Do microorganisms contain water?

Do microorganisms contain water?

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This may sound a bit strange question, but I am very new to biology. I would like to ask that do microorganisms like viruses, bacteria, amoebas, etc also contain water, as every living thing contains water?

The short answer, is yes, pretty much!

Do microorganisms contain water?*

Bacteria and eukaryotic microorganism

Bacteria and eukaryotic microorganisms (including amoebas) have a membrane that separates the interior from the exterior. And yes, they have water inside, in which all chemical reactions take place.


Viruses, on the other hand, do not really have a membrane that separates the interior from the exterior. They are really just a bunch of proteins stuck together. As such, it is hard to tell whether you would consider the water in which those proteins float part of the organism or not.

Note however, that some viruses have a viral envelope (that can be derived from a host cell membrane). In such viruses, there is more clearly an interior and an exterior, and yes, there is water in the interior too! However, there is (except very few exceptions) no metabolism inside this envelope. This, by the way, is part of the reason viruses are not considered alive.

Dehydrated living things

Note that some organisms can survive with very little water. Some seeds can survive extremely strong dehydration. For example, some tardigrades can survive with less than 1% water in their body (see this New York Times article).

Bacteria and viruses commonly found in drinking water

A breakdown of harmful bacteria and viruses and what techniques are used to treat them.

Both bacteria and viruses are microorganisms regulated by EPA’s Maximum Contaminant Levels (MCLs) criteria. Viruses are the smallest form of microorganisms capable of causing disease, particularly those of a fecal origin infectious to humans by waterborne transmission bacteria are typically single-celled microorganisms that can also cause health problems in humans, animals or plants, despite many form’s ability to aid in water pollution control.

Common waterborne bacteria and viruses and their health concerns

Various types of bacteria/viruses are categorized as pathogens, disease-causing organisms that can be found in pretreated and/or inadequately treated water. Here is a list of EPA regulated bacteria/viruses in drinking water, and their health risks:

  • Legionella, a bacteria found naturally in the environment — typically in water, thrives in warm waters this bacteria in water is a health risk if aerosolized (e.g., in a shower or air conditioning system) and inhaled, resulting in a type of pneumonia known as Legionnaires disease.
  • Enteroviruses are small viruses, such as polioviruses, echoviruses and coxsackieviruses, living in the intestines of infected humans or animals in addition to the three different polioviruses are 62-nonpolio enteroviruses that can cause disease in humans ranging from gastroenteritis to meningitis.

Bacteria and viruses can also be listed as "indicators," which at a level outside of identified limits, may reflect "a problem in the treatment process or in the integrity of distribution system," according to the EPA. Here is a list of EPA regulated viral/bacterial indicators and their potential problems:

  • Turbidity refers to the cloudiness of water and, although not a bacterium/virus, can hinder disinfection, providing an environment for microbial growth and can indicate the presence of bacteria/viruses as well as other disease-causing organisms that can produce symptoms such as nausea, diarrhea, cramps and headaches.
  • Coliforms are bacteria naturally present in the environment and used as indicators that other possibly harmful bacteria may be present (a warning sign is if coliforms are found in more samples than allowed).
  • Fecal indicators, Enterococci or coliphage, are microbes that can indicate human or animal wastes in water they can cause short-term health effects, including: Cramps, nausea, diarrhea, headaches and more, and may pose a greater risk for people with severely weak immune systems, elderly, young children and infants (Enterococci are bacterial indicators of fecal contamination and coliphage are viruses that infect E. coli).
  • E. coli and fecal coliform are bacteria whose presence can indicate water contaminated by human or animal wastes , causing short-term health effects, including: Cramps, nausea, diarrhea, headaches and more they may also pose a greater risk for people with severely weak immune systems, elderly, young children and infants.

Popular bacteria/virus treatment technology

The amount and type of water treatment can vary depending on the type of bacteria/viruses present. Some of the most commonly used forms of disinfection technologies include: UV technology, chlorine, chloramine and ozone. Many conventional water treatments, including filtration, sedimentation and coagulation can also effectively remove viruses. Disinfectant efficacies are measured by concentration (C) in mg/l, as well as time (T) in minutes (CT value, except for UV) necessary to attain the desired logs of disinfection under the temperature and pH conditions.

  • UV technology: Proved beneficial for many years, and is still continuously rising in popularity for water treatment. UV light’s produced when an electric arc is struck in mercury. However, according to Robert Dash of Viqua UV, "The future of UV lamp technology will move away from cylindrical mercury arc lamps, and into lamps that will not contain mercury."
  • Ozone: Is an effective water treatment commonly used to reduce color, taste and odor concerns. Ozone is also used in place of, or to reduce chlorine.
  • Chlorine: Is typically an effective treatment for bacteria/viruses, but not for protozoa, especially when applied to clarified low turbidity water.
  • Chloramine: Is a reaction product of chlorine and ammonia and is less potent than chlorine it’s known to successfully reduce Legionella counts.


There are many advantages and disadvantages of each water treatment technology available for bacteria/viruses and sometimes a combination may be needed for success. However, ensuring your drinking water is clear of any harmful bacteria/viruses is detrimental to avoid potentially critical health threats.

You can find more information on bacteria/viruses, additional contaminants and drinking water regulations here.

The Water Cycle

Water is essential for all living processes. The human body is more than one-half water and human cells are more than 70 percent water. Thus, most land animals need a supply of fresh water to survive. Of the stores of water on Earth, 97.5 percent is salt water ([Figure 1]). Of the remaining water, 99 percent is locked as underground water or ice. Thus, less than one percent of fresh water is present in lakes and rivers. Many living things are dependent on this small amount of surface fresh water supply, a lack of which can have important effects on ecosystem dynamics. Humans, of course, have developed technologies to increase water availability, such as digging wells to harvest groundwater, storing rainwater, and using desalination to obtain drinkable water from the ocean. Although this pursuit of drinkable water has been ongoing throughout human history, the supply of fresh water continues to be a major issue in modern times.

Figure 1: Only 2.5 percent of water on Earth is fresh water, and less than 1 percent of fresh water is easily accessible to living things.

The various processes that occur during the cycling of water are illustrated in [Figure 2]. The processes include the following:

  • evaporation and sublimation
  • condensation and precipitation
  • subsurface water flow
  • surface runoff and snowmelt
  • streamflow

The water cycle is driven by the Sun’s energy as it warms the oceans and other surface waters. This leads to evaporation (water to water vapor) of liquid surface water and sublimation (ice to water vapor) of frozen water, thus moving large amounts of water into the atmosphere as water vapor. Over time, this water vapor condenses into clouds as liquid or frozen droplets and eventually leads to precipitation (rain or snow), which returns water to Earth’s surface. Rain reaching Earth’s surface may evaporate again, flow over the surface, or percolate into the ground. Most easily observed is surface runoff: the flow of fresh water either from rain or melting ice. Runoff can make its way through streams and lakes to the oceans or flow directly to the oceans themselves.

In most natural terrestrial environments rain encounters vegetation before it reaches the soil surface. A significant percentage of water evaporates immediately from the surfaces of plants. What is left reaches the soil and begins to move down. Surface runoff will occur only if the soil becomes saturated with water in a heavy rainfall. Most water in the soil will be taken up by plant roots. The plant will use some of this water for its own metabolism, and some of that will find its way into animals that eat the plants, but much of it will be lost back to the atmosphere through a process known as evapotranspiration. Water enters the vascular system of the plant through the roots and evaporates, or transpires, through the stomata of the leaves. Water in the soil that is not taken up by a plant and that does not evaporate is able to percolate into the subsoil and bedrock. Here it forms groundwater.

Groundwater is a significant reservoir of fresh water. It exists in the pores between particles in sand and gravel, or in the fissures in rocks. Shallow groundwater flows slowly through these pores and fissures and eventually finds its way to a stream or lake where it becomes a part of the surface water again. Streams do not flow because they are replenished from rainwater directly they flow because there is a constant inflow from groundwater below. Some groundwater is found very deep in the bedrock and can persist there for millennia. Most groundwater reservoirs, or aquifers, are the source of drinking or irrigation water drawn up through wells. In many cases these aquifers are being depleted faster than they are being replenished by water percolating down from above.

Rain and surface runoff are major ways in which minerals, including carbon, nitrogen, phosphorus, and sulfur, are cycled from land to water. The environmental effects of runoff will be discussed later as these cycles are described.

Figure 2: Water from the land and oceans enters the atmosphere by evaporation or sublimation, where it condenses into clouds and falls as rain or snow. Precipitated water may enter freshwater bodies or infiltrate the soil. The cycle is complete when surface or groundwater reenters the ocean. (credit: modification of work by John M. Evans and Howard Perlman, USGS)

Biological Oxygen Demand (BOD) and Water

You don't often think that water bodies contain oxygen, but water does contain a small amount of dissolved oxygen. A small amount, but it is essential for life in the water. Biological oxygen demand (BOD) generally represents how much oxygen is needed to break down organic matter in water.

Biological Oxygen Demand (BOD) and Water

Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.

When you look at water in a lake the one thing you don't see is oxygen. In a way, we think that water is the opposite of air, but the common lake or stream does contain small amounts of oxygen, in the form of dissolved oxygen. Although the amount of dissolved oxygen is small, up to about ten molecules of oxygen per million of water, it is a crucial component of natural water bodies the presence of a sufficient concentration of dissolved oxygen is critical to maintaining the aquatic life and aesthetic quality of streams and lakes.

The presence of a sufficient concentration of dissolved oxygen is critical to maintaining the aquatic life and aesthetic quality of streams and lakes. Determining how organic matter affects the concentration of dissolved oxygen (DO) in a stream or lake is integral to water- quality management. The decay of organic matter in water is measured as biochemical or chemical oxygen demand. Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower DO concentrations.

Certain environmental stresses (hot summer temperatures) and other human-induced factors (introduction of excess fertilizers to a water body) can lessen the amount of dissolved oxygen in a water body, resulting in stresses on the local aquatic life. One water analysis that is utilized in order to better understand the effect of bacteria and other microorganisms on the amount of oxygen they consume as they decompose organic matter under aerobic (oxygen is present) is the measure of biochemical oxygen demand (BOD).

Determining how organic matter affects the concentration of dissolved oxygen in a stream or lake is integral to water-quality management. BOD is a measure of the amount of oxygen required to remove waste organic matter from water in the process of decomposition by aerobic bacteria (those bacteria that live only in an environment containing oxygen). The waste organic matter is stabilized or made unobjectionable through its decomposition by living bacterial organisms which need oxygen to do their work. BOD is used, often in wastewater-treatment plants, as an index of the degree of organic pollution in water.

Dissolved Oxygen and Water

Dissolved oxygen (DO) is a measure of how much oxygen is dissolved in the water - the amount of oxygen available to living aquatic organisms. The amount of dissolved oxygen in a stream or lake can tell us a lot about its water quality.

USGS scientist is measuring various water-quality conditions in Holes Creek at Huffman Park in Kettering, Ohio.

The USGS has been measuring water for decades. Some measurements, such as temperature, pH, and specific conductance are taken almost every time water is sampled and investigated, no matter where in the U.S. the water is being studied. Another common measurement often taken is dissolved oxygen (DO), which is a measure of how much oxygen is dissolved in the water - DO can tell us a lot about water quality.

Dissolved Oxygen and Water

Although water molecules contain an oxygen atom, this oxygen is not what is needed by aquatic organisms living in natural waters. A small amount of oxygen, up to about ten molecules of oxygen per million of water, is actually dissolved in water. Oxygen enters a stream mainly from the atmosphere and, in areas where groundwater discharge into streams is a large portion of streamflow, from groundwater discharge. This dissolved oxygen is breathed by fish and zooplankton and is needed by them to survive.

Dissolved oxygen and water quality

A eutrophic lake where dissolved-oxygen concentrations are low. Algal blooms can occur under such conditions.

Rapidly moving water, such as in a mountain stream or large river, tends to contain a lot of dissolved oxygen, whereas stagnant water contains less. Bacteria in water can consume oxygen as organic matter decays. Thus, excess organic material in lakes and rivers can cause eutrophic conditions, which is an oxygen-deficient situation that can cause a water body to "die." Aquatic life can have a hard time in stagnant water that has a lot of rotting, organic material in it, especially in summer (the concentration of dissolved oxygen is inversely related to water temperature), when dissolved-oxygen levels are at a seasonal low. Water near the surface of the lake– the epilimnion– is too warm for them, while water near the bottom–the hypolimnion– has too little oxygen. Conditions may become especially serious during a period of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely result from this problem.

Dissolved oxygen, temperature, and aquatic life

Water temperture affects dissolved-oxygen concentrations in a river or water body.

As the chart shows, the concentration of dissolved oxygen in surface water is affected by temperature and has both a seasonal and a daily cycle. Cold water can hold more dissolved oxygen than warm water. In winter and early spring, when the water temperature is low, the dissolved oxygen concentration is high. In summer and fall, when the water temperature is high, the dissolved-oxygen concentration is often lower.

Dissolved oxygen in surface water is used by all forms of aquatic life therefore, this constituent typically is measured to assess the "health" of lakes and streams. Oxygen enters a stream from the atmosphere and from groundwater discharge. The contribution of oxygen from groundwater discharge is significant, however, only in areas where groundwater is a large component of streamflow, such as in areas of glacial deposits. Photosynthesis is the primary process affecting the dissolved-oxygen/temperature relation water clarity and strength and duration of sunlight, in turn, affect the rate of photosynthesis.

Hypoxia and "Dead zones"

You may have heard about a Gulf of Mexico "dead zone" in areas of the Gulf south of Louisiana, where the Mississippi and Atchafalaya Rivers discharge. A dead zone forms seasonally in the northern Gulf of Mexico when subsurface waters become depleted in dissolved oxygen and cannot support most life. The zone forms west of the Mississippi Delta over the continental shelf off Louisiana and sometimes extends off Texas. The oxygen depletion begins in late spring, increases in summer, and ends in the fall.

Dissolved oxygen in bottom waters, measured from June 8 through July 17, 2009, during the annual summer Gulf of Mexico Southeast Area Monitoring and Assessment Program ( SEAMAP ) cruise in the northern Gulf of Mexico. Orange and red colors indicate lower dissolved oxygen concentrations.

The formation of oxygen-depleted subsurface waters has been associated with nutrient-rich (nitrogen and phosphorus) discharge from the Mississippi and Atchafalaya Rivers. Bio-available nutrients in the discharge can stimulate algal blooms, which die and are eaten by bacteria, depleting the oxygen in the subsurface water. The oxygen content of surface waters of normal salinity in the summer is typically more than 8 milligrams per liter (8 mg/L) when oxygen concentrations are less than 2 mg/L, the water is defined as hypoxic (CENR, 2000). The hypoxia kills many organisms that cannot escape, and thus the hypoxic zone is informally known as the “dead zone.”

The hypoxic zone in the northern Gulf of Mexico is in the center of a productive and valuable fishery. The increased frequency and expansion of hypoxic zones have become an important economic and environmental issue to commercial and recreational users of the fishery.

Measuring dissolved oxygen

Multi-parameter monitor used to record water-quality measurements.

Field and lab meters to measure dissolved oxygen have been around for a long time. As this picture shows, modern meters are small and highly electronic. They still use a probe, which is located at the end of the cable. Dissolved oxygen is dependent on temperature (an inverse relation), so the meter must be calibrated properly before each use.

Do you want to test your local water quality?

Water test kits are available from World Water Monitoring Challenge (WWMC), an international education and outreach program that builds public awareness and involvement in protecting water resources around the world. Teachers and water-science enthusiasts: Do you want to be able to perform basic water-quality tests on local waters? WWMC offers inexpensive test kits so you can perform your own tests for temperature, pH, turbidity, and dissolved oxygen.

Do you think you know a lot about water properties?
Take our interactive water-properties true/false quiz and test your water knowledge.


The mitochondria produce most of the energy needed by a eukaryotic cell. A cell may contain hundreds or even thousands of these organelles. Each mitochondrion contains a double membrane. The inner one forms folds called cristae. The organelle contains enzymes that break down complex molecules and release energy. The ultimate source of the energy is glucose molecules.

Energy released by mitochondrial reactions is stored in chemical bonds in ATP (adenosine triphosphate) molecules. These molecules can be quickly broken down to release energy when the cell needs it.

Anammoxosomes have been found in some bacteria. They have a different structure from mitochondria and perform different chemical reactions, but as in mitochondria, energy is released from complex molecules inside them and stored in ATP.

Structure of a chloroplast

Do microorganisms contain water? - Biology

The Exploratorium is more than a museum. Explore our online resources for learning at home.

All foods are continually assaulted by many kinds of microorganisms, racing to eat as much as possible. When you pickle vegetables by fermentation, you help one type of microbe win this "race."

More specifically, you create special conditions in your pickle crock that keep away "bad" spoilage-causing microorganisms, and that allow a unique class of "good" bacteria, called lactic acid bacteria, to colonize your cucumbers.

Why are lactic acid bacteria good?

As lactic acid bacteria grow in your pickle crock, they digest sugars in the cucumbers and produce lactic acid. Not only does this acid give the pickles their characteristic sour tang, it controls the spread of spoilage microbes. Also, by gobbling up the sugars, lactic acid bacteria remove a potential food source for bad bacteria.

Salt gives the good guys an edge.

Adding salt to your pickling brine is one important way to help lactic acid bacteria win the microbial race. At a certain salt concentration, lactic acid bacteria grow more quickly than other microbes, and have a competitive advantage. Below this "right" concentration, bad bacteria may survive and spread more easily, possibly out-competing lactic acid bacteria and spoiling your pickles.

Too much salt is also a problem: Lactic acid bacteria cannot thrive, leaving your vegetables unpickled. What’s more, salt-tolerant yeasts can spread more quickly. By consuming lactic acid, yeasts make the pickles less acidic—and more hospitable to spoilage microbes.

Oxygen gives the bad guys one leg up.

During fermentation, it’s important to keep your crock covered to seal out the air. That’s because oxygen encourages the spread of spoilage microbes. Any exposed pickle or brine becomes a breeding ground for the bad microbes, which can spread to spoil the entire batch.

Too hot . . . too cold . . . just right.

A pickle-maker can also control the microbial garden in a pickle crock by adjusting the temperature. The ideal temperature range for lactic acid bacteria—and successful fermentation—is 70° F㫣° F. If it’s too chilly or too toasty in the room, other microbes may gain a competitive advantage over lactic acid bacteria.

Examples of Extreme Communities

Deep Sea. The deep sea environment has high pressure and cold temperatures (1 to 2 degrees Celsius [33.8 to 35.6 degrees Fahrenheit]), except in the vicinity of hydrothermal vents, which are a part of the sea floor that is spreading, creating cracks in the earth's crust that release heat and chemicals into the deep sea environment and create underwater geysers. In these vents, the temperature may be as high as 400 degrees Celsius (752 degrees Fahrenheit), but water remains liquid owing to the high pressure. Hydrothermal vents have a pH range from about 3 to 8 and unusual chemistry. In 1977, the submarine Alvin found life 2.6 kilometers (1.6 miles) deep near vents along the East Pacific Rise. Life forms ranged from microbes to invertebrates that were adapted to these extreme conditions. Deep sea environments are home to psychrophiles (organisms that like cold temperatures), hyperthermophiles (organisms that like very high temperatures), and piezophiles (organisms adapted to high pressures).

Hypersaline Environments. Hypersaline environments are high in salt concentration and include salt flats, evaporation ponds, natural lakes (for example, Great Salt Lake), and deep sea hypersaline basins. Communities living in these environments are often dominated by halophilic (salt-loving) organisms, including bacteria, algae, diatoms, and protozoa. There are also halophilic yeasts and other fungi, but these normally cannot tolerate environments as saline as other taxa.

Deserts. Deserts can be hot or cold, but they are always dry. The Atacoma desert in Chile is one of the oldest, driest hot deserts, sometimes existing for decades without any precipitation at all. The coldest, driest places are the Antarctic Dry Valleys, where primary inhabitants are cyanobacteria, algae, and fungi that live a few millimeters beneath the sandstone rock surface. Although these endolithic (living in rocks) communities are based on photosynthesis, the organisms have had to adapt to long periods of darkness and extremely dry conditions. Light dustings of snow that may melt in the Antarctic summer are often the only sources of water for these organisms.

Ice, Permafrost, and Snow. From high-altitude glaciers, often colored pink from red-colored algae, to the polar permafrost, life has evolved to use frozen water as a habitat. In some instances, the organisms, such as bacteria, protozoa, and algae, are actually living in liquid brine (very salty water) that is contained in pockets of the ice. In other cases, microorganisms found living on or in ice are not so much ice lovers as much as ice survivors. These organisms may have been trapped in the ice and simply possessed sufficient adaptations to enable them to persist.

Atmosphere. The ability for an organism to survive in the atmosphere depends greatly on its ability to withstand desiccation and exposure to ultraviolet radiation. Although microorganisms can be found in the upper layers of the atmosphere, it is unclear whether these constitute a functional ecosystem or simply an aerial suspension of live but largely inactive organisms and their spores.

Outer Space. The study of extremeophiles and the ability of some to survive exposure to the conditions of outer space has raised the possibility that life might be found elsewhere in the universe and the possibility that simple life forms may be capable of traveling through space, for example from one planet to another.

Rocco L. Mancinelli and Lynn J. Rothchild

Investigation: What Organisms Are Found in Ponds?

Does your community have ponds, streams, or lakes? Students enjoy working with real biology, and though it may not be possible to take students to a lake, you can bring the lake to the student. This open-ended activity gives students the opportunity to explore pond water and compare the types of species found in two separate samples. They can propose reasons why one sample of water might contain different species and differing levels of diversity, such as location, temperature, or human impacts. Each pond represents an ecosystem, so this investigation is a good beginning or end to an ecology unit.

A pond identification guide can be printed, or you can provide field guides to help students identify organisms. This macroinvertebrate field guide can be printed and laminated for multiple uses.

Students do not need to correctly identify each organism they see, and in many cases, unless you are an expert in limnology, you won’t be able to determine every creature that might be swimming in the sample. Most ponds will contain macroinvertebrates, like beetles and nymphs, as well as microinvertebrates and protozoa.

Microscopes and stereoscopes can be used to looking at microbes that are not visible with the unaided eye. Depending on where you live, you might find amoeba, paramecium, daphnia, tardigrades and even flatworms.

The activity requires students to create a table to share data and sketches and to present their findings as a lab report or infographic. Rubric for grading is included.

Grade Level: 9-12 (could be modified for younger students)
Time Required: 40-55 minutes for gathering data 30-60 minutes to complete report

HS-LS2-6 Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem

HS-LS2-7 Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity.*


Laboratory Manual Biology for class XII - Published by NCERT.


Significance & Overview Of Biology Class XII Practicals

There are altogether twenty-five exercises in the present manual which are based on Biology curriculum for Class XII.

For each practical work, principle, requirements, procedure, precautions, observations, discussion and the questions are given in the book. The methodology of preparation of any reagent, if required, has been given along with the requirements, for the convenience of students and teachers. The questions are aimed to develop learner’s understanding of the related problems. Precautions must be well understood by the learners before proceeding with the experiments and projects. In addition to the core experiments enlisted in the syllabus for Class XII emphasis has also been given for pursuing Investigation Project Work. Appropriate appendices related to the observation and study of organisms are given along with the experiment. International symbols for units, hazards and hazard warnings are given at appropriate places in the book.