? GREEN!!

Chromatography Can be used to separate plant pigments based on their molecular size Watch a video! Rf Values: Distance Pigment Moved (mm) Distance Solvent Moved (mm) NOTES: Rf value will always be less than 1 The higher the Rf value, the smaller the pigment

Location of Photosynthesis http://micro.magnet.fsu.edu/cells/plants/images/chloroplast.jpg Chloroplasts Thylakoid Membranes = photosynthetic sacs (site of light absorption) Granum = stack of thylakoids Stroma = liquid outside/surrounds the thylakoids

Overview of Photosynthesis Definition: Process in which plants convert energy from the sun into stored chemical energy (glucose). 2 main reactions in photosynthesis: 1) Light Dependent Reaction 2) Light Independent (Dark) Reaction The General Reaction for Photosynthesis: CO2 + H20  C6H12O6 + 02 (can you balance this equation?) C6 H12 O6 CO2 H20 CO2 Temperature and Light Intensity can both affect the rate of photosynthesis, but it will either decrease or level off at some point.

5 things needed for photosynthesis Water Sunlight Carbon Dioxide Chlorophyll (a light capturing pigment) Enzymes

The Light-Dependent Reactions Location: occurs in the thylakoid membranes Function of First Stage: Harvested light energy is converted from sunlight to electrical energy (ETC) Uses energy from the sun to produce ATP and NADPH needed for next reaction Important events you should know: Chlorophyll is energized Water is split ATP and NADPH are formed Hydrogen is trapped

The Light-Dependent Reactions ☼ (photons/light energy) ↓ Pigments in photosystem II and then photosystem I absorb energy Electron Transport Chain ↓ ↓ Energy splits H20 ADP +  ATP* ↓ ↓ O2 2H trapped by NADP+ (forms NADPH *) Energy used to form ATP from ADP Both products here are used in the dark reaction

Electron Transport Chain Process starts in a photosystem located on a thylakoid. Absorption: Photosystem II absorbs energy from photons Passage: electrons are passed to Photosystem I. Transfer: electrons are transferred along the chain generating “electricity”. Splitting: Electricity drives the splitting of water to form H+ and free oxygen. Formation: Electrons provide energy for NADP+ to gain a H+ and form NADPH, also ATP is formed ATP and NADPH are then used in the Dark Reaction/Calvin Cycle Light Reaction Video

Calvin Cycle Calvin Cycle (Dark/Light-Independent Reactions): Location: takes place in the stroma Function: Uses energy from ATP and NADPH to produce high energy carbohydrates (sugars) Does not require light to occur (can actually occur in light or dark) Reactions form organic compounds using energy stored from Light-dependent reactions in bonds of NADPH and ATP Named after American scientist, Melvin Calvin, who discovered this in the early 1950’s

The Calvin Cycle/Dark Reaction These reactions can occur with or without Light!! This begins and ends with RuBP = a 5-carbon sugar found in chloroplasts CO2 + RuBP + ATP* (from Light Reaction) ↓ 2(PGA) + 2H* (from Light Reaction)   2(PGAL) H20 (released as a waste product)   RuBP (80%) Glucose (20%) Calvin Cycle Animation CO2 given off

Calvin Cycle Diffusion: Carbon dioxide diffuses into the stroma Combination: CO2 binds with 5-carbon molecule called RuBP. This forms an unstable 6-carbon molecule. Splitting: This six carbon unstable molecule splits immediately into two molecules called PGA. Conversion: PGA is changed into PGAL when: A. PGA receives phosphate group from an ATP molecule from the light reaction B. PGA accepts Hydrogen Ions from NADPH also from the light reaction In summary, the Calvin Cycle fixes carbon dioxide and regenerates RuBP, produces PGA, then PGAL which may be converted to glucose.

Regulation of Photosynthesis Stomata/Stoma: opening on underside of most leaves, entry site of carbon dioxide, release of oxygen from photosynthesis occurs here, water vapor is released here (transpiration) Guard Cells: specialized cells that regulate opening and closing of stomata, open and close using a H+ pump and by manipulating the turgor pressure of the cells