Biology is the study of living organisms and to understand anatomy and physiology, a
nurse must first grasp the science of biology. While you may not use your knowledge of
biology directly every day, biology serves as a prerequisite before moving on to other
sciences such as anatomy, physiology, and microbiology.
Here are some key concepts you should understand in order to do well on the Biology
section of the HESI exam:
Classification of Organisms
Early biologists faced difficulty in devising a method for discerning living organisms from
nonliving things. After developing rules to differentiate life from nonlife, scientists then
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faced the struggle of organizing and classifying life. Taxonomy, or the science of
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classifying, resulted from these early struggles. Many years of classification have
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occurred since, and because of advancements in biotechnology, scientists can now
categorize life based on similarities and differences at the genetic level. Scientists utilize
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a hierarchical system for classifying organisms. Six Kingdoms contain the taxonomic
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breakdown of life. These Kingdoms are further divided into Phyla, then Class, Order,
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Family, Genus, and Species. A common mnemonic for remembering this hierarchy is,
“King Phillip Came Over For Great Spaghetti,” where the first letter of every word
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indicates the corresponding taxonomic class. Over the years, the taxonomic
classification schemes have changed and will continue to change as we further our
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understanding of genetics. Currently, scientists use Six Kingdoms to subdivide life:
Bacteria, Protozoa, Chromista, Plantae, Fungi, and Animalia make up these Six
Kingdoms. Scientists categorize organisms within one of these Kingdoms by
investigating the organisms’ cellular composition, methods for obtaining and using
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energy, genotypic similarities, and other techniques.
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The Scientific Method
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The Scientific Method is a way of devising and performing experiments that yield
meaningful results. It involves a procedural approach to gaining information about the
physical world that begins with a formulated question and ends with the rejection of a
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hypothesis and the reevaluation of the experiment.
The Scientific Method can be summarized as the following:
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, Question ― A curiosity about a phenomenon arises 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 helps give
some direction in how to set up or approach the question.
Hypothesis ― The scientist then generates a hypothesis, or an educated guess, as to
what could be causing the phenomenon. This step helps narrow down the possible
options for experimentation.
Experiment ― Using available measuring tools and technology, an experiment is
designed to provide valuable data for the scientist to investigate.
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?
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Conclusion ― Finally, the scientist will decide if the hypothesis is confirmed, in which
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case other scientists will then recreate the same experiment to confirm that the results
hold true in a different time or place using the same methods. If the hypothesis is not
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confirmed, the scientist may choose to adjust some of the experimental methods or
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Overall, the Scientific Method provides a methodical approach for investigating
experiments, data, and drawn conclusions. It is worthwhile to know that developments
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in scientific research do not arise from haphazard guessing and checking, but rather
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through logical design and reasoning. Even a basic familiarity with the method will prove
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useful when making sense of scientific experiments.
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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
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called eukaryotes. The major difference between these two groups is that eukaryotes
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possess a nucleus and membrane bound organelles while prokaryotes do not.
Beginning with an understanding of the cell, its form and function, we can start to make
sense of how life operates, and what cellular features enable this operation. Learning
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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 example, the nucleus houses genetic
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