Photosynthesis Introduction

What is photosynthesis? Photosynthesis: to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules Photosynthesis occurs in plants, algae, some other protists, and some prokaryotes Nourishes almost all of the living world directly or indirectly!

Autotrophs Autotroph: an organism that obtains organic food molecules without eating other organisms or substances derived from other organisms They make their own food! Autotrophs can be separated by the source of energy that drives their metabolism. Photoautotrophs use light as the energy source. Chemoautotrophs harvest energy from oxidizing inorganic substances, including sulfur and ammonia. Chemoautotrophy is unique to bacteria.

Heterotrophs Heterotroph: an organism that obtains organic food molecules by eating other organisms or their byproducts Consumers of the biosphere Some feed on plants and other animals. Others decompose and feed on dead organisms and on organic litter, like feces and fallen leaves. Almost all depend on photoautotrophs for food and for oxygen, a byproduct of photosynthesis.

Where does photosynthesis take place? Chloroplasts are the site of photosynthesis in plants half a million chloroplasts per square millimeter of leaf surface! Chlorophyll: the green pigment in the chloroplasts. important for the absorption of light energy during photosynthesis

Leaf Anatomy Mesophyll: the tissue in the interior of the leaf Where chloroplasts are found Stomata: microscopic pores that allow CO2 to enter and O2 to exit the leaf Veins: deliver water from the roots and carry off sugar from mesophyll cells to other plant areas.

Chloroplast Parts Each chloroplast has two membranes around a central aqueous space, the stroma. In the stroma are membranous sacs, the thylakoids. Inside area is called the thylakoid space Stacked into grana

The Equation 6CO2 + 6H2O + light energy  C6H12O6 + 6O2 hydrogen extracted from water is incorporated into sugar along with the carbon dioxide the oxygen is released to the atmosphere Photosynthesis is a redox reaction. reverses the direction of electron flow in respiration Water is split and electrons transferred with H+ from water to CO2, reducing it to sugar.

1. Light Reactions: Overview light reactions: convert solar energy to chemical energy light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP+,forming NADPH. NADPH, an electron acceptor, provides energized electrons, reducing power, to the Calvin cycle. also generates ATP by photophosphorylation for the Calvin cycle occurs in the thylakoids

2. Calvin Cycle: Overview Calvin cycle: incorporates CO2 from the atmosphere into an organic molecule and uses energy from the light reaction to reduce the new carbon piece to sugar. begins with the incorporation of CO2 into an organic molecule via carbon fixation carbon backbone is reduced with electrons provided by NADPH ATP from the light reaction also powers parts of the Calvin cycle occurs in the stroma

Review Draw a diagram of the chloroplast. Label all the parts. Label where the light reaction and the Calvin cycle (dark reaction) occur. Write a detailed three-sentence summary of photosynthesis.