Development, Processes, Interactions and Microscopy
Essentially, multicellular organisms are made up of more than one cell. As such, they are different from
unicellular (single celled) organisms that only consist of a single cell. Like
unicellular organisms, there are a wide range of plant and animal multicellular
organisms in existence.
Compared to unicellular organisms, multicellular are also more complex given that they are made up of different types
of specialized cells that carry out different functions. A majority of animal
species, plants (on land) and fungi are multicellular organisms. These range
from fungi human beings.
* Multicellular should not be confused
with colonial organisms. Colonial organisms are made up of a group of identical
cells such as the staphylococci bacteria which can survive on their own as
single cells. This is because these individual cells can independently carry
out all the functions that are necessary for life.
Colonial organisms are
therefore different from multicellular organisms that consist of different
types of differentiated cells which serve different functions. Moreover,
individual cells of multicellular organisms cannot carry out all the functions
that are necessary for life.
Main Differences Between Unicellular Organisms (single celled) and Multicellular
All the life activities of
a unicellular organisms are carried out by the individual cell and its organelles.
Multicellular have differentiated cells that form the different
tissues and organs (liver, heart, vessels etc) that carry out different
functions for the survival of the organism.
The area to volume ratio
factor prevents single cells from becoming large in size while multicellular
organisms grow and enlarge in size with cells dividing and increasing.
The life span of single
celled organisms is short (this is due to the load of work they perform) while
the life span of multicellular organism cells is longer given that different
cells carry out specific functions.
Multicellular Organisms Development
While all consist of
more than one cell, they start out as a single cell. The cell proliferates to
produce many more cells that result in the multicellular organism. The process
starts with a single fertilized cell that increasingly divides to form many
more cells. In the process, the genome causes the cells specialize through
selective gene expression.
This is the first process and it involves the
growth and division of the cells. Here, the cells divide through a process
known as mitosis (somatic cell division) Produce two equal copies of
During this phase, growth factor signaling pathways serve to
activate the cells to enter the cell cycle. This process of cell proliferation
is highly regulated to ensure that there is balance between the different types
This phase is largely involved in the production
of many cells from the first fertilized cell.
2. Cell Specialization
Cell specialization is the process that is
responsible for the production of cells with different traits at different positions.
This process sees cells (embryonic cells) changing from their simple form into
more specialized cells both in structure and function. This is all made
possible by a process known as gene expression where given genes are either
turned on or off consequently dictating the manner in which the cells will
Cell differentiation is particularly important
among multicellular organisms. It can be argued that this is one of the most
important processes that sets multicellular organisms from simple, unicellular
organisms. This is due to the fact that the process results in the transformation
of the simple zygote in to a complex organism with different types of tissues
For instance, whereas the heart and blood are both made up of cells,
they are made up of various types of cells that have specialized to carry out
different functions, which ensures the survival of the organism.
Differentiation continues into adulthood to
ensure that the body has all the cells it needs. For instance, in the event that the body encounters a new
antigen, cell differentiation of the stem cells will produce the cells required
to counter the new and potentially harmful antigen.
While all the cells contain the genetic material
(genes) responsible for cell development, the some of the genes, in the cells
are either expressed or repressed allowing a group of cells to differentiate
into specific types of cells for a given function. This is made possible by
certain signals inside and outside the body that trigger which genes will be
expressed or depressed.
This is an important process given that it helps in the development of different types of cells
that serve different functions in the body. As the cells differentiate, they
change in shape and size depending on their functions. With each types of cells
carrying out their respective functions, they ensure are able to support life
of the organisms.
3. Cell-Cell Interactions
This process is responsible for coordinating the
behaviors of respective cells in relation to the neighboring cells.
Simply put, this involves direct interaction of
the surfaces of the cells, which is essential in both the development and
functioning of the organism. This interaction may also occur through the matrix
(fluid between the cells) allowing communication between the cells through
The process (cell-cell interaction) is important for multicellular
organisms in that it is responsible for a variety of physiological processes
that take place. This therefore contributes to the coordinated functioning of
the organism. This interaction (communication) between cells is made possible
by a number of molecules including peptides, proteins, amino acids and steroids
The extracellular spaces are filled with fluids.
This spaces also contain various constant signals. However, any given group of
cells can only respond to given signals while ignoring others because they have
specific cell surface receptors that can only receive and respond to given
signals. The surface receptors allows the for binding with specific molecules
so that the cell can respond appropriately.
Types of Cell-Cell Interaction
There are different types of cell-cell
interactions. These include:
Some of the eukaryotic cells have proteins,
carbohydrates as well as lipids on their surface which extend outward. This
makes it possible for some of these cells to come into contact especially when
they are close to each other. This type of cell interaction is particularly
common during early development
This type of signaling is short-lived and only
affects the local cells. It occurs when signal molecules are released to cells
and travel through the extracellular fluids to reach other cells that are
closely located. This is largely due to the fact that most of the molecules are
either destroyed by enzymes or removed from the extracellular spaces
prohibiting them from travelling far.
As a result, they can only relay signals
to nearby cells. This type of interaction also takes place during early
Endocrine signaling is the type of interaction
where the signal molecule (hormones) is able to travel throughout the body
through such systems as the circulatory system to reach their target. Unlike
Paracrine signaling, hormones have a longer life span, which allows them to
reach distant cells and cause them to respond.
This types of cell interaction is particularly
common among the cells of the nervous system. Neurotransmitters serve as the
signal molecules, allowing the cells to rapidly communicate with other distant
Here, the signal molecules travel through extensions of the nerve cells
and are released at the tip that borders the target cells. Once in contact with
the target cells, the neurotransmitters cause the cells to respond.
4. Cell Movement
Cell movement is the process through which the
cells are rearranged so as to form the necessary tissues and organs.
During embryonic development, cells go through a
complex process of events that lead to their respective shape and positioning
in the formation of all the essential tissues and organs in multicellular
This process occurs once the cells start receiving signals that
influence a complex and well coordinated mechanism that moves the cells in the
right direction to the intended destination. Failure to move to in the right
direction and to the right destination is likely to result in problems of
development of the fetus and deformation.
As previously mentioned, multicellular organisms
are complex organisms with different types of differentiated cells that are organized
to form tissues, organs as well as various organ systems in the body.
the multicellular organisms are visible to the naked eye, which means that it
is possible to view them without using the microscope. However, some, like
mites are too small and require a microscope for observation.
A number of
microscopic techniques are required to view and study various multicellular organisms,
their structure as well as their cells.
Microscopy is also used for research
purposes as is the case with studying cancerous cells and other pathological
Stereo microscopes, also known as dissecting
microscopes, are a type of binocular microscope that can be used for viewing
the finer details of larger specimens, in this case multicellular organisms.
of the biggest advantage of using a stereomicroscope to view such multicellular
organisms like flies, ants or mosquitoes among others is that students can view
the fine details (such as filaments) more closely while the organism is still
alive. This means that the organism can be viewed without being stained.
This technique only allows for the external structures (surface) of the
organism to be viewed. However, staining can be use to view such organisms as
Viewing Mites under Stereo Microscope
House dust (dust can also be
collected from head pillows)
Saturates sodium chloride
45um mesh sieve
Place 0.05 grams of the
dust sample in 30 mL of sodium chloride solution a
Add five drops of detergent
Subject the dust to 20
minutes of ultrasonic treatment
Rinse the suspension using
45um mesh sieve
Stain using crystal violet
View under stereomicroscope
* Alternatively, dust mites can be viewed by
simply placing a small amount of the dust on water surface and observing under
As for the larger multicellular organisms, they
can be viewed under the microscope by simply placing the organism (insect, leaf
etc) under the stereomicroscope and adjusting the magnification to view the
surface of the organisms.
The compound microscope provides higher
magnification compared to the dissecting microscope. For this reason, it is the
best tool for viewing multicellular organisms at the cellular level. For
instance, using the compound microscope, it's possible to view and study the
epithelial cells that line the inside of the mouth or cells of such plants as
onions among others.
The following is a procedure to viewing cheek
cells under the microscope:
Microscope glass slide
Glass cover slip
Place one drop of saline
water at the center of the glass slide
Using a cotton swab, scrub
the inner lining of the cheek and introduce the cells to the saline drop on the
Add a drop of methylene
blue solution to the preparation on the glass slide
Cover the slide using a cover
slip and observe under the compound microscope starting with low power to high
Sketch the cells as they appear under low and high power
In medicine, biology and research, histology
involves studying the anatomy of cells and tissues of multicellular organisms
using a microscopy. This is used to study tissues as well as for diagnosis
purposes by pathologists. Unlike viewing epithelial cells of the cheek, viewing
body tissue required more complex preparation of the sample.
Very thin sections are required for microscopic
observation of tissues. However, fresh tissues tends to be delicate and thus
require a great deal of care to be taken when preparing the sample in order to
get a better view of the tissue. Therefore, the samples have to be supported in
order to cut and obtain good, thin sections.
There are two main techniques that
are used to fix the tissue in order to cut them and obtain quality samples for
Freezing - The tissues is frozen while cutting
to obtain good thin samples for microscopy. Sections obtained through this
technique are referred to as frozen sections
Paraffin wax - Apart from freezing, paraffin can
be used to fix the sample. Here, the liquid is used to infiltrate the sample
that is then converted in to solid to cut thin sections. This process is known
as embedding tissue where the tissue is embedded in paraffin wax blocks. A
sharp blade in a holder (or a microtome) is set at an angle and used to slice
(sectioning) the block to obtain quality thin sections of the sample.
Some of the other fixatives used in histology
Once the thin sections have been obtained,
staining is carried out before viewing under the microscope.
Staining starts with the removal of the paraffin
wax (or the fixative that was used). This process is known as deparaffination
and involves using xylens, alcohol and water. The fixed section is run through
xylenes then through alcohol and finally through water to wash the section and
To view the section under the microscope, the section (s) is
stained using specific stains depending on the diagnosis.
Some of the stains used in histology include:
Hematoxylin and Eosin
Oil Red O
Multicellular organisms consist of “multiple" cells. However, they not only have many cells, but specialized cells that carry out different functions. Groups of cells form tissues and organs, which perform different functions for the survival of the organism.
Students have the opportunity to observe a wide range of multicellular organisms fro plants to animal and compare different tissues and cells that make up these tissues.
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