Natural Science Passages · Lesson 2

Details, sequence and numbers

Detail questions in a science passage are generous: the answer is stated, usually in one sentence. The work is finding that sentence fast and reading it exactly. Use the stem’s key noun (eggs, soil temperature, the final molt) and the paragraph it names as your search terms.

Numbers need extra care. A science passage may hold six or eight of them: years, weeks, centimeters, degrees. Every one of them is attached to something specific. The question asks about one thing, and the wrong choices offer numbers that are really in the passage but belong to something else. Before you choose a number, read the whole sentence it comes from and say what it measures.

Sequence questions ask what happens first, next or last. Find each event in the passage and look at the signal words around it: begins, after, then, as it grows, in the spring of the final year, one last time. When the passage tells the steps in order, the paragraph order is the time order; when it doesn’t, the signal words decide.

The Long Wait of the Periodical Cicada

This passage is from an article about the life cycle of periodical cicadas.

1Most insects live their whole lives within a single year. Periodical cicadas, found in the forests of eastern North America, take far longer. Depending on the kind, they spend either 13 or 17 years underground, and then, within a few weeks, nearly all the adults of a population appear above ground at once.

2The cycle begins in a tree. After mating, a female uses a bladelike organ at the tip of her abdomen to cut small slits in a young twig, and she lays her eggs inside them, as many as several hundred in all, spread across many twigs. The eggs hatch after about six to ten weeks. The newly hatched young, called nymphs, are smaller than a grain of rice. They drop from the branches to the ground and burrow into the soil.

3Underground, a nymph finds a root and attaches to it, drinking the watery sap that the root carries up toward the tree. The sap is thin and poor in nutrients, which helps explain why growth is so slow. As it grows, the nymph sheds its outer skin, or molts, several times, passing through five stages in all before it is ready to leave the soil. Most nymphs feed between a few centimeters and about half a meter below the surface.

4In the spring of the final year, the mature nymphs dig tunnels up toward the surface and wait. They come out when the soil about 20 centimeters down warms to roughly 18 °C, usually on a warm evening. Each nymph climbs the nearest tree trunk or plant stem, grips it, and molts one last time. The adult pulls itself out through a split in the back of its old skin, leaving the empty shell clinging to the bark. Its wings expand within about an hour, but its body takes several days to harden fully.

5The adults live only a few weeks. Males gather in trees and call with a loud, buzzing song that attracts females, and after mating, the females begin the cycle again. Because so many cicadas appear at once, predators such as birds and squirrels eat all they can and still leave most of the population alive, a strategy biologists call predator satiation.

Worked example Easy

Show the whole passage

The Long Wait of the Periodical Cicada

This passage is from an article about the life cycle of periodical cicadas.

1Most insects live their whole lives within a single year. Periodical cicadas, found in the forests of eastern North America, take far longer. Depending on the kind, they spend either 13 or 17 years underground, and then, within a few weeks, nearly all the adults of a population appear above ground at once.

2The cycle begins in a tree. After mating, a female uses a bladelike organ at the tip of her abdomen to cut small slits in a young twig, and she lays her eggs inside them, as many as several hundred in all, spread across many twigs. The eggs hatch after about six to ten weeks. The newly hatched young, called nymphs, are smaller than a grain of rice. They drop from the branches to the ground and burrow into the soil.

3Underground, a nymph finds a root and attaches to it, drinking the watery sap that the root carries up toward the tree. The sap is thin and poor in nutrients, which helps explain why growth is so slow. As it grows, the nymph sheds its outer skin, or molts, several times, passing through five stages in all before it is ready to leave the soil. Most nymphs feed between a few centimeters and about half a meter below the surface.

4In the spring of the final year, the mature nymphs dig tunnels up toward the surface and wait. They come out when the soil about 20 centimeters down warms to roughly 18 °C, usually on a warm evening. Each nymph climbs the nearest tree trunk or plant stem, grips it, and molts one last time. The adult pulls itself out through a split in the back of its old skin, leaving the empty shell clinging to the bark. Its wings expand within about an hour, but its body takes several days to harden fully.

5The adults live only a few weeks. Males gather in trees and call with a loud, buzzing song that attracts females, and after mating, the females begin the cycle again. Because so many cicadas appear at once, predators such as birds and squirrels eat all they can and still leave most of the population alive, a strategy biologists call predator satiation.

According to the passage, periodical cicada eggs hatch about how long after they are laid?

  1. Within about an hour
  2. After several days
  3. After about six to ten weeksAnswer
  4. After 13 or 17 years

How to solve it

  1. Search for the key noun, eggs. It appears in paragraph 2.
  2. Read the sentence: “The eggs hatch after about six to ten weeks.”
  3. Notice that every other choice is a real number from the passage attached to a different event.

Why each choice is right or wrong

  • A. Incorrect. About an hour is how long the adult’s wings take to open: “Its wings expand within about an hour.”
  • B. Incorrect. Several days is how long the adult’s body takes to harden: “its body takes several days to harden fully.”
  • C. Correct. Paragraph 2 states it directly: “The eggs hatch after about six to ten weeks.”
  • D. Incorrect. 13 or 17 years is the time the cicadas “spend either 13 or 17 years underground,” not the time before hatching.

Worked example Medium

Show the whole passage

The Long Wait of the Periodical Cicada

This passage is from an article about the life cycle of periodical cicadas.

1Most insects live their whole lives within a single year. Periodical cicadas, found in the forests of eastern North America, take far longer. Depending on the kind, they spend either 13 or 17 years underground, and then, within a few weeks, nearly all the adults of a population appear above ground at once.

2The cycle begins in a tree. After mating, a female uses a bladelike organ at the tip of her abdomen to cut small slits in a young twig, and she lays her eggs inside them, as many as several hundred in all, spread across many twigs. The eggs hatch after about six to ten weeks. The newly hatched young, called nymphs, are smaller than a grain of rice. They drop from the branches to the ground and burrow into the soil.

3Underground, a nymph finds a root and attaches to it, drinking the watery sap that the root carries up toward the tree. The sap is thin and poor in nutrients, which helps explain why growth is so slow. As it grows, the nymph sheds its outer skin, or molts, several times, passing through five stages in all before it is ready to leave the soil. Most nymphs feed between a few centimeters and about half a meter below the surface.

4In the spring of the final year, the mature nymphs dig tunnels up toward the surface and wait. They come out when the soil about 20 centimeters down warms to roughly 18 °C, usually on a warm evening. Each nymph climbs the nearest tree trunk or plant stem, grips it, and molts one last time. The adult pulls itself out through a split in the back of its old skin, leaving the empty shell clinging to the bark. Its wings expand within about an hour, but its body takes several days to harden fully.

5The adults live only a few weeks. Males gather in trees and call with a loud, buzzing song that attracts females, and after mating, the females begin the cycle again. Because so many cicadas appear at once, predators such as birds and squirrels eat all they can and still leave most of the population alive, a strategy biologists call predator satiation.

Which of the following lists three events in the order in which they happen to a periodical cicada?

  1. It burrows into soil; it attaches to a root; it tunnels toward the surface.Answer
  2. It attaches to a root; it burrows into the soil; it climbs a tree trunk.
  3. It digs a tunnel toward the surface; it burrows into the soil; it molts on a tree trunk.
  4. It burrows into the soil; it climbs a tree trunk; it attaches to a root.

How to solve it

  1. Locate each event: burrowing in paragraph 2, the root in paragraph 3, the tunnel and the climb in paragraph 4.
  2. Here the paragraphs follow the life cycle, and signal words confirm it: “Underground,” “In the spring of the final year,” “one last time.”
  3. Check each choice event by event and drop it at the first step out of order.

Why each choice is right or wrong

  • A. Correct. Nymphs “drop from the branches to the ground and burrow into the soil” (paragraph 2), then “Underground, a nymph finds a root and attaches to it” (paragraph 3), and finally “the mature nymphs dig tunnels up toward the surface” (paragraph 4).
  • B. Incorrect. The nymph must be underground before it can find a root; it burrows first, then attaches.
  • C. Incorrect. The tunnel up toward the surface comes in “the spring of the final year,” long after the nymph first burrows in.
  • D. Incorrect. Climbing a trunk is the last step before the final molt, so it can’t come before attaching to a root underground.

Trap The right number for the wrong thing

A wrong choice that quotes a number from the passage feels safe, because you remember seeing it. Ask what the number measured. In the cicada passage, 20 centimeters is a soil depth and 18 °C is a soil temperature; several days is hardening time and about an hour is wing time. Read the full sentence before you trust a number.