Scientific Inquiry & Diversity of Life — Chapter Practice, Grade 7

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

Problem 1

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 2

Two plant groups differ in both soil and water. What claim is too strong?
Answer and explanation

A claim that water alone caused their difference is too strong because soil could also influence growth; separate or control the factors.

Problem 3

Why should an unexpected trial remain in the record?
Answer and explanation

It may represent real variation or reveal a problem worth investigating. Removing it only because it disagrees with a prediction biases the evidence.

Problem 4

Does repeating an unfair test make it fair?
Answer and explanation

No. Repetition can reveal variability while repeating the same confound. The method must change to separate the competing explanations.

Problem 5

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 6

A class repeats this same light-confounded comparison ten times. Can it now identify water’s separate effect?
Answer and explanation

No. Repetition does not remove the linked light difference. Redesign the comparison so light is comparable, and use independent seedlings with recorded starting sizes.

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 7

Which is the dependent variable in a water-and-growth test?
  1. Daily water amount
  2. Height change
  3. Container material
  4. Plant species
Answer and explanation

Height change

Height change is the measured response; daily water is the changed factor.

Problem 8

A seedling starts at 3 cm and ends at 8 cm. Find height change.
Answer and explanation

5 cm

Final minus initial: 8−3=5 cm.

Problem 9

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 10

Does changing from 40× to 100× make the real cell larger?
Answer and explanation

No. It enlarges the image and changes the viewed area; the actual cell size is unchanged.

Problem 11

A cell image is half the length of a 100-micrometer scale bar. What size is supported?
Answer and explanation

Its estimated length is 50 micrometers, assuming the bar belongs to that image and both are measured in the same direction.

Problem 12

Why does not seeing ribosomes fail to show that a cell lacks them?
Answer and explanation

They are too small for many classroom microscopes to resolve. Instrument limits can explain the missing visible detail.

Problem 13

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 14

A drawing is enlarged while its copied scale bar is left unchanged. Can that bar still calibrate the enlarged cell?
Answer and explanation

No. The bar no longer has the same image-to-specimen relationship. Resize it with the image or provide a new valid calibration.

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 15

Which improves the ability to separate nearby details?
  1. A larger caption
  2. Resolution
  3. Changing the real cell size by focusing
  4. Removing units
Answer and explanation

Resolution

Resolution concerns distinguishable detail, whereas magnification concerns enlargement.

Problem 16

A 10× eyepiece and 25× objective give what total magnification?
Answer and explanation

250 ×

10×25=250×.

Problem 17

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 18

How can uneven time spacing mislead a reader?
Answer and explanation

It can make the same change appear faster or slower because equal horizontal distances no longer represent equal times.

Problem 19

Does a mean of 5 cm require each plant to be 5 cm?
Answer and explanation

No. Different combinations of measurements can average 5 cm. Inspect the original values and their spread.

Problem 20

Why is extending a seven-day growth line to a year uncertain?
Answer and explanation

The extension assumes the same growth rate and conditions far beyond the measured interval; resource limits and development can change the pattern.

Problem 21

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 22

A graph shows an association between rainfall and plant height. Does the association alone prove rainfall caused every difference?
Answer and explanation

No. Other conditions such as soil, species, light, and initial size may differ. A causal explanation needs a plausible mechanism and comparisons addressing alternatives.

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 23

Which graph is suitable for separate habitat categories?
  1. A bar graph
  2. A drawing without labels
  3. A graph with changing scale intervals
  4. A pie chart with no totals
Answer and explanation

A bar graph

Bars can compare separate habitat categories when units and sampling effort are comparable.

Problem 24

Find the mean of 2, 4, and 9 cm.
Answer and explanation

5 cm

(2+4+9)/3=15/3=5 cm.

Problem 25

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 26

How is reasoning different from listing numbers?
Answer and explanation

Reasoning explains a scientific connection between the observations and the claim. Numbers become relevant evidence through that connection.

Problem 27

Why should a model have a legend?
Answer and explanation

A legend explains what symbols represent so readers can distinguish meaningful relationships from invented display choices.

Problem 28

Does naming a limitation make an explanation worthless?
Answer and explanation

No. It makes the conclusion more accurate and identifies what further evidence would strengthen or change it.

Problem 29

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 30

A student changes a model after repeated contradictory observations. Is this automatically dishonest?
Answer and explanation

No. Revising a model in response to accurately recorded evidence is part of science. Concealing or inventing observations would be a different problem.

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 31

Which is evidence rather than a causal explanation?
  1. The cover reduces exposure
  2. The covered sample lost 5 g
  3. The method is perfect
  4. All evaporation stopped
Answer and explanation

The covered sample lost 5 g

The measured 5 g loss is evidence; explanations and universal conclusions need further reasoning.

Problem 32

Uncovered loss is 15 g and covered loss is 6 g. Find the difference.
Answer and explanation

9 g

15−6=9 g less measured loss.

Problem 33

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.

Problem 34

Why is “all living things eat other organisms” incorrect?
Answer and explanation

Photosynthetic organisms can build sugars using inorganic inputs and light. Organisms differ in how they obtain food and energy.

Problem 35

Can a living cell lack a nucleus?
Answer and explanation

Yes. Bacteria and other prokaryotes lack a membrane-enclosed nucleus but carry genetic material and perform cellular processes.

Problem 36

Does a classification key by itself show ancestry?
Answer and explanation

Not necessarily. It identifies using chosen features; an ancestry claim requires evidence supporting inherited relationships.

Problem 37

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 38

A fungus has walls but no chloroplasts. Must it be an animal or a plant?
Answer and explanation

No. Those two categories do not exhaust biological diversity. Fungi have their own characteristics; combine cell features, nutrition, and relationship evidence rather than forcing a two-category choice.

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 39

Which record supports a prokaryotic cell?
  1. No DNA at all
  2. DNA and ribosomes but no membrane-enclosed nucleus
  3. A nucleus and no membrane
  4. Only a plastic motor
Answer and explanation

DNA and ribosomes but no membrane-enclosed nucleus

Prokaryotes contain genetic material and ribosomes without a membrane-enclosed nucleus.

Problem 40

Why can an individual unable to reproduce still be living?
Answer and explanation

Living status involves functioning cellular organization and interacting life processes. Reproduction characterizes life cycles and populations; it is not required from every individual at every time.

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