11 Photosynthesis-S
11 Photosynthesis-S
11 Photosynthesis-S
Period 4
10/24/20
AP Biology
Photosynthesis
How do light-dependent and light-independent reactions provide food for a
plant? Why?
Plants are the original solar panels. Through photosynthesis a plant is able to convert electromagnetic
(light) energy into chemical energy. This energy is used not only to keep the plant alive, but also to sustain
all creatures that rely on the plant for food and shelter. Plants and photosynthetic algae are also the source
of all oxygen on Earth, allowing the inhabitants of Earth to benefit from our most plentiful renewable
energy resource.
Model 1 – Chloroplast
6CO2 +
12H2O + sunlight energy ⎯→ C6H12O6 +
6O2 +
6H2O
Outer membrane
Inner membrane
Stroma
12H2O
Site of the Calvin cycle, or light independent
6CO2 reactions.
6O2
2. The structures inside the organelle in Model 1 are called thylakoids. What compound necessary
for photosynthesis is contained in the thylakoids?
chlorophyll
Photosynthesis 1
3. Consider the chemical reaction in Model 1. This represents photosynthesis.
hat substances are the reactants in photosynthesis? Include the name and chemical formula
a. W
of each substance in your answer.
Carbon dioxide (CO2) & Water (H2O)
here in the organelle are these molecules stored before they are used in photosynthesis?
b. W
stroma
5. Considering your answers to Question 4, what compound is best able to absorb the light energy
from the Sun and convert it into chemical energy?
Chlorophyll
6. What substances are produced during photosynthesis? Include the name and chemical formula of
each substance in your answer.
Glucose (C6H12O6) & Oxygen (O2)
Reactions Light
Light
2 NADPH (to Calvin Cycle)
Photosystem II
H+
ETC
Chlorophyll
2 NADP+ + 2H+
High
Energy H+
O
2H2 O2 Photosystem
I Inner
H+
H+
H+
Potential
Electron
H+ H+
H+
Stroma
H+
H+ H+ H+ ATP
H + +
H + H
Thylakoid
9. In the light-dependent reactions electrons are released from molecules in two ways.
ind two places in Model 2 where electrons are released from chlorophyll by a photon of light
a. F
coming from the Sun.
The stromas at Photosystem I & II
ind one place in Model 2 where electrons are released from water molecules.
b. F
hen the electrons are released from water molecules, what other products are
c. W
formed?
Photosynthesis 3
Read This!
The light-dependent reactions of photosynthesis include three major processes:
+
A. Excited electrons leave chlorophyll and reduce NADP into NADPH.
B. Excited electrons moving through the electron transport chain provide the free energy
needed to pump hydrogen ions into the inner thylakoid.
C. Hydrogen ions flowing out of the thylakoid via a protein channel provide the free energy
needed to convert ADP to ATP.
10. In Model 2, label the diagram with “A,” “B,” and “C” to indicate where the three steps in the
Read This! box are occurring.
A = 2 NADPH (to Calvin Cycle) & 2 NADP+ + 2H+
B = Light enters photosystem II and electrons begin moving through chain
C = 3 ADP + 3Pi & 3 ATP (to Calvin Cycle)
11. The light-dependent reactions include an electron transport chain system that works in a very
similar fashion to the electron transport chain in respiration. Briefly describe how this system
works and what job it performs in the light-dependent reactions. (Your answer should include a
discussion about concentration gradient.)
In light dependent reactions, the electron transport chain uses energy from excited
electrons to transport hydrogen ions across the thylakoid membrane against the
concentration gradient, producing a high concentration of hydrogen ions in the
membrane.
12. Refer to Model 2.
ame the embedded protein complex found in the thylakoid membrane that uses excited
a. N
+
electrons to reduce NADP into NADPH.
Photosystem I
ame the embedded protein complex found in the thylakoid membrane that provides excited
b. N
electrons to the electron transport chain.
Photosystem II
ame the embedded protein complex found in the thylakoid membrane that converts ADP
c. N
to ATP using free energy from a flow of hydrogen ions.
ATP synthase
ccording to Model 2, what is the source of replacement electrons for those released from
b. A
photosystem II?
Electrons from the splitting of water
b. I n the photosynthesis reaction in Model 1, twelve water molecules are shown as reactants, but
six water molecules are shown as products. Are any of the twelve water molecules products
of the light-dependent reactions?
No
alculate the total number of oxygen, NADPH, and ATP molecules that are produced when
c. C
twelve water molecules complete the light-dependent reactions.
6 O2 + 12 NADPH + 18 ATP
16. Where do the ATP and NADPH produced during the light-dependent reactions go when the
process is complete?
The Calvin Cycle
Photosynthesis 5
Model 3 – The Light-Independent Reactions (Calvin Cycle)
O C O
Carbon dioxide
(CO2)
3 CO2
OH O
O– O–
O–
O –
O– O CH
–
2C
CH CH CH2 O P O C CH CH2
P O P O–
O O OH O OH O
3 RuBP 6 PGA
Ribulose biphosphate Carbon
(RuBP) Fixation 6 ADP
5 PGAL
6 PGAL
O
Phosphoglycerate
(PGA)
6 ATP
1 PGAL
(a three-carbon produce C CH CH2 O P O– O
sugar used by glucose and
the cell to OH
H
other biomolecules) e (PGAL)
Phosphoglyceraldehyd
17. According to Model 3, what are the three phases of the Calvin cycle?
Carbon fixation, reduction, regeneration
alculate the total number of carbon atoms represented in all of the RuBP molecules used in
c. C
one turn of the Calvin cycle.
15 carbon atoms (3 molecules, 5 atoms each)
ow many PGA molecules are made in one turn of the Calvin cycle?
b. H
Six
alculate the total number of carbon atoms represented in all of the PGA molecules used in
d. C
one turn of the Calvin cycle.
18 carbon atoms (6 molecules, 3 atoms each)
20. Explain what happened to the carbon atoms from the carbon dioxide molecules that entered the
Calvin cycle.
The carbon atoms were incorporated into the PGA molecules
21. Consider the term “carbon fixation.” Think individually for a moment what this term might
mean, then share ideas among the group. Record the group’s consensus definition for
carbon fixation here.
Process where inorganic carbons are converted into organic compounds by living
organisms
Read This!
Model 3 is a simplified version of the Calvin cycle. Each of the three phases in the cycle consist of
multiple reactions that are catalyzed by enzymes specific to that reaction. These enzymes have names
like RuBisCo, phosphoglycerate kinase, and PGAL hydrogenase.
22. Refer to the reduction phase of the Calvin cycle in Model 3.
hat molecule does the PGA molecule turn into during this phase of the Calvin cycle?
a. W
PGAL
escribe specifically how the structures of the two molecules in part a a re different.
b. D
c. I dentify the types and numbers of molecules that provide the free energy necessary for the
reduction of the PGA molecules.
6 ATP & 6 NADPH
d. I s the total number of carbon atoms present in the Calvin cycle changed during the reduction
phase? Support your answer with evidence from Model 3.
NO, because the 6 PGAL molecules have a total of 18 carbon atoms
Photosynthesis 7
23. Water is a product of the reduction phase of the Calvin cycle.
ow many water molecules are produced?
a. H
Six
xplain where the hydrogen and oxygen atoms in these water molecules originated.
b. E
The oxygen was removed from PGA and converted into PGAL. The hydrogen atoms
came from the process when NADPH was converted into NADP+
24. Refer to the regeneration phase of the Calvin cycle in Model 3.
ow many PGAL molecules continue on to the regeneration phase of the Calvin cycle?
a. H
Five
b. I dentify the types and numbers of molecules that provide the free energy necessary for the
regeneration of these molecules.
3 ATP molecules
ow many total carbon atoms remain in the Calvin cycle at this point?
c. H
15
e. How many total carbon atoms leave the Calvin cycle before the regeneration phase?
Three
hat happens to the PGAL molecule that does not continue on in the Calvin cycle?
f. W
Read This!
As you have learned from your careful study of the Calvin cycle illustrated in Model 3, three atoms of car
bon enter the cycle as carbon dioxide and three carbon atoms leave the cycle as PGAL. It is easy to
assume that the three atoms that leave are one and the same with the three that entered, but that is
incorrect. It may be that none of the carbon atoms from the carbon dioxide become incorporated into a
molecule of PGAL that leaves the cycle. Alternatively, it is also possible that one of the carbon atoms
from the carbon dioxide will become part of a PGAL molecule that leaves the cycle. Eventually all of the
carbon atoms that enter the cycle will leave as part of a PGAL molecule, but they must wait their turn.
ow many turns of the Calvin cycle will it take to make one molecule of glucose?
b. H
Two
alculate the total number of ATP and NADPH molecules used in the production of one
c. C
molecule of glucose.
18 ATP & 12 NADPH molecules
+
26. Where do the ADP and NADP go after they are used in the Calvin cycle?
They return to the thylakoid
27. Explain in detail, using complete sentences, how the two reactions (light-dependent and light
independent) depend on each other.
To actually power the light-independent reaction, 18 ATP & 12 NADPH are required.
However, 18 ADP & 12 NADP+ return to the light-dependent reaction/cycle.
28.Under each molecule in the equation below, indicate whether it is involved (either used or
produced) in the light-dependent reactions or the Calvin cycle.
6CO2 +
12H2O → C6H12O6 +
6O2 +
6H2O
6CO2 = used in calvin cycle
12H2O = used in light-dependent reaction
C6H12O6 = produced in calvin cycle
6O2 = produced in light-dependent reaction
6H2O = produced in calvin cycle
29. Throughout photosynthesis, energy is transferred from light to several molecules with increas
ingly higher potential energy. Use the words below to summarize the order in which the energy
flow occurs.
electrons ATP glucose sunlight
Sunlight → electrons → ATP → glucose
30. Although photosynthesis does produce some ATP, these molecules are not used to do the
work of the plant cells. What other process occurs in the cells that provides the ATP
necessary to do cellular work such as make proteins, divide cells, and move substances across
membranes?
Cellular respiration uses glucose from photosynthesis
Photosynthesis 9
Extension Questions
Model 4 – The Study of Photosynthesis
Carbon dioxide
Oxygen
Concentration RuBP of molecules
Time
sing the information from this activity explain why the equation above is a vastly
b. U
oversimplified representation of the actual process.
Photosynthesis itself is a generally complex group of reactions where each reaction
performs different action by using both used and new products and reactants. The
equation however, shows the essential parts that would often be considered the
makeup of photosynthesis: light, CO2, water.