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Corals are animals that get much of their food from tiny algae living inside their tissues. When the water gets too warm, many corals push the algae out and turn white. This is called bleaching. Bleached corals can recover if the water cools in time, but many die.
Marine scientists surveyed coral colonies at reef sites during one summer and recorded the highest water temperature reached at each site.
Peak summer water temperature (°C)
Coral colonies bleached (%)
28
2
29
5
30
18
31
47
32
81
Each row is the average of several sites that reached that peak temperature.
Which statement best describes the findings of the coral survey?
Hint
Find how much the bleaching percentage increases with each 1 °C step.
Step-by-step solution
Where the answer comes from: the table rows run from "| 28 | 2 |" and "| 29 | 5 |" up to "| 30 | 18 |", "| 31 | 47 |" and "| 32 | 81 |".
Bleaching stays low (2% and 5%) at 28 °C and 29 °C.
Above 29 °C, each extra degree adds a much larger amount, so bleaching rises sharply.
Correct answer: B.
Check: the steps (3, 13, 29, 34) are not equal, so a "same amount each degree" statement is wrong; and at 30 °C only 18% bleached, so "most colonies" is wrong there.
Tip: To describe a table, compute the change between rows. Unequal changes tell you the pattern speeds up or slows down.
Question 2 of 10 · Comprehending scientific presentations
Select allA Meadow Food Web
A food web is a model that shows how energy moves through a community of living things. In the food web below, each arrow points from an organism to the organism that eats it. The arrow therefore shows the direction in which energy flows.
Plants such as grass are producers: they capture energy from sunlight. All the animals in the web are consumers.
Based on the food web, which organisms eat the mouse? Select all that apply.
Select all that apply.
Hint
Find every arrow that starts at Mouse. Where do those arrows point?
Step-by-step solution
Use the rule from the passage: "each arrow points from an organism to the organism that eats it." So we look for arrows that start at Mouse.
Step by step:
Two arrows leave the Mouse box: one points up-left to Snake, and one points up to Hawk.
So the snake and the hawk both eat the mouse.
The arrow between Grass and Mouse points into Mouse, which means the mouse eats grass, not the other way around.
Frog and Rabbit have no arrows connected to Mouse.
The correct answers are A (Snake) and C (Hawk).
Tip: For "who eats X?" follow arrows out of X. For "what does X eat?" follow arrows into X. Say it out loud to avoid reversing the direction.
Question 3 of 10 · Comprehending scientific presentations
Drop-downA Model of Blood Circulation
The heart is a muscular pump with two sides. The diagram is a simplified model of the path blood takes through the human body. Each arrow shows the direction in which blood flows. The key explains the two kinds of arrows.
Blood picks up oxygen in the lungs. Body tissues, such as muscles, use that oxygen for energy, so blood returning from the tissues carries little oxygen. In this model, the right side of the heart pumps blood only to the lungs, and the left side pumps blood to the rest of the body.
Complete the sentence based on the diagram.
Blood returning from the body tissues first enters the , and it becomes oxygen-rich when it passes through the .
Choose an answer from each menu.
Hint
Find the arrow that leaves Body tissues. Then find where the arrows change from solid blue to dashed red.
Step-by-step solution
Turn the diagram into words by following the arrows.
Step by step:
The arrow that leaves Body tissues is solid blue and points up into the Right side of heart box. So returning blood first enters the right side of the heart.
The arrows change from solid blue (oxygen-poor) to dashed red (oxygen-rich) at the Lungs box. The passage agrees: 'Blood picks up oxygen in the lungs.'
The correct answers are right side of the heart and lungs.
Check: The left side of the heart receives blood from the lungs, not from the body. The body tissues use oxygen; they do not add it, which is why blood leaving them is oxygen-poor.
Tip: When a diagram has a key, use it. A change in arrow color or style usually marks the place where something happens to the material being carried.
Question 4 of 10 · Investigation design
A Sports Drink Study
A beverage company wanted to show that its new sports drink, called Drink Z here, helps people run faster. The volunteers chose which Saturday they wanted to take part.
Saturday 1, 8:00 a.m. (55 °F): 10 volunteers drank one bottle of Drink Z and then ran a 5-kilometer course.
Saturday 2, 3:00 p.m. (88 °F): 10 different volunteers drank one bottle of water and then ran the same course.
Group
Number of runners
Average time (minutes)
Drink Z
10
26
Water
10
29
Based on these results, the company concluded that Drink Z makes runners faster.
Which change would make this study a fair test of whether Drink Z makes runners faster?
Hint
A fair test keeps everything the same except the drink, and makes the two groups as alike as possible.
Step-by-step solution
To isolate the effect of the drink, both groups must run under the same conditions, and the groups should be formed by random assignment so that faster runners are not more likely to end up in one group. In the original study "the volunteers chose which Saturday they wanted to take part" and the two runs happened at different temperatures.
Step by step:
Choice C removes the time and temperature difference (same day, same time) and uses random assignment. Only the drink differs.
Choice A keeps the hot-versus-cool problem; it just repeats it.
Choice B has no comparison group at all, so there is nothing to compare to.
Choice D lets people choose, which can create groups that differ from the start (for example, serious runners might prefer the sports drink).
The correct answer is C.
Tip: The gold-standard design is: random assignment into groups + same conditions + only one difference (the treatment).
Question 5 of 10 · Evaluating conclusions with evidence
Predators and Prey on Kestrel Island
Kestrel Island is a fictional island. Ecologists counted the deer and the wolves on the island every winter for 10 years. Wolves are the main predator of the deer, and deer feed on shrubs and young trees. The graph shows the counts. Read the deer line with the left axis and the wolf line with the right axis.
An ecologist claims: "Wolves alone caused the drop in the deer population after Year 4." Which new evidence would most challenge this claim?
Hint
To challenge a claim that one factor ALONE caused something, look for evidence of a different cause.
Step-by-step solution
The claim says wolves alone caused the decline. Evidence that challenges it would show another cause was also at work.
Step by step:
Choice B gives a second cause: deer starving in a harsh winter. If many deer died from cold and hunger in Year 5, then wolves were not the only reason the deer population fell.
Choice A is consistent with the claim. It already matches the graph, since wolves rose to 27 in Year 5 while deer fell.
Choice C (wolves eating deer) supports the idea that wolves had an effect. It does not show another cause.
Choice D is about Years 8–10, when deer were increasing again. It says nothing about the cause of the drop after Year 4.
The correct answer is B.
Tip: Evidence supports a claim when it agrees with it and challenges it when it points to a different explanation or contradicts it. Words like alone and only make a claim easier to challenge.
Question 6 of 10 · Expressing scientific information
Reading the Layers of a Cliff
A geologist studied a cliff where flat layers of sedimentary rock are exposed. Her field notes say:
The shale lies directly on top of the limestone. The sandstone is the top layer of the cliff. The conglomerate, a rock made of rounded pebbles cemented together, lies directly below the limestone and is the bottom layer I can see. A layer of coal lies between the sandstone and the shale.
In undisturbed layers of sedimentary rock, each layer formed on top of the layers that were already there. So the deepest layer is the oldest, and the top layer is the youngest. This idea is called the law of superposition.
Which list correctly shows the rock layers from top to bottom, as described in the field notes?
Hint
Start with the layers whose positions are fixed (top and bottom), then place the others using "directly on top of" and "between."
Step-by-step solution
Where the answer comes from: the notes say "The sandstone is the top layer of the cliff.", the conglomerate "lies directly below the limestone and is the bottom layer I can see", "The shale lies directly on top of the limestone." and "A layer of coal lies between the sandstone and the shale."
Step by step:
Top: sandstone. Bottom: conglomerate.
Limestone is directly above the conglomerate (second from the bottom).
Shale is directly on top of the limestone (third from the bottom).
Coal is between the sandstone and the shale (second from the top).
Top to bottom: sandstone, coal, shale, limestone, conglomerate.
Correct answer: B.
Check: re-read each sentence of the notes against your list. Every statement is true for this order, and for no other order.
Tip: When you turn a written description into a diagram or list, place the fixed items first and fill in the rest with the relationship words.
Question 7 of 10 · Scientific theories
Fill inClocking a Pronghorn
The pronghorn of the western United States is one of the fastest land animals in North America. A wildlife biologist used a GPS collar to track one pronghorn during a sprint. The collar recorded that the animal ran 800 meters in 32 seconds at a nearly constant speed.
Correct answer: 90 km/h (about 56 miles per hour).
Check: in one hour the animal would go 25 \times 3600 = 90{,}000 m = 90 km ✓
Tip: A shortcut: 1\text{ m/s} = 3.6\text{ km/h}, so multiply m/s by 3.6. Always check that the units you don't want cancel out.
Question 8 of 10 · Probability and statistics in science
Robin Clutch Sizes
A clutch is the set of eggs a bird lays in one nesting attempt. A wildlife biologist surveyed 20 American robin nests in a city park in May and counted the eggs in each.
Eggs in nest
Number of nests
2
5
3
6
4
7
5
2
Each nest was counted once. The biologist plans to compare these results with nests in a rural area next year.
Based on the survey, what is the probability that a randomly chosen nest from this park contained at least 4 eggs?
Hint
'At least 4' means 4 or more. Add those nests and compare with the total number of nests.
Step-by-step solution
Where the answer comes from: the table shows 7 nests with 4 eggs and 2 nests with 5 eggs, out of 20 nests surveyed.
Step by step:
"At least 4 eggs" means 4 or 5 eggs: 7 + 2 = 9 nests.
Probability = \dfrac{9}{20} = 0.45 = 45\%.
Correct answer: B (45%).
Why the others are wrong: 35% counts only the nests with exactly 4 eggs (\tfrac{7}{20}). 55% is the probability of fewer than 4 eggs (\tfrac{11}{20}), the complement. 9% treats the count of 9 nests as if it were a percent without dividing by 20.
Check:45\% + 55\% = 100\% ✓
Tip: A probability from data is a relative frequency: the number of times something happened divided by the total. Read phrases like at least, at most and more than carefully.
Question 9 of 10 · Investigation design
Drag and dropModeling Meteorite Craters
Craters on the Moon form when rocks from space, called meteorites, crash into its surface. To model this, Ana fills a tray with flour 8 cm deep and sprinkles a thin layer of cocoa powder on top so the craters are easy to see.
Ana wants to know whether the mass of a falling object affects the size of the crater it makes. She uses four balls that are all 2.5 cm across but are made of different materials, so they have different masses: 10 g (plastic), 20 g (glass), 64 g (steel) and 93 g (lead-filled). She drops each ball from a height of 1.0 m and measures the crater's diameter with a ruler. She smooths the flour and adds fresh cocoa powder after every drop, and she drops each ball three times.
Ball mass (g)
Average crater diameter (cm)
10
4.1
20
5.0
64
6.8
93
7.6
Ana kept some factors fixed, changed one and measured one. Place each factor from her crater model in the correct column.
Independent variable
Dependent variable
Controlled variables
Tap a tile, then tap a box to place it.
Hint
One factor was changed on purpose, one was measured and the rest were kept the same.
Step-by-step solution
Sort each factor by asking how Ana treated it.
Step by step:
Changed on purpose → independent: ball mass (10, 20, 64, 93 g).
Measured → dependent: crater diameter, measured with a ruler.
Kept the same → controlled: drop height (1.0 m), ball diameter (2.5 cm across) and flour depth (8 cm).
The correct sorting is ball mass → independent; crater diameter → dependent; drop height, ball diameter and flour depth → controlled.
Check: Ball diameter is the trickiest tile. It might seem to vary because the balls are made of different materials, but the passage says they 'are all 2.5 cm across.' Ana kept size constant so that mass is the only difference between balls.
Tip: Watch for factors that sound like they should vary but are described as equal. The passage, not your expectation, decides which box a factor goes in.
Question 10 of 10 · Reasoning from data
Phosphorus and Algae in Lake Marlow
Algal blooms are sudden, large growths of algae that can turn lake water green and use up oxygen that fish need. Phosphorus is a nutrient that helps algae grow. Scientists monitored Lake Marlow, a fictional lake, for 8 years. The graph shows the lake's average phosphorus level and the number of days each year with an algal bloom.
The table shows how much lawn fertilizer containing phosphorus was sold in the county around the lake. A county ban on selling lawn fertilizer that contains phosphorus took effect in the middle of Year 6.
Year
1
2
3
4
5
6
7
8
Phosphorus lawn fertilizer sold (tons)
110
125
140
160
175
60
40
35
By about what percent did the number of algal bloom days decrease from Year 5 to Year 8?
Hint
Percent change = (change ÷ original value) × 100. The original value is the Year 5 value.
Step-by-step solution
Read the bloom-day values from the red line (right axis): Year 5 = 34 days, Year 8 = 15 days.
Step by step:
Change: 34 - 15 = 19 days fewer.
Divide by the original (starting) value, Year 5:
\text{percent decrease} = \frac{34 - 15}{34} \times 100 = \frac{19}{34} \times 100 \approx 55.9\%
Round: about 56%.
Traps: 19% treats the number of days as a percent. 44% is \tfrac{15}{34}, the part that remains, not the part that was lost. 127% divides by the new value (15) instead of the original.