CHAPTER 5 PHOTOSYNTHESIS Title CHAPTER 5 PHOTOSYNTHESIS http://www.biology.ualberta.ca/facilities/multimedia/uploads/alberta/Photo.html

THE BASICS OF PHOTOSYNTHESIS 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 (c) Euglena (d) Cyanobacteria (b) Kelp (a) Mosses, ferns, and flowering plants

Photosynthesis title, definition and equation.

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

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

Why does a leaf look green?

WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED Chloroplasts absorb light energy and convert it to chemical energy Reflected light Light Absorbed light Transmitted light Chloroplast

Action spectrum of photosynthesis shows wavelengths used for light dependent reactions. Different colours are different wavlengths. The green region is not used, so green light is reflected and seen.

Absorption spectrum of chlorophyll a vs action spectrum of photosynthesis. Chlorophyll b is used to ‘fill the gaps’ in the action spectrum.

Fig. 7.2

Image source unknown. Question from the IBO. Chloroplast: structure’s relationship with function Image source unknown. Question from the IBO.

Chloroplasts contain several pigments Chloroplast Pigments Chloroplasts contain several pigments Chlorophyll a (dark green) Chlorophyll b (light green) Carotene (orange) Xanthophyll (yellow) Lycopene (red) Figure 7.7

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

Absorption Spectrum for Various Plant Pigments

Excitation of chlorophyll in a chloroplast the photons of light excite electrons in chlorophyll. When they lose this energy the electrons emit a longer wavelength - red. e e Excited state 2 Heat Light Light (fluorescence) Photon Ground state Chlorophyll molecule (a) Absorption of a photon (b) fluorescence of isolated chlorophyll in solution

There are 2 sets of reactions in Photosynthesis 1) Light dependent reactions (photo) 2) Light independent reactions (synthesis)

Light dependent reactions (photo) Solar energy is trapped by pigments and used to generate 2 high-energy compounds: ATP and NADPH and O2 This occurs in the thylakoids in the chloroplasts

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

Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product Primary electron acceptor Electron transport chain Electron transport Photons PHOTOSYSTEM I PHOTOSYSTEM II Energy for synthesis of by chemiosmosis

Plants produce O2 gas by splitting H2O The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. Energy from the electron transport chain between PSII and PSI is used to pump H+ ions from the stroma to the inner thylakoid space

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. A concentration gradient of H+ ions is generated because the thylakoid membrane is impermeable to H+ ions.

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. ATP synthase, embedded in the thykaloid membrane, is the only pathway for the H+ ions to move down their concentration gradient, so it acts like a dam.

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. In a dam, water flows down and turns turbines to generate electrical energy.

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. Similarly, the H+ ions flowing through ATP synthase generates the energy to add a phosphate to ADP to make the high energy ATP.

Chemiosmosis The linking of H+ ions moving down a concentration gradient to the synthesis of ATP from ADP. In the stroma,the energy from the electron transport chain of PSI provides the energy to combine H+ ions with NADP+ to form NADPH

How the Light Reactions Generate ATP and NADPH Primary electron acceptor NADP Energy to make Primary electron acceptor 3 2 Light Electron transport chain Light Primary electron acceptor Reaction- center chlorophyll 1 NADPH-producing photosystem Water-splitting photosystem 2 H + 1/2

Stop here

In the light reactions, electron transport chains generate ATP, NADPH, & O2 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

Chemiosmosis powers ATP synthesis in the light reactions 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

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

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

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

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

Fig. 7.4

Fig. 7.7

Fig. 7.8

Photosynthesis Animations http://www.stolaf.edu/people/giannini/flashanimat/metabolism/photosynthesis.swf http://www.phschool.com/science/biology_place/biocoach/photosynth/intro.html http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter10/animations.html#

The Calvin-Benson Cycle (light-independent reactions)

Fig. 7.9

Calvin cycle (Light-independent reactions) http://www.science.smith.edu/departments/Biology/Bio231/calvin.html http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html http://www.sinauer.com/cooper5e/animation0305.html http://www.quia.com/cb/524959.html (photosynthesis game – boys vs girls!) http://www.quia.com/rr/216175.html (Rags to Riches game – photosynthesis)

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