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Teacher Packet
AP* is a trademark of the College Entrance Examination Board. The College Entrance Examination Board was not
involved in the production of this material.
by Campbell & Reece, Benjamin Cummings, 2002, 6th edition. Permissions Pending.
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Lab Review
General Strategies for Lab Based Exam Questions
To review the student and introduce strategies pertaining to the concepts and processes necessary
to successfully answer questions over laboratory topics.
Laboratory experiments are addressed on page 10 of the College Board AP Biology Course
Description Guide as described below.
To allow students to show their mastery of laboratory science skills and knowledge, each
year some questions on the objective portion of the AP Biology exam and/or one or more of
the four mandatory essay questions may reflect the topics and objectives associated with the
12 AP Biology labs.
AP Biology Exam Connections
With the exception of 2003 form B, a lab based question has appeared on both the form A and
form B version of the AP Biology test since the early 1990’s. As with many AP Biology free
response questions, lab topics are often intertwined with content or conceptual knowledge. The
list below identifies free response questions and the corresponding lab number that have been
previously. These questions are available from the College Board and can be downloaded free of
charge from AP Central
Free Response Questions
2008 B Question #1 Lab 12
2008 Question #2 Lab 12
2008 B Question #3 Lab 8
2007 Question #4 Lab 6
2007 B Question #1 Lab 11
2006 Question #3 Lab 9
2006 B Question #3 Lab 9
2005 Question #1 Lab 5
2005 B Question #4 Lab 1
2004 Question #3 Lab 4B
2004 B Question #2 Lab 12
2003 Question #1 Lab 7
2002 B Question #2 Lab 10
2002 Question #2 Lab 11
2002 Question #4 Lab 1
2001 Question #3 Lab 12
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Lab Review
General Strategies for Lab Based Exam Questions
Lab Questions & The AP Biology Exam: The Unwritten Rules
Based on previous history from released and practice exams, ~20-30% of the Multiple Choice (MC)
section and ~25% of the Free Response (FR) section are lab based.
Multiple Choice
Free Response
The lab based MC questions are typically found
1 of the 4 free response questions will usually
at the end of the exam.
combine lab material with conceptual (textbook)
material. This review packet has a specific
“Integrating Content” section for each lab to aid in
These questions are usually found as question
sets (1 passage or data set with 3-4 questions about preparation for this type of question.
the passage).
The free response lab question is significantly
more likely to be based on one of the College
These questions are sometimes based on the
Board recommended labs, often with a twist.
College Board recommended labs.
There seem to be two categories of lab questions:
Type I: The “experimental design”
Type II: The “Here’s the lab we did.
Here’s the data we produced. Analyze it
and explain it” question
*Type II seems to be much more common on Form
A of the exam (the form that is taken in the U.S.).
Terminology + explanation = 1 pt on the FR section. Stating that “a substance moves from high to low
concentration” or that “a substance diffuses” may not earn a point. A statement such as “the substance
diffuses from high to low concentration” will surely earn a point.
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Lab Review
The Type I Free Response Lab Question: Experimental Design
If asked to “Design an experiment testing the effect of X on Y…”
1. Hypothesis: Be able to define hypothesis and provide a valid hypothesis. An “if, then” statement is an
easy way to start. Example: “If I give a plant fertilizer A then it will grow faster than a plant given
fertilizer B.”
2. Constant Environment: List a few constants and state that only one variable will change (the
independent variable). Example “Each plant will get 300mL of water per day, identical amounts of soil,
and will be exposed to X amount of light, etc. The only experimental variable that I will introduce is
fertilizer. Plant A will receive brand A, Plant B will receive brand B, etc.”
3. Variables: An independent variable is the variable that is manipulated. I change the Independent
variable. The dependent variable is what is measured as a result of the independent variable. Be sure to
identify and/or define both. Example: “The independent variable is the type of fertilizer used. The
dependent variable is the mass of the plant at time X.”
4. Result validation: How will measurements and conclusions be reached? What apparatus will be used?
Example: “I will determine which fertilizer creates the most overall plant growth over time X by simply
measuring the plant’s entire mass with an electronic balance”
5. Large testing groups: Explain why large sample sizes are necessary and specifically mention large
sample size relative to the lab. Example: “I will test the largest sample size of plants possible, hundreds
for example. Small sample sizes allow for greater variation due to chance. Larger sample sizes ensure
greater validity. ” OR “We will compile class data to increase sample size in order to reduce the
likelihood of variation due to chance”
6. Graphs: It may be necessary to estimate and draw a rough sketch of what the data might look like.
Example: “Here are my expected results graphed out.” Be sure to title graphs, label axes, and provide
units if appropriate.
7. Conclusions: If a graph or data is presented, make a conclusion statement. This simply means putting
the graph into words. Example: “If you notice in my graphs, I can conclude that fertilizer A resulted in
more plant mass than fertilizer B” OR “If you notice the slope of the line representing growth is steeper
for plant A than plant B. Plant A is growing at a faster rate.”
8. Discussion- It may be necessary to discuss WHY these results are what they are. Example: “Here is
why I think plant fertilizer A resulted in a faster growth rate than fertilizer B….”
9. If appropriate introduce the idea that statistical analysis will be used to determine if the results are
valid. In an experiment with an expected outcome for example, chi square analysis could be used.
10. Repeat- Repetition will also increase validity. Example: “I would repeat this experiment over and
over to validate my findings.”
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Lab Review
The Type II Free Response Lab Question: Here’s the data. Analyze. Explain.
If given a set of lab data and asked to graph and explain the results….
1. There of course may be overlap from advice given in the “Type I” question section…such as
hypothesis, etc.
2. Graphing- Realize that there are usually 2-3 pts given for “7th grade graphing skills.” Do not get in a
rush and miss out on these easy points:
Title the graph
Label X and Y axis
Provide units on your axis labels
Typically the dependent variable is on the y-axis and the independent variable (often time) is on
the x-axis.
Legend- provide a legend if multiple data sets are graphed.
3. Conclusion statement: see #7 above.
4. The question may then ask for a prediction of outcome given a different variable. Example: “What
would happen if the temperature were increased in this experiment?” Be sure to make a prediction and
justify your prediction with conceptual knowledge and if possible the data provided.
5. The question will then likely ask for additional conceptual knowledge about the topic.
The lab question typically has the highest average score of all 4 free response questions (~4-5 out of 10
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Lab: Physiology of the Circulatory System
Lab Specific Background Information
Blood pressure is essentially a measurement of arterial pressure during ventricular contraction
(systolic) and ventricular filling or relaxing (diastolic). Blood pressure is represented as a
fraction (systolic/diastolic).
Obviously pressure should be highest during ventricular contraction, so the fraction will have a
higher number in the numerator in a normal individual. The most commonly cited number for
“normal” is ~120/80 though this number is in actuality age dependent.
Measuring Blood Pressure: Using a Sphygmomanometer & Stethoscope
1. The sphygmomanometer (hereafter called the blood pressure or b.p. cuff) is inflated to a pressure
that exceeds the pressure inside the brachial artery. The pressure in the artery succumbs to the
external pressure of the b.p. cuff and is closed. Blood will no longer be rushing through the
brachial artery as evidenced by the lack of sound via stethoscope (see pic #2 above).
2. Pressure is slowly dialed down on the b.p. cuff releasing air and alleviating pressure. Once the
pressure in the cuff is less than that inside the artery, blood will begin to once again rush through
the artery. One will now be able to hear a pulsing of blood via the stethoscope (see pic #3 above).
The initial pulse sound represents the systolic pressure. One can usually see the b.p. dial
“pulsing” with the heart rate as well, though the stethoscope reading is typically used for the sake
of precision.
3. As pressure is decreased further, the pulse sounds will eventually cease. This point is the
diastolic pressure. At this point the lack of pressure in the b.p. cuff is such that it artery is
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The Experimental Design: Effects of Exercise on Heart Rate (HR) and Blood Pressure (BP)
Hypothesis: If the amount of exercise/activity increases, then the heart rate and blood pressure will
Independent Variable: Exercise
After the subject has been reclining for 10 minutes, take a HR and BP reading. After the subject
has been seated for 10 minutes take a HR and BP reading. Have the subject stand for 10 minutes
and take a HR and BP reading. Have the subject walk for 10 minutes and immediately take a
reading. Have the subject walk a flight of stairs for 10 minutes and immediately take a reading.
Measurement: HR and BP
Measure HR by feeling for the pulse of the radial artery. Count for 15 seconds and multiply by 4.
Follow instructions in the previous section for obtaining a BP with a b.p. cuff and stethoscope.
Constants: All other variable will remain constant.
The subject will not talk, eat, drink, etc.
Control: The control group does not exercise.
The control group in this lab is the reclining person.
Graph data: The dependent variable Heart Rate (beats per minute) vs. the independent variable Intensity
of Exercise (arbitrary units)*
*Note the lab calls for calculating a fitness level by also including changes in blood pressure from sitting
to standing, etc. This is less likely to appear on the exam. It is more likely that the student will be asked
to explain why blood pressure would increase/decrease or the concepts behind how a blood pressure cuff
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Integrating Content: The role of the brain, red blood cells, and hemoglobin
The Brain
Cells that are working heavily (muscles during exercise) will require more O2 (final electron
acceptor in the ETC) and will produce more CO2 (due to Krebs cycle and pyruvate oxidation).
Humans are water based organisms. When CO2 dissolves in water it is converted to carbonic acid
which, due to instability is further decomposed into bicarbonate ions. Most CO2 transport occurs
as bicarbonate ions dissolved in the red blood cells.
CO2 +H2O
HCO3- + H+
The medulla oblongata of the brain monitors the pH level of blood. When the pH is low, the
brain will increase heart and respiratory rates in order to maintain homeostasis. Contrary to what
many students assume, the brain indirectly monitors CO2 levels primarily as opposed to O2 when
determining rates of respiration and heart rate.
Red Blood Cells & Hemoglobin
Hemoglobin (Hb) carried by red blood cells (RBC’s) also responds to pH. Like all proteins, Hb
will begin to change shape as it encounters warmer or more acidic environments. In this case
however, Hb will undergo slight conformational changes as it encounters warmer, more acidic
tissues. These fully reversible, slight changes in shape result in Hb holding on “less tightly”
(decreased affinity) to O2. Exercising muscles are warm (friction) and acidic (lactic acid). Hb
will therefore “know” to drop off more O2 molecules at muscles that are contracting due to
Lab: Enzyme Catalysis
Lab Specific Background Information
The published version of this lab utilizes catalase enzyme and the substrate H2O2. Catalase is
found in essentially all living cells. Hydrogen Peroxide is broken down via the equation below
2H2O2 2H2O + O2
One could measure the rate of reaction by measuring the appearance of one of the products (H2O
or O2) or the disappearance of the reactant H2O2. If this system is sealed, the release of O2 could
be measured as an increase in pressure.
Note: In this particular lab set up, reaction rate is measured in real time. It is therefore not
necessary to stop the reaction prior to measurement (unlike the published AP lab). If one needed
to run an enzymatic reaction for a specific amount of time exactly, then one could stop an
enzymatic reaction at will by adding an adequate amount of a strong acid such as H2SO4 that is
highly concentrated (6M for example). This drastic drop in pH will denature the enzyme and stop
further reactions. In this case, the H2SO4 will have no effect on the reactants or product of the
above reaction and will only affect the enzyme.
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The Experimental Design: Appearance of Oxygen vs. Enzyme Concentration
Hypothesis: If enzyme concentration increases, then the pressure due to the appearance of O2 will
Independent Variable: Enzyme concentration
With X drops of enzyme in a test tube Measure increase in pressure due to appearance of O2.
Repeat the experiment for 2X drops and 3X drops of enzyme.
Constants: All variables will be kept constant, except the independent variable.
The amount of substrate (H2O2) will be the same in all test tubes. The temperature will be the
same as an increase in temperature could artificially increase pressure readings (PV=nRT) or
increase the actual reaction rate.
Control: The control group does not receive the treatment.
One test tube will receive a benign liquid such as water instead of the enzyme solution. This will
ensure that the natural breakdown of H2O2 due to light exposure is negligible (reality) or at least
calculable (theoretically).
Graph: The dependent variable pressure as measured in ATM, kPa, etc will be placed on the Y-axis. The
independent variable enzyme concentration as measured in drops, mL, etc. will be placed on the X-axis.
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Integrating Content: Biochemistry + Inhibition
Biochemistry- Importance of Shape
Enzymes are typically proteins (ribozymes are an exception for example). Proteins are made up
of amino acids joined in a specific sequence as coded by DNA (primary structure). They may
then be folded into 2 primary shapes: alpha helices and beta pleated sheets. These secondary
structures are stabilized by hydrogen bonding. When secondary structures interact with one
another, tertiary structures are created. Tertiary structures are stabilized by disulfide bridges.
Quaternary structures are due to entirely separate strands of amino acids (each with its own
tertiary structure) interacting one with another.
All proteins have a “window of life.” Temperatures that are out the functional range of the
enzyme will likely result in a protein conformation that is a more stable, yet useless form
(denaturation). Extremely low temperatures will reduce the molecular collisions to such a level
that an enzyme cannot generate product fast enough. Likewise, extremes in pH or other ion
concentrations may interfere with intermolecular interactions resulting in a useless enzyme.
Inhibition: Reversibly Turning Enzymes Off
Enzyme shape is determined by the
biochemistry described above. The shape of
the active site is critically important to the
function of the enzyme. Through inhibition,
an enzyme can be controlled and “turned off”
when not needed.
Competitive inhibitors bind to and compete
for the active site.
Non-competitive inhibitors bind to a
secondary site called the allosteric site.
Binding to this site causes a conformational
change in the enzyme which changes the
shape of the active site thus turning the
enzyme off.
Lab: Pigment Chromatography
Lab Specific Background
After placing leaf extract at the bottom of chromatography paper, the student will place the paper
in the various solvent solutions.
Some pigments are primarily nonpolar and are therefore more soluble in nonpolar solvents.
Some pigments are primarily polar and will therefore stick to the paper which is polar.
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Experimental Design: Separation of Pigments
Hypothesis: If the chromatography paper is placed in a nonpolar solvent solution, then the pigments will
separate in the following order: a,b,c,d.
Independent variable: Solvent solution
Various solvent solutions may be used in this lab. Each solution represents an independent
Constants: All variables will be kept constant, except the independent variable
Students will use the same types of containers, leaves, etc. while performing the experiments.
Control: The control group does not receive the treatment
A control group with water as a solvent may be used.
Data: Rf Values
Students will measure Rf values by dividing the distance migrated of a specific pigment by the
distance of the solvent front. All values will be less than or equal to 1.
Integrating Content: Plant Pigments & Biochemistry
Recall that oxygen is highly electronegative meaning that it will more strongly attract electrons
when covalently bonded than a hydrogen atom for example. This unequal sharing is responsible
for the slight negative charge of oxygen and the slight positive charge of hydrogen in water for
example. The same holds true for N-H bonds as well since Nitrogen is highly electronegative.
Recall that hydrocarbon chains are generally nonpolar since sharing of electrons is somewhat
Recall that paper is made primarily of cellulose. Cellulose is a polymer of glucose. Glucose is
fairly polar due to the number –OH groups attached to the ring structure.
Conclusion Be able to determine the relative polarity of molecules based on the number of polar
groups and nonpolar groups. Realize that highly polar pigments will Hydrogen bond with the
chromatography paper and will move more slowly (if at all) up the paper in the presence of
nonpolar solvents. Nonpolar pigments will move up with the solvent phase. Like dissolves like!
*It is possible that a free response question might then delve into the light reactions of photosynthesis
from this point. Be prepared to explain the role of pigments and electron transfer.
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Multiple Choice
Questions 1-3 refer to the diagram below in which the “Reaction Coordinate” of the y-axis represents
1. This letter best represents the expected effect produced by an enzyme.
Enzymes reduce the activation energy (represented by B). This reduction in
activation energy increases the rate at which reactants form products.
2. This letter represents the total energy change from reactants to products.
Reactant energy is represented by the 2nd horizontal dashed line. After reacting via
the enzyme catalyzed (B) or the non enzyme catalyzed pathway (C), the energy of
products is represented by the 3rd dashed line. The total energy change is therefore
the difference between the 2nd and 3rd dashed lines, or answer choice E.
3. This letter represents the amount of energy released during the reaction
The difference between reactant energy and product energy in an exergonic reaction
represents the amount of energy released. This question was written in part to train
students that it is permissible to use an answer choice more than once on question
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Question 4 refers to the following graphs of enzymatic reactions.
4. ATP is coupled to many cellular reactions in order to drive them to completion. Which of the
graphs best represent the reaction of ATP ADP + Pi?
(A) I only
(B) II only
(C) III only
(D) IV only
Answer choice C represents an endergonic reaction. The breakdown of ATP must be
exergonic if it is to provide energy to otherwise unfavorable reactions. Answer
choices B and D are unlikely if not absolutely impossible due to what may be
describes as a “reverse activation energy hump.”
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Questions 5-7 refer to the following lab scenario.
Using filter paper and a nonpolar solvent solution, Caleb performed a chromatography experiment on pen
ink. After performing the experiment, Caleb found that 3 bands migrated up the paper at different rates
while 1 band remained stationary.
5. What can Caleb safely conclude about his experiment?
I. Three of the dyes would have several hydrogen bonding sites.
II. One of the dyes would have several hydrogen bonding sites.
III. Three of the dyes are polar.
(A) I only
(B) II only
(C) III only
(D) I and III only
(E) II and III only
The polar dyes would be attracted to the polar paper. The nonpolar dyes will more
easily dissolve and migrate with the nonpolar solvent. Since one of the bands did not
migrate, one of the dyes is very polar. It is likely that this polarity is the result of
may Hydrogen bonding sites.
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After performing the experiment, Caleb compiled the following data:
Rf value
6. All of the following statements are correct EXCEPT:
(A) Pigment B is more polar than pigment C.
(B) Pigment D traveled the furthest of all of the ink dyes.
(C) Pigment A contains many sites available for hydrogen bonding.
(D) The separation of pigments is due primarily to molecular size and gravity
(E) The separation of pigments will produce the same results each time if the experiment is
repeated with precision.
The separation of pigments is not primarily due to molecular size and gravity.
Polarity is the property resulting in separation.
7. When attempting to repeat the experiment, Caleb ran out of the original solvent solution and
decided to use a highly polar solvent instead. Which of the following statements is most likely to
be correct?
(A) The highest Rf value will exceed 1.0.
(B) The dyes will not travel up the paper.
(C) The solvent will fail to travel up the paper.
(D) Nonpolar ink dyes will travel up the paper at a faster rate.
(E) Rf values will be different for each ink dye when compared to the original experiment.
As solvents change so do the Rf values. It is mathematically impossible for an Rf
value to exceed 1.0. It is likely that the polar dye will dissolve more readily in the
highly polar solvent and travel up the paper. The nonpolar dyes will travel up the
paper at a slower rate and in reverse order.
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Questions 8-10 refer to the following graph displaying experimental data on hemoglobin saturation.
8. Which of the following statements is most correct with regard to the graph above?
(A) The slope is greatest from 80 mmHg onward.
(B) As the partial pressure of O2 increases, the percent saturation of O2 decreases.
(C) Hemoglobin has more bound O2 at 20 mmHg than at 40 mmHg.
(D) On average, hemoglobin will have 2 bound O2 molecules at 26.8 mmHg.
(E) Increasing the partial pressure of O2 from 100 mmHg to 150mmHg would result in a
significant increase in O2 saturation.
At 26.8 mmHg hemoglobin is 50% saturated. Because hemoglobin contains 4
binding sites for O2, it is correct to state that on average each hemoglobin molecule
will be carrying 2 O2 molecules.
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9. Which of the following would decrease the slope of the line between 0mmHg and 40mmHg on
the graph above?
I. increase in temperature
II. decrease in pH
III. increase in glucose
(A) I only
(B) II only
(C) I and II only
(D) II and III only
(E) I, II, and III
Both an increase in temperature and a decrease in pH will promote a conformational
change in the shape of hemoglobin resulting in the release of O2. As hemoglobin
release O2 the slope of the line will therefore decrease and become slightly more
10. If all other variables were to remain constant, which of the following best predicts and/or explains
the expected difference as hemoglobin passes through the leg of a man that is sprinting.
(A) A 26.8 mmHg partial pressure of O2 would give greater than 50% O2 saturation of
(B) The shape or protein conformation of hemoglobin will remain unchanged.
(C) Hemoglobin will more readily release O2 to the surrounding cells
(D) Hemoglobin will have an increased affinity for O2.
(E) Hemoglobin will denature.
The structure of hemoglobin is such that it is more likely to release O2 to cells that
need it. Warm, acidic cells with low partial pressure of O2 will receive more oxygen
than inactive, relatively cool cells for example. Hb has a decreased affinity for O2
when in a warm, acidic environment.
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Free Response
1. Enzymes are involved in nearly all chemical reactions in an organism.
A. Describe a controlled experiment in which one is trying to determine the temperature range for
optimum reaction rate for Enzyme X that naturally produced in the human body. Be sure to
include a description of how you would go about collecting data and how you would present and
analyze the data using a graph.
6 points maximum for each of the following
_Identifying the independent variable
_Identify the dependent variable
_Explaining how the dependent variable will be measured
_Identifying or explaining the significance of a control group
_Identifying of explaining the significance of constants
_Identifying frequency at which measurements are taken
_Stating that the experiment will be repeated for validity
_Graphic display that must include an optimum “peak” somewhere between 95O and 105O F.
_X and Y axis labels
B. Enzyme activity may be hindered by inhibition. Describe non-competitive inhibition and contrast
it with competitive inhibition.
3 points maximum for each of the following
_Noncompetitive inhibition does not bind to the active site (competitive does).
_Noncompetitive inhibitors bind at the allosteric site.
_Binding at the allosteric site results in a conformational change or change in shape of the active site.
_Inhibition is reversible.
C. An excessively high fever can lead to death. Though multiple causes may be involved in reality,
hypothesize as to why this occurs using your knowledge of enzymes.
3 points maximum for each of the following
_The molecular shape of proteins or enzymes is important to the function of those enzymes.
_Excessive heat destabilizes bonding of the amino acids.
_Heat denatures enzymes/proteins.
_This change in protein shape results in a loss of function.
_Denaturation is generally not reversible.
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Free Response
2. Dan used a mixture of nonpolar solvents to separate the 4 pigments depicted below from a plant leaf by
paper chromatography. It should be noted that paper is made of cellulose. Note: lutein = xanthophyll
A. Using the diagram provided, list the order of separation of the 4 pigments and explain how you
determined the order of separation. Be sure to comment on chemical properties of the various
pigments, the paper, and the solvent that allow for separation.
5 points maximum for each of the following
Top -- Carotene - Lutein - Chlorophyll a - Chlorophyll b -- Bottom
_ _2 points if all 4 pigments are in the correct order
_1 point if after removing one incorrect pigment, the other 3 are in the correct order.
_The paper is polar primarily due to the hydroxyl (-OH) groups found in the glucose molecules.
_The pigments separate in the appropriate order due to the ability or lack thereof to form H bonds.
_Description of at least 1 molecule and why it will hydrogen bond with the paper or why it will not
hydrogen bond with the paper. The student must identify groups (-OH) or lack thereof that make this
_Chemical explanation of polarity (electronegativity, unequal sharing of electrons)
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B. Chlorophyll is essential for capturing light energy for photosynthesis. Explain how chlorophyll
pigments capture light and subsequently how this energy is utilized in the light reactions of
6 points maximum for each of the following
_Chlorophyll is located in photosystems.
_Photosystems are embedded in the thylakoid membrane which is shaped so as to increase surface area.
_Energy from the sun excites electrons of chlorophyll a to a higher energy level
_The excited electrons are passed to proton pumps where they will “drop” back down in energy levels.
_Proton pumps increase the H+ ion concentration inside the thylakoid.
_H+ ions will flow down the electrochemical gradient through ATP synthase resulting in the
phosphorylation of ADP.
_Electrons will be “reenergized” in photosystem II.
_Electrons will combine with NADP+ to make NADPH at the end of the light reactions.
_These electrons will eventually be shipped to the Calvin cycle where they will end up in the bonds of
G-3-P / glucose / starch.
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