IAL Biology Unit 5 Scientific Article October 2026 Guide

The WBI15 pre-release article for 27 October 2026 is about bacteria living inside fish brains: what it covers, the spec topics it touches, and how to prepare.

Check your paper: Pearson has published separate WBI15/01 and regional WBI15/01A scientific articles for October 2026. Confirm which article applies to your exam entry with your exams officer before using this guide. Pearson explains the two versions.

TL;DR: The October 2026 IAL Biology Unit 5 scientific article is "Fish Have a Brain Microbiome. Could Humans Have One Too?" by Yasemin Saplakoglu. It describes a five-year study at the University of New Mexico that found living bacteria inside the brains of healthy trout and salmon, and asks whether humans have a brain microbiome too. Question 8 is worth 20 marks out of 90 and pulls from Unit 5, Unit 4 and even Unit 1. In June 2026, every one of the seven parts of Question 8 was a question we had already prepared in my session. Read the article three times, annotate it, and then join the live session on Friday 2 October at 5 pm Kuwait time.

Jump to: What the article is about · Why Question 8 matters · Five takeaways · Specification links · How to prepare · FAQ

What is the October 2026 IAL Biology Unit 5 scientific article about?

The October 2026 WBI15 pre-release article is about a study that found living bacteria inside the brains of healthy salmon and trout, and it asks whether the human brain could have a microbiome of its own. It is adapted from a Quanta Magazine article published in December 2024 and runs to 20 numbered paragraphs. Here is the story in plain English. For a very long time, scientists assumed that bacteria simply cannot live in a healthy brain. Why? Because of the blood-brain barrier. This is the wall of blood vessels and surrounding brain cells that only lets certain molecules in and out and keeps invaders, especially large ones like bacteria, out. Irene Salinas, an immunologist at the University of New Mexico, had a hunch. The nose is loaded with bacteria, and the nose is only millimetres away from the olfactory bulb, the part of the brain that processes smell. So she asked a simple question: are bacteria leaking from the nose into the brain? Her team extracted DNA from the olfactory bulbs of trout and salmon, some wild-caught and some raised in the lab, and matched the sequences against a database to identify the species. The big problem was contamination. Bacterial DNA is everywhere, so the team also sampled the rest of the brain, the gut and the blood, and even drained the blood out of the brain capillaries before testing. They repeated the experiments many, many times. The project took five years. What did they find? The olfactory bulb had bacteria, as expected. But the rest of the brain had even more. The bacteria were alive, not dead or dormant. Some species were found nowhere else in the body, which suggests they colonised the brain early in development, before the blood-brain barrier had fully formed. Others came from the blood and gut and keep leaking in. Some bacteria produce molecules called polyamines that open and close the junctions in the barrier, like little doors. Others produce molecules that help them evade the immune response. The article ends with the open question. Fish are not humans. But if fish have a brain microbiome, and early results show hints of one in mice, then a human brain microbiome is no longer outlandish. Are the bacteria there for a reason, or by mistake? Nobody knows yet.

Why does the pre-release article matter so much for Question 8?

Question 8 of the Unit 5 paper is worth 20 marks out of 90, and every part of it is built on the pre-release article. That is more than one fifth of the paper, and Pearson states clearly in its guidance that it will not tell centres which parts of the article will be assessed. So what does Question 8 look like? Each part points you to a paragraph number, quotes a phrase from it, and then asks a question from the specification. The phrase is only the trigger. The marks come from your own knowledge. That's why students who only read the article on the night before the exam lose most of these 20 marks. Here is the June 2026 Question 8 broken down, part by part, so you can see the pattern for yourself. Note how the questions reach back into Unit 4 and Unit 1, not just Unit 5.

Seven parts, 20 marks, three different units. In June 2026, every one of those seven parts was a question we had already prepared in my article session. That is not luck. Once you have analysed enough of these papers against the mark schemes, you can see exactly which paragraphs the examiner cannot resist. The IAL Biology Unit 5 page has the full unit breakdown if you want to see where Question 8 sits in the whole paper.

Five takeaways from the October 2026 article

Here are the five things you must take away from this article before you walk into the exam on 27 October.

1. The blood-brain barrier is made of capillaries with very tight junctions. In most of your body, capillary walls are one cell thick with small gaps, and that's how tissue fluid forms. In the brain, the endothelial cells are sealed together by what we call tight junctions, and the surrounding brain cells reinforce the wall. Only small, lipid-soluble molecules pass through freely. Bacteria are far too large. Make sure that you can describe a normal capillary and then explain what makes the brain capillary different. That is a very very likely question.

2. Bacteria cross the barrier using polyamines that open the junctions. Paragraph 12 is the key paragraph. Some bacteria produce molecules called polyamines that open and close the junctions between the endothelial cells. Think of it as a molecule that loosens the lock on the door. Once the junction opens, the bacterium squeezes through. Expect a question that asks you to suggest how a bacterium could move through the barrier, and expect the mark scheme to reward the words junction, endothelial cell and membrane.

3. Contamination is the reason this took five years. Paragraphs 7 and 8 are basically a lesson in validity. Bacterial DNA is everywhere, in the lab, on the skin, in the blood. So the team sampled every organ, drained the capillaries, and repeated the experiments many times. Why? Because if the DNA came from the blood, the whole conclusion collapses. Questions about controls, repeats and why other scientists were "not involved in the study" appear in almost every Question 8.

4. DNA sequencing identified the species. The team extracted bacterial DNA and matched it to a database. You have met this in Unit 4 with PCR and profiling, and in Unit 2 with molecular classification. Be ready to describe how you would amplify a tiny sample of DNA and how comparing sequences tells you which species you have.

5. Fish are a model organism, and that raises an ethical question. The article moves from fish to mice to humans. Scientists cannot take brain tissue from healthy people, so they use animals. That is straight out of Unit 5, and the examiner loves asking you to discuss it from two ethical standpoints.

Which specification topics does the article hint at?

The article touches at least eleven specification points across Unit 5, Unit 4, Unit 2 and Unit 1, and Question 8 will reach into all of them. Here are the links I am comfortable sharing publicly. The rest I go through, paragraph by paragraph, in the live session. From Unit 5, you need the structure and function of the nervous system, the regions of the brain including the olfactory bulb and where it sits, the role of the blood-brain barrier, how neurones communicate at synapses, and the ethical use of animals in medical research. From Unit 4, you need the structure of a bacterial cell, how the non-specific immune response deals with invaders, phagocytosis, and DNA amplification and profiling. The Unit 4 page covers the immunity section in full. From Unit 1 and Unit 2, you need capillary structure and the formation of tissue fluid, membrane structure and transport across membranes, prokaryotic cell structure, and how DNA sequences are used to classify organisms. On the other hand, there are three or four links in this article that almost nobody spots on a first read. For instance, one sentence in paragraph 11 connects to a Unit 2 topic that most students have not revised since Year 12. I will show you exactly which one on Friday. If you want to check any of these against the official wording, the Edexcel IAL A2 Biology specification is laid out topic by topic.

How should you prepare for the scientific article question?

Read the article at least three times, annotate every technical term with the specification point it belongs to, and then practise answering exam-style questions on each paragraph. Here is the plan I give my own students.

Step one: read it once for the story. Do not stop to annotate. Just understand what happened and why it matters.

Step two: read it again with a highlighter. Every technical term gets a mark. Blood-brain barrier, olfactory bulb, polyamines, junctions, immune cells, DNA sequences, model organism. Every one of these is a potential trigger phrase.

Step three: write the specification point next to each term. This is the step that earns the marks. When the question says "explain what is meant by the blood-brain barrier (paragraph 10)", you should already know that the answer is capillary structure from Unit 1 plus nervous tissue from Unit 5.

Step four: predict the questions. Go paragraph by paragraph and ask yourself: what could the examiner ask here? Write the question down, then write a mark-scheme style answer.

Step five: solve past Question 8s. Pull the last four or five Unit 5 papers and solve Question 8 in each one, with the article in front of you. You will notice the same command words, the same mark allocations and the same habit of quoting a phrase and asking for your own knowledge. Remember that you cannot take your annotated copy into the exam. Pearson places a fresh copy of the article inside the question paper, so your preparation has to be in your head, not on the page.

Join the live session on Friday 2 October

If you would rather have all of this done for you, I am running a live session on Friday 2 October 2026 at 5 pm Kuwait time. I explain the article paragraph by paragraph, link every sentence to its specification point, and hand you a package of predicted questions with model answers written in mark-scheme language. In June 2026, every part of Question 8 came from that package. You can reserve your place on the October 2026 article study hub and the recording stays available until the exam.

FAQ

Do I need to memorise the scientific article for the Unit 5 exam? No. A fresh copy is printed inside the question paper. What you need to memorise is the specification content that each paragraph points to, because that is where the marks are.

How many marks is Question 8 worth in IAL Biology Unit 5? Question 8 is worth 20 marks out of 90, which is more than one fifth of the paper. Every part is based on a paragraph of the pre-release article.

Does the scientific article question only test Unit 5? No. The June 2026 paper asked about oxygen transport from Unit 1 and inflammation from Unit 4. The October 2026 article reaches into Unit 1, Unit 2 and Unit 4 as well.

When is the IAL Biology Unit 5 exam in October 2026? The WBI15/01 paper is on Tuesday 27 October 2026, in the morning, and lasts 1 hour 45 minutes.

Can I bring my annotated article into the exam? No. Pearson does not allow annotated copies in the exam room. You will be given a clean copy with the paper. That's all for today. I hope that this was helpful and I wish you all best of luck in your exam.

About the author: Hosni Showike is the author of eight published science textbooks with more than 20,000 copies sold worldwide. He has taught IGCSE and International A Level Chemistry and Biology for over 20 years, including 16 years teaching to Cambridge and Edexcel mark schemes at A-level, and writes at chem-bio.info where he publishes grade-threshold analysis, solved past papers and live exam-preparation classes.