Photosynthesis
Photosynthesis
• The process that converts light energy in
to chemical energy (glucose)
• Occurs in the chloroplast of plant cells
– Stroma: fluid filled space
– Thylakoids- stacks of “disks” that contain chlorophyll,
the pigment that makes plants green
• Happens in two stages
Net Equation
Sunlight
(Energy)
6H2O + 6CO2
Water
Carbon
Dioxide

C6H12O6 + 6O2
Glucose
Oxygen
Photosynthesis Animation
• http://www.pbs.org/wgbh/nova/nature/photosynthesis.html
Light Dependent Reactions
CONVERTS PHYSICAL ENERGY (LIGHT)
INTO
CHEMICAL ENERGY (ATP and NADPH)
• This occurs in the thylakoid membranes of the
chloroplasts
• The pigment CHLOROPHYLL traps the light
energy and uses it to split water and make the
energy molecules NADPH and ATP
• O2 is released as waste
Light Independent Reactions
AKA- Calvin Cycle
Uses CO2 to make Glucose
• Occurs in the stroma of chloroplasts
• Uses ATP and NADPH from Light
Dependent Reactions as fuel
• A series of reactions that use C02 to form
Glucose (carbohydrate)
Photosynthesis
Stage
Light
Dependent
Reactions
Light
Independent
Reactions
Description
Light splits
water into H
and O
CO2 and H
are combined
to make
glucose
Reactants
H2O
Products
O2
(ATP and
NADPH for
next stage)
CO2
(ATP and
NADPH from
first stage)
Glucose
Occurs
Where?
Thylakoid
membranes of
Chloroplast
Stroma of
chloroplast
What’s next?
• After plants make glucose through photosynthesis they
use that glucose for cellular respiration
• So in plants the energy transformation goes:
sunlight  glucose  ATP
(Photosynthesis)
(Cellular Respiration)
• Animals can’t use sunlight directly, they get energy from
food. So the energy transformation goes:
glucose  ATP
(Cellular Respiration)
Comparing
Cellular Respiration & Photosynthesis
Cellular Respiration
C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP
glucose
oxygen
carbon
water
energy
dioxide
Photosynthesis
sunlight + 6H2O + 6CO2  C6H12O6 + 6O2
Energy
Water
Carbon
Dioxide
Glucose
Oxygen
Comparing PS and CR
• Photosynthesis and Cellular Respiration
are opposite processes. The products of
one become the reactants of the other.
• The sun is the ultimate source of all energy for
life on earth
– Plants convert the light (physical energy) into food
(chemical energy)
– primary consumers get energy by eating the plants
– secondary consumers get energy by eating the
primary consumers