In this lesson we will learn the following:
- What is the difference between procaryotic and eucaryotic cells?
- Where are eucaryotic cells found in the environment?
Read the online lecture.
A eucaryotic cell is larger and more complex than a procaryotic cell and found in animals, plants, algae, fungi, and protozoa.
When you look at a eucaryotic cell with a microscope you'll notice a highly organized structure of organelles that are bound by a membrane. Each organelle performs a specialized function for the cell's metabolism.
Depending on the organism, a eucaryotic cell may contain external projections called flagella and cilia. The projections are used for moving substances along the cell's surface or for moving the entire cell. Flagella move the cell in a wavelike motion within its environment. Cilia move substances along the cell's surface and also aid in movement of the cell.
Structure of the Eucaryotic Cell
Many eucaryotic cells have a cell wall. The composition of the cell wall differs with each organism. In contrast, protozoa have no cell wall and instead have a pellicle, which is a flexible, proteinaceous covering.
The plasma membrane surrounds a eucaryotic cell and serves as a barrier between the inner cell and its environment. In a eucaryotic microorganism, the cytoskeleton provides support and shape for cells and helps transport substances through the cell. The plasma membrane of a eucaryotic cell functions like the plasma membrane of a procaryotic cell. Substances enter and leave the cell through the cytoplasmic membrane by using simple diffusion, facilitated diffusion, osmosis, and active transport. Eucaryotic cells extend parts or sections of their plasma membrane, called pseudopod, which means "false foot". Pseudopods are used to engulf substances and bring them into the cell, which is called endocytosis (a type of active transport). There are two types of endocytosis. These are phagocytosis (eat) and pinocytosis (drink).
The amoebae feed mainly upon bacteria and algal unicells, as do most of the ciliates. Whereas the amoebae ingest food particles by absorbing them with their pseudopodia, the ciliates feed by either actively capturing and engulfing prey organisms, or by using their cilia to create currents in the surrounding water which bring the food organisms to their mouths. The captured organism is enclosed in a food vacuole, a membrane-bound vesicle which moves through the cytoplasm as digestion occurs. Undigested remains are discharged into the surrounding water, usually at a definite location in the organism's outer pellicle.
Cytoplasm and Nucleus
The cytoplasm of a eucaryotic cell contains cytosol, organelles, and inclusions, which is similar to the cytoplasm of the procaryotic cell. A eucaryotic cell uses a method of cell division during reproduction called mitosis. This is the formation of two daughter cells from a parent cell.
Utilizing Energy in the Cell
The endoplasmic reticulum contributes to the mechanical support and distribution of the cytoplasm and is the pathway for transporting lipids and proteins throughout the cell.
The Golgi complex is considered the "Fedex System" of the cell because it packages and delivers proteins, lipids, and enzymes throughout the cell and to the environment.
A lysosome is a sphere in animals cells that is formed by, but is separate from, the Golgi complex. It contains enzymes used to digest molecules that have entered the cell. Think of lysosomes as the digestive system of the cell.
The mitochondrion is an organelle that is comprised of a series of folds called cristae that is responsible for the cell's energy production and cellular respiration. The mitochondrion is the powerhouse of the cell where ATP is produced.
Eucaryotic cells of green plants and algae contain plastids, one of which is chloroplast. Chloroplasts are organelles that contain pigments of chlorophyll and carotenoids used for gathering light and enzymes necessary for photosynthesis.
A centriole is a pair of cylindrical structures near the nucleus that is comprised of microtubules and aids in the formation of flagella and cilia. The centriole also has a part in eucaryotic cell division.
Procaryotes and Eucaryotes: How They Are Different
Despite their apparent differences, procaryotes and eucaryotes have a lot in common. They perform most of the same kinds of functions, and in the same ways, however eucaryotic cells are much larger and much more complex than procaryotic cells.
The major differences between the two are:
- Eucaryotes have a nucleus and membrane-bound organelles; procaryotes do not.
- The DNA of procaryotes floats freely around the cell; The DNA of eucaryotes is held within the nucleus.
- The organelles of eucaryotes allow them to exhibit higher levels of intracellular division of labor than is possible in procaryotes.
Humans, of course, are an example of multicellular eucaryotes, while Streptococcus pyogenes, the bacterium that causes strep throat, is an example of procaryotes, as is all bacteria. Other examples of eucaryotes are animals, plants, fungi, protozoans, and algae.
Protozoans are found in all moist habitats within the United States, but we know little about their specific geographic distribution. They are unicellular organisms that range in size from a few microns to several hundred microns. Polluted waters often have a rich and characteristic protozoan fauna. The relative abundance and diversity of protozoa are used as indicators of organic and toxic pollution.
Although protozoa are frequently overlooked, they play an important role in many communities where they occupy a range of trophic levels. As predators upon unicellular or filamentous alge, bacteria, and microfungi, protozoa play a role both as herbivores and as consumers in the decomposer link of the food chain.
Both in organic pollution of the natural environment and in the biological processing of human and domestic animal sewage, the ceaseless activity of the protozoa, particularly the colonial ciliates, in the extraction and digestion of bacteria and other suspended particles is the main element of the natural process by which the water supply is rendered once again fit for consumption by humans and other creatures. Any change in our environment which threatens the life of a balanced community of protozoans threatens also the continuity of a clean water supply for humans. This is particularly relevant in the light of our current over-use of kitchen and lavatory disinfectants and their effect upon the ciliates at sewage processing plants and in the waterways beyond.
Most protozoa are asexual and reproduce in one of three ways: fission, budding, and multiple fission. Some protists are sexual and exhange genetic material from one cell to another through conjugation, which is the physical contact between cells.
A protist can survive in an adverse environment by encapsulating itself with a protective coating called a cyst. The cyst defends the protist in extreme temperatures against toxic chemicals and even when there is a lack of oxygen, moisture, and food.
Factors Affecting Growth and Distribution
Most free-living protozoa reproduce by cell division (exchange of genetic material is a separate process and is not involved in reproduction in protozoa). Protozoa are found living actively in nutrient-poor to organically rich waters and in fresh water varying between 0°C (32°F) and 50°C (122°F). Nonetheless, it appears that rates of population growth increase when food is not constrained and temperature is increased.
Protists receive nutrients by breaking down organic matter and can grow in both aerobic and anaerobic environments, such as protists that live in the intestine of animals. Some receive nutrients from organic matter and photosynthesis because they contain chlorophyll. These protists are considered both algae and protozoa. Protists obtain food in one of three ways: absorption, ingestion, and engulfing. Food is digested in the vacuole after the food enters the cell. The vacuole is a membrane-bound organelle. Waste products are excreted using a process called exocytosis.
Diseases Caused by Protozoa
Several protozoa can cause waterborne diseases. The most common of these pathogenic protozoa are Cryptosporidium , Entamoeba , Giardia , and Toxoplasma. These species are all able to form cysts , or protective coatings, which allow them to survive outside a host for extended periods of time. Protozoan cysts also protect the organism from chlorine, so these species are not effectively controlled by chlorination. Instead, protozoa are usually removed from water by filtration.
Cryptosporidium is a sporozoa which is one of the most common pathogens responsible for waterborne diseases in the United States. Scientists estimate that between 1% and 5% of Americans are infected with Cryptosporidium at any one time. Cryptosporidiosis, the disease caused by Cryptosporidium infection, results in diarrhea, abdominal cramps, and fever. Healthy adults usually do not require treatment for cryptosporidiosis since the body will heal itself naturally within a couple of weeks.
Cryptosporidium , like most other waterborne pathogens, is spread to new hosts through the ingestion of contaminated food and drinking water. In addition, several outbreaks have been found to result from fecal accidents in swimming pools. Water treatment plants find it difficult to prevent the spread of Cryptosporidium since the cysts are very resistant to chlorination and can sometimes pass through filters. Instead, the cysts can be killed by ozonation or by boiling the water for at least a minute.
Entamoeba histolytica is an amoeboid protozoan which lives in anaerobic environments. Like the other pathogenic protozoa, Entamoeba is capable of forming cysts which can remain dormant for extended periods of time in the water, in soil, or in food. These cysts spread to new hosts when we ingest contaminated food or water.
In humans, Entamoeba causes amoebic dysentery, which is usually treated with antibiotics. Entamoeba outbreaks are rare in the United States but are quite common in developing countries when raw sewage contaminates drinking water supplies or when the soil is fertilized with untreated wastes. In the water treatment plant, Entamoeba can be removed from water using a sand filter.
Giardia lamblia is a flagellate protozoan which is capable of forming cysts. The species is the most important cause of waterborne disease outbreaks in the United States.
Infection with Giardia lamblia results in a disease called giardiasis, which is also known as traveler's diarrhea or Montezuma's Revenge. Symptoms of giardiasis include diarrhea, abdominal cramps, fatigue, and weight loss. Although most people who contract giardiasis heal naturally within a week or two, the illness sometimes lingers for up to a year, in which case antibiotics may be prescribed.
Giardia lamblia is spread when people ingest contaminated food or water. In the water treatment plant, chlorine is somewhat effective at inactivating the cysts at a dosage of 1.5 mg/L chlorine with a contact time of 10 minutes. Filtration and boiling are more effective at killing Giardia .
Toxoplasma gondii is a sporozoa which causes a disease known as toxoplasmosis. In most cases, toxoplasmosis has mild flu-like symptoms which are often unnoticed or undiagnosed and do not require treatment. However, a pregnant woman may pass on the infection to her unborn child, in which case the child will have much more serious symptoms.
Toxoplasma gondii has a complex life cycle involving at least two different hosts. The protozoan reproduces sexually within its primary host, the cat, and releases cysts in the cat's feces. The cysts are then ingested by intermediate hosts, which include a large number of vertebrate species such as pigs, cows, and humans. In the intermediate host, the cysts develop into an active form of the protozoan which reproduces asexually. The offspring produced in the intermediate host then infect a cat, completing the cycle.
In most cases, humans contract toxoplasmosis by eating contaminated meat or by handling cats or changing cats' litter boxes. However, a recent outbreak of toxoplasmosis linked to drinking water in Canada has alerted us to the possibility of Toxoplasma gondii being spread in water.
Amoebae, like those shown above, are protozoans which move by extending finger-like protrusions of their cells called pseudopodia. Amoebae are slow-moving and possess a cytoplasm that "flows" against a thin,flexible cell membrane. The flowing action "pushes" the cell membrane and provides the organism with locomotion. Extenstion and contraction of the cell membrane caused by the flowing action of the cytoplasm is referred to as a pseudopodia ("false foot") mode of locomotion, which is used to engulf or capture substances and bring them into the cell. This is called endocytosis (a type of active transport). There are two types of endocytosis. These are phagocytosis (eat) and pinocytosis (drink). You can see several engulfed food particles as circles within each amoebae cell above.
Amoebae itself is found in freshwater, typically on decaying vegetation from streams, also found in salt water, in wet soil, and in animals (including people); but large, naked Amoebae are not especially common in nature. However, because of the ease with which they may be obtained and kept in the lab, they are common objects of study, both as representative protozoa and to demonstrate cell structure and function.
A good method of collecting amoebae is to lower a jar upside down until it is just above the sediment surface. Then one should slowly let the air escape so the top layer will be sucked into the jar. Deeper sediment should not be allowed to get sucked in. It is possible to slowly move the jar when tilting it to collect from a larger area. If no amoebae are found, one can try introducing some rice grains into the jar and waiting for them to start to rot. The bacteria eating the rice will be eaten by the amoebae, thus increasing the population and making them easier to find.
Amoebae usually are present in high numbers during start up of a treatment plant recovery from a toxic discharge to the treatment plant or low dissolved oxygen levels. If amoebae are present as the dominant protozoan group, this could indicate an unstable wastewater environment and a sludge that is in poor health.
Flagellates are single-celled protists with one or more flagella, which are whip-like organelles often used for propulsion. The flagella is used for movement through the liquid. Eucaryotic flagella are not the same as flagella of bacteria. The flagella found in flagellates has an internal structure composed of small tubules of protein called microtubules.
Some flagellates live as colonial entities, while others function as a single cell. Most are free-living organisms, however, a number are parasitic or pathogenic for animals and humans. They multiply by binary fission and some species possess cyst stages. Flagellates range in size from 5-20 µm. Many flagellates are able to feed autotrophically (fix their own energy from inorganic sources) as well as heterotrophically(depend upon energy and carbon fixed by some other organism). Flagellated protozoa are oval in shape and have one or more whip-like structures or flagella. The whipping action propels the protozoa through the activated sludge in a "cork-screw" pattern of locomotion. While in motion, flagellates accidentally "hit" substrate. With decreasing numbers of suspended bacteria, flagellates find it more difficult to find substrate.
There are two primary groups of flagellates. The Peranema belongs to the group which ingests its food. The other group of flagellates is more like bacteria. They don't ingest whole food. They take in food that is already partially "digested." Dinoflagellates are important primary producers (photosynthesisers) in lakes and oceans, yet they can also ingest prey and feed in an animal-like fashion. Some types of flagellates commonly found in wastewater are Euglena, Trigonomonas, and Monas.
Like their relatives the amoebae, flagellates are usually present when there are large amounts of soluble food available (high F:M or high BOD). They are found during start up when the sludge is young or after an upset, but will quickly predominate over the amoebae because they are more efficient feeders. They are often found in trickling filters, oxidation ponds, lagoons and activated sludge. Flagellates are one of the few protozoan form present in sludges that are strongly loaded. Their presence may indicate high soluble BOD levels. Flagellates usually are present in very large numbers during initial start-up of a wastewater treatment plant, during recovery from a toxic discharge to the treatment plant, or at low D.O. levels. If flagellates are present as the dominant protozoan group, this could indicate an unstable wastewater environment and a sludge biomass that is very young. Usually found in low MCRT or low HRT for activated sludge systems. Lagoon systems are different and flagellates are often found in lagoons since it is harder to develop an older sludge in a lagoon with high flows.
Flagellates prefer soluble nutrients and dead or decaying material. They compete with bacteria for food in the activated sludge process, but can only dominate when the nutrient level is high. Some of the larget flagellates eat bacteria in the sludge but can not keep up with the logarithmic growth rate of the bacteria in the activated sludge. Therefore flagellates can only dominate early in the treatment process when the soluble organic nutrients are high enough for both flagellates and bacteria to eat. In a continuosly fed batch process, the dominance of these microorganisms is short lived.
Flagellates reproduce through binary fission since it consists of a cell splitting in half. As you can see in the animation above, the microorganism first makes a second copy of its DNA in a process known as replication . Next, the cell begins to constrict in the middle, leaving one set of DNA and organelles on each side of the constriction. Eventually, the cell splits apart into two identical daughter cells. Once these daughter cells enlarge to adult size, each one is ready to split into two more daughter cells.
The Ciliates are more complex organisms than the amoebae and flagellates. The three types of ciliated protozoa are free-swimming ciliates, crawling ciliates, and stalked ciliates. All of these have short hair-like structures or cilia that beat in unison to produce a water current for locomotion and capturing bacteria. The water current moves suspended bacteria into a mouth opening. Ciliates feed on bacteria, not on dissolved organics. They are usually an indicator of good quality sludge and typically found in young to medium age sludge. They are important because they work with the bacteria in the activated sludge process by feeding on them and helping to clarify the effluent.
Free-swimming ciliates such as Litonotus and Paramecium possess ciliate on all surfaces of the body and usually can be found suspended or simming freely in the bulk solution. Free-swimmers swim faster than fiagellates so they can out compete them for food. Free-swimmers are usually found when no large flocs have been formed so that it is easier to swim around.
The rapid beating of the cilia permits the organism to move in a straight line. Free-swimming ciliates are found in large numbers when the bacterial population and dissolved oxygen concentration of the treatment process are relatively high. If free-swimming ciliates are present as the dominant protozoan group, this could indicate a wastewater environment that is not yet stabilized and a sludge that is intermediate in health.
Free-swimming ciliates reproduce by conjugation. Each cell has a large macronucleus and a smaller micronucleus. Conjugation is a form of sexual reproduction in which the individual cells fuse together and swap nuclear DNA in the form of small micronuclei. Conjugation is unlike the fusion of gametes in other protists and animals. It involves the division and fusion of micronuclei from opposite paramecia. After conjugation each paramecium continues on its way, genetically altered from its brief encounter because of different chromosomal combinations. The genetically altered paramecia continue to produce clones of themselves by asexual cell division, a process known as fission
Crawling ciliates, such as Aspidisca and Euplotes, possess ciliate only on the ventral or belly surface where the mouth opening is located. The beating of the cilia gives the appearance that it is crawling as it moves across the surface of floc particles. Some of the cilia are modified to form "spikes" that help to anchor the organism to the floc particle. Crawling ciliates are found in large numbers when the bacterial population and dissolved oxygen concentration of the treatment process are high and the wastewater environment is stable. In order for crawling ciliates to be dominant, there must be large floc structures present that impede the free-swimmers and flagellates movement and provide a surface for the crawlers to "walk" on. This means the F/M is getting lower and the bacteria have started to formulate floc structures. Crawlers also require a high D.O. content in the mixed liquor. Sludge age is closer to middle ages than young. Crawling ciliates indicate a stable wastewater environment and a healthy sludge.
Stalked ciliates, such as Carchesium and Voticella, have cilia around the mouth opening only and are attached to floc particles. Stalked ciliates have an enlarged anterior portion or "head" and a slender posterior portion or "stalk". Some , such as Vorticella, have a contractile filament within the stalk that permits springing action. The beating of the cilia and the springing action of the stalk produce a water vortex that draws dispersed bacteria into the mouth opening. Of all ciliated feeding mechanisms, the stalked ciliates mechanism is the most efficient in capturing stray bacteria. Stalked ciliates are also capable of swimming freely. This may occur during low dissolved oxygen levels within the treatment process. Stalked ciliates are found in large numbers when the bacterial population and dissolved oxygen concentration are high, the wastewater environment is stable and a mature floc has developed. Stalked ciliates indicate a stable wastewater environment and a healthy sludge.
Protozoans are found in all moist habitats within the United States and the relative abundance and diversity of them are used as indicators of organic and toxic pollution. Protozoans that are important in the activated sludge process in removing bacteria are the amoebae, flagellates and ciliates.
Amoebae are protozoans which move by extending finger-like protrusions of their cells called pseudopodia. Amoebae usually are present in high numbers during start up of a treatment plant recovery from a toxic discharge to the treatment plant or low dissolved oxygen levels. If amoebae are present as the dominant protozoan group, this could indicate an unstable wastewater environment and a sludge that is in poor health.
Flagellates are single-celled protists with one or more flagella, which are whip-like organelles often used for propulsion. Like their relatives the amoebae, flagellates are usually present when there are large amounts of soluble food available (high F:M or high BOD). They are found during start up when the sludge is young or after an upset, but will quickly predominate over the amoebae because they are more efficient feeders. Flagellates can only dominate early in the treatment process when the soluble organic nutrients are high enough for both flagellates and bacteria to eat.
The Ciliates are more complex organisms than the amoebae and flagellates. The three types of ciliated protozoa are free-swimming ciliates, crawling ciliates, and stalked ciliates. All of these have short hair-like structures or cilia that beat in unison to produce a water current for locomotion and capturing bacteria. Ciliates feed on bacteria, not on dissolved organics. They are usually an indicator of good quality sludge and typically found in young to medium age sludge. They are important because they work with the bacteria in the activated sludge process by feeding on them and helping to clarify the effluent.
Free-swimming ciliates possess ciliate on all surfaces of the body and are usually found when no large flocs have been formed so that it is easier to swim around. Crawling ciliates possess ciliate only on the ventral or belly surface where the mouth opening is located. In order for crawling ciliates to be dominant, there must be large floc structures present that impede the free-swimmers and flagellates movement and provide a surface for the crawlers to "walk" on. Stalked ciliates have cilia around the mouth opening only and are attached to floc particles. Stalked ciliates have an enlarged anterior portion or "head" and a slender posterior portion or "stalk". Stalked ciliates are found in large numbers when the bacterial population and dissolved oxygen concentration are high, the wastewater environment is stable and a mature floc has developed. Of all ciliated feeding mechanisms, the stalked ciliates mechanism is the most efficient in capturing stray bacteria.
Complete the assignment on Protozoa Identification .and send in to your instructor either by e-mail, mail or fax.
There is no lab associated with this lesson.
Answer the questions in the Lesson 5 Quiz . When you have gotten all the answers correct, print the page and either mail or fax it to the instructor. You may also take the quiz online and directly submit it into the database for a grade.