Photosynthesis
By C Kohn
Agricultural Sciences
In a nutshell…
O Photosynthesis is the process in which water and carbon dioxide
are converted into sugars and oxygen using the energy of the sun.
O Light energy is used to split a water
molecule in order to obtain the
hydrogen needed to power
ATP Synthase in the plant cells.
O ATP Synthase in the chloroplasts
of plant cells produces the ATP
needed to make glucose from both
CO2 and the hydrogen from water.
Source: phschool.com
O Key Points of Photosynthesis:
O Light energy is used to split H2O into H+ and oxygen
O H+ powers the production of ATP by ATP Synthase
O ATP is needed to power the creation of glucose from CO2 and H+
Photosynthesis in a nutshell…
●Sunlight is used to split water
into H+ and oxygen.
● H+ powers ATP Synthase.
● ATP powers the production of
glucose from H+ and CO2.
The Plant Cell
O We have already discussed several key cellular structures
including…
O The cell membrane:
protects the inside
of the cell
O The nucleus:
where DNA is stored
O The ribosomes:
protein factories
O The mitochondria:
ATP factories/cell power plants
Source: teamcarterlces.com
O Plant cells have two key structures that animal cells do not,
including…
O Chloroplast: where photosynthesis and glucose (sugar) production
occurs.
O Cell Wall: the rigid “candy shell” of a plant cell
Photosynthesis
O In order to photosynthesize, a cell NEEDS a chloroplast
O The only organisms that have chloroplasts in their cells
are plants and some kinds of algae
O These are the only organisms that can produce their own
sugars through photosynthesis.
O ALL other living organisms are dependent on
photosynthetic organisms for energy.
O They can only acquire energy through consuming
photosynthetic organisms directly or indirectly
Source: scq.ubc.ca
Source: teamcarterlces.com
The Chloroplasts
O Chloroplasts are organelles found inside the plant cell.
O Like the mitochondria, nucleus, and ribosomes, the chloroplasts are
a type of cellular organelle.
O Chloroplasts are not found in animals cells; only in plants & algae.
O Inside each chloroplast organelles are structures called
thylakoids that look like little green pancakes.
O The thylakoids are the thin green pancakes.
O Each “stack” of pancakes is called a grana.
O A grana is a “group” of thylakoids
O The empty space around the
pancakes is called stroma.
O If thylakoids are “pancakes”, stroma
is the “syrup”
O Thylakoids are “hydrogen barrels” –
they store the hydrogen protons (H+)
that power ATP Synthase.
O Their function is very similar to that
of the intermembrane space of the
mitochondria.
Source: withfriendship.com
Thylakoids vs. Intermembrane Space
O The inside of a thylakoid serves the same purpose as
the intermembrane space of the mitochondria.
O Both store hydrogen (H+) protons in order to power ATP
Synthase.
Thylakoids – green hydrogen pancakes
O Thylakoid organelles have a number of important molecules that
line their membranes, including...
O ATP Synthase: produces ATP when turned by the hydrogen protons
(H+) as they leave the inside of the thylakoid.
O Pigments: these are molecules
that absorb the energy of light
needed to separate H+ from water.
O Electron Transport System:
carries energy from light on
electrons (the “wires”) and moves
H+ into the thylakoid.
O NADP+: the “taxi cab” that
carries moves hydrogen.
O NADP+ is very similar to NAD+
in cellular respiration.
Source: 00leesa.blogspot.com
Chlorophyll Pigments
O Each thylakoid organelle is lined with light-absorbing pigments.
O The primary light-absorbing
pigment is called chlorophyll.
O Chlorophyll is what absorbs
the energy of the light
O This energy is needed to remove
H+ from water molecules
O Chlorophyll is also what makes
plants green.
O Chlorophyll absorbs red and blue
wavelengths of light and reflects
green wavelengths of light.
O “Chlorophyll is what makes plants
colorful”
Source: bio1100.nicerweb.com
Light Energy
O Photosynthesis is powered by the light energy absorbed by pigment
molecules in the thylakoid structures.
O Light energy is a kind of radiation.
O Radiation is any kind of energy that is emitted (moving)
O Radiation is energy that travels from one point to another
O All kinds of radiation are organized by the amount of energy found
in their photons
O A photon is simply a “bundle” of energy
O Visible light is part of the electromagnetic spectrum
O Electromagnetic spectrum: a way to compare all the kinds of radiation
that exist from strongest to weakest
O
X-rays and gamma rays have the most energy from their photons (which is why
they can do the most
damage to your body
and why you need that
lead apron for an X-ray).
Source: hyperphysics.phy-astr.gsu.edu
Radiation & The Light Bulb
O A light bulb is a good example of how radiation can change
depending on its strength of its photons.
O An incandescent bulb only uses 10% of it’s energy to produce
light.
O The other 90% is lost as heat.
O Most of the energy of the bulb is used to raise the temperature
until a strong-enough radiation can be produced to make visible
light.
O If an incandescent light bulb does not receive enough energy, it
will only produce weaker, non-visible kinds of radiation that our
eyes cannot detect.
O Similarly, a hot stove starts to “glow” as it gets hotter.
O The stove is producing radiation that is strong
enough to be detected by our eyes.
O When it cools, less radiation and weaker
radiation are given off.
Light Radiation
O The only way in which light radiation is different
from any other kind of radiation is that it has a
very specific amount of energy in its photons.
O Our eyes and structures in plant cells can only
detect visible light because they are adapted to
this specific range of energy.
O Just like we cannot hear a dog whistle because that
type sound cannot be detected by our ears, we
cannot “see” other forms of electromagnetic
radiation that are not visible light.
O The range of energy found in light is powerful
enough to power photosynthesis but weak
enough to not cause damage to cells.
O If cells were exposed to any radiation more powerful
than light (e.g. ultraviolet rays), they would have
problems (e.g. mutations, skin cancer, etc.).
Source: http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Split Water Molecules
O The light energy that is absorbed by the
chlorophyll pigments is used to split a
water molecule (H2O)
O
H2O is split into 2 H+’s and an
oxygen atom
O The oxygen atom pairs with another
oxygen atom and is released as O2
O This is where the oxygen released
by plants comes from
O The only reason plants
need sunlight for photosynthesis
is to provide the energy needed to
split the hydrogen from the oxygen
in water.
O
O
The H+ protons are used to power
ATP Synthase
ATP Synthase makes ATP.
O ATP powers the production of sugar from
CO2 and the H+ from water.
Source: phototroph.blogspot.com
Steps in Photosynthesis
O Photosynthesis can be broken down into 3 steps:
O Photosystem II: light energy is absorbed and used to
remove hydrogen from a water molecule so that H+ can
be used to power ATP production.
O This ATP is used to power the combination of
CO2 and H+ into glucose.
O Photosystem I: ATP Synthase is powered
by H+ from the thylakoid, making ATP.
H+ is carried from ATP Synthase by
NADP+ so that it can be combined
with CO2 in order to form glucose.
O Calvin Cycle: CO2 is absorbed and
combined with H+ to produce G3P
and then glucose.
O This process is powered by ATP from
Photosystem II
O G3P is a 3-carbon molecule that is a
building block for all other plant
molecules.
Source: bio1100.nicerweb.com
Steps of Photosystem II
O Step 1: Light is absorbed by chlorophyll and other pigments.
O Primarily red and blue wavelengths are absorbed. Green is reflected
O Step 2: Photons from light excite
electrons in the pigments.
O This energy is used to split a water
molecule into hydrogen protons and oxygen.
O Step 3: Hydrogen protons (H+) are
stuffed into a thylakoid and power ATP
production
O H+ protons do this by moving
through ATP Synthase to get out of
the thylakoid and into the stroma.
O ATP Synthase then turns, producing ATP
O Oxygen atoms bind to each other
and are released from the plant
as O2
Source: hyperphysics.phy-astr.gsu.edu
Steps of Photosystem I
O Step 1: Hydrogen leaves the thylakoids through ATP
Synthase after powering the production of ATP, making
ATP
O Step 2: Hydrogen protons are added to a NADP+ (the
hydrogen taxi) to form NADPH
O Step 3: NADPH moves
to the stroma
O In the stroma the H+
can be added to CO2
to form glucose during
the Calvin Cycle.
Source: hyperphysics.phy-astr.gsu.edu
Steps of the Calvin Cycle
O Step 1: CO2 is absorbed into the stroma (empty space) of the
chloroplast organelles.
O Carbon is separated from the two oxygen molecules.
O Oxygen is released as O2
O Step 2: The lone carbon is combined with a 5-carbon molecule called
Rubisco to form an intermediate 6-carbon molecule.
O Step 3: The 6-carbon molecule is split
to form two G3P molecules
O G3P is the precursor to all plant
molecules (sugars, amino acids,
lipids, etc.)
O Step 4: (not shown) One of the G3P’s joins
a second G3P to form glucose.
O The other G3P reforms the
Rubisco enzyme
Source: methuen.k12.ma.us
The Calvin Cycle is powered
by ATP (not shown)
Calvin Cycle
1. CO2 is absorbed.
Carbon is separated from
oxygen. O2 is released.
2. The carbon atom
separated from CO2 is
combined with 5-carbon
Rubisco.
3. The 6-carbon molecule
is split into two 3-carbon
molecules (G3P). One G3P
is used to make sugars or
other plant molecules. The
other is paired with 2
carbon atoms to re-make
Rubisco.
Click for explanations
Photosynthesis (PSI, PSII, & Calvin)
Calvin Cycle: CO2
combines
with
Rubisco to make 2
G3P’s. and then
glucose sugar. H+
atoms are added
to the glucose
molecule.
Photosystem II: light energy
is used to split water; the
H+ is used to power ATP
production in ATP Synthase
Photosystem I: ATP is
made; H+ is picked up by
NADP+ to form NADPH. It
is taken to the stroma to
be added to CO2 to make
glucose.
Photosynthesis in a nutshell…again
Photosystem II: light energy
is used to split water; the
H+ is used to power ATP
production in ATP Synthase
Photosystem I: ATP is
made; H+ is picked up by
NADP+ to form NADPH. It
is taken to the stroma to
be added to CO2 to make
glucose.
Calvin Cycle: CO2
combines
with
Rubisco to make 2
G3P’s. and then
glucose sugar. H+
atoms are added
to the glucose
molecule.
The Cycle of Respiration &
Photosynthesis
O When glucose is broken
down in respiration, CO2
and H2O are produced.
O CO2 and H2O are used to
produce glucose and
oxygen during
photosynthesis.
O These two processes are
cyclical – the leftover
products of one process
are the precursors of
another.
Source: terra.dadeschools.net
Summary
O The chloroplast is an organelle found in plant cells; it is
where photosynthesis occurs.
Chloroplasts have structures inside that include:
O Thylakoids – where H+ is stored; ATP Synthase is found
on the membrane of the thylakoids
O The thylakoids have the same function as the
intermembrane space of the mitochondria
O Grana – a group (or ‘stack’) of thylakoids
O Stroma – the empty space around the thylakoids; it is
where the manufacturing of the glucose molecule
occurs.
Summary
O Thylakoid membranes are lined with chlorophyll pigment.
O This pigment absorbs sunlight.
O The energy from light is needed to separate hydrogen from
oxygen in an H2O molecule.
O Chlorophyll absorbs red and blue light but reflects green light.
O Light is a form of radiation (moving energy).
O Radiation can be categorized based on the amount of energy
found in its photons (bundles of energy).
O The electromagnetic spectrum a way to compare all the kinds
of radiation that exist from strongest to weakest
O Plants use visible light to power photosynthesis because it is
strong but not so strong that it would cause cellular damage.
Summary
O Photosynthesis can be broken down into 3 steps:
O Photosystem II: light energy is absorbed and used to remove
hydrogen from a water molecule so that H+ can be used to power
ATP production.
O This ATP is used to power the combination of CO2 and H+ into glucose.
O Photosystem I: H+ leaves through ATP Synthase (making ATP) and
is carried from ATP Synthase by NADP+ so that it can be
combined with CO2 in order to form glucose.
O Calvin Cycle: CO2 is absorbed; its carbon is added to 5-carbon
Rubisco and then combined with H+ to produce G3P and then
glucose.
O This process is powered by ATP from Photosystem II
O G3P is a 3-carbon molecule that is a building block for all other plant
molecules.
O The products of photosynthesis (oxygen and glucose) are used in
respiration to make ATP. The byproducts of respiration (CO 2 and
H2O) are used in photosynthesis to produce glucose and oxygen.