Photosynthesis
Definition The process by which cells harvest light energy to make sugars (glucose). -Sugar is used to power the process of cellular respiration, which produces the ATP that cells utilize as an energy source
Equation for Photosynthesis 6CO 2 + 6H 2 0 + light energy C 6 H 12 O 6 + 6O 2 Reactants Carbon dioxide, water, and light energy Products Sugar and Oxygen
Energy for Life Process Autotrophs- an organism that uses energy to synthesize organic molecules (sugar) from inorganic substances (ex. Light) Can make its own food Includes-plants, some bacteria, and algae Heterotrophs must obtain energy from source other than self Includes animals (humans), fungi, some protista
Biochemical pathway Light Photosynthesis Autotrophs Sugars and oxygen Carbon dioxide and water Cellular Respiration Autotrophs & Heterotrophs Biochemical Pathway series of reactions that are linked, the products of one reaction are consumed in the next reaction.
Light absorption in Chloroplasts Pigment- substance that absorbs certain colors more strongly than others -Pigment color comes from color of light reflected, not absorbed. White = all light reflected Black = all light absorbed
Light Physics Light and pigments Light is composed of variety of colors-visible spectrum (ROYGBIV) Light can be reflected, transmitted, or absorbed Green chlorophyll - absorbing red and blue wavelengths-reflecting green wavelengths
Light Spectrum
Light absorption Chloroplast pigments: Chlorophyll a Only chlorophyll a is directly involved in light reaction of photosynthesis Blue/Red Chlorophyll b helps to capture light energy = accessory pigment Blue/little red Carotenoids = accessory pigment Yellow and oranges
Check Yourself, foo! 1. What is a pigment? 2. Why is it advantageous for a plant to have multiple pigments? 3. What would you prefer to wear in the summer- a black t-shirt or a white t-shirt (if you had to pick one) and Why?
Where Photosynthesis Occurs Chloroplast Structure Grana Thylakoid- structural unit of photosynthesis. Flattened sacs containing photosynthetic pigments Grana pancake-like stacks of thylakoids Stroma Area between the thylakoids and grana Thylakoid Stroma
Chloroplast Redrawing
Photosynthetic Reactions 3 major steps Light Dependent (needs light) 1. Absorption of light (photon) 2. Conversion of light to chemical energy -Electron Transport Chain (ATP and NADPH creation) Light Independent (does not need light) 3. Formation of sugar (using chemical energy from step 2)
Light Absorption Pigments absorb light energy is absorbed electrons are excited electrons move to a chlorophyll a molecule in Photosystem II (reaction center)
Light Dependent Reactions Occurs in the thylakoid membrane Steps 1. Absorption of light via chlorophylls and other pigments Needs water to donate electrons 2. Passage of elections in the electron transport chain (ETC) 3. Production of NADPH and Oxygen (this O 2 will go into the atmosphere) 4. Formation of ATP This will be used to help make sugars.
Significance of Light Reaction In Photosystem II: Oxygen is produced from the breakdown of water During electron transport, H+ ions accumulate inside thylakoid this drives ATP production (Chemiosmosis) In Photosystem I: Electrons combine with a proton to make the energy carrier NADPH.
Light Independent Reaction (Calvin Cycle) Here CO 2 is converted into carbohydrates (sugars) ATP provides the energy for these reactions NADPH donates an electron to help form the sugar Happens in the stroma of the chloroplast
Calvin Cycle
Steps of the Calvin Cycle 1. CO 2 molecule bonds with 5 Carbon molecule. The product (6 carbon molecule) immediately splits into two 3 carbon molecules called PGA. 2. PGA is converted to PGAL by an addition of a phosphate from ATP and an electron from NADPH. 3. One PGAL leaves Calvin Cycle to make organic compounds, other PGAL molecules regenerated into cycle. 4. 6 turns of the cycle makes one molecule of glucose!
Rate of photosynthesis Affected by plant s environment Light intensity- as light, photosynthesis until light saturation point. Carbon Dioxide CO 2, photosynthesis Temperature Chemical reactions general with temperature If it gets too hot the enzymes can denature and the reaction
Special Adaptations Most plants are C3 plants C4 plants Found in hot dry weather They have stomata closed during the hottest part of the day to save up CO 2 and water Corn, sugar cane, and crabgrass CAM Also found in hot day climates Keep stoma open and night and closed during the day to save extreme amounts of water Cactus and pineapple
Check Yourself Again, foo! 1. Why is photosynthesis and cellular respiration considered a biochemical pathway? 2. Why are plants green? 3. What part of photosynthesis makes sugars (light reactions, electron transport chain or the Calvin cycle)? 4. What is required from the light reactions in order to fuel the Calvin cycle?