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Question 1 of 20 · Earth systems and living things
Fill inWildfires in Pine County
Pine County is a fictional forested county in the western United States. A wildfire needs three things: fuel (dry grass, brush and dead trees), oxygen, and heat to start it. Hot, dry summers dry out fuel, so fires start more easily and spread faster. Most U.S. wildfires are started by people, for example by campfires, equipment sparks or downed power lines; lightning starts most of the rest.
Year
Average summer high temperature (°F)
Days with no rain, June–September
Acres burned
2014
84
61
12,000
2016
86
70
18,500
2018
85
88
41,000
2020
88
79
36,000
2022
88
65
15,500
2024
87
92
54,000
Communities lower wildfire risk in several ways. They clear brush and dead wood within about 30 meters (100 feet) of homes, called defensible space. Fire crews use prescribed burns, small fires set on purpose in safe weather, to remove fuel that has built up on the forest floor. Builders also use fire-resistant roofs and siding.
Using the table, by what percent did the number of acres burned in Pine County increase from 2014 to 2024?
%
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Percent change = (new − old) ÷ old × 100.
Step-by-step solution
Where the answer comes from: the table gives 12,000 acres burned in 2014 and 54,000 acres in 2024.
Step by step:
Find the change: 54{,}000 - 12{,}000 = 42{,}000 \text{ acres}
Divide by the starting (2014) value: \frac{42{,}000}{12{,}000} = 3.5
Change to a percent: 3.5 \times 100 = 350\%
The acres burned increased by 350%.
Check: A 350% increase means adding 3.5 times the original: 12{,}000 + 3.5 \times 12{,}000 = 12{,}000 + 42{,}000 = 54{,}000 ✓
Tip: Always divide by the old value. Dividing by 54,000 instead gives about 78%, a common wrong answer.
Question 2 of 20 · Earth and its system components
Locating an Earthquake
When an earthquake happens, energy travels outward through Earth as seismic waves. Two kinds reach a seismograph station first. P waves (primary waves) are faster, so they arrive first. S waves (secondary waves) are slower and arrive later. The farther a station is from the epicenter (the point on the surface directly above where the earthquake started), the longer the gap between the P-wave and S-wave arrivals.
Table 1. Time gap between P and S waves and distance to the epicenter
S-wave arrival minus P-wave arrival (seconds)
Distance to epicenter (km)
10
80
20
160
30
240
50
400
60
480
A time gap tells scientists only how far away the epicenter is, not in which direction. So they draw a circle around each station with a radius equal to its distance. The epicenter is where the circles from at least three stations meet.
Earthquake strength is reported as magnitude. On the magnitude scale, each increase of 1 means the ground shaking (wave amplitude) is 10 times larger and the energy released is about 32 times greater.
A seismograph station records S waves arriving 40 seconds after P waves. Based on Table 1, about how far is the station from the epicenter?
Hint
40 seconds is not in the table. Look at the pattern: how many kilometers does each 10 seconds add?
Step-by-step solution
Where the answer comes from: Table 1 lists 30 s → 240 km and 50 s → 400 km, with every 10 seconds adding 80 km (10 → 80, 20 → 160, 30 → 240).
Step by step:
Find the pattern: distance = 8 km for each second of gap (80 \div 10 = 8).
Apply it to 40 seconds: 40 \times 8 = 320 \text{ km}
Check with the table: 40 s lies halfway between 30 s (240 km) and 50 s (400 km), and halfway between 240 and 400 is 320 ✓
The station is about 320 km from the epicenter.
Tip: When a value falls between two rows, find the pattern (or the midpoint) instead of copying the nearest row.
Question 3 of 20 · Earth and its system components
Hot spotRock Layers at Canyon Point
Geologists read rock layers like the pages of a history book. Three ideas help them put events in order:
Superposition: in undisturbed sedimentary layers, the oldest layer is at the bottom and the youngest is at the top.
Cross-cutting relationships: a feature that cuts across rock layers is younger than the layers it cuts. Examples are a fault (a crack along which rock has moved) and a dike (a sheet of igneous rock that forced its way in as magma and hardened).
An unconformity is a buried erosion surface. It marks a time when rock was worn away before new layers were laid down on top.
The diagram shows a cliff at Canyon Point, a fictional site. Layers A–E are sedimentary rock. F is an igneous dike, G is a fault, and the wavy line is an unconformity.
Based on the passage and the diagram, click the oldest sedimentary layer at Canyon Point.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Use superposition: in a stack of sedimentary layers, where is the first layer that was laid down?
Step-by-step solution
Where the answer comes from: the passage states the rule of superposition: "in undisturbed sedimentary layers, the oldest layer is at the bottom and the youngest is at the top." In the diagram, layer A is at the bottom on both sides of fault G.
Step by step:
Find the sedimentary layers: A, B, C, D and E.
The fault moved the right-hand block down, but the order of the layers on each side is still A, B, C, D from bottom to top.
Layer E lies on top of everything, so it is the youngest layer.
Dike F cuts every layer, so it is younger than all of them, and it is igneous, not sedimentary.
The oldest layer is layer A (either side of the fault).
Check: Layer A is the only layer with no other layer beneath it in the diagram ✓.
Tip: A fault can shift layers up or down, but it does not flip their order. Follow one side of the fault from the bottom up.
Question 4 of 20 · Human body and health
Fill inHandling Heat at Work
A workplace safety team studied how the body handles heat. A healthy 40-year-old man sat quietly for 60 minutes in a room heated to 40 °C. Then he moved to a room at 22 °C for 30 minutes. Every 15 minutes, the team recorded his core body temperature (deep inside the body), his skin temperature, and the amount of sweat he produced during the previous 15 minutes.
When the brain senses that the blood is getting warmer, it signals sweat glands to release sweat. As sweat evaporates from the skin, it carries heat away. Blood vessels near the skin also widen, so more warm blood flows near the surface, where it can lose heat. Sweat cools the body only when it evaporates.
Time (min)
Room
Core temperature (°C)
Skin temperature (°C)
Sweat in previous 15 min (mL)
0
40 °C
37.0
33.0
0
15
40 °C
37.2
35.5
120
30
40 °C
37.4
36.0
180
45
40 °C
37.5
36.2
200
60
40 °C
37.5
36.3
210
75
22 °C
37.2
33.5
60
90
22 °C
37.0
32.5
10
How many milliliters of sweat did the man produce in total during his 60 minutes in the 40 °C room?
mL
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Each sweat value covers the 15 minutes before it was recorded. Which rows describe time spent in the hot room?
Step-by-step solution
Evidence: the sweat column shows 120, 180, 200, and 210 mL at minutes 15, 30, 45, and 60. Each value is the sweat "produced during the previous 15 minutes."
Step by step:
The man was in the 40 °C room from minute 0 to minute 60. The four 15-minute periods ending at minutes 15, 30, 45, and 60 cover that time.
The minute 0 row (0 mL) is the starting point, not a period of sweating. The rows at 75 and 90 minutes are in the cool room, so leave them out.
Add: 120 + 180 + 200 + 210 = 710\text{ mL}
The answer is 710 mL.
Check: adding all six values gives 780 mL; subtracting the cool-room values 60 + 10 = 70 gives 780 - 70 = 710 ✓
Tip: before adding up a column, decide exactly which rows the question asks about. Labels like "previous 15 min" tell you what each number covers.
Question 5 of 20 · Life functions and energy intake
Yeast and Temperature
Yeast are single-celled fungi. Without oxygen, yeast break down sugar for energy by fermentation, a type of anaerobic respiration. Fermentation produces carbon dioxide gas and ethanol. Each step is controlled by enzymes, proteins that speed up reactions. Enzymes work fastest within a certain temperature range and can be permanently damaged, or denatured, by high heat.
A student mixed equal amounts of yeast, sugar, and water in six flasks. She placed each flask in a water bath at a different temperature and collected the carbon dioxide gas produced in 20 minutes.
Which statement best explains why CO₂ production decreased from 40 °C to 60 °C?
Hint
Re-read the last sentence of the passage's first paragraph about enzymes.
Step-by-step solution
Evidence: CO₂ produced fell from 26 mL at 40 °C to 12 mL at 50 °C and 1 mL at 60 °C. The passage says enzymes "can be permanently damaged, or denatured, by high heat."
Step by step:
From 10 °C to 40 °C, CO₂ rose (2 → 26 mL): warmer temperatures speed up enzyme-controlled reactions.
Above 40 °C, production dropped sharply. The passage gives the reason: high heat denatures enzymes, so fermentation slows or stops.
Eliminate B: every flask had equal sugar, and higher temperatures produced less gas, not more, so sugar was not used up faster. Eliminate C: yeast at 10 °C made only 2 mL, so cold is not ideal. Eliminate D: warm water holds less dissolved gas, not more, and the passage points to enzymes.
The answer is A.
Tip: an up-then-down curve with temperature is the classic enzyme pattern: an optimum temperature, then a fast drop as heat damages the enzymes.
Question 6 of 20 · Energy flow in ecosystems
Rabbits and Foxes on an Island
On a small island, foxes are the main predator of rabbits. The island's grasses are the rabbits' only food. Scientists counted both populations every spring for 10 years. Note that the graph uses two different scales: rabbits are read on the left axis, and foxes are read on the right axis.
Which statement best explains the decrease in the rabbit population from year 3 to year 6?
Hint
What was happening to the fox population just as the rabbits began to decline?
Step-by-step solution
Evidence: rabbits fell from 1,300 (year 3) to 400 (year 6). Foxes were near their peak, 65 (year 3) and 80 (year 4), as the decline began. The passage says "foxes are the main predator of rabbits."
Step by step:
A large predator population eats more prey.
Foxes had grown to their peak just as rabbits began to fall, so predation was greatest then.
Eliminate B: foxes were increasing from year 3 to 4, not decreasing. Eliminate A: rabbits eat grass; they are consumers and do not need sunlight directly. Eliminate D: foxes were present the whole time.
The answer is C. (A shortage of grass from so many rabbits could also contribute, but of the choices, only C fits the data.)
Tip: in predator-prey graphs, prey usually fall when predators are near their peak, and predators fall after prey have become scarce.
Question 7 of 20 · Energy flow in ecosystems
Fill inEnergy in a Grassland
Ecologists estimated how much energy was stored in each trophic level of a grassland in one year. Energy is given in kilojoules per square meter (kJ/m²). Producers capture only about 1% of the sunlight energy that reaches them. After that, only about 10% of the energy at one trophic level becomes part of the next level; the rest is used for life processes and lost as heat, or stays in parts that are not eaten.
Trophic level
Example organisms
Energy stored (kJ/m² per year)
Producers
grasses, wildflowers
25,000
Primary consumers
grasshoppers, mice
2,500
Secondary consumers
spiders, snakes
250
Tertiary consumers
hawks
?
Use the 10% rule in the passage. About how much energy is stored in the tertiary consumers (hawks)?
kJ/m² per year
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Each level gets about 10% of the level below it. Which level is directly below the hawks?
Step-by-step solution
Evidence: the passage says "only about 10% of the energy at one trophic level becomes part of the next level." The table shows 250 kJ/m² in the secondary consumers.
Step by step:
The level directly below the tertiary consumers is the secondary consumers: 250 kJ/m².
Ten percent of 250: 250 \times 0.10 = 25\text{ kJ/m}^2
The table follows the same pattern all the way up: 25{,}000 \rightarrow 2{,}500 \rightarrow 250 \rightarrow 25.
The answer is 25 kJ/m² per year.
Check:25 \times 10 = 250 ✓
Tip: moving up a pyramid, divide by 10 for each step. Moving down, multiply by 10.
Question 8 of 20 · Organization of life: cells, tissues, organisms
Drag and dropFour Mystery Samples
A lab technician examined cells from four unlabeled samples with a powerful microscope. She knows that one sample is a bacterium, one is from an animal, one is from the leaf of a green plant, and one is from a mushroom (a fungus). Fungus cells have a nucleus and a cell wall but no chloroplasts. She recorded which structures she saw and the typical width of the cells.
Structure
Sample 1
Sample 2
Sample 3
Sample 4
Cell membrane
Yes
Yes
Yes
Yes
Ribosomes
Yes
Yes
Yes
Yes
Nucleus
No
Yes
Yes
Yes
Mitochondria
No
Yes
Yes
Yes
Cell wall
Yes
Yes
Yes
No
Chloroplasts
No
No
Yes
No
Typical width (micrometers)
2
8
40
20
Drag a sample into each box to identify the source of the cells. One sample is not used.
Bacterium
Animal
Green plant leaf
Tap a tile, then tap a box to place it.
Hint
Use one "clue" structure for each box: no nucleus → ?; no cell wall → ?; chloroplasts → ?
Step-by-step solution
Where the answer comes from: the table rows for Nucleus, Cell wall and Chloroplasts are the only ones that differ. The passage adds that "Fungus cells have a nucleus and a cell wall but no chloroplasts."
Step by step:
Bacterium: the only cell with no nucleus (and no mitochondria) is Sample 1.
Animal: animal cells have a nucleus but no cell wall. Only Sample 4 has "No" in the Cell wall row.
Green plant leaf: leaf cells carry out photosynthesis in chloroplasts. Only Sample 3 has chloroplasts (and it has a cell wall, as plant cells do).
Not used: Sample 2 has a nucleus and a cell wall but no chloroplasts, which matches the description of the fungus.
Check: every sample is used once at most, and each box matches exactly one clue.
Tip: rows where every sample says "Yes" (membrane, ribosomes) are useless for sorting. Cross them out first and focus on the rows that differ.
Question 9 of 20 · Heredity and genetics
Fill inPink Snapdragons
Snapdragon flower color shows incomplete dominance: neither allele fully hides the other. A plant with two red alleles (RR) has red flowers. A plant with two white alleles (WW) has white flowers. A plant with one of each (RW) has pink flowers, a color in between.
A student crossed two pink-flowered snapdragons (RW × RW). She planted 400 of the seeds they produced and recorded the flower color of each new plant.
Flower color
Number of plants
Red
98
Pink
205
White
97
Total
400
According to a Punnett square for the RW × RW cross, how many of the 400 offspring would be expected to have pink flowers?
plants
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Draw the 2 × 2 Punnett square. What fraction of the boxes are RW? Multiply that fraction by 400.
Step-by-step solution
Where the answer comes from: the passage says pink plants are RW and the parents are RW × RW, with 400 offspring.
Step by step:
Punnett square:
R
W
R
RR
RW
W
RW
WW
RW boxes: 2 out of 4, so P(\text{pink}) = \dfrac{2}{4} = \dfrac{1}{2}.
Check: expected red = \tfrac{1}{4} \times 400 = 100 and expected white = 100, so 100 + 200 + 100 = 400 ✓
Answer: 200 plants. The student observed 205, close to the prediction. Real results vary a little by chance, and larger samples usually come closer to the expected ratio.
Tip: expected number = probability × total. Use the Punnett square for the probability, not the observed data.
Question 10 of 20 · Energy: conservation, transformation, flow
A 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.
Compare the bob at point B with the bob at point D. Which statement is correct?
Hint
Look at the heights of B and D. The lower point has turned more of its potential energy into motion.
Step-by-step solution
Evidence: The diagram labels B at 0.05 m and D at 0.10 m above the lowest point. The passage explains that as the bob drops, "gravitational potential energy changes into kinetic energy"; the bob also starts with a fixed amount of energy at A.
Step by step:
Potential energy depends on height (PE = mgh). B (0.05 m) is lower than D (0.10 m), so the bob has less potential energy at B.
The bob's total energy cannot increase after it is released, and air resistance only removes a little. The energy "missing" from potential energy at B is kinetic energy.
So the bob has more kinetic energy (it moves faster) at B than at D.
Direction of travel does not matter: B is on the way down and D is on the way up, but only the height decides the split.
The answer is The bob has more kinetic energy at B than at D, because B is lower.
Check: At the very top of each side (A and E) the bob is momentarily still. D is close to E, so it should be fairly slow.
Tip: In a swinging or rolling system, compare heights: lower point = less potential energy = more kinetic energy.
Question 11 of 20 · Energy: conservation, transformation, flow
Fill inElectromagnetic Waves at Home
Many everyday devices send or use electromagnetic (EM) waves. All EM waves travel through empty space at the same speed, about 3.0 \times 10^8 m/s. For any wave, speed equals frequency times wavelength: v = f\lambda. The higher the frequency of an EM wave, the more energy it carries.
Device
Type of EM wave
Frequency (Hz)
AM radio
Radio wave
1.0 \times 10^{6}
Wi-Fi router
Microwave
5.0 \times 10^{9}
TV remote control
Infrared
3.0 \times 10^{14}
Tanning lamp
Ultraviolet
9.0 \times 10^{14}
Dental X-ray machine
X-ray
3.0 \times 10^{18}
Visible light has frequencies between about 4.0 \times 10^{14} Hz (red) and 7.5 \times 10^{14} Hz (violet).
Use the table and the wave equation v = f\lambda from the passage.
What is the wavelength of the waves sent by the Wi-Fi router?
m
Type your answer in the box. Fractions like 3/4 are fine.
Hint
Solve the wave equation for λ: divide the speed by the frequency. Subtract the exponents when you divide powers of ten.
Step-by-step solution
Evidence: The passage gives the speed of all EM waves, "about 3.0 \times 10^8 m/s," and the table gives the Wi-Fi router's frequency as 5.0 \times 10^{9} Hz.
Step by step:
Rearrange the equation: \lambda = \dfrac{v}{f}.
Divide the front numbers and the powers of ten separately:
\lambda = \frac{3.0 \times 10^8}{5.0 \times 10^9} = \frac{3.0}{5.0} \times 10^{8-9} = 0.6 \times 10^{-1}
Simplify: 0.6 \times 10^{-1} = 0.06 m (6 cm).
The wavelength is 0.06 m.
Check: Multiply back: (5.0 \times 10^9) \times 0.06 = 3.0 \times 10^8 m/s. Microwaves are known to have wavelengths of a few centimeters, so 6 cm is reasonable.
Tip: On the GED calculator, enter scientific notation with the ×10ⁿ key to avoid exponent mistakes: 3×10ⁿ8▶÷5×10ⁿ9enter (the right arrow leaves the exponent).
Question 12 of 20 · Work, motion and forces
A Bike Ride to the Store
Marcus rode his bike in a straight line from his home toward a store. A fitness app on his phone recorded his distance from home every few seconds. The graph shows his trip, which has four parts, labeled A through D.
On a distance-time graph, the slope (steepness) of the line shows speed. A steeper line means a greater speed, and a flat line means the object is not moving. Average speed is found by dividing the distance traveled by the time it took.
What was Marcus's average speed for the entire trip shown on the graph?
Hint
Average speed uses the total distance and the total time, including any time spent stopped.
Step-by-step solution
Evidence: The graph ends at (500 s, 1,000 m): Marcus traveled 1,000 m in 500 s. The passage says average speed is found "by dividing the distance traveled by the time it took."
Step by step:
Total distance: he ends 1,000 m from home, starting at 0 m, so 1,000 m.
Total time: the trip lasts from 0 s to 500 s, which is 500 s. This includes the 100 s he was stopped in part B.
Average speed:
v = \frac{1{,}000\text{ m}}{500\text{ s}} = 2\text{ m/s}
Check against the segment speeds: A = 3, B = 0, C = 5 and D = 1 m/s. The average falls between them, so 2 m/s is reasonable.
The answer is 2 m/s.
Tip: Never average the segment speeds. Segments last different amounts of time, so you must divide total distance by total time.
Question 13 of 20 · Chemical properties and reactions
Hot spotThe pH Scale
The pH scale measures how acidic or basic a water solution is. It runs from 0 to 14. A pH of 7 is neutral. Solutions with a pH below 7 are acids, and solutions with a pH above 7 are bases. Acids taste sour and contain many hydrogen ions (H⁺); bases taste bitter, feel slippery and contain many hydroxide ions (OH⁻).
The pH scale is logarithmic: each change of one pH unit means a tenfold change in acidity. A solution with a pH of 4 has 10 times the hydrogen ion concentration of a solution with a pH of 5, and 100 times that of a solution with a pH of 6. When an acid and a base are mixed, they neutralize each other, and the pH of the mixture moves toward 7.
On the pH scale, click the substance that is 100 times less acidic than black coffee.
Click on the figure to mark your answer (or focus it and use the arrow keys).
Hint
Each pH unit is a factor of 10. How many pH units make a factor of 100? Which direction is less acidic?
Step-by-step solution
Evidence: The diagram shows black coffee at about pH 5. The passage explains that "each change of one pH unit means a tenfold change in acidity."
Step by step:
100 times = 10 \times 10, so you need a change of 2 pH units.
"Less acidic" means moving up the scale, toward 7 and beyond.
5 + 2 = 7. The substance at pH 7 is pure water.
Traps: vinegar (pH 3) is 2 units in the wrong direction (100 times more acidic); baking soda solution (pH 9) is 4 units away, a factor of 10,000.
The answer is pure water.
Tip: First count the pH steps (10^{\text{steps}}), then pick the direction: lower pH = more acidic, higher pH = less acidic.
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.
Which statement best describes the relationship between temperature and the percentage of seeds that germinated?
Hint
Follow the germination column from the top row to the bottom row. Does it move in only one direction?
Step-by-step solution
Look at the whole germination column, not just one part of it: 8, 35, 70, 92, 95, 80, 40.
Step by step:
From 5 °C to 25 °C the percentage rises: 8 → 35 → 70 → 92 → 95.
From 25 °C to 35 °C the percentage falls: 95 → 80 → 40.
So germination rises to a peak near 25 °C and then drops at higher temperatures. This also matches the class's note that the seeds have a best range of temperatures.
The correct answer is C: germination increased as the temperature rose to about 25 °C and then decreased at higher temperatures.
Check: Choice A only describes the first five rows. Choice B is the reverse of the first five rows. Choice D ignores a clear pattern.
Tip: Before choosing a trend statement, check the first, the peak and the last values. A trend that changes direction needs a two-part description.
Question 15 of 20 · Reasoning from data
Heating a Pot of Water
A student heated 1 liter of water in a pot on a stove that stayed at the same setting the whole time. She measured the water's temperature with a thermometer every 2 minutes, starting when she turned on the burner. The experiment took place at sea level, where pure water boils at 100 °C. The water began to boil at the 10-minute reading.
According to the graph, what was the temperature of the water after 4 minutes of heating?
Hint
Start at 4 on the time axis, go straight up to the line, then straight across to the temperature axis.
Step-by-step solution
Read the value directly from the graph. The x-axis is time heated (minutes) and the y-axis is water temperature (°C). Find 4 minutes on the x-axis and move straight up to the data point. From there, move across to the y-axis: the point sits a little above the 50 °C gridline, at 52 °C.
Step by step:
Name the axes: time across, temperature up.
Locate 4 on the time axis.
Go up to the point and across: 52 °C.
The correct answer is 52 °C.
Check: The temperature rises 16 °C every 2 minutes. Starting at 20 °C, after 2 minutes it is 36 °C and after 4 minutes it is 36 + 16 = 52 °C. That matches.
Tip: Before reading any graph value, say the two axes out loud. It keeps you from reading the wrong point or the wrong axis.
Question 16 of 20 · Evaluating conclusions with evidence
Select allDoes Music Help Plants Grow?
A gardener read online that music helps plants grow, and she decided to test the idea. She bought six bean seedlings that were each 5 cm tall. She placed three seedlings in her sunny kitchen, where a radio played classical music 8 hours a day. She placed the other three on her shaded back porch, where there was no music. She watered all six plants whenever the soil looked dry. After four weeks, she measured how much each plant had grown.
Plant
Location
Music?
Growth in 4 weeks (cm)
1
Kitchen
Yes
13
2
Kitchen
Yes
11
3
Kitchen
Yes
12
4
Porch
No
9
5
Porch
No
7
6
Porch
No
8
She concluded: "Music makes plants grow taller."
Which are weaknesses in the gardener's evidence for her conclusion? Select all that apply.
Select all that apply.
Hint
Look for anything that could produce the result even if music has no effect, or that makes the result less trustworthy.
Step-by-step solution
A weakness is anything that could explain the result without music, or that makes the result less certain.
Step by step:
A, different locations: "sunny kitchen" vs. "shaded back porch". Light and temperature differ, a confound. ✓
B, small sample: "three seedlings" per group. One unusual plant could change the average a lot. ✓
C, watering not controlled: she watered "whenever the soil looked dry." A sunny kitchen may dry soil faster, so the groups may have received different amounts of water. ✓
D: all seedlings started at 5 cm. That is good design, not a weakness. ✗
E: measuring growth in centimeters is fine. ✗
The correct answers are A, B and C.
Tip: Check every condition in the procedure: was it identical for both groups? Anything left to judgment ("whenever it looked dry") may not be controlled.
Question 17 of 20 · Scientific theories
Select allEvidence from the Seafloor
The theory of plate tectonics states that Earth's outer layer is broken into large plates that slowly move. At mid-ocean ridges, hot rock rises from below, cools and forms new seafloor. The new seafloor then moves away from the ridge on both sides, a process called seafloor spreading. If the theory is correct, the youngest rock should be found at the ridge, and rock should get older with distance from it.
Scientists drilled into the seafloor at several sites in one study area east and west of a mid-ocean ridge and dated the rock.
Distance from ridge
Age of rock, west side
Age of rock, east side
0 km
0 (forming now)
0 (forming now)
50 km
2.0 million years
2.0 million years
100 km
4.0 million years
4.0 million years
200 km
8.0 million years
8.0 million years
The spreading rate of one side is the distance the seafloor has moved divided by the time it took:
Geologists usually report spreading rates in centimeters per year. (1 km = 100,000 cm.)
Select all of the findings below that support the theory of plate tectonics described in the passage.
Select all that apply.
Hint
A supporting finding should show that continents or seafloor have moved, or that rock ages follow the pattern the theory predicts.
Step-by-step solution
Where the answer comes from: the passage says plates "slowly move," new seafloor forms at ridges and moves away "on both sides," and if the theory is correct "the youngest rock should be found at the ridge, and rock should get older with distance from it."
Evaluate each finding:
A — supports. The table itself shows rock ages rising evenly with distance on both sides, exactly as predicted.
B — supports. A small freshwater reptile could not swim across an ocean. Finding its fossils only on two continents now an ocean apart suggests those continents were once joined and later moved apart.
C — supports. Matching rock layers on facing coasts suggest the rocks formed together before the continents separated.
D — does not support. Saltiness of ocean water is unrelated to plate movement.
E — contradicts. If ages did not change with distance, the seafloor-spreading prediction would fail.
Correct answers: A, B and C.
Tip: For "select all that support" items, test each option separately against the theory's prediction. Watch for true-but-unrelated facts (D) and findings that point the other way (E).
Question 18 of 20 · Scientific theories
Fill inGalaxies Moving Apart
In the 1920s, astronomers found that light from distant galaxies is shifted toward the red end of the spectrum. This redshift means the galaxies are moving away from us. The farther away a galaxy is, the faster it moves away. This pattern is described by Hubble's law:
v = H_0 d
where v is the galaxy's speed away from us in km/s, d is its distance in megaparsecs (Mpc; 1 Mpc is about 3.26 million light-years), and H_0 is the Hubble constant, about 70 km/s per Mpc.
The Big Bang theory explains this pattern: the universe began in a hot, dense state about 13.8 billion years ago and has been expanding ever since, carrying distant galaxies away from one another. The theory is also supported by the faint cosmic microwave background, leftover radiation detected from every direction in the sky.
A few very close galaxies, such as the Andromeda Galaxy, are moving toward us. Over short distances, the gravity between neighboring galaxies is stronger than the effect of expansion. The expansion pattern shows up over large distances.
An astronomer measures a galaxy moving away from Earth at 21,000 km/s. Using Hubble's law and the value of H_0 in the passage, how far away is the galaxy?
Mpc
Type your answer in the box. Fractions like 3/4 are fine.
Hint
The distance is the unknown. Divide the speed by the Hubble constant.
Step-by-step solution
Where the answer comes from: the passage gives Hubble's law, v = H_0 d, with H_0 "about 70 km/s per Mpc." The galaxy's speed is 21,000 km/s.
Step by step:
Solve for d: divide both sides by H_0, so d = \dfrac{v}{H_0}.
Substitute: d = \dfrac{21{,}000\text{ km/s}}{70\text{ km/s per Mpc}}.
Divide: 21{,}000 \div 70 = 300.
The km/s units cancel, leaving Mpc.
Correct answer: 300 Mpc (about a billion light-years).
Check:70 \times 300 = 21{,}000 km/s ✓. Multiplying instead would give 1{,}470{,}000 Mpc, far larger than the observable universe.
Tip: Let the units guide you. To end with Mpc, you must divide km/s by "km/s per Mpc".
Question 19 of 20 · Energy: conservation, transformation, flow
On a sunny afternoon at the beach, the air just above the hot sand warms up, expands and rises. Cooler air from above the ocean flows toward the shore to take its place, creating a steady breeze.
Which type of heat transfer does this moving air show?
Hint
Ask yourself: is the energy carried by touching, by a moving fluid, or by waves?
Step-by-step solution
Evidence: The stem says the warm air "expands and rises" and cooler air "flows toward the shore to take its place." Thermal energy is being carried from place to place by a fluid (air) that is moving.
Step by step:
Conduction is transfer by direct contact, particle to particle, such as a hot pan handle warming your hand. The breeze is not about two objects touching.
Convection is transfer by the movement of a fluid (a liquid or a gas). Warm fluid is less dense and rises; cooler, denser fluid sinks or flows in to replace it. That is exactly the circulation described.
Radiation is transfer by electromagnetic waves, like sunlight crossing space. The Sun heats the sand by radiation, but the moving air itself is convection.
The answer is convection.
Check: A convection current always has a loop: warm fluid rises, cool fluid moves in. The sea breeze has both parts.
Tip: Link each method to a key word: contact = conduction, moving fluid = convection, waves / no matter needed = radiation.
Question 20 of 20 · Work, motion and forces
A passenger is standing in a bus that is moving forward at a steady speed. The driver brakes suddenly, and the passenger lurches forward even though nothing pushed them forward.
Which idea best explains the passenger's motion?
Hint
Think about what the passenger's body 'wants' to keep doing when the bus slows down.
Step-by-step solution
Evidence: The bus was "moving forward at a steady speed," so the passenger was moving forward with it. The brakes act on the bus, not directly on the passenger.
Step by step:
Newton's first law (inertia): an object in motion keeps moving at the same speed and direction unless a net force acts on it.
When the brakes slow the bus, the passenger's body keeps moving forward at the old speed for a moment, because nothing has yet acted on it to slow it.
Relative to the slowing bus, the passenger seems to be thrown forward. No forward force is actually needed.
The forward lurch stops when the floor (friction on feet), a pole or a seat back pushes the passenger backward.
The answer is The passenger's body tends to keep moving forward at the bus's earlier speed (inertia).
Check: The same idea explains why seat belts are needed: they supply the backward force that a passenger's body needs to slow down with the car.
Tip: If an object seems "thrown" with no push, look for inertia. Objects resist changes to their motion; they do not need a force to keep moving.