HESI A2 biology and chemistry: the topics in the optional science sections
Written and reviewed by Rebecca Moore, MSN, RN, CEN · 3 min read · Updated October 2026
Short answer
Biology and Chemistry are optional HESI A2 science sections that only some programs require. Biology covers cells and organelles, mitosis and meiosis, DNA and RNA, genetics, and classification. Chemistry covers atomic structure, the periodic table, bonding, reactions, acids and bases, and states of matter. Check your program first, then study only what it scores.
Does your program require them?
Programs pick sections. The University of Arizona's MEPN program requires Biology alongside Reading, Vocabulary, and Math, and says additional sections such as Chemistry are not counted. Tarrant County College does not offer Biology or Chemistry at all. Before you open a chemistry book, read your program's admissions page.
The Texas State Technical College study guide lists Biology and Chemistry at 25 scored items plus 5 pilot items each, with a suggested 25 minutes each. Your testing site sets the actual time limit. If you are applying to several programs, compare their lists: one may need Biology and another Chemistry, and planning for both at once can save a second sitting.
Biology topics
The same study guide lists the parts of a cell and their functions, the structure and function of organelles, cell differentiation, mitosis versus meiosis, and photosynthesis versus cellular respiration. Genetics carries weight: DNA and RNA structure and roles, mutations, genes and chromosomes, phenotype versus genotype, and Mendel's laws with Punnett squares.
It also lists natural selection and adaptation, and the biological classification system. A good approach is to draw each process, such as the stages of mitosis, until you can sketch it from memory, then answer questions on it.
Chemistry topics
The listed chemistry skills include protons, neutrons, and electrons; measurable properties of atoms such as mass and charge; patterns in the periodic table; and how chemical bonds form when electrons are shared or transferred. Reactions follow: balancing equations, oxidation and reduction, acid and base reactions, catalysts, and enzymes as proteins.
Expect states of matter and changes between them, such as evaporation and condensation, the properties of water, the pH scale, and kinetic versus potential energy. Balancing equations is the most procedural skill on the list, so practise it by hand until it is routine.
Our HESI A2 biology practice questions and HESI A2 chemistry practice questions each come with explanations, so you can see which topics need more time.
Common questions
Is chemistry on the HESI A2?
Chemistry is one of the sections Elsevier offers, but only some programs require it. Your program's admissions page will say whether it counts for you.
How many biology questions are on the HESI A2?
Texas State Technical College lists 25 scored items plus 5 pilot items. Confirm the format with your testing site, since it sets the sitting.
Is physics on the HESI A2?
Physics is offered as a section, but study guides note that only a few programs require it. Check your program before studying it.