Bellringer Without fail, I forget to water my plants. My house’s temperature (electric heat = dry) is kept at 72 o F. Explain, using your botannical vocabulary, why my house plants shriveled up and died over the winter.

Set up lab, lecture, finish lab Today’s goal: –Define pigment. –Explain why plants are green. –Give examples of the accessory pigments and explain their role in photosynthesis.

All you ever wanted to know about photosynthesis Part One

Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water AN OVERVIEW OF PHOTOSYNTHESIS Carbon dioxide WaterGlucoseOxygen gas PHOTOSYNTHESIS

Energy can be transformed from one form to another FREE ENERGY (available for work) vs. HEAT (not available for work)

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE ON EARTH

Almost all plants are photosynthetic autotrophs, as are some bacteria and protists –Autotrophs generate their own organic matter through photosynthesis –Sunlight energy is transformed to energy stored in the form of chemical bonds (a) Mosses, ferns, and flowering plants (b) Kelp (c) Euglena (d) Cyanobacteria THE BASICS OF PHOTOSYNTHESIS

Ingredients and Components 6 CO H 2 O + light energy → C 6 H 12 O O 2

Food Chain

THE FOOD WEB

WHY ARE PLANTS GREEN? It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that… Kermit the Frog

Electromagnetic Spectrum and Visible Light Gamma rays X-raysUV Infrared & Microwaves Radio waves Visible light Wavelength (nm)

Sunlight Form of energy (photons) Measured in wavelengths Sun radiates full spectrum, atmosphere screens out most, allows primarily only visible light through ( nm) Amount of energy is inversely related to the wavelength of light

Different wavelengths of visible light are seen by the human eye as different colors. Gamma rays X-raysUVInfrared Micro- waves Radio waves Visible light Wavelength (nm)

Pigment Substances that absorb visible light Different pigments absorb light of different wavelengths Color we see is the color most reflected or transmitted by the pigment

Sunlight minus absorbed wavelengths or colors equals the apparent color of an object. The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others. Reflected light

Why are plants green? Reflected light Transmitted light

Chlorophyll a Chl a has a methyl group Chl b has a carbonyl group Porphyrin ring delocalized e - Phytol tail

Spectrophotometer

WHY ARE PLANTS GREEN?

Predict: action spectrum Measure photosynthetic output against the various wavelengths of light…

Action spectrum

So chlorophyll isn’t the whole story here…

The Pigments Chlorophyll a: blue-green; only pigment that can participate directly in photosynthesis Accessory (antennae) pigments - absorb light and transfer it to chlorophyll a: Chlorophyll b: yellow-green Carotenoids: various shades of yellow and orange Xanthophylls: purples Anthocyanin: yellow

Fall colors

So what? Demonstration!

Electron Excitation

Excited state ee Heat Light Photon Light (fluorescence) Chlorophyll molecule Ground state 2 (a) Absorption of a photon (b) fluorescence of isolated chlorophyll in solution Excitation of chlorophyll in a chloroplast ee

Okay…still, so what?

Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis Noncyclic Photophosphorylation Photosystem II regains electrons by splitting water, leaving O 2 gas as a by-product

Parts of the chloroplast Thylakoids: flattened sac, pigments of photosynthesis located in their membranes Grana: stacks of thylakoids (literally, “stacks of coins”) Stroma: interior portion

The location and structure of chloroplasts LEAF CROSS SECTION MESOPHYLL CELL LEAF Chloroplast Mesophyll CHLOROPLAST Intermembrane space Outer membrane Inner membrane Thylakoid compartment Thylakoid Stroma Granum StromaGrana

Go home and read. Pp Make sure to keep the structure of the chloroplast forefront as you read.

ALL YOU WANTED TO KNOW ABOUT PHOTOSYNTHESIS Day two

The Calvin cycle makes sugar from carbon dioxide –ATP generated by the light reactions provides the energy for sugar synthesis –The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose Light Chloroplast Light reactions Calvin cycle NADP  ADP + P The light reactions convert solar energy to chemical energy –Produce ATP & NADPH AN OVERVIEW OF PHOTOSYNTHESIS

Review of photosynthesis… The reactants: CO 2 and H 2 O Driving the reaction: sunlight Products: Glucose and O 2 Sunlight captured by pigments (chlorophylls and others) Pigments located in the chloroplasts

Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light Absorbed light Transmitted light Chloroplast

What is a pigment? Substance that absorbs visible light Different pigments absorb light of different wavelengths Arranged into clusters called photosystems (more on that later!)

Chloroplasts: Sites of Photosynthesis Photosynthesis –Occurs in chloroplasts, organelles in certain plants –All green plant parts have chloroplasts and carry out photosynthesis The leaves have the most chloroplasts The green color comes from chlorophyll in the chloroplasts The pigments absorb light energy

Photosystems In the membrane of the thylakoid Contains several hundred molecules of chlorophyll a and b along with accessory pigments Named by the wavelength of light they absorb (P680 and P700)

Why have photosystems? To harvest light over a larger surface area and larger portion of the spectrum than any single pigment could harvest.

Primary electron acceptor Photon Reaction center PHOTOSYSTEM Pigment molecules of antenna Molecular Game of “Hot Potato”

Photon Water-splitting photosystem NADPH-producing photosystem ATP mill Two types of photosystems cooperate in the light reactions

Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis Noncyclic Photophosphorylation Photosystem II regains electrons by splitting water, leaving O 2 gas as a by-product

The O 2 liberated by photosynthesis is made from the oxygen in water (H + and e - ) Plants produce O 2 gas by splitting H 2 O

2 H  + 1 / 2 Water-splitting photosystem Reaction- center chlorophyll Light Primary electron acceptor Energy to make Electron transport chain Primary electron acceptor Primary electron acceptor NADPH-producing photosystem Light NADP  How the Light Reactions Generate ATP and NADPH

Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons The excited electrons are passed from the primary electron acceptor to electron transport chains –Their energy ends up in ATP and NADPH In the light reactions, electron transport chains generate ATP, NADPH, & O 2

The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H + through that membrane –The flow of H + back through the membrane is harnessed by ATP synthase to make ATP –In the stroma, the H + ions combine with NADP + to form NADPH Chemiosmosis powers ATP synthesis in the light reactions

The production of ATP by chemiosmosis in photosynthesis Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM IIPHOTOSYSTEM IATP SYNTHASE

Cyclic Pathway

A Photosynthesis Road Map Chloroplast Light Stack of thylakoids ADP + P NADP  Stroma Light reactions Calvin cycle Sugar used for  Cellular respiration  Cellulose  Starch  Other organic compounds

Join me, on the dark side of photosynthesis

overview

Redox reactions Reduction: gains electrons (escorted by hyrdrogens) Oxidation: loses electrons

ATP is a limiting factor: more is used by calvin cycle Need a way to fill deficit

Cyclic Photophosphorylation Process for ATP generation associated with some Photosynthetic Bacteria Reaction Center => 700 nm

Review: Photosynthesis uses light energy to make food molecules Light Chloroplast Photosystem II Electron transport chains Photosystem I CALVIN CYCLE Stroma Electrons LIGHT REACTIONSCALVIN CYCLE Cellular respiration Cellulose Starch Other organic compounds A summary of the chemical processes of photosynthesis

It's not that easy bein' green… but it is essential for life on earth!

Balancing Act

climate

photorespiration

Adaptations C4 Plants: spatial separation CAM Photosynthesis: temporal separation