hesi biology

The Comprehensive HESI Biology Study Guide In 2024

Are you gearing up to take the hesi biology test? We'll go into detail about what the Biology exam entails and some tips to study for it.

Updated at March 13, 2023

Are you prepared for the HESI A2 Biology exam? If so, you should read this blog article! We’ll go into detail about the Hesi biology test’s requirements, how to prepare for them, followed by some useful tips.

HESI A2 Biology Review

There are 30 questions on the exam and we recommend that the time limit for the Biology test is 25 minutes. Most schools will, but there is a possibility that your school may establish a different time limit, so before exam day, be sure to check it. All information that you need is on the nursing school’s website.

What’s on the HESI A2 Biology Test?

hesi biology

To do well on the Biology section of the HESI exam, There are some main concepts that need to know:

Classification of Organisms

Living things are classified by a system developed by Carl Linnaeus. Organisms are often named by the binomial system of genus and species. 

The classification of species allows the subdivision of living organisms into smaller and more specialized groups.


The first division of living things in the classification system is to put them into one of five kingdoms. They are: 

  • animals (all multicellular animals)
  • plants (all green plants)
  • fungi (molds, mushrooms, yeast)
  • protists (Amoeba, Chlorella, and Plasmodium)
  • prokaryotes (bacteria, blue-green algae)

Further divisions

We can rank the living things according to:

  • phylum
  • class
  • order
  • family
  • genus
  • species

The kingdom is broken into Phylum that has many different organisms. For examples:

  • Chordata, which have backbones
  • Arthropod, which has jointed legs and an exoskeleton
  • Annelids, which are segmented worms

The class follows Phylum. For example, class results in the Chordata phylum being divided into:

  • Mammals
  • Birds
  • Amphibians
  • Fish
  • Reptiles

The order follows class and as an example, mammals can be further subdivided into a variety of different groups such as:

  • Carnivores
  • Primates

The Family follows the order. Here are some examples of which carnivores can be split into:

  • Canidae – dogs
  • Felidae – cats

Genus, the Felidae family can be further divided into 4 genus examples:

  • Acinonyx – cheetah
  • Panthera – lion and tiger
  • Neofelis – clouded leopard
  • Felis – domestic cats

Species is the final classification stage. The genus Panthera includes:

  • Panthera leo (lion)
  • Panthera tigris (tiger)

As an example, the complete breakdown of the classification of lions:

  • kingdom – animal
  • phylum – vertebrate
  • class – mammal
  • order – carnivorous
  • family – cat
  • genus – big cat
  • species – lion

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The Scientific Method

The Scientific Method is a method of devising and performing experiments that yield meaningful results. It includes a procedural approach to collecting information about the physical world that starts with a formulated question and ends with the rejection of a hypothesis and the reevaluation of the experiment.

We can summarize The Scientific Method as the following:

Question – A curiosity about a phenomenon increases and, in response, a question is formulated. Early thinkers looked at the sky and wondered why it was blue or looked at the grass and wondered why it was green.

Research – After formulating a question, a scientist looks for any relevant research or data already discovered and provided for the phenomenon in question. This is useful in giving some direction in how to build or approach the question.

Hypothesis – The scientist then created a hypothesis, or an educated guess, as to what could be causing the phenomenon. This step is useful in narrowing down the possible options or experimentation.

Experiment – Using available measuring tools and technology, to provide valuable data for the scientist to investigate, an experiment is designed.

Evaluation – The data will then be analyzed and assessed for its validity. Do the observations made support the hypothesis, or do they support a different hypothesis?

Conclusion – In the end, the scientist will determine if the hypothesis is confirmed, in which case other scientists will then recreate the same experiment to identify that the results hold true at a different time or place not using the different methods. The scientist may select to change some of the experimental methods or devise a new hypothesis if the hypothesis is not confirmed.

In summary, the Scientific Method provides a methodical method for investigating experiments, data, and drawing conclusions. It is worthwhile to see that developments in scientific research do not increase from haphazard guessing and checking, but rather through logical design and reasoning. Even a basic familiarity with the method will prove useful while making sense of scientific experiments.

Cells, Tissues, and Organs

The most fundamental unit of life is the cell. Organisms that exist as a single cell, like bacterium, are called prokaryotes and those that are multicellular, like humans, are called eukaryotes. The main difference between these two groups is that eukaryotes possess a nucleus and membrane-bound organelles while prokaryotes do not.

Starting with the knowledge of the cell, its form, and function, we can begin to make sense of how life operates, and what cellular features enable this operation. Learning the components of the cell is not a difficult task, but it can be tedious.

One great way to learn about cells is to complement lists of cellular components/features with drawings of cells – this is particularly useful for eukaryotic cells and their organelles. Accompany these drawings with the name of the cell “part” and what its function or purpose is. For instance, the nucleus houses genetic information and instructions for cellular operations; the mitochondrion helps generate ATP to provide energy for the cell… In studying the differences between plant, animal, and bacterial cells, a mini whiteboard can be a huge asset. Repeatedly diagramming the elements of the various cell types and their parts (noting similarities and differences) will cause long-term retention.

When a group of cells functions together to accomplish tasks, they are operating as tissue. Due to the differences at the cellular level, plants and animals organize into different types of tissue. Plants possess meristematic tissues, which enable them to increase in size, and permanent tissues, which enable them to maintain their form.

Animals possess connective, epithelial, muscle, and nervous tissues. As the tissues in plants, these groups serve different functions and have different forms. Connective tissues provide structure to organisms. Epithelial tissues are those found where cells line and cover organs. Muscle tissue allows animals to move, and nervous tissue enables animals to send and receive signals to its different parts.

Just as cells combine to form tissues, tissues combine to form organs. Humans possess an extensive list of organs that all serve a particular function: some help digest food to provide energy, while others help circulate air and blood. And, like tissues, organs act collaboratively to form organ systems.

The same approach of studying the cells and their functions can be applied to tissues, organs, and then organ systems. It is most important to generate your own diagrams when learning the form and function of these different systems. It is easy to believe that one has a solid grasp of these things when reading from a book or even a page of notes; however, this is much different from being able to work from the ground up in describing the composition of organisms. Condense lists of organismal features into its basic parts, and work through repeatedly processing this information with the aid of a whiteboard and note cards.

Genetics and Heredity

Heredity is the passing on of genetic traits from one generation to the next; it is the reason that children resemble parents, and why humans give birth to other humans. Genetics is the study of the principles underlying heredity.

Workable knowledge of genetics is impossible without becoming familiar with DNA (deoxyribonucleic acid). This familiarity entails its composition [knowing that guanine, cytosine, adenine, and thymine (also known as GCAT) are its nucleotides, knowing how they pair, and knowing that its strands run antiparallel, among other features], as well as its function (to house and maintain the instructions for a cell’s operations).

An understanding of “the central dogma” of molecular biology, which states that genetic information flows from DNA to RNA to proteins, can serve as a great outline for how gene transfer takes place. Before moving on to transcription and translation, understanding can help you be familiar with DNA replication, the details of which can be processed through learning the names and functions of the various structures and enzymes involved. Because this is a systematic procedure that incorporates many different parts, drawing and redrawing diagrams can prove worthwhile for the long-term retention of the operations.

When these operations are understood, a more general understanding of genetics can be studied. A familiarity with Gregor Mendel and his laws (Law of Dominance, Law of Segregation, and the Law of Independent Assortment) can act as a solid foundation for genetic transfer beyond the microscopic scale. This will lead one to learn about parents, first and second generations, and the expression of phenotypes as predicted with Punnett squares.

Much difficulty in studying genetics and heredity stems from the necessity of learning an exhaustive number of terms and definitions. Intelligent utilization of flashcards and diagrams can address these problems.

Mitosis and Meiosis

Mitosis and meiosis are processes by which cells reproduce. Mitosis is a form of asexual reproduction where the resulting cell is genetically identical to the parent cell, whereas meiosis results in a cell that contains only half of the chromosomes found in the parent cell. It is wise to note both the similarities and the differences when reviewing the two processes. Similar to the method used for recalling the various taxonomic classes, a mnemonic device can prove valuable in learning the stages of mitosis and meiosis.

While these two reproduction methods share essentially the same steps, it can be useful to think that because meiosis is involved in sexual reproduction, a method for diversifying life; it is more complicated than mitosis. Recalling this can help you remember which mnemonic goes with which process.

Familiarity with the cell cycle is helpful in understanding these two processes. Cells do not arbitrarily reproduce, nor do they reproduce nonstop. Instead, there are triggers and signals that must be present before a cell will begin reproduction. Mitosis can be broken down into four main stages: prophase, metaphase, anaphase, and telophase. But there are two additional “stages” of interphase and cytokinesis. The acronym IPMATC can be useful in recalling the order in which these stages happen.

Meiosis shares the same stages, but it occurs in two ordered sequences, so there is an IPMAT 1 and an IPMAT 2. The best method for retaining the details involved in both processes is to utilize a whiteboard and diagrams, drawing and redrawing the steps until this can be done without the aid of any reference material. It may sound repetitive, but this method of learning is invaluable for gaining functional knowledge of this material.


Photosynthesis is the process by which plants transform the energy in light into chemical energy that can be used to fuel life functions. A solid grasp of photosynthesis entails an understanding of what cellular structures enable the process (think chloroplasts, and other structures present in plant cells that are not in animal cells) as well as how the process happens (without carbon dioxide and water the process cannot take place).

Just as you should be familiar with the chemical equation governing cellular respiration (the energy liberating process in animal cells), you should also understand the chemical equation relating to the reactants and products of photosynthesis. Both of these processes rely upon the transfer of free electrons to generate chemical energy. And, just as animal cells carry out the Krebs cycle to generate ATP, plants carry out the Calvin cycle to generate energy. Analogs like this are very useful to recognize as they can reduce two distinct processes into a single concept and thus simplify the material to be learned.

Familiarity with the different types of photosynthesis is also useful to learn. Some types require the presence of light whereas others can be performed in the absence of light. An understanding of what biological purpose or function this serves can be helpful. Similarly to all of the other systems and processes, the usage of a whiteboard and diagrams, as well as a complementary list of the cellular features necessary, can prove invaluable when reviewing involved procedures such as photosynthesis. However, when you can already generate the information without the aid of reference materials, you can be certain that you have developed a firm comprehension of the concept.

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Helpful tips for the HESI A2 biology test

Make flashcards. You can either make them yourself with the help of friends, classmates, or family members; you could buy pre-made cards from stores like Target and Walmart; or if not, use sites online such as StudyBlue to create your own deck of study cards at no cost. Flashcards serve as a great way to review important concepts.

Take practice quizzes, exams, and tests before the HESI A21 Biology exam date. This allows you to get a feel for what will be on your test so that when it comes time for the actual exam day, you’ll know what to expect. It also helps reduce anxiety as many people are more nervous about recalling information than putting it together.

Use a study planner to help you plan your time during the week and divide up work for each day so that you’re not overwhelmed. You can make this as simple or detailed as you want, but just try to map out when and how much studying will happen on any given day of the week.

Never start studying for the HESI A21 Biology exam without knowing what you’re going to do after. If that means taking a break from study, make sure you establish when and why it’s appropriate to take one before starting your work.

When studying for the exam, it’s important to work on your strengths and weaknesses. If you’re really struggling with a particular subject or concept, take notes in class so that you can spend more time drilling down into what you find difficult later.

Hesi A2 Biology Practice Test Resource

Where to get more Hesi A2 Test Resources and Materials? We are pleased to present our HESI practice website, which includes comprehensive instructions, practice tests with explanations, and quick assessments to gauge your understanding. By providing you with a solid math foundation, it can aid your exam day preparation. Try our HESI A2 practice test free today!