Biology by Bradford · Lab Companion
Biology by Bradford · Nature of Science

Mystery
Canisters

You'll build the best explanation the evidence allows — then never find out if you were right. That's not a flaw in the activity. It's the point.

A companion to the practical — not the method sheet. It builds the idea behind the investigation and helps you make sense of what you find. Work through it before the practical, after it, or alongside it — it all fits.
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One · The idea

Science can't open the box

In this practical you meet sealed canisters, each hiding one object. You work out what's inside using only your senses — and you never open them to check.

That constraint is doing real work. A scientist is in exactly the same position: reality doesn't come with a lid you can lift to see the "true answer." You gather evidence, build the explanation it best supports, and hold that explanation open to revision. The canister isn't a party trick — it's a working model of how knowledge is made.

Nature of science Scientific knowledge is built from evidence, not read off from a hidden answer key. Certainty isn't on offer — the best-supported explanation is.
Two · The skill

Observation, then inference

The whole activity hinges on one habit scientists live by: separating what you detect from what you conclude. An observation is fixed evidence. An inference is your interpretation of it — and interpretations can be argued with.

Read each statement. Is it an observation or an inference?

Tap a button to start.
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Why it matters When two groups clash over a canister, they almost never disagree about the observations — they disagree about the inferences drawn from them. Naming which is which is where the argument gets useful.
Three · The trap

"A careful enough test reveals the truth"

It's the most natural assumption in the room — that if you just investigate hard enough, you'll eventually know for sure. Commit to an answer before you read on.

A group shakes, weighs and listens to a canister for a full ten minutes. What have they earned?

A stronger idea — never certainty. Ten minutes of careful work makes an explanation more trustworthy, not more proven. The lid never lifts. That feels like a limitation, but it's actually how science operates: no experiment hands you the final answer, only better or worse support for competing explanations.

The misconception this corrects: that science delivers fixed, proven facts. It doesn't. It delivers the best explanation available so far — powerful, reliable, and always open to revision if new evidence arrives.

Four · The evidence

Gather what you can

Tap the canister. Each shake surfaces one piece of evidence — and no single one settles it. Collect the set, then notice how your mind rushes to a conclusion before the evidence is really in.

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Tap the canister to gather evidence…
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Notice By clue two or three you already had a favourite answer. That pull toward an early conclusion is exactly what scientists guard against — it's why they demand more evidence, and why they show their reasoning to others.
Five · Make sense of it

Whose case is stronger?

This is the science-conference moment. When groups reach different conclusions from the same sealed canister, you don't settle it by opening the box — you settle it by weighing the evidence and the reasoning behind each claim.

Group A · Canister 4Wooden block — light, slides, dull knock
Group B · Canister 4Cork — too light for wood, no sharp knock
Exam-style question[6 marks]
Two groups investigated the same sealed canister. Group A recorded: light, slides end to end, a dull knock — and concluded "a small wooden block." Group B recorded: very light, slides, no sharp knock — and concluded "a piece of cork." Neither group may open the canister.
  1. State one observation that both groups agree on. [1]
  2. Explain why the class cannot be certain which conclusion is correct. [2]
  3. Justify which conclusion the evidence best supports — or argue that the two cannot yet be distinguished. [3]

(a) State — 1 mark

  • The object is light / it slides rather than rolls / there is a single solid object [1]

(b) Explain — 2 marks

  • The canister cannot be opened, so the true contents can never be directly checked [1]
  • The evidence available (weight, sound, movement) is consistent with more than one object, so it cannot single out one answer [1]

(c) Justify — 3 marks

  • A valid case for either: e.g. the very low weight and absence of a sharp knock support cork over dense wood [1]
  • …supported by explicit reference to the recorded evidence, not just the label [1]
  • Recognises the honest limit: light wood and cork may be indistinguishable through a sealed tube, so "cannot yet be distinguished" is itself a creditworthy, evidence-based conclusion [1]

Accept: a well-argued case for wood, for cork, or for "insufficient evidence to decide", provided it is justified from the observations. Do not accept: "just open it and check" / a conclusion asserted with no reference to the evidence.

Nature of science Making your reasoning public so others can challenge it is peer review — the quality control of science. The strongest-supported argument wins, not the loudest voice or the biggest group.
Six · Say it like a scientist

The takeaway, in your words

Fill the blanks so the sentence reads as a model answer.

Scientists gather and use it to build the best-supported . Because reality cannot be "opened" to check, scientific ideas are — open to revision. Sharing reasoning for others to challenge is called , and it keeps the process honest.

Seven · Leave with this

Four ideas about how science works

01 · Evidence, not answers

Explanations are built

Scientists can't check reality's answer key. They construct the best explanation the evidence allows.

02 · Tentative

Ideas stay revisable

New evidence can refine, revise, or overturn today's best idea. "Tentative" means open to revision, not flimsy.

03 · Peer review

Going public is the check

Sharing reasoning so others can challenge it is quality control. The best-supported case wins.

04 · Human

Science is social & creative

Observation, inference, discussion and imagination drive it — the same skills for a canister or a cell.

Hold the tension Some ideas become so well-supported that no reasonable person disputes them — gravity, the Earth orbiting the Sun. Tentative doesn't mean uncertain about everything. It means honest about where the evidence currently stands.