Science Mixed Practice Test 2

Where the answer comes from: the graph shows speed rising steadily with distance, from Galaxy A (50 million light-years, 1,100 km/s) to Galaxy E (470 million light-years, 10,200 km/s). The passage says redshift means a galaxy is "moving away from us," and "an observer in any galaxy would see the other galaxies moving away in this same pattern."

Step by step:

1. All five galaxies are moving away (all are redshifted with positive speeds).
2. The farther the galaxy, the faster it recedes. The points lie close to a straight line through the origin.
3. This is exactly what happens if space itself is expanding: every galaxy moves away from every other one.
4. Because observers in every galaxy would see the same pattern, it does not put us at the center.

The best conclusion is that the universe is expanding, with more distant galaxies moving away faster. This evidence supports the Big Bang theory.

Tip: Reject conclusions that go further than the evidence ("we are at the center") or that reverse the trend.

Where the answer comes from: the table's diameter column: Ceres 940 km, Pluto 2,377 km, Haumea about 1,600 km, Makemake 1,430 km, Eris 2,326 km.

Step by step:

1. Look only at the last column, "Diameter (km)."
2. The two largest values are Pluto (2,377 km) and Eris (2,326 km).
3. Compare digit by digit: 2,377 is greater than 2,326 by 51 km.

The largest dwarf planet by diameter is Pluto.

Check: Eris is the farthest dwarf planet and has the longest orbital period, which tempts readers to pick it, but it is slightly smaller ✓.

Tip: Say the column name to yourself before you compare values. Being biggest in one column (distance) does not mean biggest in another (size).

Evidence: rabbits peak at 1,300 in year 3 and foxes peak at 80 in year 4. Rabbits rise again to 1,250 in year 9, and foxes rise to 75 in year 10. The passage warns that "rabbits are read on the left axis, and foxes are read on the right axis."

Step by step:

1. Rabbit peak (year 3) → fox peak one year later (year 4). Rabbit peak (year 9) → fox numbers still climbing in year 10.
2. Why the lag? More rabbits mean more food for foxes, so more fox pups survive, but that takes time.
3. Eliminate B: the peaks happen in different years. Eliminate C: the largest fox count is 80; the largest rabbit count is 1,300; reading both lines on one axis causes this error. Eliminate A: foxes fall from 80 to 25 between years 4 and 7.

The answer is D.

Tip: with two vertical axes, match each line to its axis using the legend and axis colors before comparing values.

Evidence: in the web, arrows run from algae and pondweed to snail, and from snail to frog. Pondweed has only one arrow leaving it, to the snail.

Step by step:

1. The snail is the only organism shown that eats pondweed.
2. With most snails gone, almost nothing is eating the pondweed, so the pondweed is likely to increase.
3. Check the others: frogs lose a food source, so they are more likely to decrease (C is backward). Zooplankton would have more algae, not less (B is backward). Herons do not eat snails, and fewer frogs would mean less food for herons, not more (D).

The answer is A.

Tip: when one species disappears, look first at what it ate (that food may increase) and at what ate it (those predators may decrease).

Evidence: paragraph on oxpeckers: they "eat ticks off their skin," but "researchers have also seen oxpeckers peck at open wounds and drink blood, which can keep the wounds from healing."

Step by step:

1. The oxpecker benefits (food) in both behaviors: +.
2. The rhino gains from tick removal (+), but it is harmed when wounds are kept open (−).
3. +/+ is mutualism, and +/− is parasitism. The evidence supports parts of both, so the relationship is not clearly mutualism; it may depend on how much each behavior happens.
4. Eliminate B (it ignores the wound-feeding evidence), C (the rhino is affected, both helped and harmed, so it is not +/0), and D (oxpeckers do not kill and eat rhinos).

The answer is A.

Tip: the GED likes evidence that does not fit neatly. The best answer accounts for all the evidence, not just the part that supports the first idea.

Where the answer comes from: in the first table, every codon is the same except codon 4, which is GAG in the normal gene and GTG in the sickle cell gene. The second letter changed from A to T. The total number of bases (18) is unchanged.

Step by step:

1. Compare codon by codon: codons 1, 2, 3, 5 and 6 match.
2. Codon 4: G-A-G becomes G-T-G. One base was swapped for another.
3. A swap of one base for another is a substitution (point mutation).
4. Effect: in the codon table, GAG is glutamic acid and GTG is valine, so one amino acid in hemoglobin changes. That single change is enough to cause sickle cell disease.

Answer: a substitution, in which one base is replaced by another.

Why the others fail: an insertion would add a base (19 bases), and a deletion would remove one (17 bases); the count did not change. A change in chromosome number affects whole chromosomes, not one letter in a gene.

Tip: to classify a mutation, first count the bases. Same count with one letter changed is a substitution. A different count is an insertion or deletion.

Where the answer comes from: the passage says "The allele for a black coat (B) is dominant over the allele for a white coat (b)."

Step by step:

1. Translate each genotype into a phenotype:
   • BB → black (two dominant alleles)
   • Bb → black (the dominant B hides b)
   • bb → white (no dominant allele)
2. Find the pair with the same coat color but different letters: BB and Bb are both black.
3. Check the others: Bb and bb look different (black vs. white); BB and bb look different; bb and bb have the same genotype.

Answer: a BB guinea pig and a Bb guinea pig.

Check: this is why the black parents in the table cannot be identified just by looking at them; both BB and Bb guinea pigs are black.

Tip: a dominant phenotype always has two possible genotypes (homozygous or heterozygous). A recessive phenotype has only one.

Evidence: The passage says "All EM waves travel through empty space at the same speed" and "speed equals frequency times wavelength: v = f\lambda." The table lists the AM radio's frequency as 1.0 \times 10^{6} Hz, the smallest in the table.

Step by step:

1. Since v is the same for every EM wave, \lambda = \dfrac{v}{f}. A smaller frequency gives a longer wavelength.
2. Compare the powers of ten: 10^{6} (AM radio) < 10^{9} (Wi-Fi) < 10^{14} (remote, tanning lamp) < 10^{18} (X-ray).
3. The AM radio has the lowest frequency, so its waves have the longest wavelength. In fact, \lambda = \dfrac{3.0 \times 10^8}{1.0 \times 10^6} = 300 m.

The answer is the AM radio.

Check: The X-ray machine has the largest frequency, so it has the shortest wavelength, the opposite end of the list.

Tip: For EM waves, frequency and wavelength move in opposite directions. Big frequency number means short wavelength and high energy.

Evidence: The passage gives the rover's mass as "900 kg," the formula W = mg, and the table lists Mars's g as 3.7 m/s².

Step by step:

1. Use the mass (it is the same everywhere): m = 900 kg.
2. Use Mars's gravitational field strength: g = 3.7\ \text{m/s}^2.
3. Multiply: W = 900 \times 3.7 = 3{,}330\text{ N}

The rover weighs 3,330 N on Mars.

Check: On Earth it would weigh 900 \times 9.8 = 8{,}820 N. Mars's answer is less than half of that, which fits 3.7 being less than half of 9.8.

Tip: Mass (kg) never changes with location; weight (N) does. To get weight, always multiply the mass by the local g.

Evidence: In Trials 1–4 the tablets are all "Whole" while the water temperature rises from 10 °C to 55 °C, and the times drop from 72 s to 45 s to 28 s to 18 s. The passage says "A shorter time means a faster reaction."

Step by step:

1. Only one variable changes in Trials 1–4: the water temperature. Tablet form and water volume stay the same.
2. As the temperature goes up, the time goes down every time.
3. Shorter time = faster reaction, so warmer water makes the reaction faster.
4. The experiment measured time, not the amount of gas, so a claim about more gas is not supported.

The answer is The reaction is faster in warmer water.

Check: In warmer water, particles move faster and collide more often and with more energy, which is the scientific reason reactions speed up with temperature.

Tip: Before choosing a conclusion, identify which variable changed and what was measured. A conclusion must be about those two things only.

Evidence: The graph shows the solubility of sugar at 60 °C as 287 g per 100 g of water. The passage says the graph shows "the greatest mass of sugar that can dissolve in 100 g of water at different temperatures."

Step by step:

1. Find 60 °C on the x-axis (water temperature).
2. Move straight up to the plotted line. The data point is just below the 300 g gridline.
3. Read across to the y-axis: about 287 g.
4. Do not confuse this with neighboring points: 238 g at 40 °C and 362 g at 80 °C.

About 287 g of sugar can dissolve at 60 °C.

Check: 287 g lies between the 40 °C value (238 g) and the 80 °C value (362 g), as expected because the curve rises steadily.

Tip: When reading a graph, say the axis labels aloud: x is temperature, y is grams dissolved. That prevents reading the wrong axis.

The control group goes through the same procedure as the experimental group but does not receive the treatment being tested. Here the treatment is the sanitizer.

Step by step:

1. The experimental group rubbed '2 mL of the sanitizer over their hands for 20 seconds.'
2. The other group rubbed '2 mL of plain water over their hands for 20 seconds,' the same action without the sanitizer.
3. Comparing the two groups shows how much of the drop in bacteria is due to the sanitizer and how much is due to simply rubbing the hands. (Water alone lowered the average from 81 to 66; sanitizer lowered it from 84 to 9.)

The correct answer is C, the six volunteers who rubbed plain water on their hands.

Check: The 'before' plates are a baseline for each person, but the group that tells you what happens without sanitizer is the plain-water group. The incubator is a controlled condition, not a group.

Tip: A good control matches the treatment group in every step (here, same volume, same rubbing time) except the one factor being tested.

A confounding variable is a factor other than the one being tested that differed between groups and could cause the results. The plain-water group was tested in an 18 °C room, but the caffeine group was tested in a 25 °C room, using room-temperature water.

Step by step:

1. List what differed between groups: caffeine, day, time of day and room (and water) temperature.
2. The passage says Daphnia 'are always the same temperature as the water around them, and their heart rate rises as their body temperature rises.'
3. So the warmer water on Wednesday could raise heart rate even with no caffeine. The 80-beat difference cannot be credited to caffeine alone.

The correct answer is B.

Check: A is not a difference: both groups were counted the same way. C is a weakness, but a small sample alone does not explain why one group was consistently higher. D is the same for both groups.

Tip: When a passage gives you a background fact (such as the link between Daphnia body temperature and heart rate), it is usually the key to spotting the confound.

Where the answer comes from: the table rows "| 10° | 120 | 30 |", "| 20° | 260 | 45 |" and "| 30° | 510 | 70 |" give the soil lost (in grams) from the bare and grass-covered trays.

Step by step:

1. At every slope, the grass-covered tray lost less soil than the bare tray.
2. The gap grows with slope: 120 - 30 = 90 g, then 260 - 45 = 215 g, then 510 - 70 = 440 g.
3. Both columns rise with slope, but the bare column rises much faster.

Correct answer: C.

Check: the bare tray lost 4 times as much at 10° (120 \div 30) and about 7 times as much at 30° (510 \div 70 \approx 7.3), so the ratio is not a steady "about twice."

Tip: To describe a finding, state the direction (less soil lost with grass) and how the difference changes across conditions (bigger on steeper slopes).

Where the answer comes from: the table lists one number for each of four magnitude ranges, from "| 5.0–5.9 | 1,300 |" to "| 8.0 and higher | 1 |".

Step by step:

1. The data are counts for separate categories (magnitude ranges). Comparing categories is the job of a bar graph.
2. A line graph shows change over time, but the table has no years.
3. A scatter plot needs two measured values for each item; the table does not list energy values.
4. A map needs locations, which the table does not include.

Correct answer: D.

Check: a bar graph lets the reader see at a glance that the 5.0–5.9 bar is far taller than the others.

Tip: Match the display to the data's job: categories → bar graph; change over time → line graph; parts of a whole → circle graph; two measured variables → scatter plot.

Evidence: In the expression 2\,\text{Ca(NO}_3\text{)}_2, the coefficient 2 means two formula units of calcium nitrate. The subscript 2 after the parentheses doubles everything inside them.

Step by step:

1. Inside the parentheses, \text{NO}_3 has 3 oxygen atoms.
2. The subscript 2 outside the parentheses means two \text{NO}_3 groups: 3 \times 2 = 6 oxygen atoms in one \text{Ca(NO}_3\text{)}_2.
3. The coefficient 2 in front means two of these units: 6 \times 2 = 12 oxygen atoms.

There are 12 oxygen atoms.

Check: Count the other atoms the same way: calcium 1 \times 2 = 2, nitrogen 1 \times 2 \times 2 = 4. Total atoms = 2 + 4 + 12 = 18.

Tip: A coefficient multiplies the whole formula. A subscript after parentheses multiplies everything inside the parentheses. A subscript after one symbol applies only to that element.

Evidence: A chemical change produces one or more new substances with new properties. Common signs are an unexpected gas, a new color, light or heat given off, or a new solid (precipitate) forming when liquids are mixed.

Step by step:

1. Bubbles in boiling water: the bubbles are water vapor, still water. This is a change of state (physical).
2. Two clear, colorless solutions forming a yellow solid when mixed: a solid that was not there before, with a new color, appears. This is a precipitate, strong evidence of a new substance (chemical).
3. Drink powder disappearing in water and turning it red: dissolving is a physical change; the powder's own color simply spreads through the water, and evaporating the water would give the powder back.
4. Ice cubes slowly shrinking in a freezer: the ice turns directly into water vapor (sublimation), a change of state (physical).

The answer is Two clear, colorless solutions are mixed, and a yellow solid forms.

Check: Only choice B produces a substance with properties (yellow, solid, does not dissolve) that none of the starting materials had.

Tip: Bubbles and color alone are not proof. Ask whether a new substance formed or whether the same substance just changed state or mixed.