Intro to
Photosynthesis
& the Light
Reactions
AP Biology
Chapter 10.1-10.2
Learning Target 1 (10.1)
I can describe how photosynthesis converts light
energy into the chemical energy of food.
Quick Review: Obtaining
Energy
 Life
on Earth is solar
powered


Directly: autotrophs
Indirectly: heterotrophs
Chloroplasts

Photosynthetic prokaryotes lack chloroplasts

photosynthetic membranes = enfolded regions
of the plasma membrane
Key structures:
o Stroma
o Thylakoid
o Grana
Photosynthesis
 Equation:
oxidation
reduction
 Part
I: Light Dependent Reactions (thylakoid
membrane)
 Part II: Light Independent Reactions (stroma)
Plant Structure



Roots
Stems
Leaves

Epidermis


Mesophyll


Waxy covering to prevent excess
water loss
Contains photosynthetic cells
Stoma


Openings for gas exchange
Guard cells control
Learning Target 2 (10.2)
I can explain how the light reactions work to convert
solar energy to the chemical energy of ATP and
NADPH.
Light
 Form
of electromagnetic radiation
 Energy is inversely related to its
wavelength

Shorter wavelengths pack more energy
 Visible
light is 380-750 nm
Plants are green because…
 Chlorophyll


absorbs two wavelengths of light:
Blue (420 nm)
Red (660 nm)
 Green
light is reflected
Light Reactions
Part of photosynthesis that prepares to make
glucose
Photosystems
 Photosynthetic
grana
units within chloroplast
Electron Carrier
 NADP+
 Same
function as carriers in CR
 Remember “P” for photosynthesis
Light Dependent Reactions –
Non-cyclic (Linear) Electron Flow
 Produces
ATP and NADPH using
Photosystems I & II
1.
2.
Sunlight strikes the
Photosystem II complex
and excites electrons,
eventually passing it to
the primary electron
acceptor
Excited electron splits
H2O into H+ ions and O2
gas
3.
4.
5.
Electrons flow through a series of membrane
proteins, pumping H+ ions into the thylakoid
space
Collection of H+ ions pass back to stroma through
ATP synthase in thylakoid membrane
ADP is converted into ATP
6.
7.
Sluggish electrons receive another
photon of light in PSI
Excited electrons are passed to NADP
reducing it into NADPH
Light Reaction Summary
 Reactants:




H2 O
Light
NADP+
ADP + Pi
 Products:



O2
NADPH
ATP
Light Dependent Reactions –
Cyclic Electron Flow
 Produces
ATP only using photosystem I
 Evolutionary “leftover” of photosynthetic
bacteria?
Light Dependent Reaction
Animation
 http://highered.mcgraw-
hill.com/olc/dl/120072/bio13.swf