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

Photosynthesis Summary

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

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?