Photosynthesis
Energy and Life
 Autotroph:
organisms that make
their own food
 Heterotrophs: organisms that obtain
energy from the foods they
consume
 To live, all organisms, including
plants, must release the energy in
sugars and other compounds
Chemical Energy and ATP
 ATP:
(adenosine triphosphate) used by all
cells as their basic energy source.

ATP consists of adenine, a 5-carbon sugar
called ribose, and three phosphate groups.
 The
bonds between the last two phosphates is
where the energy is stored!
 ADP
+ P + energy  ATP
•
Photosynthesis – plants use the
energy of sunlight to convert
water and carbon dioxide into
high energy carbs. (glucose)
and oxygen (waste)
The Photosynthesis Equation

The overall reaction is:
6CO2 + 6H2O LIGHT> C6H12O6 + 6O2
OR
Carbon Dioxide + Water light> Glucose + Oxygen
The Importance of Photosynthesis
1.
2.
The oxygen in the air comes from
photosynthesis. The plants continue to
replenish the oxygen in the air.
All of our food comes directly or indirectly
from photosynthesis.
What Is a Plant?
 Nearly
all plants are autotrophs.
 All are multi-cellular
 All plants are eukaryotes.
 Plants
cells are surrounded by cell walls.
Plant Parts
• Roots anchor a plant in the
ground, absorb water and
minerals from the soil, and
sometimes store food.
Stems
 Contains
the vascular tissue.
 Helps Supports the plants.
Leaves
 Leaves
capture and use the sun’s energy to
make food (photosynthesis)
 Leaf Structure



Blade: the most important part; food-making part
Veins: contains the vascular tissue
Stomata: tiny openings on the underside of the leaf
Leaf Structure
 Epidermis:
a protective cover
that prevent excess loss of
water.
 Mesophyll: the layer
underneath epidermis that
contains the chloroplast
Mesophyll
Cell
Chloroplast
Stoma
Stomata (stoma)
Pores in a plant’s cuticle through which
water and gases are exchanged
between the plant and the
atmosphere.
Oxygen
(O2)
Carbon Dioxide
(CO2)
Guard
Cell
Guard
Cell
Found on the underside of leaves
Chloroplast
Organelle where photosynthesis takes place.
Stroma
Outer Membrane
Inner Membrane
Thylakoid
Granum
Thylakoid stacks are connected together
Thylakoid: sac-like photosynthetic
membranes
Thylakoid Membrane
Granum
Thylakoid Space
Grana are stacks of thylakoids
Chlorophyll Molecules
 Located
in the thylakoid membranes
 Chlorophyll pigments harvest energy (photons)
by absorbing certain wavelengths (blue-420 nm
and red-660 nm are most important)
 Plants are green because the green wavelength
is reflected, not absorbed.
Absorption of Light by
Chlorophyll
Absorption
violet
blue
green
yellow
wavelength
orange
red
 In
Fall Colors
addition to the chlorophyll pigments,
there are other pigments present
 During the fall, the green chlorophyll
pigments are greatly reduced revealing the
other pigments
 Carotenoids are pigments that are either
red, orange, or yellow
Stage of Photosynthesis
Redox Reaction
The transfer of
electrons from
another
Two types:
1. Oxidation is
2. Reduction is
one or more
one reactant to
the loss of ethe gain of e-
Oxidation Reaction
The loss of electrons from a
substance or the gain of
oxygen. (in this case splitting
of water using energy from
the sun)
Oxidation
6CO2 + 6H2O 
C6H12O6 + 6O2
glucose
Reduction Reaction
The gain of electrons to a
substance or the loss of oxygen.
(Carbon Fixation – building of
glucose)
Reduction
6CO2 + 6H2O  C6H12O6 + 6O2
glucose
22
Two Parts of Photosynthesis
Two reactions make up
photosynthesis:
1.Light Reaction or Light Dependent
Reaction –
Happens in the thylakoid
Produces energy from solar power
(photons) in the form of ATP and
NADPH.
Two Parts of Photosynthesis
2. Calvin Cycle or Light
Independent Reaction or Dark
Reaction
Happens in the stroma
Also called Carbon Fixation
Uses energy (ATP and NADPH)
from light reaction to make sugar
(glucose).
Factors Affecting Photosynthesis
The
amount of water
Temperature.
 Best
between 0 and 35 ºC.
Intensity
of light
The Concentration of CO2
Electron Carriers
 Electron
carriers are molecules that can
accept a pair of high-energy electrons and
later transfer them along with most of the
energy to another compound.
 Example:
 NADPH
– which carry the high-energy electrons
elsewhere in the cell.
 High
energy electrons are used to build a variety of
molecules the cell needs like glucose.
 Electron
transport chain: uses electron
carriers to pass electrons to other carriers,
releasing energy as they are transferred.
Light Reactions
 Requires
light
 Happens in the thylakoids of the chloroplast
 Produces ATP and NADPH and oxygen gas
by splitting water molecules.
 ATP
synthase is a membrane protein
(enzyme)
 Allows
H+ ions to pass through the cell
membrane in order to make ATP
 Overall result of the light reactions is the
conversion of light energy to chemical energy
stored in two compounds: NADPH and ATP
The Dark Reactions or LightIndependent Reactions
 Takes
place outside the thylakoid membrane
in the stroma.
 Uses ATP and NADPH from the light reactions
along with CO2 to produce glucose
 Carbon dioxide is broken and “fixed” into
glucose or fructose molecules in the CALVIN
CYCLE!
Stage of Photosynthesis
1.
2.
Chloroplast
Stroma