PHOTOSYNTHESISThe Most Important Chemical Process on Earth

PHOTOSYNTHESISPHOTOSYNTHESIS

“light” “to make or compose”

PHOTOSYNTHESIS• food-making process in plants• process by which green plants

convert light energy into chemical energy• complex chemical reaction or

process by which plants put together carbohydrates• also called photophosphorylation

and carbon fixation

OVERVIEW OF PHOTOSYNTHESIS

Nature of Light

OVERVIEW OF PHOTOSYNTHESIS

The Leaf Structure

OVERVIEW OF PHOTOSYNTHESIS

OVERVIEW OF PHOTOSYNTHESIS

Process Location Reactants Products

Light Dependent Reactions

(Photosystems)

Thylakoid membranes

• sunlight• H2O

• ATP• NADPH• O2

Light Independent Reactions

(Calvin Cycle)

Stroma • ATP• NADPH• CO2

sugar

Historical Background of Photosynthesis

Aristotle Jan Baptista van HelmontStephen Hales Joseph Priestly

Jan IngenhouszJean SenebierNicolas de SaussureRuben and Kamen

ARISTOTLE

384-322 B.C.

• since plants grew from the soil, it seemed evident to Aristotle that their substance must come from the soil

• regarded the soil as equivalent to a vast stomach that prepares and supplies the food of plants

JAN BAPTISTA VAN HELMONT1648

• considered water to be the source of life and the basic nutrient for plants

• demonstrated that soil contributes very little to the increase in weight of plants and it must be water

STEPHEN HALES

1727

• recognized the importance of light and

air in plant nourishment

• described the leaves as organs of transpiration and he postulated that plants exchange gases

with their surrounding air

JOSEPH PRIESTLY1772

• unknowingly

discovered oxygen and

demonstrated that plants

produce the gas

• was the first to prove the different qualities of the gases released by plants and the ones exhaled by animals

JAN INGENHOUSZ

1779

• demonstrated the importance of light in the production of oxygen by

green plants

• systematically investigated the release

of air from green parts of plants during day time

especially from the lower side of leaves

Device used by Ingenhousz to investigate photosynthesis

JEAN SENEBIER1772

• showed the importance of a “fixed air” (carbon dioxide) in the process

• showed that plants absorb carbon dioxide and release oxygen (dephlogisticated air)

NICOLAS THEODORE

DE SAUSSURE

1804

• showed the importance of water for the

production of organic materials by the plants

• verified Ingenhousz´s hypothesis that plants

assimilate carbon dioxide from the air while nitrogen and other

nutrients are derived from the soil

SAM RUBEN

MARTIN KAMEN1940

s

• revised the basic equation into 2 types of reactions as:

Light reaction:2H2O + light → 4H + O2

Dark reaction:

4H + CO2 → CH2O + H2O

During 1900s – extensive studies on photosynthesis arise and equation of

photosynthesis had been formulated as:

6CO2 + 6H2O C6H12O6 + 6O2light

chlorophyll

6CO2 + 12H2O C6H12O6 + 6H2O + 6O2

light

chlorophyll

Revised (by Ruben and Kamen):

The Nature of LightLight – considered to have both particle and wave nature

Photons particles or packets of

light smallest divisible units of light move in wave-like behavior

carry a fixed amount of energy

Wave characterized by

wavelength frequency

c = 299,792,458 m/s or 3 x 108 m/s

Wavelength distance between two light waves

distance moved by a photon during one of its vibrations distance from peak to peak (or trough to trough)

Wavelength

the shorter the wavelength, the more energy each photon contains

arranged from shorter to longer wavelengths known as electromagnetic spectrum

measured in nanometers (nm)

sunlight is composed of different colors (ROYGBIV)

leaves absorb all colors except green

pigments in leaves absorb those wavelengths within the visible light portion with a wavelength of 400-700 nm

theoretically, photosynthesis requires approximately 12 photons to convert one mole of CO2 to carbohydrates WHY DO PLANTS

ONLY USE VISIBLE LIGHT?

52%44%

4%

Composition of SunlightInfrared Visible Light Ultraviolet

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The Leaf Structure

main photosynthetic organ of the plant

usually broad, flat and thin to ensure the exposure of all cells to light

usually green in color

The Leaf StructureCarbon dioxide enters, while oxygen exits through a leaf’s stomata

contains large number of stomata

The Leaf Structure

contains numerous chloroplasts containing the green pigment chlorophyll

The Leaf Structure

The Leaf Structure

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Power plants: Researchers explore how to harvest electricity directly from plants

•Ramaraja Ramasamy (right) and

•Yogeswaran Umansakar

developed a way to interrupt photosynthesis

modified thylakoids