A Bit of Photosynthesis History

1643 – Jan van Helmont Planted a seed into A pre-measured amount of soil and watered for 5 years Weighed Plant & Soil. Plant Was 75 kg, Soil The Same. Concluded Mass Came From Water

1771 – Joseph Priestley Burned Candle In Bell Jar Until It Went Out. Placed Sprig Of Mint In Bell Jar For A Few Days. Candle Could Be Relit And Burn. Concluded Plants Released Substance (O2) Necessary For burning.

1979 – Jan Ingenhousz Proved that Priestleys’s experiment only occurred in the presence of light Light is necessary for plants to produce Oxygen (burning gas)

1949 – Melvin Calvin First to trace the path that carbon (CO 2 ) takes in forming Glucose Does NOT require sunlight Called the Calvin Cycle or Light Independent Reaction Also known as the Dark Reaction

1992 – Rudolph Marcus First to describe the electron transport chain.

Photosynthesis Video

Photosynthesis Equation Photosynthesis uses sunlight energy to convert water (H 2 O) and carbon dioxide (CO 2 ) into high energy sugars and oxygen. (light) Carbon Dioxide + Water Sugar + Oxygen (light) 6 CO H 2 O C 6 H 12 O O 2

Light and Pigments The suns energy travels to Earth in the form of light energy –Unit of light energy = photon Light is made up of different wavelengths with different colors

Light and Pigments Pigments are light absorbing molecules –Different pigments absorb different wavelengths of light Photons “excite” electrons in the pigments of plants –This moves the excited electrons to a higher energy level

Chlorophyll a In all plants, algae and cyanobacteria Makes photosynthesis possible Directly participates in light reactions Can receive energy from chlorophyll b

Chlorophyll b Chlorophyll b is an accessory pigment Chlorophyll b acts indirectly in photosynthesis by transferring the light it absorbs to chlorophyll a

Chloroplast Stroma Thylakoid Granum Inner membrane Outer membrane

Chloroplast Structure Double Membrane –Smooth outer membrane –Inner membrane forms thylakoids; saclike Thylakoids are in stacks called grana Gel like material that surrounds the grana is Stroma

Stroma Function Light Independent reactions (Calvin Cycle) occur here ATP used to make carbohydrates like glucose

Thylakoid Membranes Light Dependent reactions occur here Photosystems are embedded in the thylakoid membranes Photosystems are made up of clusters of chlorophyll molecules There are two: –Photosystem I –Photosystem II

Photosynthesis Overview

Electron Carriers NADP+ (Nicotinamide adenine dinucleotide phosphate) Picks Up 2 high-energy electrons and H+ from the Light Reaction to form NADPH NADPH carries energy to be passed on to another molecule

Light Dependent Reaction Uses light energy Occurs across the thylakoid membranes Produce Oxygen from water Convert ADP to ATP Also convert NADP+ into the energy carrier NADPH

Light Dependent Reaction

Photosynthesis Begins Photosystem II absorbs light energy Electrons are energized and passed to the Electron Transport Chain Lost electrons are replaced from the splitting of water into 2 H +, free electrons, and Oxygen 2 H + pumped across thylakoid membrane Photosystem II Video

Photosystem I High-energy electrons are moved to Photosystem I through the Electron Transport Chain Energy is used to transport H+ from stroma to inner thylakoid membrane NADP + converted to NADPH when it picks up 2 electrons & H +

Phosphorylation ATP synthase (an enzyme in the thylakoid membrane) uses energy from ions passing through it to convert ADP to ATP

Light Dependent Reaction Summary Reactants: –H2O –Light Energy Energy Products: –ATP – NADPH

Light Independent Reaction (Calvin Cycle) Occurs in the stroma ATP & NADPH from light reactions used as energy Atmospheric CO 2 is used to make sugars like glucose and fructose Six-carbon Sugars made during the Calvin Cycle

The Calvin Cycle CO 2 Enters the Cycle Energy from ATP and NADPH are used to form several intermediate compounds (PGA) 6-Carbon sugar is produced A 3-carbon molecule called Ribulose Biphosphate (RuBP) is used to regenerate the Calvin cycle

Factors Effecting Photosynthesis Water availability Temperature Light intensity