It’s Not Easy Being Green! (Photosynthesis – Part 1)

What is Photosynthesis? The process of converting light energy to chemical energy Occurs inside chloroplasts (plant cells and algae) and in the cell membrane (some bacteria)

Equation for Photosynthesis 3 CO2 + 3 H20 ------> C3H6O3 + 3 O2 (carbon dioxide) (water) (sugar) (oxygen)

Stages of Photosynthesis Stage 1 -- Energy is captured from sun. Leaves contain light absorbing substances called pigments Pigments absorb certain wavelengths of light and reflect others

Chlorophyll: the primary pigment involved in photosynthesis Absorbs blue & red light Reflects green & yellow light (causes plants to look green) Carotenoids: pigments that produce red, orange, & yellow colors (fall leaves, fruits, flowers, etc.) Both types of pigments are needed for photosynthesis . . . they absorb different wavelengths of light

Impact of Pigments on Light Absorption

Clusters of pigments are embedded inside the chloroplasts (specifically, in the thylakoids) Thylakoids: membrane-bound compartments found inside chloroplasts Light strikes the thylakoids inside the chloroplasts & energy is transferred to the chlorophyll. Water molecules are split to form oxygen gas (O2).

Stage 2 -- Light energy is converted to chemical energy. Excited electrons jump to nearby molecules in the thylakoid membrane Then the electron is passed down a series of molecules along the thylakoid membrane (electron transport chain) ETC provides the energy needed to make ATP

Stage 3 -- Energy is stored in organic compounds (sugars). Carbon dioxide fixation: the transfer of CO2 from atmosphere to organic compounds Calvin cycle: a series of enzyme-assisted chemical reactions that produces a 3-carbon sugar (uses energy from ATP) 3 CO2 molecules enter the cycle & produce a 3-carbon sugar These sugars provide organisms energy to maintain life

Photosynthesis increases as light intensity increases Photosynthesis increases as the concentration of CO2 increases Water must be available for photosynthesis to occur Photosynthesis is most efficient within a certain temp range (enzymes)