4.2 Overview of Photosynthesis
The overall process of photosynthesis produces sugars that store chemical energy.
6CO2 + 6H2O C6H12O6 + 6O2
4.2 Overview of Photosynthesis
Photosynthetic organisms are producers.
• Producers make their own source of chemical energy (food).
• Plants use photosynthesis and are producers.
• Photosynthesis captures energy from sunlight to make sugars.
4.2 Overview of Photosynthesis
• Chlorophyll is a molecule that absorbs light energy.
chloroplast
leaf cell
leaf
• In plants, chlorophyll is found in organelles called chloroplasts.
• Chlorophyll reflects green light!
4.2 Overview of Photosynthesis
Photosynthesis in plants occurs in chloroplasts.
• Photosynthesis takes place in two parts of chloroplasts.
– grana (stack of thylakoids)
– Stroma (chloroplast fluid)
chloroplast
stroma
grana (thylakoids)
4.2 Overview of Photosynthesis
There are 2 stages of photosynthesis
• Light Dependent Reactions (uses light) (Light Reactions)
•Light Independent Reactions (doesn’t use light) (Dark Reactions)
4.2 Overview of Photosynthesis
The light-dependent reactions capture energy from sunlight.
– take place in thylakoids– water and sunlight are needed– chlorophyll absorbs energy– energy is transferred along thylakoid membrane then to
light-independent reactions (dark reactions)– oxygen is released
4.2 Overview of Photosynthesis
• The light-independent (dark) reactions make sugars.
– take place in stroma– needs carbon dioxide from atmosphere– use energy from light reactions to build a sugar in a
cycle of chemical reactions
4.2 Overview of Photosynthesis
The equation for the overall process is:
6CO2 + 6H2O C6H12O6 + 6O2
C6H12O6
granum (stack of thylakoids)
thylakoid
sunlight
1 six-carbon sugar
6H2O
6CO2
6O2
chloroplastchloroplast1
2
43
energy
stroma (fluid outside the thylakoids)