Chapter 5_2 Photosynthesis

The Stages of Photosynthesis Energy is captured from sunlight. Light Energy is converted into chemical energy, which is temporarily stored in ATP and the energy carrying molecule NADPH. The chemical energy stored in ATP and NADPH powers the formation of organic compounds, using CO2

Photosynthesis occurs in the Chloroplasts of plants cells and algae, and some prokaryotes.

Photosynthetic Equation Reactants Products   Chlorophyll 6CO2 + 6H2O + Energy --------- > C6H12O6 + 6O2

Absorption of Light Energy Pigments – light-absorbing substances. Absorb only certain wavelengths of light and reflect others. Chlorophyll – primary pigment found in photosynthesis. Absorbs mostly blue and red light and reflects green and yellow. Two types: Chlorophyll a Chlorophyll b Carotenoids – produce yellow and orange fall leave colors and colors of fruits, flowers and vegetables. Absorb different wavelengths of light than chlorophyll.

Visible Spectrum ROY G. BIV

Production of Oxygen Thylakoids – disc-shaped structure containing clusters of embedded pigments. When light strikes the thylakoid, energy is transferred to electrons in chlorophyll. Cause electrons to jump to a higher energy level = “excited.” How plants first capture energy from sunlight.

Electron Transport Chain

Electron Transport Chain Excited electron jumps to nearby molecule in the thylakoid membrane. Electrons passed through a series of molecules. First electron transport chain (Photosystem II) produces ATP and hydrogen ions. Second electron transport chain (Photosystem I) provides energy to make NADPH. The above two reactions are Light-dependent reactions. Read page 100 to 101, and look at Fig. 8, page 100.

Storage of Energy Light-independent reaction (“dark reactions”). Carbon Dioxide Fixation – carbon atoms from carbon dioxide in the atmosphere. Used to make organic compounds in which chemical energy is stored.

Calvin Cycle Calvin Cycle – series of enzyme-assisted chemical reactions that produce a three carbon sugar. Four Steps: Each molecule of carbon dioxide is added to a five-carbon compound by an enzyme. Resulting six-carbon compound split into two three-carbon compounds. Phosphates from ATP and electrons from NADPH are added to the three carbon compounds, forming three-carbon sugars. One of the three-carbon sugars used to form starch and glucose for energy storage for later use. Other three-carbon used to regenerate the initial five-carbon compound, completing the cycle.

Calvin Cycle

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi Or 3 CO2 + 6 C21H29N7O17P3 + 5 H2O + 9 C10H16N5O13P3 → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9C10H15N5O10P2 + 8 Pi

Quiz True or False? Explain answer. Chloroplasts are found within the thylakoid membranes. True or false? Explain answer. Carbon dioxide fixation takes place during the Calvin cycle? The electron transport chain converts light energy to chemical energy during the _____________ stage of photosynthesis.

Project Draw the Calvin Cycle and explain.