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Introduction
Prokaryotic organisms are classified into two domains, Archea and Bacteria. Typically, their cells are smaller in size compared to eukaryotic cells and lack a true nucleus confining the genetic material. The cells of most prokaryotes are surrounded by a cell wall which contains peptidoglycan. This cell wall aids in maintaining cell shape with three common morphologies possible: coccus (spherical), bacillus (rod shaped) and spiral.
The Archea are probably the least familiar of the two to most people, but include some very important organisms. Prokaryotic thermopiles, which can survive extreme temperatures are used in biotechnology (specifically Polymerase Chain Reaction), while others are responsible for ‘marsh gas” (methane) produced as a by product of respiration when oxygen levels in moist soils have been depleted (anaerobic conditions).
The Bacteria are more familiar probably due to the pathogenic species which we often confront. Strep throat, tuberculosis, and Lyme disease are all caused by bacteria; however not all bacteria are harmful. In addition to parasitic relationships, bacteria may also form commensal or mutualistic associations with hosts. Others are important autotrophs, while yet others function as decomposers and play an important role in nutrient cycling.
All eukaryotic life is classified in the domain Eukarya. Included in this domain are the protists. The term protist is used to describe a diverse assemblage of mostly single-celled eukaryotic organisms. Traditionally, kingdom Protista existed as a single taxon. Recent biochemical data and increasing technology have allowed scientists to separate protists into as many as five separate lineages!! And this classification continues to change.
For this reason, we shall consider the traditional informal (no taxon level) groupings of protists: the algae and the protozoans and look at the life history of several examples.
The algae are a collection of photosynthetic organisms that live in water or extremely moist areas because they lack specialized vascular tissues for water and nutrient transport. Algae may be unicellular, colonial, or multicellular. Large multicellular algae ( macroalgae ) do not form specialized tissues but they do reach considerable sizes. Algae are enormously important in aquatic and marine food chains providing essential carbon fixation and supplying oxygen as a byproduct.
Protozoans are heterotrophic single-celled eukaryotes and obtain nutrients by ingestion as they form food vacuoles. Many of these organisms are classified based upon the cellular structures used for locomotion. While many protozoans are free-living, others are important symbionts (either as parasites, commensals, or mutualists).
Bacteria & Protists
Laboratory
Review Questions:
- Which of the three domains contains prokaryotic organisms?
- What is a thermophile?
- Describe the difference between an autotroph and a heterotroph.
- List and differentiate between the three forms of symbiosis:
- List an important ecological benefit of algae.
- What are the three basic shapes of most bacteria?
- Where is peptidoglycan found in a bacterial cell?
STATION 2: Pond Water Observation
For this exercise you will examine a culture of ‘pond water’. Most aquatic systems are teeming with tiny life forms and many are protists; it is amazing to see what kinds of life can occur in a drop of water.
- Obtain a clean depression slide
- Using a pipette, first expel the air form the bulb then place in the pond water culture. Attempt to collect sediment or other suspended materials that may be present.
- Transfer one drop of the sample to the well on the depression slide. Next, carefully place one drop of Detain ™ in the well on your sample (this will slow the movements of the critters!). Do not overfill the well.
- Carefully place a clean coverslip over the well.
Using the microscope, examine the sample. Use the spaces below to sketch a few of the organisms you observe. You may also use the laminated protist keys to help identify some of the organisms. When you are finished, rinse and clean your slide and dispose of the coverslip.
Review Questions:
- Can you identify any algae? How can you tell algae from other life forms seen in the sample?
- Are all of the organisms seen in the sample protists? How can you tell?
- Can you identify any protozoans? Why are these protozoans important?
STATION 3A: The Algae
Euglenoids –Example: Euglena About one third of the euglenoids are photosynthetic, possessing chlorophyll a , chlorophyll b , and carotenoids. Euglenoids are single-celled with a long whip-like flagellum used for locomotion. Because they inhabit freshwater, the euglenoids have star-shaped contractile vacuoles to rid the cell of excess water. A common euglenoid, Euglena , also possesses an eyespot ( parabasal body ) located near the flagellum that detects light intensity. Euglena are unique in that they can alternate between being photosynthetic and heterotrophic. If light is not available, the chloroplasts cease to function, and the Euglena collects food through its gullet. The food is then digested within food vacuoles (fyi – not seen on model). Identify these structures on the model using the keys provided. Be sure to know their respective functions.
Euglena – Using the key provided, label the bold structures listed above.
Red Algae This group consists primarily of multicellular macroalgae. Red algae have chlorophyll a , chlorophyll c , phycoerythrin and phycocyanin; the combination of theses pigments gives them a reddish coloration. The red algae are relatively small, delicate algae with a feathery appearance. They collect calcium salts and are partially responsible for the formation of coral reefs. Use the space below to sketch representative red algae as seen on the herbarium sheet.
Brown Algae All brown algae are multicellular macroalgae, some growing more than two hundred feet in length. Brown algae contain chlorophyll a , chlorophyll c and carotenoids. Because of their size, many large brown algae called kelps provide habitats for other marine organisms. Kelps may have leaf-like blades , stem-like stipes , root-like holdfasts , and gas-filled floats ( bladders ) that provide buoyancy. Sargassum is a common brown algae on the Texas Gulf- Coast. It is free-floating and drifts on the gulf currents providing an important habitat for a host of marine organisms. Use the space below to make a sketch of and label the brown algae specimens.
Sargassum Laminaria Fucus
Review Questions
- Name the structure a Euglena uses for: locomotion - detect light – osmoregulaiton -
- Name the structure in a Euglena where the photosynthetic pigments are located.
- Name the process by which sexual reproduction occurs in Spirogyra. Name the structure which allows for the passage of the genetic material.
- Describe the shape of a Spirogyra chloroplast.
- Are the blades of kelp analogous or homologous to the leaves of plants?
- Organisms known as kelps belong to which group of algae?
- Name the structure kelp use to anchor itself to the sea floor.
Amoebas – Amoeba Amoebas are protozoans which are constantly changing their shape. The do this buy extending cytoplasm into pseudopodia (sing – pseudopodium or pseudopod ) which they use for locomotion as well as prey capture. They move using their pseudopodia until a food item is located (such as cyanobacteria ). They ingest the food item by phagocytosis (endocytosis), using their pseudopodia to surround the prey and form a food vacuole. Members of the genus Amoeba have a single large nucleus , while other amoebas are multinucleated. Most amoebas are harmless aquatic predators; however, some are important parasites and pathogens such as Entamoeba histolytica which causes amoebic dysentery.
Amoeba – Label the structures listed in bold above.
Flagellates - Trypanosoma
Flagellated protozoans use a flagellum for locomotion. There are many different flagellates, some are beneficial mutualistic protists while others are dangerous pathogens. Members of the genus Trypanosoma have a single nucleus and are deadly pathogens. African sleeping sickness is caused by a trypanosome. The trypanosomes are transmitted from one host to the next by tse tse flies (called the vector of disease, the vector transmits the disease from one host to the next) and live in the blood. They are able to move in the host’s blood using the flagellum and the undulating membrane (resembles a fin on the cell membrane). Use the microscope to examine the trypanosomes in the blood. You should be able to see the red blood cells in the sample as well as the flagellated trypanosomes. Use the space below to sketch and label the trypanosomes observed on the slide.
Station 1
Introduction Bacteria Protists
Nostoc slide demo
Station 1
Introduction Bacteria Protists
Nostoc slide demo
Station 3 A
Algae
Spirogyra slide demo Euglena model macroalgae herbarium sheets
Station 3B
Protozoans
Paramecium model Amoeba model Trypanosoma slide demo
Station 2
Pond water observation
Station 2
Pond water observation
30 minutes
15 minutes each
30 minutes
