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

• Stems• Tissues• Cells• Leaves• Photosynthesis