HESI Biology Test Overview

The Biology section of the HESI A2 exam evaluates a student’s foundational understanding of life science concepts. Biology underpins nearly every aspect of healthcare education — from understanding how the body functions at the cellular level to grasping how diseases develop and how treatments work. A solid biology background gives students a meaningful head start in courses like anatomy, physiology, microbiology, and pharmacology.

Purpose and Context

Nursing and allied health programs require students to rapidly absorb complex biological concepts. Whether learning about cellular respiration, genetic inheritance, or how the immune system responds to pathogens, students who arrive with strong biology fundamentals adapt more quickly and perform better academically. The HESI Biology section confirms that applicants have the scientific literacy needed to succeed in these rigorous programs.

Test Format

The Biology section typically consists of 25 questions and is allotted approximately 25 minutes, maintaining the one-minute-per-question pace seen across the exam. It is computer-based and entirely multiple choice. While shorter than some other sections, the Biology test covers a surprisingly broad range of concepts, so efficient and accurate recall matters greatly.

Topics and Skills Assessed

Basic Biology and the Chemistry of Life The test begins at the most fundamental level — the building blocks of living systems. You should understand the basic properties of water and why they matter to living organisms, including cohesion, adhesion, and water’s role as a solvent. The chemistry of life also encompasses the four major macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Knowing the structure, function, and examples of each is essential. Questions may also address basic concepts like pH, acids and bases, and how chemical bonds hold biological molecules together.

The Cell Cell biology is one of the most heavily tested areas on the HESI Biology section. You should be comfortable with the differences between prokaryotic and eukaryotic cells, and between plant and animal cells. Familiarity with the major organelles and their functions is critical — this includes the nucleus, mitochondria, ribosomes, endoplasmic reticulum (both rough and smooth), Golgi apparatus, lysosomes, vacuoles, chloroplasts, and the cell membrane. Understanding the cell membrane’s structure — the phospholipid bilayer and the concept of selective permeability — is particularly important.

Cellular Transport Questions on how substances move in and out of cells appear regularly. You should understand passive transport — including diffusion, osmosis, and facilitated diffusion — and how each works without the expenditure of energy. Active transport, which requires ATP to move substances against a concentration gradient, is also tested. Concepts like tonicity (hypertonic, hypotonic, and isotonic solutions) and their effects on cells are frequently included, as they have direct clinical relevance in areas like IV fluid administration.

Cellular Respiration This topic covers how cells produce energy in the form of ATP. You should understand the overall process of cellular respiration, including the roles of glycolysis, the Krebs cycle, and the electron transport chain. Knowing where each stage occurs within the cell, what inputs are required, and what outputs are produced — particularly the net ATP yield — is important. The distinction between aerobic and anaerobic respiration, and examples of anaerobic processes like fermentation, is also tested.

Photosynthesis While more plant-focused than most healthcare content, photosynthesis appears on the HESI Biology section as a foundational life science concept. You should understand the overall equation for photosynthesis, the roles of the light-dependent and light-independent (Calvin cycle) reactions, and where these reactions occur within the chloroplast. Understanding photosynthesis as essentially the reverse of cellular respiration — in terms of inputs and outputs — can help you keep the two processes organized in your mind.

Mitosis and Meiosis Cell division is a consistently tested topic. Mitosis, which produces two genetically identical daughter cells, is used for growth and tissue repair. You should know the stages — prophase, metaphase, anaphase, and telophase — and what happens during each. Meiosis, which produces four genetically unique haploid cells, is used in sexual reproduction. Understanding the key differences between mitosis and meiosis, including the significance of crossing over in meiosis, is important. Questions may also address the cell cycle, including interphase and the checkpoints that regulate it.

Genetics and Heredity This category covers the principles of inheritance established by Gregor Mendel. You should understand dominant and recessive alleles, homozygous and heterozygous genotypes, and how to use a Punnett square to predict the outcomes of genetic crosses. Phenotype versus genotype, and the relationship between the two, is frequently tested. Co-dominance and incomplete dominance may also appear, as may basic concepts related to sex-linked traits and how they are inherited differently from autosomal traits.

DNA and Protein Synthesis You should understand the structure of DNA — the double helix, complementary base pairing (adenine with thymine, cytosine with guanine), and the role of the sugar-phosphate backbone. The processes of DNA replication, transcription, and translation should be familiar, including where each occurs in the cell and what molecules are involved. Understanding the flow of genetic information — DNA to RNA to protein — is a central concept in modern biology and appears regularly on the HESI.

Evolution and Natural Selection Basic evolutionary concepts appear on the Biology section, though not in great depth. You should understand Darwin’s theory of natural selection, the concept of adaptation, and how populations change over time in response to environmental pressures. Familiarity with terms like fitness, variation, and selective pressure is helpful, as are the basic mechanisms of evolution such as mutation and genetic drift.

Ecology Some questions address ecological concepts — the relationships between organisms and their environments. This includes understanding food chains and food webs, the flow of energy through ecosystems, trophic levels, and the roles of producers, consumers, and decomposers. Basic concepts like carrying capacity, population dynamics, and symbiotic relationships (mutualism, commensalism, and parasitism) may also appear.

Scoring

The Biology section is scored on the same 0–100% scale as all other HESI A2 sections. Most programs require a minimum of 75%, with more competitive programs setting the bar at 80% or above. Because the section contains only 25 questions, each question carries more weight than in longer sections — a single incorrect answer has a greater impact on your overall percentage score, making careful preparation across all topic areas important.

How It Compares to Other Sections

The Biology section is relatively short but conceptually broad. Students with a recent high school or college biology course under their belt often find the content familiar, though the pace and question density can still be challenging. Those who have been away from science coursework for several years may find this one of the more demanding sections to prepare for, as the content requires genuine understanding rather than simple memorization. Rote recall of facts helps, but many questions ask you to apply concepts — predicting the outcome of a genetic cross, determining what will happen to a cell placed in a hypertonic solution, or identifying where a particular stage of cellular respiration occurs.

Preparation Tips

Review a general biology textbook or study guide. A solid introductory biology textbook — or a condensed study guide covering the same material — provides the most comprehensive foundation. Focus especially on the chapters covering cell biology, genetics, and cellular respiration, as these are the most heavily represented on the exam.

Draw and label diagrams. Visual learners benefit greatly from drawing the cell and labeling its organelles, sketching out the stages of mitosis and meiosis, or mapping the flow of cellular respiration. The act of drawing reinforces memory and helps you organize complex processes spatially.

Understand processes, not just facts. Many Biology questions ask you to reason through a scenario rather than simply recall a definition. Make sure you understand why and how biological processes work, not just that they exist.

Use Punnett squares until they are automatic. Genetics questions involving Punnett squares are among the most straightforward on the test if you’ve practiced them — and among the most time-consuming if you haven’t. Run through a variety of monohybrid and dihybrid crosses in your preparation.

Connect biology to clinical contexts. Wherever possible, link biological concepts to their healthcare relevance. Understanding osmosis becomes more memorable when connected to IV fluid tonicity. Understanding cellular respiration becomes more meaningful when connected to why oxygen delivery is critical in patient care. These connections deepen understanding and make recall more reliable.

Use the official Elsevier study guide. The HESI Admission Assessment Exam Review contains biology practice questions that closely mirror the format and difficulty of the real exam and is the most targeted preparation resource available.

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Overall, the HESI Biology section rewards students who combine solid foundational knowledge with the ability to apply concepts in new contexts. With focused review across the major topic areas — particularly cell biology, genetics, and cellular processes — most students can achieve a strong score even if their last biology course was several years ago.