Key Ideas and Details - Natural Science (ACT Reading)

Understanding Natural Science Passages

The ACT Reading section includes one Natural Science passage that discusses topics from:

• Biology
• Chemistry
• Physics
• Earth Science
• Astronomy
• Environmental Science
• Geology
• Ecology

These are NOT science passages in the traditional sense — they're reading comprehension passages about scientific topics.

You don't need science knowledge! You need strong reading skills.

Key Reading Skills

1. Identifying Main Ideas

Main idea = The central point or purpose of the passage

Where to find it:

• Often in first or last paragraph
• Topic sentences of paragraphs
• Repeated concepts throughout

Question formats:

• "The main purpose of this passage is to:"
• "The passage as a whole is best described as:"
• "The primary focus of the passage is:"

Strategy:

1. Read first and last paragraphs carefully
2. Look for thesis statement or concluding point
3. Eliminate choices that are too narrow (one detail) or too broad (beyond passage scope)
4. Choose option that encompasses whole passage

Example:

Passage discusses how octopuses camouflage, change color, problem-solve, and escape predators.

Wrong: "to explain how octopuses change color" (too narrow — just one detail)
Wrong: "to describe all marine animals" (too broad — passage is only about octopuses)
Right: "to illustrate the remarkable adaptations and intelligence of octopuses"

2. Finding Supporting Details

Supporting details = Specific facts, examples, or evidence in passage

Question formats:

• "According to the passage, X occurs when:"
• "The passage states that Y is caused by:"
• "Which of the following is mentioned as an example of Z?"

Strategy:

1. Note key words in question
2. Scan passage for those words (or synonyms)
3. Read surrounding sentences carefully
4. Find exact answer stated in passage

Don't: Rely on memory — go back and verify!

Example question: "According to the passage, photosynthesis occurs in which part of the plant cell?"

Strategy:

• Scan for "photosynthesis" and "plant cell"
• Read that section
• Find specific answer: "chloroplasts"

3. Understanding Sequence

Sequence = Order of events, steps in a process, chronological development

Signal words:

• First, second, third
• Next, then, finally
• Before, after, during
• Subsequently, previously
• Initially, eventually

Question formats:

• "According to the passage, which event occurred first?"
• "The passage indicates that X happens before:"
• "The process described follows which sequence?"

Strategy:

1. Create mental timeline or list
2. Note transition words
3. Pay attention to verb tenses
4. Check each step in order

Example:

Passage describes star formation: gas cloud collapses → gravity pulls material together → pressure and temperature increase → nuclear fusion begins

Question: "According to the passage, nuclear fusion begins after:"

Answer: "pressure and temperature increase"

4. Cause and Effect

Cause = Why something happens
Effect = What happens as a result

Signal words:

• Because, since, due to → introduce cause
• Therefore, thus, as a result, consequently → introduce effect
• Leads to, causes, produces, results in

Question formats:

• "The passage suggests that X is caused by:"
• "According to the passage, Y resulted from:"
• "What was the effect of Z?"

Strategy:

1. Identify what's being asked (cause or effect?)
2. Find the relationship in passage
3. Don't confuse direction (A causes B vs. B causes A)

Example:

Passage states: "Rising ocean temperatures cause coral bleaching. When water gets too warm, corals expel their symbiotic algae, turning white."

Question: "According to the passage, coral bleaching is caused by:"

Answer: "Rising ocean temperatures" (or "warm water")

5. Making Comparisons

Comparison = How two or more things are similar or different

Signal words:

• Similarity: similarly, likewise, also, both, like
• Difference: however, unlike, whereas, in contrast, but

Question formats:

• "Unlike X, Y is described as:"
• "Both X and Y are characterized by:"
• "The passage indicates that X differs from Y in that:"

Strategy:

1. Find both items being compared
2. Read descriptions of each
3. Identify specific similarities or differences
4. Match to answer choices

Example:

"Hurricanes form over warm ocean water, while tornadoes develop in thunderstorms over land."

Question: "Unlike hurricanes, tornadoes:"

Answer: "form over land" or "develop in thunderstorms"

Specific Question Types

Type 1: Main Idea Questions

"The main purpose of the passage is to:"

How to answer:

• Read first paragraph (intro)
• Read last paragraph (conclusion)
• Identify overall topic and author's purpose
• Eliminate too-narrow and too-broad choices

Common purposes:

• Explain a scientific phenomenon
• Describe a discovery or theory
• Argue for/against a scientific practice
• Trace historical development
• Compare competing theories

Type 2: Detail Questions

"According to the passage, [specific fact]..."

How to answer:

• Find key words from question
• Scan passage for those words
• Read 2-3 sentences around the word
• Find answer directly stated
• No inference needed!

ACT Rule: Answer must be explicitly stated in passage

Type 3: Vocabulary in Context

"As it is used in line 42, the word 'complex' most nearly means:"

How to answer:

• Go to that line
• Read full sentence
• Try each answer choice in place of word
• Choose one that maintains meaning of sentence
• Consider context (scientific vs. everyday meaning)

Example:

"The experiment required a complex apparatus with multiple sensors and controls."

Question: "Complex most nearly means:"

A. Difficult to understand
B. Complicated in structure
C. Emotionally troubled
D. Multi-building facility

Answer: B (matches "multiple sensors and controls")

Type 4: Function Questions

"The author mentions X in order to:"

How to answer:

• Find where X is mentioned
• Read surrounding context
• Ask: Why did author include this?
• Common purposes: provide evidence, illustrate concept, introduce topic, transition

Example:

"Scientists studied the migration patterns of monarch butterflies, which travel up to 3,000 miles. This remarkable journey..."

Question: "The author mentions the 3,000-mile distance in order to:"

Answer: "emphasize the remarkable nature of the journey"

Type 5: Inference Questions (Careful!)

"The passage suggests that:" or "It can be reasonably inferred that:"

How to answer:

• Must be supported by passage evidence
• Small logical step from stated facts
• Not wild speculation!
• Still very close to text

Example:

Passage states: "The fossil was found in rock layers dating to 65 million years ago, the same time period when dinosaurs went extinct."

Question: "It can be reasonably inferred that:"

Reasonable inference: "The fossil is approximately 65 million years old"

Too much of a leap: "The fossil proves dinosaurs went extinct from asteroid impact" (specific cause not mentioned)

Reading Strategies for Natural Science

Strategy 1: Active Reading

Annotate as you read:

• Underline topic sentences
• Circle key scientific terms
• Note cause-effect relationships
• Mark transitions (however, therefore, etc.)

Strategy 2: Paragraph Purpose

After each paragraph, quickly note:

• What's the main point?
• How does it relate to previous paragraphs?

Example mental map:

• Paragraph 1: Introduces plate tectonics theory
• Paragraph 2: Explains how plates move
• Paragraph 3: Describes effects (earthquakes, mountains)
• Paragraph 4: Gives specific examples (Himalayas, San Andreas)

Strategy 3: Don't Get Lost in Details

Natural science passages have lots of facts!

Don't: Try to memorize everything
Do: Note where information is located

You can always go back to find specific details when questions ask for them

Strategy 4: Focus on Relationships

More important than isolated facts:

• What causes what?
• How are concepts related?
• What's the sequence?
• What contrasts exist?

Strategy 5: Watch for Author's Purpose

Ask yourself:

• Is author explaining something?
• Arguing for/against something?
• Describing a debate?
• Tracing historical development?

Knowing the purpose helps answer main idea and function questions

Common Mistakes

❌ Using outside science knowledge
Answer based only on passage, not what you know from biology class

❌ Not going back to verify
Don't trust your memory — reread relevant section!

❌ Choosing answers with familiar scientific terms
ACT loves to use scientific vocabulary to trick you — make sure it actually matches passage

❌ Overthinking inference questions
If you're making a huge logical leap, probably wrong — stick close to text

❌ Getting bogged down in technical details
Understand general concept, note location of details for later

❌ Skipping the introduction
First paragraph often has main idea and sets context

Quick Tips

✓ Read actively — underline, circle, annotate
✓ Note paragraph purposes — helps with structure questions
✓ Go back to passage — verify every answer
✓ Use line references — they're there to help you!
✓ Eliminate wrong answers — process of elimination works!
✓ Watch for extreme language — "always," "never," "only" often signal wrong answers
✓ Trust the passage — not outside knowledge
✓ Read all answer choices — even if A looks good, D might be better

Practice Approach

For Natural Science passages:

1. Read the passage (3-4 minutes)

   • Read actively with annotations
   • Note main idea and structure
   • Don't memorize details

2. Go to questions (5-6 minutes total)

   • Read question carefully
   • Identify question type
   • Go back to relevant section
   • Find answer in passage
   • Eliminate wrong choices
   • Choose best answer

3. Time management:

   • Aim for ~8-9 minutes total per passage
   • If stuck on question, skip and return
   • Don't let one hard question eat all your time

4. Check your work:

   • If time remains, verify answers
   • Make sure you didn't misread question
   • Confirm answer is actually stated

Remember: Natural Science passages test reading comprehension, not science knowledge. Focus on understanding what the passage says, finding supporting details, and sticking close to the text. Don't overthink — the answer is in the passage!