Free HESI A2 Biology practice test
23 original Biology questions on biology basics, water, biological molecules, metabolism, the cell, cellular respiration, photosynthesis, cellular reproduction, genetics, dna.
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HESI A2 Biology practice test
- 23 questions
- Biology
- 19 min in exam mode
- Practice mode, no timer
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Questions are original practice items written to the published exam content, not real exam questions.
Which level of biological organization is the smallest unit that can carry out all the functions of life?
Correct answer: C
The cell is the smallest unit of structure and function in living things, and cell theory states that the cell is the basic unit of life. Levels below it, such as organelles and molecules, are parts of a cell and cannot live on their own. Levels above it, such as tissues, are built from many cells.
- A An organelle is a part inside a cell; it cannot carry out all life functions on its own.
- B Molecules such as DNA are needed for life but are not alive by themselves; this confuses a building block with a living unit.
- C Correct: the cell is the smallest level that is alive on its own; everything below it is only a part of a cell.
- D A tissue is a group of similar cells, so it is a higher level built from cells, not the smallest unit.
Learn this topic: What counts as alive, and how biologists sort living things 5-minute lesson
Source: OpenStax Biology 2e, 1.2 Themes and Concepts of Biology · OpenStax Biology 2e, 4.1 Studying Cells ·
A newly discovered single-celled organism has a plasma membrane, ribosomes, and DNA located in a region of the cytoplasm with no membrane around it. It has no membrane-bound organelles. Which conclusion is best supported?
Correct answer: C
Prokaryotes (bacteria and archaea) have no nucleus and no membrane-bound organelles; their DNA sits in a region called the nucleoid. Ribosomes, a plasma membrane, cytoplasm, and DNA are found in all cells, so they do not show that a cell is eukaryotic. Being single-celled does not make an organism a protist, because bacteria and archaea are single-celled too.
- A All cells, prokaryotic and eukaryotic, have ribosomes, so ribosomes cannot identify a eukaryote.
- B Lacking a nucleus does not make a cell nonliving; prokaryotes are living cells without a nucleus.
- C Correct: DNA in a nucleoid with no nucleus and no membrane-bound organelles is the defining pattern of a prokaryote.
- D Protists are eukaryotes with a nucleus; being single-celled alone does not make an organism a protist.
Learn this topic: What counts as alive, and how biologists sort living things 5-minute lesson
Source: OpenStax Biology 2e, 4.2 Prokaryotic Cells · OpenStax Biology 2e, 1.2 Themes and Concepts of Biology ·
Two animal species are placed in the same order but in different families. Which other taxonomic rank must they also share?
Correct answer: A
Taxonomic ranks are nested from broadest to most specific: domain, kingdom, phylum, class, order, family, genus, species. Organisms in the same order must share every broader rank above it (class, phylum, kingdom, domain). Because they are in different families, they cannot share any narrower rank, such as genus or species.
- A Correct: class is broader than order, so two members of the same order always belong to the same class.
- B Genus is narrower than family; organisms in different families cannot be in the same genus.
- C Species is the most specific rank; different families rule out sharing a species.
- D The stem says they are in different families; this reverses the direction of the nested ranks.
Learn this topic: What counts as alive, and how biologists sort living things 5-minute lesson
Source: OpenStax Biology 2e, 20.1 Organizing Life on Earth ·
A water strider insect can stand on the surface of a pond without sinking. Which property of water mainly explains this?
Correct answer: B
Cohesion, the attraction of water molecules to each other through hydrogen bonds, creates surface tension at the surface of water. Surface tension lets light objects such as a needle or a water strider rest on the surface. Adhesion is water sticking to other surfaces, and specific heat is about temperature change, not support.
- A Specific heat describes how much heat water absorbs before its temperature changes; it does not hold objects up.
- B Correct: cohesion between water molecules creates surface tension, which supports a water strider.
- C Adhesion is water attaching to other surfaces, such as climbing a glass tube; it confuses water-to-surface with water-to-water attraction.
- D The low density of ice explains why ice floats, not why an insect can stand on liquid water.
Learn this topic: Why water behaves the way it does 5-minute lesson
Source: OpenStax Biology 2e, 2.2 Water ·
During exercise, a runner sweats and her skin cools. Which statement best explains the cooling?
Correct answer: B
Turning liquid water into vapor takes a large amount of energy, because hydrogen bonds between water molecules must be broken. As sweat evaporates, it takes that energy as heat from the skin, so the skin cools. This is called evaporative cooling.
- A Water has a high specific heat, not a low one; this reverses the property.
- B Correct: evaporation absorbs heat energy from the surface it leaves, which cools the skin.
- C Breaking hydrogen bonds during evaporation absorbs energy rather than releasing it, so this has the energy flow backward.
- D Water is a good solvent, but dissolving ions does not remove heat; this confuses the solvent property with cooling.
Learn this topic: Why water behaves the way it does 5-minute lesson
Source: OpenStax Biology 2e, 2.2 Water ·
Suppose water molecules were nonpolar and could not form hydrogen bonds with each other. Which change would most likely result?
Correct answer: D
Water's high specific heat comes from its hydrogen bonds, which absorb and release heat before the molecules speed up or slow down. Without hydrogen bonds, water would change temperature much more easily. Water's polarity is also what lets it dissolve ions and stick to glass, so a nonpolar water would do those things worse, not better.
- A Oil separates from water because oil is nonpolar and water is polar; nonpolar water would be more like oil, not less.
- B Water dissolves salt because its charged ends surround Na+ and Cl- ions; nonpolar water would dissolve salt less easily.
- C Climbing a glass tube depends on adhesion and cohesion from polarity; nonpolar water would climb less, not more.
- D Correct: hydrogen bonds give water its high specific heat, so without them its temperature would change faster.
Learn this topic: Why water behaves the way it does 5-minute lesson
Source: OpenStax Biology 2e, 2.2 Water · OpenStax Concepts of Biology, 2.2 Water ·
Which process is an example of a catabolic pathway?
Correct answer: C
Catabolic pathways break complex molecules into simpler ones and release energy, such as the breakdown of glucose. Anabolic pathways do the opposite: they use energy to build complex molecules from simpler ones. Building proteins, DNA, or sugar are all anabolic.
- A Building a protein from amino acids makes a larger molecule and uses energy, so it is anabolic.
- B Making sugar from carbon dioxide builds a complex molecule from simple ones, an anabolic example.
- C Correct: breaking glucose down into simpler molecules releases energy, which is the definition of catabolism.
- D Joining nucleotides into DNA builds a polymer and requires energy, so it is anabolic.
Learn this topic: How cells build, break down, and speed up reactions 5-minute lesson
A molecule binds to an enzyme's active site and blocks the substrate from binding there. Which change would most likely restore the reaction rate?
Correct answer: A
A molecule that blocks the active site is a competitive inhibitor, because it competes with the substrate for the same spot. Flooding the reaction with substrate makes it more likely that substrate, not inhibitor, occupies the active site, so competitive inhibition can be overcome. Extreme temperature or pH would denature the enzyme and lower activity further.
- A Correct: competitive inhibition can be overcome by a high concentration of substrate, which outcompetes the inhibitor.
- B Temperatures far above the optimum denature the enzyme and reduce activity, which makes the problem worse.
- C A noncompetitive inhibitor binds elsewhere and changes the enzyme shape, so it would slow the reaction even more.
- D A pH far from the optimum can denature the enzyme; this would lower activity, not restore it.
Learn this topic: How cells build, break down, and speed up reactions 5-minute lesson
Source: OpenStax Biology 2e, 6.5 Enzymes ·
An enzyme that works best near pH 2 is placed in a solution at pH 8, at its usual temperature. What is the most likely result?
Correct answer: B
Each enzyme works best within a certain pH range, and conditions far from that range can change its shape, or denature it. When the active site changes shape, the substrate no longer fits well and the reaction slows. Enzymes are never used up by the reactions they speed up, and they lower activation energy without changing the reaction's overall energy change.
- A This enzyme is adapted to strongly acidic conditions; moving it far from its optimum pH lowers activity rather than raising it.
- B Correct: a pH far from the optimum can denature the enzyme, distorting the active site and reducing activity.
- C Enzymes are not consumed by the reactions they catalyze; they come out unchanged and can be reused.
- D Enzymes lower activation energy but never change the total energy a reaction releases or absorbs.
Learn this topic: How cells build, break down, and speed up reactions 5-minute lesson
Source: OpenStax Biology 2e, 6.5 Enzymes ·
Where in a eukaryotic cell does glycolysis take place?
Correct answer: B
Glycolysis, the splitting of glucose into two pyruvate molecules, happens in the cytoplasm of both prokaryotic and eukaryotic cells. The later stages move into the mitochondrion: pyruvate oxidation and the citric acid cycle in the matrix, and the electron transport chain in the inner membrane.
- A The mitochondrial matrix is where pyruvate oxidation and the citric acid cycle happen, after glycolysis.
- B Correct: glycolysis takes place in the cytoplasm.
- C The nucleus stores DNA; no stage of cellular respiration takes place there.
- D The inner mitochondrial membrane holds the electron transport chain, the final stage, not glycolysis.
Learn this topic: How cells turn glucose into ATP 5-minute lesson
Source: OpenStax Biology 2e, 7.2 Glycolysis ·
What is the role of oxygen in aerobic cellular respiration?
Correct answer: A
Oxygen is the final electron acceptor of the electron transport chain in the inner mitochondrial membrane. It picks up spent electrons and hydrogen ions and becomes water. The CO2 released during respiration comes from the carbon of glucose, removed during pyruvate oxidation and the citric acid cycle, and glycolysis does not use oxygen at all.
- A Correct: oxygen is the final electron acceptor in the electron transport chain and is reduced to water.
- B The CO2 comes from carbon atoms stripped from pyruvate and acetyl CoA; the citric acid cycle does not use oxygen directly.
- C Glycolysis splits glucose without using oxygen, so oxygen plays no role in that step.
- D ATP synthase attaches an inorganic phosphate to ADP; oxygen does not supply phosphate.
Learn this topic: How cells turn glucose into ATP 5-minute lesson
Source: OpenStax Biology 2e, 7.4 Oxidative Phosphorylation · OpenStax Biology 2e, 7.3 Oxidation of Pyruvate and the Citric Acid Cycle ·
A human skeletal muscle cell is working hard and runs short of oxygen. Which change is most likely?
Correct answer: C
Without enough oxygen, the electron transport chain cannot accept electrons, so NADH builds up and NAD+ runs short. Lactic acid fermentation turns pyruvate into lactate and regenerates NAD+, which lets glycolysis keep producing its 2 ATP per glucose. Alcohol fermentation, which makes ethanol and CO2, happens in yeast, not in human muscle.
- A Glycolysis does not need oxygen; fermentation lets it keep running and making a small amount of ATP.
- B The Krebs cycle depends on the oxygen-using electron transport chain to recycle its carriers, so it slows rather than speeds up.
- C Correct: muscle cells short on oxygen reduce pyruvate to lactate, regenerating NAD+ so glycolysis can continue.
- D Ethanol and CO2 are products of alcohol fermentation in yeast, not of fermentation in human muscle.
Learn this topic: How cells turn glucose into ATP 5-minute lesson
Source: OpenStax Biology 2e, 7.5 Metabolism without Oxygen · OpenStax Biology 2e, 7.2 Glycolysis ·
In which part of the chloroplast do the light-dependent reactions of photosynthesis take place?
Correct answer: A
The light-dependent reactions happen in the thylakoid membrane, where chlorophyll and the photosystems are embedded. The Calvin cycle happens in the stroma, the fluid around the thylakoids. The mitochondrial matrix is a site of cellular respiration, not photosynthesis.
- A Correct: the light-dependent reactions occur in the thylakoid membrane, which holds chlorophyll.
- B The outer membrane encloses the chloroplast but does not hold the photosystems.
- C The stroma is where the Calvin cycle (light-independent reactions) takes place; this mixes up the two stages.
- D The mitochondrial matrix is part of a mitochondrion and hosts the citric acid cycle, not photosynthesis.
Learn this topic: How plants turn light into sugar 5-minute lesson
Source: OpenStax Biology 2e, 8.1 Overview of Photosynthesis ·
The oxygen gas released by a plant during photosynthesis comes from which molecule?
Correct answer: C
In the light-dependent reactions, photosystem II replaces its lost electrons by splitting water, and this releases oxygen gas. The carbon dioxide is used in the Calvin cycle, where its carbon is built into sugar. A simple rule: water gives the oxygen, carbon dioxide gives the carbon.
- A RuBP is the five-carbon molecule that accepts CO2 in the Calvin cycle; it does not release oxygen.
- B Carbon dioxide supplies carbon for sugar in the Calvin cycle; it is not split to release O2.
- C Correct: splitting water in the light-dependent reactions releases the oxygen gas.
- D Glucose is a product of photosynthesis, not the source of the oxygen released.
Learn this topic: How plants turn light into sugar 5-minute lesson
Source: OpenStax Biology 2e, 8.1 Overview of Photosynthesis · OpenStax Biology 2e, 8.2 The Light-Dependent Reactions of Photosynthesis ·
The Calvin cycle is called light-independent, yet it still depends on light indirectly. Which statement best explains this dependence?
Correct answer: D
The Calvin cycle does not use light as a reactant, but it runs on the ATP and NADPH made by the light-dependent reactions, so it needs the light reactions to keep supplying them. That is why it depends on light indirectly. The old name "dark reactions" is misleading, because it suggests the cycle happens only at night or has nothing to do with light.
- A Light is not a reactant in the Calvin cycle; RuBisCO attaches CO2 to RuBP without absorbing light.
- B Chlorophyll sits in the thylakoid membrane, not the stroma, and the Calvin cycle does not absorb light.
- C Oxygen is a byproduct of the light reactions; the Calvin cycle does not use it to make G3P.
- D Correct: the Calvin cycle spends ATP and NADPH, and only the light-dependent reactions make them.
Learn this topic: How plants turn light into sugar 5-minute lesson
Source: OpenStax Biology 2e, 8.3 Using Light Energy to Make Organic Molecules · OpenStax Biology 2e, 8.1 Overview of Photosynthesis ·
During which phase of mitosis do sister chromatids separate and move to opposite ends of the cell?
Correct answer: B
In anaphase, the sister chromatids pull apart and move to opposite poles, so each end of the cell gets a full set of chromosomes. Before that, chromosomes condense in prophase and line up at the metaphase plate in metaphase. In telophase, new nuclear envelopes form around the two sets.
- A In prophase, chromosomes condense and the spindle forms; the chromatids are still joined.
- B Correct: sister chromatids separate and move to opposite poles in anaphase.
- C In metaphase, chromosomes line up at the metaphase plate but have not yet separated.
- D In telophase, the chromatids have already reached the poles and new nuclear envelopes form.
Learn this topic: How one cell becomes two, or four 6-minute lesson
Source: OpenStax Biology 2e, 10.2 The Cell Cycle ·
Which event happens in meiosis but not in mitosis, and helps make each gamete genetically different?
Correct answer: A
In prophase I of meiosis, homologous chromosomes pair up and nonsister chromatids exchange segments, which is called crossing over. This mixes genetic material and, along with the random alignment of pairs in metaphase I, makes each gamete different. DNA copying, chromosomes lining up, and sister chromatids separating all happen in mitosis too.
- A Correct: crossing over between homologous chromosomes in prophase I occurs only in meiosis and creates genetic variety.
- B DNA is copied in the S phase before both mitosis and meiosis, so it does not distinguish them.
- C Sister chromatids separate in anaphase of mitosis and in anaphase II of meiosis, so this is not unique to meiosis.
- D Chromosomes line up at the metaphase plate in both mitosis and meiosis.
Learn this topic: How one cell becomes two, or four 6-minute lesson
A diploid cell with 8 chromosomes (2n = 8) undergoes meiosis. At the end of meiosis I, how many chromosomes does each new cell have, and what is true of the sister chromatids?
Correct answer: C
Meiosis I is the reduction division: homologous chromosomes separate in anaphase I, so each new cell gets one chromosome from each pair and becomes haploid (n = 4). The sister chromatids of each chromosome stay joined at the centromere until anaphase II. No DNA is copied between meiosis I and meiosis II.
- A Halving 8 gives 4, not 2; and the sister chromatids have not yet separated at this point.
- B The number is right, but sister chromatids separate in anaphase II, not in meiosis I.
- C Correct: separating homologous pairs halves the number to 4, and sister chromatids stay joined until meiosis II.
- D Keeping all 8 chromosomes describes mitosis; meiosis I separates homologs and halves the number.
Learn this topic: How one cell becomes two, or four 6-minute lesson
Source: OpenStax Biology 2e, 11.1 The Process of Meiosis · OpenStax Biology 2e, 10.1 Cell Division ·
A molecule is made of one glycerol molecule bonded to three fatty acid chains. What type of molecule is it?
Correct answer: D
Fats are lipids built from one glycerol and three fatty acids, which is why they are also called triglycerides. Phospholipids have only two fatty acids; a phosphate group takes the third spot, and they form cell membranes. Steroids, such as cholesterol, look very different: four carbon rings linked together.
- A A phospholipid has only two fatty acid chains on its glycerol backbone; a phosphate group takes the third spot.
- B A steroid is built from four linked carbon rings, not from glycerol and fatty acids.
- C A polysaccharide is a long chain of sugar units such as glucose; it has no fatty acids.
- D Correct: glycerol plus three fatty acids is a fat, also called a triglyceride ("tri" for the three fatty acids).
Learn this topic: The four macromolecules of life and how cells build them 5-minute lesson
Source: OpenStax Biology 2e, 3.3 Lipids ·
Cells in the adrenal cortex make large amounts of steroid hormones, which are lipids. Which organelle would you expect to be especially well developed in these cells?
Correct answer: B
The endoplasmic reticulum (ER) comes in two forms. Rough ER is covered with ribosomes and makes proteins; smooth ER has no ribosomes and makes lipids, including phospholipids and steroid hormones. Match the cell's main product to the organelle that makes it.
- A Rough ER is studded with ribosomes and mainly makes proteins, such as secreted enzymes, not lipid hormones.
- B Correct: smooth ER is the main site of lipid synthesis, including phospholipids and steroid hormones.
- C Lysosomes hold enzymes that break down worn-out cell parts; they digest molecules rather than build hormones.
- D The nucleolus is the region of the nucleus where ribosomes are made; it does not make lipids.
Learn this topic: How a cell is built, fed, and copied 6-minute lesson
Source: OpenStax Anatomy and Physiology 2e, 3.2 The Cytoplasm and Cellular Organelles · OpenStax Anatomy and Physiology 2e, 17.6 The Adrenal Glands · OpenStax Biology 2e, 4.3 Eukaryotic Cells ·
A bacterial cell and a human liver cell are compared. Which structure do both cells have?
Correct answer: D
All cells share four parts: a plasma membrane, cytoplasm, DNA, and ribosomes. Bacteria are prokaryotes, so they lack a nucleus and every other membrane-bound organelle; mitochondria and the ER are found only in eukaryotic cells. When a question asks what all cells share, look for one of those four parts.
- A Bacteria are prokaryotes, so their DNA sits in the cytoplasm with no nucleus around it.
- B Mitochondria are membrane-bound organelles, which prokaryotes such as bacteria lack.
- C The endoplasmic reticulum is a membrane-bound organelle found only in eukaryotic cells.
- D Correct: every cell needs ribosomes to make proteins, so prokaryotic and eukaryotic cells both have them.
Learn this topic: How a cell is built, fed, and copied 6-minute lesson
In pea plants, round seeds (R) are dominant to wrinkled seeds (r), and yellow seeds (Y) are dominant to green seeds (y). The two genes sort independently. Two plants that are both RrYy are crossed. What fraction of the offspring are expected to have round, yellow seeds?
Correct answer: A
When two genes sort independently, solve each gene as its own one-gene cross, then multiply. Rr × Rr gives 3/4 round, and Yy × Yy gives 3/4 yellow, so 3/4 × 3/4 = 9/16 are both round and yellow. This is where the classic 9:3:3:1 ratio of a dihybrid cross comes from.
- A Correct: each trait alone gives 3/4 dominant, and for independent genes you multiply: 3/4 × 3/4 = 9/16.
- B 3/16 is the fraction with one dominant and one recessive trait, such as round and green (3/4 × 1/4).
- C 1/16 is the fraction with both recessive traits, wrinkled and green (1/4 × 1/4).
- D 3/4 is the chance of one dominant trait; for both traits at once you must multiply the two chances.
Learn this topic: How traits pass from parents to children 6-minute lesson
The coding part of an mRNA molecule is 300 nucleotides long, not counting the stop codon. How many amino acids does this sequence code for?
Correct answer: D
The genetic code is read in groups of three nucleotides called codons, and each codon in the coding part stands for one amino acid. Divide the number of coding nucleotides by 3 to get the number of amino acids. A stop codon ends translation and adds no amino acid, which is why it is left out of the count.
- A This assumes each nucleotide codes for one amino acid, but each amino acid takes three nucleotides.
- B This treats a codon as two nucleotides; codons are three nucleotides long.
- C This multiplies by 3 instead of dividing; each amino acid uses three nucleotides, so there are fewer amino acids than nucleotides.
- D Correct: each three-nucleotide codon codes for one amino acid, so 300 ÷ 3 = 100.
Learn this topic: How a gene in DNA becomes a protein 6-minute lesson
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Each program picks the sections and sets its own minimum.
| Program | Sections | Minimum |
|---|---|---|
| Baylor University | Math, English composite | 80 or better on each |
| Lone Star College, ADN | Reading, Grammar, Vocabulary, A&P, Math, Critical Thinking | 80 on each section (750 for Critical Thinking) |
| University of Arizona | Math, Reading, Vocabulary, Biology | 75% combined score |
| CNM (New Mexico) | Grammar, Reading, Vocabulary, Biology, Chemistry, Math | 75% on every section and 75% composite |
Your score is the percent you got right in each section. The real HESI A2 also scores each section as percent correct, and your cumulative score is the average of the sections you took.
Rules change every year. Always check your own program’s page. Checked October 15, 2026.
HESI A2 format
| Section | Questions (scored) | Suggested time |
|---|---|---|
| Reading | 55 (50) | 60 min |
| Vocabulary | 55 (50) | 50 min |
| Grammar | 55 (50) | 50 min |
| Math | 55 (50) | 50 min |
| Biology | 30 (25) | 25 min |
| Chemistry | 30 (25) | 25 min |
| Anatomy & Physiology | 30 (25) | 25 min |
Five questions in each section are unscored pilot items. Elsevier doesn’t publish these numbers; they come from nursing programs’ pages.
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Sources (checked October 15, 2026)
- Elsevier, HESI NG A2 faculty guide (schools choose modules, calculator and time)
- South Texas College, HESI exam information (50 scored + 5 pilot items)
- Tarrant County College, HESI A2 exam information
- Baylor University, HESI A2 information
- Lone Star College, HESI A2 test
- University of Arizona, HESI admission assessment
- CNM, HESI A2 exam