Capturing Free Energy
Capture and Store Free Energy
• Autotrophs: capture free energy from the physical environment
– Photosynthetic – sunlight
– Chemosynthetic – inorganic molecules
• Heterotrophs: capture free energy in carbon compounds
Chemosynthesis
• The process by which bacteria produce organic molecules (glucose) using chemicals (i.e. hydrogen sulfide, methane) as the energy source, rather than sunlight
• Commonly occurs around hydrothermal vents where sunlight is absent
Chemosynthesis
REDOX Reaction
• An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two atoms or molecules
Photosynthesis REDOX Reaction
• Oxidize – lose electrons
• Reduce – gain electrons
Electromagnetic Spectrum
Chlorophyll a and b Absorption
Chloroplast
Light Absorption by Chlorophyll Pigments
• Photosystems are clusters of chlorophyll molecules embedded within the thylakoid membranes of chloroplasts
Light Absorption by the Chlorophyll Molecules
• Clusters of chlorophyll pigments called
photosystems absorb light energy (photons)
• Light energy “excites” electrons of the chlorophyll pigments to a higher energy state
• Shorter wavelengths of light have more energy and are therefore more effective at “exciting” electrons
Light Dependent Reactions
Chemiosmosis and Photophosphorylation
LightDependent Reactions (occurs within thylakoid membranes)
• Light energy splits water molecules into hydrogen ions (H+) and oxygen gas (photolysis)
• Two high energy compounds, ATP and NADPH, are also produced (energy building reactions)
• ATP and NADPH transfer free energy to the light-independent reactions (Calvin Cycle)
Calvin Cycle(within the stroma)
• “Carbon fixation” occurs – “fixing” inorganic carbon (from CO2) into organic carbon (G3P molecules)
• CO2 combines with a five-carbon sugar called RuBP(forms an intermediate 6-carbon compound)
• Energy stored in ATP and NADPH is used to convert the temporary 6-C intermediate compound into G3P molecules
G3P Molecules
• Glyceraldehyde 3-phosphate
• End product of photosynthesis
• G3P molecules:
– Immediate food nutrient in plants
– Combined to form monosaccharides (glucose)
– Transported to other cells
– Packaged for storage in polysaccharides (starch and cellulose)
Where does plant mass come from?