Photosynthesis
CA Biology Standards
Cell Biology
• Students know usable energy is captured from
sunlight by chloroplasts and is stored through the
synthesis of sugar from carbon dioxide.
Ecology
• Students know how water, carbon, and nitrogen
cycle between abiotic resources and organic matter
in the ecosystem and how oxygen cycles through
photosynthesis and respiration.
Photosynthesis
Chapter 8
1. Summarize how energy is captured from sunlight
during the light dependent reactions of
photosynthesis.
2. Analyze the function of electron transport chains
during the light dependent reactions of
photosynthesis.
3. Relate the Calvin cycle to carbon dioxide
fixation in photosynthesis.
4. Identify three environmental factors that affect
the rate of photosynthesis.
Photosynthesis Song!
Using the
Energy in
Sunlight
• Plants, algae, and some
bacteria capture 1% of the
sunlight that reaches earth and
convert it to chemical energy
through the process of
photosynthesis.
History of the Discovery of
Photosynthesis
The following people all contributed to the discovery
of photosynthesis.
• Van Helmont (1600’s)
• Priestley (1700’s)
• Ingenhousz (1779)
• Mayer (1845)
• Ruben and Kamen (1941)
• Melvin Calvin (1948)
• Rudolph Marcus (1992)
Jan van Helmont
• He wondered where the mass of
a tree came from- perhaps the
soil?
• To find out, he did an
experiment where he weighed a
seedling and a pot of soil. After
5 years, he reweighed them both.
• The soil was the same mass but
the tree had gained mass. Where
did it come from?
• He concluded it came from the
water!
Joseph Priestley (1700’s)
• He put a jar over a candle and found?
• The candle went out!
• But when he placed a living plant
under the jar with the candle, it stayed
lit longer. Why???
• The plant produced….OXYGEN!
Jan Ingenhousz
• He did the same experiment as
Priestley, but in the dark and in the
light.
• It only worked in the light, proving
that plants need light to make
oxygen!
What is the equation for
photosynthesis?
Photosynthesis Equation
Oxygen
What we breathe
6 CO2 + 6 H2O  C6H12O6 + 6O2
Carbon Dioxide
What we exhale
Water
Glucose
What we use for
energy
Photosynthesis is…
• The process where plants, algae and some
bacteria convert light energy into chemical
energy (glucose), using water and carbon
dioxide and releasing oxygen gas as a
byproduct.
Where does
photosynthesis
occur in a plant?
Usually in the
leaves, but
anywhere it is
green!
Photosynthesis
The raw materials of
photosynthesis, water
and carbon dioxide, enter
the cells of the leaf, and
the products of
photosynthesis, sugar and
oxygen, leave the leaf.
• Cross section of a leaf, showing the anatomical
features important to the study of photosynthesis:
stoma, guard cell, mesophyll cells, and vein.
• Water enters the root and is transported up to the leaves
through specialized plant cells known as xylem (pronounced
zigh-lem).
Land plants must guard against desiccation (drying
out) and so have evolved specialized structures
known as stomata to allow gas to enter and leave the
leaf. (stoma = singular; stomata = plural; Greek for
mouth)
Stomata
Consists of:
Stomatal
Opening and
2 Guard Cells
CO2
What
enters and
exits the
stomata?
• CO2 enters the leaf through the stomata.
• O2 exits the leaf through the stomata.
• H2O can also escape through the stomata,
especially on hot, dry days. This is called
transpiration, or the evaporation of water through
plants. So when it’s hot, the stomata close.
• Carbon dioxide enter the leaf through the stoma flanked by
two guard cells.
• Oxygen produced during photosynthesis can only pass out
of the leaf through the opened stomata.
How would
stomata closure
affect
photosynthesis?
When the stomata close, CO2 levels drop rapidly
within the leaf, inhibiting the light-independent
reactions.
This then causes photosynthesis to stop.
Stomata on a leaf of corn.
Stomata and Guard cells
LIGHT AND PIGMENTS
• Light has different
wavelengths.
• You can only see visible
light.
Visible spectrum
• Sunlight contains a
mixture of all the
wavelengths (colors)
of visible light.
• When sunlight passes
through a prism, the
prism separates the
light into different
colors.
Pigments
Pigments are light-absorbing
molecules which absorb only
certain wavelengths and reflect all
of the others.
Chlorophyll is
the pigment in
plants that
makes them
appear green.
GREEN is
reflected, while
all other colors
are absorbed.
Chlorophyll • Absorbs mostly blue and red light and
reflects green and yellow light.
• Thus, the plant looks green.
Carotenoids • Pigments in plants that absorb blue and
green light and reflect yellow and orange.
Autumn Colors
In the fall, as it gets colder, chlorophyll gets broken down
because photosynthesis can’t occur in the winter. Why?
• Water freezes!
• And if water freezes, it can’t do its part in photosynthesis.
Pigments are located in
the chloroplasts of leaf
cells
What are the little green dots?
Chloroplasts!
PLANT CELL
Chloroplasts
Inside a Chloroplast
CHLOROPLAST STRUCTURE
Thylakoids
• Are disk shaped structures
containing clusters of pigments
embedded in their membranes.
• This is where the LightDependent Reactions occur.
Great Animation of
Photosynthesis!
• http://www.fw.vt.edu/dendro/forestbiology
/photosynthesis.swf
Fun Overview of Photosynthesis
Animation
• http://www.pbs.org/wgbh/nova/methuselah/
photosynthesis.html
Photosynthesis Occurs in
Two Stages:
1. The Light-Dependent Reactions
(occur in the thylakoid membranes)
2. The Calvin Cycle
(occurs in the stroma)
Overview of The LightDependent Reactions
• Where do they
occur?
• What are they?
• The Thylakoid
Membranes where
there is chlorophyll!
• The light-dependent
reactions use water,
produce oxygen gas
and convert ADP and
NADP+ into the
energy carriers ATP
and NADPH.
Overview of The LightDependent Reactions
• What part of the
photosynthesis
equation is
involved?
• Water (H2O) is broken
apart for its electrons.
• Oxygen gas (O2) is
given off as a waste
product.
Glucose
STEPS OF THE LIGHT
DEPENDENT REACTIONS
1. Light strikes chlorophyll in the thylakoid membrane
and transfers solar energy to its electrons.
2. This energy transfer
from light
causes the electrons to
become “excited”.
3. These high-energy
electrons are
transferred to NADP+.
NADP+ is an energy carrier
molecule.
• It can accept high-energy electrons (e-)
from chlorophyll and become NADPH (the
negative electrons attract a hydrogen ion).
• This is how the energy from sunlight is
converted into chemical energy! COOL!
• But now chlorophyll is missing electrons…
• Where does it get more?
WATER!
Glucose
4. Water molecules are
split by
enzymes
to form electrons
(from the H atoms)
which the
chlorophyll takes to
replace lost e-’s.
5. Leftover oxygen
atoms from water
combine to make
oxygen gas.
6. Electrons begin to move along the Electron
Transport chain
6. Electron Transport chain
A. Hydrogen
ions move
into the
thylakoid and
become
concentrated
inside.
6. Electron Transport chain
B. Hydrogen ions
pass through
ATP synthase
(a protein in
the thylakoid
membrane)
which
catalyzes the
reaction where
a phosphate
group is added
to ADP to
become ATP!
ATP Synthase Animation
• http://www.stolaf.edu/people/giannini/flash
animat/metabolism/photosynthesis.swf
6. Electron Transport Chain
C. NADPH is
made by
adding H+ ions
to NADP+
Remember:
NADPH is an electron carrier that
provides the high-energy
electrons needed to make carbonhydrogen bonds in the third stage
of photosynthesis.
ATP is the molecule that provides
energy for the plant to make
glucose!
NADPH provides hydrogen
atoms for the plant to make
glucose!
Summary of Light dependent reaction
1. Pigments in the thylakoids of chloroplasts
absorb light energy.
2. Electrons in the pigments are excited by light
and move through electron transport chains in
thylakoid membranes.
3. These electrons are replaced by electrons from
water molecules, which are split by an enzyme.
4. Oxygen atoms from water molecules combine to
form oxygen gas.
5. Hydrogen ions accumulate inside thylakoids,
setting up a concentration gradient that provides
the energy to make ATP.
Light Dependent Reactions
Review of Light Dependent Reactions!
Pigment molecules absorb energy at which
stage of photosynthesis?
The beginning of the Light-Dependent Reactions!
At which stage of photosynthesis is light energy
stored as ATP and NADPH?
The end of the Light-Dependent Reactions!
At which stage of photosynthesis are excited
electrons passed along an electron transport chain?
Light-Dependent
Reactions!
Where do the light-dependent reactions occur?
The thylakoid
membranes!
What goes into the light-dependent reactions?
Light excites the electrons of chlorophyll.
Water is split to replace lost e-’s in chlorophyll.
ADP gets a phosphate group to become ATP.
NADP+ gets hydrogen ions to become NADPH.
What is produced in the light-dependent reactions?
ATP and NADPH go into the Calvin Cycle.
Oxygen gas is released into the atmosphere.
Light Reactions Animation
• http://www.johnkyrk.com/photosynthesis.html
Glucose
The Calvin Cycle!
What is it?
The Calvin Cycle
uses ATP and
NADPH from the
light-dependent
reactions and
CO2 from the air
to make highenergy sugars
(glucose)!
Glucose
Where does the Calvin Cycle occur?
The Calvin Cycle occurs in the stroma of the
chloroplast.
What parts of the photosynthesis equation
are involved in the Calvin Cycle?
CO2 is broken
down to create
glucose
(C6H12O6)
C6H12O6
Steps of the Calvin Cycle
Calvin Cycle
1. Six CO2 molecules enter the leaf through the stoma
and diffuse into the stroma. They are added to a 5
carbon compound by an enzyme.
2. They are split
into twelve 3carbon
compounds.
3. Energy from
ATP and
electrons from
NADPH are
used to convert
the 3-carbon
compounds
into 3-carbon
sugars.
Calvin Cycle
Calvin Cycle
4. Two of the resulting 3-carbon sugars is used to
make organic compounds – including GLUCOSE,
starch and sucrose – in which energy is stored for
later use by the organism.
Calvin Cycle
5. The other ten 3-carbon sugars are used to regenerate the
initial 5-carbon compound, thereby completing the cycle.
Review of Calvin Cycle
Where does the Calvin Cycle
occur?
• In the stroma of the chloroplast!
What goes into the Calvin Cycle?
• ATP and NADPH are used for energy
• CO2 is broken apart to create C6H12O6
Animation of Overview of
Photosynthesis
• http://wps.prenhall.com/wps/media/objects/
486/498596/CDA7_1/CDA7_1d/CDA7_1d.
htm
Photosynthesis is directly
affected by environmental
factors such as:
The intensity of light
2. The concentration of
carbon dioxide
3. Temperature.
Factors that
Affect
Photosynthesis 1.
PHOTOSYNTHESIS QUIZ
1.
2.
3.
4.
5.
6.
7.
15 points
Where in a plant cell does photosynthesis occur?
What are the 2 stages of photosynthesis and where do
they occur?
Why are plants green?
What is the balanced equation for photosynthesis?
What are the reactants and products of the light
dependent reactions?
What are the reactants and products of the Calvin
Cycle?
What are two reasons we depend on plants for our
survival?
Review
1. Summarize how photosynthetic organisms
capture the energy in sunlight.
2. Compare the roles of water molecules and
hydrogen ions in electron transport chains.
3. Describe the role of the Calvin cycle in
photosynthesis.
4. Critical Thinking Organizing Information
Make a table in which you identify the role of
each of the following in photosynthesis: light,
water, pigments. ATP. NADPH. and carbon
dioxide.
5. Critical Thinking Inferring
Relationships What combination of
environmental factors affects the rate of
photosynthesis?
6. Standardized Test Prep During
photosynthesis, plants store energy in
A ADP.
B carbon dioxide.
C 3-carbon sugars.
D water.
• What happens when a phosphate group is removed from an
ATP molecule?
Energy is released
• What happens to the electrons of a chlorophyll
molecule that are raised to a higher energy level
They enter the electron transport chain.
• Why does chlorophyll look green?
• Because it reflects green wavelengths of light.
• Because of photosynthesis the atmosphere is rich
in which gas?
• oxygen
Photosynthesis
• 1. Energy is captured from
sunlight
Photosynthesis
2. Light energy is
converted to
chemical energy,
which is
temporarily stored
as ATP and the
energy carrier
molecule NADPH
Photosynthesis
3. The chemical energy stored in
ATP and NADPH powers the
formation of organic
compounds, using carbon
dioxide, CO2.
photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
photosynthesis
6CO2 + 6H2O + light C6H12O6 + 6O2
At which stage of photosynthesis do the pigment
molecules absorb energy?
Stage 1 of photosynthesis
• Light energy is converted to chemical
energy by what process?
Photosynthesis
What is the major by-product of photosynthesis
which goes into the atmosphere?
Oxygen
photosynthesis
6CO2 + 6H2O + light  C6H12O6 + 6O2
• Plants use the organic
compounds to carry out
their life processes.
• Starch is stored in the
plant to be used later to
be broken down into
sugar and ATP.
photosynthesis
• ATP is used to
power
metabolism.
• All proteins,
nucleic acids
and other
molecules are
assembled from
fragments of
organic
compounds
being made into
sugar.