Topic 3 review
Name ____________Key_______________________________
Respiration
1. What is a catabolic pathway?______ The breakdown of organic molecules is exergonic
2. What are two catabolic pathways? _____fermentation, aerobic respiration, anaerobic respiration, cellular
respiration__________
3. Why is cell resp also called aerobic resp? _________________________________________________________
Aerobic respiration consumes organic molecules and O2 and yields ATP. Oxygen is required
4. Write the equation for resp. ____________________________________________________________
5. What type of reaction is cell resp? _______redox (oxidation – reduction reaction), exergonic__________
6. In the space below, draw a flow chart of glycolysis to explain what goes in, what comes out, and what is made in
the process.
Glucose (6C) is split into 2 molecules of pyruvate (ionized form of pyruvic acid) (3C) in a 10 step process each controlled
by a specific enzyme
For each glucose molecule entering glycolysis the end
products are:
a. Net gain of 2 ATP
b. 2 NADH produced
c. 2 molecules of pyruvate
Summary equation for glycolysis:
C6H12O6 + 2NAD+ + 2ADP + 2Pi 2C3H4O3 (pyruvate) + 2NADH + 2H+ + 2ATP + 2H2O
7. Explain why there is a discrepancy in the gain and net gain of ATP. 2 ATP are used in Energy Investment Phase
8. After glycolysis, if oxygen is present, what happens? ______ ____The citric acid cycle, also called the Krebs cycle,
takes place within the mitochondrial matrix.
9. Where does the pyruvate go? __________________ pyruvate enters the mitochondrion where enzymes of the
citric acid cycle complete the oxidation of glucose to carbon dioxide ____ In the presence of O2, pyruvate enters
the mitochondrion. Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links
the cycle to glycolysis. The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn. ___
10. How does it get there? ___transport protein__ pyruvate must be converted to acetyl CoA, which links the cycle
to glycolysis. ___
11. What happens to the pyruvate before it enters the CAC? What is made during the process? _________
Junction between glycolysis and the Citric Acid Cycle. As pyruvate enters the mitochondria by active transport,
a multienzyme complex modifies the pyruvate into acetyl CoA which enters the Citric Acid Cycle in the matrix.
Requires 3 rxns:
a. A carboxyl group is removed as CO2.
b. A pair of electrons is transferred to NAD+ to form NADH.
c. The oxidized fragment, acetate, combines with coenzyme A to form acetyl CoA.
12. What is the CAC also known as? _____Krebs Cycle________________________________
13. Why does the CAC require two turns? _____because glucose yields two pyruvates____
14. What is the total amount of products made (per glucose) in the CAC? 2 CO2,3 NADH, 1 oxaloacetate, 1 ATP, 1
FADH2
15. What are the two ways ATP can be made? ___oxidative phosphorylation, substrate-level phosphorylation_____
16. Which way does glycolysis and CAC make it? __________ substrate-level phosphorylation __________________
17. After the CAC, which electron carriers enter the ETC? _______ NADH and FADH2 ___________________
18. Which enters at the beginning of the chain? _____ NADH ______________________________________
19. The energy of moving electrons pumps ___H+____ out of the mitochondrial matrix.
20. Hydrogen ions are also called ___protons_____.
21. What acts as the final electron acceptor at the end of the ETC? ________O2________________________
22. When it accepts those electrons, what is made? ___Water_____________________
23. What has been formed by pumping protons out of the mitochondrial matrix? _________proton gradient__
24. How do they get back in the matrix? _______ATP synthase which harnesses proton motive force________
25. What is that process called and what does that process make? _ATP synthase harnesses the proton motive force
– the gradient of hydrogen ions – to phosphorylate ADP, forming ATP. The proton moive force is in place
because the inner membrane of the mitochondria is impermeable to hydrogen ions. . Electrons are held behind
the inner membrane with their only exit ATP synthase. This is called chemiosmosis – which is an energy coupling
mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular
work_______________
26. What are the ETC and chemiosmosis called together? _Oxidative phosphorylation____________
27. Where is most ATP made? ___Oxidative phosphorylation, specifically Chemiosmosis__________________
28. According to your review book, what is the maximum ATP output? _36 - 38_ What was it according to your
textbook? _____________
29. If oxygen is not present after glycolysis, what happens in yeast cells? What about muscle cells? __anaerobic
respiration – fermentation which consists of glycolysis and reactions that regenerate NAD+. In glycolysis oxygen
is not needed to accept electrons; NAD+ is the electron acceptor.
Yeast – alcohol fermentation – pyruvate is converted to ethanol, releasing CO2 and oxidizing NADH in the process to
create more NAD+
Humans – lactic acid fermentation – pyruvate is reduced by NADH (NAD+ is formed in the process), and lactate is
formed as a waste product
30. Explain the products and byproducts of both of these processes. ___
Alcoholic Fermentation
Carried out by bacteria and yeast
Produces 2 CO2, 2 ATP, and 2 molecules of ethanol (C2H6O)
Regenerates NAD+
Lactic Acid Fermentation

Carried out in muscle cells of animals under anaerobic conditions

Produces 2 ATP and 2 molecules of lactic acid (C3H6O3)

Regenerates NAD+

Lactic acid produced by muscle cells causes “muscle fatigue” and is toxic to cells

Lactic acid is carried to liver and converted back to pyruvate when O2 is available.
31. The importance of fermentation is that __ NAD+. ____ is regenerated for further use in glycolysis.
32. How much ATP is made in the one process of fermentation including glycolysis? _2
33. What is the difference between facultative and obligate anaerobes? _____
Obligate Anaerobes- organisms that cannot survive in the presence of oxygen. Carry out only fermentation or
anaerobic respiration.
Facultative Anaerobes- organisms that can survive using fermentation or respiration.
34. What acts as a regulator of respiration? _____ Cells respond to changing metabolic needs by controlling rxn
rates. Feedback inhibition is the most common mechanism for control. If ATP concentration begins to drop,
respiration speeds up; when there is plenty of ATP, respiration slows down. Control of catabolism is based
mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
Phosphofructokinase—regulating enzyme of glycolysis
-pacemaker of glycolysis and respiration
-stimulated by ADP or AMP
Photosynthesis
35. What is the difference between autotrophs and heterotrophs? ___autotrophs – producers, make their own
food, self- feeders, sustain themselves without eating anything derived from other organism
heterotrophs – consumers, live on compounds produced by other organisms, _______________________
36. Draw a chloroplast and correctly label the parts.
37. What is the most important pigment in photosynthesis? ___chlorophyll_____________
38. Where are most chloroplasts found? in cells of the mesophyll, the interior tissue of the leaf
39. What is the function of stomata? ______ . CO2 enters and O2 exits the leaf through microscopic pores ______
40. What is the equation for photosynthesis? ___ 6 CO2 + 12 H2O* + light energy
C6H12O6 + 6 O2* + 6H2O
Simplest photosynthetic equation:
CO2 + H2O
[CH2O] + O2
41. What do pigments do? ____ Pigments are substances that absorb visible light
Different pigments absorb different wavelengths
Wavelengths that are not absorbed are reflected or transmitted
Leaves appear green because chlorophyll reflects and transmits green light
42. Which colors of light are most effective in driving photosynthesis? ___ Chlorophyll a is the main photosynthetic
pigment and absorbs best in the red and blue wavelengths, and least in the green.
Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis
Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll
-known as photoprotective
43. What is carbon fixation? ________when CO2 from the air is incorporated into organic molecules_______
44. What is photophosphorylation? _______the process in which light reactions also generate ATP, using
chemiosmosis to power the addition of a phosphate group to ADP__________
45. What two products are made in the light reactions and used in the calvin cycle? ___NADPH and ATP______
46. What product of the light reactions is released? ______O2_____________________
47. What are the major parts to photosynthesis? ______light reactions and Calvin cycle (Dark Reactions)_________
48. What are the two major parts to the light reactions? ______photosystems and Electron transport chains
3. Photosystems have two parts – light harvesting complex_ consists of a reaction-center complex (a type of
protein complex) surrounded by light-harvesting complexes. The light-harvesting complexes (pigment molecules
bound to proteins) funnel the energy of photons to the reaction center. A primary electron acceptor in the
reaction center accepts an excited electron from chlorophyll a. Solar-powered transfer of an electron from a
chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions
49. What are photosystems? How many are there? Which comes first? ___groups of pigment molecules in the
thylakoid membrane of chloroplasts, 2 of them, PS II comes first___
Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of
680 nm. The reaction-center chlorophyll a of PS II is called P680
Photosystem I (PS I) is best at absorbing a wavelength of 700 nm
The reaction-center chlorophyll a of PS I is called P700
50. Explain the difference between cyclic and noncyclic electron flow?
Linear Electron Flow – the flow of electrons through the photosystems in the thylakoid membrane
During the light reactions, there are two possible routes for electron flow: cyclic and linear
1 - Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using
light energy
2 - A photon hits a pigment and its energy is passed among pigment molecules until it excites P680
3 - An excited electron from P680 is transferred to the primary electron acceptor
4 - P680+ (P680 that is missing an electron) is a very strong oxidizing agent
5 - H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it
to P680
6 - O2 is released as a by-product of this reaction
7 - Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I
8 - Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane
9 - Diffusion of H+ (protons) across the membrane drives ATP synthesis
cyclic electron flow – uses PS I, but not PSII. Uses a short circuit of linear electron flow by cycling the excited electrons
back to their original starting point in PSI. Cyclic electron flow produces ATP by chemiosmosis, but no NADPH is
produced and no oxygen is released
51. Sunlight stimulates the __chlorophyll a molecule in the P680 reactions center____.
52. What happens to the electrons from photosystem II? ___original excited electron passes from the primary
electron acceptor of PSII to PSI through an electron transport chain___________________
53. What is created in the process? __O2 are formed in the splitting of water molecules.
The energy from the transfer of electrons down the electron transport chain is used to pump protons, creating a
gradient that is used in chemiosmosis to phosphorylate ADP to ATP _________________________________
54. What happens to electrons in PS I? ____10 - In PS I (like PS II), transferred light energy excites P700, which loses
an electron to an electron acceptor
11 - P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain
55. How does each photosystem replace its electrons? _____electrons just donated by PSI are replaced by the
electrons from PSII, the ultimate source of electrons is water_____________
56. Explain how chemiosmosis occurs. ___Each electron “falls” down an electron transport chain from the primary
electron acceptor of PS I to the protein ferredoxin (Fd). The electrons are then transferred to NADP+ and reduce
it to NADPH. The electrons of NADPH are available for the reactions of the Calvin cycle. In chloroplasts, protons
are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma. . ATP and
NADPH are produced on the side facing the stroma, where the Calvin cycle takes place. In summary, light
reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH
Calvin Cycle - 3 phases = Carbon fixation, reduction, and regeneration of RuBP
57. What enters the Calvin cycle? ______3 -CO2__________ IT combines with __the enzyme Rubisco and Ribulose
Bisphosphate (RuBP)__ to form ___a shrort-lived intermediate (3 phosphoglycerate)_____. Then _____6 (2 per
CO2)_____ ATP and 6 ___NADPH (2 per CO2)_ are added to make ___6 G3P______, which is the actual final
product of the Calvin cycle.
58. _1__ G3P exits. What happens to the other five? _____to regenerate the 5 G3P___________
59. How is glucose made? ______Two G3P molecules can combine to form glucose_____________
60. What are alternative mechanisms of carbon fixation? ________C4 and CAM Plants___________
61. Explain the difference between the two.
C4 1. C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells
2. This step requires the enzyme PEP carboxylase
3. PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low
4. These four-carbon compounds are exported to bundle-sheath cells, where they release CO2 that is then used in the
Calvin cycle
5. Adaptive process which enhances carbon fixation under conditions that favor photorespiration (hot, arid)
6. Occurs in corn, sugarcane, agricultural grasses
CAM1. Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon
2. CAM plants open their stomata at night, incorporating CO2 into organic acids
3. Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle