There's nothing quite like sitting down with a past paper, pencil in hand, absolutely convinced you know your stuff, and then staring at a question about parsimony analysis in cladograms A3.2 like it's written in a foreign language.

I sat the May 2026 IB Biology papers after my students this year. In the past I've actually asked to be registered for the AP Biology exam, but you can't if you teach the class (that's another story). I even repeated all the past papers for the new syllabus, every single one. And yes, it was humbling. Yes, there were moments of quiet panic. And yes, I would recommend it to every biology teacher without hesitation, because there is simply no better way to find the gaps in what you've actually taught versus what you think you've taught.

Here's what the experience reminded me.

We have to play the game

The IB isn't just testing biology. It's testing attention to detail, for teachers and students alike: whether students can read, interpret, respond under pressure, and know exactly where the mark scheme is going. You can't coach that from the sidelines. Sitting the papers yourself forces you to feel the exam the way your students do: the awkward wording, the data you have to wrestle with, the moment you realise you glossed over something in October and it's now worth four marks.

A few things came up that I hadn't emphasised enough. Some genuinely interesting biology I'd either rushed past or buried, quite a few tbh, but I've selected just a few here.

Sieve tube elements B3.2

Sieve tube elements have no nucleus, and that's not a mistake, it's the point. They're living cells sustained entirely by companion cells through plasmodesmata. The nucleus is removed so sap can flow unobstructed through sieve plates. Cell theory says cells need a nucleus. Sieve tubes politely disagree.

FACE experiments C1.3

Free-Air CO2 Enrichment: pipes arranged in a circle pump elevated CO2 around real outdoor plots. The whole point is ecological validity, you can't stuff a forest into a greenhouse. Results show increased photosynthesis in C3 plants, but the effect diminishes over time. This is the named application in the photosynthesis section and it kept appearing.

Cocaine and the dopamine transporter C2.2

Cocaine blocks the dopamine transporter (DAT), preventing reuptake, so dopamine floods the synapse and the reward signal is artificially amplified. The neuroscience is elegant, even if the application is grim. It came up in the context of synaptic pharmacology and I hadn't been explicit enough about the mechanism.

Ethylene and the one bad apple C3.1

Ethylene is a gas. An actual gas. The only plant hormone that is. It diffuses through air, triggers ripening via positive feedback: one fruit produces ethylene, neighbouring cells produce more ethylene, everything ripens at once. Hence the barrel and the one bad apple. It's a brilliant system.

POSITIVE FEEDBACK · ETHYLENE C3.1 + feedback ETHYLENE PRODUCED IN ONE FRUIT 01 ETHYLENE GAS DETECTED BY NEARBY FRUIT 02 NEARBY FRUIT BEGINS TO RIPEN AND RELEASE ETHYLENE 03 ETHYLENE PRODUCTION INCREASES 04 MORE FRUIT RIPENS 05 C₂H₄ C₂H₄ C₂H₄

A bunch of bananas releases ethylene (C2H4). Neighbours detect it, ripen, and release more. Production keeps climbing until the whole bowl ripens at once. Positive feedback in a fruit basket.

Endler's guppies D4.1

Endler's guppies. They always come up - don't forget them. The first year I taught this I ran my normal natural selection skit and missed the example entirely. I checked the syllabus, but creating new curriculum documents is a massive undertaking. Where is the two-page IB document that says hey teachers, heads up, here's a distilled version of what changed and what you might miss? Instead it's good luck disseminating 132 pages. We get upset because we care, so don't play with my emotions.

The short version: bright male guppies are attractive to females and attractive to predators - two selection pressures pulling in opposite directions. In low-predation streams, sexual selection wins and spots increase. In high-predation streams, the bright ones get eaten first and spots decrease. Endler demonstrated this in artificial ponds over 14 months - actual measurable evolution, visible in his lifetime, counted fish by fish. The data is almost insultingly clean: two lines diverging from the same starting point. One up, one down. If a student can't explain why the lines go in opposite directions, they haven't understood natural selection, they've just memorised it.

ENDLER'S GUPPY EXPERIMENT · 14 MONTHS D4.1 0 6 14 MONTHS 14 12 10 8 SPOTS / FISH LOW predation HIGH predation

Both populations start at ~11.8 spots. Without predators, sexual selection drives spots up. Add pike cichlids, and the bright ones get eaten first - selection runs the other way. Two pressures, two outcomes, one elegant experiment.

The point

The point isn't that I'm a bad teacher. The point is that this syllabus is deep, the past papers are the best revision tool in existence, and the only way to really know what you've missed is to sit in the room and find out the hard way.

Do the papers. Feel the pain. Fix the gaps. Your students will thank you for it.