DO NOW A tree begins as a seed, where does all the mass (the stuff that makes up the wood, and roots and leaves) come from?

Photosynthesis

ATP = energy of life! ATP = adenosine triphosphate 5 carbon sugar Nitrogen containing base 3 phosphate groups ATP  ADP when lost phosphate group Phosphate groups = key to ATP energy Energy contained in bonds between PO ₄ s

Pigments & Chlorophyll Chloroplasts have light-absorbing molecules called pigments which capture energy from sunlight. Chlorophyll A-D = green pigments Carotenoids – red, orange or yellow pigments Phycobilins – blue or red pigments When chlorophyll absorbs light, energy from the sun is transferred to the electrons in the chlorophyll molecule Creates high energy electrons

Chloroplast Structure Double membrane organelle Thylakoids = membrane sacs Chlorophyll in thylakoid membrane Grana = thylakoid stacks Lamallae = connects stacks of grana Stroma = gel like substance that fills up chloroplast and surrounds thylakoids

High Energy Electrons & NADP ⁺ High energy electrons of chlorophyll must have “carrier” to be transferred (with their energy) to other molecules. In photosynthesis, carrier molecule = NADP ⁺ Transfers 2 high energy electrons and one H ⁺ ion (from water) NADP ⁺  NADPH (reduction) Traps sunlight energy into chemical form

Photosynthesis Overview In words: Uses energy from sunlight to convert water and carbon dioxide (reactants) into high-energy sugars and oxygen (products) In chemical symbols: 2 Sets of Reactions: light-dependent and light-independent

Light Dependent Reaction Who? Light, light-absorbing pigments and water. What happens? Energy from sunlight is used to make ATP and NADPH. Oxygen is released as a byproduct. Where? Within thylakoid membranes of chloroplast.

Light Independent Reactions Who? Requires carbon dioxide, ATP and NADPH. What happens? ATP and NADPH used to create high energy sugars from carbon dioxide. Where? Stroma of the chloroplast

Overview: Light Dependent Reaction Reactants: 2 H ₂ O 2 NADP ⁺ ADP (many) Products: O ₂ 2 NADPH ATP (many)

Light Dependent Reaction Animation

Photosystem II Electron Transport Chain Photosystem I ATP Synthase Process: Light Dependent Reaction

Step 1: Photosystem II Chlorophyll absorbs sunlight in photosystem II 2 H ₂ O  4 e ⁻ + 4 H ⁺ + O ₂ Excited electrons from chlorophyll are passed to electron transport chain. Hydrogen ions released into thylakoid space. Oxygen is released

Step 2: Electron Transport Chain Made up of a series of electron carrier proteins Energy from excited electrons moves H+ ions from stroma into thylakoid space (active transport!) Passes electrons from Photosystem II to Photosystem I

Step 3: Photosystem I Electrons of chlorophyll are re- energized by sunlight 4 e ⁻ move to stroma with 2 H ⁺ ions 2 H ⁺ + 2 NADP ⁺ + 4e ⁻  2 NADPH

Step 4: ATP Synthase H ⁺ ions move through ATP synthase out of thylakoid space with the concentration gradient ATP synthase rotates in membrane and causes chemiosmosis Chemiosmosis – synthesis of ATP from ADP + phosphate

Light-Independent Reaction (Calvin Cycle) Reactants CO ₂ ATP NADPH Products ADP NADP ⁺ 3 carbon molecule (G3P)

What is the purpose of the light-independent reaction? To convert energy from molecules of ATP and NADPH into stable, high-energy carbohydrate compounds What is an example of a high energy compound produced by photosynthesis? GLUCOSE!

Step 1 Carbon is fixed to RuBP using the enzyme RuBisCo. Results in 1 (6 C) molecule Called carbon fixation 6 C molecules splits into 2 (3 C) molecules called PGA

Step 2 Using ATP and NADPH, 3 PGA molecules are turned into G3P (3 C) PGAL = intermediate ATP becomes ADP and NADPH becomes NADP ⁺ PGAL

Step 3 1 G3P is used to create sugars and other organic molecules Remaining G3P is used to replenish RuBP that begins the Calvin Cycle Requires ATP!

Light Independent Reaction Animation

What about when there’s no CO ₂? Most plants are C3 plants due to 3 carbon PGA Photorespiration will occur when CO is not available Photorespiration = BAD for plant cells, makes useless product that takes energy to break down 2 alternatives to provide carbon to the Calvin Cycle C ₄ CAM

Stomata Pore that is used to control gas exchange on surface of plants Important to make sure plants don’t lose water via transpiration Allow CO ₂ to diffuse into plant

CAM Plants Stomata open at night to allow CO ₂ into cell CO ₂ stored in vacuole as malic acid Converted back to CO ₂ when needed for Calvin Cycle CAM plants: cactus, orchids, jade plants

C ₄ Plants Leave stomata partially open at hottest part of day Occurs in mesophyll and bundle sheath cells Can fix CO ₂ into malate (4 C compound) Examples: corn, sugar cane and crabgrass