Ch. 10 PHOTOSYNTHESIS

History Jan Van Helmont Mass of plant, container and soil, document mass of water – new growth was greater Joseph Priestley Mint plant keeps candle lit inside jar, plants produce oxygen Also discovered/named oxygen Jan Ingenhousz Plants only produce oxygen if in the light Melvin Calvin Steps of dark reactions using radioactive tracers CARBON DIOXIDE COMING INTO PLANT – CREATING CARBOHYDRATES ….. BIOMASS

Energy Flow Energy flow is one directional From sun (solar energy) to chemical then mechanical energy….. Eventually heat Elements/ nutrients/ matter cycles C cycle, N cycle, Water cycle, etc. Food webs Autotrophs = self feeding; photoautotrophic and chemoautotrophic Heterotrophs = other feeding; herbivores, carnivores, omnivores, detritivores, decomposers, parasites, etc.

Leaf Structure Chlorophyll is a chemical/ pigment Chloroplasts are structures that contain chlorophyll Many layers (Membranes) Other plastids chromoplast leukoplast amyloplasts Specialized cells/ tissues

From chloroplast to leaf

Light Reactions Require light to occur Require water Light energy is used to split a water molecule Thylakoid is site of reaction Provides H for NADPH, e- and Generates oxygen that is released

Light Reaction Details Photons (units of light), at  just below 500 reach chloroplast and strike chlorophyll on thylakoid membrane e- on chlorophyll are excited e- are passed to primary acceptor Heat is given off Water is split Oxygen helps oxidize reaction, O loses H and e- returns to chlorophyll NADPH and ATP are generated

Noncyclic electron flow

Cyclic electron flow

Dark Reactions Occurs in stroma of chloroplast Does not require dark ( or light ) Needs NADPH and ATP from light reactions Uses CO 2 Generates glycerol 3 phosphate (1/2 of a glucose…. aka PGAl )

Details of Calvin cycle Phase 1: CO2 is incorporated, called ‘carbon fixation’ Phase 2: phosphorylation, ATP spent, e- from NADPH reduce the C chain so it stores more potential energy 6 molecules with 3 C are made – 5 are recycled and one is released as a future glucose Phase 3: cycles

Summary Rubisco is the enzyme that catalyzes the first step of Calvin cycle – since in all chloroplasts of all cells of all leaves, it’s the most abundant protein on Earth. sunlight 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 chlorophyll

Compare and contrast PHOTOSYNTHESIS Chloroplast stroma and inner membrane ETC and cycle ETC first CO2 in, O2 out Fixes C into chains Stores energy RESPIRATION Mitochondria matrix and inner membrane ETC and cycle ETC last C cpd in, CO2 out Breaks C bonds Releases energy

Alternatives C3 plants ( rice and wheat; grasses) Close stomata, hot dry weather, less sugar – do photorespiration Photorespiration – process adds O 2 by rubisco and this product then splits releasing CO 2 C4 plants Sugar cane and corn Make 4 C cpd first then Calvin – making PEP that can fix CO 2 easily, even when hot. CAM Succulent plants like cactus and pineapples Crassulacean Acid Metabolism make and store organic acids to be broken down to CO 2 and used over night when cooler