Unicellular organisms consist of a single cell and include protists, bacteria, and viruses. Protists such as amoebas, euglenas, and paramecia are eukaryotic organisms that can be plant-like, animal-like, or fungus-like. Bacteria are prokaryotic and can be found almost everywhere on Earth. Viruses are non-cellular and can only reproduce inside host cells.

1. Unicellular
Microorganism
M. Vasquez Rev. 2.1

2. Unicellular Microorganism…
A unicellular organism, also known as a single-celled
organism, is an organism that consists of only one cell.
Unicellular (one celled) organisms are good models for
membrane transport, because they need to perform many
functions with one cell, rather than many types of cells
In single-celled organisms, all life processes are carried
out in just one cell.

3. Unicellular Microorganism (Single celled
organisms) can be classified into 3 main
categories:
– Protists
– Bacteria
– Viruses

4. Protists are primarily classified according
to how they obtain nutrition:
a.Animal-like—heterotrophs
(eat other organisms)
b. Plant-like—autotrophs
They contain chloroplasts
and make their own food
(photosynthesis).
a. Fungus-like—
Decomposers/Heterotrophs
Didinium
Paramecium
eating
Green like plants!
Water mold

5. Protists
• contain a cell membrane, nucleus and various organelles.
• Some protists contain chloroplasts.
• These organisms play an important role in the worlds oxygen
production.
• They are also an important part of many aquatic food chains.

6. • Some protists cause disease.
• These “bad” protists are known as pathogens.
• Amoebic dysentery and malaria are two diseases caused by such
pathogens.

7. Euglena: a genus of microscopic organisms in the Protista
Kingdom
- lives in fresh water, and are especially common in warm
seasons, when they populate drainage ditches and ponds.
Euglena has a spindle-shaped body, and range in size from
1/1000 to 1/100 of an inch (0.025 to 0.254 mm) long.
-Some species also eat small particles of food.
-moves via a flagellum, which is a whip- like
appendage that sticks out of the body.

8. - some Euglena also have a specialized “eye spot”, which
serves as a light sensor, directing them toward available light.
Chloroplasts
Flagellum

10. Euglena Hibernation/Reproduction
Hibernation: when conditions are bad
(dry or too hot/cold)
Euglena forms into a sphere, called the palmelloid stage.
Each euglena then discards its flagellum, and forms a mucus
outer covering.

11. Euglena undergo reproduction called “binary fission”
Each euglena first creates two of everything, then splits evenly
into two halves.

12. Paramecium: another genus of Protists, often called “slipper
protists” because of their shape like a bedroom slipper.
• - usually less than 0.01 inches (.25mm) in length, and
covered with very small hair like projections called cilia.
• Cilia are used in movement, and during feeding.
• Paramecium does NOT have chloroplasts so therefore is a
strict consumer.
• -It eats small particles of food or bacteria from fresh water
where it lives.
• The most common paramecium is Paramecium caudata,
which is used for research

13. • Paramecium makes movements with cilia to sweep prey
organisms, along with some water, through the oral groove,
and inside the mouth opening. The food passes through
the cell mouth into the gullet.
• Ciliates' bodies are covered with fine cytoplasmic hair-
like structures called cilia.
• Contractile vacuoles function in regulating the water content
within the cell and may also be considered excretory structures,
since the expelled water contains metabolic wastes.
• Paramecia have two kinds of nuclei: a large ellipsoidal nucleus
called a macronucleus and at least one small nucleus called a
micronucleus.

14. Paramecium Anatomy

15. Paramecium Reproduction
Paramecium have two
ways to reproduce.
They can reproduce
Asexually, and split
into two (binary fission)
This type of reproduction does NOT
involve the swap of genetic material, and
makes a clone of the parent.

16. The second form of reproduction is
called conjugation(cell-to-cell contact or by a bridge-like
connection between two cells.), and involves the
paramecium swapping genetic material
This type of reproduction
does not result in a clone,
but an individual with a
new set of genetic
instructions.
This will lead to genetic variation within
the population of paramecium.

17. Amoeba: one of the simplest of the protists.
- Amoeba possess a very flexible cell membrane, and
constantly moving Cytoplasm
moves by “pouring” cytoplasm into extensions of the cell
membrane, called pseudopodia (a temporary protrusion of the surface of
an amoeboid cell for movement and feeding)
- the shape of the amoeba continually changes as new
pseudopodia are created, and others disappear.
Eats by surrounding its prey with pseudopods, and
slowly engulfing it. This is called phagocytosis.

18. • Amoeba’s are tiny single-celled organisms which need to be
viewed using a microscope. There are many different species,
but the biggest is only 1 mm across.
• Amoeba’s have pseudopods or ‘false feet’. These are produced
when the amoeba changes its body shape and help it move
around.

20. Unicellular Algae:
a. Phytoplankton provides a source of nourishment
for other organisms
b. Protists recycle sewage and waste materials.

21. Prevention…
The nose is the pathway of the amoeba, so
infection occurs most often from diving, water skiing, or
performing water sports in which water is forced into the
nose.
There are some steps to take to try to avoid contracting the
brain-eating amoeba.
• Avoid hot springs
• Swim in salt water or heavily chlorinated water
• Don’t swim in poorly maintained swimming pools
• Consider wearing a nose plug when swimming
• Don’t swim with an open wound

22. Bacteria These are the smallest and simplest forms of life on earth.
• Bacteria consist of only a single cell each, whereas each one of
you is made up of about 10,000,000,000,000 cells! If there is
just one of them, we call it a bacterium.
• Bacteria lack most of the organelles that other cells have.
• Bacteria have many different shapes. Some have 'tails' (called
flagella) that let them swim. They rotate their flagella like tiny
propellers to move themselves through liquids.
• They do not have a nucleus or nuclear membrane
• Bacteria can be found almost everywhere! Bacteria live on or in
just about every material and place on Earth, from soil to water
to air, and from your body.

24. Can live in colonies
• Strepto – in chains
• Staphylo – grape-like clusters
• Diplo – pairs
Types of Bacteria
• Gram positive bacteria have a thick cell wall and stain
purple
• Gram negative bacteria have a thin cell wall with an outer
lipid layer and stain pink.

25. Bacteria Reproduction
• Bacteria contain a single strand of DNA that controls all of
their functioning.
• In addition, they may contain one or more plasmids.
• Plasmids are circular DNA molecules that contain non-
essential genes.
BACTERIA REPRODUCES BY FISSION

26. Bacteria can reproduce sexually - conjugation or asexually -
binary fission.

27. CONJUGATION

28. Most motile bacteria move by the use of flagella, rigid
structures 20 nm in diameter and 15-20 µm long which protrude
from the cell surface, e.g. the Chromatium cells in the video. In
some bacteria, there is only a single flagellum – such cells are
called monotrichous

29. 29
STRUCTURE OF BACTERIAStructure Function
Cell Wall Protects and gives shape
Outer
Membrane
Protects against antibodies (Gram Neg. Only)
Cell
Membrane
Regulates movement of materials, contains
enzymes important to cellular respiration
Cytoplasm Contains DNA, ribosomes, essential compounds
Chromosome Carries genetic information
Plasmid Contains some genes obtained through
recombination
Capsule &
Slime Layer
Protects the cell and assist in attaching cell to
other surfaces
Endospore Protects cell against harsh environments
Pilus Assists the cell in attaching to other cells
Flagellum Moves the cell

31. Salmonella
Vibrio cholerae

33. 33
Bacteria and Disease
Disease Pathogen Areas
affected
Mode of
transmission
Botulism Clostridium botulinum Nerves Improperly
preserved food
Cholera Vibrio cholerae Intestine Contaminated water
Dental Caries Streptococcus mutans,
sanguis, salivarius
Teeth Environment to
mouth
Gonorrhea Neisseria gonorrhoeae Urethra,
fallopian
Sexual contact
Rocky
Mountain SF
Rickettsia recketsii Blood,
skin
Tick bite
Strep throat Streptococcus pyogenes URT,
blood,
skin
Sneezes, coughs,
etc.
Tetanus Costridium tetani Nerves Contaminated
wounds
Tuberculosis Mycobacterium tuberculosis Lung,
bones
coughs

34. Prevention…
The best way to prevent bacterial disease is
through sanitation.
Washing your hands, food, and plates before eating prevents
large amounts of bacteria from entering our bodies.

35. Virus - A virus is a non-cellular particle made up of
genetic material and protein that can invade living cells
• Viruses are smaller than bacteria, they range in size
between 20-300 nanometer (nm)
• Viruses contain only one type of nucleic acid, either DNA or
RNA, but never both.
• Viruses consist of nucleic acid surrounded by a protein coat.
Some viruses have additional lipoprotein envelope.
• Viruses lack cellular organelles, such as mitochondria and
ribosomes.
• Viruses are obligate cellular parasites. They replicate only
inside living cells.

36. ™
• Viruses are not classified into any of the biological
classification system.
• They lie in the threshold of They lie in the threshold of life
and nonlife.
• Viruses replicate through replication of their nucleic acid and
synthesis of the viral protein.
• Viruses do not undergo binary fission.
• The capsid is composed of small structural units called
capsomeres

37. • Viruses composed of nucleic acid either DNA or RNA,
surrounded by a protein coat called the capsid.
• The capsid protects nucleic acid from inactivation by the
outer physical conditions.

38. Virus size Viruses are
smaller than bacteria.
Viruses are too small even
to be seen by a light
microscope. The biggest
size virus is about 240-
300nm (1/10 of red blood
cells/ size of the smallest
bacteria) The tiniest virus is
20nm – smaller than a
ribosome.
Virus Size

39. Virus origin According to a hypothesis, viruses are bits of
nucleic acid that ‘escaped’ from cellular organism.
• Some traces are from animal cells, plant cells and bacterial
cells.
• Their multiple origins explain why viruses are species-
specific.
• However, some other have broader range of host cells
• Have 2 parts:
– Protein cover
– Genetic material

40. Bacteriophage

41. Bacteriophage
• Much of the knowledge comes fromstudying bacteriophage,
because they cane cultured easily within living bacteria.
• Bacteriophage possessed DNA inside their capsid (protein
head).
• The capsid functions as protection of their genetic material.
• Their tail fibers are the base used to attach themselves to
bacterial host cell.
• The tail is the channel for their genetic material to be
injected to the host cell.

42. • To be able to reproduce, a virus needs a host cell.
• Once inside, viruses “hijack” the host’s DNA and enzymes to
reproduce itself.
• Some modify the genetic info in the DNA
• When viral particles are produced, they are released from the
cell (lysis)
• Examples: influenza (flu), smallpox, measles, HIV

43. Virus shape
Virus shape Virus shape can be based on the capsid
• Helical (rod-shaped) e.g. tobacco mosaic virus
• Polyhedral / Icosahedral (many-sided shaped) e.g.
adenovirus.
• Complex combination of both by having structures like tail
(helical and polyhedral) e.g. bacteriophage iv.
• Most enveloped virus have spherical shape e.g. influenza
virus

46. Reproduction of Viruses
Two types:
lytic cycle – destroys the host cell very quickly
lysogenic cycle – a.k.a. ‘slow’ or latent virus. Can remain in a
cell for years before becoming active destroying the cell

55. Virus-like agents
• Viruses is considered as the Viruses is considered as the
smallest living / nonliving microbe. smallest living / nonliving
microbe. ™
• However, there are even smaller However, there are even
smaller infectious agents found infectious agents found –
viroids and prions.

58. Living qualities of viruses
- they could only reproduce within the living cells that
they infect. They use their genetic information to force the host
cell to replicate themselves.
1. Capsid or protein coat
2. genetic material either DNA or RNA
3. Some have enzymes (proteins)
4. Some have a lipid coat or capsule

59. Non-living qualities of viruses
- they do not have the components to carry metabolic
activities.
1. Acellular (Non-cellular)
2. Do not grow
3. Do not make or use energy
4. Do not respond to stimuli
5. Cannot reproduce on their own
6. Can be crystallized

60. Are viruses alive?
• viruses require cells to reproduce, and are not cellular
• they don’t fit the Cell Theory: all living things are composed
of cells
No, they are not considered to be alive!
Thank You!