Transcript 4.2 Overview of Photosynthesis

4.2 Overview of Photosynthesis
KEY CONCEPT
The overall process of photosynthesis produces
sugars that store chemical energy.
4.2 Overview of Photosynthesis
Photosynthetic organisms are producers.
• Producers make their own
source of chemical energy.
• Plants, algae, some bacteria
and protists
• Photosynthesis captures
energy from sunlight to make
sugars.
4.2 Overview of Photosynthesis
• Pigments are molecules that
absorb light energy of specific
wavelengths.
• In plants, the pigment chlorophyll
is found in organelles called
chloroplasts
– Chlorophyll a
– Chlorophyll b
– absorb slightly different
wavelengths of light
• other pigments may be present in
the leaf
chloroplast
leaf cell
leaf
4.2 Overview of Photosynthesis
4.2 Overview of Photosynthesis
Photosynthesis in plants occurs in chloroplasts.
• Photosynthesis takes place in
– Grana – stacks of
membrane bound
sacs called thylakoids
– Stroma- fluid surrounding
the grana
grana (thylakoids)
chloroplast
stroma
4.2 Overview of Photosynthesis
• Light-Dependent reactions -capture energy from sunlight.
 take place in thylakoids
 water and sunlight are needed
 chlorophyll absorbs sun energy…used to:
 create a small amount of ATP
 split H2O into:
 Hydrogens are used later
 O2 – released into
the air
4.2 Overview of Photosynthesis
• Light-Independent reactions - make sugars.
– take place in stroma
– does not use light
– needs:
– ATP and H from light dependent reactions
– CO2 from atmosphere
– builds a glucose (sugar) molecule in a cycle of chemical
reactions – the Calvin Cycle
4.2 Overview of Photosynthesis
Glucose
• Formula is C6H12O6
– Carbon from carbon dioxide – CO2
– Hydrogen from water – H20
– Oxygen from…
- CO2
- (oxygen from water is released in the light
dependent reaction!)
4.2 Overview of Photosynthesis
• The equation for the overall process is:
6CO2 + 6H2O  C6H12O6 + 6O2
granum (stack of thylakoids)
1
chloroplast
6H2O
thylakoid
6CO2
3
6O2
2
energy
stroma (fluid outside the thylakoids)
1 six-carbon sugar
4
C6H12O6