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1.4.9.17: Decomposers and Recyclers - Biology

1.4.9.17: Decomposers and Recyclers - Biology


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Learning Objectives

  • Describe the importance of fungi to the balance of the environment

The food web would be incomplete without organisms that decompose organic matter (Figure 1). Some elements—such as nitrogen and phosphorus—are required in large quantities by biological systems, and yet are not abundant in the environment. The action of fungi releases these elements from decaying matter, making them available to other living organisms. Trace elements present in low amounts in many habitats are essential for growth, and would remain tied up in rotting organic matter if fungi and bacteria did not return them to the environment via their metabolic activity.

The ability of fungi to degrade many large and insoluble molecules is due to their mode of nutrition. As seen earlier, digestion precedes ingestion. Fungi produce a variety of exoenzymes to digest nutrients. The enzymes are either released into the substrate or remain bound to the outside of the fungal cell wall. Large molecules are broken down into small molecules, which are transported into the cell by a system of protein carriers embedded in the cell membrane. Because the movement of small molecules and enzymes is dependent on the presence of water, active growth depends on a relatively high percentage of moisture in the environment.

As saprobes, fungi help maintain a sustainable ecosystem for the animals and plants that share the same habitat. In addition to replenishing the environment with nutrients, fungi interact directly with other organisms in beneficial, and sometimes damaging, ways (Figure 2).

Importance of Fungi in Human Life

Although we often think of fungi as organisms that cause disease and rot food, fungi are important to human life on many levels. As we have seen, they influence the well-being of human populations on a large scale because they are part of the nutrient cycle in ecosystems. They have other ecosystem roles as well. As animal pathogens, fungi help to control the population of damaging pests. These fungi are very specific to the insects they attack, and do not infect animals or plants. Fungi are currently under investigation as potential microbial insecticides, with several already on the market. For example, the fungus Beauveria bassiana is a pesticide being tested as a possible biological control agent for the recent spread of emerald ash borer. It has been released in Michigan, Illinois, Indiana, Ohio, West Virginia and Maryland (Figure 3).

The mycorrhizal relationship between fungi and plant roots is essential for the productivity of farm land. Without the fungal partner in root systems, 80–90 percent of trees and grasses would not survive. Mycorrhizal fungal inoculants are available as soil amendments from gardening supply stores and are promoted by supporters of organic agriculture.

We also eat some types of fungi. Mushrooms figure prominently in the human diet. Morels, shiitake mushrooms, chanterelles, and truffles are considered delicacies (Figure 4). The humble meadow mushroom, Agaricus campestris, appears in many dishes. Molds of the genus Penicillium ripen many cheeses. They originate in the natural environment such as the caves of Roquefort, France, where wheels of sheep milk cheese are stacked in order to capture the molds responsible for the blue veins and pungent taste of the cheese.

Fermentation—of grains to produce beer, and of fruits to produce wine—is an ancient art that humans in most cultures have practiced for millennia. Wild yeasts are acquired from the environment and used to ferment sugars into CO2 and ethyl alcohol under anaerobic conditions. It is now possible to purchase isolated strains of wild yeasts from different wine-making regions. Louis Pasteur was instrumental in developing a reliable strain of brewer’s yeast, Saccharomyces cerevisiae, for the French brewing industry in the late 1850s. This was one of the first examples of biotechnology patenting.

Many secondary metabolites of fungi are of great commercial importance. Antibiotics are naturally produced by fungi to kill or inhibit the growth of bacteria, limiting their competition in the natural environment. Important antibiotics, such as penicillin and the cephalosporins, are isolated from fungi. Valuable drugs isolated from fungi include the immunosuppressant drug cyclosporine (which reduces the risk of rejection after organ transplant), the precursors of steroid hormones, and ergot alkaloids used to stop bleeding. Psilocybin is a compound found in fungi such as Psilocybe semilanceata and Gymnopilus junonius, which have been used for their hallucinogenic properties by various cultures for thousands of years.

As simple eukaryotic organisms, fungi are important model research organisms. Many advances in modern genetics were achieved by the use of the red bread mold Neurospora crassa. Additionally, many important genes originally discovered in S. cerevisiae served as a starting point in discovering analogous human genes. As a eukaryotic organism, the yeast cell produces and modifies proteins in a manner similar to human cells, as opposed to the bacterium Escherichia coli, which lacks the internal membrane structures and enzymes to tag proteins for export. This makes yeast a much better organism for use in recombinant DNA technology experiments. Like bacteria, yeasts grow easily in culture, have a short generation time, and are amenable to genetic modification.


Also known as saprotrophs, saprobionts are microbes which habitat detritus. They use extracellular digestion, known as saprobiotic nutrition, to digest their food. Digestive enzymes break down the detritus into soluble substances. These are then broken down further into water, carbon dioxide and mineral ions.

Detritivores are little invertebrates, like woodlice or earthworms. They ingest the detritus (holozoic nutrition). Their bodies absorb the soluble products and the insoluble waste is egested. Detritivores assist saprobionts by:

  • egesting faeces which is more accessible to saprobionts than large pieces of plant tissue
  • their faeces also contains beneficial minerals, like urea, which can be metabolised by saprobionts
  • they aerate the soil which assists saprobionts to respire aerobically

Function of Decomposers

Decomposers play an important role in every ecosystem. Without decomposers, dead organisms would not be broken down and recycled into other living matter. The reason decomposers decompose, however, is simply because they need to survive. Decomposers are heterotrophic, which means they get their energy from ingesting organic material. A dead organism provides nutrients for decomposers like bacteria and fungi to use in order to grow and reproduce, propagating their own species. The side effect of this basic need to survive is that organic material and nutrients are cycled throughout the ecosystem as other organisms consume the bacteria and fungi.


Roles of Decomposers and Detritivores

Food Chain

Organisms in this level of the food chain provide nutrients for the producers (plants) who in turn are eaten by the consumers in the next level who are then eaten by tertiary consumers. Fungi release enzymes that break down dead organic matter and release it into the soil while earthworms excrete nutrient-rich waste that adds more vitality to the soil. The tunneling action of earthworms also helps to break up and aerate the soil.

Soil bacteria such as Bacillus subtilis and Pseudomonas fluorescens are extensively involved at the decomposer level as well. They are critical for the early stages of decomposition before fungi and earthworms take over. Bacteria not only feed on dead leaves and weeds but they also fix nitrogen in the soil so it is not lost to the air or water (see below).

Nutrient Cycling

Nitrogen Fixation

Decomposer bacteria are responsible for fixing nitrogen in the soil, meaning they transform nitrogen into a form that can be used by other organisms in the food chain. Specifically, the bacteria take atmospheric nitrogen and turn it into molecules such as ammonia, nitrate and nitrite which can be used by plants. In some plants like legumes, the bacterium Rizobium lives in nodules on the roots of the plants in a symbiotic relationship. In turn for giving them a place to live, the bacteria return the favor by fixing nitrogen for the plants to use.


The image above shows nitrogen-fixing nodules on the roots of a legume plant.

Ecosystem Maintenance

Decomposers are like the housekeepers of an ecosystem. Without them, dead plants and animals would keep piling up with the nutrients the soil needs trapped inside. Decomposers clean up the dead material by processing it and returning the nutrients to the soil for the producers. If the decomposer community is damaged or dies, the whole biogeochemical cycle of an ecosystem is affected. Should this happen on a larger scale, the entire planet would be in peril.


What Is the Role of Decomposers in the Carbon Cycle?

Decomposers help reclaim carbon from dead organisms and put it back into the carbon cycle so living organisms can use it. Decomposers break down dead plants, animals and waste products. This process releases carbon dioxide through cellular respiration.

Living things on Earth are carbon-based life forms. These living things need carbon to grow and reproduce. The amount of carbon on Earth is not infinite, but it is abundant and takes many forms. Decomposers use the carbon dioxide in the bodies of dead organisms for food or fuel. This feeding process releases carbon dioxide into the atmosphere through cellular respiration. Carbon dioxide can also be released into the atmosphere when dead organisms are burned.

Decomposers are bacteria, fungi and worms. Bacteria can break down most types of organic matter and is a significant decomposer. Fungi are primary decomposers in forests where they break down fallen trees and other woody organisms. Worms are scavengers that hasten bacterial decay by breaking an organism down so the nutrients are more available to bacteria.

The carbon cycle explains how carbon is made available to life forms. The main processes of the carbon cycle are photosynthesis, respiration, decomposition, natural weathering of rocks and burning fossil fuels. Primary producers use photosynthesis to take in carbon. Plants absorb it from the atmosphere in the form of carbon dioxide. Carbon moves up the food chain when animals feed on plants and the carbon is transferred. While alive, animals release carbon dioxide back into the atmosphere through respiration. After an organism has died, the carbon is recycled by decomposers.


Orion-designsource

Decomposer Definition Biology. Decomposers include bacteria and fungi. Other articles where decomposer is discussed:

Decomposers play a critical role in the environment. In these environments, fungi play a major role as decomposers and recyclers. As decomposers, pathogens, and mutualistic symbionts with plants and animals, fungi play a major role in ecosystem processes including nutrient cycling, bioconversions, and energy flows. They are a vital part of the food chain because they return nutrients into the soil for other organisms to use. Their role is ecologically essential as they recycle the nutrients through a natural biological process.

Which is an example of a decomposer from trusttheengineer.com Decomposers feed on dead matter. A worm is eating a dead plant. An organism, often a bacterium or fungus, that feeds. As decomposers, pathogens, and mutualistic symbionts with plants and animals, fungi play a major role in ecosystem processes including nutrient cycling, bioconversions, and energy flows. These organisms carry out the process.

Decomposers play a critical role in the environment.

Definition of decomposer in the definitions.net dictionary. An organism such as a bacterium or fungus that makes dead plant and this is a potential indication of a decomposer's adaptation to specific substrates in a tropical forest. An organism that feeds on and breaks down a dead animal or plant tissue example: Dr.samanthi udayangani holds a b.sc. The organisms that decompose or break down dead organisms and return the nutrients to the soil are called as decomposers. Study decomposers explanation with biology terms to review biology course for online degree. Covers characteristics and classifications of consumers and decomposers. Like herbivores and predators, decomposers are heterotrophic. These organisms carry out the process. According to schaum's outline of biology, the definition of decomposers(p.352) says bacteria, fungi, plants, or animals that feed on dead organisms and release the bound organic material of the. Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. Other articles where decomposer is discussed: In these environments, fungi play a major role as decomposers and recyclers.

These organisms carry out the process. Learn decomposers definition in biology with explanation to study what are decomposers. An organism such as a bacterium or fungus that makes dead plant and this is a potential indication of a decomposer's adaptation to specific substrates in a tropical forest. Covers characteristics and classifications of consumers and decomposers. In essence, all living things, including humans.

Review Games for Producers, Consumers, Decomposers and . from 1.bp.blogspot.com Fungi are the major decomposers of nature Covers characteristics and classifications of consumers and decomposers. …as co2 by decay, or decomposer, organisms (chiefly bacteria and fungi) in a series of microbial transformations. Home » science » biology » taxonomy » difference between scavenger and decomposer. Decomposers feed on dead matter.

Decomposers are organisms that break down dead or decaying organisms and wastes.

Decomposers include bacteria and fungi. Fungi are the major decomposers of nature Other articles where decomposer is discussed: Nature has its own recycling system: The function of decomposers a decomposer is defined as an organism that decomposes or breaks down the organic material including the remains of dead organisms. Covers characteristics and classifications of consumers and decomposers. Decomposers get the nutrients they need by eating dead and decaying materials. Definition of decomposer in the definitions.net dictionary. An organism whose ecological function involves the recycling of nutrients by performing the natural process of decomposition as it feeds on decaying organisms. As decomposers, pathogens, and mutualistic symbionts with plants and animals, fungi play a major role in ecosystem processes including nutrient cycling, bioconversions, and energy flows. All types of decomposers are fungi, worms, bacteria, snails and slugs. Home » science » biology » taxonomy » difference between scavenger and decomposer. Learn decomposers definition in biology with explanation to study what are decomposers.

A worm is eating a dead plant. Home » science » biology » taxonomy » difference between scavenger and decomposer. Decomposers include bacteria and fungi. They must break down deceased living matter and allow nutrients to reenter the soil and be cycled through an ecosystem. The function of decomposers a decomposer is defined as an organism that decomposes or breaks down the organic material including the remains of dead organisms.

Decomposers and Detrivores - YouTube from i.ytimg.com Study decomposers explanation with biology terms to review biology course for online degree. Like herbivores and predators, decomposers are heterotrophic. An organism such as a bacterium or fungus that makes dead plant and this is a potential indication of a decomposer's adaptation to specific substrates in a tropical forest. In essence, all living things, including humans. Information and translations of decomposer in the most comprehensive dictionary definitions resource on the web.

Dr.samanthi udayangani holds a b.sc.

Decomposers are organisms that break down dead or decaying organisms In these environments, fungi play a major role as decomposers and recyclers. An organism, often a bacterium or fungus, that feeds. Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. Decomposers play a critical role in the environment. Learn decomposers definition in biology with explanation to study what are decomposers. Consumers are organisms that obtain food by eating other organisms. Decomposer synonyms, decomposer pronunciation, decomposer translation, english dictionary definition of decomposer. According to schaum's outline of biology, the definition of decomposers(p.352) says bacteria, fungi, plants, or animals that feed on dead organisms and release the bound organic material of the. An organism such as a bacterium or fungus that makes dead plant and this is a potential indication of a decomposer's adaptation to specific substrates in a tropical forest. In essence, all living things, including humans. An organism whose ecological function involves the recycling of nutrients by performing the natural process of decomposition as it feeds on decaying organisms. The fungi on this tree are decomposers decomposers (or saprotrophs) are organisms that break english dictionary.

Decomposers are the organisms that eat, digest and break down once living things which have died. A decomposer is an organism that decomposes, or breaks down, organic material such as the remains of dead organisms. In these environments, fungi play a major role as decomposers and recyclers. Their role is ecologically essential as they recycle the nutrients through a natural biological process. An organism that feeds on and breaks down a dead animal or plant tissue example:

Source: biologydictionary.net

Other articles where decomposer is discussed: Nature has its own recycling system: Like herbivores and predators, decomposers are heterotrophic. …as co2 by decay, or decomposer, organisms (chiefly bacteria and fungi) in a series of microbial transformations. An organism whose ecological function involves the recycling of nutrients by performing the natural process of decomposition as it feeds on decaying organisms.

Learn decomposers definition in biology with explanation to study what are decomposers. They are absolutely essential in the nutrient cycles. Nature has its own recycling system: They carry out decomposition, a process possible by only certain kingdoms, such as fungi. Decomposers include bacteria and fungi.

Source: d20khd7ddkh5ls.cloudfront.net

In these environments, fungi play a major role as decomposers and recyclers. Learn decomposers definition in biology with explanation to study what are decomposers. Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. A worm is eating a dead plant. Nature has its own recycling system:

…as co2 by decay, or decomposer, organisms (chiefly bacteria and fungi) in a series of microbial transformations. Covers characteristics and classifications of consumers and decomposers. When you have an empty bottle, do you recycle it so the plastic or glass can be used again? Decomposers are the organisms that eat, digest and break down once living things which have died. Decomposer — an organism that breaks down complex materials into simpler.

Source: photos.demandstudios.com

They break down organic matter which would otherwise not be recycled.

They carry out decomposition, a process possible by only certain kingdoms, such as fungi.

As decomposers, pathogens, and mutualistic symbionts with plants and animals, fungi play a major role in ecosystem processes including nutrient cycling, bioconversions, and energy flows.

Source: upload.wikimedia.org

Dr.samanthi udayangani holds a b.sc.

Other articles where decomposer is discussed: SPECIAL EVENT!: Evolution of the Genus Iris</p> <p>According to schaum's outline of biology, the definition of decomposers(p.352) says bacteria, fungi, plants, or animals that feed on dead organisms and release the bound organic material of the.</p>

FIGURE 15.9. The Carbon Cycle

Carbon atoms are cycled through ecosystems. Carbon dioxide (green arrows) produced by respiration is the source of the carbon that plants incorporate into organic molecules when they carry on photosynthesis. These carbon-containing organic molecules—carbohydrates, fats, and proteins—(black arrows) are passed to animals when they eat plants and other animals. Organic molecules in waste products or dead organisms are consumed by decomposers. In the process, decomposers break down organic molecules into inorganic molecules. All organisms (plants, animals, and decomposers) return carbon atoms to the atmosphere as carbon dioxide when they carry on cellular respiration. Oxygen (blue arrows) is being cycled at the same time that carbon is. The oxygen is released during photosynthesis and taken up during cellular respiration.

The same carbon atoms are used over and over again. In fact, you are not exactly the same person today that you were yesterday. Some of your carbon atoms are different. Furthermore, those carbon atoms have been involved in many other kinds of living things over the past several billion years. Some of them were temporary residents in dinosaurs, extinct trees, or insects, but at this instant, they are part of you. Other organic molecules have become part of fossil fuels.

Carbon and oxygen combine to form the molecule carbon dioxide (CO2), which is present in small quantities as a gas in the atmosphere and dissolved in water. During photosynthesis, carbon dioxide from the atmosphere is taken into the leaves of plants where it is combined with hydrogen from water molecules (H2O), which are absorbed from the soil by the roots and transported to the leaves. Many kinds of aquatic organisms such as algae and some bacteria also perform photosynthesis but absorb carbon dioxide and water molecules from the water in which they live. (Actually about 50% of photosynthetic activity on Earth takes place in the oceans due to the activity of algae and photosynthetic bacteria.)

The energy needed to perform photosynthesis is provided by sunlight. As a result of photosynthesis, complex organic molecules such as carbohydrates (sugars) are formed. Producer organisms use these sugars to provide themselves with energy and to make other kinds of organic molecules needed for growth and reproduction. At the same time that carbon is being incorporated into organic molecules, oxygen molecules (O2) are released into the atmosphere or water—because during the process of photosynthesis, water molecules are split to provide hydrogen atoms necessary to manufacture carbohydrate molecules.

Herbivores can use the complex organic molecules of producers as food. When an herbivore eats plants or algae, the complex organic molecules in their food are broken down into simpler organic molecular building blocks, such as simple sugars, amino acids, glycerol, and fatty acids, which then can be reassembled into the specific organic molecules that are part of the herbivore’s chemical structure. Thus, the atoms in the herbivore’s body can be traced back to the plants it ate. Nearly all organisms also carry on the process of respiration, in which oxygen from the atmosphere is used to break down organic molecules into carbon dioxide and water. Much of the chemical-bond energy released by respiration is lost as heat, but the remainder is used by the herbivore for movement, growth, and other activities.

In similar fashion, when an herbivore is eaten by a carnivore, some of the carbon-containing molecules of the herbivore become incorporated into the body of the carnivore. The remaining organic molecules are broken down in the process of respiration to obtain energy, and carbon dioxide and water are released.

3. The Role of Decomposers

The organic molecules contained in animal waste products and dead organisms are acted upon by decomposers that use these organic materials as a source of food. The decay process of decomposers involves respiration and releases carbon dioxide and water so that organic molecules are typically recycled. (Many human-made organic compounds—plastics, industrial chemicals, and pesticides—are not readily broken down by decomposers.) How Science Works 15.1 describes how human alteration of the carbon cycle has affected climate.

Water molecules are the most common molecules in living things. Because all the metabolic reactions that occur in organisms take place in a watery environment, within cells or body parts, water is essential to life. During photosynthesis, the hydrogen atoms (H) from water molecules (H2O) are added to carbon atoms to make carbohydrates and other organic molecules. At the same time, the oxygen atoms in water molecules are released as oxygen molecules (O2). The movement of water molecules can be traced as a hydrologic cycle (figure 15.10).

FIGURE 15.10. The Hydrologic Cycle

The cycling of water through the environment follows a simple pattern. Moisture in the atmosphere condenses into droplets, which fall to the Earth as rain or snow. Organisms use some of the water and some of it evaporates from soil and organisms, but much of it flows over the Earth as surface water or through the soil as groundwater. It eventually returns to the oceans, where it evaporates back into the atmosphere to begin the cycle again.

Most of the forces that cause water to be cycled do not involve organisms but, rather, are the result of normal physical and geologic processes. Because of the kinetic energy possessed by water molecules, at normal Earth temperatures liquid water evaporates into the atmosphere as water vapor. This can occur wherever water is present it evaporates from lakes, rivers, soil, and the surfaces of organisms. Because the oceans contain most of the world’s water, an extremely large amount of water enters the atmosphere from the oceans.

Water molecules also enter the atmosphere as a result of transpiration by plants. Transpiration is a process whereby water is lost from leaves through small openings called stomates. The water that is lost is absorbed from the soil into roots and transported from the roots to leaves, where it is used in photosynthesis or evaporates. This movement of water carries nutrients to the leaves, and the evaporation of the water from the leaves assists in the movement of water upward in the stem. Thus, transpired water can be moved from deep layers of the soil to the atmosphere.

Once the water molecules are in the atmosphere, they are moved along with other atmospheric gases by prevailing wind patterns. If warm, moist air encounters cooler temperatures, which often happens over landmasses, the water vapor condenses into droplets and falls as rain or snow. When the precipitation falls on land, some of it runs off the surface, some of it evaporates, and some penetrates into the soil. The water that runs off the surface makes its way through streams and rivers to the ocean. The water in the soil may be taken up by plants and transpired into the atmosphere, or it may become groundwater. Much of the groundwater eventually makes its way into lakes and streams and ultimately arrives at the ocean, from which it originated.

The nitrogen cycle involves the cycling of nitrogen atoms between the abiotic and biotic components and among the organisms in an ecosystem. Nitrogen is essential in the formation of amino acids, which are needed to form proteins, and in the formation of nitrogenous bases, which are a part of ATP and the nucleic acids, DNA and RNA. Nitrogen is found as molecules of nitrogen gas (N2) in the atmosphere. Although nitrogen gas (N2) makes up approximately 80% of the earth’s atmosphere, it is not readily available to most organisms because the two nitrogen atoms are bound very tightly to each other and very few organisms are able to use nitrogen in this form. Since plants and other producers are at the base of nearly all food chains, they must make new nitrogen-containing molecules, such as proteins and DNA. Plants and other producers are unable to use the nitrogen in the atmosphere and must get it in the form of nitrate (—NO3) or ammonia (NH3).

1. The Role of Nitrogen-Fixing Bacteria

Because atmospheric nitrogen is not usable by plants, nitrogen-containing compounds are often in short supply, and the availability of nitrogen is often a factor that limits the growth of plants. (Most aquatic ecosystems are limited by the amount of phosphorus rather than the amount of nitrogen.) Certain kinds of soil bacteria are the primary source of the nitrogen-containing molecules plants need to make proteins and DNA.

Some bacteria, called nitrogen-fixing bacteria, are able to convert the nitrogen gas (N2) that enters the soil into ammonia (NH3) that plants can use. Certain kinds of these bacteria live freely in the soil and are called free-living nitrogen-fixing bacteria. Others, known as symbiotic nitrogen-fixing bacteria, have a cooperative relationship with certain plants and live in nodules in the roots of plants such as legumes (peas, beans, and clover) and certain trees such as alders. Some grasses and evergreen trees appear to have a similar relationship with certain root fungi that seem to improve the nitrogen-fixing capacity of the plant.

2. The Role of Producers and Consumers

Once plants and other producers have nitrogen available in a form they can use, they can construct proteins, DNA, and other important nitrogen-containing organic molecules. When herbivores eat plants, the plant protein molecules are broken down to smaller building blocks called amino acids. These amino acids are then reassembled to form proteins typical for the herbivore. Nucleic acids and other nitrogen-containing molecules are handled similarly. During the animal’s manipulation and transformation of amino acids, and some other molecules, some nitrogen is lost in the organism’s waste products as ammonia, urea, or uric acid. These same processes occur when carnivores eat herbivores.

3. The Role of Decomposers and Other Soil Bacteria Bacteria and other types of decay organisms are involved in the nitrogen cycle also. Dead organisms and their waste products contain molecules, such as proteins, urea, and uric acid, that contain nitrogen. Decomposers break down these nitrogen-containing organic molecules, releasing ammonia (NH3), which can be used directly by many kinds of plants. Still other kinds of soil bacteria, called nitrifying bacteria, are able to convert ammonia to nitrite (—NO2), which can be converted by other bacteria to nitrate (—NO3). The production of nitrate is significant because plants can use nitrate as a source of nitrogen for synthesis of nitrogen-containing organic molecules.

Finally, bacteria known as denitrifying bacteria are, under conditions where oxygen is absent, able to convert nitrite to nitrogen gas (N2), which is ultimately released into the atmosphere. Atmospheric nitrogen can reenter the cycle with the aid of nitrogen-fixing bacteria.

4. Unique Features of the Nitrogen Cycle

Although a cyclic pattern is present in both the carbon cycle and the nitrogen cycle, the nitrogen cycle shows two significant differences. First, most of the difficult chemical conversions are made by bacteria and other microorganisms. Without the activities of bacteria, little nitrogen would be available and the world would be a very different place. Second, although nitrogen is made available to organisms by way of nitrogen-fixing bacteria and returns to the atmosphere through the actions of denitrifying bacteria, there is a secondary loop in the cycle that recycles nitrogen compounds from dead organisms and wastes directly back to producers. Figure 15.11 summarizes the roles of various organisms in the nitrogen cycle.

FIGURE 15.11. The Nitrogen Cycle

Nitrogen atoms are cycled through ecosystems. Atmospheric nitrogen is converted by nitrogen-fixing bacteria to nitrogen-containing compounds, which plants can use to make proteins and other compounds. Proteins are passed to other organisms when one organism is eaten by another. Dead organisms and their waste products are acted upon by decay organisms to form ammonia, which can be reused by plants and converted to other nitrogen compounds by nitrifying bacteria. Denitrifying bacteria return nitrogen as a gas to the atmosphere.

5. Agriculture and the Nitrogen Cycle

In naturally occurring soil, nitrogen is often a limiting factor of plant growth. To increase yields, farmers provide extra sources of nitrogen in several ways. Inorganic fertilizers are a primary method of increasing the nitrogen available. These fertilizers may contain ammonia, nitrate, or both.

Since the manufacture of nitrogen fertilizer requires a large amount of energy and uses natural gas as a raw material, fertilizer is expensive. Therefore, farmers use alternative methods to supply nitrogen and reduce their cost of production. Several different techniques are effective. Farmers can alternate nitrogen-yielding crops such as soybeans with nitrogen-demanding crops such as corn. Since soybeans are legumes that have symbiotic nitrogen-fixing bacteria in their roots, if soybeans are planted one year, the excess nitrogen left in the soil can be used by the corn plants grown the next year. Some farmers even plant alternating strips of soybeans and corn in the same field. A slightly different technique involves growing a nitrogen-fixing crop for a short period of time and then plowing the crop into the soil and letting the organic matter decompose. The ammonia released by decomposition serves as fertilizer to the crop that follows. This is often referred to as green manure. Farmers can also add nitrogen to the soil by spreading manure from animal production operations or dairy farms on the field and relying on the soil bacteria to decompose the organic matter and release the nitrogen for plant use.

HOW SCIENCE WORKS 15.1

Scientists Accumulate Knowledge About Climate Change

Humans have significantly altered the carbon cycle. As we burn fossil fuels, the amount of carbon dioxide in the atmosphere continually increases. Carbon dioxide allows light to enter the atmosphere but does not allow heat to exit. Because this is similar to what happens in a greenhouse, carbon dioxide and the other gases that have similar effects are called greenhouse gases. Therefore, many scientists are concerned that increased carbon dioxide levels are leading to a warming of the planet, which will cause major changes in our weather and climate.

In science, when a new discovery is made or a new issue is raised, it stimulates a large number of observations and experiments that add to the body of knowledge about the topic. Concerns about global climate change and the role that carbon dioxide plays in causing climate change have resulted in scientists studying many aspects of the problem. This has been a worldwide effort and has involved many different branches of science. This effort has resulted in critical examination of several basic assumptions about climate change, the collection of much new information, and new predictions about the consequences of global climate change.

Several significant studies include:

• Examination of gas bubbles trapped in the ice of glaciers has allowed scientists to measure the amount of carbon dioxide in the atmosphere at the time the ice formed. This provides information about carbon dioxide concentrations prior to human-caused carbon dioxide releases and allows scientists to track the rate of change.

• Long-term studies of the atmosphere at various locations throughout the world show that carbon dioxide levels are increasing.

• Measurements show that sea level is rising almost 2 millimeters per year.

• Measurements of the temperature of the Earth's atmosphere have allowed tracking of temperature. According to NASA, 10 of the warmest years on record occurred in the 12-year period between 1998 and 2009.

• Satellite images of the Arctic Ocean show reduced ice cover.

• Observations of bird migration in Europe document that birds that migrate long distances are arriving in Europe earlier in the spring.

• Many studies of the rate at which different ecosystems take up carbon dioxide have been done to determine if assumptions about the carbon dioxide trapping role of natural ecosystems are correct.

• Warming of the Arctic has resulted in less permafrost.

• Increased water temperatures have been linked to increases in the number and extent of blooms of cyanobacteria in lakes and oceans.

• Studies suggest that an increase in the level of carbon dioxide in the atmosphere could result in increased amounts of dissolved carbon dioxide in the ocean. Increased carbon dioxide will lower the pH of the ocean, which could have a negative effect on animals that make shells.

• Warming of the oceans is linked to more intense hurricanes.

• Earlier arrival of spring is linked to increased numbers and intensity of forest fires in the western United States.

The United Nations established the Intergovernmental Panel on Climate Change (IPCC)—a panel of scientists, political leaders, and economists—to analyze the large amount of information generated on the topic of climate changes. The IPCC has issued several reports about the nature, causes, and the impacts of climate change on ecosystems and culture.

Phosphorus is another atom common in the structure of living things. It is present in many important biological molecules, such as DNA, and in the membrane structure of cells. In addition, animal bones and teeth contain significant quantities of phosphorus. Most of the processes involved in the phosphorus cycle are the geologic processes of erosion and deposition. The ultimate source of phosphorus atoms is rock. In nature, new phosphorus compounds are released by the erosion of rock and are dissolved in water. Plants use the dissolved phosphorus compounds to construct the molecules they need. Animals obtain phosphorus when they consume plants or other animals. When an organism dies or excretes waste products, decomposer organisms recycle the phosphorus compounds back into the soil, where they can be reused. Phosphorus compounds that are dissolved in water are ultimately precipitated as mineral deposits. This has occurred in the geologic past and typically has involved deposits in the oceans. Geologic processes elevate these deposits and expose them to erosion, thus making phosphorus available to organisms. Animal wastes often have significant amounts of phosphorus. In places where large numbers of seabirds or bats have congregated for hundreds of years, their droppings (called guano) can be a significant source of phosphorus for fertilizer (figure 15.12).

In many soils, phosphorus is in short supply and must be provided to crop plants in fertilizer to get maximum yields. Phosphorus is also in short supply in aquatic ecosystems.

FIGURE 15.12. The Phosphorus Cycle

The primary source of phosphorus is phosphorus-containing rock. The erosion of rock and the dissolving of phosphorus compounds in water makes phosphorus available to the roots of plants. Animals obtain phosphorus in their food. Decomposers recycle phosphorus compounds back into the soil.

Nutrient Cycles and Geologic Time

The nutrient cycles we have just discussed act on a short-term basis in which elements are continually being reused among organisms and on a long-term basis in which certain elements are tied up for long time periods and are not part of the active nutrient cycle. In our discussion of the phosphorus cycle it was mentioned that the source of phosphorus is rock. While phosphorus moves rapidly through organisms in food chains, phosphorus ions are not very soluble in water and tend to precipitate in the oceans to form sediments that eventually become rock on the ocean floor. Once this has occurred, it takes the process of geologic uplift followed by erosion to make phosphorus ions available to terrestrial ecosystems. Thus, we can think of the ocean as a place where phosphorus is removed from the active nutrient cycle (this situation is known as a sink).

There are also long-term aspects to the carbon cycle. Organic matter in soil and sediments are the remains of once-living organisms. Thus, these compounds constitute a sink for carbon, particularly in ecosystems in which decomposition is slow (tundra, northern forests, grasslands, swamps, marine sediments). These materials can tie up carbon for hundreds to thousands of years. Fossil fuels (coal, petroleum, and natural gas), which were also formed from the remains or organisms, are a longer-term sink that involves hundreds of millions of years. The carbon atoms in fossil fuels at one time were part of the active carbon cycle but were removed from the active cycle when the organisms accumulated without decomposing. The organisms that formed petroleum and natural gas are thought to be the remains of marine organisms that got covered by sediments. Coal was formed from the remains of plants that were buried by sediments. Once the organisms were buried, their decomposition would be slowed, and heat from the Earth and pressure from the sediments helped to transform the remains of living things into fossil fuels. The carbon atoms in fossil fuels have been locked up for hundreds of millions of years. Thus, the formation of fossil fuels was a sink for carbon atoms.

Oceans are a major carbon sink. Carbon dioxide is highly soluble in water. Many kinds of carbonate sedimentary rock are formed from the precipitation of carbonates from solution in oceans. In addition, many marine organisms form skeletons or shells of calcium carbonate. These materials accumulate on the ocean floor as sediments that over time can be converted to limestone. Limestone typically contains large numbers of fossils. The huge amount of carbonate rock is an indication that there must have been higher amounts of carbon dioxide in the Earth’s atmosphere in the past.

Since fossil fuels are the remains of once-living things and living things have nitrogen as a part of protein, nitrogen that was once part of the active nitrogen cycle was removed when the fossil fuels were formed. In ecosystems in which large amounts of nonliving organic matter accumulates (swamps, humus in forests, and marine sediments), nitrogen can be tied up for relatively long time periods. In addition, some nitrogen may be tied up in sedimentary rock and, in some cases, is released with weathering. However, it appears that the major sink for nitrogen is as nitrogen in the atmosphere. Nitrogen compounds are very soluble in water, so when sedimentary rock is exposed to water, these materials are dissolved and reenter the active nitrogen cycle.

10. Trace the flow of carbon atoms through a community that contains plants, herbivores, decomposers, and parasites.

11. Describe four roles that bacteria play in the nitrogen cycle.

12. Describe the flow of water through the hydrologic cycle.

13. List three ways the carbon and nitrogen cycles are similar and three ways they differ.

14. Describe the major processes that make phosphorus available to plants.


Habitats

Although fungi are primarily associated with humid and cool environments that provide a supply of organic matter, they colonize a surprising diversity of habitats, from seawater to human skin and mucous membranes. Chytrids are found primarily in aquatic environments. Other fungi, such as Coccidioides immitis, which causes pneumonia when its spores are inhaled, thrive in the dry and sandy soil of the southwestern United States. Fungi that parasitize coral reefs live in the ocean. However, most members of the Kingdom Fungi grow on the forest floor, where the dark and damp environment is rich in decaying debris from plants and animals. In these environments, fungi play a major role as decomposers and recyclers, making it possible for members of the other kingdoms to be supplied with nutrients and live.


Bugs 101: Insect-Human Interactions

Of all the animals on earth, which are the strongest for their size? What about the fastest? Who were the first animals to evolve flight? Insects take all of these titles and more! As the most abundant animals on the planet, insects and other arthropods affect our lives in so many ways. From beneficial interactions like pollination and biological pest control, to the transmission of life threatening diseases this course will teach you about the big ways that these little arthropods impact our lives. In Bugs 101: Insect-Human Interactions, you will be plunged into the diverse (and sometimes alien) world of arthropods to learn how they work, what they do, and how insects and humans interact every day. After completing this course, you will be able to: Describe the evolutionary relationships between insects and their arthropod relatives Inventory major groups of insects and their diversity Demonstrate evolutionary adaptations that make insects successful Discuss insect biology and human-insect interactions Evaluate positive and negative interactions between insects and humans Propose practical and symbolic roles insects play in human societies

Получаемые навыки

Biology, Entomology, Science, Ecology

Рецензии

An absolutely fantastic course with logically set-out modules and enthusiastic, inspiring and engaging presenters. Very useful for anyone involved in Science outreach and/or widening participation.

Best instructor and teaching assistants. they start from very based and and slowly increase the difficulty of topics. i used to love buys ,after doing this course now i love bugs more the before.

Without decomposers, dead trees and leaves would pile up in forests, and we would be walking knee deep in dung and animal carcasses. Insect decomposers help to recycle these materials and many others back into the earth, recycling the nutrients to be used by other organisms again. This module unearths the importance of these decomposers to our ecosystem, and even discusses some ways these insects can be used to help solve crimes.

Преподаватели

Dr. Maya Evenden

Текст видео

Insects provide important ecosystem services that significantly impact our way of life. A good example of this is nutrient cycling. Many insects and other arthropods are decomposers that help recycle essential nutrients within an ecosystem. In this module, we will break down the concept of nutrient cycling and introduce some of the insects that facilitate this green process. Later in this module, we discuss how environmental conditions, especially temperature and moisture influence insect development rates, which in turn will have an effect on the rates of decomposition. We will also use this opportunity to re-introduce metamorphosis and moulting, two important concepts in the field of forensic entomology. Thanks to movies and television, you may already be familiar with some aspects of forensic entomology. In this module, we will show you how forensic entomologists apply information about insect development in criminal investigations. Stick with us as we dig into the intriguing field that combines entomology with criminology. Before we begin, we would like to warn you that some of the images and footage in the upcoming videos may be disturbing to some learners, though fascinating at the same time.


The Role of Decomposers in an Ecosystem

A decomposer is an organism that breaks down dead plant or animal matter. This may arouse the yuk response in many readers, but the fact is that ecosystems could not function without decomposers. This is because ecosystems depend on recycling in order to function. Humans are used to throwing away things they don’t want, but in nature, all materials are recycled endlessly.

Dead bodies contain many useful substances that are often in short supply in ecosystems: carbon tied up in large carbohydrate molecules, calcium and other minerals, organic nitrogen bound up in proteins. Without the help of decomposers, these elements would be removed from the food chain and gradually become so rare that the ecosystem would cease to function.

Carbon, hydrogen, oxygen, nitrogen and the other necessary elements of life are all recycled. The oxygen we breathe in today was once breathed in by dinosaurs. The carbon dioxide that we breathe out is used by plants to create sugars in the process of photosynthesis. When animals eat plants, those simple sugars and carbohydrates are broken down and used as the building blocks for animal fats, carbohydrates and proteins.

When plants and animals die, those large complex compounds cannot be directly used again. Instead the decomposers break them down and make them available. So what are these decomposers? Bacteria and fungi do the majority of decomposition work. Worms and maggots also help. Fungi work mainly on plant materials, breaking down even cellulose and lignin, the largest of the complex carbohydrates. Bacteria work on everything from animal proteins to plant carbohydrates. Once these are broken down into smaller molecules, they can be ingested by small animals such as insects or taken up by plant roots and thus made part of the food chain again.

Nitrogen is an interesting element. It is present in the air we breathe as N2 but this is not a form that animals can use directly. Yet we need nitrogen to make proteins, the building blocks of our bodies. So where can we get it from? We can recycle organic nitrogen by eating meat but only nitrogen fixing bacteria can provide new sources of nitrogen from the air. Without bacteria to break down the proteins in dead bodies and fixing the nitrogen in the air, animals could not get enough nitrogen to make the proteins necessary for them to grow and function.

So next time you walk through a forest, think of the tiny but necessary organisms beneath your feet. Without their constant work to recycle the dead, the living ecosystem around you could not function or continue to exist. All life depends on the decomposers just as they depend on us.


Watch the video: The Dirt on Decomposers: Crash Course Kids # (May 2022).