Download life in a drop of water

LIFE IN A
DROP OF WATER
Educational Video
24 Minutes
Copyright, MMI
Rainbow Educational Media, Inc.
Distributed by:
United Learning
1560 Sherman Ave., Suite 100
Evanston, IL. 60201
800-323-9084
www.unitedlearning.com |
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PRINCIPLE CREDITS
Producer, Writer &
Director:
Consultants:
Peter Matulavich
Ira Jones, Ph.D.
Dept. of Biological Sciences,
California State University,
Long Beach
Michael Worosz, M.A.
Curriculum Consultant
Videography, Animation
& Editing:
Peter Matulavich
Special Thanks To:
Steve Barlow, Ph. D.
Electron Microscope Center,
San Diego State University
Dan McKinney
Swift Instruments
Jones Biomedicals &
Laboratory
Pinecrest School,
Woodland Hills, CA
Video and Teacher's Guide produced for
Rainbow Educational Media
by Peter Matulavich Productions
San Dimas, California
TABLE OF CONTENTS
Introduction
2
Objectives
3
Summary
4
Review Questions
7
Discussion Questions
10
Activities
12
Glossary
14
Bibliography
18
Websites
20
Script
22
INTRODUCTION
This video is designed to introduce students to the wide
variety of microscopic organisms that inhabit fresh
water. There are tens of thousands of different types and
they can be found in every lake, pond, stream and
puddle. Hundreds, even thousands, can be found in a
single drop of water.
The video discusses the proper methods of obtaining
water samples at a pond, and how to prepare specimens
for study under a microscope.
Students learn that the organisms found in pond water
share much in common with humans, in that they are all
composed of cells. A cell is the basic unit of which all
living things are composed and consist, at the very least,
of a nucleus which controls cell activity, cytoplasm, a
liquid in which many cell reactions occur, and the
membrane, which holds the cell together.
Much of the video is devoted to featuring the many
fascinating organisms found in pond water, including
bacteria, microscopic algae, protozoa, and various multicellular organisms. These organisms are important
because all of them form the bottom of the food chain,
some produce oxygen, and many are used in scientific
studies.
The video concludes with a discussion of how some of
these organisms are carriers of disease and that millions
of people die each year due to diseases carried by some
types of bacteria and protists.
After viewing this video, students will be left with a
greater appreciation for these fascinating organisms, and
that while they may be small, they are an essential part of
the world around us.
OBJECTIVES
After viewing this video, students should know:
• microscopic organisms can be found in every
body of water, including lakes, ponds, streams,
and puddles
• hundreds, even thousands of pond organisms,
can be found in a single drop of water
• microscopic pond organisms share much in
common with humans, in that they are composed
of cells
•
organisms that inhabit pond water include bacteria, algae, protozoa, and multicellular organisms
• common types of protozoa include
Paramecium, Blepharisma, Spirostomum,
Dileptus, Stentor, Vorticella, Bursaria,
Didinium, and amoebas
• common multicellular microscopic organisms
include rotifers, Daphnia, Cyclops, and hydras
• microscopic pond organisms form the bottom of
the food chain
• algae are responsible for producing most of the
air that we breath
• protists are often used in the study of genetics
• some bacteria and protists are carriers of disease
SUMMARY
The video opens with a fast-paced sequence featuring a
variety of fascinating pond organisms. The narrator then
states that these organisms can be found in every lake,
pond, stream and puddle. Mostly microscopic in size,
hundreds, even thousands, can be found in a single drop
of water.
Students are then featured at a pond collecting pond
water to study later at school. They start by collecting
pond scum which is usually filled with micro-organisms.
Then they add water and cap their jar.
Back in the classroom, the students use an eyedropper to
deposit a drop of water onto a glass slide. The slide is
then covered with a coverslip and placed on a microscope
stage. The narrator explains that while the organisms
found in a drop of water may look strange, they share
much in common with us, because they are composed of
cells just as we are. To emphasize this point, a student is
shown scraping the inside of his cheek with a toothpick
and then dabbing this on a glass slide for examination
under the microscope. The student discovers that the
inside of his mouth is made up of tiny uniform structures
called cells that are not that much different from the ones
that make up the organisms found in a drop of water.
Animation is then used to show how an animal cell is
similar to an amoeba, a single-celled organism found in
pond water. Both cells contain a nucleus, cytoplasm, and
a membrane. It is explained that the nucleus is the
control center of the cell, that cytoplasm is a fluid in
which many cell reactions occur, and that the cell
membrane controls what goes into and comes out of a
cell.
The narrator explains that the smallest organisms that
can be seen with an ordinary microscope are bacteria.
Most bacteria are so small it would take about 10,000 of
them laid end to end to equal one centimeter. While they
may be small, they grow in great numbers and are an
important food for other microscopic organisms which
feed on them practically non-stop.
Another important food source for many pond organisms
are the algae, which are plantlike organisms. Algae
belong to a larger group called protists, which include
organisms that are neither plant nor animal. Most algae
are filled with chlorophyll, a green substance that can be
compared to blood in animals, and which permits
photosynthesis. Several types of algae are then featured,
including some that have a thin, barely visible tail called
a flagellum which helps propel them through water.
Students learn that protists that possess flagella are
called flagellates. Other featured algae include Volvox
and Spirogyra. Also featured are euglenas and diatoms,
which are closely related to algae.
The video then introduces the protozoa, which are protists
that are more animallike than plantlike. A well-known
protozoan is the paramecium, which resembles a tiny
slipper as it swims about looking for food. Paramecium
is referred to as a ciliate because it is covered by rows of
short hairlike strands called cilia. Most protozoa are
ciliates. Like most protozoa, para-mecia use structures
called contractile vacuoles to maintain the proper amount
of water within their bodies. Paramecia reproduce
themselves during a process called fission in which it
appears that two paramecia are joined at the ends.
Sometimes confused with fission, is conjugation, during
which two paramecia are joined at the sides in order to
exchange cell material.
Protozoa featured in the video are Blepharisma,
Spirostomum, Dileptus, Lacrymaria Olor, Stentor,
Vorticella, Bursaria, Didinium, and amoeba.
Microscopic multicellular organisms featured are rotifers,
Daphnia, Cyclops, seed shrimp, and hydras.
The video concludes with a discussion that while these
organisms may be small, they are very important. All of
them form the bottom of the food chain, some are
responsible for producing most of the air that we breath,
many are used in scientific studies, and some are carriers
of disease. So as small as these organisms are, they are
an essential part of the world around us.
REVIEW QUESTIONS
1. In what bodies of water can you find
freshwater microscopic organisms?
They can be found in every lake, pond, stream and
puddle.
2. How many different kinds of pond organisms are
there?
Tens of thousands.
3. What do we share in common with pond
organisms?
We are all composed of cells.
4. What do you call a cell's control center?
The nucleus.
5. What is the name of the fluid that surrounds the
nucleus?
Cytoplasm.
6. What gives a cell its shape?
The membrane.
7. What are the smallest organisms that can be seen
with an ordinary microscope?
Bacteria.
8. Why are bacteria important?
They are an essential food for other micro organisms.
9. What is another important food source for
many pond organisms?
Algae.
10. How do algae obtain their food?
Through photosynthesis.
11. What is the green substance found in most
algae?
Chlorophyll.
12. What are clusters of algae called?
Colonies.
13. What are protists that possess flagella called?
Flagellates.
14. Why is a euglena's eyespot important? It
enables it to find areas of light.
15. What does protozoa mean?
First animals.
16. What are protozoa which possess cilia called?
Ciliates.
17. What structures in protozoa allow them to
take in and expel water?
Contractile vacuoles.
18. How do most protozoa reproduce?
Through fission.
19. What is the name of the process during which
protozoa exchange cell material?
Conjugation.
20. What is the name of the enclosure a protozoan
forms when it enters a state of suspended
animation?
A cyst.
21. How does an amoeba move?
By sending out streams of cytoplasm called
pseudopods.
22. What is the name of the bubbles which
protozoa form to surround food?
Food vacuoles.
23. In what ways are protists important?
All of them form the bottom of the food chain,
some are responsible for producing most of the air
that we breath, many are used in scientific studies,
and some are carriers of disease.
DISCUSSION QUESTIONS
1. The video mentions that hundreds, even thousands of microscopic organisms can be found in a
drop of water.
Is it possible to find even more?
Yes. Some protozoa are just a few microns (a few
thousandth of a millimeter) long. Tens of thousands
of these could easily fit into a drop of water. Some
bacteria are even smaller. Millions, even billions,
could be found in a drop of water.
How large are the largest freshwater protozoa?
The largest include some amoeba, which can
range from one to five millimeters in length.
2. Only freshwater protozoa are featured in this
video.
Are protozoa found elsewhere?
They are also found in saltwater, in damp soil, and
within the bodies of other organisms.
3. The video mentions how an animal cell shares
similarities with the single cell of a protozoa.
How are these cells different?
A protozoan cell is a complete life form capable of
living independently of other cells. An animal cell is
highly specialized and is dependent on other types
of cells to live.
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4. The nucleus is the control center of a cell?
Do protozoa have only one nucleus?
A few protozoa, including some types of amoebas,
have more than one nucleus. Some ciliates have a
macronucleus and a micronucleus, the latter controlling reproduction.
5.
When photographed, many ciliates like Paramecium appear to have cilia lining only their
outer edges.
Are those the only places cilia are found?
The bodies of Paramecium and many other ciliates
are completely covered with cilia. When viewed
through the backlight of a microscope, only the cilia
lining an organism's edges are usually visi ble.
11
ACTIVITIES
These activities are designed to encourage
students to learn more about some of the
things covered in the video.
1. The video features students observing a variety of
pond organisms.
Activity: Have students collect pond water to study
later in class.
2. Students are shown drawing a pond organism as
they observe it through a microscope.
Activity: Have students do the same. They might
use a protozoa reference book to assist them.
3. Some bacteria and protists are known to
cause disease.
Activity: Have students research and report
on a plague or disease caused by bacteria or
protists.
4. A variety of organisms are shown in the
video.
Activity: Have students research and report on
any of these organisms, or any others they
might be interested in.
5.
The video features a boy examining his own
cheek cells.
Activity: Have students scrape the inside of their
cheeks with toothpicks in order to observe their
own cheek cells through a microscope.
12
6. The video discusses how euglena favor light.
Activity: Obtain a thick euglena culture from a
biological supply company and pour it into a petri
dish. Cover it with a lid that is half covered with
foil. Place this near a window. Have students
examine the dish the next day. Students should
discover that the euglena favor that part of the dish
exposed to light and will congregate there, making
that part of the dish darker green from the greater
number of euglena.
7. Bacteria are featured in the video.
Activity: Have students produce their own culture
rich in bacteria by adding dried egg yolk, rice grains,
or the broth obtained from boiling wheat kernels to
a sample of spring water. Have them make periodic
observations to see what changes occur over time.
8. Protozoa are easy to keep.
Activity: Have students keep a protozoa culture
several weeks, adding spring water when necessary.
Have them make periodic observations to see what
changes occur in the culture over time.
9. Cyclops and hydras are multicellular organisms
named after characters from Greek mythology.
Activity: Have students research these characters to
see why their names were lent to the mentioned
organisms.
13
GLOSSARY
algae: plantlike protists that rely on photosynthesis
amoeba: a single-celled pond organism which moves by
sending out streams of cytoplasm
bacteria: the smallest and simplest single-celled
organisms; some cause disease
Blepharisma: a protozoan with a large oral funnel lined
with long cilia
brood chamber: the enclosure in some organisms in
which eggs are carried
Bursaria: a very large protozoan with a gaping mouth
used to swallow other protozoa whole
cell: the basic unit of which all living things are composed
chlorophyll: the green substance in plants and some
protists that can be compared to blood in animals
cilia: the hairlike structures found on the surface of
some protists used for propulsion and food gathering
ciliate: a protozoan with cilia
colony: a group of organisms that live together for a
common good
compound eye: a multi-faceted eye
conjugation: the process by which some simple
organisms exchange cell material
14
contractile vacuole: a round structure found in protozoa
which is used like a pump to take in and expel water
coverslip: a thin piece of glass used to cover a specimen
on a glass slide
Cyclops: a multicellular pond organism with a single eye
and long drooping antennae
cyst: a protective enclosure in which protozoa protect
themselves while dormant
cytoplasm: the cell fluid in which many reactions occur
Daphnia: a micro crustacean with large antennae
related to shrimp, crabs, and lobsters
diatom: a hard-shelled protist related to algae
Didinium: a fast-moving protozoa which remains in
constant motion searching out Paramecium, its only food
Dileptus: a protozoan with a long trunk which it
waves through the water
euglena: a protist related to algae that relies on photosynthesis
fission: the process by which some simple organisms
reproduce themselves
flagellate: a protist that possesses at least one flagel-lum
flagellum: a thin, hairlike structure used by some protists for propulsion
15
food chain: a model that shows how energy moves in
an ecosystem, based on large animals eating smaller
animals which eat even smaller animals
food vacuole: a bubble-like enclosure a protozoan
forms to surround captured prey and food
Giardia: a protist that can cause sickness in animals
when swallowed
glass slide: a rectangular piece of glass upon which a
specimen is placed for microscopic study
hydra: a multicellular pond organism with tentacles
Lacrymaria Olor: a protozoan with a long neck and
which resembles a swan
membrane: the thin layer of tissue that surrounds
cells
micro-organism: a microscopic organism
nucleus: the control center of a cell
oral groove: a channel along the side of Paramecium
which is used for directing food into its gullet
Paramecium: a single-celled organism that resembles a
slipper
photosynthesis: a process in which sunlight is converted
into food
protist: an organism that is neither plant nor animal
protozoa: microscopic, single-celled organisms
pseudopod: a stream of cytoplasm sent out by an
amoeba; false foot
16
rotifer: a multicellular organism with cilia on top of its
head which resemble two spinning rotors
seed shrimp: a multicellular pond organism enclosed in
a seed-like enclosure
Spirogyra: algae with spiral-shaped structures that
contain chlorophyll and which form long strands sometimes referred to as pond scum
Spirostomum: a large, worm-like protozoan
stage: a platform on which a specimen is placed for
study under a microscope
Stentor: a large protozoan with a large mouth lined with
long cilia
tentacle: a long, slender part growing around the head
or mouth of some animals
Volvox: a ball-shaped colony of green algae Vorticella:
a bell-shaped protozoan with a coiled stalk
17
BIBLIOGRAPHY
Burgess, Jeremy and Marten, Michael and Taylor,
Rosemary. Under the Microscope. Cambridge
University Press, 1987
Dobell, Clifford. Antony Van Leeuwenhoek and His
"Little Animals". Dover Publications, Inc.
Ford, Brian J. Single Lens. Harper & Row, Publishers,
1985
Headstrom, Richard. Adventures with a Microscope.
Dover Publications, Inc.
___________. Adventures with Freshwater
Animals. Dover Publications, Inc., 1964
Johnson, Gaylor and Bleifeld, Maurice. Hunting with the
Microscope. Arco Publishing, Inc. 1985
Kelley, Susan G. and Post, Frederick J. Basic
Microbiology Techniques. Star Publishing
Company, 1982
Kudo, Richard R. D.Sc. Protozoology. Charles C
Thomas, Publisher, 1966
McCormick, J.B., M.D. and Turner, Gerard L'e, M.Sc.
Antique Microscopes. Replica Rara Limited, 1975
Pennak, Robert. Fresh-Water Invertebrates of the
United States, John Wiley & Sons, 1978
Rainis, Kenneth G. Exploring with a Magnifying
Glass. Franklin Watts, 1991
18
Reid, George K., Ph.D. Pond Life. Golden Press, 1967
Singleton, Paul and Sainsbury, Diana. Introduction to
Bacteria. John Wiley & Sons, 1981
Stehli, Georg, Dr. The Microscope and How to Use it.
Dover Publications, Inc., 1960
VanCleave, Janice. Microscopes and Magnifying
Lenses. John Wiley & Sons, Inc., 1993
Worvill, Roy, M.Sc. The Telescope & Microscope.
Ladybird Books Ltd., 1971
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WEBSITES
The following list includes some of the best websites
devoted to pond organisms, protists and microscopy.
Protist Image Data
(http://megasun.bch.umontreal.ca/protists/protists.html)
This award-winning site provides pictures and information on selected algae and protozoa. While the text is
advanced, the picture gallery features top quality images.
Each featured species has articles on appearance,
reproduction, classification and much more.
Steve Durr's Homepage
(http://www.durr.demon.co.uk) This site is put together by
the photographer of the Institute of Neurology in
London. Steve's goal is to make a permanent record of
the interesting plant and animal life found in freshwater
in and around London. Steve's images are outstanding
and so is his text.
Society of Protozoologists
(http://www.uga.edu/~protozoa) Maintained by America's
leading protozoology organization, this site features
images and articles on a wide variety of protists.
CellsAlive
http://www.cellsalive.com
This site features a rich assortment of photographs, artwork and articles dealing with cells, including protists
and bacteria.
Light Microscopy Forum
(http://www.microimaging.ca)
This site features images and articles on microscopes,
pond organisms and polarized light.
20
Micscape
(http://www.microscopy-uk.org.uk) This acclaimed site,
devoted to the miniature world, includes a handy pulldown menu that leads to a variety of interesting topics,
including articles and images on algae, protozoa, crystals,
bat droppings, snow — just about anything that can be
placed under a microscope and examined.
Molecular Expressions
(http://micro.magnet.fsu.edu/micro/gallery.html) This
outstanding site features an expansive photo gallery with
hundreds of images, and articles on microscopes and
microscopy. One of the highlights is a section featuring
antique microscopes.
NanoWorld
(http://www.uq. oz.au/nanoworld/images_l.html) This site
features a wide variety of fascinating specimens
photographed with an electron microscope.
Project Micro
(http://www.msa.microscopy.com/ProjectMicro/PMHo
mePage.html)
Sponsored by the Microscopy Society of America, this
site offers suggestions on how to incorporate microscopy
into the classroom and makes recommendations for
books, videos and CD-ROMs related to microscopy.
Note: Some servers have difficulty reaching every site
address. If you encounter troubles, try reaching the site
by entering its name in a search engine.
21
SCRIPT
You are looking at some of the most fascinating life
forms on earth. Organisms like these inhabit every lake,
pond, stream and puddle. There are tens of thousands of
different types. Mostly microscopic in size, hundreds,
even thousands, can be found in a single drop of water.
Let's find out more about these fascinating organisms.
The journey into a drop of water begins with a visit to
your local pond. These students are collecting pond
water to study later at school. They start by collecting
some pond scum. This is usually filled with microorganisms. Then they add water. Finally, they cap their
jar. There's enough air in the water to keep the
organisms alive for a day or two. They'll also collect
water from several spots.
Back in the classroom, an eyedropper is used to deposit a
drop of water onto a glass slide. The slide is then
covered with a thin piece of glass called a cover-slip. The
slide is then placed on a microscope stage beneath two
clips.
The organisms you see in a drop of pond water may look
strange, but they share much in common with you and
me.
Here's how you can prove it. Scrape the inside of your
cheek with a toothpick. Dab this on a glass slide and
cover it with a coverslip. Then place this under your
microscope.
As you can see, the inside of your mouth is made up of
tiny uniform structures called cells. A cell is the basic
unit of which all living things are composed.
22
A person's entire body is made up of cells. Billions of
cells, that are not that much different from the ones that
make up the organisms you find in a drop of water.
In this example, the model on the right is meant to represent an animal cell, and the one on the left, an amoeba,
a single-celled organism you find in pond water.
Both cells contain a nucleus. Some amoebas may contain more than one. The nucleus is the control center of
the cell. Its job is to control the cell's activities including
reproduction.
This is the nucleus of a cheek cell.
Surrounding the nucleus is a substance called cytoplasm. This is a fluid in which many cell reactions
occur.
In the amoeba, the cytoplasm is constantly flowing,
carrying cell materials with it.
Every cell is surrounded by a membrane. The membrane
is something like a sack that holds the cell together and
gives it its shape. The cell membrane controls what goes
into and comes out of a cell.
In this dying organism, the membrane has broken and
the organism explodes, spewing out its cytoplasm and
other cell material.
All organisms on earth are made up of one or more
cells.
Many of the ones you find in a drop of water are made
up of a single cell. Each one possesses everything it
needs to live as separate organism. Each cell is a complete, independent life form.
23
The smallest organisms you can see with an ordinary
microscope are bacteria. They're the tiny specks jittering
about. Most bacteria are so small it would take about
10,000 of them laid end to end to equal one centimeter.
While they may be small, they grow in great numbers
and are an important food for other microscopic
organisms which feed on them practically nonstop. In this
scene, a tiny pond organism creates a current, directing
countless bacteria into its mouth.
Another important food source for many pond organisms
are the algae. These are plantlike organisms which
appear in a variety of forms. Some resemble plants you
find on land. Algae belong to a larger group called
protists, which include organisms that are neither plant
nor animal. But like plants, most algae are filled with
chlorophyll, a green substance that is similar to blood in
animals, and which permits photosynthesis, a process in
which sunlight is converted into food. Under a
microscope, you can often see the movement of
chlorophyll within algae.
Some algae exist as single cells, but many others join
together in clusters called colonies. Each of these cells
has a thin, barely visible tail called a flagellum which
helps propel it through water. Protists that possess flagella are called flagellates.
This colony is called Volvox and can consist of thousands
of cells. Volvox colonies appeared billions of years ago
and are thought to be the ancestors of multi-cellular
plants we find throughout the world today.
The cells in this colony move by sliding back and
forth. They resemble a carpenter's folding ruler.
The cells in other colonies form long stands. This one is
called Spirogyra. It gets its name from the spiral
structures filled with chlorophyll.
24
While pretty to look at under the microscope, large
masses of it form the green, smelly substance we refer to
as pond scum.
Closely related to algae are the euglenas. As with many
algae, these protists are filled with green chlorophyll and
rely on photosynthesis to obtain much of their food.
They move by wriggling their bodies and by waving
their flagella which are located at their front ends.
Euglenas have a reddish eyespot which enables them to
find areas of light which is important for their survival.
Other organisms closely related to the algae are the
diatoms. They have hard outer walls and are found in
both fresh water and oceans. Some diatoms are quite
beautiful and are sometimes referred to as jewels of the
sea. Some companies sell microscope slides with
diatoms arranged in beautiful snowflake patterns.
Common one-celled organisms found in pond water are
the protozoa, of which there are thousands of types. Like
algae, they too belong to the protists, but protozoa are
more animallike than plantlike.
Protozoa means "first animals" and they may very well
resemble some of the first single-celled organisms that
lived on earth billions of years ago.
Among the most common protozoa is the paramecium, of
which there are many types. These organisms resemble
tiny slippers as they swim about looking for food.
Paramecia are covered by rows of short hairlike strands
called cilia, which are visible here along their outer
edges. A protozoan that has cilia on any part of its body
is called a ciliate. Most of the protozoa you will
encounter are ciliates.
A paramecium moves by beating its cilia and spinning
its body in a spiral motion. In open water it can reach
25
remarkable speeds. It is one of the fastest protozoa.
In tight spaces, a paramecium is able to bend its body
back on itself in order to make a sharp turn.
They can distort their bodies to squeeze into narrow
channels.
They can contort their bodies so much, it can be difficult
to tell what they are.
A paramecium eats by swimming back and forth
through pond debris, feeding mostly on bacteria.
A paramecium doesn't have a mouth. Instead, it has an
oral groove. This is a channel along the side of its body
which directs food into its gullet or stomach.
You can see the oral groove more clearly as paramecia
rotate their bodies.
When you examine the interior of a paramecium, you
will notice several round structures that open and close.
These are called contractile vacuoles and work like little
pumps, as a protozoan takes in and expels water. The
vacuoles maintain the proper amount of water within a
protozoan.
You can learn a lot more about an organism by drawing it
as you observe it. Your pictures don't have to win any
awards. They're merely meant to help you become a
better observer.
Sometimes you will come across what appears to be two
paramecia connected at the ends. This is actually a
single paramecium reproducing itself in a process called
fission. A single paramecium may divide up to three
times in a single day.
Other times you may encounter two paramecia joined
26
at the sides. This is called conjugation. It is sometimes
confused with fission, but it is not. During fission, a
single paramecium reproduces itself lengthwise. During
conjugation two paramecia join at the sides in order to
exchange cell material. Conjugation enables organisms
to live longer and to better adapt to their environment.
As you examine organisms under a microscope, you may
wonder how small they really are.
This may give you an idea. These are paramecia
swimming about within an eye of a needle. As you can
see, they are very small indeed.
Another common protozoan you find in pond water is
Blepharisma. Like paramecia, it swims along feeding
mostly on bacteria. Blepharisma has a large oral funnel,
or mouth, lined with long cilia which it uses to direct
food into the funnel. As with paramecia and many other
protozoa, Blepharisma reproduces itself through fission.
These look like worms, but they're not. They're cili-ates
belonging to the group Spirostomum. They are just
about the longest protozoa you'll find in a drop of water.
They're gentle giants and feed mostly on bacteria.
Dileptus is an unusual looking protozoan because of its
long neck, or trunk. It waves this through the water,
directing food toward its mouth, located here at the base
of the trunk. Dileptus feeds mostly on bacteria and tiny
protozoa.
Another protozoan with a long neck is Lacrymaria Olor,
sometimes referred to as the "swan" because of rts
resemblance to that bird. It whips it's neck in and °ut of
pond debris searching for food.
27
This protozoan, called Stentor, likes to anchor itself to
pond debris as it sways back and forth through the water,
feeding on bacteria and small protozoa. Its large mouth
is lined with long cilia which it uses to create a current
that helps direct food into its stomach. When it is
disturbed, it will suddenly contract, disappearing into
pond debris. Stentor takes on a different appearance
when it detaches itself to swim freely through the water.
The cilia lining its mouth are then used to help propel it.
The delicate vorticella is another protozoan that likes to
anchor itself to pond debris as it feeds. The cilia lining
its mouth create twin currents, pulling in bacteria. Larger
organisms like these green algae get caught in the
current as well, but are not consumed. Vorticella have
coiled stalks which they can extend and contract quickly.
They often appear in a cluster and seem to take turns
extending and contracting.
One of the largest protozoa is Bursaria. It is a giant in
this microscopic world. With a large gaping mouth, it can
swallow other protozoa whole. This unlucky paramecium is stuck in this bursaria's stomach and will soon
be digested.
When it comes to hunting paramecia, none are better at it
than Didinium. These are the sharks of the microscopic
world. They hunt by staying in constant motion as they
search out paramecia, their only food. Once a didinium
comes in contact with a paramecium, it stabs it with a
needle-like organ that paralyzes the paramecium. The
paramecium may struggle, but seldom is it able to
escape. The didinium then sucks the paramecium into its
stomach. Just a few didinia can wipe out a large group of
paramecia in a very short time.
When there are no more paramecia, didinia will enter into
a state of suspended animation in which they resemble
spheres called cysts. They will remain
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inactive like this until there are more paramecia on
which to feed. Many other protozoa form cysts as well,
enabling them to survive unfavorable conditions such as
drought.
Among the best known protozoa are the amoebas, of
which there are many types. This one is called
Pelomyxa and is among the largest known amoebas.
The stream of cytoplasm an amoeba sends out is called a
pseudopod, which means false foot. Pseudopods not
only enable an amoeba to move, but they are also used in
obtaining food, circling and trapping unsuspecting
organisms. Some organisms, like this tiny protozoan,
appear to be attracted to amoebas, hoping to feed on
their contents, but frequently end up being swallowed
themselves.
If you examine an amoeba's cytoplasm, you will often
find still-living organisms, struggling within it. An
amoeba forms a bubble, called a food vacuole, around its
food. The food, in this case a paramecium, is then
digested within the vacuole.
This organism resembles a protist but is actually a
rotifer, a multicellular animal. It gets its name from the
cilia on top of its head which resemble two spinning
rotors, and which draw in small organisms. Here, you
can also see its tiny, rapidly beating heart.
A rotifer will stay anchored in one area as long as conditions are favorable, spinning its cilia, and stretching its
body in one direction, then another.
When it's time to move on, it'll release its foot, and
squiggle its way to a different spot.
The daphnia is another multicellular animal. It is considered a micro crustacean, and is distantly related to
shrimp, crabs, and lobsters. It moves by flicking its
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pair of large antennae.
It has a single compound eye. While the eye is quite
large, the daphnia's vision is probably poor.
It is near its back where you find its heart, which beats at
three hundred times a minute.
Females are sometimes seen carrying as many as forty
eggs in its brood chamber.
Another interesting micro crustacean is the cyclops,
named after the mythical giant that possessed one eye.
Cyclops are easy to identify by their long drooping
antennae, which they use as sensory organs and for
swimming. One of the cyclop's favorite foods is paramecia, which it snaps up so quickly, it is difficult to see.
Seed shrimp are unusual because they are nearly entirely
enclosed in a shell. Only their antennae and legs are
exposed. They're not really shrimp, but they are related.
The dark spot you see near the top of this one's shell is
its eye. When a seed shrimp dies, and its shell opens, it
sometimes resembles a delicate butter-fly.
The carnivorous hydra is named after the mythical
monster with nine heads. It is normally seen attached to
plants, stones, or debris, with its tentacles extended high
above it. The tentacles are lined with sharp barbs that
attach themselves to the hydra's prey. This daph-nia,
though, is too large, and breaks away from the hydra's
grasp. This small cyclops is much more to the hydra's
liking, and the hydra is able to stuff the cyclops into its
mouth at the base of its tentacles.
You have seen just a few of the fascinating organisms
that you can find in a drop of water. While they may
appear small, they are very important.
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Together, they form the bottom of the food chain and are
an important food source for a variety of larger
organisms, including fish.
The algae are responsible for producing most of the air
that we breath, which is a byproduct of photosynthesis.
Because they reproduce so quickly, protists are often
used in the study of genetics.
And some of these organisms are carriers of disease. This
protist, called Giardia, can infect people when they drink
contaminated water.
And when these organisms are swallowed, they release
bodies that can invade people's intestines.
Millions of people die each year due to diseases carried by some types of bacteria and protists.
Those are some of the reasons why scientists study these
important organisms, so that they can learn more about
them.
Dr. Barlow
Even though they're very small, they are an
important part of the world we live in. Organisms
eat smaller organisms which eat the smallest
organisms which are the protists. Protists provide a
lot of the oxygen that we breath. Protists can be
responsible for disease. Because they're easy to
grow, scientists can use them to study a number of
different scientific principles. So, although small,
they're very important.
In this program, we have seen how the strange organisms found in a drop of water share much in common
with you and me and consist one or more cells.
A cell is the basic unit of which all living things are
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composed and consist, at the very least, of a nucleus
which controls cell activity; cytoplasm, a liquid in
which many cell reactions occur; and the membrane,
which holds the cell together.
A single cell can be a complete organism in itself or it
may be part of multicellular organism.
Single-celled organisms include bacteria, some algae,
and a wide variety of protozoa.
Multicellular organisms include rotifers, daphnia,
hydras, and many others.
These organisms are important because all of them form
the bottom of the food chain, some produce oxygen,
many are used in scientific studies, and a few of them
cause disease.
So as small as these organisms are, they are an essential
part of the world around us.
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