Using light to make food.
Life depends on photosynthesis.
What would happen in the sun just “turned off” one
How would this affect cellular respiration?
Photosynthesis is the basis of all life on this planet.
All energy you eat comes from the sun through
New technologies are using photosynthesis in energy
production, food production, and in climate change
The equation for photosynthesis.
6CO2 + 6H2O → C6H12O6 + 6O2
Light energy is inorganic, and can’t be used by
organisms to perform cellular work.
The kinetic energy in light is converted into potential
energy of sugars, which is an organic source of energy.
The carbon in carbon dioxide (an atmospheric gas) is
converted to sugars.
Between the six carbons are chemical bonds.
How do organisms get energy?
Autotrophs are the “producers” of a system.
These are called the “self feeders.”
There are two main types:
Chemo-autotrophs get their energy from chemicals.
Photo-autotrophs get their energy from sunlight.
Heterotrophs are the “consumers” of a system.
These are called “other feeders.”
Must get organic energy from other organisms.
Examples of autotrophs:
This is a “pool” of
This plant is performing
producing oxygen gas.
Examples of heterotrophs:
A shark wanting to give you a kiss.
A lonely cat wanting to make a friend.
These organisms get their energy from other living creatures.
Where did this energy come from?
In plant cells, photosynthesis occurs in
chloroplasts, located within plant cells.
Know the structure of a chloroplast, and be
able to compare it to a mitochondria.
Terms to ponder:
Be able to draw and label a chloroplast.
Outer and inner
How atmospheric is oxygen made?
6CO2 + 6H2O → C6H12O6 + 6O2
Scientists once thought that carbon dioxide,
when split, produced our oxygen.
Experiments found that water is actually the
source of the oxygen which you breath.
Do you remember oxidation and reduction
Photosynthesis is a redox reaction.
Carbon dioxide is reduced into sugars.
Water is oxidized into molecular oxygen.
If you think about it, the electrons in carbon
dioxide are placed into sugar, which we use
Scientists always pondered the question of how
First evidence of the evolution of photosynthesis
dates to about 3 billion years ago.
What was the impact of photosynthesis on Earth?
Decreased atmospheric CO2 levels.
Lowered global temperature.
Increased atmospheric O2 levels
This created an aerobic environment which changed life forever.
It took quite a while for photosynthesis to result in
an increase in atmospheric oxygen.
Once this happened, the world’s environment changed.
A quick overview of photosynthesis:
Sunlight enters the
chloroplast, splitting water,
and making O2.
ATP and NADPH are
This is the link between
sunlight and sugar.
The Calvin cycle captures
CO2, and using ATP and
NADPH, makes sugars.
When you look at something, how do you see it?
What you “see” is light bouncing off.
What is light?
Light is made of small particles called photons.
It’s the photons which contain the kinetic energy
needed to drive photosynthesis.
Plants look “green” because the green and
yellow wavelengths are bounced off.
Notice that the other colors
Blue/reds are used the best
Because of their
The Electromagnetic Spectrum
All energy is located within
the EM spectrum.
Visible light is only a small
fraction of this energy.
Purple light has more energy
than red light.
Its this energy, which is on
this spectrum, which is
harvested to make sugar.
“Photosystems” capture light.
Photosystems are located within
thylakoid membranes of the
They contain pigments, which capture
This is the main pigment.
Accessory pigments help
chlorophyll a do its job.
Capture other frequencies.
This is chlorophyll a:
You don’t need to know this
structure, just understand that this
is the primary pigment used in
photosynthesis. The accessory
pigments help Chlorophyll a do its
Notice that the accessory pigments expand the
light waves which are captured.
Look at the wavelength for
chlorophyll a only.
Which frequencies are easiest for
it to absorb?
Which are more difficult?
Now look at the other pigments:
How do they “help” chlorophyll
a do its job?
Do they make photosynthesis
more or less efficient?
Photosynthesis is a two step process:
Occur in the thylakoid membranes.
Occur during the daytime (why?).
Split water, make O2, ATP, and NADPH.
Occur in the stroma anytime (day or night).
Use CO2, ATP and NADPH to make sugar.
These “depend” on light, and
only occur when light is
They capture photons, split
water, and send the electrons
down an ETC.
At the end, an ATP and an
NADPH is made.
The kinetic energy of sunlight
is now trapped as potential
Why two photosystems?
Only type found in bacteria.
Only photosynthesis for 1 billion years.
Makes ATP only.
Makes ATP, O2, NADPH.
Increases the amount of sunlight used.
Light-independent reactions (Calvin cycle)
These reactions occur in the stroma.
These reactions actually make sugar.
By using the ATP and NADPH
They occur all day and night, taking
Three carbons enter (as CO2), and
three carbons exit (as PGAL).
Each turn takes 9ATP and 3NADPH.
This cycle takes two turns to make
Things to ponder:
What would happen to the amount of CO2 in the atmosphere
if photosynthesis stopped?
When carbon dioxide gets trapped as sugar, and the buried,
what happens to this carbon?
When carbon is trapped (buried), what happens to the carbon when
we dig this up (as fossil fuels) and burn them?
What would happen if you placed a plant into a building that
only allowed in green light waves?
Not all plants are equally efficient.
Some use more light than others.
Most are 0.10% efficient.
This is 1/10 of 1%. Not efficient at all.
Photosynthetic efficiency depends on:
Amount of sunlight (winter?)
Temperature (cold vs. hot)
Water availability (desert?)
How do plants deal with their inefficiency in
Plants first appeared in water, and migrated onto land,
eventually adapting to even the most extreme terrestrial
environments of the deserts.
In order to do this, plants evolved three different photosynthetic
As plants get hot, they close their stomata to prevent water
However, this increases oxygen levels.
The enzyme in the Calvin cycle (Rubisco) uses O2 instead of CO2.
This is called photorespiration (consuming O2 and releasing CO2).
This can severely slow down sugar production.
Found in all plants. The most ancient form of photosynthesis.
This is what we have been discussing up to this point.
Other types of photosynthesis.
Evolved hot and dry environments.
Instead of a 3-carbon molecule, they produce a 4-carbon.
Closes its stomata, but can still make sugars.
Contains mesophyll cells.
Enzymes have a high affinity for CO2, and can obtain it even when
concentrations are low.
The four-carbon molecule acts as a “shuttle” of carbon.
Also contains bundle sheath cells.
Receives the four-carbon “shuttle” molecule, releasing CO2, making sugars.
These plants include grasses, like sugarcane.
Evolved much later, in hot, dry environments.
Evolved in cactus, succulent plants, pineapples, and many of our local
species like buckwheat and sage.
Conserves water by opening its stomata only at night.
CO2 is stored in a “bank” at night, and released during the day
This process is found in all
G3P is used to make sugars.
When it gets hot, plants close
This prevents water loss.
But also prevents CO2 and O2
This can cause photorespiration.
No CO2 intake, therefore
photosynthesis shuts down.
Evolved in hot/moist tropical
C4 in mesophyll cells.
C3 occurs in bundle-sheath cells.
C4 plants use half the water that
0.4% of all known plants are
Examples: Corn, millet, sugarcane,
Crassulacean Acid Metabolism
The most extreme plant adaptation.
Found in very hot/dry environments (like the desert).
Stores CO2 at night.
Close stomata during daytime.
Forms a carbon “bank” of organic acids.
Stores acids in the central vacuole.
10% of all plant species.
Cacti, succulents, sage, buckwheat.
A comparison of all three types.
Plant Adaptation Table
Answer the following questions, and turn
them in at your next lecture.
1, 2, 4, 5, 6, 8, 9, 10, 14.
Wow! That’s it!
Make sure to read your text…
Some of this may be confusing at first.
This is the end of the material for the first lecture exam!
Think of how plants make sugar.
Why is photosynthesis important?
How does this affect your life?