Edexcel IAL A2 Biology — Units 4, 5 and 6
A2 is where the IAL grade is decided. Three papers — Unit 4, Unit 5 and the practical paper Unit 6 — carry half the qualification and all of the A* rule. This page is the map: what each unit examines, what the last six years of papers actually rewarded, and where the notes, solved papers and lessons for each unit live.
The three A2 units
Watch first
Three minutes on how UMS works across AS and A2 — and why the A2 units decide the A*.
Study these 10 topics for your IAL Unit 4 Biology Exam
Unit 4
10 Unit 5 IAL Biology Topics That Could Save Hours of Revision
Unit 5
IAL Biology Unit 6: Last-Minute Exam Advice
Unit 6
How the A2 year is assessed
The International A Level in Biology is six units. AS is Units 1–3; A2 is Units 4, 5 and 6, sat after a further year of study. Unit 4 and Unit 5 are each 90 marks in 1 hour 45 and each worth 20% of the full qualification; Unit 6 is a 50-mark written practical-skills paper worth 10%. All three are available in January, June and October, and every unit can be resat with the better result counting.
Two rules shape A2 revision. First, Units 4 and 5 are synoptic: any question can draw on Units 1 and 2, most often membranes, proteins, enzymes, the heart and circulation. Second, the A* is earned at A2. You need an A overall (480 of 600 UMS) and at least 90% of the UMS across Units 4, 5 and 6 — 270 of 300. A student with strong AS marks and average A2 marks gets an A; the reverse is where the A* comes from.
What the three A2 papers actually reward
I classified every question part in 51 WBI14, WBI15 and WBI16 papers from 2020 to 2026 — 1,578 parts — by topic, command word and difficulty. The pattern is consistent across sittings. In Unit 4, four topics — global warming, microbiology, ecology and active immunity — carry about 60% of the marks. In Unit 5, the nervous system alone is 24%, followed by regulation of breathing and heart rate, respiration and the kidney. In Unit 6, ecology of a habitat is the most examined practical at 17%, but 38% of marks come from unfamiliar investigations that test the same planning and analysis skills in a new context.
"Explain" is the leading command word in both theory papers; "Describe" leads in Unit 6. That is the single most useful fact on this page: A2 marks are lost not because students do not know the biology but because they write it in their own words rather than the mark scheme's. Every solved question on this site is written in the words the examiner ticks.
How to use this hub
Each unit has its own page with the full topic checklist, the marks-by-topic data, the videos for that unit and links to its solved papers. Start with the unit you are sitting next. If you are in the last eight weeks before an exam, go straight to the unit page's "How to revise in the right order" list and work through the solved papers for the top three topics. If you are starting A2, use the specification checklist below to plan the year, one topic a week, ticking each point as it is mastered.
FAQ
What is the difference between AS and A2 in Edexcel IAL Biology?
AS is Units 1–3, usually sat in the first year; A2 is Units 4–6 in the second. Both halves are 300 UMS. AS grades run A–E; the A* is awarded only on the full IAL and depends on A2 performance.
Can I sit A2 units without finishing AS?
You can enter any unit in any series, but the A2 papers are synoptic and assume Units 1 and 2. Most students complete AS first.
Which A2 unit should I revise first?
The one you are sitting soonest. Within each unit, start with the highest-mark topics listed on its page — in Unit 5 that is the nervous system, in Unit 4 the four topics that share 60% of the marks.
Are the solved papers written for the 2018 specification?
Yes. Every paper from 2020 to 2026 is on the current specification (Issue 2), classified by topic so you can practise one topic at a time.
About
About this page. A2 Biology at Chem Bio covers Units 4, 5 and 6 of the Pearson Edexcel International Advanced Level in Biology (YBI11): Energy, Environment, Microbiology and Immunity (WBI14); Respiration, Internal Environment, Coordination and Gene Technology (WBI15); and Practical Skills in Biology II (WBI16). The three units are 300 of the qualification's 600 UMS and determine the A*. Resources on this site for A2 include the notes eBooks, solved past papers 2019–2026 classified by topic, the recorded A2 course, live classes and the specification checklists. Written by Hosni Showike, Head of Science, 21 years teaching Edexcel IAL Biology.
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Last updated 3 September 2026
