Microbiology, part 26: Growth - Binary Fission & Bacterial Growth

Hi. I'm Cathy with Level Up RN. In this video, I will be doing a high-level review of biogeochemical cycles, including the carbon cycle, the nitrogen cycle, the sulfur cycle, and the phosphorus cycle. And at the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on biogeochemical cycles so you can follow along with me. And of note, our flashcards are also available in digital format via Flashables.

A biogeochemical cycle is the movement of chemical elements between organisms and the environment. So let's first talk about the carbon cycle, which is the recycling of carbon between organisms and the environment. Two key processes that take place during the carbon cycle include carbon fixation and decomposition. Carbon fixation occurs during photosynthesis when photoautotrophs, such as plants, algae, and cyanobacteria use energy from the sunlight to convert carbon dioxide into organic molecules. Carbon decomposition occurs during cellular respiration when chemoheterotrophs, such as animals, break down organic molecules which produces carbon dioxide. In addition, microbes in the soil and water break down dead plants and animals, which also produces carbon dioxide or methane in some cases. In terms of carbon storage, the vast majority of carbon can be found in rocks, such as limestone. Carbon can also be found in oceans and in fossil fuels such as coal, oil, and natural gas. And burning of these fossil fuels releases a large amount of carbon dioxide into the atmosphere. And it's important to note that carbon dioxide is the primary greenhouse gas and the main contributor to climate change.

Next, let's discuss the nitrogen cycle. Key processes involved in the nitrogen cycle include fixation, nitrification, assimilation, ammonification, and denitrification. And bacteria play an essential role in every step of the nitrogen cycle. During nitrogen fixation, prokaryotic organisms convert nitrogen gas in the atmosphere to ammonia in the soil. So plants are unable to use nitrogen in the air. So nitrogen fixation converts nitrogen to a form that plants can use. During nitrification, other prokaryotic organisms convert ammonia into nitrite and then into nitrate. So nitrate is the form of nitrogen that is most commonly used by plants for growth and development. During assimilation, inorganic nitrogen compounds, such as nitrates, are taken up by plants and other organisms and converted into organic nitrogen compounds, such as amino acids. During ammonification, decomposers such as prokaryotic organisms and fungi convert organic nitrogen found in waste products and in the remains of dead organisms into ammonia, which can then be converted into nitrates via nitrification. And then during denitrification, bacteria convert nitrates into atmospheric nitrogen gas, which can then be converted into ammonia via nitrogen fixation. So you can see how nitrogen is constantly recycled between organisms and the environment.

Let's now review the key components of the sulfur cycle. Sulfur is found in the atmosphere as sulfur dioxide and is dissolved in precipitation. It is also released by rocks via weathering and combines with oxygen in the air to form sulfate. Plants take in sulfur, and some plants are consumed by animals. And during decomposition of plants and animals, microbes, which include some of the oldest prokaryotic organisms on the planet, remove sulfur groups from the amino acids. This produces hydrogen sulfide gas, which is released into the atmosphere, which starts the whole process over again.

Lastly, let's talk briefly about the phosphorus cycle. Most phosphorus is found in rocks and sediments, and weathering causes the rocks to release phosphate ions into the water and soil. Plants take in the inorganic phosphate, and some plants are consumed by animals. So when plants and animals die, organic phosphate is released into the soil. And then bacteria convert this organic phosphorus into its inorganic form where it can be taken up by plants again.

All right. It's quiz time, and I have four questions for you. And they are multiple choice. You guys ready? All right. Question number one. During the carbon cycle, blank is the process in which carbon dioxide is converted into organic molecules via photosynthesis. A, decomposition, B, fixation, C, ammonification, and D, assimilation? The answer is, B, fixation. Question number two, during the carbon cycle, blank is the process in which organic molecules are broken down during cellular respiration, producing carbon dioxide. A, decomposition, B, fixation, C, ammonification, or D, assimilation? The answer is, A, decomposition. Question number three, during the nitrogen cycle, blank is the process in which decomposers convert organic nitrogen found in the remains of dead organisms into ammonia. A, decomposition, B, fixation, C, ammonification, or D, assimilation? The answer is, C, ammonification. And finally, number four, during the nitrogen cycle, blank is the process in which inorganic nitrogen is taken up by plants and is converted into organic nitrogen compounds. A, decomposition, B, fixation, C, ammonification, or D, assimilation? The answer is, D, assimilation.

All right. That's it for this video. I hope it was helpful. Thank you so much for watching, and good luck with studying.

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Bacteria convert nitrates into atmospheric nitrogen gas.