To my student, before we go any further: I hope my coffee breath didn't inspire this IA.

I've got a student working on this right now C1.1:

Working research question What is the effect of a change in the concentration of caffeine within the range 0 to 400 mg/L on the activity of lipase, as measured by the time taken in seconds for phenolphthalein to change from pink to colourless?

Working question. Still being refined. But already better than most.

They've done something simple and underrated: they've justified their range. 400 mg/L is roughly four cups of coffee. They want to see the full extent of any inhibition whilst keeping it grounded in something real. That decision alone shows they're thinking, not just filling in boxes.

400 mg/L CAFFEINE INHIBITOR? ACTS ON LIPASE triglyceride

Coffee at four cups, a caffeine molecule, a hungry lipase. The IA asks whether the second one slows the third one down.

Two things we're wrestling with

First: why caffeine? Why would it inhibit lipase? This is where a lot of students reach for Google and copy something that sounds plausible. What I want is a reasoned argument, even if it's uncertain. Caffeine inhibits phosphodiesterase, which affects cAMP signalling and lipid metabolism downstream. Whether that produces a clean, measurable effect at these concentrations is genuinely unclear. Say that. Justify it anyway. That's what the introduction is for.

Second: the endpoint. Phenolphthalein turns colourless as fatty acids lower the pH. Neat. Except, when exactly is it colourless? When you think it is? When your partner thinks it is? These are not the same moment, and everyone in the room knows it.

So is that a problem? I'd argue no.

Or at least, not in the way students think.

Research Design is worth 6 marks. A perfect method, and I mean genuinely optimised and watertight, gets you 2 of those 6 at best. The rest is Evaluation. So a method with a real, honest limitation, and the awareness to articulate it, is more valuable to a student's mark than a method that's technically tidy but gives them nothing to say afterwards.

RESEARCH DESIGN: 6 MARKS TIDY METHOD 2 of 6 marks at best HONEST LIMITATION + EVALUATION 4 of 6 marks where the marks actually live MARKS 1 2 3 4 5 6 A flawed method you can talk about beats a tidy method you can't.

Two marks reward the build. Four reward the awareness. A flawed but honest method gives students more to write about, and the rubric pays for the writing.

Use a colorimeter if you have access to one. If not, use the colour change, flag it clearly, and evaluate it properly. That's the game. I tell my students to play it.

The ask.

I'm always curious what other teachers guide students towards for IAs: the experiments that reliably generate interesting data and give students something real to analyse. The ones where the biology is actually visible in the results. If you've got a favourite, write to me, or drop it in the forum. I'll collect what comes in and post a follow-up.