Sec. 8.2, Photosynthesis Main Idea: Light energy is trapped and converted into chemical energy during photosynthesis.

Overview Most autotrophs make glucose by the process of photosynthesis. Chemical equation for photosynthesis: Glucose can be used to make other molecules like larger carbohydrates, lipids, proteins, and nucleic acids. 6CO2 + 6H2O + light → C6H12O6 + 6O2

Chloroplasts Chloroplasts—organelles that capture light energy Parts of a chloroplast: Thylakoids—flattened sac-like membranes arranged in stacks; this is where the pigments are found Grana—stacks of thylakoids Stroma—the fluid-filled space surrounding grana

Phase One: Light Reactions Absorption of light is the first step in photosynthesis. Happens in the thylakoids in chloroplasts. Water molecules are also required for this step.

Pigments—light-absorbing colored molecules Main pigment is chlorophyll. Reflects green light wavelengths and absorbs others, so leaves look green.

Electron Transport The light energy absorbed by pigments causes some electrons to become “excited”. These electrons are passed through a chain of molecules in the thylakoid membrane; this is called the electron transport chain (ETC). End result is the production of energy- storing molecules NADPH and ATP which are used in Phase Two of photosynthesis.

Phase Two: The Calvin Cycle Energy storage in organic molecules is the second phase of photosynthesis. Carbon dioxide is required for this part of the process, but light is not. Happens in the stroma in chloroplasts.

Calvin Cycle Calvin Cycle is a series of steps using ATP and NADPH from Phase One to convert carbon in CO2 into simple sugars used to make glucose. Glucose can be used for quick energy or to build other molecules. Other organisms can eat plants and use these materials for their own energy, etc.

Photosynthesis Summary