Scientific Inquiry & Diversity of Life — Problem set, Grade 7

Five focused units, a three-session investigation, chapter review, and chapter quiz.

Review the key ideas

Questions, Variables & Fair Investigations

Science begins with questions about the natural world that observations can help answer. A question such as whether equal-sized paper samples absorb different amounts of water specifies something we can compare. A preference such as which color is nicest needs a stated judgment criterion; a measurement cannot decide everyone’s preference. Asking a testable question does not require predicting the correct answer in advance.

Measurements, Microscopes & Scale

A measurement combines a number, a unit, and a method. A length of 12 is incomplete until we know whether it means millimeters, centimeters, or meters. Microscopes let us observe features too small for unaided eyes, but a larger image is not automatically a clearer image. Magnification describes enlargement; resolution describes whether nearby details can be distinguished.

Tables, Graphs & Patterns in Data

Data are recorded observations or measurements. A table preserves individual values, conditions, and units; a graph helps display relationships. Selecting a graph depends on the question. A line graph can show change over an ordered time sequence, while a bar graph compares separate categories. A graph makes a pattern easier to see but does not create evidence that was not measured.

Models, Claims, Evidence & Reasoning

A scientific explanation connects a claim with evidence and reasoning. The claim answers the question; the evidence consists of relevant observations or measurements; reasoning explains why a scientific idea connects that evidence to the claim. Restating a claim in different words is not enough. An explanation should also identify what the evidence does not settle.

Characteristics of Life & Biological Diversity

Living organisms are organized into cells and carry out interacting processes such as using matter and energy, responding to conditions, maintaining internal conditions, growing, and producing new organisms across their life cycle. No single visible action is a complete definition. A moving toy is not alive because it moves, and a dormant seed does not become nonliving simply because it currently shows little visible activity.

Problem 1

Illustrative record: Group A receives 10 mL daily and bright light; Group B receives 5 mL and dim light. After seven days, A gains 4 cm and B gains 1 cm. Identify the intended variable, measured outcome, and confound. Propose a fairer comparison and explain what the current data do establish.
Answer and explanation

The record shows a 3 cm difference in height gain, but both water and light differ. It cannot isolate water’s effect. A revised comparison would keep light, species, starting conditions, and times comparable while changing only the defined water treatment; independent seedlings and recorded variation would strengthen the evidence.

Identify water amount as the intended factor.

Measure height change in centimeters over seven days.

Recognize light as an additional changed factor.

Match light and other conditions, then use several seedlings per group.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 2

Why does defining the outcome before testing help?
Answer and explanation

It keeps the comparison consistent and reduces the temptation to choose whichever observation later supports a favorite explanation.

Problem 3

Illustrative image record: a 4 cm scale bar represents 200 micrometers; the cell image spans 1.2 cm. A microscope setting lists a 10× eyepiece and a 40× objective. Calculate estimated cell length and total magnification. Explain why these are different quantities and state a calibration assumption.
Answer and explanation

The cell length is approximately 60 micrometers, and the stated total magnification is 400×. Length describes the specimen estimate; magnification describes image enlargement. Both assume the provided record is correct, and the scale calculation assumes uniform resizing of the cell and bar. Magnification alone does not supply the real cell length.

Find the ratio 1.2/4=0.3.

Multiply 0.3 by 200 micrometers.

Multiply lens factors 10×40.

Check that image and scale bar were resized together.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 4

Why is “a cell is 20 long” incomplete?
Answer and explanation

It omits the unit and measurement method. A cell might be 20 micrometers long, but the number alone cannot establish its size.

Problem 5

Illustrative records: Treatment A height gains are 3, 4, and 5 cm; B gains are 1, 4, and 7 cm under the same stated interval. Calculate the means and numerical ranges. Describe one similarity, one difference, and what the summaries cannot establish.
Answer and explanation

Both means are 4 cm. A’s numerical range is 2 cm; B’s is 6 cm. The means agree but B’s observations are more spread out. These small illustrative sets do not establish why variability differs or whether a treatment caused the pattern. Keep individual records, examine methods, and use more independent observations.

A sum is 12 cm and B sum is 12 cm.

Divide each by three.

Subtract smallest from largest in each set.

Compare spread without inventing a cause.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

Why is a missing measurement not automatically zero?
Answer and explanation

Missing means no valid observation was recorded. Zero claims that the measured quantity was actually zero.

Problem 7

Illustrative observation: covered soil loses 5 g over a day; uncovered soil loses 12 g in the same setting. Starting water, container, and temperature are stated comparable. A claim says a cover always prevents all evaporation. Write a better claim, cite numerical evidence, explain a plausible mechanism, and identify a limit.
Answer and explanation

The cover is associated with 7 g less measured water loss in this comparison. Reducing exposed soil can reduce evaporation under comparable conditions, but the covered sample still lost 5 g. The record therefore does not support “all evaporation prevented” or “always.” Repeated matched trials and checks for other loss pathways would strengthen the explanation.

Calculate the measured loss difference: 12−5=7 g.

State reduced loss in the observed setting.

Connect the cover with reduced exposure under the model.

Notice that 5 g was still lost and other settings were not tested.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 8

Which part of “the soil is wet because it rained” is an inference?
Answer and explanation

The proposed rainfall cause is an inference; wet soil is the stated observation. Watering or another source could also explain it.

Problem 9

Illustrative records: A is a seed with cells that later germinates; B is a battery toy that moves; C is a bacterium with a membrane and DNA but no enclosed nucleus. Use several characteristics to classify living status and explain why movement and a nucleus are not sufficient tests.
Answer and explanation

A and C are living under the supplied records. A’s cellular organization and germination support that conclusion despite its earlier dormancy. C can function without an enclosed nucleus because it is prokaryotic. B’s movement alone does not establish cellular life. The comparison relies on the supplied biological observations, not a rule that every moving object is alive.

Identify cellular organization in A and C.

Use germination as evidence of a seed’s life process.

Separate powered toy motion from cellular activity.

Recognize C as a prokaryotic organism.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 10

Why does movement alone not establish life?
Answer and explanation

Nonliving objects can move through motors, wind, or gravity. Cellular organization and interacting life processes provide stronger evidence.

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