Download the plant-like protists: the algae

INTRODUCTION TO PROTISTA
Learning Objectives:
Describe differences between 2 major groups of protists (animal-like
and plant-like).
Gain an appreciation of the diversity of organisms found in this
kingdom.
Understand some of the different methods of feeding and movement in
protozoa.
Explain the key role that protists play in supporting life in aquatic
communities, as well as sustaining human life on the planet.
Table of Contents:
Introduction
Animal-like Protists: Protozoa
Ciliated Protozoa
Amoeboid Protozoa
Flagellated Protozoa
Plant-like Protists: Algae
Euglenoids
Dinoflagellates
Green Algae
Golden-brown Algae
Red Algae
Brown Algae
Ecological Importance of Protists
End of Lab Questions
INTRODUCTION
Some of the simplest eukaryotic organisms belong to the Domain Eukarya,
Kingdom Protista. If only one word could be used to describe this kingdom, it
might be the word diversity. Members of this very large kingdom
(approximately 100,000 species) show considerable variation in their forms,
habits, lifecycles, habitats, and methods of obtaining nutrients. The kingdom
can be divided into three groups: the animal-like protists or protozoa, and the
plant-like protists or algae, and the fungi-like protists or slime molds. Today in
lab we will be examining selected species from this kingdom.
ANIMAL-LIKE PROTISTS: THE PROTOZOANS
The protozoa are the animal-like protists. Since organisms in the Kingdom
Animalia are heterotrophic and motile, we would expect protozoa to also be
heterotrophic and motile. Indeed, they are. The prefix "proto-," as in
prototype, means the first or before, and the suffix, "-zoa," represents "zoo" for
animals. So, the word protozoa means "the first animals."
Protozoa are single-celled, heterotrophic organisms. They are distributed
worldwide and inhabit both terrestrial and aquatic environments. They are
complete organisms that possess all the necessary tools for performing the
same metabolic functions that humans perform: ingest food, digest food,
expel waste, and obtain oxygen. In protozoa, this is all accomplished within a
single cell. Many protozoa have forged symbiotic relationships with other
organisms (living with them), and some are responsible for causing some of
humankind's most dreaded diseases (Malaria, African Sleeping Sickness, and
amebic dysentery). Structurally, most protozoa are enclosed in a simple cell
membrane, covered by a layer of protein called the pellicle. Some groups of
protozoa manufacture a hard outer covering, or test, composed of calcium
carbonate or silica; it is called a test to distinguish it from the notion of a cell
wall, which would sound plant-like. Protozoa may reproduce asexually (no
exchange of genetic material between two individuals), or sexually
(exchange of genetic material between two individuals). Taxonomists classify
protozoa according to their method of movement, and it is the mode of
locomotion that we will base our study of the protists today.
Ciliated Protozoa: “Ciliates”
The ciliates are a large group of protozoa that move and obtain food by means
of short, hair-like structures called cilia. A cilium (singular) is an extension of
the cell membrane and contains bundles of microtubules within it. Cilia are
used to sweep smaller protists, bacteria, and non-living organic matter into
an oral groove. At the distal end of the oral groove a food vacuole will be
formed. Cilia are very abundant and cover the entire cell surface. Ciliates
occupy a variety of habitats including freshwater, soil and as symbiotes in the
guts of vertebrates. The photo above is of a common ciliate known as a
Paramecium.
Amoeboid Protozoa: “Sarcodines”
The amoeboid protozoa move by
means of amoeboid movement, or
pseudopodia. Pseudopodia are
protoplasmic extensions that move
the organism in a particular
direction. The organism uses these
"false feet" for locomotion and food
capture by endocytosis. The bestknown members of this group are
the amoebas. Amoebas are widely
distributed organisms of mostly
freshwater environments. They occur commonly on undersides of vegetation
in slow-moving streams or ponds. Some species of Amoeba inhabit soil, salt
water, and a few are important endoparasites of humans and other animals.
Flagellated Protozoa: “Zooflagellates”
Flagellated protozoa locomote my means of a
long, whip-like flagellum. Zooflagellates are
generally able to absorb food through their cell
membranes. Many live in lakes and streams,
where they absorb nutrients from decaying
organic material. Others live within the bodies of
other organisms, taking advantage of the food
that the larger organism provides. Most reproduce
asexually, however some have a sexual life cycle
as well. Peranema is an example of this type of
protozoan, and is shown in this photo to the right.
Peranema uses its flagellum to pull, rather than
push, itself through the water. It is pretty fun to
watch. Some other flagellated protozoa are not
so much fun, because they can cause some
human diseases.
THE PLANT-LIKE PROTISTS: THE ALGAE
The algae are the plant-like protists. As such, you would think that algae
would have the following characteristics:
autotrophic (whether it is by chlorophyll or not)
nonmotile
cell walls
Many of the algae stick to this list, but, certainly, there are exceptions. Some
algae can move using flagella. Some algae don't have cell walls. And one
kind of algae can even adopt a heterotrophic life style when stuck in the
mud at the bottom of a pond or when there's little sunlight. Here's a
more thorough description of the algae...
Algae are autotrophic (photosynthetic)
organisms. Like the protozoa, some algae are
single-celled. Unlike the protozoa however,
many representatives are multicellular,
attaining lengths of 100 or more meters, and
possess cell walls. Many species are aquatic,
with most occupying marine habitats.
Terrestrial habitats are not devoid of algae.
Certain species can be found in damp soil,
building and rock surfaces, and on tree bark. Some are quite at home in the
fur of mammals, in swimming pools, birdbaths, flowerpots, and roof gutters of
homes. It is safe to say that algae can be generally found anywhere there is
an abundance of moisture and sunlight. Over 30,000 species of algae have
been described by phycologists (phycology is the study of algae).
Taxonomists use several criteria to classify algae, the most common method
being the dominant photosynthetic pigment color found in the chloroplasts
of the algal cells. We will use this characteristic to group the algae that we
observe. You see, algae can live in all sorts of aquatic environments-- some
live at really deep regions of the ocean. Not all wavelengths of light can
make it down to the bottom of the ocean. The green light that bounces off
our chloroplasts in land plants is great on the land, but not so great in the
depths of the ocean. So other wavelengths of light have to be used by
algae. You will see green, golden-brown, red, and brown algae.
Although algae can be multicellular, they are not multicellular in the same
way as plants are. Plants are complex multicellular organisms. Algae are
simple. That means that even though there are many cells in one organism,
the cells are all of the same type, or almost all of the same type. Multicellular
algae can organize their cells into filaments, colonies, or even tissue-like
sheets. The filaments are cells lined up end-to-end, like boxcars. The colonies
are spherical clumps of cells. And the sheets are like you see in seaweed.
Euglenoids
Euglenoids are very cool. These
organisms have characteristics of
both protozoa and algae. An
example of a euglenoid is Euglena, a
freshwater protist. Algal
characteristics include the ability to
photosynthesize and store starch.
Protozoan characteristics include the
lack of a cell wall, and the ability to
ingest food (which they do when
they can't get enough light).
Euglenas are excellent swimmers.
Two flagella emerge from a gullet at one end of the cell, and the
longer of these two flagella spins in a pattern that pulls the organism
rapidly through the water. Near the gullet end of the cell is a cluster of
reddish pigment known as the eyespot, which helps the organism find
sunlight to power photosynthesis. If sunlight isn’t available, euglenas
can also live as heterotrophs. Euglenas do not have cell walls, but they
do have an intricate cell membrane called a pellicle. The pellicle is
tough and flexible, letting the euglenas crawl through mud when there
is not enough water for them to swim. Euglenas reproduce asexually
by binary fission. Some species of Euglena are very tolerant of polluted
waters, and act as water quality indicators for humans when expensive
pollution monitoring equipment is not available.
Dinoflagellates
Dinoflagellates are bizarre looking
algae. The prefix "dinos-" means
whirling. They are freshwater
algae, but they exhibit the
protozoan characteristic of being
able to move using flagella. In
fact, they have two flagella that
they move independently.
These two flagella extend at right
angles from each other, so that
the dinoflagellate can move
along, spinning away using
flagellar movement; the spinning, or whirling movements they make, is how
they got their name. Dinoflagellates are algae, though, and are able to use
photosynthesis. They are surrounded by a cell wall that has an odd
appearance, since it looks like a suit of armor. There are some dinoflagellates
that contain a red pigment and, when in high enough numbers in the ocean,
cause the ocean to have a reddish hue; this is called red tide. The
dinoflagellates in the red tide are toxic to many of the ocean organisms, so
where the red tide goes, ocean life perishes. Peridinium is not at all harmful.
Green Algae
Green algae are the largest group of algae, consisting of unicellular, colonial,
simple multicellular and more complex multicellular members. They are
members of the phylum Chlorophyta which means “green plants” in Greek.
Green algae share many characteristics with plants, including their
photosynthetic pigments and cell wall
composition. Green algae have cellulose in their
cell walls, contain chlorophyll a and b, and store
food in the form of starch, just like land plants.
These characteristics lead scientists to
hypothesize that the ancestors of modern land
plants looked a lot like certain species of living
green algae.
Some members of the green algae are single-celled
organisms. For example, Chlamydomonas is singlecelled. Some Chlamydomonas-like organisms have
been found fossilized in rock dating back nearly 1
billion years. Each individual is composed of a single
chloroplast, nucleus, a light-sensing eyespot (or
stigma), a starch storage area called a pyrenoid,
and two flagella. Other green algae are
multicellular, like Volvox.
Golden-brown Algae
Members of this group possess both chlorophyll and another pigment called
xanthophyll. These photosynthetic pigments impart a golden-brown color to
the algae. The best-known members of this group are the diatoms. Diatoms
are unicellular algae and are found in abundance in both terrestrial, marine,
and freshwater environments. Economically they are of tremendous value to
humans.
The defining characteristic of diatoms is the presence of their glass-like cell
walls composed of silica. The walls are arranged in overlapping halves, much
like a candy box or petri dish fits together. Once the organism dies, the
protoplast inside decomposes but the glass-like walls remain intact for
hundreds or thousands of years. Over thousands of years significant deposits
of these may accumulate on the ocean floor. These deposits may be
extensive to be commercially mined. This material is better known as
diatomaceous earth. Humans use this material in a wide array of products,
including paints, cement, fertilizers, toothpaste, polishes, and cleaners.
Diatomaceous earth also kills snails and slugs.
Red Algae
The red algae are almost exclusively multicellular and many are marine. Red
algae tends to have a very hard cell wall, made of calcium carbonate. This
is the same stuff that contributes to the hard shell around shellfish. So, when
you step on this seaweed, it hurts more than feels slimy!
Brown Algae
The brown algae are exclusively multicellular and marine, like the red algae.
Characteristic coloration comes from a combination of at least 4
photosynthetic pigments. These algae are most common in cooler marine
waters, and range in size from microscopic filaments to giant kelp that may
attain lengths of up to 100 meters.
An important representative of the brown algae is
Laminaria or kelp. Kelp might seem a bit too
complicated to be considered "simple." Yet, it still
is truly a simple multicellular organism. All the cells
of the leaves (the blades) are basically the same.
Each kelp "plant" also has a stalk-like stipe, and an
area that is root-like to hold it into the ground (the
holdfast). The leaf-like blade is the site of most
photosynthesis. Keep in mind that algae are not
plants-they lack true stems, leaves and roots.
Distributed along the blade may be several or
many air bladders that help to keep the blade
buoyant.
Kelp may grow in large concentrations or
underwater "forests" in certain areas, and are
extremely important ecologically in the oceans. Many marine mammals, fish,
and invertebrates depend on these kelp forests for protection from storms,
hiding places, and as nurseries for young.
Ecological Importance of Protists
While responsible for causing many dreaded human diseases (malaria, African
sleeping sickness, and giardiasis to list a
few), protozoa also benefit humans
tremendously. Protozoa are important
nutrient recyclers in natural ecosystems.
Without organisms like bacteria, fungi
and protozoa, soils would quickly
become depleted of nutrients making
plant growth impossible. All organisms
on earth depend on healthy plant
populations for survival. Protozoa also play a key role in wastewater
treatment plants by consuming enormous quantities of bacteria, and are
important components of food chains.
Algae is much more than simply "seaweed" or "pond scum"--it is a vital
component of our biosphere, and the survival of humans would be
jeopardized without it. Indeed, algae produced more than 50% of the
oxygen molecules that your cells consumed during this laboratory! Algae also
form the base of aquatic food pyramids. This algae is primarily microscopic,
and is called phytoplankton. Without algae in lakes, rivers, and oceans, there
could be no life in these environments since all aquatic life either directly
feeds on algae, or feeds on organisms that feed on algae. Humans usually
feed at the top of the food pyramid. Without phytoplankton in the oceans,
salmon, tuna, cod, shrimp, lobsters and a myriad of other seafood products
would not be available to us.
Itty Bitty City: The Microscopic World In A Drop Of
Pond Water
PURPOSE: To examine the variety of living organisms in pond water.
INTRUCTIONS:
1. Make wet mounts slides of the living culture (pond water).
2. Put one drop of culture on slide (this is usually sufficient unless specified
differently).
3. Squeeze the bulb of the pipette firmly BEFORE inserting into culture. Pull from the
bottom or near plant life.
4. Observe the drop of pond water under Low Power to scan and find the
organisms. Once you have found an organism, rotate through the Medium
Power, then to High Power.
5. If the organisms are moving too fast and therefore difficult to observe, add one
drop of Protoslo or Detain to a drop of culture on the slide. If this is unavailable
place 2 or 3 strands of cotton on the slide first before you add the drop of pond
water. These procedures will slow the organisms.
YOU MUST BE PATIENT
6. Locate and diagram at least 4 different species of protists.
7. Repeat steps #1-5, from above, as many times as necessary to obtain the
different protists.
8. Each diagram must have a heading ,with the common name of the organism
(internet research), as well as:
a. A brief description of its color and shape
b. A brief description of its movement pattern and whether it has cilia or flagella?
c. A brief description of its feeding.
d. Evidence that it responds to stimuli such as light, obstacles, etc...
e. Determine its size (the diameter of the field of view under high power is
400µm, medium power 1500µm, and low power 4000µm).
f. At least one other observation you observed.
OBSERVATIONS:
Name:__________________
__________________
a.(Color/Shape)
a.
b.(Movement)
b.
c.(Feeding)
c.
d.(Stimuli)
d.
e.(Size)
e.
f.(Other)
f.
__________________
__________________
a.
a.
b.
b.
c.
c.
d.
d.
e.
e.
f.
f.
ANALYSIS:
1. Why was it necessary to begin your observation using the low power objective
first?
2. What life characteristics did the organisms in the pond water possess? How did
you distinguish between living and non-living matter?
3. From what observation can you infer that pond water organisms expend
energy?
4. What characteristics of pond water organisms are difficult to observe in this type
of investigation?
5. What characteristics might be used to distinguish between plant like and animal
like organisms?
6. Which of the following dichotomies describes the majority of protists you
observed?
a. Single or Multicellular
b. Heterotrophic or Autotrophic
c. Sexual or Asexual Reproduction
d. Mobile or Sessile
e. Aerobic or Anaerobic
7. Compare your observations with your classmates, and compile a list of
generalizations about organisms found in pond water.
8. Construct a possible food chain from your sampling.
CONCLUSION QUESTIONS:
1. How long ago did protists appear in the fossil record?
2. What advantages/ adaptations did they have over the prokaryotic cells that
were well established on Earth?
3. “Endosymbiosis” is the leading theory for the evolution of the mitochondria
and plastids. Explain this theory.
4. Plasmodium, an Apicomplexan, is the parasite that causes malaria. Describe
the life cycle of this protist.
5. Several types of protists have a stigma, also known as an eyespot. Describe
how this structure functions in “primitive sight”.
6. Several Ciliated Protozoans are binucleate. What is the function of each
nucleus (macro and micro) and the advantage this provides the organism.
7. Paramecium are capable of conjugation. Compare and contrast the
Paramecium conjugation with that of Prokaryotic conjugation.
8. Explain the key role that protists play in supporting life in aquatic communities,
as well as sustaining human life on the planet.