Natural Science Passages · Lesson 1

Read for the process, not the jargon

A natural science passage explains how something in nature works or how scientists found something out. It is written for a general reader, so you are not expected to know the science already. The technical terms the questions depend on are usually defined in the passage, often in the same sentence that introduces them or the next one.

That changes how you read. Don’t stop at an unfamiliar word like saltation or cambium; look for the definition nearby. Signals include a colon (saltation: a grain is lifted...), a comma phrase (the windward slope, the long, gentle side), called or known as, and or (sheds its outer skin, or molts). Once you have the plain meaning, use it and keep going.

Most of these passages describe a process: a set of steps where one thing causes the next. As you read, jot or think a few words per paragraph: P2 wind lifts grains up the gentle side; P3 grains drop past the top, slide down steep side; P4 so dune shifts downwind. That map answers most process questions and tells you where to look for the rest.

How passages define their terms
SignalWhat it looks like
called, known asa slower motion called creep
a colon after the termsaltation: a grain is lifted, travels..., and lands
a comma phrasethe windward slope, the long, gentle side
or plus a simpler wordsheds its outer skin, or molts

How a Dune Walks

This passage is from an article about how wind moves sand dunes.

1From a distance, a sand dune looks as permanent as a hill. Watch one for a few years, though, and you find that many dunes are on the move, creeping downwind by several meters a year and sometimes much farther. The dune does not slide as a single block. It travels one grain at a time, and the whole journey depends on two slopes that face in opposite directions.

2The first is the windward slope, the long, gentle side that faces into the wind. Wind blowing up this slope picks up loose grains and carries them forward in short hops. Geologists call this hopping motion saltation: a grain is lifted, travels a few centimeters through the air, and lands, often knocking other grains loose as it strikes. Most of the sand that moves across a dune moves this way, close to the surface, rarely rising more than a meter or so above the ground. Grains too heavy to be lifted are nudged along by the impacts of the hopping grains, a slower motion called creep.

3At the top of the dune, called the crest, the wind loses its grip. The air spreading out past the crest slows down, and the grains it was carrying drop onto the second slope, the slip face. The slip face is short and steep, and it faces away from the wind. Sand piles up near the top of the slip face until the pile becomes too steep to hold itself up. Then a small avalanche of sand slides down the face, and the slope settles back to its steepest stable angle, known as the angle of repose. For dry sand, that angle is roughly 30 to 35 degrees.

4Put the two slopes together and the motion becomes clear. Sand is stripped from the windward slope and dumped onto the slip face, so the dune loses material on its upwind side and gains it on its downwind side. Grain by grain, the whole shape shifts downwind, even though no single grain stays with the dune for long. A grain that lands on the slip face today may be buried for years, uncovered as the dune passes over it, and then lifted onto the windward slope of the same dune again.

5How fast a dune moves depends largely on its size. A small dune holds less sand, so the wind needs to move fewer grains to shift it by a meter, and small dunes generally travel faster than large ones. Plants can slow the process down. Their roots bind the grains, and their stems slow the wind near the ground, which is why stabilizing a moving dune usually begins with planting grasses that can survive being partly buried.

Worked example Easy

Show the whole passage

How a Dune Walks

This passage is from an article about how wind moves sand dunes.

1From a distance, a sand dune looks as permanent as a hill. Watch one for a few years, though, and you find that many dunes are on the move, creeping downwind by several meters a year and sometimes much farther. The dune does not slide as a single block. It travels one grain at a time, and the whole journey depends on two slopes that face in opposite directions.

2The first is the windward slope, the long, gentle side that faces into the wind. Wind blowing up this slope picks up loose grains and carries them forward in short hops. Geologists call this hopping motion saltation: a grain is lifted, travels a few centimeters through the air, and lands, often knocking other grains loose as it strikes. Most of the sand that moves across a dune moves this way, close to the surface, rarely rising more than a meter or so above the ground. Grains too heavy to be lifted are nudged along by the impacts of the hopping grains, a slower motion called creep.

3At the top of the dune, called the crest, the wind loses its grip. The air spreading out past the crest slows down, and the grains it was carrying drop onto the second slope, the slip face. The slip face is short and steep, and it faces away from the wind. Sand piles up near the top of the slip face until the pile becomes too steep to hold itself up. Then a small avalanche of sand slides down the face, and the slope settles back to its steepest stable angle, known as the angle of repose. For dry sand, that angle is roughly 30 to 35 degrees.

4Put the two slopes together and the motion becomes clear. Sand is stripped from the windward slope and dumped onto the slip face, so the dune loses material on its upwind side and gains it on its downwind side. Grain by grain, the whole shape shifts downwind, even though no single grain stays with the dune for long. A grain that lands on the slip face today may be buried for years, uncovered as the dune passes over it, and then lifted onto the windward slope of the same dune again.

5How fast a dune moves depends largely on its size. A small dune holds less sand, so the wind needs to move fewer grains to shift it by a meter, and small dunes generally travel faster than large ones. Plants can slow the process down. Their roots bind the grains, and their stems slow the wind near the ground, which is why stabilizing a moving dune usually begins with planting grasses that can survive being partly buried.

As it is used in paragraph 2, the term saltation refers to:

  1. the sliding of sand down the slip face once the pile there becomes too steep.
  2. a motion in which wind lifts a grain, carries it a short way, and drops it.Answer
  3. the slow movement of heavy grains that are pushed along by other grains.
  4. the slowing of the wind as it spreads out past the crest of the dune.

How to solve it

  1. Find the term: saltation is in paragraph 2, in the sentence “Geologists call this hopping motion saltation.”
  2. Read the definition that follows the colon: the grain is lifted, travels a few centimeters, and lands.
  3. Watch for the nearby term. Creep is defined two sentences later, and a wrong choice describes it.

Why each choice is right or wrong

  • A. Incorrect. Sand sliding down the slip face is the “small avalanche” of paragraph 3, a different step with a different name.
  • B. Correct. The passage defines the term right after it, with a colon: “a grain is lifted, travels a few centimeters through the air, and lands.”
  • C. Incorrect. This describes creep, the term defined at the end of the same paragraph: “Grains too heavy to be lifted are nudged along by the impacts of the hopping grains, a slower motion called creep.”
  • D. Incorrect. The slowing wind belongs to paragraph 3: “The air spreading out past the crest slows down.” It is not what saltation means.

Worked example Medium

Show the whole passage

How a Dune Walks

This passage is from an article about how wind moves sand dunes.

1From a distance, a sand dune looks as permanent as a hill. Watch one for a few years, though, and you find that many dunes are on the move, creeping downwind by several meters a year and sometimes much farther. The dune does not slide as a single block. It travels one grain at a time, and the whole journey depends on two slopes that face in opposite directions.

2The first is the windward slope, the long, gentle side that faces into the wind. Wind blowing up this slope picks up loose grains and carries them forward in short hops. Geologists call this hopping motion saltation: a grain is lifted, travels a few centimeters through the air, and lands, often knocking other grains loose as it strikes. Most of the sand that moves across a dune moves this way, close to the surface, rarely rising more than a meter or so above the ground. Grains too heavy to be lifted are nudged along by the impacts of the hopping grains, a slower motion called creep.

3At the top of the dune, called the crest, the wind loses its grip. The air spreading out past the crest slows down, and the grains it was carrying drop onto the second slope, the slip face. The slip face is short and steep, and it faces away from the wind. Sand piles up near the top of the slip face until the pile becomes too steep to hold itself up. Then a small avalanche of sand slides down the face, and the slope settles back to its steepest stable angle, known as the angle of repose. For dry sand, that angle is roughly 30 to 35 degrees.

4Put the two slopes together and the motion becomes clear. Sand is stripped from the windward slope and dumped onto the slip face, so the dune loses material on its upwind side and gains it on its downwind side. Grain by grain, the whole shape shifts downwind, even though no single grain stays with the dune for long. A grain that lands on the slip face today may be buried for years, uncovered as the dune passes over it, and then lifted onto the windward slope of the same dune again.

5How fast a dune moves depends largely on its size. A small dune holds less sand, so the wind needs to move fewer grains to shift it by a meter, and small dunes generally travel faster than large ones. Plants can slow the process down. Their roots bind the grains, and their stems slow the wind near the ground, which is why stabilizing a moving dune usually begins with planting grasses that can survive being partly buried.

According to paragraph 4, a dune moves downwind mainly because:

  1. the wind pushes the whole dune forward at once as a single block of sand.
  2. its grains stay with the dune as they roll steadily along its base.
  3. grasses on the windward slope trap sand that the wind carries in.
  4. it loses sand on its upwind side and gains sand on its downwind side.Answer

How to solve it

  1. Use your map: paragraph 2 is the windward slope, paragraph 3 the slip face, paragraph 4 puts them together.
  2. Paragraph 4 states the result: sand is “stripped from the windward slope and dumped onto the slip face.”
  3. Check each wrong choice against a line: the single block is denied in paragraph 1, and grains staying with the dune is denied in paragraph 4.

Why each choice is right or wrong

  • A. Incorrect. Paragraph 1 rules this out directly: “The dune does not slide as a single block.”
  • B. Incorrect. Paragraph 4 says the opposite: “no single grain stays with the dune for long.”
  • C. Incorrect. Plants appear in paragraph 5, where they “slow the process down”; they are not what makes a dune move.
  • D. Correct. Paragraph 4 explains the motion: “the dune loses material on its upwind side and gains it on its downwind side.”

Trap Swapping two defined terms

Science passages often define two or three terms close together: saltation and creep, windward slope and slip face. Wrong answers love to give you the right definition for the wrong term. Before you choose, put your finger on the exact word the question asks about and read only its definition.