The HESI A2 is a critical entrance exam for nursing and allied health programs across the United States. It evaluates a candidate’s academic readiness across multiple subjects, with biology and chemistry representing two of the most scientifically demanding sections on the entire test. Nursing schools use these scores to determine whether applicants have the foundational science knowledge needed to succeed in rigorous healthcare education programs. A strong performance in these two areas significantly improves admission chances.
Many applicants enter HESI A2 preparation without fully appreciating how deeply the biology and chemistry sections test conceptual knowledge rather than simple memorization. Both sections require candidates to apply what they know to answer questions about processes, relationships, and outcomes. Students who build genuine comprehension of the underlying science rather than relying on surface-level memorization consistently outperform those who simply review notes without truly engaging with the material at a meaningful conceptual level.
Cell Biology Fundamental Concepts
Cell biology forms the backbone of the HESI A2 biology section, and a thorough review of cellular structure and function is essential for every candidate. The exam tests knowledge of both prokaryotic and eukaryotic cells, including the distinguishing features of each cell type. Candidates must be able to identify and describe the function of major organelles such as the nucleus, mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, and the cell membrane. Understanding how these structures work together to sustain cellular life is central to performing well.
Cell division is another high-priority topic within this category. Mitosis and meiosis are both tested, and candidates must understand the distinct phases of each process as well as the biological purpose each type of division serves. Mitosis produces genetically identical daughter cells for growth and tissue repair, while meiosis produces genetically diverse gametes for sexual reproduction. Knowing the key differences between these two processes, including the number of divisions, the resulting cell count, and the chromosome number in daughter cells, is critical for answering exam questions accurately.
Genetics and Heredity Review
Genetics is a consistently tested topic on the HESI A2 biology section, and candidates should devote significant study time to understanding how traits are inherited and expressed. Mendelian genetics provides the foundational framework, covering concepts such as dominant and recessive alleles, homozygous and heterozygous genotypes, and the use of Punnett squares to predict the probability of specific trait combinations in offspring. Being comfortable with monohybrid and dihybrid crosses is important because these types of problems appear regularly on the exam.
Beyond basic Mendelian principles, candidates should also review more complex inheritance patterns including codominance, incomplete dominance, and sex-linked traits. Understanding how blood type inheritance works, how X-linked conditions are passed through families, and how phenotype ratios shift under different inheritance models gives candidates the analytical tools needed to tackle a wide range of genetics questions. Practicing Punnett square problems regularly until they become fast and automatic is one of the best investments a candidate can make during HESI A2 preparation.
Biological Macromolecules Explained
The four major biological macromolecules, carbohydrates, lipids, proteins, and nucleic acids, are a foundational topic in the HESI A2 biology section. Each macromolecule has a distinct chemical structure, a specific set of biological functions, and characteristic building blocks that candidates must be able to identify. Carbohydrates serve primarily as energy sources and structural components, lipids function in energy storage and membrane structure, proteins carry out an enormous variety of structural and functional roles, and nucleic acids store and transmit genetic information.
Understanding the monomer-polymer relationship for each macromolecule group is particularly important. Monosaccharides build polysaccharides, amino acids build proteins, fatty acids and glycerol build lipids, and nucleotides build DNA and RNA. Knowing the types of chemical bonds that hold these monomers together, such as peptide bonds in proteins and glycosidic bonds in carbohydrates, adds an additional layer of understanding that helps candidates answer more detailed exam questions. Reviewing the structure of DNA versus RNA and the roles of each in protein synthesis also falls within this study area.
Photosynthesis and Cellular Respiration
Photosynthesis and cellular respiration are two interconnected biological processes that are regularly tested on the HESI A2 biology section. Photosynthesis occurs in chloroplasts and converts light energy into chemical energy stored in glucose, using carbon dioxide and water as raw materials and releasing oxygen as a byproduct. Candidates must be familiar with the two main stages of photosynthesis, the light-dependent reactions and the Calvin cycle, and understand what inputs and outputs are associated with each stage.
Cellular respiration is the complementary process by which cells break down glucose to release the energy stored in its chemical bonds, producing ATP for cellular work. The three main stages, glycolysis, the Krebs cycle, and the electron transport chain, each occur in different cellular locations and yield different amounts of ATP. Candidates who understand the overall flow of energy through these stages, including the role of electron carriers such as NADH and FADH2, are well equipped to answer both straightforward recall questions and more analytical process-based questions on the exam.
Evolution and Natural Selection
Evolution is another topic that appears on the HESI A2 biology section, and candidates should review the core principles of natural selection and evolutionary change. Charles Darwin’s theory of natural selection rests on the observations that organisms within a population vary in their traits, that some traits improve survival and reproduction in a given environment, and that advantageous traits are passed to offspring at higher rates over successive generations. Over time, this process drives changes in the genetic composition of populations and can eventually lead to the formation of new species.
Candidates should also be familiar with related concepts such as genetic drift, gene flow, mutation, and the role each plays in driving evolutionary change. The Hardy-Weinberg principle, which describes the conditions under which allele frequencies in a population remain stable across generations, is also worth reviewing. Comparative anatomy, fossil evidence, molecular homology, and biogeography are among the types of evidence that support evolutionary relationships between species, and being able to connect these lines of evidence to evolutionary conclusions is a useful skill for answering higher-order biology questions.
Basic Atomic Structure Chemistry
The chemistry section of the HESI A2 begins with foundational concepts in atomic structure, and candidates should ensure they have a solid grasp of this material before moving on to more complex topics. Every atom consists of a nucleus containing protons and neutrons surrounded by electrons arranged in energy levels or shells. The number of protons in an atom defines its atomic number and determines which element it represents, while the mass number reflects the combined count of protons and neutrons in the nucleus.
Isotopes are atoms of the same element that differ in their number of neutrons, resulting in different mass numbers. Candidates should understand what isotopes are, how to identify them, and why they matter in biological and medical contexts, as radioactive isotopes have applications in diagnostic imaging and cancer treatment. The periodic table organizes elements by atomic number and groups them according to shared chemical properties, and being able to read and interpret the information presented on the periodic table is a fundamental chemistry skill for the exam.
Chemical Bonding and Reactions
Chemical bonding is a core chemistry topic on the HESI A2, and candidates must be comfortable with the different types of bonds that hold atoms and molecules together. Ionic bonds form when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other. Covalent bonds form when atoms share electrons, and the degree of electron sharing can be equal in nonpolar covalent bonds or unequal in polar covalent bonds depending on the relative electronegativity of the bonded atoms.
Chemical reactions involve the breaking of existing bonds and the formation of new ones, resulting in the conversion of reactants into products. Candidates should be able to identify and balance basic chemical equations, recognizing that matter is neither created nor destroyed during a chemical reaction. Understanding the difference between endothermic and exothermic reactions, knowing what catalysts do, and being familiar with common reaction types such as synthesis, decomposition, single replacement, and double replacement reactions all contribute to a stronger performance on the chemistry portion of the exam.
Acids Bases and pH
Acids and bases are a high-priority topic on the HESI A2 chemistry section and are also deeply relevant to biology because the pH of biological fluids profoundly affects cellular function. An acid is a substance that donates protons or hydrogen ions to a solution, while a base accepts protons or donates hydroxide ions. The pH scale runs from zero to fourteen, with values below seven indicating acidic conditions, seven representing neutrality, and values above seven indicating basic or alkaline conditions.
The body maintains tight pH regulation through buffer systems that resist changes in pH when acids or bases are added to biological fluids. Blood pH, for example, is maintained within a narrow range of approximately 7.35 to 7.45, and deviations from this range can have serious physiological consequences. Understanding how buffers work, knowing the difference between strong and weak acids and bases, and being able to predict how changes in hydrogen ion concentration affect pH are all important skills for answering chemistry questions that touch on biological applications.
Solutions and Concentration Concepts
Solutions are homogeneous mixtures in which a solute is dissolved in a solvent, and the chemistry of solutions is another tested area on the HESI A2. Water is the most biologically important solvent, and its polar nature makes it highly effective at dissolving ionic compounds and polar molecules. Candidates should understand what it means for a substance to be hydrophilic or hydrophobic and how solubility relates to the chemical properties of both the solute and the solvent.
Concentration describes the amount of solute dissolved in a given volume of solution, and candidates should be familiar with common ways of expressing concentration including molarity and percentage solutions. Osmosis, the movement of water across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration, is a concept that bridges chemistry and biology and appears regularly on the HESI A2. Understanding the difference between isotonic, hypertonic, and hypotonic solutions and predicting how cells respond when placed in each type of solution is essential exam knowledge.
Periodic Table Element Groups
The periodic table is an organizational tool that reveals patterns in element properties, and familiarity with the major element groups gives candidates a significant advantage on the HESI A2 chemistry section. Alkali metals in Group 1 are highly reactive metals that readily lose one electron to form positive ions. Alkaline earth metals in Group 2 are also reactive but less so than alkali metals, and they play important biological roles, with calcium and magnesium being essential nutrients for human health.
The halogens in Group 17 are highly reactive nonmetals that readily gain one electron to form negative ions and are known for their use in disinfection and water treatment. Noble gases in Group 18 are chemically inert under normal conditions because their outermost electron shells are completely filled. Transition metals occupy the central block of the periodic table and include many biologically important elements such as iron, which carries oxygen in hemoglobin, and zinc, which plays a structural role in many proteins. Recognizing the properties associated with each major group helps candidates answer questions about element behavior and chemical reactivity more confidently.
Biochemistry Bridging Both Subjects
Biochemistry sits at the intersection of biology and chemistry, and its principles appear in both sections of the HESI A2. Enzyme function is one of the most important biochemistry topics to review. Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for a reaction to proceed. Each enzyme has a specific active site that binds to its substrate, forming an enzyme-substrate complex that facilitates the chemical transformation before releasing the product.
Factors that affect enzyme activity including temperature, pH, substrate concentration, and the presence of inhibitors or activators are all tested on the exam. Competitive inhibitors block enzyme activity by occupying the active site, while noncompetitive inhibitors bind elsewhere on the enzyme and alter its shape. Understanding how these variables influence reaction rates helps candidates answer questions about enzyme behavior in both normal physiological conditions and abnormal situations such as fever, acidosis, or drug interactions, all of which are relevant to nursing practice.
Effective Study Habits Formation
Building effective study habits is just as important as knowing the content when preparing for the HESI A2. Passive review of notes is rarely sufficient for a science exam that demands genuine comprehension and application. Active study strategies such as explaining concepts aloud, drawing diagrams from memory, teaching material to a study partner, and working through practice questions all engage the brain more deeply and produce stronger long-term retention of the material being studied.
Spacing study sessions over several weeks rather than attempting to cover everything in a few intensive days before the exam leads to significantly better outcomes. The spacing effect is a well-documented learning principle that demonstrates information reviewed at regular intervals over time is retained far more reliably than information reviewed in a single concentrated session. Creating a weekly study schedule that revisits biology and chemistry topics multiple times before the exam date, rather than covering each topic once and moving on, is one of the most evidence-based approaches to HESI A2 preparation.
Practice Questions and Mock Tests
Working through practice questions and full-length mock exams is one of the most effective preparation strategies available to HESI A2 candidates. Practice questions expose candidates to the style and difficulty level of actual exam questions, help identify knowledge gaps, and build the test-taking stamina needed to maintain focus across a lengthy exam. Many HESI A2 preparation books and online platforms offer subject-specific question banks as well as full-length practice tests that simulate the real exam experience.
Reviewing every incorrect practice question in detail after completing a practice session is just as valuable as answering the questions themselves. Understanding why a particular answer was wrong and identifying the correct reasoning behind the right answer prevents the same mistake from recurring on the actual exam. Keeping a running log of topics where errors occur most frequently helps candidates prioritize their remaining study time and ensures that the final days before the exam are spent reinforcing the most problematic areas rather than reviewing content that is already well understood.
Conclusion
Success on the HESI A2 biology and chemistry sections is not a matter of luck or raw intelligence but rather the direct result of deliberate, consistent, and well-organized preparation. Both sections test a meaningful breadth of scientific knowledge that builds cumulatively, meaning that foundational concepts must be understood before more advanced topics can be properly grasped. Candidates who approach their preparation systematically, starting with the basics and layering in complexity over time, consistently achieve stronger results than those who study randomly or without a clear plan.
Biology preparation should prioritize cell structure and function, genetics, macromolecules, photosynthesis, cellular respiration, and evolution, as these topics form the core of what the exam tests most frequently. Chemistry preparation should focus on atomic structure, chemical bonding, acids and bases, solutions, the periodic table, and biochemical principles, particularly enzyme function, which bridges both subject areas in a way that is highly relevant to nursing education. Knowing which topics carry the most exam weight allows candidates to allocate their limited study time more strategically and effectively.
Active learning strategies, consistent practice with exam-style questions, and regular review sessions spaced over several weeks are the most reliable tools for building the deep conceptual understanding that the HESI A2 demands. Passive reading and highlighting are not sufficient for an exam that expects candidates to apply their knowledge rather than simply recall isolated facts. Engaging with the material through diagrams, practice problems, self-explanation, and peer discussion produces the kind of durable understanding that holds up under the pressure of a timed, high-stakes testing environment.
Mental preparation and physical wellness in the days leading up to the exam also deserve attention. Adequate sleep, proper nutrition, and a calm, confident mindset contribute meaningfully to exam performance. Candidates who have prepared thoroughly and taken care of their physical wellbeing arrive at the testing center in the best possible state to demonstrate what they have learned. Last-minute cramming is rarely productive and often increases anxiety without adding meaningfully to the knowledge base that weeks of consistent preparation have already built.
Every nursing school applicant who commits fully to HESI A2 preparation gives themselves a genuine competitive advantage in a selective admissions process. Biology and chemistry are not subjects to fear but rather disciplines that reward curiosity, patience, and consistent effort. The scientific knowledge tested on the HESI A2 is also directly relevant to nursing practice, meaning that the time invested in preparation is not wasted after the exam but continues to pay dividends throughout the entire healthcare education journey that follows a successful admission.