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 occurRequire waterLight energy is used to split a water

moleculeThylakoid is site of reactionProvides 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 chloroplastDoes not require dark ( or light )Needs NADPH and ATP from light

reactionsUses CO2

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.

sunlight6CO2 + 6H2O C6H12O6 + 6O2

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 O2 by rubisco and this product then splits releasing CO2

C4 plants Sugar cane and corn Make 4 C cpd first then Calvin –

making PEP that can fix CO2 easily, even when hot.

CAM Succulent plants like cactus and

pineapples Crassulacean Acid Metabolism

make and store organic acids to be broken down to CO2 and used over night when cooler