Archaebacteria and Eubacteria also known as the "prokaryotes" and are usually referred to as bacteria are structurally the simplest kinds of organism. They resemble the earliest forms of life. Most are unicellular with cell membrane and a rigid cell wall. There are no mitochondria, chloroplasts, nuclei, or other membrane bound organelles within the cell. The DNA exists as one large, circular molecule suspended in the cytoplasm. The DNA is not associated with histone proteins and does not form into chromosomes. Reproduction in bacteria is by fission (cell division).
Most bacteria are heterotrophic so they need to gain nutrients from the environment. Many are saprophytic, meaning they send out digestive enzymes into the environment and thereafter take up the digested nutrient molecules. Some bacteria are parasitic and can only survive on other living organisms. Some are pathogens that cause diseases such as strep throat or gangrene. Other bacteria are autotrophic, meaning they can produce their own food. Autotrophic bacteria can be either photosynthetic utilizing energy from the sun or chemosynthetic utilizing energy from non-organic chemical reactions.
Eubacteria are the most numerous organisms on earth and they flourish in almost every environment. Billions of them can be found in a handful of soil. They are also found in your digestive tract, on your skin, and between your teeth.
Archaebacteria are found in extreme environments such as hydrothermal vents on the ocean floor which reach temperatures well in excess of 100°C, and within cracks of rocks in the Antarctic desert - the driest and coldest place on earth. Archaebacteria are also fount in such extremes as salty water, anaerobic water, or water rich in sulfur.
Bacteria can be classified simply on the basis of their shape. Three commonly recognized shapes are bacillus (rod-shaped), coccus (round or spherical), and spirillum (spiral-shaped). Examine the demonstrations of different shaped bacteria. Make a drawing of what you see on each slide below.
A large number of bacteria of many different kinds can be obtained by placing a few peas or beans in a beaker of water at 39°C approximately 3 days prior to the beginning of lab. The asexual reproduction of bacteria by binary fission during the 3-day period gives rise to the abundant bacteria in the beaker.Procedure
Note the numerous bacteria of different shapes and sizes on the slide. Make drawings and describe the different types of bacteria seen on your preparation below.
Why do you think such a large number of bacteria are present in the beaker?
What do the peas/beans contribute to make the beaker solution a suitable bacterial environment?
Where do the bacteria come from?
Cyanobacteria (blue-green algae), which are always photosynthetic, contain chlorophyll, but other pigments often mask the green color. Cyanobacteria, sometimes called blue-green algae, are prokaryotes that grow in many types of environments. Only about half of the cyanobacteria are actually blue-green in color. Others range in color from brown to olive green. Cyanobacteria reproduce by fission and are often surrounded by a jelly-like sheath. Because cyanobacteria are prokaryotes, they are not related to other algae, which are all eukaryotic. Cyanobacteria commonly grow on the surface of water as part of "pond scum," and they are often responsible for many disagreeable tastes, colors, and odors in water.
First examine the material on the slide under scanning power and find the filaments of Oscillatoria. The cells of this cyanobacterium form a filament. Examine the filaments more closely under low and high power. Note the absence of nuclei and membrane bound organelles. Make a drawing of a filament of Oscillatoria below.
Make a wet mount of the living Oscillatoria. The filaments of this alga exhibit an oscillatory movement. Examine the filaments under high power and look for this movement.
Prepare a wet mount of living Anabaena. The cells of this cyanobacterium form chains. Look for specialized cells called heterocysts, which play a role in nitrogen fixation. Heterocysts usually have a slightly thicker cell wall compared to the other cells. Examine the chains under low and high power. Make a drawing of Anabaena and label the heterocysts below.
This cyanobacterium grows as a jelly-like mass, floating in water or attached to the substrate. The masses can be broken open so you can see the individual chains normally found inside the jelly-like mass. Make a wet mount of living Nostoc and examine under low and high power. Look for heterocysts in the chains. Make a drawing of Nostoc and label the heterocysts below.
The "Protista" is the first group of eukaryotic organisms that you will examine. Eukaryotes include all the other forms of life excluding the Archaebacteria and Eubacteria (see classification). Eukaryotes are organisms made of cells having membrane bound organelles and membrane bound nuclei. Their DNA is linear, associated with histone proteins, and condenses into chromosomes. Most eukaryotes have a diploid (2n) stage in their life cycle and reproduce sexually. Protistan cells can go through mitosis and meiosis.
Protista is the oldest, most diverse, and most difficult to characterize of the eukaryote groups. It is one of the first lineages to evolve from ancestral prokaryotes. Most researchers believe the group is paraphyletic and is usually characterized by what they lack compared to other organisms, instead of what they possess as evolutionary novelties.
In general, members of the Protista are single-celled eukaryotic organisms that lack the distinctive features of other eukaryotes such as plants, animals, and fungi. Protists are mostly microscopic and probably share common ancestry with multicellular plants, animals, and fungi. In the following lab exercises you will examine organisms from the Protista.
To complete this section of the lab exercise, you will need to make two wet mounts in order to observe swimming movements and the 2 types of nuclei present in Paramecium.Observation of Living Paramecium:
Procedure
- Put a drop or 2 of the Paramecium culture on a slide and add a cover slip. Examine the preparation under scanning power of the microscope to observe the swimming movements of Paramecium. Paramecia swim by means of cilia; the entire surface of this ciliate is covered with rows of cilia. Make a series of drawings (below) to show the course of movement of a Paramecium. Does the body rotate during movement or does it remain stationary? Indicate this on your drawing below.
- Make a new preparation by putting a drop or 2 of the Paramecium culture on a slide. Add a small drop of the dye methylene blue to the preparation and add a cover slip. Turn the preparation over (cover slip down) on a paper towel to remove the excess fluid. Find some of the paramecia under scanning, low and high power and try to identify the stained micronucleus and macronucleus.
Amoebas move and capture prey by means of pseudopodia (false feet). The formation of pseudopodia is a complex process and involves actin and myosin microfilaments. The pseudopodia are flowing projections of the cytoplasm that extend and move the Amoeba forward or engulf food particles (endocytosis).Slide of Amoeba proteus
Examine the slide under scanning power to find the stained amoebas on the slide. Switch over to low and high power to observe the general shape of Amoeba proteus, the pseudopodia, and the stained nucleus. Make a drawing of Amoeba proteus below.Living Amoeba proteus:
Procedure
Members of the Zoomastigophora use flagella as a means of locomotion. Most of the Zooflagellates have from one to a few flagella, although some, such as the protozoan found in the gut of termites, have many flagella. Recall that flagella are longer than cilia, although flagella and cilia are identical in fine structure.Demonstration slide of a Trypanosome rhodesiense:
Observe the demonstration and note the elongate shape of the flagellates, the stained nucleus, and the flagellum extending free at the anterior end of the trypanosomes. Actually the flagellum arises near the posterior end of the cell and runs along the edge of the cell forming the undulating membrane. This Trypanosoma (Trypanosome rhodesiense) is one of 2 species of the Trypanosoma responsible for causing African sleeping sickness in man. These parasitic flagellates are found free in the blood of humans. Make a drawing of Trypanosoma rhodesiense and label all parts below.
The Euglena belongs to the Euglenophyta and is considered an algal protist. However, the Euglena does possess a flagellum.Slide of Euglena:
Examine the organisms on the slide under scanning, low, and high power. Note the general shape of this protist, and identify the nucleus, chloroplasts, and if possible, the flagellum. Make a drawing of Euglena below.Observation of Living Euglena:
Procedure