Where does photosynthesis take place? Leaves : the photosynthetic organs of the plant Mesophyll: main photosynthetic tissue a. Palisade layer: full of chloroplasts b. Spongy layer: fewer chloroplasts and many air spaces

What are the reactants and products of photosynthesis? Light CO2 + H2O  O2 + 3 C sugar chlorophyll Light-dependent reactions = convert light energy to the chemical energy of ATP which occur in the thylakoid membranes of the chloroplast. Calvin Cycle = using the products of the light reactions to convert carbon dioxide and water to sugars. These reactions occur in the stroma of the chloroplast.

Why is Chlorophyll Necessary? Pigments that are capable of absorbing portions of visible light chlorophyll a and chlorophyll b absorb the blue and red spectrum and reflect the green The double bonds in the molecule release electrons when light hits them

Why Leaves Change Color? A color palette needs pigments, and there are 3 types: 1. Chlorophyll a & b 2. Xanthophyll 3. Carotenoids

Chloroplast Structure? Stroma – large central compartment, where Calvin cycle takes place Thylakoids – flattened sacs within stroma that contain chlorophyll Grana – stacks of thylakoids Thylakoid space – within thylakoid, where light reactions take place

What is the first Set of reactions of photosynthesis? Light dependent reactions- A)occurs in thylakoid membrane B)pigments release electrons as light hits Photosystems C) Photolysis occurs Chemical energy products are made that are used in the next set of reactions

What are photosystems? pigment complex that serves as antennae to gather solar energy embedded into the thylakoid membrane energy is passed from one pigment to the next until it reaches chlorophyll a electrons escape as they become excited

Light-Dependent Reactions 1. PSII absorbs energy and transfers e- to PSI 2. Light energy causes water to split (called photolysis) Thus giving off O2 AND electrons – Those electrons replace those lost by PSII 3. The electrons move through the ETS and H+ from water is carried into thylakoid space 4. The electrons from PSI are then picked up by NADP reductase. The H+ that has built up in the thylakoid space diffuses through ATP synthase(a protein) which helps form ATP (chemical energy) The H that is now out in the stroma also gets picked up by NADP and changes NADP to NADPH 7. The products : ATP and NADPH move to Calvin cycle

Overview of Light-Dependent Reactions

How is the chemical energy formed? Calvin Cycle CO2 diffuses into leaf through the stomata and is fixed by RuBp(5C) = 6C This is called: Carbon Fixation This is unstable and splits into 2 (3C)molecules called PGA PGA uses a Phosphate (P) from ATP (made in light reactions) to form PGAP PGAP is converted to PGAL with the H from NADPH (made in Light reactions) PGAL is converted to RuBP and sugar

Calvin Cycle CO2 is brought in by diffusion - through the stomata - controlled by the turgor pressure of the guard cells CO2 combines with 5 carbon RuBP ribulose biphosphate 1st step/ Called: Carbon Fixation Catalyzed by enzyme called Rubisco

Calvin Cycle (cont’d) Occurs in the stroma of the Chloroplast Powered by light reactions NADPH2 ATP Three turns of cycle, each picking up CO2, makes six molecules of PGAL Five molecules of PGAL go to make more RuBP One molecule goes to make sugar

OVERALL PHOTOSYNTHESIS Oxidation-loss of electron coupled with loss of hydrogen proton Reduction- gain of electron coupled with gain of hydrogen proton

Rates of Photosynthesis (limiting factor) Four things affect rate of P.S. Light intensity increases rate of p.s. up to light saturation point as temperature increases, p.s. rate increases to point, then decreases concentration of CO2 increases rate of p.s. as oxygen increases, p.s. rate decreases

Photorespiration If there is a higher concentration of oxygen than carbon dioxide, the enzyme rubisco binds with oxygen and combines with RuBP which converts it to 1 PGA molecule and glycolate. PGA will eventually be used to form simple sugar Glycolate is transported out of chloroplast and eventually releases CO2. No new CO2 is fixed and RuBP releases CO2(like respiration)

What is advantage of C4 plants? Can reduce amount photorespiration because CO2 is delivered to bundle sheath cells that have chloroplasts

Heat adaptations C4 plants such as sugarcane, corn, and crabgrass use specialization of fixing carbon Bundlesheath surrounds vein and mesophyll cells surround sheath Mesophyll cell fixes carbon producing 4 carbon molecule 4 carbon molecule transported to bundlesheath where it is converted to CO2 Increases efficiency by reducing photorespiration

What is the advantage of partitioning space in a C4 plant? Avoid photorespiration and can keep stomates open longer CO2 is converted to oxaloacetate and delivered to bundle sheath cells water is lost as stomates are opened

Heat Adaptations CAM Found in snake plants, jade, and cactus Allow s for stomates to be open at night Stores CO2 chemically for use when light is out Slow growers

What is the advantage of partitioning in time? Can keep stomates open longer because CO2 is stored as malate in vacuoles during the evening and used by Calvin cycle at night Stomates closed during day