Nutritional Factors of Microbial Growth - Online Tutor, Practice Problems & Exam Prep

Microorganisms are classified based on three nutritional factors: energy source, electron source, and carbon source. Organisms can be phototrophs, obtaining energy from sunlight, or chemotrophs, deriving energy from chemical compounds. Electron sources categorize organisms as lithotrophs, using inorganic molecules, or organotrophs, using organic molecules. Carbon sources distinguish autotrophs, which fix inorganic carbon like CO₂, from heterotrophs, which consume organic molecules. Understanding these classifications is essential for studying microbial growth and metabolism.

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: 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 corresponds with the numbers in the image below.

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. Later in our course in a different video, we'll define phototrophs and chemotrophs. But for now, you should know that the energy source will classify organisms either as phototrophs or chemotrophs.

Regarding the electron source, this refers to the electron transport chain or the ETC for short. Scientists will classify organisms either as lithotrophs or as organotrophs. Later in our course, in a different video, we'll define what lithotrophs and organotrophs are. But for now, what you should know is that the electron source will classify organisms depending on the molecule supplying the electrons, either as lithotrophs or organotrophs.

Then, the carbon source refers to the original carbon-based molecule that supplies carbon for creating other cell components. Scientists will classify organisms either as autotrophs or as heterotrophs. We will be able to define what these autotrophs and heterotrophs are more in our future videos. But for now, this concludes our brief introduction to the nutritional factors of microbial growth.

As we move forward in our course, we will cover the energy source first in more detail, then we'll discuss the electron source, and 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. And so organisms can be classified into 2 groups based on their energy source. So the first group are going to be the phototrophs. Phototrophs are organisms that obtain their energy directly from sunlight. That's because the root "photo" means light. Now chemotrophs, on the other hand, as their name somewhat implies, are going to be organisms that obtain their energy directly from chemical compounds that they must obtain from their environments.

If we take a look at our image below, on the left-hand side, we're showing you 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 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. 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 source 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 two groups based on their electron source. Recall from our previous lesson videos that the electron source is referring to the original molecule that supplies electrons to the electron transport chain (ETC). These two groups that organisms can be classified into are the lithotrophs or the organotrophs.

Now, lithotrophs are organisms that supply their electron transport chain with electrons from reduced inorganic molecules. Inorganic molecules are molecules that do not contain carbon and hydrogen, such as water and iron. Neither of these contains carbon and hydrogen and so are inorganic molecules. Many times, these inorganic molecules are found in nonliving substances such as rocks and, again, water itself. It is important to note that all plants are lithotrophs because they harvest electrons from splitting water during carbon fixation. Because they use water as their electron source, that makes them lithotrophs.

Organotrophs, on the other hand, supply their electron transport chain with electrons from organic molecules. Organic molecules are molecules that contain carbon and hydrogen, for example, glucose. If we look at our image down below, on the left-hand side, what we're showing you are the lithotrophs. Lithotrophs obtain their electrons from inorganic molecules found in nonliving things such as rocks and water. Here, we have a lithotroph stating, "I litho - I mean, I love eating rocks." Hopefully, this helps you remember that lithotrophs obtain their electrons from inorganic molecules.

On the right-hand side, what we're showing you are the organotrophs. Organotrophs obtain their electrons from organic molecules that contain carbon and hydrogen, such as glucose. Glucose, that sugar, can be found in organics usually within living substances such as trees, apples, and other items. Notice that this organotroph is saying, "I only eat organics and obtain electrons from organics."

This 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. Now, microorganisms are classified into 2 groups based on their source of carbon, and whether that carbon source is organic or inorganic. And again, 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. Now, autotrophs are going to be using carbon fixation, in order to capture carbon and make their own food and other cell components as well. And so, autotrophs are going to be making their own food. Usually, the carbon that is going to be fixated is some kind of inorganic carbon such as carbon dioxide. Now, heterotrophs, on the other hand, are going to consume rather than make their own food, and they use organic molecules. These organic molecules are what are supplying the carbon that the cell needs to create other cell components. And so, if we take a look at our image down below, on the left-hand side over here, we're focusing on the autotrophs. The autotrophs are going to be making their own food by using carbon fixation to capture inorganic carbon, such as carbon dioxide. So, they fix carbon dioxide to supply their carbon. And so, here we're showing you how carrots can use photosynthesis and carbon fixation to fix inorganic carbon. Now over here on the right-hand side, what we're showing you are heterotrophs. A heterotroph would be the bunny rabbit over here. And so, this bunny rabbit must consume organic molecules in order to supply itself with carbon. And so, notice that this bunny rabbit, which is the heterotroph, is eating the autotroph, which is the carrot. And so, the carrot is the autotroph, and the bunny rabbit is the heterotroph. And so, this here concludes our brief introduction to the carbon source as well as heterotrophs and autotrophs. 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.

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 3 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 chains, 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. And heterotrophs, on the other hand, are going to, instead of making their own food, they 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 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. Over here are all 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 take a 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 a chemoorganotroph. It's a chemotroph because it uses chemical energy, and it is an organotroph because it uses organic compounds as the electron source. Now if it were inorganic compounds that it uses as the electron source, then it would be a chemolithotroph. You can see that we are starting to combine these roots that we talked about previously. 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. If we were to take a 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. 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 chemoorganoautotrope. Notice that there are no known organisms for Chemo Organoautotrophs. Now, if the chemolithotroph had a carbon source that was organic carbon, then it would be a chemolithoheterotroph. If it had a chemolithotroph with a carbon dioxide or inorganic carbon source, it would be a chemolithoautotrope. 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. The 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 photoorganoautotrope. Once again there are no known organisms for that. If we had a photolithotroph with an organic carbon source, it would be a photolithoheterotroph. Again, no known organisms for that. And if we had a photolithotroph with inorganic carbon sources then it would be a photolithoautotrope. Basically all of the ones that you see 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 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, and 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. 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. 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.

Here’s what students ask on this topic:

What are the three main nutritional factors that classify microorganisms?

The three main nutritional factors that classify microorganisms are the energy source, electron source, and carbon source. The energy source can be either sunlight (phototrophs) or chemical compounds (chemotrophs). The electron source is categorized into lithotrophs, which use inorganic molecules, and organotrophs, which use organic molecules. Lastly, the carbon source distinguishes autotrophs, which fix inorganic carbon like CO₂, from heterotrophs, which consume organic molecules. Understanding these classifications is essential for studying microbial growth and metabolism.

How do phototrophs and chemotrophs differ in their energy sources?

Phototrophs and chemotrophs differ in their energy sources. Phototrophs obtain their energy directly from sunlight, utilizing solar energy to power their metabolic processes. The term 'photo' means light, indicating their reliance on light energy. In contrast, chemotrophs derive their energy from chemical compounds found in their environment. These chemical compounds, such as glucose, provide the necessary energy for their metabolic activities. The distinction between these two groups is crucial for understanding how different microorganisms adapt to their environments and obtain the energy needed for growth and survival.

What is the difference between lithotrophs and organotrophs in terms of electron sources?

Lithotrophs and organotrophs differ in their electron sources. Lithotrophs obtain electrons from reduced inorganic molecules, such as water (H₂O) and iron (Fe), which do not contain carbon and hydrogen. These inorganic molecules are often found in nonliving substances like rocks and water. On the other hand, organotrophs acquire electrons from organic molecules that contain both carbon and hydrogen, such as glucose (C₆H₁₂O₆). These organic molecules are typically found in living or once-living organisms. This distinction is important for understanding the metabolic pathways and ecological roles of different microorganisms.

How do autotrophs and heterotrophs differ in their carbon sources?

Autotrophs and heterotrophs differ in their carbon sources. Autotrophs use carbon fixation to capture inorganic carbon, such as carbon dioxide (CO₂), and convert it into organic molecules to make their own food. This process allows them to be self-sufficient in terms of carbon supply. In contrast, heterotrophs consume organic molecules, which already contain carbon and hydrogen, to obtain the carbon needed for creating other cell components. Heterotrophs rely on external sources of organic carbon, such as plants or other organisms, for their nutritional needs.

What are the possible combinations of energy, electron, and carbon sources in microorganisms?

Microorganisms can be classified based on combinations of their energy, electron, and carbon sources. For energy, they can be phototrophs (light) or chemotrophs (chemical compounds). For electron sources, they can be lithotrophs (inorganic molecules) or organotrophs (organic molecules). For carbon sources, they can be autotrophs (inorganic carbon like CO₂) or heterotrophs (organic molecules). Combining these factors, we get groups like chemoorganoheterotrophs (chemical energy, organic electron source, organic carbon source) and photolithoautotrophs (light energy, inorganic electron source, inorganic carbon source). Some combinations, like chemoorganoautotrophs, have no known organisms.