8-3 The Reactions of
Photosynthesis
The difference is night and day!
Interactive: pgs. 208-214
Inside a Chloroplast
• Thylakoids
– Saclike membranes
– Arranged in stacks called grana
– Organize the chlorophyll into clusters
called photosystems
• Stroma
– Area outside the thylakoid membrane
Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Grana
Stroma
Inner
membrane
Stroma
Thylakoid
Thylakoid
compartment
Electron Carriers
(The electron transport chain)
• Sunlight gives energy to electrons in the
chlorophyll of a plant
• NADP+
– A carrier molecule
– Can carry 2 high energy electrons and 1 H+
• NADPH
– Results from adding 2 electrons
– Traps the energy in chemical form
• Can be used by chemical reactions in the cell
Light Dependent Reactions
• In the thylakoid membrane of the
chloroplasts
• Use energy from light to make O
• Converts ADP to ATP
• Converts NADP+ to NADPH
5 Steps
(Light Dependent Reactions)
• 1. Photosystem II- absorbs light and breaks up water
• 2. Electron Transport Chain- moves high energy eand transports H+ inside the thylakoid
• 3. Photosystem I uses the e- & H+ to turn NADP+ into
NADPH
• 4. Hydrogen Ion movement makes the outside - and
inside +.
• 5. ATP formation- H+ move outside the membrane
and ATP synthase creates ATP.
Light Dependent Reactions
Thylakoid
compartment
(high H+)
Light
Light
Thylakoid
membrane
Antenna
molecules
Stroma
(low H+)
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
The Calvin Cycle
• Uses ATP and NADPH made during the
light dependent reactions
• Makes High Energy Sugars like
Glucose
• Does not require light
• Occurs in the Stroma
4 Steps
• 6 CO2 molecules + 6 C5 molecules = 12 C3
• The resulting 12 C3 molecules are converted to
higher energy molecules by using ATP and NADPH
• 2 of the C3 high energy molecules are used to make
sugars, lipids, amino acids for metabolism and
growth
• The remaining 10 C3 molecules are recycled back
into 6 C5 molecules to start the cycle again.
Factors that Affect the Rate of
Photosynthesis
• Amount of Water
• Temperature
– Photosynthetic enzymes function best at 035 degrees C
• Light Intensity
Review: Photosynthesis uses light
energy to make food molecules
Chloroplast
Light
Photosystem II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE
Stroma
Cellular
respiration
Cellulose
Starch
https://www.youtube.com/w
atch?v=uixA8ZXx0KU
LIGHT REACTIONS
CALVIN CYCLE
Other
organic
compounds
Quiz Ch.8
1. What type of organism uses light energy to
make its own food
2. Which compound is used to release energy to
power the cell: ATP or ADP?
3. What is the name of the process that converts
light energy into high energy carbohydrates?
4. Write the equation for the above process.
(you may use words or chemical formulas)
5. What is the main light absorbing pigment in
plants?