Predict diffusion changes with temperature and gradient
Make qualitative predictions while keeping the other diffusion factors fixed.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall random motion and the concentration gradient.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which comparison isolates temperature?
What you will learn
- Make qualitative predictions while keeping the other diffusion factors fixed.
- Apply the idea to a supplied biological example or investigation.
Temperature changes particle motion
At a higher temperature, average particle kinetic energy increases and diffusion usually proceeds faster in a comparable non-living model. Temperature is not the concentration difference: these are separate factors. Keep the exposed area, diffusion distance and initial solutions comparable when testing temperature.
Do not infer an exact doubling of diffusion rate from a doubling of temperature in degrees Celsius. Celsius zero is not zero kinetic energy, and no proportional rate law has been supplied. In living tissues extreme temperatures can also damage membranes.
A steeper gradient strengthens net transfer
A greater concentration difference across the same distance is a steeper concentration gradient. It generally produces faster net diffusion when area, temperature and the pathway remain comparable. As the difference becomes smaller during an experiment, the driving gradient diminishes.
Compare differences only when the distances are the same. For simple supplied examples, 9 versus 1 units gives a larger difference than 5 versus 3 units. A prediction about faster initial transfer is not a claim that the final equilibrium concentrations must remain unequal.
Sources for this lesson
Pause and explain
The concentration difference falls during diffusion. What tends to happen to net transfer?
Worked example
At equal temperatures and distances, compare concentration pairs 10 and 2 units with 6 and 4 units.
Show the worked solution
- Differences are 8 and 2 units.
- The first setup has the steeper gradient.
- Other factors are stated equal.
Answer The 10-to-2 setup favours faster initial net diffusion.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare gradients 12 to 4 and 7 to 5 over equal distances.
Give me a hint
Subtract each pair.
Compare my reasoning
- Differences are 8 and 2.
- Other conditions must match.
The 12-to-4 gradient is steeper.
Look for these in your work
- Use difference and the equal-distance condition.
A dye spreads faster at 30°C than at 15°C. Give a particle explanation.
Give me a hint
Connect temperature to movement.
Compare my reasoning
- Higher temperature raises average kinetic energy.
- Random movement can produce faster spreading.
Greater average kinetic energy supports faster diffusion.
Look for these in your work
- Do not claim an exact twofold rate.
A student changes both temperature and concentration difference and sees faster transfer. Can the result isolate temperature?
Give me a hint
Identify the second changed variable.
Compare my reasoning
- The gradient changed too.
- Either or both factors could contribute.
- Repeat with matched gradients to isolate temperature.
No; the changed gradient confounds the temperature comparison.
Look for these in your work
- Name the confound and improvement.
Common mistakes
- Keep gradient separate from temperature.
- Do not invent a precise rate multiplier.
What can you explain now?
The concentration difference falls during diffusion. What tends to happen to net transfer?
Compare with the explanation
It slows as the gradient becomes less steep.
The directional imbalance decreases.
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Make it stick
List the four syllabus factors affecting diffusion.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.