Name ___________________________________
Class _____ Date ____________________
AP Biology – Unit 2 Active Reading Guide
Unit 2.1: A Tour of the Cell
1.
The study of cells has been limited by their small size, and so they were not seen and described until
1665, when Robert Hooke first looked at dead cells from an oak tree. His contemporary, Anton van
Leeuwenhoek, crafted lenses and with the improvements in optical aids, a new world was opened.
Magnification and resolving power limit what can be seen. Explain the difference.
2.
The development of electron microscopes has further opened our window on the cell and its
organelles. What is considered a major disadvantage of electron microscopes?
3.
Study the electron micrographs in your text. Describe the different types of images obtained from:
scanning electron microscopy (SEM): transmission
electron microscopy (TEM):
4.
In cell fractionation, whole cells are broken up in a blender, and this slurry is centrifuged several
times. Each time, smaller and smaller cell parts are isolated.
This will isolate different organelles and allow study of their biochemical activities. Which
organelles are the smallest ones isolated in this procedure?
5.
Which two domains consist of prokaryotic cells?
6.
A major difference between prokaryotic and eukaryotic cells is the location of their DNA. Describe this
difference.
7. Refer to slide 16 and give the function of description of the following structures:
Structure
Function or Description
cell wall
plasma membrane
bacterial chromosome
nucleoid
cytoplasm
flagella
8.
Why are cells so small? Explain the relationship of surface area to volume.
9.
What are microvilli? How do these structures relate to the function of intestinal cells?
10. Describe the nuclear envelope. How many layers is it? What connects the layers?
11. What is the nuclear lamina? Nuclear matrix?
12. Found within the nucleus are the chromosomes. They are made of chromatin. What are the two
components of chromatin? When do the thin chromatin fibers condense to become distinct
chromosomes?
13. When are the nucleoli visible? What are assembled here?
14. What is the function of ribosomes? What are their two components?
15. Ribosomes in any type of organism are all the same, but we distinguish between two types of
ribosomes based on where they are found and the destination of the protein product made.
Complete this chart to demonstrate this concept.
Type of Ribosome
Location
Product
Free ribosomes
Bound ribosomes
16. List all the structures of the endomembrane system.
17. The endoplasmic reticulum (ER) makes up more than half the total membrane system in many
eukaryotic cells. Explain the lumen, transport vesicles, and the difference between smooth and rough
ER.
18. List and describe three major functions of the smooth ER.
19. Why does alcohol abuse increase tolerance to other drugs such as barbiturates?
20. The rough ER is studded with ribosomes. As proteins are synthesized, they are threaded into the
lumen of the rough ER. Some of these proteins have carbohydrates attached to them in the ER to form
glycoproteins. What does the ER then do with these secretory proteins?
21. Besides packaging secretory proteins into transport vesicles, what is another major function of the
rough ER?
22. The transport vesicles formed from the rough ER fuse with the Golgi apparatus.
Describe what happens to a transport vesicle and its contents when it arrives at the Golgi apparatus.
23. What is a lysosome? What do they contain? What is the pH range inside a lysosome?
24. One function of lysosomes is intracellular digestion of particles engulfed by phagocytosis.
Describe this process of digestion. What human cells carry out phagocytosis?
25. A second function of lysosomes is to recycle cellular components in a process called autophagy.
Describe this process.
26. What happens in Tay-Sachs disease? Explain the role of the lysosomes in Tay-Sachs.
27. There are many types of vacuoles. Briefly describe:
a. food vacuoles:
b. contractile vacuoles:
c. central vacuoles in plants (give at least three functions/materials stored here):
28. Explain how the elements of the endomembrane system function together to secrete a protein
and to digest a cellular component.
29. What is an endosymbiont?
30. What is the endosymbiont theory? Summarize three lines of evidence that support the model of
endosymbiosis.
31. Mitochondria and chloroplasts are not considered part of the endomembrane system, although they
are enclosed by membranes. Sketch a mitochondrion here and label its outer membrane, inner
membrane, inner membrane space, cristae, matrix, and ribosomes.
32. Now sketch a chloroplast and label its outer membrane, inner membrane, inner membrane space,
thylakoids, granum, and stroma. Notice that the mitochondrion has two membrane compartments,
while the chloroplast has three compartments.
33. What is the function of the mitochondria?
34. What is the function of the chloroplasts?
35. Recall the relationship of structure to function. Why is the inner membrane of the mitochondria
highly folded? What role do all the individual thylakoid membranes serve? (Notice that you will
have the same answer for both questions.)
36. Explain the important role played by peroxisomes.
37. What is the cytoskeleton?
38. What are the three roles of the cytoskeleton?
39. There are three main types of fibers that make up the cytoskeleton. Name them.
40. Microtubules are hollow rods made of a globular protein called tubulin. Each tubulin protein is a dimer
made of two subunits. These are easily assembled and disassembled. What are four functions of
microtubules?
41. Animal cells have a centrosome that contains a pair of centrioles. Plant cells do not have centrioles. What
is another name for centrosomes? What is believed to be the role of centrioles?
42. Describe the organization of microtubules in a centriole. Make a sketch here that shows this
arrangement in cross section.
43. Cilia and flagella are also composed of microtubules. The arrangement of microtubules is said to be
“9 + 2.” Make a cross-sectional sketch of a cilium here.
44. Compare and contrast cilia and flagella.
45. How do motor proteins called dyneins cause movement of cilia? What is the role of ATP in this
movement?
46. Microfilaments are solid, and they are built from a double chain of actin. Explain three examples of
movements that involve microfilaments.
47. What are the motor proteins that move the microfilaments? ___________________
48. Intermediate filaments are bigger than microfilaments but smaller than microtubules. They are more
permanent fixtures of cells. Give two functions of intermediate filaments.
49. What are three functions of the cell wall?
50. What is the composition of the cell wall?
51. What is the relatively thin and flexible wall secreted first by a plant cell?
52. What is the middle lamella? Where is it found? What material is it made of?
53. Explain the deposition of a secondary cell wall.
54. Animal cells do not have cell walls, but they do have an extracellular matrix (ECM).
Give the role of each.
55. What are the intercellular junctions between plant cells? What can pass through them?
56. Animals cells do not have plasmodesmata. Summarize the role of the three types of intercellular
junctions seen in animal cells.
Unit 2.2: Membrane Transport and Cell Signaling
1. Phospholipids are amphipathic. Explain what this means.
2. In the 1960s, the Davson-Danielli model of membrane structure was widely accepted. Describe this
model and then cite two lines of evidence that were inconsistent with it.
3. The currently accepted model of the membrane is the fluid mosaic model. Who proposed it? When?
Describe this model.
4. What is meant by membrane fluidity? Describe the movements seen in the fluid membrane,.
5. Describe how each of the following can affect membrane fluidity:
a. Decreasing temperature
b. Phospholipids with unsaturated hydrocarbon chains:
c. Cholesterol:
6. Membrane proteins are the mosaic part of the model. Describe each of the two main categories:
a. Integral proteins:
b. Peripheral proteins:
7. Study slide 17 in the lecture. Use it to briefly describe the following major functions of membrane
proteins.
Function
Description
Transport
Enzymatic Activity
Attached to the
Cytoskeleton and
ECM
Cell-Cell Recognition
Intercellular Joining
Signal Transduction
8. Membrane carbohydrates are important in cell-cell recognition. What are two examples of this?
9. Distinguish between glycolipids and glycoproteins.
a. Glycolipids:
b. Glycoproteins:
10. Distinguish between channel proteins and carrier proteins.
11. Are transport proteins specific? Cite an example that supports your response.
12. Peter Agre received the Nobel Prize in 2003 for the discovery of aquaporins. What are they?
13. Consider the following material that must cross the membrane. For each, tell ow it is moved across.
Material
Method
Co2
Glucose
H+
O2
H2O
14. Define the following terms:
Term
Definition
Diffusion
Concentration
Gradient
Passive Transport
Osmosis
Isotonic
Hypertonic
Hypotonic
Turgid
Flaccid
Plasmolysis
15. What is facilitated diffusion? Is it active or passive? Cite two examples.
16. Why does the red blood cell burst when placed in a hypotonic solution, but not the plant cell?
17. Describe active transport. What type of transport proteins are involved, and what is the role of ATP
in the process?
18. The sodium-potassium pump is an important system for you to know. Use slides 41-43 to
understand how it works, and briefly summarize what is occurring in each step.
19. For each type of transport, give an example of a material that is moved in this manner.
Method
Facilitated Diffusion with
a Carrier Protein
Facilitated Diffusion with
a Channel Protein
Active Transport with a
Carrier Protein
Material
Simple Diffusion
20. What is membrane potential? Which side of the membrane is positive?
21. What are the two forces that drive the diffusion of ions across the membrane? What is the
combination of these forces called?
22. What is cotransport? Explain how understanding it is used in our treatment of diarrhea.
23. Define each of the following, and give a specific cellular example
Term
Exocytosis
Endocytosis
ReceptorMediated
Endocytosis
Phagocytosis
Pinocytosis
Definition
Example
24. What is a ligand? What do ligands have to do with receptor-mediated endocytosis?
25. Are the processes you described in question 20 active or passive transport? Explain your response.
26. What is signal transduction pathway?
27. Complete the chart of local chemical signaling in cell communication in animals.
Term
Description
Specific Example
Paracrine
signaling
Synaptic
signaling
28. How does a hormone qualify as a long-distance signaling example?
29. A signal transduction pathway has three stages. Use slide 67 to explain each step.
a. Reception:
b. Transduction:
c. Response:
30. Explain the term ligand. (This term is not restricted to cell signaling. You will see it in other
situations during the year.)
31. Describe the role of the three components of G protein-coupled receptor.
a. G protein-coupled receptor:
b. G protein:
c. GDP:
32. Equally important to starting a signal is stopping a signal. (Failure to do so can lead to serious
problems, like cancer) Describe how the signal is halted.
33. What activates a G protein?
34. A G protein is also a GTPase enzyme. Why is this important?
35. Look next at ion channel receptors. This figure shows the flow of ions into the cell. Ion channel
receptors can also stop the flow of ions. These comparatively simple membrane receptors are
explained in three steps. Explain the role of the following momlecules.
a. Ligand
b. Ligand-gated ion channel receptor
c. Ions
36. Slide 73 shows what has happened with the binding of the ligand to the receptor. Explain what
occurs.
37. The ligand attachment to the receptor is brief. Explain what happens as the ligand dissociates.
38. In what body system are ligand-gated ion channels and voltage-gated ion channels of particular
importance?
39. Intracellular receptors are found either in the cytosplasm or nucleus of target cells. In order to be
able to pass through the plasma membrane, the chemical messengers are either hydrophobic or very
small, like nitric oxide. Explain how testosterone, a hydrophobic steroid hormone, works as an
intracellular receptor.
40. What are two benefits of multistep pathways?
41. Explain the role in transduction of these two categories of enzymes.
a. Protein kinase:
b. Protein phosphates:
42. What is the difference between a first messenger and a second messenger?
43. Two common second messengers are cyclic AMP (cAMP) and calcium ions (Ca2+). Explain the role
of the second messenger cAMP in slide 82 in the lecture.
44. What is the important relationship between the second messenger and protein kinase A?
45. Slide 82 explains a cellular response is initiated; how might that response be inhibited?
46. Use your new knowledge of cell signaling to explain the mechanism of disease in cholera.
47. When cell signaling causes a nuclear response, what normally happens?
48. When cell signaling causes a cytoplasmic response, what normally happens?
Unit 2.3: An Introduction to Metabolism
1. Define metabolism.
2. There are two types of reactions in metabolic pathways: anabolic and catabolic.
a. Which reactions release energy? ____________________
b. Which reactions consume energy? ____________________
c. Which reactions build up larger molecules? ____________________
d. Which reactions break down molecules? ____________________
e. Which reactions are considered “uphill”? ____________________
f.
What type of reaction is photosynthesis? ____________________
g. What type of reaction is cellular respiration? ____________________
h. Which reactions require enzymes to catalyze reactions? _________________
3. Contrast kinetic energy with potential energy.
4. Which type of energy does water behind a dam have? A mole of glucose?
5. What is meant by a spontaneous process?
6. What is free energy? What is its symbol?
7. For an exergonic reaction, is ΔG negative or positive?
8. Is cellular respiration an endergonic or an exergonic reaction? What is ΔG for this reaction?
9. Is photosynthesis endergonic or exergonic? What is the energy source that drives it?
10. To summarize, if energy is released, ΔG must be what?
11. List the three main kinds of work that a cell does. Give an example of each.
a.
b.
c.
12. Look at slide 32 of an ATP molecule in your textbook.
a. Which bond is likely to break?
b. By what process will that bond break?
c. Explain the name ATP by listing all the molecules that make it up.
d. When the terminal phosphate bond is broken, a molecule of inorganic phosphate Pi is
formed, and energy is ____________________.
e. For this reaction: ATP à ADP + Pi, ΔG = ____________________
f.
Is this reaction endergonic or exergonic? ____________________
13. What is energy coupling?
14. In many cellular reactions, a phosphate group is transferred from ATP to some other molecule in
order to make the second molecule less stable. The second molecule is said to be _________________.
15. If you could not regenerate ATP by phosphorylating ADP, how much ATP would you need to
consume each day?
16. What is a catalyst?
17. What is activation energy (EA)?
18. Refer to slides 43 and 45 to answer the following questions
a. What effect does an enzyme have on EA?
b. Is ΔG positive or negative? _____
c. How is ΔG affected by the enzyme?
19. Define each of the following terms:
Term
Definition
Enzyme
Substrate
Active site
Products
20. What is meant by induced fit?
21. Explain how protein structure is involved in enzyme specificity.
22. Enzymes use a variety of mechanisms to lower activation energy. Describe four of these
mechanisms.
a.
b.
c.
d.
23. Many factors can affect the rate of enzyme action. Explain each factor listed here.
a. initial concentration of substrate:
b. pH:
c. temperature:
24. Recall that enzymes are globular proteins. Why can extremes of pH or very high temperatures affect
enzyme activity?
25. Name a human enzyme that functions well in pH 2. Where is it found?
26. Distinguish between cofactors and coenzymes. Give examples of each.
27. Compare and contrast competitive inhibitors and noncompetitive inhibitors.
28. What is allosteric regulation?
29. How is allosteric regulation somewhat like noncompetitive inhibition? How might it be different?
30. Explain the difference between an allosteric activator and an allosteric inhibitor.
31. Although it is not an enzyme, hemoglobin shows cooperativity in binding O2. Explain how
hemoglobin works at the gills of a fish.
32. Refer to slide 68 and answer the following questions:
a. What is the substrate molecule to initiate this metabolic pathway? ___________
b. What is the inhibitor molecule? ____________________
c. What type of inhibitor is it? ____________________
d. When does it have the most significant regulatory effect? _________________
e. What is this type of metabolic control called? ____________________
Unit 2.4: Cellular Respiration and Fermentation
1. Explain the difference between fermentation and cellular respiration.
2. Give the formula (with names) for the catabolic degradation of glucose by cellular respiration.
3. Both cellular respiration and photosynthesis are redox reactions. In redox, reactions pay attention to
the flow of electrons. What is the difference between oxidation and reduction?
4. The following is a generalized formula for a redox reaction. Draw an arrow showing which
component (X or Y) is oxidized and which is reduced.
Xe– + Y à X + Ye–
_______ is the reducing agent in this reaction, and _______ is the oxidizing agent.
5. When compounds lose electrons, they _______ energy; when compounds gain electrons, they
_______ energy.
6. In cellular respiration, electrons are not transferred directly from glucose to oxygen. Following the
movement of hydrogens allows you to follow the flow of electrons. The hydrogens are held in the
cell temporarily by what electron carrier? What electron carrier is hydrogen transferred to first?
7. The correct answer to question 6 is NAD+. It is a coenzyme. What are coenzymes?
8. Describe what happens when NAD+ is reduced. What enzyme is involved?
9. It is essential for you to understand the concept of oxidation/reduction and energy transfer. For the
following pair, which molecule is the oxidized form, and which is reduced? Which molecule holds
higher potential energy? Which is lower in potential energy?
NAD+ ________________________________________
NADH ________________________________________
10. What is the function of the electron transport chain in cellular respiration?
11. Electron transport involves a series of electron carriers.
a. Where are these found in eukaryotic cells? _________________________
b. Where are these found in prokaryotic cells? _________________________
12. What strongly electronegative atom, pulling electrons down the electron transport chain, is the final
electron acceptor?
13. Three types of phosphorylation (adding a phosphate) are covered in the text, and two of these occur
in cellular respiration. Explain how the electron transport chain is utilized in oxidative
phosphorylation.
14. The second form of phosphorylation is substrate level. Explain the direct transfer of a phosphate
from an organic substrate to ADP to form ATP.
15. What is the meaning of glycolysis? What occurs in this step of cellular respiration?
16. The starting product of glycolysis is the six-carbon sugar __________, and the ending products are
two __________-carbon molecules of ___________________.
17. The ten individual steps of glycolysis can be divided into two stages: energy investment and energy
payoff. These steps are shown in slides 31-36, which details the enzymes and reactions at each of the
ten steps. While you are not expected to memorize these steps and enzymes, you should study the
figure carefully. The next few questions will help you focus your study.
a. What are the two specific steps where ATP is used? __________ __________
b. The second step in glycolysis is the energy payoff phase. Note that it provides both ATP and
NADH.
i. What are the two steps where ATP is formed? __________ __________
ii. What is the one step where NADH is formed? __________ __________
The final figure shows the net gain of energy for the cell after glycolysis. Most of the energy is still
present in the two molecules of pyruvate.
18. Notice that glycolysis occurs in the ___________________ of the cell. Is oxygen required? __________
19. To enter the citric acid cycle, pyruvate must enter the mitochondria by active transport. Three things
are necessary to convert pyruvate to acetyl CoA. Explain the three steps in the conversion process.
a.
b.
c.
20. Use slides 43-52 to help you answer the following summary questions about the citric acid cycle:
a. How many NADHs are formed? _____
b. How many total carbons are lost as pyruvate is oxidized? _____
c. The carbons have been lost in the molecule ____________________.
d. How many FADH2 have been formed? ______
e. How many ATPs are formed? ______
f.
How many times does the citric acid cycle occur for each molecule of glucose? ________
21. The step that converts pyruvate to acetyl CoA at the top of the diagram occurs twice per glucose.
This oxidation of pyruvate accounts for two additional reduced ________________ molecules and
two molecules of CO2.
22. Explain what has happened to each of the six carbons found in the original glucose molecule.
23. Oxidative phosphorylation involves two components: the electron transport chain and ATP
synthesis. Referring to slides 57-59, notice that each member of the electron transport chain is lower
in free __________ than the preceding member of the chain, but higher in ____________________.
The molecule at zero free energy, which is __________, is lowest of all the molecules in free energy
and highest in electronegativity.
24. Oxygen is the ultimate electron acceptor. Why is this?
25. Oxygen stabilizes the electrons by combining with two hydrogen ions to form what compound?
26. The two electron carrier molecules that feed electrons into the electron transport system are
________________ and _________________.
27. Using slide 62, explain the overall concept of how ATP synthase uses the flow of hydrogen ions to
produce ATP.
28. What is the role of the electron transport chain in forming the H+ gradient across the inner
mitochondrial membrane?
29. Two key terms are chemiosmosis and proton-motive force. Relate both of these terms to the process
of oxidative phosphorylation.
30. At this point, you should be able to account for the total number of ATPs that could be formed from
a glucose molecule. To accomplish this, we have to add the ATPs formed by substrate-level
phosphorylation in glycolysis and the citric acid cycle to the ATPs formed by chemiosmosis. Each
NADH can form a maximum of ____ ATP molecules. Each FADH2, which donates electrons that
activate only two proton pumps, makes ____ ATP molecules.
31. Using slide 69, summarize the production of NADH and FADH2. How is ATP formed, and for each
step indicate whether it is by substrate-level or oxidative phosphorylation? Use the text to be sure
you understand how each subtotal on the bar below the figure is reached.
32. Why is the total count about 30 or 32 ATP molecules rather than a specific number?
33. Fermentation allows for the production of ATP without using either ____________ or any
_________________________________.
34. For aerobic respiration to continue, the cell must be supplied with oxygen—the ultimate electron
acceptor. What is the electron acceptor in fermentation? _______
35. Alcohol fermentation starts with glucose and yields ethanol. Explain this process, and be sure to
describe how NAD+ is recycled.
36. Lactic acid fermentation starts with glucose and yields lactate. Explain this process, and be sure to
describe how NAD+ is recycled.
37. Explain why pyruvate is a key juncture in metabolism.
38. What three organic macromolecules are often utilized to make ATP by cellular respiration?
39. Explain the difference in energy usage between the catabolic reactions of cellular respiration and
anabolic pathways of biosynthesis.
40. Explain how AMP stimulates cellular respiration while citrate and ATP inhibit it.
41. Phosphofructokinase is an allosteric enzyme that catalyzes an important step in glycolysis. Explain
how this step is a control point in cellular respiration.
Unit 2.5: Photosynthesis
This chapter is as challenging as the one you just finished on cellular respiration. However, conceptually it
will be a little easier because the concepts you have already learned - namely, chemiosmosis and an electron
transport system – will play a central role in photosynthesis.
1. As a review, define the terms autotroph and heterotroph. Keep in mind that plants have
mitochondria and chloroplasts and do both cellular respiration and photosynthesis!
2. Take a moment to place the chloroplast in the leaf by working through slide 11. Draw a picture of
the chloroplast and label the stroma, thylakoid, thylakoid space, inner membrane, and outer
membrane.
3. Use both chemical symbols and words to write out the formula for photosynthesis (use the one that
indicates only the net consumption of water). Notice that the formula is the opposite of cellular
respiration. You should know both formulas from memory.
4. Using 18O as the basis of your discussion, explain how we know that the oxygen released in
photosynthesis comes from water.
5. Photosynthesis is not a single process, but two processes, each with multiple steps.
a. Explain what occurs in the light reactions stage of photosynthesis. Be sure to use NADP+ and
photophosphorylation in your discussion.
b. Explain the Calvin cycle, utilizing the term carbon fixation in your discussion.
6. The details of photosynthesis will be easier to organize if you can visualize the overall process.
Using slides 19-23 identify the items that are cycled between the light reactions and the Calvin cycle.
7. Some of the types of energy in the electromagnetic spectrum will be familiar, such as X-rays,
microwaves, and radio waves. The most important part of the spectrum in photosynthesis is visible
light. What are the colors of the visible spectrum?
8. Notice the colors and corresponding wavelengths. Explain the relationship between wavelength and
energy.
9. Study slide 33 carefully; then explain the correlation between an absorption spectrum and an action
spectrum.
10. Describe how Englemann was able to form an action spectrum long before the invention of a
spectrophotometer.
11. A photosystem is composed of a protein complex called a ____________________ complex
surrounded by several ____________________ complexes.
12. Within the photosystems, the critical conversion of solar energy to chemical energy occurs. This
process is the essence of being a producer! Using slide 43 as a guide, explain the role of the
components of the photosystem listed below.
a. Reaction center complex:
b. Light-harvesting complex:
c. Primary electron acceptor:
13. Photosystem I (PS I) has at its reaction center a special pair of chlorophyll a molecules called P680.
What is the explanation for this name?
14. What is the name of the chlorophyll a at the reaction center of PS I called? _______________
15. Linear electron flow is, fortunately, easier to understand than it looks. It is an electron transport
chain, somewhat like the one we worked through in cellular respiration. While reading the section
“Linear Electron Flow” and studying slide 50 in in the lecture, briefly summarize each step.
Step
Brief Summary
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
16. The following set of questions deals with linear electron flow:
a. What is the source of energy that excites the electron in photosystem II? _______________
b. What compound is the source of electrons for linear electron flow? _______________
c. What is the source of O2 in the atmosphere? ___________________________
d. As electrons fall from photosystem II to photosystem I, the cytochrome complex uses the
energy to pump _______________ ions. This builds a proton gradient that is used in
chemiosmosis to produce what molecule? _______________
e. In _______________, NADP+ reductase catalyzes the transfer of the excited electron and H+
to NADP+ to form NADPH.
*Notice that two high-energy compounds have been produced by the light reactions: ATP and NADPH.
Both of these compounds will be used in the Calvin cycle.
17. The last idea in this challenging concept is how chemiosmosis works in photosynthesis. Describe
four ways that chemiosmosis is similar in photosynthesis and cellular respiration.
a.
b.
c.
d.
18. Use two key differences to explain how chemiosmosis is different in photosynthesis and cellular
respiration.
19. List the three places in the light reactions where a proton-motive force is generated by increasing the
concentration of H+ in the stroma.
a.
b.
c.
20. To summarize, note that the light reactions store chemical energy in _________________ and
_________________, which shuttle the energy to the carbohydrate-producing _______________ cycle.
The Calvin cycle is a metabolic pathway in which each step is governed by an enzyme, much like the citric
acid cycle in cellular respiration. However, keep in mind that the Calvin cycle uses energy (in the form of
ATP and NADPH) and is therefore anabolic. In contrast, cellular respiration is catabolic and releases energy
that is used to generate ATP and NADH.
21. The carbohydrate produced directly from the Calvin cycle is not glucose, but the three-carbon
compound _________________________. Each turn of the Calvin cycle fixes one molecule of CO2;
therefore, it will take _____ turns of the Calvin cycle to net one G3P.
22. Explain the important events that occur in the carbon fixation stage of the Calvin cycle.
23. The enzyme responsible for carbon fixation in the Calvin cycle, and possibly the most abundant
protein on Earth, is ____________________.
24. In phase two, the reduction stage, what molecule will donate electrons, and so is the source of the
reducing power? __________
25. In this reduction stage, the low-energy acid 1,3-bisphosphoglycerate is reduced by electrons from
NADPH to form the three-carbon sugar ___________.
26. Examine slide 65 in your text while we tally carbons. This figure is designed to show the production
of one net G3P. That means the Calvin cycle must be turned three times. Each turn will require a
starting molecule of ribulose bisphosphate (RuBP), a five-carbon compound. This means we start
with _____ carbons distributed in three RuBPs. After fixing three molecules of CO2 using the
enzyme _______________, the Calvin cycle forms six G3Ps with a total of _______ carbons. At this
point the net gain of carbons is _______, or one net G3P molecule.
27. Three turns of the Calvin cycle nets one G3P because the other five must be recycled to RuBP.
Explain how the regeneration of RuBP is accomplished.
28. The net production of one G3P requires _______ molecules of ATP and _______ molecules of
NADPH.
29. Explain what is meant by a C3 plant.
30. What happens when a plant undergoes photorespiration?
31. Explain how photorespiration can be a problem in agriculture.
32. Explain what is meant by a C4 plant.
33. Explain the role of PEP carboxylase in C4 plants, including key differences between it and rubisco.
34. Conceptually, it is important to know that the C4 pathway does not replace the Calvin cycle but
works as a CO2 pump that prefaces the Calvin cycle. Explain how changes in leaf architecture help
isolate rubisco in regions of the leaf that are high in CO2 but low in O2.
35. Explain the three key events in the C4 pathway.
a.
b.
c.
36. Compare and contrast C4 plants with CAM plants. In your explanation, give two key similarities
and two key differences.