1. Photosynthesis Photosynthesis is the process of converting light energy to chemical energy. Plants, algae, cyanobacteria, and some protists produce organic compounds from inorganic materials and light energy and are classified as photoautotrophs. – Chloroplasts are the site of photosynthesis

2. Photosynthesis Discoveries leading to development of our understanding – Jan van Helmont… determined that plants added water from the soil to their product (carbohydrate) but very little from the soil added to their mass Calculated mass lost by the soil and gained by a plant – Joseph Priestly… showed that that plants removed the product of combustion (CO 2 ) and added purified air (O 2 ) Could keep a candle burning and a mouse alive in the presence of plants in a closed container – Jan Ingenhousz… showed that plants need light to produce O 2 Showed that aquatic plants produced O2 bubbles only in the presence of light – Julius Mayer… proposes that plants convert light energy into chemical energy – Melvin Calvin… discovers the path that CO 2 takes as it is added to the growing glucose molecule… called the Calvin Cycle – Rudolph Marcus… describes the electron transport chain and shows how electrons are used to store energy

3. Photosynthesis Photosynthesis: The production of carbon compounds with the use of light energy Photosynthesis like cellular respiration is performed through a series of redox reactions with glucose being reduced (gaining charge) through the oxidation of water. – 6CO 2 + 12H 2 O + light energy  C 6 H 12 O 6 + 6 O 2 + 6H 2 O – 6CO 2 + 6H 2 O + light energy  C 6 H 12 O 6 + 6 O 2 (simplified formula) CO 2 + H 2 O  [CH 2 O] n + O 2 (reduced formula) – the reduced formula is necessary to visualize that the sugar molecule is built one carbon at a time – Tracking the atoms through photosynthesis Production of O 2 is from the splitting of water (not CO 2 ) – confirmed by C.B. van Neil using the isotope O-18 Carbon in the glucose comes from CO 2 Hydrogen in the new water and in the water come from reactant water Oxygen in the glucose and the new water come from the CO 2 in the reactants

4. The Light Reaction The light reaction of photosynthesis takes advantage of the photoelectric effect (ability of photons to exert inertia on electrons) and the photosynthetic pigment chlorophyll. There are 3 main pigments (2 types of chlorophyll) used in plants. The action spectrum describes which wavelength of light works best for each (studied by looking at CO 2 uptake and O 2 production). – Chlorophyll a blue-green in color absorbs violet and red best reflects blue & green – Chlorophyll b yellow-green in color absorbs blue and red best reflects yellow & green – Carotenoids various shades of red, orange, and yellow called accessory pigments absorbs violet & blue-green