Photosynthesis
Chloroplasts
● Site of photosynthesis
● 2 main parts
○ thylakoids- sacs filled with
chlorophyll, arranged in
stacks called grana
○ stroma- fluid-filled region
surrounding thylakoids
Photosynthesis
● 2 major steps:
○ Light-dependent reaction- occurs in thylakoid,
absorbs light energy to make ATP & NADPH
(another energy storing molecule)
○ Light-independent reaction (Calvin cycle)- occurs in
stroma, uses ATP, NADPH, and CO2 to make
glucose
Photosynthesis
Light-Dependent Reaction
● Requires light to work
● Produces O2
● Converts ADP and
NADP+ into ATP and
NADPH
● Steps divided into
photosystems
Light-Dependent Reaction Steps
1. Photosystem II
● Light is absorbed by chlorophyll, energy
breaks H2O into hydrogen ions (H+),
oxygen, and energized electrons
● Oxygen is released as O2
Light-Dependent Reaction Steps
2. Electron Transport Chain (ETC)
● High-energy electrons travel
down the thylakoid membrane
● Electron energy is used to move
H+ ions into the thylakoid
Light-Dependent Reaction Steps
3. Photosystem I
● Electrons re-energized by light absorption
● Electrons bond with 2 H+ and NADP+ to
form NADPH
● NADPH stores energy to be used in the
Calvin cycle
Light-Dependent Reaction Steps
4. ATP synthase
● Inside of thylakoid has high concentration
of H+ ions
● H+ moves to low concentration through
ATP synthase
● ATP synthase converts ADP + Pi into ATP
Light-Independent Cycle (Calvin Cycle)
● Does not need light
● Uses 6 CO2 and a renewable 5carbon molecule to create
glucose
● Uses energy from ATP and
NADPH made in the lightdependent cycle
Limitations of Photosynthesis
● Water shortage: water is a reactant of photosynthesis
● Temperature: cold temperature inhibits enzymes
needed for photosynthesis
● Light intensity: less light = slower rate of photosynthesis