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Photosynthesis
Botany
Light Reactions
• Photosynthesis is the process by which
photosynthetic organisms use light (photo)
energy to drive the synthesis of organic
compounds.
• Occurs in plants, algae, cyanobacteria
– Some bacteria do not give off oxygen as a
byproduct of photosynthesis
• Chemical equation is:
6CO2 + 12H2O
C6H1206 + H2O + 602
• What’s the end product?
– Usually stated as glucose, yet starch is the main
product created, which is a combination of two
monosaccharides put together.
Why Care?
• Green plants & algae provide almost all
energy & organic matter on Earth
• Provides all oxygen required for aerobic
processes
• It is the largest Biosynthetic process on Earth
– Photosynthetic organisms remove about 200
billion metric tons of Carbon per year from the
atmosphere…about 10% of total CO2 in
atmosphere.
– Almost all CO2 fixed by plants returns to
atmosphere by microbial, plant, and animal
metabolism, as well as biomass combustion (fire)
Where does it happen?
• In plants it happens in leaves, specifically the
organelle called the chloroplast
• Chloroplast is made up of several
compartments or layers.
– Outer envelope: outmost membrane which is
permeable to most substances, and acts as the
skin that holds everything in.
– Inner envelope: inner membrane which is
impermeable to most molecules, contains
transport proteins that control movement of
substances in & out of chloroplast
– Thylakoids: system of internal membranes
containing photosystems & electron transport
chain; site of light reactions; organized into
stacked & unstacked regions…stacked called
grana, fluid inside known as lumen.
– Stoma: a protein filled gel containing water
soluble enzymes and metabolites. Site of dark or
light independent reactions; known as Calvin
cycle or photosynthetic carbon reduction (PCR
cycle). Protein in stroma is enzyme Rubisco.
Photosynthetic Process
• Referred to as a two stage process
– Light Reactions: discover what your book
has to say about this process.
– Dark Reactions: discover what your book
has to say about this process.
Anatomy of a Leaf
Leaf Division
Leaf Shapes
Chapters to Study in the Book
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Stems
Tissues
Cells
Leaves
Photosynthesis