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Question 1 of 34 · Organization of life: cells, tissues, organisms
Potato Cells in Sugar Water
Water moves into and out of cells by osmosis. In osmosis, water crosses a cell membrane from the side where water is more concentrated (fewer dissolved particles) to the side where water is less concentrated (more dissolved particles). The membranes of potato cells let water pass through easily, but they block sucrose (table sugar).
A student cut 18 potato cores of the same size from one potato. She blotted each core dry and weighed it. She placed three cores in each of six cups of sucrose solution. The solutions ranged from 0.0 mol/L (pure water) to 1.0 mol/L. All cups were kept at 22 °C. After 24 hours, she blotted each core dry again and reweighed it.
The graph shows the average percent change for the three cores in each solution. A positive value means the cores gained mass; a negative value means they lost mass.
Which statement best explains the result for the cores in the 0.8 mol/L sucrose solution?
Hint
Did those cores gain or lose mass? Then use the passage's rule for which way water moves.
Step-by-step solution
The graph shows that the cores in the 0.8 mol/L solution changed by −18.6%, so they lost mass. The passage says water moves "from the side where water is more concentrated (fewer dissolved particles) to the side where water is less concentrated (more dissolved particles)," and that the membranes "block sucrose."
Step by step:
The cores lost mass, so something left the cells. Sucrose cannot cross the membrane, so the only thing that can move is water.
Water leaves a cell when the outside has more dissolved particles than the inside.
So the 0.8 mol/L solution had a higher sucrose concentration than the cells' contents, and water moved out of the cells by osmosis.
Correct answer: The solution had a higher concentration of dissolved sugar than the cells' contents, so water moved out of the cells by osmosis.
Tip: In osmosis questions, ask two things: (1) which way did the mass change? (2) which side has more dissolved particles? Water always moves toward the side with more dissolved particles.
Question 2 of 34 · Organization of life: cells, tissues, organisms
Fill inPotato Cells in Sugar Water
Water moves into and out of cells by osmosis. In osmosis, water crosses a cell membrane from the side where water is more concentrated (fewer dissolved particles) to the side where water is less concentrated (more dissolved particles). The membranes of potato cells let water pass through easily, but they block sucrose (table sugar).
A student cut 18 potato cores of the same size from one potato. She blotted each core dry and weighed it. She placed three cores in each of six cups of sucrose solution. The solutions ranged from 0.0 mol/L (pure water) to 1.0 mol/L. All cups were kept at 22 °C. After 24 hours, she blotted each core dry again and reweighed it.
The graph shows the average percent change for the three cores in each solution. A positive value means the cores gained mass; a negative value means they lost mass.
At one sucrose concentration, the cores would neither gain nor lose mass, because the solution would match the concentration inside the potato cells.
Assume the graph is a straight line between neighboring data points. To the nearest hundredth, at what sucrose concentration would the percent change in mass be 0%?
mol/L
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Find the two neighboring points on either side of 0%. How far along that segment does the line reach 0%?
Step-by-step solution
The line crosses 0% between the points (0.2 mol/L, +9.2%) and (0.4 mol/L, −2.4%).
Step by step:
Over this segment, the concentration increases by 0.4 - 0.2 = 0.2 mol/L.
Over the same segment, the percent change falls by 9.2 - (-2.4) = 11.6 percentage points.
To get from +9.2% down to 0%, the line must fall 9.2 points. That is \dfrac{9.2}{11.6} \approx 0.793 of the way along the segment.
Check: 0.36 is a little closer to 0.4 than to 0.2, which makes sense because −2.4% is much closer to 0 than +9.2% is.
Correct answer: 0.36 (answers from 0.34 to 0.38 are accepted).
Tip: To estimate a value between two data points (interpolation), find what fraction of the way you must go along the segment, then take the same fraction of the change in x.
Question 3 of 34 · Organization of life: cells, tissues, organisms
Hot spotPotato Cells in Sugar Water
Water moves into and out of cells by osmosis. In osmosis, water crosses a cell membrane from the side where water is more concentrated (fewer dissolved particles) to the side where water is less concentrated (more dissolved particles). The membranes of potato cells let water pass through easily, but they block sucrose (table sugar).
A student cut 18 potato cores of the same size from one potato. She blotted each core dry and weighed it. She placed three cores in each of six cups of sucrose solution. The solutions ranged from 0.0 mol/L (pure water) to 1.0 mol/L. All cups were kept at 22 °C. After 24 hours, she blotted each core dry again and reweighed it.
The graph shows the average percent change for the three cores in each solution. A positive value means the cores gained mass; a negative value means they lost mass.
Look at the graph in the passage. Click the data point for the solution whose sucrose concentration was closest to the concentration inside the potato cells.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
When the inside and outside of a cell are equally concentrated, how much water moves in or out overall?
Step-by-step solution
When the solution outside matches the concentration inside the cells, water moves in and out at the same rate, so the core's mass barely changes. The best evidence is the point whose percent change is closest to 0%.
Step by step:
Read the six values: +17.6%, +9.2%, −2.4%, −11.8%, −18.6% and −21.4%.
Ignore the sign and compare the sizes of the changes: 17.6, 9.2, 2.4, 11.8, 18.6, 21.4.
The smallest change is 2.4%, at 0.4 mol/L.
Click the 0.4 mol/L point (−2.4%).
This also agrees with the estimate that the line crosses 0% at about 0.36 mol/L, which is much closer to 0.4 than to 0.2.
Tip: "Closest to no change" means the value nearest to zero, whether it is positive or negative. Do not pick the highest or lowest point just because it stands out.
Question 4 of 34 · Organization of life: cells, tissues, organisms
Potato Cells in Sugar Water
Water moves into and out of cells by osmosis. In osmosis, water crosses a cell membrane from the side where water is more concentrated (fewer dissolved particles) to the side where water is less concentrated (more dissolved particles). The membranes of potato cells let water pass through easily, but they block sucrose (table sugar).
A student cut 18 potato cores of the same size from one potato. She blotted each core dry and weighed it. She placed three cores in each of six cups of sucrose solution. The solutions ranged from 0.0 mol/L (pure water) to 1.0 mol/L. All cups were kept at 22 °C. After 24 hours, she blotted each core dry again and reweighed it.
The graph shows the average percent change for the three cores in each solution. A positive value means the cores gained mass; a negative value means they lost mass.
The three cores in the 0.2 mol/L solution had percent changes in mass of +8.1%, +9.0% and +10.5%. Which statement about these three results is correct?
Hint
Mean = sum ÷ number of values. Range = largest value − smallest value.
Step-by-step solution
Step by step:
Mean: add the three values and divide by 3: \dfrac{8.1 + 9.0 + 10.5}{3} = \dfrac{27.6}{3} = 9.2. The mean is +9.2%, which matches the value plotted on the graph for 0.2 mol/L.
Range: largest minus smallest: 10.5 - 8.1 = 2.4 percentage points.
Correct answer: The mean is +9.2% and the range is 2.4 percentage points.
Why the others fail:
+9.0% is the median (the middle value), not the mean.
10.5 is the largest value, not the range.
+27.6% is the sum; it was never divided by 3.
Tip: The range tells you how spread out repeated trials are. A small range (here 2.4 points) means the three cores behaved similarly, which makes the average more trustworthy.
Question 5 of 34 · Work, motion and forces
Hot spotTesting a Bridge Cable
Engineers who design suspension bridges must know how a steel cable responds to a pulling force. In a test lab, a short sample of cable was clamped at both ends. A machine pulled on it with a force that was increased in steps, and the stretch (the increase in length) was measured at each step. Force was measured in kilonewtons (kN); 1 kN = 1,000 newtons.
For small forces, the stretch is directly proportional to the force: doubling the force doubles the stretch, and the cable returns to its original length when the force is removed. The largest force for which this is true is the cable's elastic limit. Beyond the elastic limit, the cable stretches more easily, and it stays permanently longer even after the force is removed. The last point on the graph shows where the sample broke.
To keep bridges safe, engineers use a safety factor of 4: the largest load a cable is allowed to carry in service is its breaking force divided by 4.
Click the point on the graph that shows the cable's elastic limit.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Find the last point that still lies on the straight line through the origin.
Step-by-step solution
The passage says that for small forces the stretch is directly proportional to the force, and that "The largest force for which this is true is the cable's elastic limit." On a graph, direct proportion is a straight line through the origin.
Step by step:
Check the early points: 10 kN at 2 mm, 20 kN at 4 mm, 30 kN at 6 mm, 40 kN at 8 mm. Each 2 mm of stretch adds exactly 10 kN, so these points lie on one straight line (5 kN per mm).
The next point is 44 kN at 10 mm. If the straight line continued, 10 mm would need 50 kN. Only 44 kN was needed, so the cable has started to stretch more easily: the line bends.
The last point on the straight part is (8 mm, 40 kN).
Correct answer: the point at 8 mm and 40 kN.
The point marked "Sample broke" (20 mm, 52 kN) is the breaking point, not the elastic limit.
Tip: When a graph changes shape, check the slope between each pair of neighboring points. The place where the slope first changes is usually what the question is about.
Question 6 of 34 · Work, motion and forces
Testing a Bridge Cable
Engineers who design suspension bridges must know how a steel cable responds to a pulling force. In a test lab, a short sample of cable was clamped at both ends. A machine pulled on it with a force that was increased in steps, and the stretch (the increase in length) was measured at each step. Force was measured in kilonewtons (kN); 1 kN = 1,000 newtons.
For small forces, the stretch is directly proportional to the force: doubling the force doubles the stretch, and the cable returns to its original length when the force is removed. The largest force for which this is true is the cable's elastic limit. Beyond the elastic limit, the cable stretches more easily, and it stays permanently longer even after the force is removed. The last point on the graph shows where the sample broke.
To keep bridges safe, engineers use a safety factor of 4: the largest load a cable is allowed to carry in service is its breaking force divided by 4.
In the range where stretch is directly proportional to force, how much would this cable sample stretch under a force of 26 kN?
Hint
Use the straight part of the graph to find how many kilonewtons produce 1 mm of stretch.
Step-by-step solution
On the straight part of the graph, the force rises by 10 kN for every 2 mm of stretch (for example, 40 kN at 8 mm).
Step by step:
Force per millimeter: \dfrac{40 \text{ kN}}{8 \text{ mm}} = 5 kN per mm.
26 kN is below the elastic limit (40 kN), so the direct proportion still applies.
Stretch: \dfrac{26 \text{ kN}}{5 \text{ kN/mm}} = 5.2 mm.
Check: 26 kN lies between 20 kN (4 mm) and 30 kN (6 mm), so the stretch must lie between 4 mm and 6 mm. 5.2 mm fits.
Correct answer: 5.2 mm.
Tip: For a direct proportion, find the constant (here 5 kN per mm) from any clean point on the line, then divide or multiply. Always check that your answer falls between neighboring data points.
Question 7 of 34 · Work, motion and forces
Testing a Bridge Cable
Engineers who design suspension bridges must know how a steel cable responds to a pulling force. In a test lab, a short sample of cable was clamped at both ends. A machine pulled on it with a force that was increased in steps, and the stretch (the increase in length) was measured at each step. Force was measured in kilonewtons (kN); 1 kN = 1,000 newtons.
For small forces, the stretch is directly proportional to the force: doubling the force doubles the stretch, and the cable returns to its original length when the force is removed. The largest force for which this is true is the cable's elastic limit. Beyond the elastic limit, the cable stretches more easily, and it stays permanently longer even after the force is removed. The last point on the graph shows where the sample broke.
To keep bridges safe, engineers use a safety factor of 4: the largest load a cable is allowed to carry in service is its breaking force divided by 4.
Using the safety factor described in the passage, what is the largest load that a cable like this sample is allowed to carry in service?
Hint
Which force does the passage say to divide by 4?
Step-by-step solution
The passage says "the largest load a cable is allowed to carry in service is its breaking force divided by 4." The graph marks the breaking point at 52 kN.
Step by step:
Breaking force = 52 kN (the point labeled "Sample broke").
Allowed load = \dfrac{52 \text{ kN}}{4} = 13 kN.
Correct answer: 13 kN.
Notice that 13 kN is well below the elastic limit (40 kN). That is the point of a safety factor: in normal service, the cable is never pulled hard enough to stretch permanently.
Tip: When a passage gives a rule in words, underline exactly which quantity it uses. Here it is the breaking force, not the elastic limit.
Question 8 of 34 · Work, motion and forces
Testing a Bridge Cable
Engineers who design suspension bridges must know how a steel cable responds to a pulling force. In a test lab, a short sample of cable was clamped at both ends. A machine pulled on it with a force that was increased in steps, and the stretch (the increase in length) was measured at each step. Force was measured in kilonewtons (kN); 1 kN = 1,000 newtons.
For small forces, the stretch is directly proportional to the force: doubling the force doubles the stretch, and the cable returns to its original length when the force is removed. The largest force for which this is true is the cable's elastic limit. Beyond the elastic limit, the cable stretches more easily, and it stays permanently longer even after the force is removed. The last point on the graph shows where the sample broke.
To keep bridges safe, engineers use a safety factor of 4: the largest load a cable is allowed to carry in service is its breaking force divided by 4.
A student says: "The sample stretched 4 mm under a force of 20 kN. Because stretch is proportional to force, the sample will stretch 16 mm under a force of 80 kN."
Which statement best evaluates the student's claim?
Hint
Does the proportion hold for every force on the graph? What happens at 52 kN?
Step-by-step solution
The student's arithmetic follows a proportion (80 \div 20 = 4, and 4 \times 4 mm = 16 mm), but the passage limits when that proportion is true.
Evidence:
The passage: stretch is directly proportional to force only up to the elastic limit. The graph shows that limit at 40 kN; after that, the line bends.
The graph's last point is labeled "Sample broke" at 52 kN.
Step by step:
80 kN is twice the elastic limit, so the direct proportion no longer applies.
Even more important, 80 kN is greater than the breaking force (52 kN). The sample would break before the force ever reached 80 kN.
So the claim extends a pattern far beyond the range of the data where it holds.
Correct answer: The claim is not valid: the proportion holds only up to about 40 kN, and the sample broke at 52 kN, so it could not carry 80 kN.
Tip: Be suspicious of any claim that extends a trend beyond the measured data. Check whether the graph changes shape or ends before the value in the claim.
Question 9 of 34 · Earth and its system components
Locating an Earthquake
An earthquake sends out several kinds of seismic waves. P waves (primary waves) are the fastest and arrive first at a seismograph station. S waves (secondary waves) travel more slowly and arrive later. The farther a station is from the earthquake's epicenter (the point on the surface directly above where the rock broke), the larger the gap between the two arrivals. This gap is called the S–P lag time.
The graph shows how long P waves and S waves take to travel different distances through the crust in one region.
Scientists also describe how much energy an earthquake releases using the moment magnitude scale. Each increase of 1.0 on this scale means the earthquake released about 32 times as much energy.
A seismograph station recorded the first P waves from an earthquake at 10:02:15 a.m. and the first S waves at 10:03:00 a.m. About how far was the station from the epicenter?
Hint
First find the S–P lag time in seconds. Then find the distance where the vertical gap between the two lines equals that time.
Step-by-step solution
Step by step:
Lag time: from 10:02:15 to 10:03:00 is 45 seconds.
On the graph, look for the distance where the S-wave line is 45 s above the P-wave line.
Read the gap at a few distances: at 300 km, P = 50 s and S = 80 s (gap 30 s); at 600 km, P = 100 s and S = 160 s (gap 60 s). The gap grows by 10 s for every 100 km.
A 45 s gap is therefore at 450 km (P = 75 s, S = 120 s, and 120 - 75 = 45).
Correct answer: 450 km.
Why the others fail:
270 km is where the P-wave line reaches 45 s, but 45 s is the lag time, not the P travel time.
170 km is where the S-wave line reaches 45 s, the same mistake with the other line.
45 km treats each second of lag as 1 km.
Tip: With two lines on one graph, ask what the question measures: one line's value, or the difference between the lines.
Question 10 of 34 · Earth and its system components
Locating an Earthquake
An earthquake sends out several kinds of seismic waves. P waves (primary waves) are the fastest and arrive first at a seismograph station. S waves (secondary waves) travel more slowly and arrive later. The farther a station is from the earthquake's epicenter (the point on the surface directly above where the rock broke), the larger the gap between the two arrivals. This gap is called the S–P lag time.
The graph shows how long P waves and S waves take to travel different distances through the crust in one region.
Scientists also describe how much energy an earthquake releases using the moment magnitude scale. Each increase of 1.0 on this scale means the earthquake released about 32 times as much energy.
A seismograph station in City A uses the S–P lag time to find that an earthquake's epicenter was 300 km away. What other information do scientists need to pinpoint the epicenter's location?
Hint
One distance tells you how far, but not in which direction. Picture all the places that are exactly 300 km from City A.
Step-by-step solution
The lag time gives only a distance, not a direction. Every point that is 300 km from City A lies on a circle with a radius of 300 km around the city. The epicenter could be anywhere on that circle.
Step by step:
Station 1 → one circle. The epicenter is somewhere on it.
Add a second station → a second circle. Two circles usually cross at two points, so there are still two possible locations.
Add a third station → a third circle. Only one point lies on all three circles: the epicenter.
Correct answer: The distances to the epicenter measured at two or more other stations, so that the circles around all the stations meet at one point.
This method of combining findings from several stations is called triangulation.
Tip: When one measurement leaves many possibilities, ask what new, independent measurement would rule them out. Repeating the same measurement in the same place adds no new information.
Question 11 of 34 · Earth and its system components
Locating an Earthquake
An earthquake sends out several kinds of seismic waves. P waves (primary waves) are the fastest and arrive first at a seismograph station. S waves (secondary waves) travel more slowly and arrive later. The farther a station is from the earthquake's epicenter (the point on the surface directly above where the rock broke), the larger the gap between the two arrivals. This gap is called the S–P lag time.
The graph shows how long P waves and S waves take to travel different distances through the crust in one region.
Scientists also describe how much energy an earthquake releases using the moment magnitude scale. Each increase of 1.0 on this scale means the earthquake released about 32 times as much energy.
Earthquake 1 had a magnitude of 5.2. Earthquake 2 had a magnitude of 7.2. About how many times as much energy did Earthquake 2 release as Earthquake 1?
Hint
Each step of 1.0 multiplies the energy by about 32. How many steps are there from 5.2 to 7.2?
Step-by-step solution
The passage says: "Each increase of 1.0 on this scale means the earthquake released about 32 times as much energy."
Step by step:
Difference in magnitude: 7.2 - 5.2 = 2.0, which is two steps of 1.0.
Each step multiplies the energy by 32, so two steps multiply it by 32 \times 32 = 32^2 = 1{,}024.
That is about 1,000 times as much energy.
Correct answer: about 1,000 times.
Why the others fail:
2 times uses the difference in magnitude as if it were the energy ratio.
64 times adds 32 + 32 instead of multiplying.
100 times uses a factor of 10 per step. (A factor of 10 per step describes how much bigger the ground shaking on a seismogram is, not the energy.)
Tip: On scales like magnitude or pH, each step is a multiplication. Two steps mean multiplying twice.
Question 12 of 34 · Heredity and genetics
Drag and dropCopying DNA in a Test Tube
The polymerase chain reaction (PCR) is a lab method that makes millions of copies of one short section of DNA. Crime labs, doctors and researchers use it when they have only a tiny sample.
A DNA molecule has two strands held together by base pairs: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). A PCR machine repeats a cycle of three temperature steps:
Denaturing (about 95 °C): heat breaks the bonds between the base pairs, and the two DNA strands separate.
Annealing (about 55 °C): short pieces of DNA called primers attach to matching (complementary) bases at each end of the target section.
Extending (about 72 °C): an enzyme called DNA polymerase adds bases one at a time, building a new strand that is complementary to each old strand.
Ideally, each cycle doubles the number of copies of the target section. The DNA polymerase used in PCR comes from Thermus aquaticus, a bacterium that lives in hot springs. Most enzymes, including those in human cells, lose their shape and stop working when heated to 95 °C, but this enzyme keeps working through many heating cycles.
The graph shows the temperature inside a PCR tube during the first two cycles.
The graph labels three parts of the first cycle P, Q and R. Drag each event into the part of the cycle when it happens.
Part P
Part Q
Part R
Tap a tile, then tap a box to place it.
Hint
Read the temperature of each labeled part on the graph, then match it to the temperatures listed in the passage.
Step-by-step solution
Match each labeled part of the graph to a temperature, then use the passage's list of steps.
Step by step:
Part P is held at about 95 °C. The passage: "Denaturing (about 95 °C): heat breaks the bonds between the base pairs, and the two DNA strands separate." → The two DNA strands separate.
Part Q is held at about 55 °C. "Annealing (about 55 °C): short pieces of DNA called primers attach…" → Primers attach to the ends of the target section.
Part R is held at about 72 °C (between the 70 and 80 grid lines). "Extending (about 72 °C): an enzyme called DNA polymerase adds bases…" → DNA polymerase builds new complementary strands.
Correct answer: P – strands separate; Q – primers attach; R – DNA polymerase builds new strands.
The order also makes sense: the strands must separate before primers can attach, and primers must attach before the enzyme can build from them.
Tip: When a graph and a passage describe the same process, find a value that links them (here, temperature) and use it to translate between the two.
Question 13 of 34 · Heredity and genetics
Copying DNA in a Test Tube
The polymerase chain reaction (PCR) is a lab method that makes millions of copies of one short section of DNA. Crime labs, doctors and researchers use it when they have only a tiny sample.
A DNA molecule has two strands held together by base pairs: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). A PCR machine repeats a cycle of three temperature steps:
Denaturing (about 95 °C): heat breaks the bonds between the base pairs, and the two DNA strands separate.
Annealing (about 55 °C): short pieces of DNA called primers attach to matching (complementary) bases at each end of the target section.
Extending (about 72 °C): an enzyme called DNA polymerase adds bases one at a time, building a new strand that is complementary to each old strand.
Ideally, each cycle doubles the number of copies of the target section. The DNA polymerase used in PCR comes from Thermus aquaticus, a bacterium that lives in hot springs. Most enzymes, including those in human cells, lose their shape and stop working when heated to 95 °C, but this enzyme keeps working through many heating cycles.
The graph shows the temperature inside a PCR tube during the first two cycles.
During annealing, a primer must attach to a section of a separated DNA strand with the bases T A C G G A. Which primer will attach to this section?
Hint
Use the base-pairing rule from the passage for each base, one at a time.
Step-by-step solution
The passage gives the base-pairing rule: "adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G)." A primer attaches to complementary bases.
Step by step:
Strand
T
A
C
G
G
A
Primer
A
T
G
C
C
T
Correct answer: A T G C C T.
Why the others fail:
T A C G G A is identical to the strand. Identical bases do not pair.
A U G C C U uses uracil (U), a base found in RNA, not DNA. The passage lists only A, T, C and G.
C G T A A G pairs T with C and A with G, which breaks the pairing rule.
Tip: In DNA, A pairs with T and C pairs with G. A memory trick: the letters with straight lines (A, T) pair together, and the curved letters (C, G) pair together.
Question 14 of 34 · Heredity and genetics
Fill inCopying DNA in a Test Tube
The polymerase chain reaction (PCR) is a lab method that makes millions of copies of one short section of DNA. Crime labs, doctors and researchers use it when they have only a tiny sample.
A DNA molecule has two strands held together by base pairs: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). A PCR machine repeats a cycle of three temperature steps:
Denaturing (about 95 °C): heat breaks the bonds between the base pairs, and the two DNA strands separate.
Annealing (about 55 °C): short pieces of DNA called primers attach to matching (complementary) bases at each end of the target section.
Extending (about 72 °C): an enzyme called DNA polymerase adds bases one at a time, building a new strand that is complementary to each old strand.
Ideally, each cycle doubles the number of copies of the target section. The DNA polymerase used in PCR comes from Thermus aquaticus, a bacterium that lives in hot springs. Most enzymes, including those in human cells, lose their shape and stop working when heated to 95 °C, but this enzyme keeps working through many heating cycles.
The graph shows the temperature inside a PCR tube during the first two cycles.
A crime lab starts with a sample containing 40 copies of a target DNA section. Assume that every cycle doubles the number of copies.
How many copies of the target section will there be after 12 cycles?
copies
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Doubling once multiplies by 2. Doubling 12 times multiplies by 2 twelve times.
Step-by-step solution
The passage says "each cycle doubles the number of copies."
Step by step:
After 1 cycle: 40 \times 2 = 80. After 2 cycles: 40 \times 2 \times 2 = 160. After n cycles: 40 \times 2^n.
For 12 cycles: 2^{12} = 4{,}096.
Copies: 40 \times 4{,}096 = 163{,}840.
Correct answer: 163,840 copies.
Calculator: on the TI-30XS, enter 2^12enter to get 4096, then multiply by 40.
Common mistakes:
40 \times 2 \times 12 = 960 treats the growth as adding the same amount each cycle.
40 \times 12^2 squares the wrong number.
Tip: "Doubles every cycle (or every generation, or every 20 minutes)" means exponential growth: start × 2^{\text{number of doublings}}. The numbers grow very fast, which is exactly why PCR works on tiny samples.
Question 15 of 34 · Organization of life: cells, tissues, organisms
Copying DNA in a Test Tube
The polymerase chain reaction (PCR) is a lab method that makes millions of copies of one short section of DNA. Crime labs, doctors and researchers use it when they have only a tiny sample.
A DNA molecule has two strands held together by base pairs: adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). A PCR machine repeats a cycle of three temperature steps:
Denaturing (about 95 °C): heat breaks the bonds between the base pairs, and the two DNA strands separate.
Annealing (about 55 °C): short pieces of DNA called primers attach to matching (complementary) bases at each end of the target section.
Extending (about 72 °C): an enzyme called DNA polymerase adds bases one at a time, building a new strand that is complementary to each old strand.
Ideally, each cycle doubles the number of copies of the target section. The DNA polymerase used in PCR comes from Thermus aquaticus, a bacterium that lives in hot springs. Most enzymes, including those in human cells, lose their shape and stop working when heated to 95 °C, but this enzyme keeps working through many heating cycles.
The graph shows the temperature inside a PCR tube during the first two cycles.
A student runs PCR using a DNA polymerase taken from human cells instead of the enzyme from Thermus aquaticus. She adds the enzyme once, at the start. After 25 cycles, the tube contains almost no new copies of the target section.
Which explanation is best supported by the passage?
Hint
Look at the first step of every cycle. What does the passage say happens to most enzymes at that temperature?
Step-by-step solution
The passage says: "Most enzymes, including those in human cells, lose their shape and stop working when heated to 95 °C, but this enzyme keeps working through many heating cycles." The graph shows that each cycle begins at 95 °C.
Step by step:
The human enzyme was added once, at the start.
Within the first 45 seconds (part P of cycle 1), the tube was heated to 95 °C.
The heat changed the human enzyme's shape, so it stopped working. Without a working polymerase, no new strands could be built in later cycles.
That is why the Thermus aquaticus enzyme is used: it comes from a bacterium that lives in hot springs and survives the repeated heating.
Correct answer: Heating to 95 °C changed the shape of the human enzyme, so it could no longer build new DNA strands.
Tip: An enzyme's shape determines its function. When a question describes high temperatures (or extreme pH) and an enzyme that "stops working," think denaturing: a change in shape.
Question 16 of 34 · Work, motion and forces
Lifting a Steel Beam
At a building site, a tower crane lifts a steel beam with a mass of 1,200 kg. An electric motor on the crane winds a steel cable around a drum, and the cable pulls the beam straight up. The diagram shows the crane and a force diagram of the beam during the lift.
During one lift, the beam started at rest on the ground, sped up briefly, moved upward at a constant speed for most of the trip, and then slowed to a stop 15 m above the ground. The whole lift took 30 seconds. During the lift, the motor used electrical energy at a rate of 9,800 watts (W).
Useful formulas:
Weight: W = mg, where g = 9.8 N/kg
Work: \text{work} = F \times d (joules, J)
Power: P = \dfrac{\text{work}}{t} (watts, W; 1 W = 1 J/s)
Efficiency: \dfrac{\text{useful power output}}{\text{power input}} \times 100 (percent)
While the beam is moving upward at a constant speed, how does the tension force in the cable compare with the weight of the beam?
Hint
If the speed is not changing, what is the net force on the beam?
Step-by-step solution
The passage says the beam "moved upward at a constant speed for most of the trip." The force diagram shows only two forces on the beam: tension (up) and weight (down).
Step by step:
Newton's first law: an object moving at a constant velocity (same speed, same direction) has a net force of zero. A net force is needed to change motion, not to keep it going.
With only two forces in opposite directions, a net force of zero means they are equal in size.
So, during the constant-speed part of the lift, tension = weight = mg = 1{,}200 \times 9.8 = 11{,}760 N.
(Tension is greater than the weight only briefly, at the start, when the beam speeds up. Near the end, when the beam slows down, tension is less than the weight.)
Correct answer: The tension equals the weight, because the net force on an object moving at a constant speed in a straight line is zero.
Tip: "Moving" does not mean "unbalanced forces." Ask whether the speed or direction is changing. If not, the forces are balanced.
Question 17 of 34 · Energy: conservation, transformation, flow
Fill inLifting a Steel Beam
At a building site, a tower crane lifts a steel beam with a mass of 1,200 kg. An electric motor on the crane winds a steel cable around a drum, and the cable pulls the beam straight up. The diagram shows the crane and a force diagram of the beam during the lift.
During one lift, the beam started at rest on the ground, sped up briefly, moved upward at a constant speed for most of the trip, and then slowed to a stop 15 m above the ground. The whole lift took 30 seconds. During the lift, the motor used electrical energy at a rate of 9,800 watts (W).
Useful formulas:
Weight: W = mg, where g = 9.8 N/kg
Work: \text{work} = F \times d (joules, J)
Power: P = \dfrac{\text{work}}{t} (watts, W; 1 W = 1 J/s)
Efficiency: \dfrac{\text{useful power output}}{\text{power input}} \times 100 (percent)
Calculate the crane's average useful power output during the whole 30-second lift, that is, the average rate at which work was done to raise the beam 15 m.
W
Type your answer in the box. Fractions like 3/4 are fine.
Hint
First find the beam's weight, then the work done to lift it 15 m, then divide by the time.
Step-by-step solution
Use the formulas in the passage. The beam starts and ends at rest, so overall the useful work done on it is the work to raise its weight 15 m.
Step by step:
Weight: W = mg = 1{,}200 \text{ kg} \times 9.8 \text{ N/kg} = 11{,}760 N.
Work: \text{work} = F \times d = 11{,}760 \text{ N} \times 15 \text{ m} = 176{,}400 J.
Power: P = \dfrac{\text{work}}{t} = \dfrac{176{,}400 \text{ J}}{30 \text{ s}} = 5{,}880 W.
Correct answer: 5,880 W.
Common mistakes:
Using the mass (1,200) instead of the weight in newtons gives 1{,}200 \times 15 \div 30 = 600, which is wrong because force must be in newtons.
Stopping at the work (176,400 J) gives energy, not power.
Reporting the motor's input (9,800 W): that includes energy wasted as heat.
Tip: Write the units at every step. Work comes out in joules and power in watts (joules per second); if your units don't match the question, you have skipped a step.
Question 18 of 34 · Energy: conservation, transformation, flow
Drag and dropLifting a Steel Beam
At a building site, a tower crane lifts a steel beam with a mass of 1,200 kg. An electric motor on the crane winds a steel cable around a drum, and the cable pulls the beam straight up. The diagram shows the crane and a force diagram of the beam during the lift.
During one lift, the beam started at rest on the ground, sped up briefly, moved upward at a constant speed for most of the trip, and then slowed to a stop 15 m above the ground. The whole lift took 30 seconds. During the lift, the motor used electrical energy at a rate of 9,800 watts (W).
Useful formulas:
Weight: W = mg, where g = 9.8 N/kg
Work: \text{work} = F \times d (joules, J)
Power: P = \dfrac{\text{work}}{t} (watts, W; 1 W = 1 J/s)
Efficiency: \dfrac{\text{useful power output}}{\text{power input}} \times 100 (percent)
Complete the description of the energy changes during the lift. Drag each form of energy into the correct box.
Energy entering the motor
Energy stored in the raised beam
Energy lost to the surroundings by the motor and moving parts
Tap a tile, then tap a box to place it.
Hint
What powers the motor? What kind of energy does an object gain by being higher above the ground? What does friction produce?
Step-by-step solution
Follow the energy from the power supply to the beam.
Step by step:
Energy entering the motor: the passage says the motor "used electrical energy at a rate of 9,800 watts." → Electrical energy.
Energy stored in the raised beam: an object lifted higher above the ground gains energy because of its position in Earth's gravity. → Gravitational potential energy. (The beam ends at rest, so it does not keep any kinetic energy.)
Energy lost to the surroundings: friction in the motor, drum and pulley, and electrical resistance in the wires, warm up the parts and the air. → Thermal energy (heat).
Correct answer: electrical → gravitational potential, with some lost as thermal energy.
This is why the motor's input (9,800 W) is larger than the useful output: energy is conserved, but some of it ends up as heat that does not help lift the beam.
Tip: In every real machine, some energy becomes thermal energy. When a question asks where the "lost" or "wasted" energy goes, the answer is almost always thermal energy.
Question 19 of 34 · Energy: conservation, transformation, flow
Lifting a Steel Beam
At a building site, a tower crane lifts a steel beam with a mass of 1,200 kg. An electric motor on the crane winds a steel cable around a drum, and the cable pulls the beam straight up. The diagram shows the crane and a force diagram of the beam during the lift.
During one lift, the beam started at rest on the ground, sped up briefly, moved upward at a constant speed for most of the trip, and then slowed to a stop 15 m above the ground. The whole lift took 30 seconds. During the lift, the motor used electrical energy at a rate of 9,800 watts (W).
Useful formulas:
Weight: W = mg, where g = 9.8 N/kg
Work: \text{work} = F \times d (joules, J)
Power: P = \dfrac{\text{work}}{t} (watts, W; 1 W = 1 J/s)
Efficiency: \dfrac{\text{useful power output}}{\text{power input}} \times 100 (percent)
What was the efficiency of the crane during this lift?
Hint
You need the useful power output first. Then compare it with the motor's power input.
Step-by-step solution
Efficiency compares useful power output with power input. The passage gives the input: "the motor used electrical energy at a rate of 9,800 watts (W)."
Step by step:
Useful output (from the lift itself): weight = 1{,}200 \times 9.8 = 11{,}760 N; work = 11{,}760 \times 15 = 176{,}400 J; power = 176{,}400 \div 30 = 5{,}880 W.
40% is the percent of the input that was wasted (100 - 60).
18% divides joules by watts (176{,}400 \div 9{,}800 = 18), which mixes up energy and power.
167% flips the fraction (9{,}800 \div 5{,}880). No machine can be more than 100% efficient, because energy cannot be created.
Tip: Efficiency is always output ÷ input, and it must be less than 100%. Make sure both numbers are the same kind of quantity (both watts, or both joules).
Question 20 of 34 · Evolution
Insect-Resistant Corn
Corn borers are moth caterpillars that tunnel into corn stalks. Scientists used genetic engineering to insert a gene from the soil bacterium Bacillus thuringiensis (Bt) into corn. The gene tells the corn's cells to make a protein that is toxic to corn borers but harmless to people. This corn is called Bt corn.
In a corn borer population, a few insects carry a rare allele that makes them resistant to the Bt toxin. The resistance allele is recessive: only borers with two copies of it can survive on Bt corn.
To slow the spread of resistance, farmers are advised to plant a refuge, an area of ordinary (non-Bt) corn next to their Bt corn. Many non-resistant borers grow up in the refuge. When a rare resistant borer from the Bt field mates with a borer from the refuge, most of their offspring have only one copy of the resistance allele.
Scientists followed two farming regions for six years. Both regions began planting Bt corn in Year 1. Farmers in Region 1 chose to plant refuges equal to 20% of their corn area. Farmers in Region 2 planted no refuges. Each year, the scientists collected corn borer larvae from each region and tested them in a lab. The table shows the percent of larvae that survived on a diet containing the Bt toxin.
Year
Region 1 (20% refuge): larvae surviving (%)
Region 2 (no refuge): larvae surviving (%)
1
0.5
0.5
2
0.6
1.2
3
0.9
3.8
4
1.5
10.5
5
2.4
24.0
6
3.6
41.0
Which statement best explains why the percent of corn borers able to survive the Bt toxin increased in Region 2?
Hint
Where did resistance come from in the first place, according to the passage? Which borers had offspring?
Step-by-step solution
The passage says "a few insects carry a rare allele that makes them resistant," and "only borers with two copies of it can survive on Bt corn." Region 2 had no refuge, so nearly all borers there fed on Bt corn.
Step by step (natural selection):
Variation already existed: a few borers carried the resistance allele before Bt corn was planted.
Selection: on Bt corn, borers with two resistance alleles survived; the others died.
Inheritance: the survivors mated and passed the resistance allele to their offspring.
Over generations: the allele became more common, so the percent surviving rose from 0.5% to 41.0%.
Correct answer: Borers that already had two resistance alleles survived on Bt corn and passed the allele to their offspring, so the allele became more common each generation.
Tip: In evolution questions, reject any choice that says individuals changed themselves or that the environment created the needed trait. Natural selection acts on variation that is already present.
Question 21 of 34 · Evolution
Drop-downInsect-Resistant Corn
Corn borers are moth caterpillars that tunnel into corn stalks. Scientists used genetic engineering to insert a gene from the soil bacterium Bacillus thuringiensis (Bt) into corn. The gene tells the corn's cells to make a protein that is toxic to corn borers but harmless to people. This corn is called Bt corn.
In a corn borer population, a few insects carry a rare allele that makes them resistant to the Bt toxin. The resistance allele is recessive: only borers with two copies of it can survive on Bt corn.
To slow the spread of resistance, farmers are advised to plant a refuge, an area of ordinary (non-Bt) corn next to their Bt corn. Many non-resistant borers grow up in the refuge. When a rare resistant borer from the Bt field mates with a borer from the refuge, most of their offspring have only one copy of the resistance allele.
Scientists followed two farming regions for six years. Both regions began planting Bt corn in Year 1. Farmers in Region 1 chose to plant refuges equal to 20% of their corn area. Farmers in Region 2 planted no refuges. Each year, the scientists collected corn borer larvae from each region and tested them in a lab. The table shows the percent of larvae that survived on a diet containing the Bt toxin.
Year
Region 1 (20% refuge): larvae surviving (%)
Region 2 (no refuge): larvae surviving (%)
1
0.5
0.5
2
0.6
1.2
3
0.9
3.8
4
1.5
10.5
5
2.4
24.0
6
3.6
41.0
Complete the description of the study.
The independent variable is . The dependent variable is . This is .
Choose an answer from each menu.
Hint
The independent variable is what differs between the groups being compared. The dependent variable is what is measured. Who decided which farms used refuges?
Step-by-step solution
Blank 1 (independent variable): the factor that differs between the groups being compared. The two regions differ in whether farms planted refuges (20% refuge vs. no refuge).
Blank 2 (dependent variable): what was measured to see the effect: the percent of larvae that survived the Bt toxin in the lab test.
Blank 3 (type of study): the passage says farmers in Region 1 "chose to plant refuges" and scientists "followed" the regions. The scientists did not assign refuges to farms, so this is an observational study, because the scientists did not decide which farms planted refuges. That matters: the regions might differ in other ways too (climate, other crops), which an experiment with random assignment would control.
Correct answers: whether farms planted refuges; the percent of larvae that survived the toxin; an observational study, because the scientists did not decide which farms planted refuges.
Tip: Ask "Who chose the groups?" If the researchers assigned the treatment, it is an experiment. If they only watched what people or nature already did, it is an observational study.
Question 22 of 34 · Evolution
Insect-Resistant Corn
Corn borers are moth caterpillars that tunnel into corn stalks. Scientists used genetic engineering to insert a gene from the soil bacterium Bacillus thuringiensis (Bt) into corn. The gene tells the corn's cells to make a protein that is toxic to corn borers but harmless to people. This corn is called Bt corn.
In a corn borer population, a few insects carry a rare allele that makes them resistant to the Bt toxin. The resistance allele is recessive: only borers with two copies of it can survive on Bt corn.
To slow the spread of resistance, farmers are advised to plant a refuge, an area of ordinary (non-Bt) corn next to their Bt corn. Many non-resistant borers grow up in the refuge. When a rare resistant borer from the Bt field mates with a borer from the refuge, most of their offspring have only one copy of the resistance allele.
Scientists followed two farming regions for six years. Both regions began planting Bt corn in Year 1. Farmers in Region 1 chose to plant refuges equal to 20% of their corn area. Farmers in Region 2 planted no refuges. Each year, the scientists collected corn borer larvae from each region and tested them in a lab. The table shows the percent of larvae that survived on a diet containing the Bt toxin.
Year
Region 1 (20% refuge): larvae surviving (%)
Region 2 (no refuge): larvae surviving (%)
1
0.5
0.5
2
0.6
1.2
3
0.9
3.8
4
1.5
10.5
5
2.4
24.0
6
3.6
41.0
Which conclusion is best supported by the passage and the data in the table?
Hint
Check each choice against both columns and every year, not just Year 6.
Step-by-step solution
Test each choice against the table.
Step by step:
Region 1 (refuge): survival rose from 0.5% to 3.6%. It increased, but slowly.
Region 2 (no refuge): survival rose from 0.5% to 41.0%, much faster.
So refuges were linked to a much slower increase in resistance, but resistance still increased. That matches the passage's explanation: when resistant borers mate with refuge borers, most offspring have only one copy of the recessive allele and die on Bt corn.
Check the other choices:
"Prevented resistance from increasing at all" is contradicted by Region 1's rise from 0.5% to 3.6%.
"Increased by the same amount each year": Region 2's yearly increases were 0.7, 2.6, 6.7, 13.5 and 17.0 points. They grew larger each year.
"Refuges made the toxin more effective": the toxin was the same lab diet for both regions. Refuges change which alleles are common, not the toxin itself.
Correct answer: Planting refuges slowed the increase in resistance but did not stop it.
Tip: Watch for overstated conclusions (prevented, always, never) and for claims that mix up what changed. A supported conclusion fits every row of the data.
Question 23 of 34 · Chemical properties and reactions
Drop-downElectricity and Carbon Dioxide
Most of the carbon dioxide (CO₂) that people add to the atmosphere comes from burning fossil fuels such as coal, oil and natural gas. CO₂ is a greenhouse gas: it absorbs heat given off by Earth's surface, and rising CO₂ levels are warming Earth's climate.
Many power plants burn natural gas, which is mostly methane (CH₄). The reaction releases energy as heat:
Every way of producing electricity releases some CO₂ when its whole life cycle is counted: mining or growing the fuel, building the plant, running it, and taking it apart at the end. The graph shows approximate life-cycle emissions, in grams of CO₂ for each kilowatt-hour (kWh) of electricity produced. (1 metric ton = 1,000,000 g.)
Balance the equation for burning methane by choosing the missing coefficients.
CH₄ + O₂ → CO₂ + H₂O
Choose an answer from each menu.
Hint
Balance carbon first, then hydrogen, then oxygen. Count every atom on each side.
Step-by-step solution
A balanced equation has the same number of each kind of atom on both sides, because atoms are not created or destroyed.
Step by step:
Carbon: 1 C in CH₄ and 1 C in CO₂. Already balanced.
Hydrogen: 4 H in CH₄. Each H₂O has 2 H, so we need 2 H₂O (4 H).
Oxygen: the right side now has 2 O (in CO₂) + 2 O (in 2 H₂O) = 4 O. Each O₂ has 2 O, so we need 2 O₂.
Final check: \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}. Left: 1 C, 4 H, 4 O. Right: 1 C, 4 H, 4 O. ✓
Correct answers: 2 O₂ and 2 H₂O.
Tip: Leave the element that appears in the most compounds (here oxygen) for last, and never change the small subscripts; only change the coefficients in front.
Question 24 of 34 · Chemical properties and reactions
Fill inElectricity and Carbon Dioxide
Most of the carbon dioxide (CO₂) that people add to the atmosphere comes from burning fossil fuels such as coal, oil and natural gas. CO₂ is a greenhouse gas: it absorbs heat given off by Earth's surface, and rising CO₂ levels are warming Earth's climate.
Many power plants burn natural gas, which is mostly methane (CH₄). The reaction releases energy as heat:
Every way of producing electricity releases some CO₂ when its whole life cycle is counted: mining or growing the fuel, building the plant, running it, and taking it apart at the end. The graph shows approximate life-cycle emissions, in grams of CO₂ for each kilowatt-hour (kWh) of electricity produced. (1 metric ton = 1,000,000 g.)
In a lab, 16 g of methane burns completely with 64 g of oxygen. The reaction produces 44 g of carbon dioxide and some water. No other substances are involved.
What mass of water is produced?
g
Type your answer in the box. Fractions like 3/4 are fine.
Hint
In a chemical reaction, the total mass of the products equals the total mass of the reactants.
Step-by-step solution
The law of conservation of mass says that in a chemical reaction, atoms are only rearranged, so the total mass of the products equals the total mass of the reactants.
Step by step:
Mass of reactants: 16 \text{ g} + 64 \text{ g} = 80 g.
Mass of products must also be 80 g.
Water: 80 \text{ g} - 44 \text{ g} = 36 g.
Correct answer: 36 g.
Check with the balanced equation: CH₄ + 2 O₂ → CO₂ + 2 H₂O. Each water molecule has a mass of about 18 units, so 2 H₂O ≈ 36, while CH₄ ≈ 16, 2 O₂ ≈ 64 and CO₂ ≈ 44. The numbers in the question match this equation exactly.
Tip: If a question gives the masses of all but one substance in a reaction, add up each side and subtract. Gases count too, even though you cannot see them.
Question 25 of 34 · Energy: conservation, transformation, flow
Electricity and Carbon Dioxide
Most of the carbon dioxide (CO₂) that people add to the atmosphere comes from burning fossil fuels such as coal, oil and natural gas. CO₂ is a greenhouse gas: it absorbs heat given off by Earth's surface, and rising CO₂ levels are warming Earth's climate.
Many power plants burn natural gas, which is mostly methane (CH₄). The reaction releases energy as heat:
Every way of producing electricity releases some CO₂ when its whole life cycle is counted: mining or growing the fuel, building the plant, running it, and taking it apart at the end. The graph shows approximate life-cycle emissions, in grams of CO₂ for each kilowatt-hour (kWh) of electricity produced. (1 metric ton = 1,000,000 g.)
According to the graph, a natural gas power plant releases about what percent less CO₂ per kWh than a coal power plant?
Hint
Percent less = (difference ÷ the value you are comparing against) × 100. Which value is the starting point?
Step-by-step solution
Read the graph: coal = 820 g/kWh, natural gas = 490 g/kWh. "Percent less than coal" means the difference is compared with coal's value.
About 60% is \dfrac{490}{820}: natural gas emits about 60% as much as coal, which is 40% less.
About 67% is \dfrac{330}{490}: it divides by the natural gas value instead of the coal value.
330% treats the difference in grams as a percent.
Tip: "Percent less than X" and "percent more than X" both divide by X, the value after "than." Also note the difference between "60% as much" and "60% less."
Question 26 of 34 · Energy: conservation, transformation, flow
Fill inElectricity and Carbon Dioxide
Most of the carbon dioxide (CO₂) that people add to the atmosphere comes from burning fossil fuels such as coal, oil and natural gas. CO₂ is a greenhouse gas: it absorbs heat given off by Earth's surface, and rising CO₂ levels are warming Earth's climate.
Many power plants burn natural gas, which is mostly methane (CH₄). The reaction releases energy as heat:
Every way of producing electricity releases some CO₂ when its whole life cycle is counted: mining or growing the fuel, building the plant, running it, and taking it apart at the end. The graph shows approximate life-cycle emissions, in grams of CO₂ for each kilowatt-hour (kWh) of electricity produced. (1 metric ton = 1,000,000 g.)
A town uses 50,000 megawatt-hours (MWh) of electricity each year (1 MWh = 1,000 kWh). The town switches its entire electricity supply from coal power to wind power.
Using the life-cycle values in the graph, by how many metric tons per year would the CO₂ emissions from the town's electricity fall?
metric tons
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Find the savings per kWh first. Convert MWh to kWh, multiply, then convert grams to metric tons.
Step-by-step solution
Read the graph: coal = 820 g CO₂/kWh; wind = 12 g CO₂/kWh.
Total savings in grams: 808 \times 50{,}000{,}000 = 40{,}400{,}000{,}000 g.
Convert to metric tons (1 metric ton = 1,000,000 g): \dfrac{40{,}400{,}000{,}000}{1{,}000{,}000} = 40{,}400 metric tons.
Correct answer: 40,400 metric tons per year.
Common mistakes:
Using only the coal value (820) gives 41,000 metric tons; the wind power still emits 12 g/kWh, so subtract it.
Forgetting to convert MWh to kWh gives an answer 1,000 times too small (40.4).
Tip: In multi-step unit problems, write each unit next to each number. Units like g/kWh × kWh = g cancel like fractions and show you whether you are on track.
Question 27 of 34 · Energy: conservation, transformation, flow
Electricity and Carbon Dioxide
Most of the carbon dioxide (CO₂) that people add to the atmosphere comes from burning fossil fuels such as coal, oil and natural gas. CO₂ is a greenhouse gas: it absorbs heat given off by Earth's surface, and rising CO₂ levels are warming Earth's climate.
Many power plants burn natural gas, which is mostly methane (CH₄). The reaction releases energy as heat:
Every way of producing electricity releases some CO₂ when its whole life cycle is counted: mining or growing the fuel, building the plant, running it, and taking it apart at the end. The graph shows approximate life-cycle emissions, in grams of CO₂ for each kilowatt-hour (kWh) of electricity produced. (1 metric ton = 1,000,000 g.)
A student writes: "Wind power and nuclear power produce zero carbon dioxide, so switching to them would completely remove CO₂ emissions from making electricity."
Which statement best evaluates this claim?
Hint
What does the passage say is counted in 'life-cycle' emissions? What values does the graph show for wind and nuclear?
Step-by-step solution
The passage says the graph counts emissions over the whole life cycle: "mining or growing the fuel, building the plant, running it, and taking it apart at the end." The graph shows 12 g/kWh for both wind and nuclear power.
Step by step:
12 g/kWh is small (about 1.5% of coal's 820 g/kWh), but it is not zero.
Those emissions come mostly from building and maintaining the plants and, for nuclear power, mining fuel, not from burning fuel.
So switching would greatly reduce emissions but would not completely remove them. The claim is not supported.
Correct answer: The claim is not supported, because the graph shows that wind and nuclear power each release about 12 g of CO₂ per kWh over their life cycles, for example while the plants are built.
Tip: Words like zero, completely and all make a claim easy to disprove: a single counterexample in the data is enough.
Question 28 of 34 · Earth and its system components
Hot spotWhere Volcanoes Form
Most volcanoes form where magma (melted rock) rises through Earth's crust. The diagram is a simplified cross-section of Earth's outer layers. Arrows show the directions in which the plates move. Four locations are labeled W, X, Y and Z.
At a mid-ocean ridge, two plates move apart. Hot mantle rock rises into the gap and partly melts.
At a subduction zone, a dense oceanic plate sinks beneath another plate, forming a deep ocean trench. Water released from the sinking plate lowers the melting point of the mantle rock above it. The magma that forms rises through thick continental crust, melts some of that crust, and becomes richer in silica.
At a hot spot, a plume of unusually hot mantle rock rises beneath the middle of a plate.
Magma at mid-ocean ridges and at hot spots under the ocean comes directly from melted mantle rock and is basaltic. The type of magma affects how a volcano erupts:
Magma type
Silica content
Viscosity (resistance to flowing)
Typical eruption
Basaltic
about 50%
low (runny); gas escapes easily
gentle lava flows
Andesitic
about 60%
medium
often explosive
Rhyolitic
about 70%
high (thick and sticky); gas is trapped
very explosive, with tall ash clouds
Click the labeled location on the diagram where one plate is sinking beneath another plate.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Look for where a plate bends downward into the mantle, and the feature the passage says forms there.
Step-by-step solution
The passage says: "At a subduction zone, a dense oceanic plate sinks beneath another plate, forming a deep ocean trench."
Step by step:
W is at the mid-ocean ridge: the arrows point away from each other, so plates move apart there.
X is the island above the rising plume: a hot spot in the middle of the plate.
Y is where the oceanic plate meets the continent and bends down beneath it, forming a trench. ✓
Z is the volcano on the continent. It sits above the sinking plate, but the sinking itself starts at the trench (Y).
Correct answer: Location Y.
Tip: In cross-section diagrams, follow the arrows. Arrows pointing apart mean a divergent boundary; a plate angled down into the mantle means subduction (a convergent boundary).
Question 29 of 34 · Earth and its system components
Where Volcanoes Form
Most volcanoes form where magma (melted rock) rises through Earth's crust. The diagram is a simplified cross-section of Earth's outer layers. Arrows show the directions in which the plates move. Four locations are labeled W, X, Y and Z.
At a mid-ocean ridge, two plates move apart. Hot mantle rock rises into the gap and partly melts.
At a subduction zone, a dense oceanic plate sinks beneath another plate, forming a deep ocean trench. Water released from the sinking plate lowers the melting point of the mantle rock above it. The magma that forms rises through thick continental crust, melts some of that crust, and becomes richer in silica.
At a hot spot, a plume of unusually hot mantle rock rises beneath the middle of a plate.
Magma at mid-ocean ridges and at hot spots under the ocean comes directly from melted mantle rock and is basaltic. The type of magma affects how a volcano erupts:
Magma type
Silica content
Viscosity (resistance to flowing)
Typical eruption
Basaltic
about 50%
low (runny); gas escapes easily
gentle lava flows
Andesitic
about 60%
medium
often explosive
Rhyolitic
about 70%
high (thick and sticky); gas is trapped
very explosive, with tall ash clouds
Geologists study a volcano whose lava contains about 70% silica. Its past eruptions were very explosive and sent ash clouds high into the air. At which labeled location is this volcano most likely found?
Hint
Use the table to name the magma type. Then use the passage to decide where that kind of magma forms.
Step-by-step solution
This question combines the table with the passage and the diagram.
Step by step:
Table: about 70% silica and very explosive eruptions with tall ash clouds → rhyolitic magma.
Passage: "Magma at mid-ocean ridges and at hot spots under the ocean ... is basaltic." So W and X would have runny, about 50% silica magma and gentle eruptions. Rule them out.
Passage: at a subduction zone, magma "rises through thick continental crust, melts some of that crust, and becomes richer in silica." High-silica magma therefore forms above the sinking plate, under the continent.
Diagram: the volcano above the sinking plate on the continent is at Z. Y is the trench itself, where the plate begins to sink; magma forms deeper, under the continent.
Correct answer: Location Z.
Tip: When a question gives a property (silica %), translate it with the table first, then use the text to connect that property to a place. Two-source questions reward doing one step at a time.
Question 30 of 34 · Earth and its system components
Drag and dropWhere Volcanoes Form
Most volcanoes form where magma (melted rock) rises through Earth's crust. The diagram is a simplified cross-section of Earth's outer layers. Arrows show the directions in which the plates move. Four locations are labeled W, X, Y and Z.
At a mid-ocean ridge, two plates move apart. Hot mantle rock rises into the gap and partly melts.
At a subduction zone, a dense oceanic plate sinks beneath another plate, forming a deep ocean trench. Water released from the sinking plate lowers the melting point of the mantle rock above it. The magma that forms rises through thick continental crust, melts some of that crust, and becomes richer in silica.
At a hot spot, a plume of unusually hot mantle rock rises beneath the middle of a plate.
Magma at mid-ocean ridges and at hot spots under the ocean comes directly from melted mantle rock and is basaltic. The type of magma affects how a volcano erupts:
Magma type
Silica content
Viscosity (resistance to flowing)
Typical eruption
Basaltic
about 50%
low (runny); gas escapes easily
gentle lava flows
Andesitic
about 60%
medium
often explosive
Rhyolitic
about 70%
high (thick and sticky); gas is trapped
very explosive, with tall ash clouds
Drag each description to the location on the diagram that it describes.
Location W
Location X
Location Z
Tap a tile, then tap a box to place it.
Hint
Match each location to the bullet in the passage that describes it: ridge, hot spot or subduction zone.
Step-by-step solution
Use the diagram and the three bullet points in the passage.
Step by step:
W is at the mid-ocean ridge, where arrows point away from each other: "two plates move apart. Hot mantle rock rises into the gap." → Plates move apart, and magma rises to fill the gap.
X is an island above a rising plume in the middle of the oceanic plate: "a plume of unusually hot mantle rock rises beneath the middle of a plate." → A plume of hot mantle rock rises beneath the middle of a plate.
Z is a volcano on the continent above the sinking oceanic plate: "Water released from the sinking plate lowers the melting point of the mantle rock above it." → Magma forms above a plate that is sinking into the mantle.
Correct answer: W – plates move apart; X – plume beneath the middle of a plate; Z – magma forms above a sinking plate.
Tip: Not every volcano is at a plate boundary. Hot spots (like the one at X) can make volcanoes far from any boundary.
Question 31 of 34 · Earth systems and living things
Where Volcanoes Form
Most volcanoes form where magma (melted rock) rises through Earth's crust. The diagram is a simplified cross-section of Earth's outer layers. Arrows show the directions in which the plates move. Four locations are labeled W, X, Y and Z.
At a mid-ocean ridge, two plates move apart. Hot mantle rock rises into the gap and partly melts.
At a subduction zone, a dense oceanic plate sinks beneath another plate, forming a deep ocean trench. Water released from the sinking plate lowers the melting point of the mantle rock above it. The magma that forms rises through thick continental crust, melts some of that crust, and becomes richer in silica.
At a hot spot, a plume of unusually hot mantle rock rises beneath the middle of a plate.
Magma at mid-ocean ridges and at hot spots under the ocean comes directly from melted mantle rock and is basaltic. The type of magma affects how a volcano erupts:
Magma type
Silica content
Viscosity (resistance to flowing)
Typical eruption
Basaltic
about 50%
low (runny); gas escapes easily
gentle lava flows
Andesitic
about 60%
medium
often explosive
Rhyolitic
about 70%
high (thick and sticky); gas is trapped
very explosive, with tall ash clouds
Before some eruptions, magma rising beneath a volcano makes the ground swell upward. Scientists want to find out whether measuring ground swelling at the volcano at location Z could give nearby towns an early warning of eruptions.
Which plan would give the most useful evidence?
Hint
To link swelling to eruptions, you need measurements before eruptions, repeated over time, and records of when eruptions happened.
Step-by-step solution
To test whether swelling can predict eruptions, scientists need to see whether swelling happens before eruptions and not at other times.
Step by step:
The plan needs repeated measurements over a long time, so there is a baseline (normal ground level) and a record of changes.
It needs measurements at several points, so one faulty instrument or a small local slide does not mislead them.
It must compare the swelling record with the dates of eruptions, to see whether swelling came first.
Only the plan that measures ground height at several points every day for several years and compares it with eruption dates does all three.
Correct answer: Measure the height of the ground at several points on the volcano every day for several years, and compare the records with the dates of any eruptions.
Tip: A good investigation measures the variable the question is about (here, ground height), measures it reliably and repeatedly, and compares it with the outcome (eruptions).
Question 32 of 34 · Heredity and genetics
Drop-downSickle Cell Trait and Malaria
Hemoglobin is the protein in red blood cells that carries oxygen. One gene for hemoglobin has two common alleles, A (normal hemoglobin) and S (sickle hemoglobin). Every person inherits one allele from each parent.
AA: normal hemoglobin.
AS:sickle cell trait. People usually have no symptoms.
SS:sickle cell disease. Red blood cells can bend into a curved sickle shape, block small blood vessels and break down early. Without medical care, many people with SS die young and have fewer children.
Malaria is a disease caused by a single-celled parasite that is spread by mosquito bites. The parasite lives inside red blood cells. Studies have found that people with the AS genotype are much less likely to die of severe malaria than people with the AA genotype.
The table shows the frequency of the S allele (the percent of all hemoglobin alleles in a population that are S) in five populations. Values are rounded and simplified for this test.
Population
Malaria common in the area for many centuries?
Frequency of S allele (%)
1
Yes
12
2
Yes
18
3
Yes
9
4
No
1
5
No
less than 1
Two parents both have sickle cell trait (genotype AS). Complete the statements about one of their children.
The probability that the child will have sickle cell disease is .
The probability that the child will have at least one S allele is .
Choose an answer from each menu.
Hint
Draw a Punnett square for AS × AS. Count the boxes for each statement.
Step-by-step solution
Each parent can pass on A or S, each with a probability of \dfrac{1}{2}.
A
S
A
AA
AS
S
AS
SS
Blank 1: sickle cell disease requires SS. One of the 4 boxes is SS, so the probability is \dfrac{1}{4} = 25%.
Blank 2: "at least one S allele" includes AS and SS. That is 3 of the 4 boxes (AS, AS, SS), so the probability is \dfrac{3}{4} = 75%.
Correct answers: 25%; 75%.
Common mistakes: choosing 50% for blank 2 counts only the AS (trait) boxes and forgets the SS box, which also has S alleles.
Tip: "At least one" questions include every outcome with one or more. A quick check: P(at least one S) = 1 − P(no S) = 1 − P(AA) = 1 − 25% = 75%.
Question 33 of 34 · Heredity and genetics
Select allSickle Cell Trait and Malaria
Hemoglobin is the protein in red blood cells that carries oxygen. One gene for hemoglobin has two common alleles, A (normal hemoglobin) and S (sickle hemoglobin). Every person inherits one allele from each parent.
AA: normal hemoglobin.
AS:sickle cell trait. People usually have no symptoms.
SS:sickle cell disease. Red blood cells can bend into a curved sickle shape, block small blood vessels and break down early. Without medical care, many people with SS die young and have fewer children.
Malaria is a disease caused by a single-celled parasite that is spread by mosquito bites. The parasite lives inside red blood cells. Studies have found that people with the AS genotype are much less likely to die of severe malaria than people with the AA genotype.
The table shows the frequency of the S allele (the percent of all hemoglobin alleles in a population that are S) in five populations. Values are rounded and simplified for this test.
Population
Malaria common in the area for many centuries?
Frequency of S allele (%)
1
Yes
12
2
Yes
18
3
Yes
9
4
No
1
5
No
less than 1
Which statements are supported by the passage and the table? Select all that apply.
Select all that apply.
Hint
Check each statement separately. Be careful about the difference between the percent of alleles and the percent of people.
Step-by-step solution
Check each statement against the evidence.
Supported. In every malaria population (12%, 18%, 9%), the S allele is more common than in either non-malaria population (1% and less than 1%). Even the lowest malaria value (9%) is higher than the highest non-malaria value (1%).
Supported. In Population 2, 18% of alleles are S, so 100\% - 18\% = 82\% are A, which is more than 80%.
Not supported. The table gives the frequency of alleles, not people. 12% of alleles being S does not mean 12% of people are SS. (Most S alleles are carried by AS people, who do not have the disease.)
Not supported. The passage describes A and S as alleles that people inherit from their parents. Nothing says mosquito bites or malaria create S alleles.
Not supported. The table shows a link between malaria and the S allele, but the passage says malaria is caused by a parasite. A correlation does not show that the S allele causes malaria.
Correct answers: statements 1 and 2.
Tip: Read the column heading every time you use a number. "Frequency of the S allele" is not "percent of people with the disease."
Question 34 of 34 · Evolution
Sickle Cell Trait and Malaria
Hemoglobin is the protein in red blood cells that carries oxygen. One gene for hemoglobin has two common alleles, A (normal hemoglobin) and S (sickle hemoglobin). Every person inherits one allele from each parent.
AA: normal hemoglobin.
AS:sickle cell trait. People usually have no symptoms.
SS:sickle cell disease. Red blood cells can bend into a curved sickle shape, block small blood vessels and break down early. Without medical care, many people with SS die young and have fewer children.
Malaria is a disease caused by a single-celled parasite that is spread by mosquito bites. The parasite lives inside red blood cells. Studies have found that people with the AS genotype are much less likely to die of severe malaria than people with the AA genotype.
The table shows the frequency of the S allele (the percent of all hemoglobin alleles in a population that are S) in five populations. Values are rounded and simplified for this test.
Population
Malaria common in the area for many centuries?
Frequency of S allele (%)
1
Yes
12
2
Yes
18
3
Yes
9
4
No
1
5
No
less than 1
The SS genotype often leads to early death, yet the S allele has remained common for many generations in Populations 1, 2 and 3. Which explanation best reconciles these two findings?
Hint
Which genotype has an advantage where malaria is common? How does that keep S alleles in the population?
Step-by-step solution
Two findings seem to clash: (1) "many people with SS die young and have fewer children," which should remove S alleles; (2) the S allele stays common where malaria has been common for centuries.
Reconciling them:
The passage says "people with the AS genotype are much less likely to die of severe malaria than people with the AA genotype."
Where malaria is common, AS people survive and have children more often than AA people. Every AS parent can pass on an S allele.
So natural selection favors AS people where there is malaria, while it works against SS people. The S alleles saved in AS survivors balance the S alleles lost in SS deaths, and the allele stays common.
Where there is no malaria (Populations 4 and 5), AS people have no advantage, and the S allele is rare.
Correct answer: Where malaria is common, AS people survive and have children more often than AA people, so natural selection keeps the S allele common even though SS is harmful.
Tip: When an allele is harmful in two copies but stays common, look for an advantage to people with one copy in that environment.