Lesson 3:

Procaryotic and Eucaryotic Cells 


 


Objective

In this lesson we will learn the following concepts:

  • The morphology of the bacterial cell.
  • The structure of the cell

 



Reading Assignment

Along with the online lecture, read Chapter 2 in Microbiological Examination of Water and Wastewater.





Lecture

Procaryotes

Introduction

 

Procaryotes are organisms which do not contain nuclei or membrane-bound organelles.  (Nuclei and organelles are both cell parts which we will define in a later section.)  All prokaryotes are unicellular, which means that each organism is made up of only one cell. 

Another trait common to all prokaryotes is their small size - a typical cell is only about 2 um long.  A micrometer, abbreviated as um and sometimes known as a micron, is equal to one millionth of a meter.  It would take about 13,000 prokaryotes lying end to end to stretch the length of one inch.   Under a light microscope, bacteria are so small that they are usually visible only as tiny dots. 

Although there are two kingdoms which contain procaryotes (Eubacteria and Archaebacteria), all procaryotes are commonly known as bacteria.  In the past, some procaryotes have been called blue-green algae, but these organisms are now known as cyanobacteria.

 

 

 

Importance

Bacteria are present in large numbers in raw wastewater, in biological treatment plants, in plant effluent, in natural waters, and throughout our environment.  In the wastewater treatment plant, they form part of the slime on trickling filters and on the discs of rotating biological contactors.  They are also present in activated sludge. 

Bacteria are heterotrophs, meaning that they get their food from eating other organisms or from eating organic matter.  (In contrast, organisms like plants which make their own food are known as autotrophs.)  As a result, bacteria are important to the wastewater operator since the bacteria are able to digest a large amount of the waste in wastewater.  On the other hand, some bacteria get their food from living inside organisms such as humans, in which case they can cause disease.  

 

 

Cell Structure

cell is the fundamental unit of all life.  In the case of unicellular organisms, a cell is the body of the organism.  In the case of multicellular organisms (organisms which consist of more than one cell), the cell is the building block from which the organism's body is made.  


Diagram of a prokaryotic cell


The diagram above illustrates a typical bacterial cell.  As with every other kind of cell, a membrane serves as a sac holding the parts of the cell together.  The membrane also regulates what passes into and out of the cell. 

Inside the membrane, the cell is filled with a fluid known as cytoplasm.  Floating in the cytoplasm are various organelles (subcellular structures with specific functions.)  We have only illustrated a few of the most important organelles.  Notice that the the DNA, which contains the genetic material of the cell, is floating freely in a mass within the cell.  In addition to the main mass of DNA, the bacterial cell contains plasmids, which are small loops of DNA which can be transferred to other bacteria, or in some cases into other organisms.  Ribosomes are the sites of protein synthesis. 

Outside the membrane, most bacteria are surrounded by two other layers.  The first of these, the cell wall, is a rigid layer made up of proteins, polysaccharides, and lipids.  The cell wall gives the bacterium a set shape.  Outside the cell wall is the capsule, a gelatinous slime layer which allows the bacterium to attach to surfaces and also protects the bacterium.  In the treatment plant, bacterial capsules are responsible for clumping the organisms into flocs, or aggregations, which can settle out of water.  In order for disinfecting agents such as chlorine to be effective, they must penetrate this protective slime layer.

The bacterium can also have various appendages.  Pili are hollow, hair-like structures which allow the bacterium to attach to other cells.  Flagella are longer projections which can move and push the bacterium from place to place.  

 

 

Endospores

 

 

 

Some bacteria are able to survive in harsh environments by forming endospores.  Endospores are small spores which develop asexually inside the bacterial cell.  An endospore consists of the bacterium's DNA surrounded by a protective cell wall.  Once the endospore has formed, the parent cell bursts open and releases the endospore.  

An endospore is able to survive in very harsh environments because it is in a dormant state and does not attempt to eat, grow, and reproduce.  Bacteria typically form endospores when they encounter an undesirable pH, electrolyte content, amount of food, or amount of oxygen in the environment.  Once the environmental conditions improve, the endospore is able to germinate and turn back into a growing bacterial cell.  

 

 

Classification

There are thousands of species of bacteria on earth, many of which have not yet been identified.  When attempting to classify a bacterium, a variety of characteristics are used, including visual characteristics and laboratory tests. 
Some bacteria can be identified through a simple visual perusal.  First, the operator considers the appearance of the bacterial colony (a group of the same kind of bacteria growing together, often on a petri dish.)  The operator also views individual bacteria under a microscope, considering their shape, groupings, and features such as the number and location of flagella. 

A variety of laboratory techniques can be used to narrow down the identity of a bacterial species if a visual survey is not sufficient.  The operator can stain the bacteria using a gram stain or an acid-fast stain.  The bacteria can be cultured on a specific medium which promotes the growth of certain species, as in the membrane filter method of testing for coliform bacteria.  Other tests can detect bacterial by-products, while yet more advanced tests actually analyze the DNA of the bacteria.  

 

 

Bacterial Shapes

The most basic method used for identifying bacteria is based on the bacterium's shape and cell arrangement.  This section will explain the three morphological categories which all bacteria fall into - cocci, bacilli, and spirilla.  You should keep in mind that these categories are merely a way of describing the bacteria and do not necessarily refer to a taxonomic relationship. 



Cocci


Cocci (or coccus for a single cell) are round cells, sometimes slightly flattened when they are adjacent to one another.  Cocci bacteria can exist singly, in pairs (as diplococci), in groups of four (as tetrads), in chains (as streptococci), in clusters (as stapylococci), or in cubes consisting of eight cells (as sarcinae.)

 



Bacilli


Bacilli (or bacillus for a single cell) are rod-shaped bacteria.  Since the length of a cell varies under the influence of age or environmental conditions, you should not use cell length as a method of classification for bacillus bacteria.  Like coccus bacteria, bacilli can occur singly, in pairs, or in chains.  Examples of bacillus bacteria include coliform bacteria, which are used as an indicator of wastewater pollution in water, as well as the bacteria responsible for typhoid fever.  

 


Spirilla


Spirilla (or spirillum for a single cell) are curved bacteria which can range from a gently curved shape to a corkscrew-like spiral.  Many spirilla are rigid and capable of movement.  A special group of spirilla known as spirochetes are long, slender, and flexible. 

 

 

Parts of Procaryotic Cells

A procaryotic cell is a cell that does not have a true nucleus. The nuclear structure is called a nucleoid, which contains most of the cell's genetic material and is usually a single circular molecule of DNA. A procaryotic organism, such as bacteria, is a cell that lacks a membrane-bound nucleus or membrane-bound organelles. The exterior of the cell usually has glycocalyx, flagellum, fimbriae, and pili.

 

http://water.me.vccs.edu/courses/ENV108/clipart/procaryotic.gif

 

 

 

Glycocalyx

Glycocalyx is a sticky, sugary envelope composed of polysaccharides and/or polypeptides that surround the cell. Glycocalyx can be firmly attached to the cell's surface, called capsule, or loosely attached, called slime layer. A slime layer is water-soluble and is used by the procaryotic cell to adhere to surfaces external to the cell.

 

 

Flagella

Flagella are made of protein and appear "whip-like". They are used by the procaryotic cell for mobility. Flagella propel the microorganism away from harm and towards food in a movement known as taxis.

Flagella can exist in the following forms:

  • Monotrichous: One flagellum
  • Lophotrichus: A clump of flagella, called a tuft, at one end of the cell.
  • Amphitrichous: Flagella at two ends of the cell.
  • Peritrichous: Flagella covering the entire cell.
  • Endoflagellum: A type of amphitrichous flagellum that is tightly wrapped around spirochetes. A spirochete is a spiral-shaped bacterium that moves in a corkscrew motion. Borrelia burgdorferi, which is the bacterium that causes lyme disease, exhibits an endoflagellum.

 

 

Fimbriae

Fimbriae are proteinaceous, sticky, bristle-like projections used by cells to attach to each other and to objects around them. Fimbriae may be responsible for the clinging of cells that leads to biofilms and other thick aggregates of cells on the surface of liquids and for the microbial colonization of inanimate solids such as rocks and glass.

 

 

Pili

Pili are tubules that are used to transfer DNA from one cell to another cell, similar to tubes used to fuel an aircraft in flight. Some are also used to attach one cell to another cell. The tubules are made of protein and are shorter in length than flagella and longer than fimbriae.

 

 

Cell Wall

The procaryotic cell's cell wall is located outside the plasma membrane and gives the cell its shape and provides rigid structural support for the cell. The cell wall also protects the cell from its environment. Pressure within the cell builds as fluid containing nutrients enters the cell. It is the job of the cell wall to resist this pressure the same way that the walls of a balloon resist the build-up of pressure when it is inflated. If pressure inside the cell becomes too great, the cell wall bursts, which is referred to as lysis.

The cell wall of many bacteria is composed of peptidoglycan, which covers the entire surface of the cell. It is made up of a combination of peptide bonds and carbohydrates. The wall of a bacterium is classified in two ways:

  • Gram-positive. A gram-positive cell wall has many layers of peptidoglygan that retain the crystal of violet dye when the cell is stained. This gives the cell a purple color when seen under a microscope.

  • Gram-negative. A gram-negative cell wall is thin. The inside is made of peptidoglycan. The outer membrane is composed of phospholipids and lipopolysaccharides.

 

 

 

 

The cell wall does not retain the crystal of violet dye when the cell is stained. The cell appears pink when viewed with a microscope.

 

 

Cytoplasmic Membrane

The procaryotic cell has a cell membrane called the cytoplasmic membrane that forms the outer structure of the cell and separates the cell's internal structure from the environment. This membrane provides a selective barrier, allowing certain substances and chemicals to move into and out of the cell.

 

http://water.me.vccs.edu/courses/ENV108/clipart/CellMembraneDrawing.gif

 

The cytoplasmic membrane regulates the flow of molecules (such as nutrients) into the cell and removes waste from the cell by opening and closing passages called channels. In photosynthetic procaryotes, the membrane functions in energy production by collecting energy in the form of light. This membrane is selectively permeable because it permits the transport of some substances and inhibits the transport of others. Two types of transport mechanisms are used to move substances through the cytoplasmic membrane. These are passive transport and active transport.

 

 

 

Passive Transport

Passive transport moves substances into and out of the cell down a gradient similar to how a rock rolls downhill, following the gradient. There are three types of passive transport:

  • Simple diffusion: Simple diffusion is the movement of substances form a higher-concentration region to a lower-concentration region. Large molecules are too large to enter the cell.

  • Facilitated diffusion: Facilitated diffusion is the movement of substances from a higher-concentration region to a lower-concentration region with the assistance of an integral protein across a selectively permeable membrane.

  • Osmosis: Osmosis is the net movement (diffusion) of a solvent (water in living organisms) from a region of higher water concentration to a region of lower concentration as in the image below.



    http://water.me.vccs.edu/courses/ENV108/clipart/osmosis.gif'

 

 

Active Transport

Active transport is the movement of a substance across the cytoplasmic membrane against the gradient by using energy provided by the cell. This is similar to pumping water against gravity through a pipe. Energy must be spent in order for the pump to work. A cell makes energy available by removing a phosphate (P) from adenosine triphosphate (ATP). ATP contains chemical potential energy that is released by a chemical reaction within the cell. It is this energy that is used to change the shape of the integral membrane protein-enabling substances inside the cell to be pumped through the membrane. For example, active transport is used to pump sodium from a cell.

 

 

Reproduction

Procaryotic cells reproduce asexually. Asexual reproduction is a process through which one parent gives rise to genetically identical offspring - in other words, two clones of the parent.  

Binary fission animation.

 

Asexual reproduction in microorganisms is often known as 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 physical and chemical requirements for growth can vary widely among different species of bacteria, but in general, the physical requirements include proper temperatures, pH and osmotic pressure. Most bacteria thrive only within narrow ranges of these conditions, however extreme those ranges may be.

 

 

Stages of Bacterial Growth

The term "bacterial growth" generally refers to growth of a population of bacteria, rather than of an individual cell. Under optimal conditions, a bacterium can divide into two daughter cells every 15 to 30 minutes.  After another 15 to 30 minutes, the two daughter cells can each divide into two more cells.  These four cells then divide into eight cells, and so on.  As you can see, microorganism populations have the potential to grow tremendously within a very short period of time.

Bacteria reproduce by a process known as transverse fission, an asexual reproduction method (although some species have a sexual mode). For growth, these microorganisms must have an energy source, typically complex carbohydrates; trace inorganics such as metals, phosphorous and nitrogen compounds; vitamins and water.

A bacterial growth curve consists of three stages - lag, log and stationary - with a generation time of several minutes to hours. In the initial lag phase, bacteria are increasing in size and adjusting to the environmental conditions. The log stage is a period of rapid growth (See Bacterial Multiplication Chart), followed by the stationary phase when available nutrients have been depleted and sometimes, toxic products produced. Without further nutrient sources, most of the bacteria will die off.

Population growth curve.

You might expect for a microorganism population to continue to grow indefinitely.  However, in a closed system (an environment such as a test tube or a batch of sewage which is separate from the outside world), microorganism populations usually follow a predictable pattern of growth and death shown in the diagram above. 

When microorganisms are first introduced to a new environment, they go through a lag phase.  The lag phase is a time when the microorganisms do not reproduce, so the number of microorganisms in the population remains constant.  During the lag period, microorganisms are adjusting to their new environment. 

After a short time, the microorganisms begin to reproduce.  At first, they reproduce relatively slowly, but the reproduction rate quickly speeds up as they pass out of  the accelerated growth phase and into the logarithmic growth phase . 

As the microorganisms grow, they begin to use up the food and oxygen in their environment.  They also excrete wastes which pollute their environment.  Eventually, the environmental conditions degrade to a point where the bacterial growth begins to slow - the decelerated growth phase .  Then the number of organisms found in the population levels off as the death rate equals the birth rate in the stationary phase . 

The environment continues to be degraded, and soon the microorganism death rate exceeds the birth rate and the population size begins to fall in the accelerated death phase .  At the maximum death rate, the population is in the logarithmic death phase in which the population shrinks very quickly until nearly all of the cells are dead.  At this point - the survival phase - the population will level off at a relatively small size. 

The wastewater operator needs to be familiar with this population growth curve since it will influence the functioning of an activated sludge system.  During conventional treatment, the activated sludge is held for a sufficient time for the microorganism population to enter the logarithmic death phase. 

 

 

Eucaryotes 

Introduction

Except for bacteria and viruses, all other organisms considered in this course are eucaryotes.  eucaryotes are unicellular or multicellular organisms which contain a nucleus and membrane-bound organelles.  A nucleus is a membrane sac within the cell which holds all of the cell's DNA.  Membrane-bound organelles within the cell can include chloroplasts, mitochondria, and several other organelle types which we will not discuss here. 


Diagram of a eukaryotic cell 

 


The diagram above shows some of the parts found in a typical eucaryotic cell.  Since there are so many different kinds of eucaryotes, several of the parts shown in the cell above will not be present in certain species.  Also, some species may contain additional parts not shown above. 

As you can see, eucaryotic cells are always bounded by a membrane, just as prokaryotic cells are.  Some eucaryotic cells are also surrounded by a cell wall, but eucaryotic cells do not have capsules.  Although they are not shown in the diagram above, eucaryotic cells can have protuberances such as flagella or cilia (tiny hairs which typically form a fringe all the way around a cell.)

Like the prokaryotic cell, the eucaryotic cell is filled with cytoplasm.  Ribosomes and various other organelles can be found floating in the cytoplasm.  The two additional organelles shown in the diagram above are membrane-bound and are found only in eucaryotic cells.  Mitochondria (mitochondrion when referring to a single organelle) are present in nearly all eucaryotic cells and produce the cell's energy by breaking down food.  Chloroplasts, in contrast, are present only in plants and algae and are used in photosynthesis, the process through which the organism uses energy from the sun to build sugars.  

Now that you understand the make-up of a typical eucaryotic cell, we're ready to explore the diversity of eucaryotic life.  The rest of this page will be concerned with the various types of eucaryotes typically found in water and wastewater.  

 

 

Fungi

Fungi are organisms which typically cannot move, which cannot make their own food (heterotrophic), and which contain a chemical known as chitin in their cell walls.  They can be multicellular or unicellular, with the unicellular organisms having relatively large cells. 

Although some fungi live in salt or fresh water, most fungi are terrestrial.  Many species are saprophytic, feeding on dead organic matter.  Others are parasites which live inside or on host animals, primarily feeding on plants though a few also live on animals.  The aquatic fungi are important in treating wastewater.  


Types of fungi. 



Classification of fungi is based primarily on reproductive structures, with all of the aquatic fungi being found in the Mastigomycota group.  We use several common names to refer to groups of fungi, but these groupings refer only to morphology and not to any relationship or scientific classification.  Yeast are single-celled fungi, molds are filamentous fungi consisting of multiple cells in threads known as hyphae, and mushrooms are the fruiting bodies of filamentous fungi.  

 

 

Algae

Introduction

Common names used to refer to algae include 'seaweed' and 'pond scum.' 


Algae are distinguished from animals, fungi, and protozoans by their ability to make their own food through photosynthesis and are distinguished from plants by their relative simplicity of structure.  All algae contain the green pigmentchlorophyll and the organelles chloroplasts, both of which are essential for photosynthesis. 

Algae may be either unicellular (in which case they are known as phytoplankton) or multicellular.  The algae which are important to water treatment are generally unicellular.  All algae contain a rigid cell wall and some also have sheaths (or thin gelatinous coatings) outside the cell wall.  Algae may be non-motile, but many are able to move using a flagella, in which case they are known as flagellates (a term based on morphology rather than taxonomy.)

 

 

Importance

Most algae are aquatic, living in salt or fresh water, though a few live in soil or on the bark of tres.  In natural waters, algae are an important source of food for other organisms.  They also produce oxygen during photosynthesis, adding to the dissolved oxygen content of the water during the day.  

Since algae require light for growth, they are restricted mostly to the top surfaces of trickling filters and ponds.  They are seldom found in large numbers except in tertiary treatment units, such as clear wells, and usually are not important for water treatment.  However, in oxidation ponds, the algae may represent a substantial portion of the microorganism population and may play a significant role in treatment.

 

 

Algae Bloom

Algae bloom. 

 


Algae can be problematic in nutrient-rich waters, especially those containing phosphorus, in which case they often reproduce rapidly and produce colored water and mats of algae known as algae blooms.  In natural waters or treatment plants, algae blooms are problematic because they can change many water characteristics. 

One of the primary factors which algae blooms influence is the dissolved oxygen content of the water.  During the day, the masses of algae produce so much oxygen that the water becomes supersaturated.  Then, at night, the algae actually use up oxygen in the water and can cause such extremely low dissolved oxygen levels that fish kills may result.

Algae blooms can also cause elevated pH levels in the water.  They may raise the pH levels as high as 9.5, which will influence many of the natural processes occurring in the water. 
In some cases, an algae bloom will consume itself.  As the algae grow and reproduce, they use up nutrients in the water.  Eventually, the nutrient levels will drop so low that the algae will have no nutrients and will die back.  In this case, the dead algae bodies will often promote a bacterial bloom as the bacteria respond to the abundance of food.  This overabundance of bacteria can cause yet more problems, depleting the dissolved oxygen levels in the water and causing the system to become anaerobic. 

The best method of dealing with algae blooms is prevention.  By limiting the nutrient levels in wastewater effluent, algae blooms in the receiving waters can be avoided.  The limitation on phosphorus in some wastewater effluents in New York State stems directly from this concern.

 

 

 

Classification

Cellular properties, the nature of the cell wall, and the arrangement of flagella all influence the classification of algae species.  However, the most important factor in algae classification is the types of photosynthetic pigments present in the cell.  Although all algae contain chlorophyll, some species also contain xanthophylls (which are yellow) or carotenoids (which are orange.)  The three phyla of algae which are commonly found in fresh water are described below.  
Chlamydomonas 


Phylum Chlorophyta consists of green algae which typically do not contain pigments other than chlorophyll.  Chlamydomonas, shown in the picture above, is a typical green alga.  Notice that this species has two flagella, and is thus able to swim freely through the water.  (When looking through a microscope, you should be aware that the algae's flagella are only visible under extremely high magnification.  Also note that some species in phylum Chlorophyta do not contain flagella and are not mobile.)  Each Chlamydomonas cell contains a single, large chloroplast which fills up most of the cell.  It also contains an eyespot which is a light-sensitive organelle which helps the Chlamydomonas know how to swim toward the light.   


Euglena 


Phylum Euglenophyta contains green or colorless flagellates commonly known as euglenoid algae.  Some scientists consider euglenoid algae to be protozoans because of the species which do not contain chloroplasts and which are able to feed on organic matter and other microorganisms in the water.  A typical euglenoid is Euglena, shown above.  Euglenoids usually have a single flagellum and several chloroplasts.  


Diatoms 


Phylum Chrysophyta contains golden-brown algae which contain carotenoids as a major pigment.  Although there are several different kinds of algae in phylum Chrysophyta, one group - the diatoms - is especially important in water treatment. Diatoms are algae which form a variety of intricate shapes and which contain silicon in their cell walls.  Although other algae in the phylum Chrysophyta have flagella, diatoms are either nonmobile or glide slowly along surfaces.   

In addition to the types of algae mentioned above, there are several other phyla which are found primarily in salt water.  Phylum Pyrrhophyta contains algae known as dinoflagellates, phylum Phaeophyta contains brown algae, phylum Rhodophyta contains red algae, and phylum Cryptophyta contains blue and red flagellates.  

 

 

Protozoa

Introduction

Protozoa are unicellular organisms which are heterotrophic and are mobile at some stage in their life.  They do not have a cell wall, although their membrane is often surrounded by a pellicle (a thin, flexible, protective coating).  A few protozoa give their cells rigidity by producing shells made out of calcium carbonate or silicon. 

Protozoa are important in both water and wastewater treatment.  They are responsible for several of the water-borne diseases.  In addition, protozoa help break down waste in aerobic wastewater treatment plants.  

 

 

Classification

Protozoa are divided into four groups based on their method of locomotion.  Scientists initially believed that these groups actually represented taxonomic relationships, but now many scientists suspect that the taxonomy of protozoa is much more complicated.  For the sake of simplicity, we will use the old method of classification here, based on mode of locomotion.  


 


Amoebae, like those shown above, are protozoans which move by extending finger-like protrusions of their cells called pseudopodia.  An amoeba can also use its pseudopodia to engulf a food particle in a process known as endocytosis, bringing the food inside the cell where it can be digested.  You can see several engulfed food particles as circles within each amoeba cell above.  Although most amoeba are free-living, one species is the cause of amoebic dysentery.   

 

 

Amoebae


Giardia 


Flagellates are protozoa which move using flagella.  This is a very diverse group which is considered by some scientists to include the euglenoid algae.  An example of a flagellate is Giardia which is found in many natural waters and causes giardiasis when ingested.  As you can see in the picture above, Giardia contains two nuclei, a trait shared by several other protozoa.  


Paramecium 


Ciliates are protozoa which use the motion of tiny hairs, called cilia, to propel them through the water.  Ciliates are usually found in large numbers in natural waters and in sewage where they act as predators and scavengers, ingesting food through "mouths."  A few species are parasitic, living inside hosts.  The image above is an example of a Paramecium, which is a typical ciliate protozoan.  Notice that the Paramecium has both a large and a small nucleus, a trait typical of ciliates.  


Sporozoan 


The final category of protozoans is the sporozoa which glide along surfaces by flexing their bodies.  The image above shows a typical sporozoan.  As you can see, the cell is very simple and lacks flagella, cilia, and pseudopodia.  All sporozoa are parasitic, and they generally produce spores during the infective stage.  Plasmodium, which causes malariais an example of a sporozoan.  

 

 

Animals

In addition to the microorganisms mentioned above, a few multicellular organisms are important in water and wastewater treatment.  In this section, we will consider two types of important multicellular organisms - rotifers and worms.  

 

 

Rotifers

Rotifers 


Rotifers are extremely simple multicellular animals like those shown above.  Although a few rotifers can be found in saltwater, most are found in fresh water.  Each rotifer is made up of about a thousand cells and is no larger than some unicellular organisms. 

Rotifers can be identified based on the wheel of cilia found at one end of their bodies.  These cilia move in a circular motion in order to draw food into the rotifer's mouth.  Some species live out their lives attached to a surface while others use the movement of their cilia to propel them through the water or use the their foot to creep along surfaces. 

Rotifers are quite common in aerobic, biological wastewater treatment processes.  They can be found either grazing on smaller microbes or attached to debris by their forked tail.  Since rotifers eat free-swimming bacteria and organic matter, they help clean water in activated sludge processes.  

 

 

Worms

Flat worm and nematode

 
Worm is a term used to refer to several unrelated organisms with a long, skinny body shape.  The two types of worms commonly found in water are nematodes and flatworms.

Nematodes can be distinguished from other aquatic worms by their cylindrical body and by the typical S-shaped, wriggling movement which they use to propel themselves through the water.  Most are microscopic, but a few can grow much larger, up to several feet in length.  Nematodes may live in water, in soil, or as parasites.  There are several species of parasitic nematodes which attack humans, but these species are believed to be associated with contaminated food rather than with contaminated water. 

The free-living aquatic nematodes eat bacteria, rotifers, and other worms and can be very important in wastewater treatment.  Nematodes are abundant in sludge and are especially common in percolating filters.  They help stabilize sludge as well as controlling film accumulation in percolating filters.  In general, nematodes are very good at dealing with moderate pollution. 

Flatworms, on the other hand, are worms with flattened bodies which glide along surfaces using tiny cilia.  The flatworm illustrated at the beginning of this section is a planaria, which is a common type of flatworm.  Notice the two eyespots found on the planaria - this is another feature which can be used to help identify planaria. 

Flatworms are usually found at the lower depths of ponds.  They range in size from a fraction of a millimeter to several centimeters in length.  Some flatworms live as parasites while other are free-living, feeding principally on algae. 

 

 


 

 

Review

A procaryotic organism, such as bacteria, is a cell that lacks a membrane-bound nucleus or membrane-bound organelles. The exterior of the cell usually has glycocalyx, flagellum, fimbriae, and pili. The procaryotic cell's cell wall is located outside the plasma membrane and gives the cell its shape and provides rigid structural support for the cell. The cell wall also protects the cell from its environment. The wall of a bacterium is classified in two ways, gram-positive or gram-negative. The procaryotic cell has a cell membrane called the cytoplasmic membrane that forms the outer structure of the cell and separates the cell's internal structure from the environment. This membrane provides a selective barrier, allowing certain substances and chemicals to move into and out of the cell. Two types of transport mechanisms are used to move substances through the cytoplasmic membrane, passive and active. The general shapes of bacteria are cocci, bacilli and spirilla. The Gram Stain Procedure is the most fundamental technique for identifying bacteria. There are three types of respiration that can occur: aerobic, anaerobic and facultative.

 

 

 

Assignment

Please answer the following questions and send via mail, fax or email (as an attachment) to your instructor.

  1. Why are bacteria important to wastewater operations?
  2. Describe the parts of the cell inside the cell membrane.
  3. Why are endospores able to survive in very harsh environments?
  4. List and explain the three morphological categories all bacteria fall into.
  5. List and explain the forms flagella can exist.
  6. List and explain the three types of passive transport.
  7. How do algae blooms influence the dissolved oxygen content of water?
  8. List and explain the three phyla of algae commonly found in fresh water.
  9. List and describe the four groups of Protozoa, based on mode of locomotion.
  10. Explain the difference between procaryotes and eucaryotes.

 

 

 

Quiz

Answer the questions in the Lesson 3 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.