Photosynthesis
Chapter 8
YouTube - MY FAVE SONG: THE
PHOTOSYNTHESIS SONG
• 8-1 Energy of Life
All living things depend on energy.
• Everything thing they do requires
energy.
• To get energy, living things need
food. The energy in food
originally comes from the sun.
• Plants and some other organisms
are able to use light energy from
the sun to produce food.
• Organisms that make their own
food are called autotrophs.
“Auto-” means self.
“-troph” means food.
• Organisms that cannot use the
sun’s energy directly must obtain
energy from the foods they
consume (eat).
• Heterotrophs obtain energy from
the foods they consume.
• Hetero- means other.
• Energy is stored in chemical
compounds. One of the main
chemical compounds that cells use
to temporarily store and release
energy is adenosine triphosphate
(ATP).
• ATP consists of adenine, a
5-carbon sugar, and 3 phosphate
groups.
These 3 phosphate groups are the key
to ATP’s ability to store and release
energy.
• The bonds between the phosphate
groups of ATP can be broken.
When the last phosphate bond is
broken, a molecule of inorganic
phosphate leaves ATP forming
ADP (adenosine diphosphate).
ATP → ADP + Pi
This process releases energy that
the cell can use to do work.
• When a cell has energy available,
it can store small amounts of it
by adding a phosphate group to
ADP molecules, producing ATP.
• ATP has enough energy to power
a variety of cellular activities.
• Any activity that requires energy
can get what it needs by breaking
down ATP.
• Even though ATP is a great
source of energy, most cells have
only a small amount of ATP,
enough to only last them for a
few seconds of activity.
• So what we need is a compound
that can store lots of energy for
long periods of time!!!
• Cells have many molecules that
can store energy. One of it’s
favorites is glucose (sugar).
• Glucose can store 90 times more
energy than ATP.
• Cells can pull the energy from
compounds like glucose to make
more ATP.
8-2 Overview of Photosynthesis.
The most important process for
energy production is
photosynthesis.
Plants – YouTube
Spongebob photosynthesis - YouTube
• Plants (an other photoautotrophs)
use the energy of sunlight to
convert water and carbon dioxide
into high-energy sugars (like
glucose) and oxygen.
• The chemical equation for these
reactions is…
6CO2 + 6H2O  C6H12O6 + 6O2
All plants need is carbon dioxide from
the air, water from the soil, and a
little sunlight and they can make
food (glucose) and release oxygen.
• The energy from the sun travels
to Earth in the form of light.
• To us, the sunlight looks white
but it is actually a mixture of
wavelengths of light.
• We think sunlight is white
because all these wavelengths
blend together producing white.
• But each different wavelength
produces different colors.
• By breaking up light into its
different wavelengths we can see
the visible light spectrum.
• The colors of the rainbow…
ROY G BIV
• Let’s take a minute and break up
some light into its different
wavelengths (colors).
• Plants gather the sun’s energy
with special chemicals called
pigments.
• The main pigment in the leaves of
plants is chlorophyll.
• Pigments absorb and get energy
from certain wavelengths of light.
• Chlorophyll absorbs light in the
blue-violet and red regions of the
light spectrum.
• Chlorophyll cannot absorb the
energy from the green region of
the light spectrum so it reflects
this wavelength…
• This is why leaves look green!!!
Plants also contain red and orange
pigments (remember they reflect
those wavelengths) called
carotenes that help in absorbing
light energy.
• The reason we don’t usually see
these pigment colors in leaves is
because there are so much more
chlorophyll than these carotenes.
• We can usually only see them in
the fall when chlorophyll moves
out of the leaves.
• I feel another song coming on!!!
• Photosynthesis - They Might Be Giants - YouTube
8-3 The Reactions of Photosynthesis
Photosynthesis takes place inside cell
organelles called chloroplasts.
The cells in the leaves is where you are
going to find plenty of chloroplasts.
• If you look inside the doublemembraned chloroplasts you will
find flat saclike structures called
thylakoids.
• These sacs are stacked up in a
structure called
grana.
• The space between the thylakoids
is filled with a gel-like substances
called the stroma.
• Photosythesis is a two-part
process.
• Let’s look at the equation for
photosynthesis again…
Sunlight
6CO2 + 6H2O  C6H12O6 + 6O2
The goal is to make glucose. We
are going to need water and
carbon dioxide to pull this off
(and of course, sunlight).
In the first part of
photosynthesis we are going to
get the energy from the sun and
convert that to chemical energy.
It’s not until the second part of
photosynthesis that we actually
assemble glucose and store that
trapped energy in that molecule.
• The first part takes place in the
membrane of a thylakoid. Sunlight
and water need to be added.
• Since light is needed, this part of
photosynthesis is called lightdependent reactions.
• To understand the lightdependent reactions we need to
become acquainted with what
makes up the thylakoid membrane.
• The thylakoid membrane looks a
lot like the cell membrane with
embedded proteins. Two main
proteins (called photosystems) are
surrounded by chlorophyll.
• The photosystems are like solar
panels that absorb sunlight.
When light hits the photosystems,
the electrons in chlorophyll get
excited and begin moving.
• The light-dependent reactions
begin at Photosystem II.
• When the sunlight excites the
electrons in chlorophyll, these
moving electrons split two waters.
• Water is separated into oxygen
gas and the hydrogen are split up
into hydrogen ions (H+) and the
electrons.
• The hydrogen ions (H+) get dumped
into the inside of the thylakoid and
the electrons are sent to the
electron transport chain. Oxygen is
released out of the cell.
• The electron transport chain
(ETC) contain carrier proteins
that shuttle the electrons from
Photosystem II to Photosystem I.
• By the time the electrons get to
Photosystem I, they have run out
of energy so it’s time to add more
sunlight to get those electrons
excited again.
• After the electrons are excited
again they will continue down the
electron transport chain.
• When the electrons get to the
end of the chain, there is a
molecule of NADP+ waiting to
catch these electrons.
• When NADP+ catches the
electrons and a H+, it becomes
NADPH.
• This molecule is going to head to
the second part of
photosynthesis.
• In the meantime, a lot of H+
have built up inside the thylakoid.
Because of diffusion, these H+
want to move from an area of
high concentration to low
concentration (which would be the
outside of the thylakoid.
• As H+ move out through a special
protein called ATP synthase, ADP
and Pi are driven together forming
ATP. This ATP will head over to the
second part of photosynthesis too.
• Let me explain… no it’s too much,
let me sum up.
• During the light-dependent reactions
in photosynthesis, light energy is used
to split water, taking those electrons
through the ETC and giving them to
NADP+ forming NADPH.
• Also ATP is made by the movement
of H+ from the thylakoid space to the
stroma.
• Now we have two high-energy
molecules moving over to the lightindependent reactions.
ATP and
NADPH are
going to be
needed in the
second part of
photosynthesis
(Calvin cycle)
where glucose
(food) is going
to finally be
made.
• Clear as mud????
YouTube - Photosynthesis (Light Reactions)
• The second part of photosynthesis
is called the light-independent
reactions…
also known as the Calvin cycle.
• All the
reactions
involved in the
Calvin cycle
take place in
the stroma
(the jelly-like
substance in
the
chloroplasts).
• The Calvin Cycle does not require
light.
• It gets its energy from the ATP
and NADPH (products of the
light-dependent reactions).
• The Calvin cycle uses this energy
to produce high-energy sugars
(usually glucose).
• The Calvin cycle uses carbon
dioxide from the air to build a 6carbon sugar.
• It takes a total of 6 carbon
dioxides to make one molecule
of sugar.
• Let’s watch the Calvin cycle in
action!
• Calvin cycle - YouTube
• Let’s
try
to
model what
is happening here!
• Plants use the sugars to meet
their energy needs.
• When organisms eat plants, they
can also use the energy stored in
carbohydrates.
• The two sets of photosynthetic
reactions work together to
produce stable, high-energy
sugars from carbon dioxide,
water,
and sunlight.
• And in the process, release
oxygen for animals!
• Many environmental factors can
affect how well a plant can carry
out photosynthesis.
• A shortage of water can slow or
even stop photosynthesis.
• Many desert plants have adapted
to dry conditions.
• Temperature can also be a
factor. Because all the chemical
reactions that take place in
photosynthesis rely on enzymes,
these enzymes must be within a
certain temperature in order to
do their job.
• Too hot or too cold and
photosynthesis may stop all
together!
• The intensity of light also affects
the rate at which photosynthesis
occurs.
Increasing sunlight increases the
rate of photosynthesis (well, to a
certain point).
http://www.youtube.com/watch?v=cX
3Iev-JDgM
• Let’s Review!!
Let’s end with another song!
Photosynthesis Rap - YouTube