Natural Science Passages · Lesson 4

Passage plus graphic

Some Reading passages come with a graph or a table. The graphic questions aren’t Science-section questions: everything you need is on the page, and the text tells you what the graphic shows. Find the sentence that introduces it (Figure 1 shows...) before you look at any numbers.

Read the graphic in order: the axis labels and units, then the series name, then the exact point the question asks about. On a line graph, go up from the x-value to the line, then across to the y-axis. If the value falls between gridlines, estimate, and then pick the choice nearest your estimate.

The hardest graphic questions mix the text and the figure. The text may discuss two related quantities while the graphic shows only one of them. Ask: which variable does the question ask about, and is that the variable on this axis? If not, the answer has to come from the text.

Warm Water, Less Oxygen

This passage is from an article about oxygen in fresh water. It includes a graph.

1A fish needs oxygen as much as you do, but it gets it from water instead of air. Its gills take in oxygen gas that has dissolved in the water, the same oxygen that mixes into a pond from the air above it and is released by water plants during the day. Biologists measure this dissolved oxygen in milligrams per liter (mg/L), the mass of oxygen held in each liter of water.

2How much oxygen water can hold depends strongly on temperature. Cold water can hold more dissolved gas than warm water. As water warms, oxygen escapes into the air more easily, so the most oxygen the water can hold falls. Figure 1 shows that maximum for fresh water at sea level, at temperatures from 0 °C to 30 °C. Real ponds and streams often hold less than this maximum, especially at night, when plants stop releasing oxygen but all the living things in the water keep using it.

3Temperature affects the fish, too. Most fish are cold-blooded, meaning that their body temperature follows the temperature of the water around them. As a fish warms, the chemical reactions in its body speed up, and it needs more oxygen each minute just to stay alive. A warm summer afternoon therefore squeezes a fish from two sides: the water holds less oxygen at the same moment that the fish needs more.

4This squeeze helps explain why cold-water species, such as trout, are found mostly in cool streams and deep lakes. Trout generally do well only where the water holds at least about 6 mg/L of oxygen, a level that many warm-water fish can tolerate going below. During a hot spell, the warmest, shallowest parts of a stream can fall below that level while shaded pools stay cooler and richer in oxygen, and trout often crowd into those pools until the weather breaks.

5The same reasoning guides people who care for ponds and aquariums. In warm weather, a fountain or an air pump that keeps the water moving helps, because a churning surface takes in oxygen from the air faster than a still one. Shade over part of a pond helps, too, by keeping the water cooler.

Figure 1
Figure 1Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.0246810121416051015202530Water temperature (°C)Maximum dissolved oxygen (mg/L)
  • Fresh water at sea level
Show the data as a table
Figure 1: data
Water temperature (°C)Fresh water at sea level (mg/L)
014.6
512.8
1011.3
1510.1
209.1
258.3
307.6

Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.

Worked example Easy

Show the whole passage

Warm Water, Less Oxygen

This passage is from an article about oxygen in fresh water. It includes a graph.

1A fish needs oxygen as much as you do, but it gets it from water instead of air. Its gills take in oxygen gas that has dissolved in the water, the same oxygen that mixes into a pond from the air above it and is released by water plants during the day. Biologists measure this dissolved oxygen in milligrams per liter (mg/L), the mass of oxygen held in each liter of water.

2How much oxygen water can hold depends strongly on temperature. Cold water can hold more dissolved gas than warm water. As water warms, oxygen escapes into the air more easily, so the most oxygen the water can hold falls. Figure 1 shows that maximum for fresh water at sea level, at temperatures from 0 °C to 30 °C. Real ponds and streams often hold less than this maximum, especially at night, when plants stop releasing oxygen but all the living things in the water keep using it.

3Temperature affects the fish, too. Most fish are cold-blooded, meaning that their body temperature follows the temperature of the water around them. As a fish warms, the chemical reactions in its body speed up, and it needs more oxygen each minute just to stay alive. A warm summer afternoon therefore squeezes a fish from two sides: the water holds less oxygen at the same moment that the fish needs more.

4This squeeze helps explain why cold-water species, such as trout, are found mostly in cool streams and deep lakes. Trout generally do well only where the water holds at least about 6 mg/L of oxygen, a level that many warm-water fish can tolerate going below. During a hot spell, the warmest, shallowest parts of a stream can fall below that level while shaded pools stay cooler and richer in oxygen, and trout often crowd into those pools until the weather breaks.

5The same reasoning guides people who care for ponds and aquariums. In warm weather, a fountain or an air pump that keeps the water moving helps, because a churning surface takes in oxygen from the air faster than a still one. Shade over part of a pond helps, too, by keeping the water cooler.

Figure 1
Figure 1Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.0246810121416051015202530Water temperature (°C)Maximum dissolved oxygen (mg/L)
  • Fresh water at sea level
Show the data as a table
Figure 1: data
Water temperature (°C)Fresh water at sea level (mg/L)
014.6
512.8
1011.3
1510.1
209.1
258.3
307.6

Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.

According to Figure 1, about how much dissolved oxygen can fresh water at sea level hold at 10 °C?

  1. 7.6 mg/L
  2. 9.1 mg/L
  3. 10.1 mg/L
  4. 11.3 mg/LAnswer

How to solve it

  1. Check the axes: x is water temperature in °C, y is maximum dissolved oxygen in mg/L.
  2. Go up from 10 °C to the line, then across to the y-axis: just above 11 mg/L, at 11.3.
  3. The other choices are the values at 15 °C, 20 °C and 30 °C, read from the wrong point.

Why each choice is right or wrong

  • A. Incorrect. 7.6 mg/L is the value at 30 °C, the right end of the line.
  • B. Incorrect. 9.1 mg/L is the value at 20 °C, two plotted points too far to the right.
  • C. Incorrect. 10.1 mg/L is the value at 15 °C, the neighboring point.
  • D. Correct. In Figure 1, the Fresh water at sea level line is at 11.3 mg/L above 10 °C.

Worked example Medium

Show the whole passage

Warm Water, Less Oxygen

This passage is from an article about oxygen in fresh water. It includes a graph.

1A fish needs oxygen as much as you do, but it gets it from water instead of air. Its gills take in oxygen gas that has dissolved in the water, the same oxygen that mixes into a pond from the air above it and is released by water plants during the day. Biologists measure this dissolved oxygen in milligrams per liter (mg/L), the mass of oxygen held in each liter of water.

2How much oxygen water can hold depends strongly on temperature. Cold water can hold more dissolved gas than warm water. As water warms, oxygen escapes into the air more easily, so the most oxygen the water can hold falls. Figure 1 shows that maximum for fresh water at sea level, at temperatures from 0 °C to 30 °C. Real ponds and streams often hold less than this maximum, especially at night, when plants stop releasing oxygen but all the living things in the water keep using it.

3Temperature affects the fish, too. Most fish are cold-blooded, meaning that their body temperature follows the temperature of the water around them. As a fish warms, the chemical reactions in its body speed up, and it needs more oxygen each minute just to stay alive. A warm summer afternoon therefore squeezes a fish from two sides: the water holds less oxygen at the same moment that the fish needs more.

4This squeeze helps explain why cold-water species, such as trout, are found mostly in cool streams and deep lakes. Trout generally do well only where the water holds at least about 6 mg/L of oxygen, a level that many warm-water fish can tolerate going below. During a hot spell, the warmest, shallowest parts of a stream can fall below that level while shaded pools stay cooler and richer in oxygen, and trout often crowd into those pools until the weather breaks.

5The same reasoning guides people who care for ponds and aquariums. In warm weather, a fountain or an air pump that keeps the water moving helps, because a churning surface takes in oxygen from the air faster than a still one. Shade over part of a pond helps, too, by keeping the water cooler.

Figure 1
Figure 1Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.0246810121416051015202530Water temperature (°C)Maximum dissolved oxygen (mg/L)
  • Fresh water at sea level
Show the data as a table
Figure 1: data
Water temperature (°C)Fresh water at sea level (mg/L)
014.6
512.8
1011.3
1510.1
209.1
258.3
307.6

Line graph of the maximum dissolved oxygen fresh water at sea level can hold, falling as temperature rises: 14.6 mg/L at 0 °C, 12.8 at 5 °C, 11.3 at 10 °C, 10.1 at 15 °C, 9.1 at 20 °C, 8.3 at 25 °C and 7.6 at 30 °C. Single series: Fresh water at sea level.

Figure 1 never drops below about 7.6 mg/L, yet paragraph 4 says parts of a stream can fall below the 6 mg/L that trout need. Based on the passage, how can that happen?

  1. Figure 1 shows that water warmer than 25 °C holds less than 6 mg/L of oxygen.
  2. Real water often holds less oxygen than the maximum that Figure 1 shows.Answer
  3. Trout themselves use up most of the oxygen in a stream on a hot afternoon.
  4. A churning stream surface releases oxygen into the air faster than still water.

How to solve it

  1. Notice what Figure 1 measures: the maximum oxygen water can hold.
  2. Find where the text says real water differs from that maximum: paragraph 2, “often hold less than this maximum.”
  3. Combine them: a warm stream holding less than its maximum can drop below 6 mg/L even though the maximum never does.

Why each choice is right or wrong

  • A. Incorrect. This misreads the figure: at 30 °C the line is still at 7.6 mg/L, above 6 mg/L.
  • B. Correct. Figure 1 shows a maximum, and paragraph 2 says “Real ponds and streams often hold less than this maximum, especially at night.”
  • C. Incorrect. The passage never says trout use up most of the oxygen; it says “all the living things in the water keep using it.”
  • D. Incorrect. This reverses paragraph 5: “a churning surface takes in oxygen from the air faster than a still one.”

Trap Right reading, wrong variable

This passage talks about two things that change with temperature: how much oxygen the water can hold and how much oxygen a fish needs. Figure 1 shows only the first. A choice can read the graph perfectly and still be wrong because it answers a question about the other variable. Before you use the graph, check that its axis measures what the question asks about.