Photosynthesis Stored Energy

What is Photosynthesis?  plants convert the energy of sunlight into the energy in the chemical bonds of carbohydrates – sugars and starches.

Requirements for Photosynthesis  Carbon Dioxide - CO 2  Water - H 2 O  Energy – In the form of sunlight

3 Main Stages  1. Energy is captured from sunlight.  2. Light energy is converted to chemical energy (ATP & NADPH)  3. ATP and NADPH power the synthesis of organic molecules, using carbon from carbon dioxide.

Where does Photosynthesis occur?  Inside plant cells – specifically chloroplasts 1. DNA 2. Ribosomes 3. & 6. Outer Membrane 4. Grana 5. Stroma 7. Starch Grain

Chloroplast  Thylakoid – flattened, membrane bound sac  Grana – stacks of thylakoids  Stroma – fluid matrix

Light Energy (Energy is captured by sunlight)  Radiant Energy – energy that is transmitted in waves that can travel through a vacuum.  Electromagnetic spectrum – complete range of radiant energy. Electromagnetic Spectrum

PHOTONS!  Tiny packets of radiant energy

When Photons strike a surface…..  1 – reflected  2 – absorbed  3 – transmitted

Green plants are green because they absorb all of the colors of the visible spectrum except the green color (aka the green wavelengths).

Pigments  Molecules containing atoms that enable it to absorb light.

Types of Pigments  Chlorophyll – the primary light- absorbing agent for photosynthesis  Carotenoids – yellow & orange pigments  Phycoerythrin – red and blue

Photosytems- molecule clusters of pigments found in the thylakoid membranes  Photosytem I boost electrons by absorbing light with a wavelength of 700 nm  Photosystem II – boosts electrons by absorbing light with a slightly shorter wavelength than 680 nm

Stage 2 Light energy is converted to chemical energy… a.k.a. Light – Dependent Reactions

Electron Carriers  Excited electrons – high energy  Special carriers – electron carriers  Electron transport chain NADP + - accepts and holds 2 high energy electrons along with a hydrogen ion (H + )  NADP + + H + = NADPH

Light-Dependent Reaction  4 Basic Processes  Light absorption  Electron transport  O 2 production  ATP formation

Light-Dependent Reaction cont.  1. Photons of radiant energy strike PSII  Energy is passes to the chlorophyll molecule  Excited electron (e - ) is boosted to….  2. A thylakoid membrane protein where… the e - is passed along a series of electron carriers called …  the electron transport chain

 3. At the end of the ETC, an ATP is released into the stroma  4. PS I gets the e - from PS II. It gets boosted to….  5. Thylakoid membrane protein where…  The e - is passed to the ETC…  6. The ETC passes the e - to the electron carrier NADP + and is converted to NADPH

 7. As e - move from chlorophyll to NADP +, more H + ions are pumped across the membrane  8. The inside of the thylakoid membrane builds up with + charge  9. Outside the thylakoid is – charged.  10. H + ions cannot exit without help. They use ATP synthase.  11. Protein channel rotates.  12. As it rotates, ADP binds with a phosphate to make ATP

Why doesn’t the chlorophyll run out of e - ?  Enzymes on the inner side of the thylakoids break up water molecules into 2 electrons, H + ions, and 1 oxygen atom!

Light-Dependent Reaction  Uses  Water  ADP  NADP +  Produces  Oxygen  ATP  NADPH

The Calvin Cycle – sometimes called Light Independent Reactions  Plants use the energy that ATP and NADPH contain to build high-energy compounds that can be stored for a long time. Uses ATP and NADPH from the light dependent reactions to produce high-energy sugars.

Steps to the Calvin Cycle  6 CO 2 molecules enter the cycle from the atmosphere  These combine with 6, 5 - carbon molecules to make 12, 3 - carbon molecules  The 12 are converted into higher-energy forms (Energy from ATP & NADPH)

Calvin Cycle cont.  2 of the 12, 3 – carbon molecules are removed from the cycle to make sugars, lipids, amino acids or other compounds  The remaining 10, 3 – carbon molecules are converted back to 6, 5 – carbon molecules.