HESI A2 Biology Study Guide: Topics, Terms & How to Study

Biology is one of the three science modules on the HESI A2, and it is the one most applicants underestimate. The questions are not graduate-level — they are first-semester general biology — but they cover a wide span of material in a short test, so a few forgotten definitions can cost you real points. This guide walks through what the Biology section actually tests, the terms that show up most often, and a study approach that fits the exam instead of fighting it.

Does your nursing program even require HESI A2 Biology?

Start here, because the HESI A2 is modular. Health Education Systems, Inc. offers a menu of sections and each nursing program picks the ones it wants. A school might require Math, Reading, Vocabulary, Grammar, Anatomy & Physiology, Biology, and Chemistry — or only three of them.

Before you build a study plan:

• Find your program’s required section list in writing (admissions page, information packet, or an email from the nursing advisor).
• Ask what score they expect and whether it is a per-section minimum or a composite average. Requirements vary a lot between schools.
• Confirm the retake policy and waiting period before your first attempt, not after.

If Biology is not on your list, spend that time on the sections that are. If it is, keep reading — it rewards focused review better than almost any other module.

What the Biology section covers

HESI A2 Biology is a general-biology survey. The content outline published for the exam centers on a handful of recurring areas:

• Water and its properties — polarity, hydrogen bonding, cohesion, surface tension, why water is a good solvent, pH and the acid/base scale.
• Biological macromolecules — carbohydrates, lipids, proteins, and nucleic acids: what each is built from and what it does.
• Cells and cellular transport — organelles and their jobs, the plasma membrane, diffusion, osmosis, active vs. passive transport.
• Metabolism — enzymes, ATP, cellular respiration, and photosynthesis at a conceptual level.
• Cellular reproduction — the cell cycle, mitosis vs. meiosis, and why the difference matters.
• Genetics and DNA — DNA structure, base pairing, replication, transcription and translation, dominant and recessive inheritance, Punnett squares.

The section is short — commonly around 25 questions, and some versions include a few unscored pilot items. Because the question count is small relative to the breadth of content, you are more likely to see one question from each topic than five questions from your favorite one. Broad, shallow review beats a deep dive into a single chapter.

The terms worth memorizing cold

A large share of Biology items are definition- or function-recognition questions. These are free points if the vocabulary is automatic:

• Organelles: mitochondria (ATP production), ribosomes (protein synthesis), rough ER (protein processing), smooth ER (lipid synthesis, detox), Golgi apparatus (packaging and shipping), lysosomes (digestion of waste), nucleus (houses DNA).
• Transport: diffusion moves solute down its gradient; osmosis moves water across a membrane; active transport moves substances against a gradient and costs ATP. Know hypotonic (cell swells), hypertonic (cell shrinks), and isotonic (no net change) — these reappear constantly in nursing coursework and IV-fluid questions later.
• Macromolecule building blocks: monosaccharides → carbohydrates; fatty acids and glycerol → lipids; amino acids → proteins; nucleotides → nucleic acids.
• Genetics: genotype (the alleles) vs. phenotype (the visible trait); homozygous vs. heterozygous; dominant vs. recessive; DNA base pairing (A–T, C–G) and RNA’s substitution of uracil for thymine.
• Division: mitosis makes two genetically identical diploid cells for growth and repair; meiosis makes four genetically varied haploid gametes.

Concepts that trip people up

Three areas account for a disproportionate number of missed questions:

1. Mitosis vs. meiosis. People memorize the phase names and then miss the question, because the item asks about the outcome: how many daughter cells, how many chromosomes, identical or varied. Learn the outcomes first and the phase names second.
2. Respiration vs. photosynthesis. Don’t try to memorize every intermediate. Hold onto the direction of each: photosynthesis uses light, carbon dioxide, and water to build glucose and release oxygen; cellular respiration breaks glucose down with oxygen to release ATP, carbon dioxide, and water. Then add the stages (glycolysis, Krebs cycle, electron transport chain) and where each happens.
3. DNA to protein. Keep the sequence straight: DNA is transcribed into mRNA in the nucleus, then mRNA is translated into a protein at the ribosome. If you can state that sentence and name the base pairs, most items in this area become answerable.

Note how much of this overlaps with the other science modules. If your program also requires them, study them in the same block rather than separately — our HESI A2 Anatomy & Physiology guide and HESI A2 Chemistry guide cover the material that sits right next to Biology on the exam.

A two-week study plan for the Biology section

This assumes Biology is one of several sections you are preparing, so it is designed to be roughly 30–45 minutes a day rather than a full study block.

• Days 1–2 — diagnose. Take a set of practice questions cold and sort your misses by topic. You are not trying to score well yet; you are building a list of weak areas.
• Days 3–8 — one topic per day. Water and pH, macromolecules, cells and transport, metabolism, cell division, genetics. Make a one-page summary of each in your own words. Writing it out beats re-reading a chapter.
• Days 9–11 — active recall. Flashcards or self-quizzing on the vocabulary above. Short, repeated sessions beat one long one.
• Days 12–13 — mixed practice. Do questions across all topics at once so you practice switching contexts, which is what the real section demands.
• Day 14 — light review and logistics. Re-read your summary pages, confirm your test time and ID requirements, and stop studying early.

One rule throughout: read the rationale on every practice question, including the ones you answered correctly. A right answer for the wrong reason will not survive a slightly reworded question.

Test-day strategy for a short section

Because the Biology module is brief, pacing mistakes are expensive. A few things that help:

• Answer every question. There is no penalty for guessing, so never leave one blank.
• Eliminate first. Most items have one clearly wrong distractor; cutting it turns a four-way guess into a coin flip.
• Trust the plain reading. HESI A2 Biology questions are generally straightforward recall and comprehension. If you find yourself inventing an elaborate exception, you have probably overthought it.
• Don’t stall. Flag the one you are stuck on, move forward, and come back — a 25-question section does not give you time to fight a single item.
• Know the rules before you arrive: what ID you need, whether a calculator is provided, and whether you are testing on campus or remotely with a proctor.

If test nerves are a bigger obstacle than the content, our test anxiety tips for nursing students are worth ten minutes of your prep time.

Next step: practice with real questions

Biology rewards exposure more than it rewards study hours. The fastest way to find the gaps in your recall is to answer questions and read every explanation, then go back to the topics that keep catching you. Work through a practice set, build your weak-topic list, and spend your remaining prep time there rather than re-reading material you already know.