Gustav Kirchhoff’s Current Law is one of the fundamental laws used for

circuit analysis. His current law states that for a parallel path the total current
entering a circuits junction is exactly equal to the total current leaving
the same junction. This is because it has no other place to go as no charge
is lost.
In other words the algebraic sum of ALL the currents entering and leaving a
junction must be equal to zero as: Σ IIN = Σ IOUT.
This idea by Kirchhoff is commonly known as the Conservation of Charge,
as the current is conserved around the junction with no loss of current.
https://www.electronics-tutorials.ws/dccircuits/kirchhoffs-current-law.html

A resistor don't have any fixed positive or negative terminal. It depends on the circuit that
which terminal of the resistor will be at positive polarity w.r.t its other terminal.

When a current flows through a resistor, the terminal through which the current enters into
the resistor will be considered as positive terminal and the other one through which the
current goes out of the resistor will be then negative terminal. But that is when the resistor is
connected in a circuit and current flows through it, otherwise a resistor alone don't have any
fixed positive or negative terminal.

https://www.quora.com/Which-is-the-positive-terminal-of-a-resistor

Current in the drawing above is shown entering the + side of the resistor. Resistors don't care which
leg is connected to positive or negative. The + means where the positive or red probe of the volt
meter is to be placed in order to get a positive reading. This is called the "positive charge" flow sign
convention. Some circuit theory classes (often within a physics oriented curriculum) are taught with
an "electron flow" sign convention.

https://en.wikibooks.org/wiki/Circuit_Theory/Resistors
 As the name states, a source is something that drives the cricuit. In other words, it
forceselectric current (either by creating a potential drop/difference between any points in
a circuit or by directly forcing a current) through the circuit to serve its purpose.

Examples of sources :

 Signal generator (or function generator) - Generates commonly used AC signals

like sinusoidal, traingular, rectangular, etc.
 Current source - Generates a DC current that is supplied to the circuit.
 DC Voltage Source - Creates a potential difference between two points in a circuit
for current to pass.
 Various electrical components like resistors, diodes, transistors, etc. can be used
to drive some part of a circuit i.e. they act as a source for some part of a circuit.

https://www.quora.com/What-is-the-source-in-a-circuit

A current source is an electronic circuit that delivers or absorbs an electric current which is
independent of the voltage across it.

A current source is the dual of a voltage source.

Applying Kirchhoff’s Rules

By applying Kirchhoff’s rules, we generate equations that allow us to find the unknowns
in circuits. The unknowns may be currents, emfs, or resistances. Each time a rule is
applied, an equation is produced. If there are as many independent equations as
unknowns, then the problem can be solved. There are two decisions you must make
when applying Kirchhoff’s rules. These decisions determine the signs of various
quantities in the equations you obtain from applying the rules.

1. When applying Kirchhoff’s first rule, the junction rule, you must label the current in
each branch and decide in what direction it is going. For example, in [link], [link],
and [link], currents are labeled , , , and , and arrows indicate their directions.
There is no risk here, for if you choose the wrong direction, the current will be of the
correct magnitude but negative.
2. When applying Kirchhoff’s second rule, the loop rule, you must identify a closed loop
and decide in which direction to go around it, clockwise or counterclockwise. For
example, in [link] the loop was traversed in the same direction as the current
(clockwise). Again, there is no risk; going around the circuit in the opposite direction
reverses the sign of every term in the equation, which is like multiplying both sides of
the equation by
[link] and the following points will help you get the plus or minus signs right when
applying the loop rule. Note that the resistors and emfs are traversed by going from a to
b. In many circuits, it will be necessary to construct more than one loop. In traversing
each loop, one needs to be consistent for the sign of the change in potential. (See [link].)

Each of these resistors and voltage sources is traversed from a to b. The

potential changes are shown beneath each element and are explained in
the text. (Note that the script E stands for emf.)

Loring Chien, Electrical engineer

Answered Feb 16, 2017 · Author has 29.1k answers and 50.2m answer views
It signifies the polarity of the terminals.

The positive marked “+” will have a higher EMF, or voltage, than the one marked “-”.

Many electronics equipment can be totally ruined by misapplication of polarity, so its really
important.

Many batteries and battery compartments have slightly different terminal mechanics to
prevent incorrect insertion. e.g. cylindrical cells have a button on the positive end and a flat
on the negative side; car batteries have posts but the posts are slightly different diameters
to prevent connecting the wrong clamp to it.

Elardus Mare, BSc Engineering & Metallurgy, University of Pretoria (1986)

Updated Aug 12, 2019
Originally Answered: What do the positive and negative ends of a battery indicate?
If it's a non-rechargeable battery, the negative pole (with negative sign) is where oxidation
takes place within the battery when it is discharging with a load connected. Oxidation
releases electrons (negatively charged) that exit the battery at that pole which in
electrochemical terms is otherwise known as the anode. It is the exiting of the negative
electrons from the battery to the load that gives the negative pole its name.

The other pole (positive or cathode; with positive sign) is so-called as this is where the
electrons re-enter the battery (think negative electrons being attracted by positive pole) after
having spent their energy on the external load. Once inside the battery the electrons bind to
positively charged ions in a reduction reaction, which is why the positive pole of a non-
rechargeable battery is also called the cathode.

If it's a re-chargeable battery, the direction of electron flow is reversed when it is charged
instead of discharging. Now electrons get pushed into the battery through the negative pole
(a non-spontaneous action, think negative into negative) and exit the battery at the positive.
'Positive’ and 'Negative' terminogy are therefore fixed conventions that technically refer to a
battery's discharging or spontaneous cycle. The terms anode and cathode, on the other
hand, do change.
When the battery is being charged, the pole that previously accommodated oxidation
(therefore the anode during discharging), now accommodates the reduction reaction,
meaning it now becomes the cathode. Likewise, the positive terminal swaps between being
the cathode (discharging) to becoming the anode during charging.

Kirchhoff's Current Law

In the picture, a junction of four conductors (wires) is shown. The

currents i2 and i3are flowing into the junction, while i1 and i4 flow out of it. In this
example, Kirchhoff's Junction Rule yields the following equation:

i2+i3=i1+i4

Kirchhoff's Voltage Law

Kirchhoff's Voltage Law describes the distribution of electrical voltage within a

loop, or closed conducting path, of an electrical circuit. Specifically, Kirchhoff's
Voltage Law states that:

The algebraic sum of the voltage (potential) differences in any loop must equal zero.

The voltage differences include those associated with electromagnetic fields

(emfs) and resistive elements, such as resistors, power sources (for example,
batteries) or devices (such as lamps, televisions, and blenders) plugged into the
circuit. In other words, you can picture this as the voltage rising and falling as you
proceed around any of the individual loops in the circuit.

Kirchhoff's Voltage Law comes about because the electrostatic field within an
electric circuit is a conservative force field. In fact, the voltage represents the
electrical energy in the system, so it can be thought of as a specific case of
conservation of energy. As you go around a loop, when you arrive at the starting
point has the same potential as it did when you began, so any increases and
decreases along the loop have to cancel out for a total change of zero. If it didn't,
then the potential at the start/end point would have two different values.
Positive and Negative Signs in Kirchhoff's Voltage Law

Using the Voltage Rule requires some sign conventions, which aren't necessarily
as clear as those in the Current Rule. You choose a direction (clockwise or
counterclockwise) to go along the loop.

When traveling from positive to negative (+ to -) in an emf (power source) the

voltage drops, so the value is negative. When going from negative to positive (- to
+) the voltage goes up, so the value is positive.

Remember that when traveling around the circuit to apply Kirchhoff's Voltage
Law, be sure you are always going in the same direction (clockwise or
counterclockwise) to determine whether a given element represents an increase
or decrease in the voltage. If you begin jumping around, moving in different
directions, your equation will be incorrect.

When crossing a resistor, the voltage change is determined by the formula I*R,
whereI is the value of the current and R is the resistance of the resistor. Crossing
in the same direction as the current means the voltage goes down, so its value is
negative. When crossing a resistor in the direction opposite the current, the
voltage value is positive (the voltage is increasing).

Applying Kirchhoff's Voltage Law

The most basic applications for Kirchhoff's Laws are in relation to electrical
circuits. You may remember from middle school physics that electricity in a
circuit must flow in one continuous direction. If you break the circuit—by flipping
off a light switch—you are breaking the circuit, and hence turning off the light.
Once you flip the switch, you re-engage the circuit, and the lights come back on.

Or, think of stringing lights on your house or Christmas tree. If just one light bulb
blows out, the entire string of lights goes out. This is because the electricity,
stopped by the broken light, has no place to go. It's essentially the same as
turning off the light switch and breaking the circuit. The other aspect of this with
regard to Kirchhoff's Laws is that the sum of all electricity going into and flowing
out of a junction must be zero: The electricity going into the junction (and flowing
around the circuit) must equal zero because the electricity that goes in must also
come out.

So, next time you're working on your junction box (or observing an electrician
doing so), stringing electric holiday lights, or even just turning on or off your TV
or computer, remember that Kirchhoff first described how it all works, thus
ushering in the age of electricity that the world now enjoys.

byAndrew Zimmerman Jones

Andrew Zimmerman Jones holds advanced degrees in physics and math, about which
he has been researching, teaching, and writing for 23 years.
Updated October 01, 2018

https://www.thoughtco.com/kirchhoffs-laws-for-current-and-voltage-2698910
Medical Microbiology, 4th edition
Editor: Samuel Baron.
Editor Information
Galveston (TX): University of Texas Medical Branch at Galveston; 1996.
ISBN-10: 0-9631172-1-1

Chapter 77Protozoa: Structure, Classification,

Growth, and Development
Robert G. Yaeger.

General Concepts
Protozoa
Protozoa are one-celled animals found worldwide in most habitats. Most
species are free living, but all higher animals are infected with one or more
species of protozoa. Infections range from asymptomatic to life threatening,
depending on the species and strain of the parasite and the resistance of the
host.

Structure
Protozoa are microscopic unicellular eukaryotes that have a relatively
complex internal structure and carry out complex metabolic activities. Some
protozoa have structures for propulsion or other types of movement.

Classification
On the basis of light and electron microscopic morphology, the protozoa are
currently classified into six phyla. Most species causing human disease are
members of the phyla Sacromastigophora and Apicomplexa.

Life Cycle Stages

The stages of parasitic protozoa that actively feed and multiply are frequently
called trophozoites; in some protozoa, other terms are used for these stages.
Cysts are stages with a protective membrane or thickened wall. Protozoan
cysts that must survive outside the host usually have more resistant walls than
cysts that form in tissues.

Reproduction
Binary fission, the most common form of reproduction, is asexual; multiple
asexual division occurs in some forms. Both sexual and asexual reproduction
occur in the Apicomplexa.

Nutrition
All parasitic protozoa require preformed organic substances—that is,
nutrition is holozoic as in higher animals.
Go to:

Introduction
The Protozoa are considered to be a subkingdom of the kingdom Protista,
although in the classical system they were placed in the kingdom Animalia.
More than 50,000 species have been described, most of which are free-living
organisms; protozoa are found in almost every possible habitat. The fossil
record in the form of shells in sedimentary rocks shows that protozoa were
present in the Pre-cambrian era. Anton van Leeuwenhoek was the first person
to see protozoa, using microscopes he constructed with simple lenses.
Between 1674 and 1716, he described, in addition to free-living protozoa,
several parasitic species from animals, and Giardia lamblia from his own
stools. Virtually all humans have protozoa living in or on their body at some
time, and many persons are infected with one or more species throughout
their life. Some species are considered commensals, i.e., normally not
harmful, whereas others are pathogens and usually produce disease.
Protozoan diseases range from very mild to life-threatening. Individuals
whose defenses are able to control but not eliminate a parasitic infection
become carriers and constitute a source of infection for others. In geographic
areas of high prevalence, well-tolerated infections are often not treated to
eradicate the parasite because eradication would lower the individual's
immunity to the parasite and result in a high likelihood of reinfection.
Many protozoan infections that are inapparent or mild in normal individuals
can be life-threatening in immunosuppressed patients, particularly patients
with acquired immune deficiency syndrome (AIDS). Evidence suggests that
many healthy persons harbor low numbers of Pneumocystis carinii in their
lungs. However, this parasite produces a frequently fatal pneumonia in
immunosuppressed patients such as those with AIDS. Toxoplasma gondii, a
very common protozoan parasite, usually causes a rather mild initial illness
followed by a long-lasting latent infection. AIDS patients, however, can
develop fatal toxoplasmic encephalitis. Cryptosporidium was described in the
19th century, but widespread human infection has only recently been
recognized. Cryptosporidium is another protozoan that can produce serious
complications in patients with AIDS. Microsporidiosis in humans was
reported in only a few instances prior to the appearance of AIDS. It has now
become a more common infection in AIDS patients. As more thorough
studies of patients with AIDS are made, it is likely that other rare or unusual
protozoan infections will be diagnosed.
Acanthamoeba species are free-living amebas that inhabit soil and water.
Cyst stages can be airborne. Serious eye-threatening corneal ulcers due
to Acanthamoeba species are being reported in individuals who use contact
lenses. The parasites presumably are transmitted in contaminated lens-
cleaning solution. Amebas of the genus Naegleria, which inhabit bodies of
fresh water, are responsible for almost all cases of the usually fatal disease
primary amebic meningoencephalitis. The amebas are thought to enter the
body from water that is splashed onto the upper nasal tract during swimming
or diving. Human infections of this type were predicted before they were
recognized and reported, based on laboratory studies of Acanthamoeba
infections in cell cultures and in animals.
The lack of effective vaccines, the paucity of reliable drugs, and other
problems, including difficulties of vector control, prompted the World Health
Organization to target six diseases for increased research and training. Three
of these were protozoan infections—malaria, trypanosomiasis, and
leishmaniasis. Although new information on these diseases has been gained,
most of the problems with control persist.
Go to:

Structure
Most parasitic protozoa in humans are less than 50 μm in size. The smallest
(mainly intracellular forms) are 1 to 10 μm long, but Balantidium coli may
measure 150 μm. Protozoa are unicellular eukaryotes. As in all eukaryotes,
the nucleus is enclosed in a membrane. In protozoa other than ciliates, the
nucleus is vesicular, with scattered chromatin giving a diffuse appearance to
the nucleus, all nuclei in the individual organism appear alike. One type of
vesicular nucleus contains a more or less central body, called an endosome or
karyosome. The endosome lacks DNA in the parasitic amebas and
trypanosomes. In the phylum Apicomplexa, on the other hand, the vesicular
nucleus has one or more nucleoli that contain DNA. The ciliates have both a
micronucleus and macronucleus, which appear quite homogeneous in
composition.
The organelles of protozoa have functions similar to the organs of higher
animals. The plasma membrane enclosing the cytoplasm also covers the
projecting locomotory structures such as pseudopodia, cilia, and flagella. The
outer surface layer of some protozoa, termed a pellicle, is sufficiently rigid to
maintain a distinctive shape, as in the trypanosomes and Giardia. However,
these organisms can readily twist and bend when moving through their
environment. In most protozoa the cytoplasm is differentiated into ectoplasm
(the outer, transparent layer) and endoplasm (the inner layer containing
organelles); the structure of the cytoplasm is most easily seen in species with
projecting pseudopodia, such as the amebas. Some protozoa have a cytosome
or cell “mouth” for ingesting fluids or solid particles. Contractile vacuoles for
osmoregulation occur in some, such as Naegleria and Balantidium. Many
protozoa have subpellicular microtubules; in the Apicomplexa, which have
no external organelles for locomotion, these provide a means for slow
movement. The trichomonads and trypanosomes have a distinctive
undulating membrane between the body wall and a flagellum. Many other
structures occur in parasitic protozoa, including the Golgi apparatus,
mitochondria, lysosomes, food vacuoles, conoids in the Apicomplexa, and
other specialized structures. Electron microscopy is essential to visualize the
details of protozoal structure. From the point of view of functional and
physiologic complexity, a protozoan is more like an animal than like a single
cell. Figure 77-1 shows the structure of the bloodstream form of a
trypanosome, as determined by electron microscopy.
Figure 77-1

Fine structure of a protozoan parasite, Typanosoma evansi, as revealed by

transmission electron microcopy of thin sections. (Adapted from Vickerman
K: Protozoology. Vol. 3 London School of Hygiene and Tropical Medicine,
London, 1977, with permission.) (more...)
Go to:

Classification
In 1985 the Society of Protozoologists published a taxonomic scheme that
distributed the Protozoa into six phyla. Two of these phyla—the
Sarcomastigophora and the Apicomplexa--contain the most important species
causing human disease. This scheme is based on morphology as revealed by
light, electron, and scanning microscopy. Dientamoeba fragilis, for example,
had been thought to be an ameba and placed in the family Entamoebidae.
However, internal structures seen by electron microscopy showed that it is
properly placed in the order Trichomonadida of flagellate protozoa. In some
instances, organisms that appear identical under the microscope have been
assigned different species names on the basis of such criteria as geographic
distribution and clinical manifestations; a good example is the
genus Leishmania, for which subspecies names are often used. Biochemical
methods have been employed on strains and species to determine isoenzyme
patterns or to identify relevant nucleotide sequences in RNA, DNA, or both.
Extensive studies have been made on the kinetoplast, a unique mitochondrion
found in the hemoflagellates and other members of the order Kinetoplastida.
The DNA associated with this organelle is of great interest. Cloning is widely
used in taxonomic studies, for example to study differences in virulence or
disease manifestations in isolates of a single species obtained from different
hosts or geographic regions. Antibodies (particularly monoclonal antibodies)
to known species or to specific antigens from a species are being employed to
identify unknown isolates. Eventually, molecular taxonomy may prove to be
a more reliable basis than morphology for protozoan taxonomy, but the
microscope is still the most practical tool for identifying a protozoan
parasite. Table 77-1 lists the medically important protozoa.

Table 77-1

Classification of Parasitic Protozoa and Associated Diseases.

Go to:

Life Cycle Stages

During its life cycle, a protozoan generally passes through several stages that
differ in structure and activity. Trophozoite (Greek for “animal that feeds”) is
a general term for the active, feeding, multiplying stage of most protozoa. In
parasitic species this is the stage usually associated with pathogenesis. In the
hemoflagellates the terms amastigote, promastigote, epimastigote, and
trypomastigote designate trophozoite stages that differ in the absence or
presence of a flagellum and in the position of the kinetoplast associated with
the flagellum. A variety of terms are employed for stages in the
Apicomplexa, such as tachyzoite and bradyzoite for Toxoplasma gondii.
Other stages in the complex asexual and sexual life cycles seen in this
phylum are the merozoite (the form resulting from fission of a multinucleate
schizont) and sexual stages such as gametocytes and gametes. Some protozoa
form cysts that contain one or more infective forms. Multiplication occurs in
the cysts of some species so that excystation releases more than one
organism. For example, when the trophozoite of Entamoeba histolytica first
forms a cyst, it has a single nucleus. As the cyst matures nuclear division
produces four nuclei and during excystation four uninucleate metacystic
amebas appear. Similarly, a freshly encysted Giardia lamblia has the same
number of internal structures (organelles) as the trophozoite. However, as the
cyst matures the organelles double and two trophozoites are formed. Cysts
passed in stools have a protective wall, enabling the parasite to survive in the
outside environment for a period ranging from days to a year, depending on
the species and environmental conditions. Cysts formed in tissues do not
usually have a heavy protective wall and rely upon carnivorism for
transmission. Oocysts are stages resulting from sexual reproduction in the
Apicomplexa. Some apicomplexan oocysts are passed in the feces of the host,
but the oocysts of Plasmodium, the agent of malaria, develop in the body
cavity of the mosquito vector.
Go to:

Reproduction
Reproduction in the Protozoa may be asexual, as in the amebas and
flagellates that infect humans, or both asexual and sexual, as in the
Apicomplexa of medical importance. The most common type of asexual
multiplication is binary fission, in which the organelles are duplicated and the
protozoan then divides into two complete organisms. Division is longitudinal
in the flagellates and transverse in the ciliates; amebas have no apparent
anterior-posterior axis. Endodyogeny is a form of asexual division seen
in Toxoplasma and some related organisms. Two daughter cells form within
the parent cell, which then ruptures, releasing the smaller progeny which
grow to full size before repeating the process. In schizogony, a common form
of asexual division in the Apicomplexa, the nucleus divides a number of
times, and then the cytoplasm divides into smaller uninucleate merozoites.
InPlasmodium, Toxoplasma, and other apicomplexans, the sexual cycle
involves the production of gametes (gamogony), fertilization to form the
zygote, encystation of the zygote to form an oocyst, and the formation of
infective sporozoites (sporogony) within the oocyst.
Some protozoa have complex life cycles requiring two different host species;
others require only a single host to complete the life cycle. A single infective
protozoan entering a susceptible host has the potential to produce an immense
population. However, reproduction is limited by events such as death of the
host or by the host's defense mechanisms, which may either eliminate the
parasite or balance parasite reproduction to yield a chronic infection. For
example, malaria can result when only a few sporozoites of Plasmodium
falciparum—perhaps ten or fewer in rare instances—are introduced by a
feedingAnopheles mosquito into a person with no immunity. Repeated cycles
of schizogony in the bloodstream can result in the infection of 10 percent or
more of the erythrocytes—about 400 million parasites per milliliter of blood.
Go to:

Nutrition
The nutrition of all protozoa is holozoic; that is, they require organic
materials, which may be particulate or in solution. Amebas engulf particulate
food or droplets through a sort of temporary mouth, perform digestion and
absorption in a food vacuole, and eject the waste substances. Many protozoa
have a permanent mouth, the cytosome or micropore, through which ingested
food passes to become enclosed in food vacuoles. Pinocytosis is a method of
ingesting nutrient materials whereby fluid is drawn through small, temporary
openings in the body wall. The ingested material becomes enclosed within a
membrane to form a food vacuole.
Protozoa have metabolic pathways similar to those of higher animals and
require the same types of organic and inorganic compounds. In recent years,
significant advances have been made in devising chemically defined media
for the in vitro cultivation of parasitic protozoa. The resulting organisms are
free of various substances that are present in organisms grown in complex
media or isolated from a host and which can interfere with immunologic or
biochemical studies. Research on the metabolism of parasites is of immediate
interest because pathways that are essential for the parasite but not the host
are potential targets for antiprotozoal compounds that would block that
pathway but be safe for humans. Many antiprotozoal drugs were used
empirically long before their mechanism of action was known. The sulfa
drugs, which block folate synthesis in malaria parasites, are one example.
The rapid multiplication rate of many parasites increases the chances for
mutation; hence, changes in virulence, drug susceptibility, and other
characteristics may take place. Chloroquine resistance in Plasmodium
falciparum and arsenic resistance in Trypanosoma rhodesiense are two
examples.
Competition for nutrients is not usually an important factor in pathogenesis
because the amounts utilized by parasitic protozoa are relatively small. Some
parasites that inhabit the small intestine can significantly interfere with
digestion and absorption and affect the nutritional status of the
host; Giardia and Cryptosporidium are examples. The destruction of the
host's cells and tissues as a result of the parasites' metabolic activities
increases the host's nutritional needs. This may be a major factor in the
outcome of an infection in a malnourished individual. Finally, extracellular or
intracellular parasites that destroy cells while feeding can lead to organ
dysfunction and serious or life-threatening consequences.
Go to:

References
1. Englund PT, Sher A (eds): The Biology of Parasitism. A Molecular and
Immunological Approach. Alan R. Liss, New York, 1988 .
2. Goldsmith R, Heyneman D (eds): Tropical Medicine and Parasitology.
Appleton and Lange, East Norwalk, CT, 1989 .
3. Lee JJ, Hutner SH, Bovee EC (eds): An Illustrated Guide to the
Protozoa. Society of Protozoologists, Lawrence, KS, 1985 .
4. Kotler DP, Orenstein JM. Prevalence of Intestinal Microsporidiosis in
HIV-infected individuals referred for gastrointestinal evaluation. J
Gastroenterol. 1994;89:1998. [PubMed]
5. Neva FA, Brown H: Basic Clinical Parasitology, 6th edition, Appleton
& Lange, Norwalk, CT, 1994 .
Copyright © 1996, The University of Texas Medical Branch at Galveston.

Bookshelf ID: NBK8325PMID: 21413323

Protozoa
Protozoa are single celled organisms. They come in many different
shapes and sizes ranging from an Amoeba which can change its shape
to Paramecium with its fixed shape and complex structure. They live
in a wide variety of moist habitats including fresh water, marine
environments and the soil.
1.

Amoeba proteus protozoa

These are freshwater single-celled microbes that feed on bacteria and smaller protozoa. They
use pseudopodia (cytoplasmic extensions) to engulf their food and for locomotion.
2.
The test (shell) of the British formaminiferan, Elphidium crispum.

Foraminifera are single-celled protozoa which construct and inhabit shells. The shells are
usually divided into chambers which are added during growth. These shells are made of
calcium carbonate but some are made from sand and even silica.
An illustration of the protozoan Trypanosoma brucei.

This illustration depicts Trypanosoma brucei moving past human red blood cells in the blood.
It is motile and has a single flagellum for locomotion.

© John Bavosi / Science Photo Library

Vorticella ciliate in compost heap.

Vorticella is bell- shaped with a contractile stalk (bottom) to anchor itself to the surface. It
has a flattened top with a mouth surrounded by a wreath of cilia (tiny hair-like projections).
By beating these cilia the organism causes the water to swirl like water down a plug hole
which draws bacteria into its mouth.
5.

Paramecium – a protozoan
 This single-celled organism lives in freshwater habitats. It is covered in cilia, short hair-like
structures used for swimming and for wafting food into its groove-like mouth (centre).
Some are parasitic, which means they live in other plants and animals including humans, where
they cause disease. Plasmodium, for example, causes malaria. They are motile and can move by:

 Cilia - tiny hair like structures that cover the outside of the microbe. They beat in a
regular continuous pattern like flexible oars.
 Flagella - long thread-like structures that extend from the cell surface. The flagella move
in a whip-like motion that produces waves that propel the microbe around.
 Amoeboid movement - the organism moves by sending out pseudopodia, temporary
protrusions that fill with cytoplasm that flows from the body of the cell.

https://microbiologyonline.org/about-microbiology/introducing-microbes/protozoa

Pseudopodia A temporary cytoplasmic extension is known as pseudopodium, which

means literally ‘false foot’. Pseudopodia are powered by microfilaments near the cellular membrane.