HESI A2 Biology: What to Study and How to Pass

The HESI A2 Biology section has 30 questions in 25 minutes and is one of the science sections that many nursing programs require. For students who haven’t taken biology since high school, this section can feel overwhelming. This guide breaks down exactly what topics you need to study and how to approach each one.

Is Biology Required for Your Program?

Not all nursing programs require the Biology section. Many only require Math, Reading, Vocabulary, Grammar, and Anatomy & Physiology. Before you invest hours studying biology, confirm with your school which sections you need. That said, if biology is required, it’s one of the most content-heavy sections, so start early.

Topic 1: Cell Structure and Function

This is the most heavily tested topic on the HESI biology section. You need to know:

• Organelles and their functions: nucleus (DNA storage), mitochondria (energy/ATP), ribosomes (protein synthesis), endoplasmic reticulum (transport), Golgi apparatus (packaging), lysosomes (digestion), cell membrane (selective barrier)
• Plant vs. animal cells: Plant cells have cell walls, chloroplasts, and large vacuoles. Animal cells do not.
• Prokaryotic vs. eukaryotic: Prokaryotes (bacteria) lack a nucleus. Eukaryotes (plants, animals, fungi) have membrane-bound organelles.

Topic 2: DNA, RNA, and Protein Synthesis

Understand the central dogma of biology: DNA → RNA → Protein.

• DNA structure: Double helix, nucleotides (A-T, G-C base pairs), sugar-phosphate backbone
• RNA vs DNA: RNA is single-stranded, uses uracil (U) instead of thymine (T), has ribose instead of deoxyribose
• Replication: DNA copies itself before cell division
• Transcription: DNA → mRNA (happens in the nucleus)
• Translation: mRNA → protein (happens at the ribosome)

Topic 3: Cell Division — Mitosis vs. Meiosis

This is a guaranteed topic on the HESI biology section. Know the key differences:

Topic 4: Genetics and Punnett Squares

You need to be able to complete simple Punnett squares and understand:

• Dominant vs. recessive alleles: Dominant (capital letter, e.g., B) masks recessive (lowercase, e.g., b)
• Genotype vs. phenotype: Genotype = genetic makeup (BB, Bb, bb). Phenotype = physical appearance
• Homozygous vs. heterozygous: Homo = same alleles (BB or bb). Hetero = different (Bb)
• Practice: If both parents are Bb, what is the probability of a bb offspring? (Answer: 25%)

Topic 5: Photosynthesis vs. Cellular Respiration

Know both equations and how they relate:

• Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ (happens in chloroplasts)
• Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (happens in mitochondria)
• They are reverse processes — the products of one are the reactants of the other

Topic 6: Classification and Taxonomy

Know the hierarchy: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

Memory trick: “Dear King Philip Came Over For Good Spaghetti”

Study Strategy: Focus on the Big 4

If you’re short on time, prioritize these four topics — they represent roughly 80% of HESI biology questions:

1. Cell structure and organelles
2. DNA/RNA and protein synthesis
3. Mitosis vs. meiosis
4. Genetics and Punnett squares

Master these four, and you’ll have a strong foundation for scoring 80%+ on the biology section.