Where It Starts – Photosynthesis Lecture 8 - Autumn 2007

Sunlight as an Energy Source Photosynthesis runs on a fraction of the electromagnetic spectrum, or the full range of energy radiating from the sun

Visible Light Wavelengths humans perceive as different colors Violet (380 nm) to red (750 nm) Longer wavelengths, lower energy

Electromagnetic Spectrum Shortest Gamma rays wavelength X-rays UV radiation Visible light Infrared radiation Microwaves LongestRadio waves wavelength

Photons Packets of light energy Each type of photon has fixed amount of energy Photons having most energy travel as shortest wavelength ( deep blue sea - blue light travels the deepest because it has the most energy )

Pigments Light-absorbing molecules Absorb some wavelengths and transmit others Color you see are the wavelengths not absorbed

Variety of Pigments Chlorophylls a and b Carotenoids Etc.

Chlorophylls Main pigments in most photoautotrophs - Organisms which make their own food Wavelength absorption (%) Wavelength (nanometers) chlorophyll b chlorophyll a

Carotenoids Found in all photoautotrophs Absorb blue-violet and blue-green that chlorophylls miss Reflect red, yellow, orange wavelengths Two types –Carotenes - pure hydrocarbons –Xanthophylls - contain oxygen

Xanthophylls Yellow, brown, purple, or blue accessory pigments

Phycobilins & Anthocyanins Red to purple pigments Phycobilins –Found in red algae and cyanobacteria Anthocyanins –Give many flowers their colors

T.E. Englemann’s Experiment - simple elegance - illuminate a long strand of photosynthetic algae with a spectrum of light, and watch were the mobile bacteria accumulate!

1.Pigments absorb light energy, give up e - which enter electron transfer chains 2.Water molecules are split, ATP and NADH are formed, and oxygen is released (waste product - lucky for us!) 3.Pigments that gave up electrons get replacements Light-Dependent Reactions

Synthesis part of photosynthesis Can proceed in the dark Take place in the stroma (special structures inside the chloroplast) Calvin-Benson cycle Synthesis part of photosynthesis Can proceed in the dark Take place in the stroma (special structures inside the chloroplast) Calvin-Benson cycle Light-Independent Reactions

Photosynthesis Equation - remember forever

Organelles of photosynthesis Chloroplasts

Inside the Chloroplast Two outer membranes enclose a semifluid interior, the stroma Thylakoid membrane inside the stroma

Inside the Chloroplast Photosystems are embedded in thylakoids, containing 200 to 300 pigments and other molecules that trap sun’s energy Two types of photosystems: I and II

Photoautotrophs –Carbon source is carbon dioxide –Energy source is sunlight (mostly) Heterotrophs –Get carbon and energy by eating autotrophs (plants) and/or one another (cannibalism too) Carbon and Energy Sources

Photoautotrophs Capture sunlight energy and use it to carry out photosynthesis –Plants –Some bacteria –Many protistans

Linked Processes Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide

Photosystem Function: Harvester Pigments Most pigments in photosystem are harvester pigments –When excited by light energy, these pigments transfer energy to adjacent pigment molecules Each transfer involves some energy loss - heat and atomic motion

ATP and NADPH Formation

Using the Products of Photosynthesis Phosphorylated glucose is the building block for: –Sucrose The most easily transported plant carbohydrate –Starch The most common storage form

Summary of Photosynthesis