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Question 1 of 20 · Earth systems and living things
Drag and dropMining, Metals and Recycling
Metals such as copper and aluminum come from ores, rocks mined from Earth's crust. Ores form over millions of years, so they are nonrenewable: once a deposit is mined out, nature does not replace it on a human time scale. Fossil fuels such as petroleum are nonrenewable for the same reason. By contrast, sunlight, wind, tides, heat from Earth's interior (geothermal energy) and trees from forests that are replanted are renewable: they are replaced naturally on a human time scale if they are used carefully.
Recycling does not create new metal, but it lets the same metal be used again, so less new ore must be mined. It also saves energy.
Table 1. World copper (approximate, early 2020s)
Known reserves
Mined per year
870 million metric tons
21 million metric tons
Reserve estimates change as new deposits are found and mining methods improve.
Table 2. Energy saved by making metal from recycled scrap instead of from ore
Metal
Energy saved
Aluminum (ore: bauxite)
about 95%
Copper
about 85%
Steel (ore: iron ore)
about 60%
An energy planner sorts six resources named in the passage. Drag each resource into the group where it belongs.
Renewable
Nonrenewable
Tap a tile, then tap a box to place it.
Hint
Ask how fast nature replaces the resource: within a human lifetime, or over millions of years?
Step-by-step solution
Where the answer comes from: the passage says ores "form over millions of years, so they are nonrenewable" and that "Fossil fuels such as petroleum are nonrenewable for the same reason." It lists tides, geothermal energy and "trees from forests that are replanted" as renewable because they "are replaced naturally on a human time scale."
Step by step:
Renewable: tidal energy, geothermal heat, timber from a replanted forest. Nature keeps supplying these as we use them (if forests are managed carefully).
Nonrenewable: petroleum, copper ore, bauxite. Each formed over millions of years, and a mined deposit is not replaced.
Bauxite is the common trap: aluminum is easy to recycle, but recycling reuses metal that was already mined. It does not make new ore.
Answer: Renewable: tidal energy, geothermal heat, timber from a replanted forest. Nonrenewable: petroleum, copper ore, bauxite.
Tip: Renewable means replaced by nature fast enough to keep using. Recyclable and renewable are different ideas.
Question 2 of 20 · Earth and its system components
Layers of the Atmosphere
Earth's atmosphere is a layer of gases, about 78% nitrogen and 21% oxygen, with small amounts of argon, carbon dioxide and water vapor. Scientists divide it into layers by how temperature changes with altitude (height above sea level).
In the troposphere, the lowest layer, air is heated mainly from below by the warm ground, so temperature drops as you go up. Nearly all water vapor and clouds, and so nearly all weather, are found here. In the stratosphere, the ozone layer absorbs ultraviolet (UV) light from the Sun. This warms the air, so temperature rises with altitude. In the mesosphere, temperature falls again; most meteors burn up here. In the thermosphere, the very thin air absorbs high-energy radiation from the Sun, and temperature climbs sharply.
The graph shows average temperatures. At sea level the average is 15 °C. At the top of the troposphere, about 11 km up, it is about −56.5 °C.
The summit of Mount Everest is about 8.8 km above sea level, inside the troposphere. Assume the sea-level temperature is 15 °C and temperature falls at the average troposphere rate shown in the passage. About what is the temperature at the summit?
Hint
First find the rate of cooling per kilometer from the passage. Then think: how much colder than 15 °C is it 8.8 km up?
Step-by-step solution
Where the answer comes from: the passage gives 15 °C at sea level and −56.5 °C at 11 km, the top of the troposphere.
Step by step:
Rate of cooling: \frac{15 - (-56.5)}{11} = \frac{71.5}{11} = 6.5\ ^\circ\text{C per km}
Cooling over 8.8 km: 6.5 \times 8.8 = 57.2\ ^\circ\text{C}
Start at 15 °C and subtract: 15 - 57.2 = -42.2\ ^\circ\text{C}
The summit temperature is about −42 °C.
Check: 8.8 km is a bit below 11 km, so the answer should be a bit warmer than −56.5 °C. −42 °C fits ✓
Tip: When you use a rate to predict, start from the known value (15 °C) and apply the change. Then check that the answer falls in a sensible range on the graph.
Question 3 of 20 · Earth and its system components
Fill inHow Big Is an Earthquake?
Earthquake size is reported as magnitude, a number that describes how much energy the earthquake releases. On the magnitude scale used today, each increase of 1.0 in magnitude means about 32 times more energy is released and about 10 times larger ground shaking (wave amplitude) on a seismograph. Small earthquakes are far more common than large ones.
Average number of earthquakes worldwide each year (approximate)
Magnitude
8.0 and higher
7.0–7.9
6.0–6.9
5.0–5.9
4.0–4.9
Earthquakes per year
1
15
134
1,319
about 13,000
Based on the passage, a magnitude 7.0 earthquake releases about how many times as much energy as a magnitude 5.0 earthquake?
times
Type your answer in the box. Fractions like 3/4 are fine.
Hint
A 2-step increase means multiplying by the energy factor twice.
Step-by-step solution
Where the answer comes from: the passage says "each increase of 1.0 in magnitude means about 32 times more energy is released."
Step by step:
From 5.0 to 7.0 is an increase of 2 steps.
Step 1 (5.0 → 6.0): energy × 32.
Step 2 (6.0 → 7.0): energy × 32 again.
32 \times 32 = 1{,}024
A magnitude 7.0 earthquake releases about 1,000 times (more exactly, about 1,024 times) as much energy. Answers from 1,000 to about 1,048 are accepted.
Check: Adding instead of multiplying gives 32 + 32 = 64, far too small. On a power scale, each step multiplies ✓.
Tip: Magnitude, like pH, is a power scale: count the steps, then multiply the factor by itself that many times. Do not confuse the energy factor (32) with the amplitude factor (10).
Question 4 of 20 · Heredity and genetics
A Family Pedigree
A genetic counselor drew the pedigree below for a family in which some members have a rare inherited trait. The trait is controlled by a single gene with two alleles. The counselor writes the dominant allele as A and the recessive allele as a. The gene is not on a sex chromosome, so males and females inherit it in the same way.
In a pedigree, squares are males and circles are females. A shaded symbol means the person has the trait. A horizontal line joining a male and a female shows a couple, and the vertical line below it leads to their children.
Which statement about the trait is best supported by the pedigree?
Hint
Look at II-1. Do her parents have the trait? What does that tell you about whether the trait's allele can be hidden?
Step-by-step solution
Where the answer comes from: in the pedigree, II-1 is shaded (has the trait) but her parents, I-1 and I-2, are both unshaded. The same pattern repeats in the next generation: III-2 has the trait, but his parents II-3 and II-4 do not.
Step by step:
If the trait were dominant, anyone with the trait would have at least one allele A, and that allele must come from a parent, who would then also show the trait. Neither of II-1's parents shows it, so the trait cannot be dominant.
If the trait is recessive, both parents can be carriers (Aa) who do not show it, and each can pass a hidden a to a child, who is then aa.
So the trait is recessive, and the unaffected parents are carriers.
Eliminate: the trait skips generation I, so it does not appear in every generation; it appears in a male (III-2), so it is not female-only.
Answer: The trait is recessive, because II-1 has the trait even though neither of her parents does.
Tip: two unaffected parents with an affected child means recessive. Two affected parents with an unaffected child means dominant. Find one of these "key families" first.
Question 5 of 20 · Heredity and genetics
A Family Pedigree
A genetic counselor drew the pedigree below for a family in which some members have a rare inherited trait. The trait is controlled by a single gene with two alleles. The counselor writes the dominant allele as A and the recessive allele as a. The gene is not on a sex chromosome, so males and females inherit it in the same way.
In a pedigree, squares are males and circles are females. A shaded symbol means the person has the trait. A horizontal line joining a male and a female shows a couple, and the vertical line below it leads to their children.
What is the genotype of individual I-1?
Hint
I-1 does not have the trait, but one of his children does. What allele must he have passed to that child?
Step-by-step solution
Where the answer comes from: in the pedigree, I-1 (male, generation I) is unshaded, so he does not have the trait. His daughter II-1 is shaded, so she does.
Step by step:
The trait is recessive (an affected child has two unaffected parents), so II-1's genotype is aa.
A child gets one allele from each parent, so II-1 received an a from I-1.
I-1 does not show the trait, so he must also have a dominant A.
Therefore I-1 is Aa, a carrier. The same reasoning shows I-2 is also Aa.
Answer: Aa.
Why the others fail: AA is impossible, because then he could not pass an a to II-1. aa would mean he shows the trait, but he is unshaded. "Cannot be determined" is tempting, but II-1's genotype gives enough information.
Tip: in pedigree problems, work from the people whose genotypes you know for sure (affected people with a recessive trait are always aa), then reason to their parents and children.
Question 6 of 20 · Heredity and genetics
One Plant, Three Gardens
Researchers studied a wild flowering plant that grows from sea level high into the mountains. They took cuttings (pieces of stem that grow into new plants) from a single plant, so all the cuttings were genetically identical. They planted the cuttings in three gardens at different elevations. After two growing seasons, they measured the average height of the plants in each garden.
Garden elevation (meters above sea level)
Average plant height (cm)
30
62
1,400
38
3,050
15
The higher gardens had colder temperatures, stronger winds and a shorter growing season.
What do the results from the three gardens best show about plant height?
Hint
The cuttings all had the same genes. So what must have caused the differences in height?
Step-by-step solution
Where the answer comes from: the passage says the cuttings came "from a single plant, so all the cuttings were genetically identical." The table shows the average height dropping from 62 cm at 30 m to 38 cm at 1,400 m to 15 cm at 3,050 m.
Step by step:
Genotype was the same in all three gardens.
Phenotype (height) was very different.
The only thing that differed was the environment (temperature, wind, length of growing season). So the environment changed the phenotype.
The data cannot show that genes do not matter at all; they show only that the same genes can produce different heights in different conditions.
Answer: The environment can change a plant's phenotype even when its genotype stays the same.
Check: the conclusion uses both pieces of the study: same genotype (the design) and different heights (the data).
Tip: phenotype = genotype + environment. When genotype is held constant, any difference in phenotype points to the environment.
Question 7 of 20 · Evolution
Fill inAntibiotic Resistance in a Hospital
Staphylococcus aureus is a common bacterium that can cause skin and blood infections. In 2000, doctors at a large hospital began using a new antibiotic widely. Each year, the hospital lab tested samples of the bacterium taken from patients to find what percent could survive the antibiotic (were resistant).
Even before 2000, a few bacteria in the population carried a gene variant that let them survive the antibiotic. Resistance is inherited: when a resistant bacterium divides, both new cells are resistant. In 2014, the hospital started a program that cut the use of the antibiotic roughly in half.
Use the graph. From 2000 to 2012 the share of resistant samples went up. What was the size of this increase?
percentage points
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Read the value for 2000 and the value for 2012, then subtract.
Step-by-step solution
Where the answer comes from: the graph shows 5% resistant samples in 2000 and 38% in 2012.
Step by step:
Find each value on the line: 2000 → 5; 2012 → 38.
Subtract the earlier value from the later one: 38 - 5 = 33.
Answer: 33 percentage points.
Check: count the steps along the way: 5 \to 10 \to 22 \to 38 means increases of 5 + 12 + 16 = 33 ✓
Tip: a change from one percent to another is measured in percentage points, found by subtracting. Do not divide: 38 \div 5 would give a ratio (7.6 times), which answers a different question.
Question 8 of 20 · Evolution
Whales With Legs
Whales live their whole lives in water, but they are mammals: they breathe air, are warm-blooded and nurse their young. Paleontologists hypothesize that whales evolved from four-legged mammals that lived on land. The table summarizes several fossil animals and modern whales. Ages are approximate.
Animal
Age (millions of years ago)
Description
Pakicetus
50
Four legs; lived on land near water; ear bones shaped like those of modern whales
Ambulocetus
49
Four short legs and large feet; lived both on land and in water
Rodhocetus
47
Short hind legs; probably swam using its tail and legs
Basilosaurus
40
Lived only in water; tiny hind legs that could not support its body
Modern whales
Today
No hind legs; small pelvic and leg bones inside the body, not attached to the spine
According to the table, modern whales have small pelvic and leg bones inside the body that do not support any legs. These bones are best described as
Hint
Think of a body part that was useful to an organism's ancestors but has little or no use today.
Step-by-step solution
Where the answer comes from: the table says modern whales have "No hind legs; small pelvic and leg bones inside the body, not attached to the spine." The fossils show that whale ancestors such as Pakicetus had four working legs.
Step by step:
A vestigial structure is a reduced body part that had a function in an organism's ancestors but has little or no function now.
The whale's hip and leg bones cannot support a leg, but they match the hip bones of four-legged mammals.
Over millions of years, as whale ancestors moved into the water, the hind legs shrank (Rodhocetus: short; Basilosaurus: tiny; modern whales: hidden inside the body).
Answer: vestigial structures, reduced leftovers of body parts that were useful to the whale's ancestors.
Check: the bones are not developing into anything new; the fossils show legs getting smaller over time, not larger.
Tip: vestigial structures are evidence of ancestry: an organism would have no reason to build a useless part unless it inherited the instructions from ancestors that used it.
Question 9 of 20 · Evolution
Drag and dropSame Bones, Different Jobs
The front limbs of many vertebrates do very different jobs. A human arm grasps tools, a cat's front leg walks and runs, a whale's flipper steers through water, and a bat's wing flies. Yet all four limbs contain the same set of bones in the same order: one upper-arm bone, two forearm bones, a group of wrist bones, and finger bones. Structures like these, which share the same basic plan because they were inherited from a common ancestor, are called homologous structures.
Other structures do the same job but are built in very different ways. A bird's wing is supported by bones and covered with feathers, while a butterfly's wing is a thin sheet with no bones at all. Such structures are called analogous structures. They evolved separately in groups that do not share a winged ancestor.
Drag one example into each box. One example is not used.
Homologous structures
Analogous structures
Vestigial structure
Tap a tile, then tap a box to place it.
Hint
Homologous: same bones, different jobs. Analogous: same job, different build. Vestigial: a reduced part with little or no use today.
Step-by-step solution
Where the answer comes from: the passage defines homologous structures as limbs that "share the same basic plan because they were inherited from a common ancestor," and analogous structures as structures that "do the same job but are built in very different ways."
Step by step:
Homologous: a bat's wing and a cat's front leg contain the same set of bones but do different jobs (flying, walking).
Analogous: a butterfly's wing and a bird's wing both fly, but one has bones and feathers and the other is a thin sheet with no bones. They evolved separately.
Vestigial: the small pelvic bones inside a whale are reduced leftovers of the hips of four-legged ancestors and support no legs today.
Not used: two kittens with different fur colors show variation within a species, not anatomical evidence comparing different groups.
Answer: Homologous = bat wing and cat front leg; Analogous = butterfly wing and bird wing; Vestigial = whale pelvic bones.
Check: only homologous and vestigial structures point to common ancestry; analogous structures show that similar environments can shape unrelated groups in similar ways.
Tip: do not judge by the job alone. Ask "Is it built the same way inside?" before deciding.
Question 10 of 20 · Energy: conservation, transformation, flow
Sand and Water Under a Heat Lamp
A student wanted to know why beach sand feels much hotter than the ocean on a sunny afternoon. She put 200 g of dry sand in one metal tray and 200 g of water in an identical tray. Both samples started at 20 °C. She hung the same model of heat lamp at the same distance above each tray and recorded each temperature every 2 minutes for 10 minutes.
The thermal energy needed to raise the temperature of 1 g of a substance by 1 °C is called its specific heat (c). Water has a specific heat of 4.18\ \text{J/(g}\cdot\text{°C)}. Dry sand has a specific heat of about 0.84\ \text{J/(g}\cdot\text{°C)}. The heat absorbed by a sample can be found with Q = mc\Delta T, where m is the mass in grams and \Delta T is the change in temperature.
According to the graph, by about how many degrees Celsius did the temperature of the sand rise each minute?
Hint
Find the total temperature change of the sand, then divide by the total number of minutes.
Step-by-step solution
Evidence: The graph shows the sand at 20 °C at 0 min and 55 °C at 10 min, rising by 7 °C between each pair of points 2 minutes apart (20, 27, 34, 41, 48, 55).
Step by step:
Find the change in temperature, not the final temperature: \Delta T = 55 - 20 = 35\text{ °C}.
Find the time: 10 - 0 = 10 minutes.
Divide:
\text{rate} = \frac{35\text{ °C}}{10\text{ min}} = 3.5\text{ °C per minute}
The points are 2 minutes apart, so each step of 7 °C covers 2 minutes, not 1 minute.
The sand warmed by about 3.5 °C each minute.
Check:3.5 \times 2 = 7 °C per 2-minute step, which matches the spacing of the points on the graph.
Tip: Always check the scale of the time axis. A rate is a change divided by the time it took, so subtract the starting value first.
Question 11 of 20 · Energy: conservation, transformation, flow
Hot spotA Swinging Pendulum
A 2.0 kg metal ball, called a bob, hangs from a 1.0 m string. A student pulls the bob to point A and releases it from rest. The diagram shows the bob at five moments during its first swing and the height of each point above the lowest point of the swing.
As the bob swings down, its gravitational potential energy changes into kinetic energy. As it swings up the other side, kinetic energy changes back into potential energy. Potential energy can be found with PE = mgh, where g = 9.8\ \text{m/s}^2, and kinetic energy with KE = \frac{1}{2}mv^2. During each swing, air resistance changes a small amount of the bob's energy into thermal energy.
During its first swing, the bob passes through five labeled positions. At which position is the bob moving fastest, so that its kinetic energy is at a maximum? Click that position on the pendulum diagram.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Kinetic energy is energy of motion. Where in its swing is the bob moving fastest?
Step-by-step solution
Evidence: The passage says that "As the bob swings down, its gravitational potential energy changes into kinetic energy." The diagram shows point C at 0 m, the lowest point of the swing.
Step by step:
The bob is released from rest at A (0.20 m), so at A all of its energy is potential energy and its kinetic energy is zero.
The farther the bob drops, the more potential energy has turned into kinetic energy.
Point C (0 m) is the lowest point, so the most potential energy has been converted there. The bob moves fastest at C.
Points B (0.05 m), D (0.10 m) and E (0.18 m) are all above C, so some energy is still stored as potential energy at each of them.
The answer is point C.
Check: At E the bob briefly stops before swinging back, so its kinetic energy there is close to zero, the opposite of C.
Tip: For pendulums, coasters and ramps: lowest point = fastest = most kinetic energy; highest point = most potential energy.
Question 12 of 20 · Work, motion and forces
Fill inA City Bus Between Stops
A transit engineer used a sensor to record the velocity of a city bus as it traveled along a straight street from one stop to the next. The loaded bus has a mass of 11,000 kg. The graph shows the bus's velocity over one minute, divided into four parts labeled P, Q, R and S.
On a velocity-time graph, the height of the line shows how fast the bus is moving, and the slope shows its acceleration. Acceleration is the change in velocity divided by the time the change takes:
a = \frac{v_{\text{final}} - v_{\text{initial}}}{t}
A negative acceleration means the bus is slowing down.
Use the graph, the passage and Newton's second law, F_{\text{net}} = ma.
What net force acted on the bus during part P?
N
Type your answer in the box. Fractions like 3/4 are fine.
Hint
First find the acceleration in part P from the graph. Then multiply by the bus's mass.
Step-by-step solution
Evidence: The passage gives the bus's mass: "The loaded bus has a mass of 11,000 kg." The graph shows part P going from 0 m/s at 0 s to 12 m/s at 10 s.
Step by step:
Acceleration in part P: a = \dfrac{12 - 0}{10} = 1.2\ \text{m/s}^2.
Newton's second law:
F_{\text{net}} = ma = 11{,}000\text{ kg} \times 1.2\ \text{m/s}^2 = 13{,}200\text{ N}
The net force was 13,200 N (forward).
Check:13{,}200 \div 11{,}000 = 1.2 m/s², the slope of part P. ✓ Using the velocity (12 m/s) instead of the acceleration would give 132,000 N, ten times too large.
Tip: Multi-step questions often hide one formula inside another. Get the acceleration from the graph's slope first, then plug it into F = ma.
Question 13 of 20 · Work, motion and forces
Testing a Delivery Drone
A delivery company tested a drone on a straight route between its warehouse and a customer's house. The table shows the three legs of the test trip.
Leg
What the drone did
Distance (m)
Time (s)
1
Flew from the warehouse to the house
1,800
120
2
Hovered while lowering the package
0
60
3
Flew back to the warehouse against the wind
1,800
180
Speed is distance divided by time: v = \dfrac{d}{t}. The average speed for a whole trip is the total distance traveled divided by the total time, including any time spent not moving.
What was the drone's average speed for the whole test trip?
Hint
Add all the distances and all the times, including the time spent hovering. Then divide.
Step-by-step solution
Evidence: The passage says "The average speed for a whole trip is the total distance traveled divided by the total time, including any time spent not moving." The table gives distances 1,800 m, 0 m and 1,800 m and times 120 s, 60 s and 180 s.
Step by step:
Total distance: 1{,}800 + 0 + 1{,}800 = 3{,}600 m.
Total time: 120 + 60 + 180 = 360 s (the hover counts).
Check: Averaging the leg speeds does not work. Leg 1 was 15 m/s and Leg 3 was 10 m/s, but the drone spent longer on the slower leg, so the true average cannot be the simple average.
Tip: Average speed is never the average of the speeds. Always use total distance ÷ total time.
Question 14 of 20 · Comprehending scientific presentations
Temperature and Radish Seed Germination
Germination is the moment a seed sprouts and begins to grow. A science class tested how temperature affects the germination of radish seeds. They placed 100 radish seeds on moist paper towels in each of seven incubators. Each incubator was set to a different temperature. The class kept all the towels equally moist and counted how many seeds had sprouted after 7 days.
Incubator temperature (°C)
Seeds germinated after 7 days (%)
Days until first sprout appeared
5
8
6
10
35
4
15
70
3
20
92
2
25
95
2
30
80
2
35
40
3
The class noted that radish seeds seem to have a range of temperatures that suits them best.
The class did not test 22 °C. Based on the table, about what percentage of radish seeds would most likely germinate after 7 days at 22 °C?
Hint
Which two tested temperatures is 22 °C between? The answer should fall between their results.
Step-by-step solution
22 °C was not tested, so you must interpolate, which means estimate a value between two measured points.
Step by step:
Find the tested temperatures on either side of 22 °C: 20 °C and 25 °C.
Read their results: 92% at 20 °C and 95% at 25 °C.
A temperature between 20 °C and 25 °C should give a result between 92% and 95%. About 93% fits.
The correct answer is B, about 93%.
Check: 75% is lower than both neighbors; 99% is higher than every value in the table; 50% would only make sense near 10–15 °C or near 35 °C.
Tip: To estimate an untested value, find the two data points that 'sandwich' it. Your estimate must lie between their results unless the text gives a reason otherwise.
Question 15 of 20 · Investigation design
Comparing How Soils Drain
Keisha wants to compare how well three types of soil drain water. She lines three identical funnels with coffee filters. She puts 300 g of sand into the first funnel, 200 g of clay into the second and 250 g of loam into the third. She sets each funnel over a plastic cup.
Keisha pours 200 mL of water into each funnel. After 5 minutes, she estimates how much water has dripped into each cup. The cups have marks only at 50, 100, 150 and 200 mL. She tests each soil once.
Soil
Water collected after 5 minutes (estimated)
Sand
about 150 mL
Loam
about 100 mL
Clay
about 50 mL
Keisha concludes that sand drains water better than the other two soils.
Keisha's measurements of the collected water are only estimates. Which change would most improve the precision of these measurements?
Hint
Look at how the cups are marked. What tool would let her read the volume more exactly?
Step-by-step solution
The passage says the cups 'have marks only at 50, 100, 150 and 200 mL' and that Keisha 'estimates' the water collected. With marks 50 mL apart, a reading of 'about 100 mL' could really be anywhere from roughly 75 to 125 mL. The measuring tool is a source of measurement error.
Step by step:
Identify the weak measurement: estimating volume in a cup marked every 50 mL.
Choose a tool with finer markings: a graduated cylinder marked every 1 mL.
Pouring each cup's water into the cylinder gives a far more precise reading.
The correct answer is A.
Check: B and C change the amount of soil or water, which does not make the reading more precise. D changes the soil type tested and does nothing about the measuring tool.
Tip: Precision depends on the smallest marking of a tool. If the question mentions estimating or rough marks, look for an answer that uses a tool with finer markings.
Question 16 of 20 · Evaluating conclusions with evidence
Hot spotAntibiotic Use and Resistance
Pine County is a fictional county. Health officials tracked how many prescriptions were written each year for Drug Z, an antibiotic. They also tested bacteria samples from patients each year to find the percent that were resistant to Drug Z (not killed by it). Read the prescription line with the left axis and the resistance line with the right axis.
At the start of Year 7, the county began a policy asking doctors to prescribe Drug Z only when it was clearly needed. The officials claim: "Heavy use of Drug Z drove the rise in resistance to Drug Z."
The officials predicted that resistance would start to fall once Drug Z was used less. Click the point on the resistance line that shows the first year resistance was lower than the year before.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Use the red dashed line with squares (right axis). Find the first square that is lower than the square just to its left.
Step-by-step solution
Read the resistance line (red, dashed, squares) with the right axis.
Evidence from the graph: Year 1 5%, Year 2 6%, Year 3 8%, Year 4 11%, Year 5 15%, Year 6 19%, Year 7 20%, Year 8 18%, Year 9 15%, Year 10 13%.
Step by step:
From Year 1 to Year 7, each value is higher than the one before.
Year 8 (18%) is the first value lower than the year before (20% in Year 7).
Click the red square at Year 8. It supports the officials' prediction: resistance began to fall a year after prescriptions dropped.
The correct answer is the resistance point for Year 8 (18%).
Check: Don't click the blue prescription line — prescriptions first fell in Year 7, but the question asks about resistance.
Tip: On dual-axis graphs, find the line named in the question first (here, the red resistance line), then read only that line.
Question 17 of 20 · Expressing scientific information
Respiration and Photosynthesis
Plants and animals both release energy from food through a process called cellular respiration. In cellular respiration, a cell combines glucose (a sugar) with oxygen. The reaction produces carbon dioxide and water and releases energy that the cell can use. For each molecule of glucose used, six molecules of oxygen are used, and six molecules of carbon dioxide and six molecules of water are made.
Plants also carry out photosynthesis, which uses light energy to make glucose. Photosynthesis is summarized by this equation:
Which statement correctly describes the photosynthesis equation in words?
Hint
The coefficient (big number in front) counts molecules. The subscript (small number) counts atoms inside one molecule.
Step-by-step solution
Where the answer comes from: the passage gives the equation 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2.
Step by step:
Left of the arrow (reactants): 6 molecules of carbon dioxide and 6 molecules of water, plus light energy.
Right of the arrow (products): 1 molecule of glucose (no coefficient means 1) and 6 molecules of oxygen.
6\text{O}_2 means six molecules, each made of two oxygen atoms.
The arrow points from reactants to products, so glucose is made, not used.
Correct answer: D.
Check: read the equation aloud: "six C-O-two plus six H-two-O, with light, yields one glucose plus six O-two." That matches the correct statement.
Tip: Translate an equation in three parts: what goes in, what comes out, and how many of each (coefficients).
Question 18 of 20 · Probability and statistics in science
Fill inA Week of High Temperatures
An earth science class kept a weather station on the school roof. The station records the daily high temperature. During one week, the sensor lost power for one day, so that day's reading is missing from the class log.
Day
High temperature (°C)
Monday
16.5
Tuesday
19.5
Wednesday
17.5
Thursday
20.5
Friday
18.0
Saturday
15.5
Sunday
missing
A nearby official weather station, which matched the school station's readings closely on every other day, reported that the mean daily high for the full seven days was 18.0 °C.
Use the official station's seven-day mean to estimate the high temperature on Sunday.
°C
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Turn the mean into a seven-day total, then subtract the six known days.
Step-by-step solution
Where the answer comes from: the table lists six highs: 16.5, 19.5, 17.5, 20.5, 18.0 and 15.5 °C. The passage says the official station "reported that the mean daily high for the full seven days was 18.0 °C" and matched the school station closely.
Step by step:
Seven-day total = mean \times number of days = 18.0 \times 7 = 126.0 °C.
Sum of the six known days: 16.5 + 19.5 + 17.5 + 20.5 + 18.0 + 15.5 = 107.5 °C.
Sunday = 126.0 - 107.5 = 18.5 °C.
Correct answer: 18.5 °C.
Check:\dfrac{107.5 + 18.5}{7} = \dfrac{126.0}{7} = 18.0 °C ✓
Common slip: taking the mean of the six known days (107.5 \div 6 \approx 17.9) does not use the official mean and does not find Sunday's value.
Tip: Mean × count = total. This one fact lets you find a missing value, add a new value or remove a value from any data set.
Question 19 of 20 · Chemical properties and reactions
Select all
A product label lists six facts about a metal used in outdoor railings. Which facts describe chemical properties of the metal? Select all that apply.
Select all that apply.
Hint
A chemical property can only be observed when the substance changes into a different substance.
Step-by-step solution
Evidence: A chemical property describes how a substance can react to form new substances. A physical property can be observed or measured without changing what the substance is.
Step by step:
Reacts with hydrochloric acid to give off hydrogen gas: a new substance (hydrogen) forms. Chemical.
Has a density of 7.9 g/cm³: measured with a balance and a ruler or cylinder; the metal stays the same. Physical.
Rusts when left in damp air: iron combines with oxygen and water to form rust, a new substance. Chemical.
Melts at 1,538 °C: melting changes the state, not the substance. Physical.
Does not burn when heated in a flame: flammability (or the lack of it) describes whether a substance reacts with oxygen, so it is a chemical property.
Is shiny and silver-gray: observed by looking. Physical.
The chemical properties are A, C and E.
Check: For each fact, ask "Would I have to make a new substance to observe this?" Only A, C and E say yes (or describe whether a reaction happens).
Tip: Words like reacts, rusts, burns, flammable, tarnishes, decomposes signal chemical properties. Words like color, density, melting point, shiny, hardness signal physical properties.
Question 20 of 20 · Chemical properties and reactions
Drag and drop
Drag each change into the correct column.
Physical change
Chemical change
Tap a tile, then tap a box to place it.
Hint
Ask of each change: is a new substance made, or is it the same substance in a new form?
Step-by-step solution
Evidence: A chemical change produces a new substance, often shown by gas, a color change, a new smell, light or heat. A physical change only alters size, shape or state.
Step by step:
Water boiling into steam — still \text{H}_2\text{O}, just a gas. Physical.
Salt dissolving in water — evaporate the water and the salt is left. Physical.
Glass shattering — smaller pieces of the same glass. Physical.
Iron nail rusting — iron combines with oxygen to form iron oxide, a new reddish substance. Chemical.
Milk turning sour — bacteria produce new substances (acids) with a new smell and taste. Chemical.
Baking a cake — heat causes reactions; gas forms and the batter becomes a new, solid food that cannot be "unbaked." Chemical.
Tip: Changes of state and dissolving are always physical. Do not be fooled because something "disappears" (dissolving) or because there are bubbles from boiling.