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Quizzes > Science > Biology

Challenge Yourself with IB Biology Practice Questions

Ready for Biology IB Questions? Dive into Our IB Biology Test Questions!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art style illustration with microscope DNA helix question mark on teal background for IB Biology practice quiz

Think you've mastered the building blocks of life? Put your skills to the ultimate test with our free ib biology practice questions quiz! Crafted especially for IB learners, this engaging ib biology quiz covers everything from cell biology to ecology through thought-provoking ib biology sample questions and challenging ib biology test questions. Dive into real-world biology ib questions, experience a timed biology practice exam , get instant feedback to track your progress and spot gaps. With friendly tips along the way, you'll boost your confidence and deepen your understanding before exam day. Ready to elevate your revision? Click "Start" now and embrace the journey to acing IB Biology!

Which organelle is the primary site of ATP production in eukaryotic cells?
Mitochondrion
Chloroplast
Golgi apparatus
Ribosome
Mitochondria are known as the powerhouse of the cell because they produce ATP via oxidative phosphorylation across the inner mitochondrial membrane. The electron transport chain pumps protons into the intermembrane space, creating a gradient that drives ATP synthase. This process is central to cellular respiration in eukaryotes. Khan Academy: Cellular Respiration
What base pairs with cytosine in a DNA double helix?
Guanine
Adenine
Thymine
Uracil
In DNA, cytosine forms three hydrogen bonds with guanine, ensuring stability and specificity in base pairing. Adenine pairs with thymine via two hydrogen bonds, and uracil is found only in RNA. Complementary base pairing is critical for DNA replication and transcription. Khan Academy: DNA Base Pairing
In enzymatic reactions, the theory that suggests enzymes have specific active sites complementary to the substrate is called?
Lock-and-key model
Induced fit model
Allosteric regulation
Competitive inhibition
The lock-and-key model proposes that substrates fit exactly into the active site of an enzyme, like a key into a lock, without altering the enzyme’s structure. This model explains enzyme specificity but does not account for minor adjustments in shape, which the induced fit model later addressed. It remains a foundational concept in enzyme kinetics. Khan Academy: Enzyme Regulation
Which process involves the movement of water molecules across a selectively permeable membrane?
Osmosis
Diffusion
Active transport
Facilitated diffusion
Osmosis is the passive movement of water molecules through a selectively permeable membrane from a region of lower solute concentration to higher solute concentration. This process helps maintain cell turgor in plants and balance fluids in animal cells. It is driven purely by concentration gradients without energy input. Khan Academy: Osmosis
What is the overall equation for photosynthesis in plants?
6CO2 + 6H2O ? C6H12O6 + 6O2
C6H12O6 + 6O2 ? 6CO2 + 6H2O
6CO2 + 6O2 ? C6H12O6 + 6H2O
C6H12O6 + 6H2O ? 6CO2 + 6O2
Photosynthesis converts carbon dioxide and water into glucose and oxygen using light energy. This reaction occurs in chloroplasts, primarily within the stroma and thylakoid membranes. The balanced equation reflects mass and charge conservation. Khan Academy: Photosynthesis Equation
Proteins are polymers of which monomeric units?
Amino acids
Nucleotides
Monosaccharides
Fatty acids
Proteins are long chains of amino acids linked by peptide bonds. There are 20 standard amino acids that differ in their side chains, determining protein structure and function. Nucleotides form nucleic acids, monosaccharides form carbohydrates, and fatty acids form lipids. Khan Academy: Proteins
Which of the following is a characteristic of prokaryotic cells but not eukaryotic cells?
Lack of membrane-bound organelles
Presence of a nucleus
Large ribosomes
Linear DNA
Prokaryotic cells, such as bacteria, do not have membrane-bound organelles or a true nucleus; their DNA is located in a nucleoid region. Eukaryotic cells contain organelles like mitochondria and a membrane-bound nucleus. Prokaryotic ribosomes are smaller (70S) compared to eukaryotic (80S). Khan Academy: Prokaryotes
An allele is best defined as:
A variant form of a gene
A type of chromosome
A gene’s expression level
A plasmid
An allele is one of two or more versions of a gene that arise by mutation and are found at the same place on a chromosome. Different alleles can result in variations in the expressed trait. Chromosomes consist of many genes, and plasmids are extra-chromosomal DNA in bacteria. Khan Academy: Classical Genetics
During the light-dependent reactions of photosynthesis, where is the proton gradient established?
Thylakoid lumen
Stroma
Cytosol
Inner mitochondrial membrane
Protons are pumped into the thylakoid lumen by the photosystems and electron transport chain during the light-dependent reactions. This gradient drives ATP synthase to produce ATP in the stroma. The process is analogous to chemiosmosis in mitochondria. Khan Academy: Light-Dependent Reactions
Which enzyme unwinds and relieves supercoiling during DNA replication?
DNA gyrase (topoisomerase)
DNA ligase
Helicase
Primase
DNA gyrase, a type of topoisomerase in prokaryotes, introduces negative supercoils or relieves positive supercoils ahead of the replication fork. Helicase unwinds the strands, primase lays down RNA primers, and ligase joins Okazaki fragments. Topoisomerases are critical for managing DNA topology. Khan Academy: DNA Replication
In a Hardy-Weinberg population with two alleles where p = 0.7, what is the expected frequency of heterozygotes?
0.42
0.21
0.49
0.09
Under Hardy-Weinberg equilibrium, heterozygote frequency is 2pq. If p = 0.7 and q = 0.3, then 2 × 0.7 × 0.3 = 0.42. This model assumes no selection, mutation, migration, or genetic drift. It provides a baseline for evolutionary change. Khan Academy: Hardy-Weinberg
Which process correctly describes transcription?
DNA ? mRNA
mRNA ? protein
DNA ? DNA
Protein ? RNA
Transcription is the synthesis of messenger RNA (mRNA) from a DNA template. RNA polymerase reads the DNA strand and assembles a complementary RNA molecule. Translation, by contrast, converts mRNA into protein. DNA replication produces new DNA. Khan Academy: Gene Expression
In the lac operon of E. coli, the repressor binds to the operator in the absence of:
Lactose
Glucose
cAMP
Allolactose
When lactose is absent, the lac repressor binds the operator region and blocks transcription of lac genes. Allolactose, an isomer of lactose, acts as the inducer by binding the repressor and causing it to release the operator. Glucose and cAMP regulate CRP-cAMP levels but not repressor binding directly. Khan Academy: Gene Regulation
Which immunoglobulin class is the first antibody produced in a primary immune response?
IgM
IgG
IgA
IgE
IgM is the first antibody class secreted during a primary immune response because its pentameric structure allows effective agglutination of antigens. Later, class switching generates IgG, IgA, or IgE for specialized functions. IgG predominates in secondary responses. Khan Academy: Immune System
What is the functional unit of the kidney where blood filtration occurs?
Nephron
Glomerulus
Loop of Henle
Bowman’s capsule
The nephron is the complete functional unit of the kidney, consisting of the glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct. Filtration occurs in the glomerulus, but the nephron handles filtration, reabsorption, secretion, and excretion. Bowman’s capsule only encloses the glomerulus. Khan Academy: Kidneys
Which term describes an enzyme regulation where binding of substrate at one active site affects binding at another?
Cooperative binding
Competitive inhibition
Irreversible inhibition
Feedback inhibition
Cooperative binding occurs in multimeric enzymes where substrate binding to one active site increases the affinity at other sites. Hemoglobin is a classic example with oxygen binding. This ability to amplify binding response is essential for many regulatory proteins. Khan Academy: Enzymes
Marine bony fish maintain osmotic balance by:
Drinking seawater and excreting excess salts
Excreting large volumes of dilute urine
Absorbing water through gills via osmosis
Producing urea to retain water
Marine bony fish live in a hypertonic environment, so they drink seawater and actively excrete excess salts through specialized chloride cells in their gills. They produce small volumes of concentrated urine to conserve water. Freshwater fish perform the opposite strategy. Khan Academy: Osmoregulation
In a cross between red-flowered (RR) and white-flowered (rr) plants showing incomplete dominance, what is the phenotypic ratio in the F2 generation?
1 red : 2 pink : 1 white
3 red : 1 white
9 red : 3 pink : 3 white : 1 variegated
1 red : 1 white
Incomplete dominance produces heterozygotes with intermediate phenotype. Crossing RR × rr yields all Rr pink flowers in F1. Selfing F1 yields F2 with genotypes RR, Rr, rr in a 1:2:1 ratio, translating to red:pink:white flowers. Khan Academy: Incomplete Dominance
How many net ATP molecules are typically produced per glucose molecule during aerobic respiration in eukaryotic cells?
32
2
4
18
Aerobic respiration yields about 30–32 ATP per glucose in eukaryotes via glycolysis, Krebs cycle, and oxidative phosphorylation. The exact number varies by shuttle systems and proton leak. This net total accounts for ATP consumed in early steps. Khan Academy: Oxidative Phosphorylation
Gene linkage distance between two loci is determined by:
Recombination frequency
Mutation rate
Gene expression level
Chromosome number
Recombination frequency, measured during meiosis, reflects the physical distance between genes on a chromosome. A 1% recombination frequency equals one map unit. Genes close together recombine less frequently. This forms the basis of genetic linkage mapping. Khan Academy: Gene Mapping
Which technique is used to transfer DNA fragments from an agarose gel onto a membrane for probe hybridization?
Southern blotting
Northern blotting
Western blotting
Eastern blotting
Southern blotting uses a DNA probe to detect specific DNA sequences transferred from a gel to a membrane. Northern blotting detects RNA and Western blotting detects proteins. Eastern blotting is a rare variant for post-translational modifications. Khan Academy: DNA Technology
Ecological succession on an abandoned agricultural field typically culminates in a:
Climax community
Pioneer community
Seral community
Transient community
Ecological succession proceeds from pioneer species colonizing bare ground to intermediate seral communities, and ultimately reaches a stable climax community with balanced energy flow. The climax community persists until disturbed. Agricultural fields often progress through predictable stages. Khan Academy: Ecological Succession
The CRISPR-Cas9 system achieves targeted genome editing by:
Creating double-strand breaks at specific DNA sequences
Methylating target DNA to silence genes
Inserting RNA directly into the genome
Cleaving single-stranded RNA transcripts
CRISPR-Cas9 uses a guide RNA to direct the Cas9 nuclease to a complementary DNA sequence, where it creates a double-strand break. The cell’s repair machinery then introduces mutations or inserts new sequences. This precise targeting revolutionized gene editing. Nature Reviews Immunology: CRISPR
Genetic drift has the greatest evolutionary impact in populations that are:
Small and isolated
Large and panmictic
Under strong selection
Experiencing high gene flow
Genetic drift refers to random fluctuations in allele frequencies, which have a larger effect in small, isolated populations due to sampling error. In large populations, allele frequencies remain more stable. Gene flow and selection operate differently. Khan Academy: Genetic Drift
In G-protein coupled receptor signaling, activation of adenylyl cyclase leads to production of:
Cyclic AMP (cAMP)
Inositol triphosphate (IP3)
Diacylglycerol (DAG)
ATP
When a GPCR activates a Gs protein, the ? subunit stimulates adenylyl cyclase to convert ATP to cyclic AMP (cAMP), a second messenger. cAMP activates protein kinase A, leading to downstream phosphorylation events. IP3 and DAG arise from phospholipase C activation by Gq proteins. Khan Academy: GPCR Signaling
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Study Outcomes

  1. Understand Fundamental IB Biology Concepts -

    Grasp key topics such as cell structure, genetics, and physiology to build a strong foundation for answering ib biology practice questions.

  2. Apply Theoretical Knowledge -

    Use your understanding of biology IB questions to solve ib biology test questions accurately and confidently.

  3. Analyze Question Stems -

    Break down ib biology sample questions to identify critical keywords and determine the precise information required for correct answers.

  4. Interpret Experimental Data -

    Read and draw conclusions from graphs, tables, and lab scenarios commonly found in ib biology quiz items.

  5. Evaluate Your Performance -

    Assess your results to pinpoint areas for improvement and tailor your study plan for the official IB exam.

  6. Develop Test-Taking Strategies -

    Learn time management and critical-thinking techniques to boost speed and accuracy on ib biology test questions.

Cheat Sheet

  1. Membrane Transport and Water Potential -

    Review diffusion, osmosis, facilitated diffusion and active transport with Fick's law (Rate ∝ (ΔC × Area)/Thickness) to predict molecule movement across membranes. Use the water potential equation (Ψ = Ψs + Ψp) and mnemonic "S for solute, P for pressure" to calculate water flow in plant cells. Practice ib biology practice questions on tonicity to master how cells respond in hypertonic, hypotonic and isotonic solutions.

  2. Enzyme Kinetics and Inhibition -

    Understand the Michaelis-Menten equation (v = Vmax [S]/(Km + [S])) and how Lineweaver - Burk plots (1/v vs. 1/[S]) linearize data for Km and Vmax determination. Differentiate competitive vs. non-competitive inhibition; remember "competes at the spot" for competitive inhibitors raising Km but not Vmax. Tackle biology ib questions that ask you to interpret rate curves under varying inhibitor concentrations.

  3. Genetic Inheritance and Hardy-Weinberg -

    Master monohybrid and dihybrid crosses using Punnett squares and understand key ratios (3:1 or 9:3:3:1). Apply the Hardy-Weinberg equations p + q = 1 and p² + 2pq + q² = 1 to calculate allele and genotype frequencies in large, stable populations. Work through ib biology test questions on genetic drift and selection pressures to see when H-W assumptions break down.

  4. Photosynthesis and Energy Conversion -

    Balance the overall photosynthesis equation (6 CO₂ + 6 H₂O → C₆H₝₂O₆ + 6 O₂) and distinguish light-dependent from Calvin cycle stages, noting where ATP and NADPH form. Recall chloroplast structure (thylakoid membranes for light reactions, stroma for carbon fixation) with the mnemonic "Tom's Stroma, Tiny Thylakoids." Practice ib biology sample questions that ask you to label diagrams and calculate energy yields.

  5. Homeostasis and Negative Feedback -

    Learn the components of feedback loops: receptor, control center, and effector - think RICE (Receptor, Integrator, Control, Effector). Examine thermoregulation case studies (e.g., vasodilation vs. vasoconstriction) to see how set-points are maintained. Test yourself with ib biology quiz scenarios on blood glucose regulation involving insulin and glucagon feedback mechanisms.

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