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100+ Free IB Biology HL Practice Questions

Pass your International Baccalaureate Biology Higher Level exam on the first try — instant access, no signup required.

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Key Facts: IB Biology HL Exam

1-7

IB grading scale

IBO Diploma Programme

240 hours

Recommended HL teaching time

IB Biology subject guide

5h 45m

Total written exam time (Papers 1+2+3)

IB Biology subject guide

20%

Internal Assessment weighting

IB Biology subject guide

May 2025

First exams under new syllabus

IB Biology subject brief

100

Free practice questions here

OpenExamPrep

IB Biology HL is the 240-hour Higher Level option in IB Diploma Group 4 Sciences. The new syllabus (first exams 2025) is built on four themes and four organisational levels, assessed by three exam papers (5h 45m total) and a 20% Internal Assessment investigation, graded 1-7.

Sample IB Biology HL Practice Questions

Try these sample questions to test your IB Biology HL exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which property of water explains why ice floats on liquid water?
A.Hydrogen bonds form a less dense crystalline lattice in ice
B.Ice molecules vibrate faster than liquid molecules
C.Water becomes ionised at 0 degrees Celsius
D.Covalent bonds in water break on freezing
Explanation: In ice, each water molecule forms four hydrogen bonds in a fixed tetrahedral lattice, holding molecules further apart than in the liquid. This lower density allows ice to float, which insulates underlying liquid water and supports aquatic life in winter.
2Why is water described as a good solvent for polar molecules?
A.Its polar O-H bonds form hydrogen bonds and dipole interactions with solutes
B.It has a low specific heat capacity
C.It is non-polar and dissolves lipids
D.It is acidic and ionises all solutes
Explanation: Water is V-shaped with partial negative charge on oxygen and partial positive on hydrogens, allowing it to surround polar and ionic solutes with shells of attracted water molecules. This dissolves sugars, amino acids and salts essential to metabolism.
3The Meselson-Stahl experiment supported which model of DNA replication?
A.Semi-conservative
B.Conservative
C.Dispersive
D.Bidirectional only
Explanation: Meselson and Stahl grew E. coli in heavy 15N nitrogen, then switched to 14N. After one generation a single intermediate-density band formed; after two generations one intermediate and one light band formed. This ruled out conservative and dispersive models and confirmed each daughter DNA contains one old and one new strand.
4Which enzyme adds new nucleotides during DNA replication?
A.DNA polymerase III
B.Helicase
C.RNA polymerase
D.Ligase
Explanation: DNA polymerase III catalyses 5' to 3' addition of complementary nucleotides to the growing strand, using the parental strand as template. Helicase unwinds, ligase seals nicks and RNA polymerase makes RNA, not DNA.
5Alternative splicing of pre-mRNA allows one gene to:
A.Produce several different polypeptides from the same primary transcript
B.Replicate without polymerase
C.Mutate at a higher rate
D.Skip translation entirely
Explanation: During alternative splicing, exons can be included, excluded or rearranged in different mature mRNAs. This means a single gene can give rise to multiple polypeptide isoforms, dramatically increasing proteome diversity from a limited genome.
6In transcription, the DNA strand read by RNA polymerase to produce mRNA is called the:
A.Template (antisense) strand
B.Coding (sense) strand
C.Leading strand
D.Lagging strand
Explanation: RNA polymerase reads the template (antisense) strand 3' to 5', synthesising an mRNA that is complementary to it and identical (with U in place of T) to the coding (sense) strand. Leading and lagging refer to replication, not transcription.
7Post-translational modification refers to:
A.Chemical changes to a polypeptide after translation, such as glycosylation or phosphorylation
B.Cutting of introns from pre-mRNA
C.Capping the 5' end of mRNA
D.Addition of a poly-A tail to mRNA
Explanation: Post-translational modifications (PTMs) include cleavage, glycosylation, phosphorylation and disulfide bond formation, often occurring in the rough ER and Golgi. They are required to make functional mature proteins such as insulin (cleaved from pre-pro-insulin).
8A single base substitution that changes one codon to a stop codon is called a:
A.Nonsense mutation
B.Missense mutation
C.Silent mutation
D.Frameshift mutation
Explanation: A nonsense mutation introduces a premature stop codon, truncating the polypeptide. Missense changes one amino acid, silent does not change the amino acid, and frameshift comes from indels, not substitutions.
9Inserting a single nucleotide into the middle of a coding sequence usually causes:
A.A frameshift altering every amino acid downstream
B.A silent mutation
C.Only the amino acid at the insertion site to change
D.DNA replication to halt permanently
Explanation: Because codons are read in non-overlapping triplets, inserting one base shifts the reading frame downstream so all subsequent codons (and amino acids) change, usually producing a non-functional protein and often a premature stop codon.
10Chromosomal mutations include all of the following EXCEPT:
A.Substitution of a single base pair
B.Deletion of a chromosome segment
C.Inversion of a chromosome segment
D.Translocation between non-homologous chromosomes
Explanation: A single base substitution is a gene-level point mutation, not a chromosomal mutation. Chromosomal mutations involve large structural changes such as deletion, duplication, inversion, translocation and changes to chromosome number (aneuploidy).

About the IB Biology HL Exam

IB Biology Higher Level is the Group 4 science option for students with strong interest in living systems, designed around four overarching themes (Unity and Diversity, Form and Function, Interaction and Interdependence, Continuity and Change) and four levels of biological organisation (molecules, cells, organisms, ecosystems). The new syllabus, first examined in May 2025, is assessed via three external papers — Paper 1 (Part A multiple choice + Part B data), Paper 2 (data + short + extended response) and Paper 3 (HL-only choice essay) — plus an Internal Assessment scientific investigation worth 20% of the final grade. HL covers all SL content plus additional depth on cells, genetics, neurobiology, immunology and ecology.

Questions

100 scored questions

Time Limit

5 hours 45 minutes total (Paper 1: 2h, Paper 2: 2h 30m, Paper 3: 1h 15m)

Passing Score

Grade 4 standard pass on 1-7 scale; final grade combines three papers and the Internal Assessment

Exam Fee

Set by school; IB subject registration fees typically USD 119 per subject (International Baccalaureate Organization (IBO))

IB Biology HL Exam Content Outline

Theme A

Unity and Diversity

Water properties, DNA structure and semi-conservative replication (Meselson-Stahl), transcription and alternative splicing, translation and post-translational modification, point/frameshift/chromosomal mutations, gene pools and allele frequency, classification, viruses and the RNA world, Hardy-Weinberg equilibrium calculations

Theme B

Form and Function

Organelles including cytoskeleton, centrioles and lysosomes; channel/carrier/receptor membrane proteins; facilitated diffusion; sodium-potassium pump (3Na:2K); primary vs secondary active transport; innate and adaptive immunity, clonal selection of B and T cells, antibody structure, monoclonal antibodies; sarcomeres and sliding filament theory; actin, myosin, calcium and troponin

Theme C

Interaction and Interdependence

Resting potential (-70 mV), voltage-gated Na+/K+ channels, depolarisation, repolarisation, hyperpolarisation, refractory periods, saltatory conduction at nodes of Ranvier; synaptic transmission, Ca2+-triggered neurotransmitter release, EPSP/IPSP, spatial and temporal summation; peptide vs steroid hormones; nitrogen cycle (fixation, nitrification, denitrification, ammonification); carbon cycle and ocean sink; trophic efficiency and energy pyramids

Theme D

Continuity and Change

Meiosis with independent assortment and crossing over at chiasmata; dihybrid 9:3:3:1 and linked genes with recombination frequency; X-linked recessive haemophilia and colour blindness; chi-squared goodness of fit and contingency tables; PCR with primers and Taq, gel electrophoresis, STR profiling, CRISPR-Cas9, recombinant DNA and GM applications; speciation, convergent vs divergent evolution, coevolution, phylogenetic trees, comparative genomics

20% IA

Internal Assessment

Scientific investigation: an individual scientific investigation of about 10 pages assessed against four criteria (research design, data analysis, conclusion, evaluation). Worth 20% of the final grade across SL and HL.

How to Pass the IB Biology HL Exam

What You Need to Know

  • Passing score: Grade 4 standard pass on 1-7 scale; final grade combines three papers and the Internal Assessment
  • Exam length: 100 questions
  • Time limit: 5 hours 45 minutes total (Paper 1: 2h, Paper 2: 2h 30m, Paper 3: 1h 15m)
  • Exam fee: Set by school; IB subject registration fees typically USD 119 per subject

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

IB Biology HL Study Tips from Top Performers

1Master the four themes crossed with the four organisational levels — Paper 3 essays explicitly demand cross-theme integration
2Drill Hardy-Weinberg (p^2 + 2pq + q^2 = 1), chi-squared and dihybrid 9:3:3:1 calculations until fluent — they recur every session
3Learn the action potential timeline (resting, depolarisation, repolarisation, hyperpolarisation, refractory) with the ion channels responsible at each step
4Practice annotating sarcomere diagrams (A band, I band, H zone, Z line) and explain length changes during sliding filament contraction
5Use IB data-response practice — Paper 1 Part B and Paper 2 demand interpretation of unfamiliar experimental graphs and tables, not memorised facts

Frequently Asked Questions

How is IB Biology HL different from IB Biology SL?

HL has 240 teaching hours versus 150 for SL, adds an extra Paper 3 (HL-only choice essay) and covers all four themes with additional HL depth — including post-translational modification, monoclonal antibodies, the sliding filament theory in detail, action potential mechanisms with voltage-gated channels, Hardy-Weinberg equilibrium calculations, dihybrid inheritance with linkage, chi-squared analysis, CRISPR-Cas9 and recombinant DNA.

What are the three exam papers in IB Biology HL?

Paper 1 is 2 hours: Part A is data-based multiple choice and Part B is a data-response section. Paper 2 is 2 hours 30 minutes with data analysis, short-answer and extended-response questions. Paper 3 is 1 hour 15 minutes (HL only) with a choice of essay questions integrating across the four themes. The three papers count for 80% of the grade and the IA scientific investigation is the other 20%.

When did the new IB Biology syllabus start?

The new IB Biology syllabus was first taught from August 2023 and first examined in May 2025. It replaces the previous Topics 1-11 / Options A-D structure with four themes (Unity and Diversity, Form and Function, Interaction and Interdependence, Continuity and Change) crossed with four levels of biological organisation (molecules, cells, organisms, ecosystems).

How is IB Biology HL graded?

Each subject is graded on a 1-7 scale, with 7 the highest. A 4 is generally considered a pass. Grades are determined by combining marks from Paper 1, Paper 2, Paper 3 and the Internal Assessment against grade boundaries set after each session. Top medical and bioscience university programmes typically expect a 6 or 7 in HL Biology.

What is the Internal Assessment for IB Biology HL?

The Internal Assessment is an individual scientific investigation of approximately 10 pages, assessed against four criteria (research design, data analysis, conclusion, evaluation) by the teacher and externally moderated by the IBO. It is worth 20% of the final grade for both SL and HL Biology.