Human body and health

Evidence: the table shows breathing rate rising from 14 breaths/min at rest to 32 breaths/min at minute 15, at the same time heart rate rose from 70 to 150 beats/min.

Step by step:

1. The question asks which system supplied extra oxygen together with the circulatory system (heart and blood vessels).
2. Oxygen enters the body through the lungs. The lungs belong to the respiratory system.
3. Faster breathing brings more oxygen into the lungs; a faster heartbeat carries that oxygen to the muscles in the blood.
4. The table measured breathing rate, and it rose with heart rate, so the two systems worked together.

The answer is A. The respiratory system.

Tip: on body-system questions, match the job in the question (taking in oxygen, digesting food, removing wastes) to the system that does that job, then check that the data actually measured it.

Evidence: body temperature was 37.0 °C at rest, rose only to 37.4 °C at minute 15 while jogging, and was back to 37.0 °C at minute 25. The passage adds that the volunteer "began sweating at about minute 10."

Step by step:

1. Range of body temperature: 37.4 - 37.0 = 0.4 °C. That is a very small change.
2. Over the same time, heart rate changed by 80 beats/min, so the body let heart rate change a lot but held temperature nearly steady.
3. Keeping internal conditions within a narrow range is homeostasis. Sweating, which began at minute 10, cools the skin as sweat evaporates.
4. Check the distractors: C says no effect (wrong, it rose 0.4 °C); D says it kept rising after jogging (it fell to 37.1); A compares it to heart rate (heart rate changed far more).

The answer is B.

Tip: words like no effect and always are risky. A small change is still a change, so check the actual numbers.

Evidence: the table shows core temperature of 37.0 °C at 0 minutes and 37.5 °C at 45 and 60 minutes, while the room was 40 °C. Skin temperature went from 33.0 °C to 36.3 °C over the same time.

Step by step:

1. Change in core temperature in the hot room: 37.5 - 37.0 = 0.5 °C. That is a small change.
2. Change in skin temperature: 36.3 - 33.0 = 3.3 °C, more than six times as much.
3. The room was 40 °C, yet the core never got close to 40 °C. The body held its inside temperature in a narrow range. That is homeostasis, helped by sweating, which the passage says carries heat away.
4. Eliminate B (the core stayed far below 40 °C), C (the skin changed more, not the core), and D (0.5 °C is a small change, but it is a change).

The answer is A.

Tip: homeostasis questions usually show one number that barely moves while the conditions around it change a lot. Compare the size of the changes before you decide.

Evidence: the table shows urine output rising from 0.6 L to 1.4 L to 2.3 L as water drunk rose from 1.0 to 2.0 to 3.0 L. The passage says that "When the body has extra water, the pituitary gland releases less ADH, and the kidneys make a larger amount of pale, dilute urine."

Step by step:

1. More water in → more urine out, and paler urine. Less water in → less urine, darker urine.
2. The passage explains why: the body adjusts urine to keep the water in the blood "within a narrow range." That is homeostasis.
3. Eliminate B (her kidneys kept working on all three days), C (on Day 1 she drank 1.0 L but made only 0.6 L, so not all of it left as urine), and D (urine output almost quadrupled).

The answer is A.

Tip: when a body output rises and falls to match an input, the body is usually keeping something inside steady. Name what is being kept steady.

Evidence: Person A starts at 85 mg/dL and is back at 85 mg/dL by 150 and 180 minutes. Person B starts at 130 mg/dL and is still at 195 mg/dL at 180 minutes. The passage says that in type 1 diabetes "the pancreas makes little or no insulin."

Step by step:

1. Person A: 85 → peak 140 → back to 85. The insulin feedback loop returned glucose to its starting level.
2. Person B: 130 → peak 260 → 195 at 180 min. It has not returned to 130.
3. Eliminate B: the passage says Person B makes little or no insulin, so B made less, not more.
4. Eliminate A: Person B started at 130 mg/dL, above the typical 70–100 range.
5. Eliminate D: Person B's line is falling from 60 to 180 minutes, and the graph ends at 180 minutes, so a rise is not supported.

The answer is C.

Tip: a supported conclusion must match every number it mentions. Test each choice against the graph, and reject any that predict beyond the data.

Evidence: the passage says "Group 2 received a placebo, a shot of salt water that looks the same," and the groups were "randomly assigned" and of equal size (5,000 each).

Step by step:

1. Group 2 is the control group. It gets everything Group 1 gets (a shot, the same follow-up) except the vaccine itself.
2. Its result, 200 cases, shows how many people get sick from Virus K without the vaccine.
3. Comparing 20 cases (vaccine) to 200 cases (placebo) is what lets researchers judge the vaccine.
4. Eliminate A: salt water is not being tested as a treatment. Eliminate C: Group 2 gets no vaccine. Eliminate B: the study counted illness, not side effects, and Group 2 tells nothing about the vaccine's safety.

The answer is D.

Tip: the control group is the comparison baseline. If a choice says the control is being "tested" or "treated," it is usually wrong.

Evidence: the table shows the placebo group had 5,000 people and 200 got sick.

Step by step:

1. Part = 200 people who got sick in the placebo group.
2. Whole = 5,000 people in the placebo group (not 10,000, which is both groups together).
3. 200 \div 5{,}000 = 0.04, which is 4\%.

Choice A (0.4%) is the vaccine group: 20 \div 5{,}000 = 0.004 = 0.4\%. Choice B (2%) divides by all 10,000 people. Choice D (40%) slips a decimal place.

The answer is C. 4%.

Tip: the whole must match the group named in the question. Circle the group ("placebo") before you calculate.

Evidence: paragraph 1 says: "If the real pathogen enters the body later, memory cells recognize it, and the immune system responds faster and more strongly."

Step by step:

1. The vaccine exposes the immune system to a harmless version or piece of the pathogen.
2. The body makes antibodies and memory cells.
3. Later, memory cells recognize the real pathogen, so the defense starts faster and is stronger, often stopping the infection before a person feels sick.
4. Eliminate B: vaccines do not kill "all viruses" (too broad). Eliminate C: antibiotics work against bacteria, not viruses, and a vaccine is not an antibiotic. Eliminate D: the passage says the body makes antibodies.

The answer is A.

Tip: "According to the passage" means the answer is restated from the text. Find the sentence, then match it.

Evidence: the skin temperature line reads 33.0, 35.5, 36.0, 36.2, 36.3, 33.5, and 32.5 °C at 0, 15, 30, 45, 60, 75, and 90 minutes.

Step by step:

1. A drop means the line goes down from left to right. Skin temperature only goes down after minute 60.
2. Minute 60 to 75: 36.3 - 33.5 = 2.8 °C drop.
3. Minute 75 to 90: 33.5 - 32.5 = 1.0 °C drop.
4. Minute 0 to 15 is a rise of 2.5 °C, and minute 45 to 60 is a rise of only 0.1 °C.
5. The biggest drop, 2.8 °C, came right after he moved into the cool room, when sweat and widened skin blood vessels kept releasing heat into cooler air.

The answer is C. From 60 to 75 minutes.

Tip: the steepest part of a line shows the fastest change. Check the direction too: a steep climb is not a drop.

Evidence: paragraph 2: "When the body is low on water, the blood becomes more concentrated. The brain senses this change, and the pituitary gland... releases more ADH into the blood. ADH signals the kidneys to return more water to the blood. As a result, the body makes a small amount of dark, concentrated urine."

Step by step:

1. Day 1 had the least water drunk (1.0 L) and the smallest, darkest urine output (0.6 L, dark yellow). That matches "low on water."
2. Follow the passage: blood more concentrated → brain senses it → pituitary releases more ADH → kidneys return more water to the blood → less urine.
3. Eliminate B (less ADH happens when there is extra water), C (she made less urine, not more), and D (the passage says the pituitary gland releases ADH, not the stomach).

The answer is A.

Tip: in a feedback question, decide first whether the body has too much or too little of something. Then pick the chain that pushes it back toward normal.

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?"

Evidence: paragraph 1: "Antibiotics do not work against viruses, which cause colds and flu, because viruses are not cells and do not have the cell parts that antibiotics attack."

Step by step:

1. A cold is caused by a virus.
2. Antibiotics attack parts of bacterial cells. Viruses are not cells and lack those parts.
3. So even the antibiotic that worked best against these bacteria (22 mm) would not help a cold.
4. Eliminate B (X actually worked best in the test), C (the 37 °C was a lab condition, not a rule about where antibiotics work), and D (colds are caused by viruses, not bacteria).

The answer is A.

Tip: a strong result in one test only applies to what was tested. These dishes held bacteria, so the results say nothing about viruses.

Evidence: the passage says "The meals were the same except for sodium: Group 1's meals contained 1,500 mg of sodium per day, and Group 2's meals contained 3,400 mg per day."

Step by step:

1. The researchers deliberately gave the two groups different amounts of sodium. That is the independent variable.
2. They then measured blood pressure to see how it responded. Blood pressure is the dependent variable.
3. Group size (100 each) and everything else in the meals were kept the same: those are controlled variables.
4. The nurses measured the results; they are part of the method, not a variable being tested.

The answer is C. The amount of sodium in the meals.

Tip: independent = what the scientist changes; dependent = what the scientist measures. Saying "the effect of ___ on ___" puts them in order: independent first.

Evidence: the passage says "Your respiratory system takes in oxygen through the lungs" and the circulatory system "carries oxygen and glucose to the muscles." It also says "Working muscles need extra oxygen and glucose."

Step by step:

1. Narrow airways let less air into the lungs, so the respiratory system takes in less oxygen.
2. Less oxygen enters the blood, so the circulatory system has less oxygen to deliver.
3. Running muscles need extra oxygen, so they get less than they need and the person tires sooner.
4. Eliminate B (glucose absorption happens in the digestive system, which asthma does not block), C (breathing harder through narrow airways does not bring in more oxygen than normal), and D (narrow airways make it harder, not easier, to breathe out carbon dioxide).

The answer is A.

Tip: for "what if" questions, follow the chain of systems in the passage one link at a time, starting from the part that is changed.

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: paragraph 2: "When an antibiotic is used, a few bacteria may happen to survive because of small differences in their genes. If these survivors multiply, they can produce a population that the antibiotic no longer kills."

Step by step:

1. Bacteria in a population already differ slightly in their genes.
2. The antibiotic kills most of them, but a few happen to survive because of those differences.
3. The survivors multiply, so the new population is made mostly of bacteria the antibiotic cannot kill. This is natural selection acting on bacteria.
4. Eliminate B (the bacteria become resistant, not the person), C (the differences already existed; the bacteria do not change on purpose), and D (bacteria do not turn into viruses).

The answer is A.

Tip: resistance is a change in a population over generations, caused by which individuals survive and reproduce. Watch for choices that say one organism changed "to" survive.

Evidence: paragraph 2: "As sweat evaporates from the skin, it carries heat away" and "Sweat cools the body only when it evaporates."

Step by step:

1. In the original test, evaporating sweat helped hold his core temperature at about 37.5 °C.
2. In very humid air, sweat cannot evaporate, so it cannot carry heat away, even though his brain would still signal the sweat glands.
3. His body would lose one of its main ways to shed heat, so his core temperature would most likely climb higher than 37.5 °C.
4. Eliminate B (the brain would still signal sweating; the problem is evaporation), C (more sweat that does not evaporate gives no extra cooling), and D (the key condition, evaporation, is different).

The answer is A.

Tip: when a question changes one condition, find the sentence in the passage that depends on that condition. Here, the word only tells you sweat without evaporation does not cool.

Evidence: average clear rings: sterile water 0 mm, Antibiotic X 22 mm, Antibiotic Y 8 mm, Antibiotic Z 15 mm. The passage says "A wider clear ring means the solution did a better job of stopping the bacteria from growing" and that all dishes had "the same kind of bacteria."

Step by step:

1. Rank by ring width: X (22) > Z (15) > Y (8) > water (0). X did the best job against this kind of bacteria.
2. Eliminate B: the test used one kind of bacteria, so it cannot show X cures every bacterial infection.
3. Eliminate C: Y made an 8 mm ring, more than the 0 mm control, so it had some effect.
4. Eliminate D: Z (15 mm) made a smaller ring than X (22 mm), so Z was less effective, not twice as effective.

The answer is A.

Tip: the best-supported conclusion stays inside the conditions of the test. Words like every and no effect are warning signs.

Evidence: the passage says "ADH signals the kidneys to return more water to the blood" and that with less ADH "the kidneys make a larger amount of pale, dilute urine." It also says that when the blood becomes concentrated, "The brain also triggers thirst."

Step by step:

1. With no ADH, the kidneys never get the signal to return extra water to the blood.
2. So they keep making large amounts of pale, dilute urine, even when the body is low on water.
3. Losing that much water makes the blood more concentrated, and the brain triggers thirst. The person feels thirsty often.
4. Eliminate B (small, dark urine is what happens when there is more ADH), C (the kidneys still filter blood; ADH controls how much water they return), and D (the brain can sense the change, but without ADH the kidneys get no signal).

The answer is A.

Tip: to predict what happens when a signal is missing, find what the signal normally does, then imagine the opposite happening all the time.

Evidence: protein and Calories per cup: soup 3 g / 90, yogurt 13 g / 150, oatmeal 6 g / 160, black beans 15 g / 230.

Step by step: protein per 100 Calories = \dfrac{\text{protein}}{\text{Calories}} \times 100

• Soup: \dfrac{3}{90} \times 100 \approx 3.3 g
• Yogurt: \dfrac{13}{150} \times 100 \approx 8.7 g
• Oatmeal: \dfrac{6}{160} \times 100 \approx 3.8 g
• Black beans: \dfrac{15}{230} \times 100 \approx 6.5 g

Black beans have the most protein per cup (15 g), but they also have the most Calories. Per 100 Calories, plain yogurt gives the most protein.

The answer is D. Plain yogurt.

Tip: read the unit in the question. "Per serving" lets you read the table directly; "per 100 Calories" means you must divide first.

Evidence: fully vaccinated: 24 cases among 48,000 children; not vaccinated: 160 cases among 2,000 children. The passage says officials compare groups using the case rate "Because the groups are very different in size."

Step by step:

1. Fully vaccinated rate: \dfrac{24}{48{,}000} \times 1{,}000 = 0.5 per 1,000.
2. Not vaccinated rate: \dfrac{160}{2{,}000} \times 1{,}000 = 80 per 1,000.
3. 80 \div 0.5 = 160, so unvaccinated children got sick at about 160 times the rate of fully vaccinated children. The vaccine greatly lowered risk, even though it did not prevent every case.
4. Eliminate B (a vaccine can work well without being perfect), C (rates solve the problem of different group sizes, so the groups can be compared), and D (unvaccinated children had 160 cases, more than the 24 among fully vaccinated children).

The answer is A.

Tip: when a claim is based on a raw count, convert to rates before judging it. Big groups produce more cases even when each person's risk is low.