Topic Quiz: Life Science

Evidence: paragraph 1: a cell "breaks one molecule of glucose all the way down to carbon dioxide and water. This releases enough energy to make about 36 molecules of ATP."

Step by step:

1. Aerobic respiration uses glucose and oxygen (reactants).
2. It produces carbon dioxide and water, and the released energy is stored as ATP (products).
3. Eliminate B (lactic acid comes from fermentation, which happens when oxygen runs short), C (oxygen is used up, not produced; glucose is the fuel), and D (that is photosynthesis, which muscle cells do not do).

The answer is A.

Tip: keep three processes straight. Aerobic respiration → CO₂ + water + lots of ATP; lactic acid fermentation → lactic acid + 2 ATP; photosynthesis → glucose + oxygen.

Evidence: the table shows Disk 1 (sterile water) had a clear ring of 0 mm, while the antibiotic disks had rings of 22, 8, and 15 mm. Every disk was the same kind of paper disk on the same dishes at 37 °C.

Step by step:

1. Disk 1 has everything the other disks have (paper, liquid, same dish, same temperature) except an antibiotic. That makes it the control.
2. Its 0 mm ring shows that a wet paper disk alone does not stop bacteria from growing.
3. So the clear rings around Disks 2 to 4 can be credited to the antibiotics.
4. Eliminate B (water is not being tested as a medicine), C (the nutrient gel feeds the bacteria; Disk 1 is not there to help them grow), and D (one disk cannot change the size of rings around other disks).

The answer is A.

Tip: a control is identical to the test items except for the one factor being tested. Ask, "What does this item lack that the others have?"

Where the answer comes from: the table shows that as side length grows from 1 to 3 cm, the surface area-to-volume ratio falls from 6 : 1 to 3 : 1 to 2 : 1, and the volume turned pink falls from 100% to 88% to 70%. The passage says "the base had soaked in about 0.5 cm from each face" in every cube.

Step by step:

1. The base moved the same distance (0.5 cm) into every cube, so the speed of diffusion did not change.
2. In a bigger cube, more of the volume lies farther than 0.5 cm from any face, so a smaller fraction is reached.
3. The bigger the cube, the smaller its surface area compared with its volume, and the smaller the share that the base reached.

Answer: As cube size increased, the surface area-to-volume ratio decreased and a smaller percent of the volume was reached by the base.

Check: the largest cube (3 cm) has the biggest surface area (54 cm²) but the lowest percent pink (70%), so "more surface area" alone does not mean better supply; the ratio is what matters.

Tip: when a table has several columns, the best conclusion usually links the variable that was changed (size) to the result that was measured (percent pink).

Where the answer comes from: the hypothesis says high-crowned teeth became common "because their ancestors began eating tough grasses as grasslands spread across North America." The table shows high-crowned teeth first appearing in Merychippus, about 15 million years ago.

Step by step:

1. To support a cause-and-effect claim, show that the cause (grasslands spreading) happened at the right time, just before or alongside the effect (high-crowned teeth).
2. Fossil grass pollen and plant remains showing that grasslands became widespread at about the time high-crowned teeth appear would directly link the two.
3. Check the others:
   • Modern horses preferring grass says nothing about when or why the teeth changed millions of years ago.
   • More Eohippus fossils with low-crowned teeth repeat what we already know about one early group.
   • Measuring modern horse heights is unrelated to teeth or diet.

Answer: Fossil pollen and plant remains showing that grasslands became widespread in North America around the time high-crowned teeth appear.

Tip: the best supporting evidence tests the specific link in the hypothesis. Evidence that is true but does not connect the cause to the effect is "true but irrelevant."

Evidence: injury absences were 60 at School A and 58 at School B, almost the same. Cold and flu absences were 320 versus 480. The passage also notes "Students were not randomly assigned to schools."

Step by step:

1. Sanitizer kills germs on hands; it should have no effect on injuries. Injury absences act as a comparison measure that the program should not change.
2. Because the schools were not randomly assigned, one worry is that School A simply has students who miss less school for every reason.
3. The injury numbers are nearly equal (60 vs. 58), so the schools look alike on a measure the sanitizer could not affect. That makes the difference in cold and flu absences more believable as an effect of the program.
4. Eliminate A (sanitizer does not prevent injuries; numbers barely differ), C (2 extra days is no meaningful difference and no cause is shown), D (the outcome of interest is cold and flu absences).

The answer is B.

Tip: when a study reports an extra measurement that the treatment should NOT affect, its job is usually to check that the groups are otherwise similar.

Evidence: the glass beads used 0.0 mL of oxygen at both temperatures, while germinating peas used 0.4 and 1.0 mL. The passage says she used "equal volumes of three materials."

Step by step:

1. Glass beads take up the same space as the peas but cannot respire. That makes the beads tube a control.
2. If changes in temperature or pressure alone moved the drop, it would show up in the beads tube too.
3. The beads tube showed no change (0.0 mL), so the drop movement in the pea tubes can be credited to the peas using oxygen.
4. Eliminate B (beads do not supply oxygen), C (beads cannot respire, so they are not a living thing being compared), and D (beads do not absorb CO₂; the chemical in each tube does).

The answer is A.

Tip: a non-living object of the same size is a classic control in respiration experiments. It rules out the equipment or the conditions as the cause.

Evidence: the table shows 0.15 ppm in yellow perch and 0.6 ppm in walleye. The passage says "a health guideline advises people to limit fish that contain more than 0.3 ppm."

Step by step:

1. Yellow perch: 0.15 ppm, which is below 0.3 ppm.
2. Walleye: 0.6 ppm, which is above 0.3 ppm (twice the guideline).
3. So the family should choose yellow perch and limit walleye. This fits biomagnification: walleye eat perch and are one level higher, so they have more methylmercury.
4. Eliminate B (walleye has the higher level), C (perch is under the guideline), and D (the low level in the water does not matter; the fish have built up much more).

The answer is A.

Tip: for questions that apply a limit, write each value next to the limit and mark it above or below before choosing.

Where the answer comes from: the table shows the starting tumor counts: metaphase 20, anaphase 10, telophase 10. The question says cells "cannot move on to anaphase" but cells "already past metaphase finish dividing normally."

Step by step:

1. Cells keep arriving at metaphase from prophase, but none can leave it. The metaphase count goes up.
2. Cells already in anaphase and telophase finish dividing, and no new cells replace them. Those counts go down.
3. The drug acts only on dividing cells, so the overall pattern is a pile-up at metaphase and an empty space after it.

Answer: More cells would be in metaphase, and fewer cells would be in anaphase and telophase.

Check: this is how such drugs are used in real labs: blocking metaphase makes chromosomes easy to count, because many cells are held at that stage.

Tip: for "what would happen if" questions about a process with steps, find the blocked step: things build up before or at the block and run out after it.