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 (CO2) 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

Photosynthesis Video

Photosynthesis Equation

Photosynthesis uses sunlight energy to convert water (H2O) and carbon dioxide (CO2) into high

energy sugars and oxygen.

(light)

Carbon Dioxide + Water Sugar + Oxygen

(light)

6 CO2 + 6 H2O C6H12O6 + 6 O2

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

StromaThylakoid

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

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 CO2 is used to make sugars

like glucose and fructose• Six-carbon Sugars made during the Calvin

Cycle

The Calvin Cycle

CO2 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