Photosynthesis Capturing Solar Energy
Overview of Photosynthesis (glucose) Occurs in some bacteria or chloroplast of plants and protists Carbon dioxide (CO2) is reduced to produce glucose Energy required is captured from the sun by chlorophyll Photosynthesis has a Light reaction and a Dark reaction
What is chlorophyll? Chloroplasts contain several pigments: Chlorophyll a Chlorophyll b Carotenoids
Chlorophyll absorbs Red and Blue light from the visible spectrum but reflects Green light.
Light-Dependant Reaction Occurs on thylakoid membranes of the chloroplast Only occurs in the presence of light Two parts: Photosystems and Electron Transport Chains (E.T.C.) Transfers light energy to energy molecules – ATP and NADPH
Photosystem II Water loses 2 electrons and releases O2 . Light energizes the 2 electrons e- passes through E.T.C. which produces ATP ATP is carried over to the Calvin cycle
Photosystem I Electrons are energized again Energized electrons bond with a proton and NADP+ to form NADPH NADPH is carried over to the Calvin Cycle.
Light Independent (Dark) Reaction Doesn't require light. Occurs in stroma of the chloroplast
Calvin Cycle 6 CO2(1C) bonds with 6 RuBP(5C) and splits to form 12 PGA (3C) ATP and NADPH (From Light Reaction) reduces 12 PGA to 12 PGAL(3C) 2 PGAL forms Glucose (6C) (or other sugars) remaining 10 form 6 RuP(5C) More ATP turns 6 RuP into 6 RuBP
Regulation of Photosynthesis • Require CO2, H2O and Light • Plants need to regulate the absorption of CO2 and H2O • Stomata – openings allow CO2 in, O2 & H2O out.
Types of Plants • C3 plants: • Use CO2 directly from the air • Are very common and widely distributed • C4 plants: • Close their stomata to save water during hot and dry weather • Can still carry out photosynthesis • CAM plants: • Are adapted to very dry climates • Open their stomata only at night to conserve water
How much photosynthesis? (Do not copy) • Photosynthetic organisms absorb more energy than humans consumes in a year • In all, photosynthetic organisms convert around 104,900,000,000,000 Kg of carbon into organic compounds each year • Bacteria have higher SA/V and consequently more efficient at absorbing light and producing glucose