Designing a Biology Investigation — Practice · Grade 10 Science

Chapter: Investigating the Chemistry of Life

What this practice covers

By the end of Designing a Biology Investigation you should be able to:

8 questions, numeric, multiple choice and written answer, each with a worked explanation.

Vocabulary used: independent variable, replicate, confounding variable.

Problem 1

Three independent rates are 4, 6, and 8 units/min. Find the mean.
Answer and explanation

6 units/min

18 ÷ 3 = 6.

Problem 2

To test temperature alone, which factor should also be kept comparable?
  1. Enzyme amount
  2. The measured reaction rate
  3. The graph height
  4. The conclusion
Answer and explanation

Enzyme amount

Changing enzyme amount would introduce another potential cause.

Problem 3

Why does measuring one sample three times differ from preparing three samples?
Answer and explanation

Repeated readings emphasize measurement variability; independent samples also reflect preparation and biological variation.

Problem 4

One plant is measured ten times after treatment. Does this establish the treatment's effect on plants generally? Explain the reasoning in your own words.
Answer and explanation

No; use independent plants, appropriate comparisons and controlled conditions to test a broader claim.

The ten readings describe repeatability for one plant.

They do not capture variation among plants or provide an untreated comparison.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 5

A test compares fertilizer treatments on one plant each. What improvement helps distinguish treatment effects from individual variation? Show the reasoning, not just the conclusion.
Hints

Replication helps assess variation but does not by itself remove confounding.

Answer and explanation

Use several comparable plants per treatment, assigned fairly, with other conditions held constant.

Problem 6

Why specify growth as a measured change rather than looks healthier?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

An operational measure such as height change or dry mass allows repeatable comparisons; appearance alone is subjective.

Problem 7

A mean summarizes a distribution without replacing itA mean summarizes a distribution without replacing itIllustrative height change (mm)Plant 110Plant 220Plant 330Plant 440Mean = 25 mm; range = 10–40 mm. Keep every result.
Original illustrative replicate outcomes. They are not evidence of a universal biological growth rate or a significance test.
Interpret the supplied visual. Would replacing these four records with “25 mm for every plant” be accurate?
Answer and explanation

No. Twenty-five is the mean, while the individual plants range from 10 to 40 mm. Retain variation and the sampling conditions.

A mean is the sum of measured values divided by their number. The range describes the spread from minimum to maximum; it is not an uncertainty interval for a population mean. These four plants have mean 25 mm and range 10–40 mm. A bar showing only the mean would hide the variation. Report sample size, units and individual results or a useful distribution plot. Do not discard a low result solely because it weakens the preferred hypothesis; exclusions require a stated reason such as a documented measurement failure.

No. Twenty-five is the mean, while the individual plants range from 10 to 40 mm. Retain variation and the sampling conditions.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 8

Two trays receive different nutrient treatments. Each tray contains one plant measured six times. Explain the true replication and redesign the comparison.
Answer and explanation

There is only one treated biological/treatment unit per condition; six readings are repeated observations. Use several independently assigned plants or trays per condition, keep light/water/species comparable and preserve all time records.

There is only one treated biological/treatment unit per condition; six readings are repeated observations. Use several independently assigned plants or trays per condition, keep light/water/species comparable and preserve all time records.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses