prokaryotes, eukaryotes or protists,
four points apply to all types of cells:
organisms contain one or more cells
cells come from pre-existing cells
life functions occur within the boundaries of cells
cells contain genetic material needed to regulate cell function and pass this
information to new cells
scientists Matthias Schleiden and Theodor Schwann are accredited with the
basics of cell theory, which was later expanded by Rudolf Virchow; many other
scientists have offered contributions, refining cell theory as the instruments
used to study cells advanced over the decades.
Prokaryotes vs. Eukaryotes – Similarities?
and Eukaryotic cells differ structurally as well as in the way they replicate.
However, it’s important to note the chemical similarities – reactions that
enable cell life.
types of cells use and/or contain:
types of cells must make and store energy to survive. Chemical reactions aid in
the ability to metabolize food and build proteins; whether autotrophic or
heterotrophic, cells need amino acids (proteins) and energy (glucose/ATP) to maintain
structure and carry out a range of functions that include cell replication.
Prokaryotes vs. Eukaryotes
– Major Differences
though at a most elemental level, all cells require the same functions to
survive, the significant differences between prokaryotes and eukaryotes include structure and
noteworthy is the lack of nucleus in bacteria and archaean – the two types of
addition, the presence of rods, spheres or spirals aid in the identification of
the three main types of prokaryotic bacteria.
A circular, easily identifiable dark object in the center of a cell, the nucleus is the first and most important characteristic of a eukaryotic cell. Encompassing three kingdoms: plants, animals and protists; plants and animals are multi-cellular, while protists consist of mostly unicellular plant-like, animal-like and fungus-like cells.
Eukaryotes contain many Organelles - Structures within the Cell
– the defining structure, often likened to the “brain" or control center of the
cell; the nucleus contains genetic material (DNA and RNA) and also manages the
activities of the other organelles within the cell; other aspects include:
– dark area within the nucleus essential to cell division; the area becomes
especially dense and dark during rRNA synthesis
Envelope – double membrane contains pores that allow for communication between
the nucleus and cytoplasm; connected to ER
– DNA proteins with a thread-like appearance when the cell is not actively
undergoing mitosis or meiosis
– contain genetic information of a cell; formed when chromatin transforms into
short, dense coils
– contained within the plasma membrane of the cell, but outside the nucleus;
microfilaments and microtubules aid in the formation of the cytoskeleton
– provides shape to the cell through a “criss-cross" arrangement of
protein-based filaments secured to the cell membrane; changes in filament
tension lend to cell movement; certain cells move via the attachment of
microtubules, cilia and flagella to the outer cytoskeleton; also plays a role
in the separation of chromosomes during the process of mitosis
Wall – most prominent in plant cells and commonly made of cellulose or chitin;
glycocalyx in animal cells make the thin wall more durable and provides a means
for cells to connect to each other
– a powerful part of a cell located in sphere-shaped double membrane structures
throughout the cytoplasm; the outer layer is smooth, while the inner membrane
contains cristae -- a progression of “folds"
along the sphere that allow for an incredibly large surface area, while the small
inner space (matrix) contains fluid; converts food into energy via aerobic
respiration; essential to the production of ATP (energy)
– the plant version of mitochondria; contains chlorophyll and enzymes required
for photosynthesis; like mitochondria, chloroplasts possess their own DNA,
which it replicates on its own
Reticulum (ER) – called the “intercellular highway," the ER transports material
around the cell; located between the pores of the nuclear envelope, the ER allows
for the transfer of compounds in and out of the cell; two types:
– covered with ribosomes and containing cisterns or sacs, rough ER is
associated with the formation and transport of proteins; can be considered an
extension of the nuclear envelope
– generates lipids; responsible for detoxification, eliminating harmful
compounds and poisons from the cell
Apparatus/Complex – responsible for preparing or “packaging" items, such as
enzymes or proteins, within cisterns transported outside the cell through a
vacuole or to another area of the cell like a lysosome; also produces/modifies
– uses an enzyme to break down food sources into usable forms such as amino
acids (proteins) or energy (glucose); also ingests bacteria, protecting the
cell from harmful intruders
– storage facility for food and water; can be very large in plant cells and, in
addition to storing nutrients and water, plant vacuoles can store metabolic
waste and other harmful substances, keeping them away from the cytoplasm so the
plant remains healthy
advanced multi-cellular eukaryotes,
cells communicate intrinsically and extrinsically. Specific organs might
contain cells with a predominant organelle; for example, the liver contains a
higher percentage of lysosomes, ridding the body of poisonous substances.
whole entities, the survival of plants and animals comes down to the function
and interaction of individual cells. Exposure to free radicals, disease,
viruses, and parasites can cause damage to multiple cells; while a nutritious
diet, aerobic exercise and limiting stress creates a positive effect on a
Under the Lens
Whenviewing eukaryotes under a microscope, organelles are most visible in the
moments before, during, and after mitosis or cell division. Tissue specimens
often contain multiple cells on a slide. Although cells from different organs
or species may look different, eukaryotes
all contain the same organelles.
studies show the miniscule differences that exist between species and phylum – even
where external variations seem much more than one or two chromosomal
background in histology and/or pathology aids in the recognition of cell
anomalies. In addition, the ability to recognize organelles under different microscopic
instruments lends to learning more and more information regarding the function
of eukaryotes on a cellular level.
such as dark field, phase contrast, and DIC, the use of different dyes,
utilizing photomicrography and computers are some of the ways hobbyists,
students, teachers, medical professionals and researchers can use to explore eukaryotes on a cellular level.
addition, possessing the skills to identify different organelles found in eukaryotes under a variety of
environments or circumstances yields numerous research possibilities.
with the nucleus, eukaryotes are
significantly different from prokaryotes – although many of the chemical
processes are similar such as those involving proteins, lipids, nucleic acids
Understanding that organelles become clearer before, during,
and after cell division helps the recognition of parts of a cell in different
states. This can decrease mistakenly calling something an artifact.
amount of knowledge associated with studying various states of eukaryotic
cells, the cellular differences between species and even the disparities that
occur in different organs of the same species is exciting.
cell, imprinted with a genetic code and micromanaged by the nucleus, reveals a
story; with the right instruments and techniques, we can observe the stages and
functions of each organelle within a eukaryotic cell.
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