Prokaryotic Metabolism - Online Tutor, Practice Problems & Exam Prep

Prokaryotic metabolism is diverse, with organisms classified as autotrophs or heterotrophs based on their carbon source. Energy sources include light (phototrophs), organic molecules (chemoorganotrophs), and inorganic molecules (chemolithotrophs). Prokaryotes play crucial roles in the nitrogen cycle through nitrogen fixation, converting atmospheric nitrogen into usable forms. They also contribute to the carbon cycle as decomposers and produce oxygen via photosynthesis. Understanding these metabolic pathways highlights the essential functions of prokaryotes in ecosystems and their interdependence with other organisms.

Nutritional Factors of Microbial Growth

In this video, we're going to begin our lesson on the nutritional factors of microbial growth. Scientists typically classify organisms into different groups based on three nutritional factors that we have numbered down below 1 through 3, and those are the energy source, the electron source, and the carbon source. Notice down below we're showing you our map of the lesson moving forward on the nutritional factors of microbial growth. Each of these numbers that we have up above and in the text corresponds with the numbers we have down below in the image. Now, in terms of the energy source, this refers to the consumed energy source for powering metabolic pathways.

Scientists will group organisms either as phototrophs or as chemotrophs in terms of the energy source. Later in our course in a different video, we'll define phototrophs and chemotrophs. But for now, you should just know that the energy source is going to classify organisms as either phototrophs or chemotrophs. Regarding the electron source, it refers to the original molecule supplying electrons to the electron transport chain or the ETC for short. Scientists will classify organisms either as lithotrophs or as organotrophs in terms of the electron source.

Once again, later in our course in a different video, we'll define what lithotrophs and organotrophs are. But for now, you should know that the electron source classifies organisms as either lithotrophs or organotrophs depending on the molecule supplying the electrons. Then, the carbon source refers to the original carbon-based molecule that, of course, is going to supply carbon for creating other cell components. In terms of the carbon source, scientists will classify organisms either as autotrophs or as heterotrophs. Once again, we'll define what these autotrophs and heterotrophs are more in our future videos.

This here concludes our brief introduction to the nutritional factors of microbial growth. As we move forward in our course, we're going to cover the energy source first in more detail, and then we'll talk about the electron source in more detail. Last but not least, we'll talk about the carbon source in more detail. I'll see you all in our next video.

Energy Source: Phototrophs vs. Chemotrophs

In this video, we're going to talk more about the nutritional energy source of microorganisms, and how scientists can classify organisms either as phototrophs or as chemotrophs depending on their energy source. Organisms can be classified into two groups based on their energy source. So the first group is going to be the phototrophs. Phototrophs are organisms that obtain their energy directly from sunlight, which is because the root "photo" means light.

Now, chemotrophs, on the other hand, as their name somewhat implies, are organisms that obtain their energy directly from chemical compounds that they must obtain from their environments. If we take a look at our image down below, on the left-hand side over here, what we're showing you are phototrophs. Phototrophs obtain their energy from the light, the solar energy, sunlight. Notice here we have the sun and the solar energy radiating down here. And here we have our phototroph, which is going to be soaking up the sun and obtaining its energy directly from the sun.

Now, the chemotrophs on the other hand are going to be getting their energy directly from chemicals, chemical compounds. They have chemical energy such as glucose, for example, which is an example of chemical energy. Notice over here we have a chemotroph that's saying "look at all this energy," and it's coming from these chemical compounds rather than coming directly from sunlight. This here concludes our brief introduction to the energy sources of phototrophs and chemotrophs, and we'll be able to get some more practice applying these concepts as we move forward. So I'll see you all in our next video.

The prefix photo- indicates that an organism will make use of _______ for energy purposes.

• A. Chemicals.
• B. Organics.
• C. Light.
• D. Inorganics

Electron Source: Lithotrophs vs. Organotrophs

In this video, we're going to talk more about the nutritional electron source of microorganisms, and how scientists can classify organisms either as lithotrophs or as organotrophs based on their electron source. Organisms can be categorized into 2 groups based on their electron source. Recall from our previous lesson videos that the electron source refers to the original molecule that supplies electrons to the electron transport chain, or the ETC for short. These two groups that organisms can be classified into are the lithotrophs or the organotrophs. Now, the lithotrophs are going to be organisms that supply their electron transport chain with electrons from reduced inorganic molecules.

Inorganic molecules are going to be molecules that do not contain carbon and hydrogen, such as, for example, water and iron. Neither contain carbon and hydrogen, and so they are inorganic molecules. Many times, these inorganic molecules are going to be found in nonliving substances such as rocks and water itself. It is important to note that all plants are lithotrophs because they harvest electrons from splitting water during carbon fixation. Because they are using water as their electron source, that makes them lithotrophs.

Now, organotrophs, on the other hand, are going to supply their electron transport chain with electrons from organic molecules. Organic molecules are going to be molecules that contain carbon and hydrogen, for example, glucose. If we take a look at our image down below, over here on the left-hand side, what we're showing you are the lithotrophs. The lithotrophs are somewhat like rock eaters in a way because they're going to be obtaining their electrons from inorganic molecules, and inorganic molecules are found in things such as nonliving things such as rocks and water. Here we have a lithotroph saying, "I litho, I mean, I love eating rocks."

Hopefully, that can help you remember that the lithotrophs are going to obtain their electrons from inorganic molecules. Then over here on the right-hand side, what we're showing you are the organotrophs. The organotrophs are going to obtain their electrons from organic molecules that contain carbon and hydrogen such as glucose. Glucose, that sugar, can be found in organics usually found in living substances such as trees, apples, and things like that. Notice that this organotroph is saying, "I only eat organics and obtain electrons from organics."

This here concludes our brief introduction to the electron source as well as lithotrophs and organotrophs. We'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

Carbon Source: Heterotrophs vs. Autotrophs

In this video, we're going to talk about the nutritional carbon source of microorganisms, and how scientists can classify organisms either as heterotrophs or autotrophs depending on the carbon source. Microorganisms are classified into two groups based on their source of carbon and whether that carbon source is organic or inorganic. Recall that "organic" just means that the substance contains both carbon and hydrogen, whereas "inorganic" means that it does not contain both carbon and hydrogen. The carbon source itself refers to the original carbon-based molecule that supplies carbon to the cell so that the cell can use that carbon to create other cell components. Autotrophs use carbon fixation to capture carbon and make their own food and other cell components.

Autotrophs make their own food, usually fixating inorganic carbon such as carbon dioxide. Heterotrophs, on the other hand, consume rather than make their own food, using organic molecules that supply the carbon needed to create other cell components. Focusing on the image below on the left hand side, we see autotrophs making their own food by using carbon fixation to capture inorganic carbon, such as carbon dioxide. They fix carbon dioxide to supply their carbon, demonstrating how autotrophs that are able to perform photosynthesis and carbon fixation fix inorganic carbon. On the right hand side, we show heterotrophs. For example, a heterotroph could be a bunny rabbit.

This bunny rabbit must consume organic molecules to supply its cells with carbon. Notice that this bunny rabbit, the heterotroph, is eating the autotroph, which is the carrot. Thus, the carrot is the autotroph, and the bunny rabbit is the heterotroph. This concludes our brief introduction to the carbon source, heterotrophs, and autotrophs. We will be able to get some practice applying these concepts as we move forward.

So, I'll see you all in our next video.

Biologists can divide living organisms into two groups:autotrophs and heterotrophs, which differ in _________.

• A. Their method of obtaining energy.
• B. The characteristics of life.
• C. Their mode of inheritance.
• D. The way that they generate ATP.

Organisms that use organic molecules as their source of carbon are called:

• A. Archaea.
• B. Chemoautotrophs.
• C. Heterotrophs.
• D. Autotrophs.

Organisms that use CO₂ as their source of carbon are called

• A. Organotrophs.
• B. Heterotrophs.
• C. Autotrophs.
• D. Chemotrophs.

Reviewing the Nutritional Growth Factors of Microbes

In this video, we're going to be reviewing the nutritional growth factors of microbes by completing the table that you see here. And so notice that we have this table organized by the three nutritional factors: energy source, electron source, and carbon source. Now, in terms of the energy source, scientists organize microorganisms either as phototrophs or chemotrophs. Phototrophs are organisms that obtain their energy directly from sunlight, whereas chemotrophs are going to be obtaining their energy from chemical compounds.

Now, in terms of the electron source, scientists organize microorganisms either as lithotrophs or organotrophs. Lithotrophs are going to be organisms that supply their electron transport chain or ETC with electrons from reduced inorganic molecules, which are molecules that do not contain carbon and hydrogen, such as, for example, water. Now, organotrophs, on the other hand, are going to be organisms that supply their electron transport chain or ETC with electrons from organic molecules or molecules that contain carbon and hydrogen, such as, for example, glucose.

Now, in terms of the carbon source, scientists will organize organisms either as autotrophs or heterotrophs. Autotrophs are going to be fixing inorganic carbon dioxide to make their own molecules of food and supply the cell with carbon. Heterotrophs, on the other hand, are going to consume premade organic molecules, rather than inorganic molecules, to supply the cell with carbon.

And so this here concludes our brief review of the nutritional factors of microbes, and we'll be able to get more practice and learn more as we move forward in our course. So, I'll see you all in our next video.

Nutritional Diversity Among Microbes

In this video, we're going to focus on the nutritional diversity among microbes. Scientists typically categorize microbes into groups based on a combination of the three nutritional factors. Those three key nutritional factors are the energy source, electron source, and the carbon source. All combinations of these three nutritional factors are theoretically possible, even though some combinations have no known organisms to date. Take a look at this image down below; it's really just a map showing you all of the possible combinations of those three key nutritional factors that we covered in our previous lesson videos.

Notice at the top it's showing you all living organisms can be grouped based on their specific energy source. Recall that the two energy sources could either be light energy or chemical energy. An example of chemical energy is glucose, like this green molecule that you see here. If chemical energy is the energy source, then the organism would be a chemotroph. But if light energy is the energy source, then the organism would be a phototroph.

All of this over here are going to be organisms that are phototrophs, and everything over here are going to be organisms that are chemotrophs. After identifying these organisms as chemotrophs or phototrophs, we can then look at the specific electron source of the organism. Recall that the electron source can be used to group organisms either as organotrophs or as lithotrophs. If the electron source is an organic compound, then, we would have ourselves a chemoorganotroph. Notice it's a chemotroph because it is using chemical energy, and it is an organotroph because it uses organic compounds as the electron source.

If it were inorganic compounds that it uses as the electron source, then it would be a chemolithotroph. Chemolithotrophs, it is a chemotroph because it uses chemical energy as the energy source, and it is a lithotroph because it uses inorganic compounds as the electron source. Now if we were to look at the phototroph side over here, in terms of the electron source if it uses organic compounds then it would be a photoorganotroph. If it uses inorganic compounds then it would be a photolithotroph.

Then of course after the electron source there is still the carbon source. The carbon source could either be organic carbon or inorganic carbon such as carbon dioxide only. So, if the chemoorganotroph has an organic carbon source then it would be a chemoorganoheterotroph. If the chemoorganotroph uses carbon dioxide only as the carbon source then it would be a chemoorganoautotroph. And notice that there are no known organisms for chemoorganoautotrophs.

If the chemolithotroph had a carbon source that was organic carbon, then it would be a chemolithoheterotroph. And if it was a chemolithotroph with a carbon dioxide or inorganic carbon source, it would be a chemolithoautotroph. What you can see here is that this is a combination of those three roots that we saw for energy source, electron source, and for carbon source. These groups that you see towards the bottom here are the more specified specific groups that classify the organisms on all three of those nutritional factors.

If we were to do the same over here with the phototrophs, notice that we have the photoorganotroph with an organic carbon source would be a photoorganoheterotroph. If we have a photoorganotroph with an inorganic carbon source such as carbon dioxide, it would be a photoorganoautotroph. And once again there are no known organisms for that. If we had a photolithotroph with an organic carbon source, it would be a photolithoheterotroph. Once again, no known organisms for that. And if we had a photolithotroph with inorganic carbon sources, then it would be a photolithoautotroph.

All of the organisms with these yellow stars at the bottom here are going to be organisms that are known to exist. The ones that specifically specify no known organisms are ones are groups in which no known organisms are known to exist in those categories. This here concludes our lesson on the nutritional diversity among microbes. You can see how much diversity there is. Scientists can group these organisms not just based on individual nutritional factors such as energy source, electron source, and carbon source, but they can also group them based on combinations of those three.

And that's exactly what we're seeing down below is all of the possible combinations for those three. This here concludes our lesson on this and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Chemoheterotrophs:

• A. Use sunlight as an energy source.
• B. Use pre-made organic chemicals as a carbon source.
• C. Obtain their energy from chemical compounds.
• D. Use preformed inorganic molecules as a carbon source.
• E. B and C.

Cyanobacteria are a group of photosynthetic bacteria. These bacteria use sunlight as their energy source and carbon dioxide as their carbon source. Cyanobacteria are ________________.

• A. Chemoautotrophs.
• B. Photoautotrophs.
• C. Chemoheterotrophs.
• D. Photoheterotrophs.

Humans are:

• A. Chemolithoautotrophs.
• B. Photooganoautotrophs.
• C. Chemoorganoheterotrophs.
• D. Chemolithoheterotrophs.

Oxygen Requirements for Microbial Growth

In this video, we're going to begin our lesson on oxygen requirements for microbial growth. And so it turns out that all organisms that utilize chemical energy require what's known as a final electron acceptor for their electron transport chain. Now, later in our course in a different video, we'll talk a lot more about these final electron acceptors and electron transport chains. But for now, here in this video, you can just imagine that the final electron acceptor and electron transport chain are important for generating energy for the cell. Now, in many microbes, the final electron acceptor in this electron transport chain is going to be oxygen gas or O2.

And so organisms that utilize oxygen gas as the final electron acceptor are referred to as aerobes. And so aerobes are really just microbes that require oxygen gas to act as the final electron acceptor in the electron transport chain. And therefore, these aerobes are going to require oxygen to be abundant in order for them to grow, and so aerobes only grow where oxygen is abundant. We call these areas, these environments that have lots of oxygen, aerobic environments. And so aerobes require oxygen for growth, and therefore they grow only in aerobic environments where there's lots of oxygen.

Now, on the other hand, anaerobes are microbes that grow where little to no oxygen is present. And when little to no oxygen is present, we refer to these as anaerobic environments. And so if we take a look at our image down below, notice on the left-hand side over here we're focusing on aerobic environments. And so in aerobic environments, there is plenty of oxygen, and aerobes are capable of surviving in aerobic environments. And so here we're showing you an aerobe because notice he's saying, "I can't live without you," speaking to the oxygen gas.

And so aerobes require oxygen to be present. An example of that is Mycobacterium tuberculosis, which is a bacterium that causes tuberculosis, a lung condition. Now, on the right hand side over here, what we're focusing on is the anaerobic environment. The anaerobic environment is the opposite of the aerobic environment. Anaerobic environments do not have a lot of oxygen, and so aerobes are capable of surviving in anaerobic environments.

And so over here, what we have is an aerobe, and notice this one has a completely different opinion of oxygen. It's saying, "No, thank you. I do not need oxygen to grow." And so, an example of this, anaerobe, I'm sorry, is going to be Bacteroides fragilis, which is a bacterium that survives in the gastrointestinal tract of humans.

And so, this here concludes our brief introduction to oxygen requirements for microbial growth and how aerobes grow in aerobic environments with lots of oxygen and anaerobes grow in anaerobic environments with little to no oxygen. And so we'll be able to learn more about the oxygen requirements for microbial growth as we move forward in our lesson. So I'll see you all in our next video.

Oxygen Requirement Classes of Microbes

In this video, we're going to begin our lesson on oxygen requirement classes of microbes. Microbes can be classified into 5 groups based on their requirement for oxygen or O₂. Notice in the table below, we're showing you the oxygen requirement classes of microbes organized into these 5 groups, numbered 1 through 5. It's important to note that each of these 5 groups has test tubes.

These test tubes are special because they allow for very high concentrations of oxygen towards the top of the test tube, represented by light blue backgrounds. As you move towards the bottom of the test tube, the oxygen concentrations decrease, reaching the lowest levels at the very bottom. This is crucial to keep in mind as we continue with this video. The first group on the far left are the obligate aerobes.

Obligate aerobes, as the name implies, are aerobic organisms or those that require environments with high oxygen concentrations. The brown speckles you see represent microbial growth, which occurs only in the region of the test tube with the highest oxygen concentration. Obligate aerobes cannot live without oxygen. Notice the obligate arrow saying, "I can't live without you," to the oxygen gas because they absolutely require oxygen gas and cannot survive without it. The next group is the facultative anaerobes.

Facultative anaerobes, as their name suggests, can survive in both aerobic and anaerobic environments. There are brown speckles throughout the entire test tube, with a higher concentration towards the top where there is more oxygen, demonstrating that facultative anaerobes grow better in the presence of oxygen gas. This is important because oxygen allows for the generation of more ATP, meaning more energy and better growth. The next group, the third, are the microaerophiles.

Microaerophiles require small amounts of oxygen; too much oxygen is toxic to them. They grow in a specific region where there's a small amount of oxygen, not at the very top where there is the most oxygen, and also not at the bottom where there is no oxygen. The next group are the obligate anaerobes, practically the opposite of obligate aerobes. Obligate anaerobes can only survive where there is no oxygen, which is toxic to them. Notice this obligate anaerobe using a protective shield and sword against oxygen, indicative of the fact that oxygen is highly toxic to these organisms. Growth is seen only at the very bottom of the tube where there is no oxygen.

The fifth and final group are the aerotolerant anaerobes, which grow equally in oxygen and areas that have no oxygen. They do not grow better in one environment over the other; they are equally tolerant to both. Notice it's saying, "I love them both," indicating it doesn't matter to these microbes whether there's oxygen or not. They grow equally in both. These are the 5 classes of oxygen requirements for microbes, and we'll get some practice applying these concepts as we move forward.

So I'll see you all in our next video.

Organisms that require oxygen for metabolism are referred to as…

• A. Facultative aerobes.
• B. Obligate aerobes.
• C. Facultative anaerobes.
• D. Microaerophiles.

Organisms that are indifferent to the presence of oxygen are…

• A. Aerotolerant anaerobes.
• B. Facultative anaerobes.
• C. Obligate aerobes.
• D. Microaerophiles.

Introduction to Biofilms

In this video, we're going to begin our introduction to biofilms. Biofilms can be defined as a group of cells that are encased in a slime-like polysaccharide layer adhered to a surface. These biofilms are really just communities or groups of microbes that live together, encased in this slime-like polysaccharide. These biofilms can be found on virtually any surface, and they can cause serious illness in many cases, being encased by a polysaccharide matrix of extracellular polymeric substances, or EPS for short.

These extracellular polymeric substances or EPS are essentially a sticky matrix of polymers. These polymers can vary a lot but will be secreted by cells supporting the biofilm structure. The polymer types can vary, and they include polysaccharides, proteins, glycoproteins, glycolipids, and lipids. All these complex diverse molecules are secreted to create this extracellular polymeric substance which encases the biofilm.

The biofilm is a community of microbes surrounded by this extracellular polymeric substance. If we take a look at this image down below, you'll notice it is an image of a biofilm. The biofilm refers to the community of microbes living together within this gel-like substance, the extracellular polymeric substance. The extracellular polymeric substance appears as the gray border and gray background that encases the biofilm, this community of microbes living together.

Zooming in to the extracellular polymeric substance or the EPS, it consists of various types of polymers including polysaccharides, proteins, glycoproteins, glycolipids, and lipids. Bacteria and archaea can all survive within these biofilms. They are of great importance because they can cause serious illnesses. Biofilms help protect the community of microbes, and therefore, can help these microbes cause illnesses.

It's of great importance to humans to study biofilms so they can learn how to counteract them and prevent illnesses. This concludes our brief introduction to biofilms, these groups of cells or communities of microbes that live together within this slime-like EPS, extracellular polymeric substance. We'll be able to get some practice applying these concepts as we move forward. I'll see you all in our next video.

______________ are complex communities of various types of microbes that adhere to surfaces.

• A. Biofilms
• B. Aggregates
• C. Colonies
• D. Cell morphologies

Biofilms can contain which of the following:

• A. Bacterial cells
• B. Proteins
• C. Archaeal cells
• D. Polysaccharides
• E. All of the choices are correct

Here’s what students ask on this topic:

What are the differences between autotrophs and heterotrophs in prokaryotic metabolism?

Autotrophs and heterotrophs differ in their carbon sources. Autotrophs synthesize their own carbon compounds using inorganic carbon sources like CO₂ or CH₄. They often use processes like the Calvin cycle to convert these gases into usable carbon compounds. Heterotrophs, on the other hand, rely on carbon compounds produced by other organisms. Essentially, heterotrophs depend on autotrophs to create the carbon compounds they need for their metabolic processes. This distinction is crucial for understanding the flow of carbon in ecosystems, as autotrophs provide the foundational carbon compounds that heterotrophs utilize.

How do phototrophs, chemoorganotrophs, and chemolithotrophs differ in their energy sources?

Phototrophs, chemoorganotrophs, and chemolithotrophs differ in their energy sources. Phototrophs use light energy to produce ATP via photophosphorylation. Chemoorganotrophs oxidize organic molecules to generate energy, often producing ATP through oxidative phosphorylation. Chemolithotrophs, on the other hand, oxidize inorganic molecules for energy, also producing ATP via oxidative phosphorylation. The key distinction lies in the type of energy source: light for phototrophs, organic molecules for chemoorganotrophs, and inorganic molecules for chemolithotrophs.

What roles do prokaryotes play in the nitrogen cycle?

Prokaryotes play a crucial role in the nitrogen cycle, primarily through nitrogen fixation. They convert atmospheric nitrogen (N₂) into forms usable by other organisms, such as ammonium (NH₄⁺) and nitrogen dioxide (NO₂). This process is essential because most organisms cannot utilize atmospheric nitrogen directly. By performing nitrogen fixation, prokaryotes make nitrogen available to plants, animals, and other organisms, thereby driving the entire nitrogen cycle and supporting life on Earth.

What is the significance of prokaryotes in the carbon cycle?

Prokaryotes are significant in the carbon cycle due to their role as decomposers. They break down organic matter, releasing carbon back into the environment, which can then be used by other organisms. Additionally, photosynthetic bacteria like cyanobacteria contribute to the carbon cycle by producing oxygen and fixing carbon dioxide through photosynthesis. This dual role in decomposition and photosynthesis highlights the essential function of prokaryotes in maintaining the balance of carbon in ecosystems.

How do prokaryotes contribute to human health and the ecosystem?

Prokaryotes contribute to human health by aiding in digestion and supporting the immune system. The gut microbiome, composed of various bacteria, helps break down food, produce essential vitamins, and protect against pathogens. In ecosystems, prokaryotes are vital for nutrient cycling, such as nitrogen fixation and decomposition, which support plant growth and maintain soil health. Their roles in both human health and ecological processes underscore their importance in sustaining life on Earth.