9.6 - Drawing Conclusions

What a conclusion question looks like

• The N5 paper asks you to state a conclusion from the results. Sometimes a second, separate conclusion is wanted too.
• It's one of the marks students most often throw away.
• The mark is not for repeating a number off the table. It's for a sentence that ties the two variables together and answers what the investigation set out to find.

A typical question

A student counted the number of gas bubbles released each minute by yeast at two temperatures, 18 °C and 42 °C. The results are shown in the table.

State a conclusion the student can make from these results.

What your answer must do

A conclusion has to do two things:

1. Name both variables - The temperature and the rate (the number of bubbles), not just one of them.
2. Give the direction of the link - As the temperature rises, the rate rises.

Putting it together:

• Put together, that is a conclusion: "the higher the temperature, the higher the rate of respiration".
• Linking the variable you changed to the variable you measured, and reading it back against the aim, is the whole idea.

Linking the variable you changed to the one you measured

• A conclusion answers the aim: how does the thing you changed affect the thing you measured.
• So it always names both variables and says which way they move together.

Writing the conclusion

The most reliable method is to fill in a single frame:

As the [variable you changed] increased, the [variable you measured] increased (or decreased).

• For the yeast experiment: "as the temperature increased, the rate of respiration increased".
• Other wordings are equally accepted:
  • "The higher the temperature, the greater the rate of respiration"
  • "The lower the temperature, the lower the rate" (said the other way round)

A conclusion is not a single reading

• Describing one measurement - "The number of bubbles went up" only names the thing you measured, never the temperature, so it doesn't link the two variables or answer the aim. A conclusion has to carry both names.
• A reading is not a conclusion - Many papers have a separate part asking you to read a value straight off a table or graph (e.g. "how many bubbles were released at 42 °C"). The answer there is just the number. The conclusion part wants the relationship - don't answer one with the other.

Is the conclusion valid?

• One N5 question type gives you a conclusion someone has written and asks you to tick valid or invalid, and explain why.
• A conclusion is valid when the data actually support it and the investigation was a fair test - only the one variable was changed, so the link is safe to claim.
• A conclusion is invalid when:
  • The results don't show that link
  • Another variable wasn't controlled
  • It goes beyond what was tested (e.g. claiming a trend continues past the range of temperatures actually used)
• Check the conclusion against the figures and against how the test was run before ticking either box.

Common exam questions

Question 1

A student investigated how sugar concentration affects the mass lost by a piece of potato. With reference to the aim, give a conclusion for this investigation.

As the concentration of the sugar solution increased, the mass lost by the potato increased. Both variables are named, the direction is given, and it answers the aim of finding how sugar concentration affects mass loss.

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Question 2

A table gives the average resting heart rate of horses and donkeys. Using this information, give a conclusion.

Donkeys have a higher (or lower) average resting heart rate than horses - whichever the figures show. The conclusion links the type of animal to the measured heart rate rather than just quoting one value.

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Question 3

A student wrote: "as light intensity increased, the number of bubbles increased, so light intensity increases photosynthesis in all plants." Tick one box to identify whether this conclusion is valid or invalid, and explain why.

Invalid. The data support the link for the plant tested, but the claim "in all plants" goes beyond what was investigated - only one plant was tested, so the conclusion cannot be extended to every plant.

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Question 4

A student concludes "the number of bubbles was 40". Why does this not score as a conclusion?

Because it quotes a single reading and never mentions the variable that was changed; a conclusion must link the two variables, for example "as the light intensity rose, the number of bubbles rose".

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Question 5

An enzyme works fastest at 40 °C and slower above and below it. Why can you not write "the higher the temperature, the faster the enzyme"?

Because the relationship is not a simple rise; the rate increases up to 40 °C and then falls, so the conclusion must say the rate was highest at 40 °C and lower on either side.

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Question 6

A question asks for a second, different conclusion. Why does "as temperature decreases, the rate decreases" not earn it?

Because it is the first conclusion written backwards, not a new point; a second conclusion has to add something different, such as identifying the temperature at which the rate was greatest.

Conclusion versus explanation

• A conclusion states what the results show - it comes straight from the data and answers the aim.
• An explanation states why it happens, using biology you already know.
• The two are asked for separately, and one does not stand in for the other.

An example - Enzyme rate and temperature

Take an investigation into how temperature affects the rate an enzyme breaks down its substrate, where the rate rose as temperature went from 10 °C to 40 °C:

• Conclusion - The rate of reaction increased as the temperature rose. This comes straight from the results and answers the aim.
• Explanation - At higher temperatures the enzyme and substrate molecules move faster, so they collide more often and more enzyme-substrate complexes form. This uses biology that isn't in the results table at all - no reading of rate or time tells you molecules are colliding.

Matching your answer to the question

• "State a conclusion" / "give a conclusion" - Wants the first kind of sentence, referring to the variable you changed and the variable you measured.
• "Explain" - Wants the biological reason behind the result.
• "Explain how the results show that..." - Use a figure from the results as evidence, then give the biological reason.