Essentially, ciliates are ciliated protozoans.
As such, they are protists that belong to the super-group known as Alveolata
along with dinoflagellates and apicomplexans. Because they are larger cells
compared to other single-celled organisms, they feed on a number of other
micro-organisms including bacteria and algae.
In addition to cilia (use for
movement), ciliates also posses other short hair-like structures (membranelles)
used for feeding.
* They are some of the most complex
Ciliates are divided into free living and
parasitic. Whereas free living ciliates (can live
outside a host) can be found in just about any given environment, parasitic
ciliates live in the body of the host.
Paramecium is an example of free living. Such paramecia as Paramecium caudatum can be found free living in
fresh water bodies where they feed on bacteria.
Ciliates like Balantidium coli
can be found in such host as human beings where they live as endoparasites and
cause ciliary dysentery.
On the other hand, ciliates like Apospathidium
terricola and Paraenchelys terricola can be found in soil. However, the
concentration of these in soil is dependent on the amount of water in
the soil. The higher the concentration of water in soil the more ciliates present.
* Their concentration will vary from one
habitat to another depending on the conditions of the environment (nutrients,
There are a two ways through which the wet mount
can be prepared for viewing under the microscope. To prepare Paramecium species
for viewing, students may obtain the organism from pond water or culture the
sample to increase their number.
Hanging Drop Technique
The hanging drop technique is the simplest
method of preparing the sample for viewing. This simply involves suspending a
drop of water on a cover slip. Here, the drop of water (pond water with the
microorganism) is suspended on the underside of the cover slip, which is placed
over a cavity of a glass slide.
Here, the water drop remains suspended between
the cover slip and the glass slide (with a cavity) and viewed under the
microscope at high power. When students use this technique, they will get an opportunity
to view the microorganism moving fast across the field of view. Although it is
transparent, students can identify them as they move about rapidly.
* Because paramecium are relatively large
compared to other single-celled organisms, they can be easily identified using
a brightfield microscope.
Wet Mount with Stained Yeast
The second technique involves preparing a wet
mount of the sample with stained yeast. One of the main benefits of this
technique over the former technique is that it causes the Paramecium to slow down, which makes it easier to view the organism and try identifying
This technique involves the following steps:
Using a spatula, place a
few grams of the baker's yeast in a beaker and add 100 ml of water (warm spring
water) to hydrate the yeast
Add about 0.3 mg/ml of
Congo red dye and heat the suspension for about 10 minutes - This will reduce
the suspension while concentrating the yeast.
Using a dropper, place a
drop of sample containing concentrated paramecium (concentration may be
achieved by using a centrifuge) in contact with a drop of the stained yeast
Put a little Vaseline on a cover
slip and gently press the cover slip on the glass slide -The Vaseline allows
for the retention of some air between the cover slip and the glass slide while
also preventing the Paramecium from being crashed.
Place the glass slide under
bright field, dark-field and phase contrast microscope to compare how
Paramecium cells appear.
* The dye used in the second technique (Congo
red) is important because it serves as a pH indicator. As pH of the suspension
changes from above 5 to below 3, color will change from red to blue.
* Compared to bright-field microscope, dark-field
and phase-contrast microscopes will allow students to clearly identify the
cilia at either ends of the cells as well as near the buccal cavity of the
While the two techniques are important for viewing the cilia as well as
a few other cell organelles of the organism, a bright-field microscope makes it
easier to identify the food vacuole of Paramecia.
As previously mentioned, ciliates are ciliated
protozoa. This means that they are a form of protozoa with hair-like
projections/organelles (cilia) originating from the cell cortex. These organelles
are important for the organism given that they are used for movement.
to studies, cilia are also used for crawling along surfaces as well as for
attachment and sensation. Therefore, apart from helping the organism move from
one region to another, they allow ciliates to sense any changes in their
environments and therefore be able to respond effectively.
Compared to flagella
present in other single-celled organisms, cilia are more numerous and short,
and may cover the entire surface of the organism. Through their coordinated
movement, they are able to rapidly move around more rapidly.
* While all have cilia, some use cilia
to crawl (Aspidisca and Euplotes) while some are capable of swimming in water
and are known as free-swimming ciliates (Paramecium etc).
Compared to other single-celled organisms,
ciliates possess two nuclei; micronucleus and a larger macronucleus - The
micronucleus consists of two copies of each chromosome making it a
Depending on the ciliate, there may be one or several
micronuclei in a single cell. The macronucleus is larger than the micronucleus
and contains short pieces of DNA (tens to thousands of copies). During cell
division, the micronuclei often undergo mitosis while the macronucleus divided
Ciliates like Paramecia have a mouth-like structure
refered to as an oral groove through which they feed. Modified cilia long the
oral groove push the food particle through the cytopharynx (acting as the
gullet) and into the food vacuole where the substrate is broken down. However,
some lack an oral groove (mouth) and use absorption to feed/obtain
Ciliates also have a contractile vacuole (Paramecia has an anterior contractile vacuole as well as a posterior
contractile vacuole) that serves to collect and remove excess water from the
When the concentration of water molecules is high inside the cell, they
move into the contractile vacuole (which has higher ion concentration) and
ultimately removed from the cell. This process allows the cell to maintain
osmotic pressure and ionic balance while also preventing the cell from bursting
due to excess water in the cell.
Ciliates may reproduce sexually (conjugation) or
During conjugation (sexual reproduction), two
ciliates come in contact with each other forming a cytoplasmic bridge between
them. This is followed by a process known as meiosis of the micronuclei of
either cell to produce haploid micronuclei.
Some of the haploid nuclei undergo
disintegration while the remaining ones divide into two through a process known
as mitosis in both cells.
One of either nuclei then moves to the other cell
through the cytoplasmic bridge where it fuses with the micronuclei of the other
cell to form a diploid nucleus ultimately forming a macronucleus once the cells
separate. This is then followed by fission of the cell (while the macronucleus
divided to two) to form two daughter cells. Each of the daughter cells will
have a macronucleus and a micronucleus.
* During the fission phase of reproduction, the
micronucleus of the cell go through mitosis (two diploid micronuclei) while the
macronucleus divides into two. The cell then divides into two (splitting in to
two daughter cells) with one of each macronucleus and micronucleus in each of
the new cells.
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