HESI A2 Study Guide 2026 (29pages)

Biology – Scientific study of life. Hierarchic organizational system for nomenclature: Kingdom, Phylum, Class, Order, Family, Genus, and Species. Kingdom is the largest and most inclusive while species is the most restrictive. The scientific method: 1. Observation: New observations made/ previous data collected and studied. 2. Hypothesis: Statement or explanation of certain events or happenings. 3. Experiment: Repeatable procedure of gathering data to support or refute the hypothesis 4. Conclusion: Where the date and its significance are fully explained. The most significant aspect of water is the polarity of its bonds that allow for hydrogen bonding between molecules. Several resulting benefits of hydrogen bonding (intermolecular bonding): 1. Waters high specific heat capacity. (specific heat – amount of temp needed to raise temp of 1 gram to 1 degree Celsius). Due to waters (H2O) high specific heat it’s able to resist changes in temperature and can stabilize environments. 2. Hydrogen bonding also results in strong cohesive (two molecules of likeness stick together) and adhesive (two molecules attract that are different) properties. Cohesion example – water tends to run together on newly waxed car. Adhesion example – When water is spread on the wall some sticks. - When water freezes it’s known as lattice crystal (only solid that floats on water). 3. The polarity of water also allows it to act as a versatile solvent. Biologic Molecules include: Carbohydrates, lipids, proteins, and nucleic acids. 1. Carbohydrates – generally long chains or polymers of sugar. The most important functions: storage, structure, and energy. Carbohydrates form the backbone of DNA and RNA. 2. Lipids (AKA Fats) – Saturated fats contain no double bonds hydrocarbon tail, as a result saturated fat are solid a room temp and related to cardiovascular problems. Unsaturated fats: have one or more double bond. - Phospholipids – two fatty acids varying in length bonded to a phosphate group. Phosphate group is charged and therefore polar and soluble in water which is important for cellular membranes which creates a barrier to protect the cell. - Steroids – lipids that are important because they are a precursor to most hormones and drugs. 3. Proteins – Most significant to cellular function and are polymers of 20 molecules called amino acids. Proteins are largest biologic molecule and are used to catalyze reactions with enzymes. Nearly all cellular function is catalyzed by some type of enzyme.