Transcript lab_1_handout

The Biology of Periphyton
You may have noticed that the ponds in the Miami area are frequently covered
with clumps of light-colored slime, what some might call “pond scum”. It might look pretty
disgusting to the average person, but to those of us who study the Everglades, it is very special
stuff. We call it periphyton. It is a community of micro and macro-organisms that lives under
the water surface in the Everglades, or floats if it accumulates enough bubbles of oxygen.
Periphyton forms on the skeletons of flowering aquatic plants, particularly the bladderworts
(genus Utricularia). As a community, periphyton consists of a variety of organisms that live in a
matrix of dead organic matter: bacteria, protozoans, green algae, diatoms, rotifers, insect larvae,
and much more. We have added several pages of illustrations of organisms that you can easily
find when you observe preparations with a microscope. This is also a good exercise for you to
learn how to use a microscope.
Periphyton is ecologically important in the Everglades because it is the source of
much of the carbon fixed in photosynthesis, and this is passed to other organisms, particularly
apple snails and small fish, in food webs. The snails and fish are eaten directly by birds, or often
by larger fish, that are then eaten by birds and alligators. So this is the stuff on which the
Everglades runs. A number of scientists at FIU are studying the effects of adding phosphorus (a
key ingredient in the water from the sugar cane farms to the north) on the function of the
wetlands ecosystems. We are finding that even modest additions of phosphorus cause the
periphyton to break apart. This may have unknown consequences for the function of this
ecosystem, and we are trying to figure this out.
Dead material
Alligators
Prawns
Crayfish
Periphyton
Gar
Rotifers
Copepods
Insect Larvae
Bass
Wading
Birds
Shellfish
Examining Periphyton Under the Microscope
In this laboratory exercise, you will observe and identify organisms in the periphyton community.
This is an enjoyable process, because you may see amazingly bizarre living organisms swimming
around in the water, or non-moving green and photosynthetic algae. Try to match what you see
to the organisms illustrated here. Make a list of the organisms you have seen. If it is unusually
interesting, share the view with your table partners.
Examining Microorganisms
Take a piece of the periphyton mat without squeezing it and place it in a petri dish. (Sometimes
there are flies in the periphyton that will bite if you squeeze the periphyton too hard.) Place the
dish on a dissecting microscope and examine the periphyton for macro-organisms. Use the
following diagrams to help you identify what you are observing. If possible, try to isolate a
few of the more interesting organisms by using tweezers.
Clam or Mussel
Hemiptera
(Water Bug)
Leech
Adult Beetle
Snail
Rotifer
Copepod
Water Mite
Stonefly Larva
Gammarus (Scud)
Mayfly larva
Midge larva
Examining Microorganisms
In order to see micro-organisms present in the periphyton, it needs to be homogenized
(ground up or pureed), diluted with water, and examined under a compound light
microscope. This has already been completed for you. Place one drop of homogenized
periphyton on a microscope slide. Gently add a cover slip, by placing one edge against the
slide and allowing it to fall over the tissue. This helps force out the air bubbles that tend to
be trapped under the coverslip. You can remove excess water by twisting an end of a
kleenex (or kimwipe) and placing it on the edge of the coverslip. It will absorb the excess
water. Then place the slide on the microscope stage and begin your observations under low
power (10X). Look for a variety of micro-organisms, as illustrated in the following pages,
in the periphyton. You can boost the power by turning the nosepiece to a higher power
objective (watch your instructor demonstrate this). You can estimate the size of the
organism by comparing its length to the diameter of the field at any given magnification.
If you see absolutely nothing, then try preparing another slide of periphyton, then look
again.
Chlamydomonas
Bulbochaete
Desmidium
Mougeotia
Volvox
Phylum Chlorophyta (green algae)
Oedogonium
Spirogyra Ulothrix
Oscillatoria
Euglena
Phylum Euglenophyta
(euglenoids)
Peridinium
Gomphonema
Frustulia
Nostoc
Fragilaria
Cyanobacteria
Phylum Pyrrhophyta
(dinoflagellates)
Phylum Navicula
Chrysophyta
Nitzchia (diatoms)
Fossils
Fossils are remnants of once living organisms. Fossils are direct evidence for organisms that lived in
the distant past. Fossils were produced under optimal conditions and only by organisms with hard
body parts that allowed such formation. These were places on the earth where dead organisms were
covered by fine sediments, oxygen was excluded from oxidizing the structures, and the organisms were
thus preserved. Fossils are only found in sedimentary rocks. Fossils may be impressions or
compressions of once-living organisms. Hard structures, as shells or skeletons may be fossilized
directly. Other fossils are formed with minerals gradually replace the once-living tissues in a process
termed petrifaction, like petrified wood. Fossils are the best evidence available on the organisms that
were present in the distant past. In this display, observe the fossils on display. For each fossil
determine its age (approximately in millions of years before present) by matching the eras during
which the organisms lived with the time scale on the poster. Determine the process by which each
fossil was formed. Finally, determine the phylum and kingdom to which each fossil belonged.
AMMONITES
These animal fossils were formed because of the hard calcareous shell secreted by the organisms. These are
members of the Cephalopoda. What living organisms do you think these organisms were related to?
These organisms lived during the Mesozoic era.
TRILOBITES
These are the most ancient of the organisms displayed among these fossils, dating back to the Cambrian era.
These fossils were formed because of a hard exoskeleton, so durable that the shape of the fossil gives a
good idea of the three dimensional shape of the organism. The exoskeleton consists of segments, with
many small appendages. What living organisms do you think these organisms were related to?
LEPIDODENDRON
This is a plant fossil, common in the coal deposits of Pennsylvania and West Virginia, dating back to the
Carboniferous. What you are looking at is the surface of the trunk of a small tree, and the diamond
shaped structures are the scars where leaves were once attached.
LEPIDOSTROBUS
This is also a plant fossil, common in the coal deposits of Pennsylvania and West Virginia, dating back to the
Carboniferous. You are looking at the surface of a cone-like structure of a plant that did not produce
seeds. This name is the example of a form genus. It was given its name as a structure. Later on other
fossils were found that connected it to the stem, Lepidodendron. Later on another form genus was
established for the roots. Yet these are all fossils of a single plant species. These fossils are of plants
that were related to the living genus Lycopodium. This genus is often given the name of a “living
fossil” because of its ancient origins.
CALAMITES
This is a plant fossil, common in the coal deposits of Pennsylvania and West Virginia, dating back to the
Carboniferous. You are looking at the surface of a stem whose branches all originate at a single node,
all the way around the stem. On the small branches, leaves also appear at the nodes. These plants
produced spores, on cone-like structures, and did not produce seeds. These fossils are of plants that
were related to the living genus Equisetum, or the scouring rush.
PETRIFIED WOOD
These are various samples of wood, deposited in sandstones in deserts of the southwest. These are the
youngest of fossils on display, produced during the Tertiary. Wood anatomists can trace the
arrangements of cells in these fossils to genera of conifers living today. Thus the names on the fossils
correspond to plants you may be familiar with, such as Taxodium (cypress). What are desert localities
today once supported coniferous forests back then. If you look carefully at parts of the wood you can
see the annual growth rings of the wood. The thickness of these rings can also analyzed to estimate
rates of growth and the types of climates in which these trees lived.
Fern Spore Germination
Ferns are a part of the plant kingdom, but do not produce flowers, fruits, or seeds like
many other plants. Instead, ferns produce spores on the underside of leaves. These
spores are dispersed by wind and will germinate if they land on moist soil.
Eventually each spore develops into a flat, heart-shaped structure called a thallus.
Once fertilization occurs, a new fern starts to grow from the thallus. Over time, this
new fern becomes much larger than the thallus and takes on the fern form that we are
familiar with. In this procedure, you will be sowing spores of the fern Ceratopteris,
a very rapidly growing fern. In two or three days, the spores will germinate and after
10-12 days, thalli should be apparent. Throughout the semester, you will observe the
development of the fern spores and record your observations. The following
procedures are based on those provided by the C-Fern company and are protected by
copyright laws.
Procedure:
1. Use small Styrofoam containers, such as those used for soup take out. There should be
one container per table, with a total of 6 per lab. Fill it with sterilized potting soil to
a depth of about 2.5 cm (or 1 inch).
2. Gently moisten the soil with the small spray bottle.
3. Using a cotton swab (or q-tip), place the cotton tip into the vial of fern spores.
4. Place the cotton tip above the soil, tap the shaft of the q-tip as you move the cotton tip
around on the soil of the dish.
5. Puncture two small holes in the lid of the dish, and label it using the label tape and
marker. Indicate your lab group, the lab section and the date.
6. Place the plastic dish on the shelf indicated by your instructor, under the fluorescent
lights.
7. Observe the changes in the development of the spores each week during the term. Note
the numbers of cells and their arrangement. Document with simple sketches.