Exercise 6: Photosynthesis

Questions that will be addressed: Where does the carbon that organic molecules are made of come from? Where does the carbon that organic molecules are made of come from? Where does the energy that drives the synthesis of organic molecules come from? Where does the energy that drives the synthesis of organic molecules come from?

The answers vary, depending on the organism Autotrophs – Self-nourishing Autotrophs – Self-nourishing – Photoautotrophs – Carbon source is CO 2 from the air and sunlight is the energy source that drives synthesis. Heterotrophs – Feed on autotrophs. Heterotrophs – Feed on autotrophs.

Photoautotrophs Plants, some bacteria, and many protistans are photoautotrophs. Plants, some bacteria, and many protistans are photoautotrophs. – Photoautotrophs synthesize organic molecules from CO 2 by a process called Photosynthesis. – Photosynthesis: energy form the sun is used to drive synthesis.

Overview of Photosynthesis 12H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O Glucose Sucrose, Starch, or Cellulose

Photosynthesis Occurs in Two Stages 1. Light-Dependent Reactions – Split water and generate ATP and NADPH 1. Light-Dependent Reactions – Split water and generate ATP and NADPH – Occur in the Thylakoid Membrane of Chloroplast 2. Light-Independent Reactions – Use the ATP and NADPH generated in the Light- Dependent reactions to make Glucose. 2. Light-Independent Reactions – Use the ATP and NADPH generated in the Light- Dependent reactions to make Glucose. – Occur in the Stroma of Chloroplast

The Light-Dependent Reactions Photoautotrophs use pigments to absorb sunlight energy. Photoautotrophs use pigments to absorb sunlight energy. This energy is then used to drive photosynthesis. This energy is then used to drive photosynthesis.

Properties of Light cont’d Visible light is in the range of nm. Visible light is in the range of nm. People and other organisms see the different s as different colors. People and other organisms see the different s as different colors. Wavelength of light (nanometers)

Light as particles The energy of light is absorbed as if it is organized into packets. These packets are called Photons. The energy of light is absorbed as if it is organized into packets. These packets are called Photons. – Each type of photon has a fixed amount of energy characterized by its wavelength. Pigments are molecules that absorb photons. Pigments are molecules that absorb photons. – Most pigments only absorb some wavelengths of light and transmit (reflect) others. The wavelengths that are transmitted, determine what color an object appears. – A pigment that absorbs all wavelengths of visible light appears black. – A pigment that reflects all wavelengths of visible light appear white.

Pigments Chlorophylls are the primary pigments in most photoautotrophs. Chlorophylls are the primary pigments in most photoautotrophs. – Chlorophyll a – mostly absorb red and blue light. – Chlorophyll b – absorbs blue and red-orange light. Carotenoids, Xanthophylls, anthocyanins, and phycobilins are accessory pigments found in photoautotrophs. Carotenoids, Xanthophylls, anthocyanins, and phycobilins are accessory pigments found in photoautotrophs. – They absorb wavelengths that chlorophylls miss, blue- violet and blue-green. They reflect red, orange, and yellow.

Absorption Spectrum percent of wavelengths absorbed wavelengths (nanometers) chlorophyll b chlorophyll a beta-carotene phycoerythrin (a phycobilin)

Absorption Spectrum chlorophyll b chlorophyll a carotenoids phycoerythrin (a phycobilin) (combined absorption efficiency across entire visible spectrum) chlorophyll a chlorophyll b Phycocyanin (a phycobilin)

Plant Pigment Paper Chromatography Chromatography is the separation of molecules in a mixture based on their solubility in a particular solvent and their interaction with the chromatography matrix. Chromatography is the separation of molecules in a mixture based on their solubility in a particular solvent and their interaction with the chromatography matrix. Pigments: Pigments: –Chlorophyll a, Chlorophyll b, Beta-carotenes, and Xanthophylls. Solvent: Petroleum Ether and Acetone are non- polar solvents. Solvent: Petroleum Ether and Acetone are non- polar solvents. The most non-polar pigments will travel further up the paper while the polar pigments will not travel as far. The most non-polar pigments will travel further up the paper while the polar pigments will not travel as far.

Plant Pigment Paper Chromatography Beta-Carotene Xanthophylls Chlorophyll a Chlorophyll b Ratio Factor (R f ) = Distance pigment moved Distance solvent moved

Measuring Photosynthesis in Elodea We will measure photosynthesis in Elodea under different light conditions. We will measure photosynthesis in Elodea under different light conditions. – White light – Oxygen Production – No light – Oxygen Consumption – Green light – Oxygen Production

White Light 12H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O Respiration Photosynthesis Net Photosynthesis

Absorption Spectrum chlorophyll b chlorophyll a carotenoids phycoerythrin (a phycobilin) (combined absorption efficiency across entire visible spectrum) chlorophyll a chlorophyll b Phycocyanin (a phycobilin)

No Light 12H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O Respiration Photosynthesis X X Net Photosynthesis + Respiration = Gross Photosynthesis

Green Light 12H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O Respiration Photosynthesis X X Net Photosynthesis

Absorption Spectrum chlorophyll b chlorophyll a carotenoids phycoerythrin (a phycobilin) (combined absorption efficiency across entire visible spectrum) chlorophyll a chlorophyll b Phycocyanin (a phycobilin)

No Green Light 12H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 + 6H 2 O Respiration Photosynthesis X X Net Photosynthesis + Respiration = Gross Photosynthesis

CO 2 Uptake H 2 O + CO 2 HCO OH Carbonic Acid