This lab will help students develop a
better understanding of characteristics of organisms belonging to Monera,
Protista, Plantae, and Fungi. Many of the smaller representatives of these
groups are called "microbes."
The Monera are single-celled organisms that
do not possess a true nucleus, they are presently divided into two large
Kingdoms, the Eubacteria and Archeobacteria. They are divided into these
groups dependant on their nuclear structure. Their nucleus has no outer
membrane and the cell is called prokaryotic. All other living organisms are
eukaryotic, which have a membrane surrounding the nucleus.
Monera (sometimes referred to as bacteria
or blue green algae) are microscopic. They are either autotrophic or
heterotrophic. An autotroph is an organism that can build its own food from
"chemicals" like carbon dioxide and water. Monera that do not make
their own food are heterotrophic and must seek a supply of food. Heterotrophs
depend on tissues, remains, and wastes of other living organisms for food.
Bacteria come in 3 different shapes. Bacillus are rod shaped, coccus are
spherical, and spirillum are spiral. Bacteria reproduce by asexual means,
usually by dividing. Bacteria can be found just about everywhere, they are in
air, water, inside you, outside you, in the frozen Arctic and even in hot
Some bacteria are responsible for food
spoilage, and others are useful in changing food to a different desirable
flavor or consistency such as in making cheeses. High temperatures kill most
bacteria and this knowledge led to the discovery of pasteurization or the
heating of milk to kill any bacteria that would lead to spoilage. Canning food
or heating food and sealing it in air tight container also prevents spoilage.
Cooling bacteria slows down their decomposing action and this led to the use
of refrigeration and freezing to retard spoilage.
Blue-green algae or cyanobacteria, unlike
some bacteria, undergo photosynthesis. They carry on cell division and
respiration. Some are harmful in that they may add to the pollution of lakes
and rivers by their rapid growth, but most are benign. Cyanobacteria are one
of the most primitive organisms found in the fossil record, making massive
mounds 600 million years ago (stromatolites).
The Kingdom Protista are single-celled
organisms that have a true nucleus (eukaryotic). Protista may be either
autotrophic or heterotrophic. Movement by protists is dependent upon certain
physical characteristics. Some protozoa have pseudopodia which can extend the
cell membrane and push forward or surround a food particle, such as an amoeba
does. A protist that possesses a single tail-like structure is called a
flagellate. The flagellum will beat back and forth and propel the organism
through the water, examples are trypanosome and trichosomes. Some Protozoa are
covered with tiny hair-like structures called cilia which move back and forth
quickly propelling the organisms through the water. A paramecium is an example
of a ciliate. Some Protozoa have axopodia, or pencil-like structures, that
help them to be planktonic or floaters in the water. Radiolaria are marine
examples of protozoa containing this feature.
There are many debates about whether
protozoa are all one-celled organisms or whether they are all one-celled
organisms that are heterotrophs. Scientists who study these groups, debate on
how to classify some of these organisms, like euglena and dinoflagellate. With
more study these groups will be better understood.
Most protozoa are helpful in that they are
important in lower levels of the food chain. They provide food for living
things such as snails, clams, and sponges. Some protozoa are capable of
causing diseases in humans and other animals. Some diseases caused by protozoa
in humans are malaria, black fever, sleeping sickness, and some types of
Organisms found in the Fungi Kingdom are
heterotrophic. Fungi obtain food by decomposing anything that is organic in
nature. Fungi live everywhere. They grow best in warm, moist places. They are
not green and do not possess chlorophyll. Fungi can grow on vegetables, bread,
meat, fur, wood, leather, or anything that is in a warm and moist area.
Fungi that obtains nutrients from
non-living organic matter are called saprobes. Other fungi obtain nutrients
directly from a living host, these are parasites. In either case, the fungi
secretes enzymes that allow digestion to take place outside of the fungal
body. Nutrients are then absorbed across the cell membranes. Together with
bacteria, fungi are the decomposers of the earth. Fungi include yeast, bread
mold, and mushrooms.
Fungus itself is made up of a fungal body
or what is called mycelium. The mycelium is a mesh of filaments that branch
out in any direction living over or within the organic matter. Each filament
is a hypha. Hypha are transparent thin walled tubes.
Fungi reproduce asexually through the
formation of spores, through fragmentation of the mycelium or by budding. Some
reproduce sexually through the formation of male and female gametes.
The organisms from the Plantae Kingdom are
different from the other groups because they photosynthesize or create their
own food from light. The algae are a group of water plants. They range in size
from large (kelp) to microscopic (algae). The microscopic group that you will
encounter in pond water will belong to some type of algae.
- During lab students will look at
examples from the different groups. Have pictures available of different
microbes so they can compare and contrast.
- If you are looking at pond water, use
the enclosed pictures of the possible different groups that students may see.
The Swift GH with a 2.5X objective will only see the largest of these. If you
have a 4X or 10X objective you will be able to see more. Use the list that can
be found after the pictures of where these organisms belong.
- Marine water also is home for many
protozoa and microscopic algae. If you live near a marine environment you may
want to sample and compare.
- Prepare the following materials for
students to observe and record on their lab sheet.
If you have an aquarium or have pond water, the students can look
at live specimens which are much more exciting. You can use the Swift GH on
the aquarium by taking the base from the microscope, putting on the 10X
objective and putting the microscope right on the glass of the aquarium. Focus
on the slimy surface of the glass and you will be able to see protozoa eating,
playing and reproducing!
Cut a fresh mushroom in thin slices. Students should be able to
look at the entire cross section with the microscope.
The only "bacteria" that the students may see in pond
water are the cyanobacteria which include Oscillatoria. Other bacteria require
at least 100X or higher magnification.
The Plantae Kingdom also has
representatives in the micro world. Plants are different from the other groups
because they can create their own food through photosynthesis. Small algae are
found in fresh and salt water. The most common in both environments are
diatoms. The Swift GH with a 2.5x objective cannot distinguish individual
diatoms. However, diatoms like to "clump" together. The clue is that
they would have a greenish-brown tint.