Photosynthesis
Essential Questions:
How does the process of photosynthesis store
energy?
What are the steps of Photosynthesis?
Why is photosynthesis important for life on
Earth?
Match the seed to its plant
1
A
3
2
B
C
The sequoia is the largest living thing on Earth!
But it starts as a TINY seed…
http://www.youtube.com/watch?v=vTx9
XHMG68Q&feature=PlayList&p=CED208
A405CBC700&index=1
How does this happen?
Where does the mass of a tree come from?
Brainstorm your idea and write it down!
Recap: Where does our energy
come from?
• We know that the source of all
energy comes from the SUN!
• Since we can’t eat sunshine to
get our energy, we must rely on
plants via a process called
photosynthesis.
– We can obtain their energy by
directly eating the plant.
– Or we can get energy indirectly
by eating other animals who got
their energy from eating plants.
Is photosynthesis
exothermic or endothermic?
Endothermic: Stores Energy!
Photosynthesis Overview
• Photo = light
• Synthesis = putting together
• Photosynthesis is the
process that plants use to
trap the sun’s energy and
build carbohydrates (called
glucose) that store energy
• Happens in 2 phases:
– 1) The Light (light-dependent)
reaction creates ATP, releases
Oxygen.
– 2) The Dark (light-independent)
reaction uses those ATP
molecules (from the light
reaction) to make glucose.
Overview of Photosynthesis
In which organ does photosynthesis take
place? Root, Stem, Leaf, Flower or Fruit?
The LEAF!
Where does photosynthesis occur?
• The top of the leaf is
where photosynthesis
occurs.
• The Chloroplast is
the cell organelle
where photosynthesis
occurs.
• In the chloroplasts are
pigments that
absorb wavelengths
of light.
Where are the
chloroplasts?
Thinking about where a chloroplast
lives is like giving directions to
where you live in your hometown.
The Chloroplast
Leaf
Mesophyll Cell
Chloroplast
Granum
Thylakoid
You
State
County
City
Neighborhood
House on Street
• Sunlight is made up of ALL
the colors together.
– Pigments reflect the color of
light that we see.
– They absorb the other colors.
• Look at the graph. Where is
absorption the lowest?
• Where is it the highest?
Chlorophyll (a and b) absorb all colors
except green so it is reflected!
That means chlorophyll absorbs a lot more light
than it reflects, which is a good thing!
Why do leaves change color in the fall?
• Remember- chlorophyll is
the pigment that captures
sunlight and what gives
plants their green color.
• In order for chlorophyll to
be produced, sunlight is
needed.
• Year round, many different
color pigments are
present, but the green
from the chlorophyll
prevents those colors from
showing through.
In Fall, trees
reabsorb chlorophyll
leaving the other
pigments visible!
CLICK HERE TO WATCH A TIME-LAPSE
OF A LEAF CHANGING COLOR!
Light-Dependent Reactions 1:2
• 1st stage of photosynthesis
requires light. (Light dependent)
• Light energizes electrons and are
passed from the chlorophyll to the
electron transport chain.
• The Electrons come from splitting
molecules of water.
• This process is called photolysis:
– Each water molecule supplies…
• ½ molecule of Oxygen gas
• 2 Hydrogen ions
• 2 Electrons
• ETC = series of proteins
embedded in the thylakoid
I’m free to
membrane of the chloroplast.
leave out
• As the electron passes on the
of the
chain between chlorophyll
stomata!
molecules, it loses a bit of energy
at each protein.
Light-Dependent Reactions 2:2
Haha!
What
am I?
• After the electron has passed
through the first chain, it
enters a second electron
chain so any e- (light)
energy isn’t wasted.
• A carrier molecule called
NADP+ is used (when with
an electron it binds with a
Hydrogen ion and becomes
NADPH.)
• Binds to the electron and
stores the energy from the
electron in a chemical form.
• NADPH plays a role in the
formation of Carbohydrates.
• Summary: Converts ADP
and NADP+ into ATP and
NADPH with Oxygen gas.
What happens to
plants when there is
no sunlight?
• Chlorophyll is “turned off.”
• Plants produce lots of glucose--enough to last
them through the night and several cloudy days.
• However, plants cannot store excess glucose.
– Instead, plants convert the excess glucose to starch.
– Starches are long term energy storage molecules
and make the cellular components of plants.
• like cellulose for their cell walls!
• When they need glucose for energy they
convert the starch back to glucose.
Light-Independent Reactions
• Does not need light! (Also
called the “Dark Reaction.”)
– Called the Calvin Cycle.
• Uses CO2 to form 6 Carbon
Sugars. (Carbohydrates)
• Takes place in the stroma of
the chloroplast.
• Called a Cycle because the
end products can be used
again to initiate the process.
• Uses the NADPH and ATP
produced in the earlier light
reactions.
– Otherwise the dark reaction could
not occur!
http://www.tracy.k12.ca.us/thsadvbio/animations/Photosynthesis.swf
Calvin
Cycle
• The Calvin cycle
uses the ATP and
NADPH from the
light dependent
reaction to create
sugar.
• Reactant:
Carbon Dioxide
• Product:
a 6 Carbon Sugar
Calvin’s in the
Dark about
Photosynthesis!
What’s the big deal about
Photosynthesis?
• The Calvin Cycle removes Carbon Dioxide from the Earth’s
atmosphere and creates sugars.
• Plants can use those sugars for food or to make larger
molecules like cellulose for growth and development.
• When we eat plants (or herbivores) eat plants, we use the
energy stored in the carbohydrates.
• A byproduct of our breathing is Carbon Dioxide, which is
used by plants for photosynthesis. It is also a greenhouse
gas contributing to global warming.
• Without plants to harvest the sun’s energy, there would be
no life for animals on Earth!
• Photosynthesis Song!
http://www.youtube.com/watch?v=R_17euLU_EM&feature=related
So, back to the
original question….
CLICK HERE
TO WATCH
THEM GROW!
• Where does the
mass of a tree
come from?
• Revisit your
original thought…
– Were you right?
– Are you surprised
by the answer?
Answer: The Mass of a tree comes from the Carbon
from atmospheric CO2 taken in during photosynthesis!
Gets converted into cellulose!
Activity: Photosynthesis Exit Ticket
• Complete the exit
ticket so I can assess
your understanding of
Photosynthesis.
• Make sure to write
down further
questions you have!
• Turn it into the box
before you leave
class today!