8.2 Photosynthesis
Pages 222-227
More on ATP
• Cells Have Enough ATP To
Last For A Few Seconds
• ATP must constantly be
made
• ATP Transfers Energy
Very Well
• ATP Is NOT Good At
Energy Storage
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3
Glucose
• Glucose is a
monosaccharide
• C6H12O6
• One Molecule of glucose
Stores 90 Times More
Chemical Energy Than
One Molecule of ATP
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4
Photosynthesis
• Photosynthesis is the process of turning light
energy into chemical energy!
Chemical Equation
http://www.youtube.com/watch?v=mpPwmvt
DjWw
Photosynthesis
Photosynthesis occurs in TWO phases.
1. Light-dependent reactions
2. Light-independent reactions (dark reactions)
Remember the “reactants”…….
1. Carbon Dioxide (CO2)
2. Water (H20)
3. Energy (sunlight)
Where do the reactants come from?
• CO2 (a gas) is in the atmosphere and enters
the plant through small openings on the back
of leaves called stomata.
The stomata is
where gas
exchange occurs.
CO2 in; O2 out
Where does everything come from?
• Water (H20)
comes from the
soil absorbed by
the plants roots.
Where does everything come from?
Light energy
comes from the
sun and is
captured by
chloroplasts.
Chloroplasts
• Chloroplasts capture light energy and are
found mainly in the LEAVES.
!REVIEW!
What are the 3 reactants and how do they get
into a plant?
1. WATER----The roots
2. Carbon Dioxide---The stomata
3. Light---The chloroplast.
Is photosynthesis catabolic or anabolic??
What organelle does photosynthesis
take place in?
Chloroplast
Inside the chloroplast.
• thylakoids – saclike
photosynthetic
membranes
• grana – stacks of
thylakoids
• stroma – space outside
the thylakoids
The spectrum of visible light
Energy from the sun travels to Earth in the form of
light. Sunlight is a mixture of different
wavelengths of light – many of these are visible
to your eyes.
How plants obtain energy
Thylakoids have light-absorbing
colored molecules called
PIGMENTS
•
•
•
•
Chlorophyll a & b = blue/green
Xanthophyll = yellow
Carotenoids = orange/red
Anthocyanin = red/purple
• The most common pigment is chlorophyll,
which gives plants their green color.
Plants don’t need green
light to make food, so it
is reflected
– which is why plants
are green!
• Plants absorb red and blue light from the sun to make food
during photosynthesis
• Plants don’t need green light to make food, so it is reflected
– which is why plants are green!
So…the best wavelengths of light for plant growth are
red and blue
while the worst wavelength of light for plant growth is
green.
• Ok… now we have all the reactants….Lets
make some SUGAR!!
up!!
The Two Phases of Photosynthesis
• Phase I - Light Dependent Reaction
(occurs in the thylakoids)
– Light energy is absorbed and TRANSFORMED to
chemical energy (ATP and NADPH molecules)
Rember Chemical energy is ATP!!
Light Dependent Reaction
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22
Light Dependent Reaction
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23
What you NEED to Know!
• At the end of Phase I, the plant
has made
1.ATP (energy)
2.NADPH (electron carrier)
3.O2 (oxygen)
• Phase II – Light Independent Reaction (or the
Dark Reaction/Calvin Cycle) (occurs in stroma)
– NADPH and ATP that were formed during light
dependent reactions are used to make glucose
How plants transform energy
Calvin Cycle converts carbon dioxide into sugar
using the NADPH & ATP energy from the lightdependent reactions.
The
enzyme
Rubisco
also helps!
Light Independent Reaction
(The Dark Reaction)
(Calvin Cycle)
1.ATP and NADPH contain a high
amount of energy, but are short
stores (no longer than a few
minutes).
2.So plants use the ATP and NADPH to
build GLUCOSE which can be stored
for a longer time.
The Calvin Cycle
1. Does not require light.
2. 6 carbon dioxide molecules are
required from the atmosphere
3. ATP & NADPH powers the cycle
Not On FIB write down
• The Enzyme Rubisco helps build the glucose
molecule during the Calvin cycle.
Reactants & products
1.The Calvin Cycle uses 6 molecules of
CO2 to produce a single 6-Carbon
sugar molecule called glucose.
2.Uses for sugars include: form starches
& cellulose. When other organisms
eat plants, they can also use the
energy stored in carbohydrates.
Summary of Photosynthesis
Light Reactions
• Inputs:
Light
Water
• Outputs:
ATP
NADPH
Oxygen (O2)
OCCURS IN THYLOKOID
Dark reactions (Calvin cycle)
• Inputs:
◦ ATP
◦ NADPH
◦ CO2
• Outputs:
◦ Sugars
OCCURS IN THE STROMA
• Light reactions
Thylakoid
Summary
Calvin Cycle
Stroma
Glucose
Light-dependent reactions
Light-independent reactions
Let’s review…
What materials come into the chloroplast
that are used in the light-dependent
reactions?
What material comes into the chloroplast
that is used by the Calvin Cycle?
What material moves out of the chloroplast
from the light-dependent reactions?
What materials move out of the chloroplast
from the Calvin Cycle?
What materials move from the lightdependent reactions to the Calvin Cycle?
What materials move from the Calvin Cycle
back to the light-dependent reactions?
Factors affecting Photosynthesis
● Water
- shortage can slow or even stop photosynthesis
- plants living in dry areas have a waxy coating to
prevent water loss
● Temperature
- enzymes used in photosynthesis function best
between 0°C and 35°C
- high or low temps slow down or stop photosynthesis
● Intensity
of light
- increasing light intensity increases the
rate of photosynthesis
- plants eventually reach their maximum
rate of photosynthesis
And Now……….
• THE PHOTOSYNTHESIS RAP!
• http://www.youtube.com/watch?v=pE82qtKS
SH4&safety_mode=true&persist_safety_mode
=1&safe=active
Chapter
8
Cellular Energy
8.2 Formative
Questions
Where in the plant cell does photosynthesis
take place?
A. chloroplasts
B. Golgi apparatus
C. mitochondria
D. vacuoles