1 Review Why are pigments such as chlorophyll
needed for photosynthesis
Predict How well would a plant grow under a pure
yellow light- Explain
2 Review What is the function of NADPH
Infer How would photosynthesis be affected if there
were a shortage of NADP+ in the cells of plants.
3 Visual Thinking Draw two leaves- one green and
one orange. Show which colors of visible light are
absorbed and which are reflected by each leaf.
CH 8 PHOTOSYNTHESIS
8.2 Photosynthesis: An Overview
Light


Energy from the sun travels to Earth in the form of
light
Sunlight is a mixture of different wavelengths
 Some
are visible to us some are not.

Pigments
 Light

absorbing molecules that gather the sun’s energy
Chlorophyll
 Plants
primary pigment.
Chlorophyll

Two types
 Chlorophyll

a and chlorophyll b
Absorb blue-violet and red regions of the spectrum
 They
appear green.
Carotene


Red orange pigment
Secondary pigment, chlorophyll hides it most of the
year
 Chlorophyll
breaks down earlier in the fall which gives
leaves the fall colors.
Chloroplasts


Organelle where photosynthesis occurs
Thylakoids
 Saclike

photosynthetic membranes in chloroplasts
Grana
 Interconnected
stacks of thylakoids

Stroma
 Fluid
portion outside of the thylakoids.
Energy Collection

Chlorophyll absorbs light and is transferred to
electrons.
High-Energy Electrons



Are highly reactive and require a special “carrier”
Carriers include:
NADP+
 Accepts and
holds two high-energy electrons, along
with a hydrogen ion (H+)
 Turns into NADPH which carries the electrons.
Photosynthesis Steps


“Plant” absorbs light energy and takes in CO2 and
H2 O
“Plant” releases O2 and makes sugar (glucose
C6H12O6).

Photosynthesis involves two sets of reactions
 Light-dependent
reactions
 Light-independent reactions.
Light-Dependent Reactions



Use energy from sunlight to produce ATP and
NADPH
Occurs in Thylakoid
Requires water and releases oxygen.
Light-Independent Reactions



ATP and NADPH molecules produce high-energy
sugars from carbon dioxide
Light is not needed
Occurs OUTSIDE of thylakoid but IN stroma.