Photosynthesis
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What is the function of chloroplasts
within photosynthetic organisms?
Photosynthesis is the process by which light
energy is changed into chemical energy that is
both storable and useable.
Sunlight Energy
Rich Organic Molecules
Biochemical Pathways are series of chemical
reactions in which the product of one reaction
becomes the reactants for the next reaction.
Phototrophs are organisms that use
photosynthesis.
H2O + CO2
O2 + C6H12O6
Cell Respiration Equation:
Photosynthesis Equation:
Photosynthesis is divided into the Light and Dark
Reactions.
The Light Reaction depends on the absorption
of light to drive it.
Thylakoids:
(1) flattened membrane sacks found in groups called
grana within chloroplasts
(2) where the light reaction occurs
Stroma:
(1) the liquid that surrounds the grana within the
chloroplasts
(2) analogous to the matrix of the mitochondria
(3) where the dark reaction occurs
Fig. 6-17
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
0.1 µm
Visible spectrum - Light which can be seen by the human
eye. It is also the portion of the electromagnetic spectrum
that is used to drive photosynthesis
Wavelength indicates the strength of a photon of light. Short
wavelength = high energy; long wavelength = low energy
Pigments absorb light at one wavelength or more.
Chlorophyll
Pigment found in chloroplasts which is responsible
for absorbing light to excite electrons
There are three types (A, B, and C) found in
different organisms
Accessory Pigments - pass absorbed light energy over
to chlorophyll to be further converted into chemical energy
Carotenoids are red, orange, or yellow pigments
Phycobins are pigments used in algae and
bacteria
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1. What does sunlight do in photosynthesis?
2. How many photosystems do plants and cyanobacteria have
and how are they organized?
3. What is different about the origin of electrons in bacterial
and plant photosynthesis?
4. What are the similarities between this part of
photosynthesis and the electron transport chain?
5. What is the role of photosystem II? How does that role
compare with the role of photosystem I?
Question of the Day!!
If glucose is broken down for energy in respiration,
is carbon dioxide broken down for energy in
photosynthesis?
Procedure: Your task is to use the simulation to determine
how wavelength and intensity affect the rate of
photosynthesis (and the production of ATP). Keep in mind
you are dealing with two variables, so in order to determine
absolutely how each factor affects photosynthesis, you must
keep one variable constant while manipulating the other
variable.
http://www.mhhe.com/biosci/ge
nbio/biolink/j_explorations/ch09
expl.htm
Lab Report must contain the following typed sections.
1. Introduction: Describe briefly the light dependent reactions and propose a hypothesis
to answer the experimental question.
2. Data: Include data tables for the simulation. The tables must show clearly trends
resulting from changes of intensity and changes of wavelength. Multiple data tables
would probably be best here. In Microsoft Word, use the "table" function to organize
your data.
3. A graph showing how the percentage of ATP changed (Y axis) as a result of changes
in wavelength and intensity (X axis). Two graphs would be best here.
4. Conclusion: Use your data to answer the experimental question. Answer clearly how
light wavelength affects the reaction, and how light intensity affects the
reactions. Offer an explanation of the results, taking into account the principles of
photosynthesis and the light reaction.
The light reaction of photosynthesis:
(1) produces the energy needed to assemble
sugars in the dark cycle
(2) is similar to the ETC from cellular respiration
(3) “extracts” electrons from water by splitting it
apart
The reactions within the light reaction look like:
(1) 2 H2O → 4 H+ + 4e- + O2
(2) ADP + Phosphate → ATP
(3) NADP+ + H+ + 2e- → NADPH
Enzymes close to Photosystem II break apart
water. The electrons move through/along the
photosystems and the hydrogen ions are pumped
during ETC and back through ATP synthase.
Pyruvate
Gylcolysis
ATP
Glucose
NAD+ &
FAD
Light
Reaction
NADH
NADP+ &
ADP
NADPH &
ATP
Dark
Reaction
CO2
Krebs
Cycle
NADH
&
FADH2
O2
ETC
Fig. 10-7
Light
Reflected
light
Chloroplast
Absorbed
light
Granum
Transmitted
light
The light reaction is separated into two
photosystems that occur in order. Both
systems are embedded within the thylakoid
membrane.
A chlorophyll reaction array is the place where
light energy excites electrons.
Photosystem II (the first one!?!?) contains a
chlorophyll reaction array, carrier proteins
(hydrogen pumps), and ATP synthase.
Photosystem I (the second one) contains a
chlorophyll reaction array and an enzyme
that makes NADPH.
Fig. 10-14
e–
ATP
e–
e–
NADPH
e–
Mill
makes
ATP
e–
n
Photo
e–
Photon
e–
Photosystem II
Photosystem I
Fig. 10-17
STROMA
(low H+ concentration)
Cytochrome
Photosystem I
complex
Light
Photosystem II
4 H+
Light
Fd
NADP+
reductase
NADP+ + H+
NADPH
Pq
H2O
THYLAKOID SPACE
(high H+ concentration)
e–
1
e–
1/
Pc
2
2
3
O2
+2 H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
STROMA
(low H+ concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
Photosystem II:
(1) Enzymes in the thylakoid membrane capture
and break apart water into hydrogen ions,
electrons, and oxygen.
(2) An electron pair that was passed to
chlorophyll and excited by a photon of light
is handed over to proteins similar to ETC.
(3) Hydrogen ions are pumped across the
membrane creating a gradient that is used
to make ATP via movement through ATP
synthase.
(4) Two oxygen ions bond to create O2 which is
released by the plant into the atmosphere.
It’s Time for Draw-rings!
Student drawings must include
(1) an enzyme for splitting water
(2) two chlorophyll reaction arrays
(3) one hydrogen pump (ETC)
(4) ATP synthase
(5) the reactants and products of splitting water
(6) the reactants and products of making ATP, and
(7) an arrow-trail or something that relates the path of an electron.
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Why do plants need water?
Question of the Day!
Why does a plant make sugar in photosynthesis as
opposed to
another type of molecule, like ATP?
The energized electrons each move from
Photosystem II to Photosystem I by traveling
down the electron transport chain. The electron
transport chain pumps H+ across the thylakoid
membrane to the inside using energy lost by
the electron. This strengthens the concentration
and charge gradient across the thylakoid
membrane.
The Calvin Cycle is also called the dark reaction.
It uses the ATP and the NADPH from the light
reaction to make a more storable and stable
energy rich molecule, sugar.
Fig. 10-16
Mitochondrion
Chloroplast
MITOCHONDRION
STRUCTURE
CHLOROPLAST
STRUCTURE
H+
Intermembrane
space
Inner
membrane
Diffusion
Electron
transport
chain
Thylakoid
space
Thylakoid
membrane
ATP
synthase
Stroma
Matrix
Key
ADP + P i
[H+]
Higher
Lower [H+]
H+
ATP
1. The Calvin Cycle “starts” as 6 five-carbon chains and
6 single carbon molecules in the form of carbon
dioxide come together to form 12 three carbon
chains.
2. The energy from 12 ATP being turned into 12 ADP
and from 12 NADPH being turned into 12 NADP+ is
absorbed to create higher energy levels in the 12
three-carbon molecules
3. Two of the 12 three-carbon molecules come together
to form one single sugar molecule that will leave the
system for storage.
4. The remaining 10 three-carbon molecules will then
take the energy from 6 more ATP breaking down
into ADP and reconfigure into 6 five-carbon
molecules.
5. The five carbon molecules that are left at the end
reenter step one with 6 new CO2 molecules and that
completes the cycle
Fig. 10-18-1
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
3P
Ribulose bisphosphate
(RuBP)
P
6
P
3-Phosphoglycerate
Fig. 10-18-2
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
P
3P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
6 NADP+
6 Pi
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
Fig. 10-18-3
Input 3
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
All fuel sources are recycled between the light
and the dark reaction. ATP made in the light
reaction is used in the Calvin Cycle and the
ADP returns to the light reaction, Similarly,
NADPH made in the light reaction is used in the
Calvin Cycle and NADP+ then returns to the
light reaction where it can regain its hydrogen
and electrons.
The Calvin Cycle is also known as the Dark
Reaction but does not occur only at night. It
occurs at all times and in fact slows down at
night due to a decrease in available fuel from
the light reaction
Fig. 10-21
H2O
CO2
Light
NADP+
ADP
+ P
i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin
Cycle
G3P
Starch
(storage)
Chloroplast
O2
Sucrose (export)
It’s Time for Draw-rings!
Student drawings must include
(1) an enzyme for splitting water
(2) two chlorophyll reaction arrays
(3) one hydrogen pump (ETC)
(4) ATP synthase
(5) the reactants and products of splitting water
(6) the reactants and products of making ATP, and
(7) an arrow-trail or something that relates the path of an electron.
Procedure
Day 1
Each lab group will get:
• one plant (that has been kept in the dark for 24 hours)
• four clear plastic squares slightly larger than the leaf
• paper clips
• two paper cut outs and/or film negatives smaller than the leaf
• scissors
• clear tape
1. Take one paper cut out and tape it to one side of the clear plastic square.
Then take the other paper cut out and tape it to one side of another clear
plastic square.
2. Cut out a large leaf shaped whole in the two other plastic squares
3. Take one plastic square with a cut out on it and one plastic square with a
hole cut out of it and use the paper clips to sandwich the leaf between
both squares. The square with the hole cut out goes on the underside of
the leaf and the square with the cut out goes on the upper side of the
leaf. Repeat this step on another leaf using the other two squares.
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
Day 2
Materials:
•
•
•
•
•
•
•
hot plate
ethanol
beakers
tweezers or tongs
paper towels
iodine solution
aluminum foil
1. Carefully remove the plastic squares from the plant
2. Cut the leaf from the plant.
3. Hold the leaf with forceps, tweezers or tongs, and
drop it in a beaker of boiling water to kill the cells.
4. Place it in a beaker of hot ethanol for two minutes to remove most of the
chlorophyll.
5. Place it in a beaker of room temperature ethanol for one minute. The leaf
should be almost white.
6. Blot the leaf on paper towels
7. Place the leaf in iodine solution on a square of aluminum foil for one minute
or less. Remove it when you can see the picture. Remove both the leaf and
the foil together and place in water to rinse. You may blot the
leaf and
press it in a book if desired.
Make a prediction for how you think the leaf will look at the end of the
experiment.
1. Why are certain parts of the leaf darker than others?
2. Is there a relationship between the areas
that received light and the areas of starch production?
3. Think about what you have learned about photosynthesis to
fully explain the relationship you observe.
Review Time
1. One of the principal chemical compounds that living things use to store energy is:
a) DNA b) ATP c) H2O d) CO2
2. In addition to light and chlorophyll, photosynthesis requires:
a) H2O & O2
b) H20 & Sugar
c) O2 & CO2
d) H2O & CO2
c) H2O & CO2
d) H2 & O2
3. The products of photosynthesis are:
a) sugars & O2
b) sugar & CO2
4. The first process in light dependent reactions of photosynthesis is:
a) light absorption
b) electron transport
c) oxygen production
d) ATP formation
5. Which substance from the light-dependent reactions of photosynthesis is a source of
energy for the Calvin Cycle?
a) ADP
b) NADPH
c) H2O
d) pyruvic acid
If plants make their own foods, why do some plants, like
Venus fly-traps, appear to be consumers rather than
producers?