Hannah Fisher
Biology Pd. 06
October 8, 2009
Unicellular Organisms:
Unicellular organisms carry out all the functions of life just like multicellular
organisms, just on the smaller scale within its single cell. Unicellular organisms
can be prokaryotic (bacteria and archaea) or eukaryotic (eukaryota). The
differences between the two types are significant because the eukaryotic cells
contain a nucleus and subcellular structures called organelles. Despite their
significant differences, there are several aspects of unicellular organisms that
apply to both types of cell.
Just like multicellular organisms, unicellular organisms vary in nutritional
diversity. Unicellular organisms can be: photoautotrophs (meaning, like plants,
they are photosynthetic), chemoautotrophs (that use inorganic substances as an
energy source), photoheterotrophs (use light as an energy form, but need to
obtain their carbon in an organic form), or chemoheterotrophs (that need to
consume organic molecules for both energy and carbon). In their metabolic
processes, unicellular organisms are rather similar to multicellular organisms.
Their processes of cellular respiration, which can be aerobic and anaerobic
(since some live exclusively by fermentation), yield the energy of life: ATP.
Unicellular organisms reproduce quickly and their reproductive processes
take cues from nutrient supplies and environmental condition. When the cells
divide through binary fission, one cell becomes two. This process would cause
overpopulation unicellular organisms if it weren’t for limitations such as exhaust
of nutrient supply and consumption by other organisms. In this sense, the growth
of unicellular organisms is limited.
The environment is important for unicellular organisms. However, they can
live in almost any environment. Most unicellular organisms have cell walls, which
protect them and prevent them from bursting in hypotonic environments. Many of
them also have ways to move in order to find light or nutrients, like tails called
flagella. Some prokaryotic unicellular organisms create endospores, which
protect the cell when a nutrient is lacking in the environment, which can remain
dormant for centuries before being rehydrated.
Altogether, the differences between unicellular and multicellular organisms
rest in scale and specification. The unicellular cell has to accomplish all of the
tasks of life, while multicellular organisms have cells that specialize in certain
tasks. And obviously, since there is only one cell, the processes take place in a
much smaller scale. However, unicellular organisms still carry out the functions of
life.