Download unit iv study guide key

UNIT IV STUDY GUIDE KEY
I.
Vocabulary Check
1. BB
2. J
3. AA
4. N
5. G
6. T
7. U
8. L
9. Q
10. KK
11. DD
12. II
13. LL
14. I
15. QQ
16. A
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32.
P
CC
X
D
C
B
Z
K
PP
EE
Y
HH
H
W
S
V
33.
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NN
R
OO
M
MM
E
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RR
FF
TT
SS
O
GG
JJ
II. Photosynthesis
1. A – thylakoid – site of Light Rxn; converts light energy to chemical, electron energy
B – thylakoid lumen – inner thylakoid space; location of build-up of H+ ions; created electrochemical gradient,
driving force for ATP synthase
C – stroma – site of Calvin Cycle; formation of glucose precursor
2. DNA & ribosomes; mitochondria
3. 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
CO2 is reduced; H2O is oxidized
4. anabolic; positive
5. mesophyll (in all plants except C4 plants)
6. Water diffuses into the roots due to lower water potential inside roots, moves up plant due to lower water
potential in leaves through adhesion and cohesion. CO2 diffuses into leaves through stomata due to concentration
gradient
7. Sucrose is actively transported into the phloem; decreased solute potential and water potential. Water moves from
xylem into phloem; increases pressure potential and water potential; pushes water through phloem to sink
(destination). When sugar is removed, water potential increases and water returns to xylem.
8. Algae – Same cellular location as plants
Cyanobacteria – Light Rxn in cell membrane; Calvin Cycle in cytosol
AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis consists of two pathways, the Light Dependent Reaction which occurs in the thylakoids and the Calvin Cycle,
which takes place in the stroma of chloroplasts.
In the first pathway, light energy is converted to chemical energy in the form of ATP and NADPH. The first step involves
Photosystem II. Light energy packaged in photons, primarily in the red and blue portions of the visible spectrum, is absorbed by
antenna pigment molecules. The energy is passed along until it reaches the reaction center, a pair of chlorophyll a molecules
known as P680. The chlorophyll molecules of the reaction center respond to this energy by losing 2 electrons to the primary
electron acceptor. The electrons then move through an electron transport chain. As the electrons move through the ETC, energy
is released and used to move H+ into the inner space (lumen) of the thylakoids. The electrons originally lost from the reaction
center are replaced by the splitting of water, producing O2 and H+ ions. The accumulation of ions creates an electrochemical
gradient (also called the proton motive force) which is used to power the enzyme complex, ATP synthase. As H + ions pass
through the enzyme complex and move into the stroma, an inorganic phosphate group is added to ADP, creating ATP. This
process is known as photophosphorylation. In Photosystem I, as light energy is captured and transferred, a pair of chlorophyll a
molecules, known as P700, are excited, causing the loss of 2 electrons. The two excited electrons are passed through a short
electron transport chain ending with the reduction of NADP+ to NADPH. The electrons lost by the reaction center in this
photosystem are replaced by electrons originally lost from P680.
There is an alternative pathway seen in some bacteria and plants which only utilizes photosystem I. This is a cyclic pathway in
which electrons are simply recycled. Although ATP is created, there is no production of NADPH or O2.
The second part of photosynthesis is known as the Calvin Cycle. There are three phases in this cycle,
Carbon Fixation, Reduction Phase, and Regeneration Phase. First, CO2 is added to ribulose biphosphate, abbreviated as RuBP.
This requires the action of the enzyme, rubisco. The resulting intermediate splits, and using energy provided by ATP, is then
reduced forming G3P, and oxidizing NADPH to NADP+ . This is known as the Reduction Phase. For every 3 turns of the cycle,
one molecule of G3P leaves the cycle to be used in carbohydrate production. Finally, in the last phase, RuBP is regenerated,
requiring additional ATP.
Synthesis of glucose requires 6 turns of the Calvin cycle. In addition other carbohydrates can be synthesized including cellulose
for plant cell walls, starch for glucose storage, and the disaccharide, sucrose (composed of glucose and fructose monomers)
often used for transport in the plant.
III. Cellular Respiration
1.
A – cristae – location of electron transport chain; allows for creation of proton motive force (electrochemical
gradient)
B – matrix – location of citric acid cycle; generates ATP, NADH, FADH2
C – intermembrane space – site into which H+ ions are pumped using energy from “falling” electrons in ETC
2. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ~38 ATP
C6H12O6 - oxidized
O2 – reduced
3. Catabolic with negative ΔG
The first step in cellular respiration is glycolysis. This occurs in the cytosol of cells and is an anaerobic pathway. It is divided into
two phases, the energy-investment phase and the energy pay-off phase. In the first phase, 2 ATP are required to provide the
energy to split glucose into 2 G3P molecules. In the 2nd phase, these molecules are oxidized, producing 2 pyruvate, 2 NADH, and
4 ATP for a net gain of 2 ATP.
If oxygen is present, the pyruvate formed from glycolysis moves into the mitochondria. An intermediate step takes place prior to
the citric acid cycle. First, a carboxyl group is given off as CO2. The remaining 2-C molecule is oxidized, reducing NAD+ to
NADH. Finally, the oxidized 2-C molecule attaches to an enzyme complex to form acetyl CoA.
This complex enters the citric acid cycle. A series of redox reactions take place, producing 6 NADH and 2 FADH2,. In addition,
carboxyl groups are removed, releasing CO2 and 2 ATP are produced through substrate-level phosphorylation. The reduced
electron carriers formed in the citric acid cycle move to the electron transport chain and the electrons are “dropped” from one
molecule to another, with each successive molecule more electronegative than the one before it. The ultimate electron acceptor
is oxygen which is reduced to form water. As the electrons fall, their energy is used to drive H+ from the matrix to the
intermembrane space, creating an electrochemical gradient. This gradient, also known as the proton motive force, powers the
enzyme complex, ATP synthase, and ADP is phosphorylated to produce ATP. Each NADH produces approximately 2.5 ATP and
each FADH2 produces about 1.5 ATP. There are 2 NADH produced in glycolysis, 2 NADH formed in the intermediate step, and 6
NADH & 2 FADH2 formed in the citric acid cycle so there is enough electron energy to produce a total of ~28 ATP. The ATP
produced through oxidative phosphorylation is added to the 2 ATP from glycolysis and the 2 ATP from the citric acid cycle for a
total of ~32 ATP produced per molecule of glucose in cellular respiration.
IV. A COMPARISON OF CELLULAR RESPIRATION & PHOTOSYNTHESIS
Characteristic
Cellular Respiration
Photosynthesis
1. Type of metabolic reaction
Catabolic, exergonic; negative ΔG
Anabolic, endergonic; positive ΔG
2. Purpose of Pathway
Convert chemical energy to ATP
Convert light energy to chemical
energy
3. Reactants required
C6H12O6 + O2
CO2 + H2O + light energy
4. End products
CO2 + H2O + ATP energy
C6H12O6 + O2
Virtually all actively-metabolizing
Cells that contain chlorophyll; All
cells require some type of energy
plants, some protists ( algae) &
pathway
bacteria (cyanobacteria)
6. Site(s) involved in eukaryotic cells
Cytosol, mitochondria
Chloroplasts
7. Site(s) involved in prokaryotic cells
Cytosol, cell membrane
Cytosol, cell membrane
8. Mechanism for ATP production
Substrate-level and oxidative
Photophosphorylation
5. Occurs in cells of what organisms?
phosphorylation
9. Electron Transport Carrier Involved
NAD+, FAD
NADP+
10. Location of ETC
Mitochondrial inner-membrane
Thylakoid membrane
11. Source of Electrons for ETC
Glucose
Water
12. Terminal Electron Acceptor
Oxygen
NADP+