Plant Cell cell wall nucleus cytosol chloroplast Plant

Plant Cell cell wall nucleus cytosol chloroplast

Plant Cell Chloroplast cell wall nucleus cytosol chloroplast Ø All photosynthetic reactions take place in the chloroplast Ø Light is captured in the chloroplasts with green pigments called cholorphylls

The Chloroplast Outer membrane Inner membrane Stroma Thylakoid Granum

Thylakoid Stroma Lamella (connects grana) Thylakoid (contains chlorophyll) Thylakoid Space (Lumen)

Stages of Photosythnesis Ø There are 2 main stages of photosynthesis: Light Reactions Dark Reactions DON’T BE FOOLED!! makes some Both light and dark reactions occur during NADPHthe day. ATP The “Dark” reactionsglucose don’t REQUIRE light while the “Light” reactions do! makes PHOTOSYNTHESIS

Stages of Photosynthesis Ø There are 2 main stages of photosynthesis: Light-Dependent Reactions Light Reactions makes NADPH Light - Independent Reactions Dark Reactions makes some ATP glucose PHOTOSYNTHESIS

The Electromagnetic Spectrum Ø The full range of wavelengths of light emitted from the sun is known as the electromagnetic spectrum Ø Visible light is between 400 -700 nm Ø Light has properties of both waves and particles

Light ~ as a particle? Photon Ø Light travels in bundles of energy called Photon photons Photon Ø The energy from photons is used to initiate photosynthesis

Capturing Light For the Light Reactions Ø Photosynthetic pigments absorb light § Each pigment can absorb light (photons) within a specific range of wavelengths § Wavelengths that are not absorbed are said to be transmitted or reflected • This is the light we see ◦ determines what colour we see

Capturing Light For the Light Reactions Ø The most common pigments in plants are Chlorophyll a and Chlorophyll b Absorbance: Chlorophyll a absorbed Chlorophyll b absorbed

Capturing Light For the Light Reactions Ø The most common pigments in plants are Chlorophyll a and Chlorophyll b Reflection: Chlorophyll a reflected Chlorophyll b What we see GREEN

Absorption Spectra for Chlorophyll

Absorption Spectra for Chlorophyll

Other pigments Ø Though chlorophylls are the most common pigments, other pigments are present in plants to absorb at other wavelengths: § Carotenoids § Phycobilins § Xanthophylls

Other pigments

Harnessing Solar Energy! Ø How do plants store energy from photons into the chemical bonds of high energy molecules? Ø It starts in the thylakoids of the chloroplasts!

The Light Reactions (light-independent reactions) Ø Groups of molecules responsible for the light reactions are called photosystems § Each photosystem has: 1. antenna pigments • 200 -400 chlorophyll b molecules, accessory pigments (ex. carotenoids) 2. reaction centre • a specialized chlorophyll a molecule with associated proteins 3. primary electron acceptor PS II a Electron Acceptor

How Photosystems Capture Light Energy Ø 2 photosystems in plants: § Photosystem I (PS I) & Photosystem II (PS II) Ø Other names (used by text) § PS I absorbs best at 700 nm; called P 700 § PS II absorbs best at 680 nm; called P 680 * Difference in absorbance is due to differences in proteins associated with chlorophyll a Thylakoid P 700 PS I P 680 PS II

How Photosystems Capture Light Energy 1. Photons of light are absorbed by antenna pigments causing them to move from ground state to an excited state. 2. “Excitation” energy is passed along chlorophyll molecules until it reaches the reaction centre. 3. Chlorophyll a in the reaction centre absorbs the energy. 4. The high-energy state of chlorophyll a causes it to emit 2 electrons. 5. The primary electron acceptor takes the electrons from chlorophyll a. Ø this process is called photoexcitation Thylakoid Electron Acceptor PS I aa PS II a

Homework Ø Read Section 3. 3 up to “The Calvin Cycle” § Do section review 1 -4 on pg. 94 § Explain the difference between the cyclic and noncyclic pathway § Tomorrow we get into the nitty gritty details of how plants make ATP and Glucose! Excited?

Still to come Ø Time permitting I will show you a video that will show you plants as you’ve never seen them. It is made by my hero, Sir David Attenborough… sneak peak…

Non-Cyclical Electron Pathway High Energy Ø Photosystem II aquires a supply of electrons by using the sun’s energy to hydrolyze water. Ø This is called photolysis. H+ H+ Low H+ H+ PS II H+ H+ O 2 Stroma Thyl akoi H+ H+ H 2 O H+ H+ d Me mb ran e H+ H+ Thylakoid Lumen H+ H+

Non-Cyclical Electron Pathway Energy High Ø Electrons are re-energized I through gradient is usedat tophotosystem generate ATP Ø The proton reaction center passes electrons through an Synthase electron transport system containing a cytochrome Ø ATP The high energy electrons are involved in a redox complexto(cytochrome reaction generate theb 6 f) high energy NADPH Ø molecule This complex generates a proton gradient H+ H+ H+ Low H+ H+ E PS II H+ T H+ ATP PS I C Stroma Thyl akoi H+ H+ O 2 H+ H+ d Me mb ran e H+ H+ Thylakoid Lumen H+ H+

Non-Cyclical Electron Pathway Energy High H+ NADP+ H+ H+ Low H+ H+ H+ ATP H+ NADPH E PS II T PS I C Stroma Thyl akoi H+ H+ H+ d Me mb ran e H+ H+ Thylakoid Lumen H+ H+

The End Result NADPH ATP Ø These end products of the light reaction can now be used to synthesize glucose

Cyclical Electron Pathway Energy High Ø Simple organisms like bacteria are able to meet their energy demands by using PS I alone to generate ATP Ø In this way they generate cellular energy without synthesizing glucose. H+ H+ H+ Low H+ H+ E H+ T H+ ATP PS I C H+ H+ Me H+ H+ mb ran e H+ H+

Cyclical Electron Pathway Energy High H+ H+ H+ Low H+ H+ E H+ T ATP PS I C H+ H+ Me H+ H+ mb ran e H+ H+ H+ ATP H+ H+ H+

The Dark Reaction

The Whole Process