Biogeochemical Cycles - Online Tutor, Practice Problems & Exam Prep

Biogeochemical cycles are essential processes that recycle chemical nutrients between biotic (living) and abiotic (non-living) components of ecosystems. Key cycles include the water cycle, carbon cycle, nitrogen cycle, and phosphorus cycle. Each cycle involves various reservoirs, such as the atmosphere, oceans, and sedimentary rocks, and processes like evaporation, photosynthesis, and decomposition. Understanding these cycles is crucial for grasping how elements like carbon and nitrogen are utilized by organisms, influencing ecosystem health and stability.

Introduction to Biogeochemical Cycles

In this video, we're going to begin our lesson on biogeochemical cycles. And so the term biogeochemical has the root bio, which means life, and the root geo, which means Earth. And so considering that, biogeochemical cycles refer to the cycling of chemicals between the Earth and life. Or in other words, biogeochemical cycles refer to processes that recycle chemical nutrients and elements between biotic and abiotic parts of an ecosystem. Now it turns out that there are several different types of biogeochemical cycles, but moving forward in our course, we're going to talk about the water cycle, the carbon cycle, the nitrogen cycle, and the phosphorus cycle in their own separate videos.

Now all of these cycles are going to consist of biological processes of life and geological processes of the Earth that actually move chemical nutrients and elements between different reservoirs, which is really just a term that refers to storage spaces for these chemical nutrients and elements. And so if we take a look at our image down below, notice that each of these four circles that we can see throughout this image represents different types of reservoirs or storage spaces for these chemical elements and nutrients. And all of these pink arrows that you can see throughout the image represent either biological and or geological processes that allow for these chemical nutrients and elements to move from reservoir to reservoir. And so moving forward in our course, we're going to see very specific examples of reservoirs and biological and geological processes that connect them. But for now, this here concludes our introduction to biogeochemical cycles, and I'll see you all in our next video.

Biogeochemical Cycles Example 1

So here we have a pretty straightforward example problem that asks, which of the following is considered a geological process? And we've got these 5 potential answer options below. Now of course, we know from our last lesson video that biogeochemical cycles include both biological processes of life and geological processes of the Earth. And so when looking for the geological process, we want to eliminate biological processes and identify the process that changes or shapes the Earth in one way or another.

Notice option a says photosynthesis, and we know certainly this is a process carried out by life. Thus, this is a biological process, not so much a geological process. Option b says cellular respiration. Again, this is a biological process, so you can cross it off. Option c says excretion, and this is again a biological process that allows life to excrete or release wastes. So we can cross that off.

Option d says decomposition, which is done by organisms called decomposers. So again, it's a biological process, and we can cross it off. This leaves us with answer option e as the only option, and it is the best option here, and that is weathering. Weather and climate is a geological process that can shape the Earth. And so, we will go ahead and indicate that e here is the correct answer.

Weathering is a geological process that can actually help to move nutrients from certain reservoirs to other reservoirs, and we'll be able to see examples of that as we move forward. But for now, this concludes this problem, and I'll see you in our next video.

Water Cycle

This video, we're going to talk about the first biogeochemical cycle in our lesson, which is the water cycle. And you can see the diagram of the water cycle here behind me. Now what's important to recall is that water is essential to all life on Earth as we know it. And the water cycle is important because it helps to ensure that water is actually available in all ecosystems, including not only aquatic ecosystems but terrestrial ecosystems too. Without the water cycle, this would not be the case, and life on Earth would not exist as we know it.

So the water cycle is incredibly important. That being said, let's go ahead and wipe this clean so that we can approach this one step at a time. Because 97% of all of Earth's water is in the oceans, this makes the oceans the largest reservoir of water on Earth. We'll start our explanation of the water cycle here. So what you should know is that over the ocean, there's going to be net evaporation of water, and that evaporated water can rise up into the atmosphere, cool, and then condense to form rain clouds like the one that you can see here.

Now, of course, some of this water can precipitate back down into the ocean. But once again, it's important to know that evaporation rates over the ocean exceed precipitation rates over the ocean, which is why this red evaporation arrow is so much larger than this blue precipitation arrow. Now the atmosphere is also going to be a reservoir of water, and these rain clouds that are formed can be moved by winds over the land, where evapotranspiration from the land can contribute to the formation of these rain clouds. Now the term evapotranspiration is a single term that includes your standard evaporation from lakes and rivers, for example, but it also includes the process of transpiration, which recalls the process of plants releasing water into the atmosphere. Now over the land, there's going to be net precipitation, which is opposite of what we said over the ocean.

And so this net precipitation blue arrow is larger over land than the evapotranspiration red arrow is over land. Now once liquid water has precipitated onto the surface of the land, this makes water available to terrestrial organisms, and water can actually run off into the oceans from streams and rivers, for example, and that completes the water cycle. But also some of the water on the surface of the land can actually percolate downwards through the soil and collect in groundwater, such as aquifers for example. And then there can be underground runoff of water back into the oceans, again completing the water cycle. So this here completes our lesson on the water cycle, and we'll be able to apply these concepts and problems.

So I'll see you in our next video.

Biogeochemical Cycles Example 2

So here we have an example problem that says, given the information from this graphic and the previous lesson, which of the following processes moves the smallest volume of water? And we've got these 4 potential answer options down below. Now taking a closer look at this graphic over here, notice that the full circle here represents all of Earth's water. And notice that 97% of all of Earth's water is salt water that falls in the oceans, and only 3% of Earth's water is fresh water, represented as this tiny sliver. And so notice answer option b says evaporation from oceans, which again accounts for the vast majority of Earth's water.

So that's going to be moving a relatively large amount of water, not the smallest volume of water. So for that reason, we can eliminate answer option b. And for a similar reason, we can also eliminate answer option d, which says precipitation over oceans. Oceans are so vast that they're going to receive a lot of precipitation. So we can eliminate answer option d.

So now we're between either option a or option c. Notice option a says evaporation from freshwater rivers and lakes, and option c says evapotranspiration over the land. Now, taking a closer look at this breakdown of the freshwater that we can see right here, notice that almost 70% of the freshwater is locked up in glaciers and snow. 30% of the freshwater is actually groundwater, such as aquifers, soil moisture, and permafrost. And less than 1% of the freshwater is actually lakes and rivers, which is just mind-blowing to think about.

But what we're saying here is that evaporation from freshwater rivers and lakes is going to represent a very small fraction of the water volume being moved. And, evapotranspiration is a term that encapsulates both evaporation and transpiration. So evapotranspiration includes the evaporation from freshwater rivers and lakes, but it also includes transpiration or water release from plants. And so evapotranspiration will move larger volumes of water than just evaporation on its own. And so for that reason, we can eliminate answer option c because it will move a larger volume of water than answer option a, which means option a moves the smallest volume of water amongst these options.

So, a here is the correct answer, and that concludes this example problem. So I'll see you all in our next video.

Imagine you’re tracking a water molecule frozen in snow on land. Which of the following is a possible path it could take to eventually end up as part of the ocean?

• A. Melting into a stream, ingested by an animal, percolate into the ocean.
• B. Melting into a stream, evaporating into the atmosphere, then runoff into the ocean.
• C. Melting into soil, taken up by a plant, evapotranspiration into the ocean.
• D. Melting into soil, percolating into an aquifer, underground runoff into the ocean.

Carbon Cycle

This video, we're going to talk about the 2nd biogeochemical cycle in our lesson, which is the carbon cycle. And you can see the diagram of the carbon cycle here behind me. Now it's important to recall that carbon is an essential element to all life as carbon makes up the structural backbone of molecules needed for all living things, including making up the backbone of proteins, nucleic acids, lipids, and carbohydrates. And the carbon cycle is important because it helps to recycle the carbon and ensure that carbon is available in different forms to all living organisms regardless of what trophic level they're in and what type of ecosystem they're in, including aquatic and terrestrial ecosystems. And so, the carbon cycle is vitally important, and life would not be able to exist as we know it without the carbon cycle.

And so that being said, let's go ahead and wipe this clean so that we can approach this one step at a time. And so one of the most important and critical reservoirs of carbon is actually the atmosphere itself, where carbon is stored as atmospheric CO₂ or atmospheric carbon dioxide gas. And this helps to ensure that carbon is available globally to be utilized by primary producers in the process of photosynthesis in both aquatic and terrestrial ecosystems, where organisms such as phytoplankton can perform photosynthesis to draw the carbon into aquatic ecosystems, and organisms such as the leaves of trees, for example, can perform photosynthesis to draw in carbon into terrestrial ecosystems. Now the carbon in these primary producers can make its way up the food chain through the process of consumption, where organisms consume other organisms at lower trophic levels and obtain the carbon in their biomass. And all of these organisms are going to perform cellular respiration, which releases carbon dioxide gas back into the atmosphere, somewhat completing the cycle here.

Now all of these organisms eventually are going to die and be decomposed, and the decomposition process is typically carried out by microbes. And the decomposition process also releases carbon dioxide gas into the atmosphere as well. Now the organic matter under the right conditions can be converted into fossil fuels, such as, for example, oil and coal. And humans are able to access those fossil fuels and use them as an energy source where burning of the fossil fuels allows humans to access the energy, but it also releases the carbon that is stored in those fossil fuels as carbon dioxide gas. And so human activity certainly does influence and contribute to the increase of carbon dioxide gas in our atmosphere.

And because carbon dioxide gas is a greenhouse gas, it's going to contribute to the warming of our planet. And so this is why human activity is associated with global warming and things of that nature. Now it's also important to note that volcanoes over time can also be a significant contributor of carbon dioxide gas into the atmosphere. Now, the last note that I'll leave you all off with is that in addition to the atmosphere being a reservoir of carbon, there are also other reservoirs of carbon. And one of the most notable ones is the ocean itself, where carbon dioxide gas can react with the water in oceans.

And again, 97% of all of the Earth's water falls in the oceans. And so that water, when it reacts with the carbon dioxide, it forms carbonic acids, and so that can allow the ocean to serve as a significant reservoir of carbon. However, when those carbonic acids are formed, it can change the pH of the water, and that could potentially be devastating to aquatic life. So we can't rely on our oceans to absorb and soak in all the carbon dioxide. And so this here completes our lesson on the carbon cycle.

We'll be able to apply these concepts and problems moving forward. So I'll see you all in our next video.

Biogeochemical Cycles Example 3

So here we have an example problem that says, while a change in local conditions such as, for example, heavy rainfall, drought, etcetera, may limit the amount of nitrogen, phosphorus, or water in an ecosystem, this is rarely the case with carbon. Why? And we've got these 4 potential answer options down below. Now option a says plants can produce their own carbon via photosynthesis, but plants aren't producing their own carbon. Instead, plants are using carbon dioxide gas in the atmosphere as a source for their carbon as they fix that carbon into their systems.

And so for that reason, option a is not going to be the best option here, so we can cross that off. Now option b says decomposers can produce their own carbon when they break organic material down. But once again, decomposers aren't really producing their own carbon. Instead, they are releasing carbon in the form of carbon dioxide as a byproduct when they break down organic material. And this is also not going to be a good explanation for this question.

So for that reason, we can eliminate answer option b. Now we're between option c and d and notice option d says plants can take up carbon from the soil more efficiently than nitrogen, phosphorus, or water. But plants don't really take up carbon from the soil. Instead, plants are able to acquire their carbon directly from the atmosphere as carbon dioxide gas. And it's not really true that they're able to take up carbon from the soil more efficiently than nitrogen, phosphorus, or water.

And so for that reason, we can eliminate answer option d. And this leaves us with answer option c is the only option and it is the correct answer, which says CO₂ or carbon dioxide gas in the air is a constant source of carbon for plants. And so unlike nitrogen, phosphorus or water, plants are able to use carbon dioxide gas from the atmosphere directly and fix the carbon dioxide gas directly from the air. Whereas that's not the case with water, That's not the case with nitrogen nor is it the case with phosphorus. And so this is unique to carbon dioxide gas and carbon in this way.

And so for that reason we can indicate that c here is the correct answer. Now nitrogen is a major part of the atmosphere, but it is going to exist as nitrogen gas or N₂, which is really an unusable form of nitrogen for plants. And so that's why it's not going to be the same as carbon dioxide gas in the atmosphere. Phosphorus does not really have an atmospheric component as we'll learn later in our course and water. Although it is a part of the atmosphere, most plants aren't readily able to use water directly from the atmosphere.

Instead, they need water to be in a different physical state. They need water to be in a liquid state, and they absorb their water from the soil in a liquid state. And so it's not acquired directly from the atmosphere. And so again, it's the fact that carbon dioxide gas directly from the air can be utilized by plants that makes it unique in this way, and that's the answer to this problem. So I'll see you all in our next video.

Which of the following statements is false?

• A. Biomass is one of the largest carbon reservoirs in the biosphere.
• B. Burning plants increases the amount of atmospheric CO₂.
• C. The carbon cycle has maintained a constant atmospheric CO₂ concentration over the last million years.
• D. Carbon can be stored in soil, rocks, and ocean water.

Nitrogen Cycle

In this video we're going to talk about the 3rd biogeochemical cycle in our lesson, which is the nitrogen cycle. And you can see the diagram of the nitrogen cycle down below here, which has many different colored arrows, including yellow arrows for terrestrial cycling of nitrogen, red arrows for aquatic cycling of nitrogen, and green arrows for industrial or human-related cycling of nitrogen. Now it's very important to recall that nitrogen is an essential element to all life, as nitrogen is found in the amino groups of amino acids that make up all proteins, and nitrogen is found in the nitrogenous bases of nucleotides that make up nucleic acids like DNA and RNA. And the nitrogen cycle is super important because it helps to recycle the nitrogen and ensure that nitrogen is always available in different forms to be utilized by all organisms regardless of what trophic levels they're in and what type of ecosystem they're in, terrestrial or aquatic. And so the nitrogen cycle is super important.

Without it, life would not be able to exist as we know it. And so what you should know is that the atmosphere is actually the largest reservoir of nitrogen, where 78% of the atmosphere is actually nitrogen gas or N2 gas. However, this nitrogen gas is actually biologically unusable to most organisms. What a shame. And so, this nitrogen gas can really enter ecosystems via nitrogen-fixing bacteria that can be found either in the soil or found in the root nodules of plant roots.

And so this unusable form of nitrogen is going to be converted to usable forms of nitrogen, via these nitrogen-fixing bacteria. And more usable forms of nitrogen include nitrates, or NO3-, and Ammonium or NH4+. And those are really the primary forms of nitrogen that plants and other primary producers are able to readily assimilate, absorb, and utilize. And so, let's go ahead and enlarge this image and wipe it clean so that we can take things step by step. And so, again, we know that the largest reservoir of nitrogen is the atmosphere itself, and it's going to contain 78% nitrogen gas or N2.

And this nitrogen gas can enter into ecosystems via nitrogen fixation, which is step number 1 of the nitrogen cycle. And nitrogen fixation can occur via bacteria in the root nodules of some plants, where that atmospheric nitrogen, N2, can be converted into more usable forms of nitrogen, such as ammonium, NH4+, which can be readily assimilated or absorbed by plants. And once plants have assimilated that nitrogen, the nitrogen can make its way up the food chain to other organisms and consumers via consumption. Now nitrogen fixation can also occur via bacteria in the soil, which can again convert the unusable nitrogen gas into more usable forms such as ammonia or NH4+.

Now in step number 2 of this process, we have a process called nitrification, which is also carried out by bacteria called nitrifying bacteria, which can convert the ammonium, NH4+, into another usable form of nitrogen called Nitrate or NO3-. So this NO3- can also be readily assimilated by plants, and once it's in the plants, it can move its way up the food chain to other organisms like this animal you see here. Now eventually, all of these animals are going to die and decompose, and the decomposition process carried out by fungi and bacteria mainly, specifically called ammonification, is the decomposition process that takes organic nitrogen in these organisms and breaks it down into raw forms of nitrogen, such as Ammonium, NH4+.

And so once this NH4+ is regenerated, it can kind of continue to go in this cycle that you see here, cycling between steps 2, 3, and 4. And the way that it can break out of the cycle is via the process of denitrification, which is step number 5 here, where nitrates can be converted back into nitrogen gas via bacteria called denitrifying bacteria. And so really that completes the terrestrial cycling of nitrogen. So now we can talk briefly about the aquatic cycling of nitrogen, and since I'm right in the way here, let me shift over so that you can see this a bit more clearly. There we go.

So over here with the aquatic cycling, really it's going to be very similar to the terrestrial cycling. In fact, we have the numbers here in the arrows that correspond with the numbers in the same processes of the terrestrial. So you can see steps 2, 3, and 4 correspond with steps 2, 3, and 4 here. And really, some of the most notable differences in the aquatic cycling is that the nitrogen fixation is carried out mainly by cyanobacteria, which are these greenish bacteria that we're showing you here in our image. And again, this steps 2, 3, and 4, which are nitrification, assimilation, and decomposition, ammonification, this cycle here can be broken, with this step number 5 of denitrification, which converts again the nitrate into nitrogen gas, completing the aquatic cycle.

Now it also turns out that humans are able to get into this cycling and get into the mix of things as well. So humans are actually able to fix nitrogen industrially to create nitrogen fertilizers, and through the burning of fossil fuels, they can also release reactive nitrogen gases that can help to complete the cycle, but these reactive nitrogen gases can also have other effects as well. For example, many of them can act as greenhouse gases that lead to global warming. Others can actually cause acidic rain, which can be devastating to some ecosystems. And some of these reactive nitrogen gases can actually dissolve the ozone layer, which is a layer in our atmosphere that protects us from solar radiation.

So humans need to be very conscious and aware of their activities and the types of reactive nitrogen gases that they're releasing. Now again, these nitrogen fertilizers can actually be added to the soil to add nitrate to the soil, so it can kind of influence the nitrogen cycle in that way. And through streams and rivers, the nitrogen fertilizers can run off into aquatic ecosystems too, contributing to aquatic cycling of nitrogen as well. Now, one of the last notes that I'll leave you off with is that nitrogen can also be fixed abiotically via lightning and volcanic activity, which is why we show you this thunderbolt right here to remind you of that abiotic fixing of nitrogen that can occur. And so, one thing that I want to draw your attention to is the numbers that you can see, again, throughout this process.

That's 1, 2, 3, 4, and 5. And the numbers that you see here in this diagram correspond really nicely with the numbers that you can see in the table on the next page. So I want to show you that here. Here it is, and you can see those numbers correspond perfectly. So you can use this table here to help facilitate your understanding and learning of the process that we just talked about.

So, here what we have are some of the reactions that occur that are associated with each of these processes. These are the 5 steps of the terrestrial nitrogen cycling and aquatic nitrogen cycling, and then here are some descriptions of each of those processes. So hopefully, this was very helpful to you. Let me move out of the way here so you can see this table, fully. And that concludes this video, so I'll see you on our next one.

You are tasked with restoring a degraded ecosystem that has experienced a shortage of nitrogen. Which of the following steps could you take?

• A. Introduce nitrogen-fixing bacteria, which convert nitrogen gas to nitrogen-containing compounds.
• B. Introduce denitrifying bacteria, which convert nitrate to nitrogen gas.
• C. Introduce nitrifying bacteria, which convert nitrate to ammonium.
• D. All of the above.

Which of the following answers correctly completes the diagram below?

• A. 1 – nitrification, 2 – ammonification, 3 – nitrogen fixation. 
• B. 1 – denitrification, 2 – nitrification, 3 – nitrogen fixation.
• C. 1 – nitrogen fixation, 2 – nitrification, 3 – denitrification.
• D. 1 – nitrogen fixation, 2 – ammonification, 3 – denitrification.

Phosphorus Cycle

In this video, we're going to talk about the 4th biogeochemical cycle in our lesson, which is the phosphorus cycle. You can see this diagram of the phosphorus cycle behind me, which has these two different colored arrows. The yellow arrows represent terrestrial cycling of phosphorus and the reddish arrows represent aquatic cycling of phosphorus. It's important to recall that phosphorus is yet another essential element to all life, as phosphorus is a component of the phosphate groups and nucleotides that make up nucleic acids like DNA and RNA with their sugar phosphate backbones. Phosphorus is also a component of molecules such as ATP, the energy molecule that's essential to so many life processes.

Phosphorus is required for life as we know it, and the phosphorus cycle is important because it helps to recycle phosphorus and ensure that phosphorus is available to all organisms, regardless of what trophic level they're in and regardless of what ecosystem they're in, whether it be terrestrial or aquatic ecosystems. This makes the phosphorus cycle vital to life as we know it. So that being said, let's go ahead and wipe this slate clean so that we can approach this one step at a time. One of the biggest takeaways that you should get of the phosphorus cycles is that unlike the water cycle, carbon cycle, and nitrogen cycle that we discussed in previous lesson videos, the atmosphere is not a reservoir of phosphorus. The atmosphere on earth does not have phosphorus in it.

This means that the phosphorus cycle is typically going to occur in local areas, and there's the cycling of phosphorus is typically going to be local. Whereas with the other cycles that have atmospheric components, those components can move around the earth freely, and that allows the cycling of those other cycles to be more on a global scale. But again, with phosphorus, since it's not part of the atmosphere, it's going to occur more locally. Instead of the atmosphere being the most significant reservoir, the most significant reservoir of phosphorus is going to be these phosphate containing sedimentary rocks, like this rock that you can see right here. Through weathering, exposure to rain and wind and things of that nature, it can actually release the phosphates that are stored in these sedimentary rocks into the soil, and the phosphorus is going to be released mainly in the form of phosphates, PO43−, which can be readily assimilated by primary producers like this plant here.

Once the plants have obtained their phosphorus, the phosphorus can move up the food chain via consumption to other organisms. And then eventually, these organisms are going to die and decompose, and the decomposition process carried out by organisms like fungi and bacteria can return the phosphorus back to the soil in the form of these phosphates, PO43−. This here completes this little terrestrial cycling that we've got going on here. So now let's focus our attention over on the aquatic cycling that we have on the right. And since I'm right in the middle here, let me move out of the way so that you can see this a little bit more clearly.

There we go. When it comes to aquatic cycling, there are several ways that the phosphate can get into the aquatic system and serve as dissolve PO43−, dissolved phosphate. It could occur through weathering of rocks where, again, the weather, exposure to weather, can release the phosphates from those phosphate containing rocks, and rivers and streams can then allow the phosphates to run off into these aquatic ecosystems. Or this process known as leaching can allow for phosphates to move from the soil directly into the aquatic ecosystems. Once the phosphates are dissolved in the aquatic ecosystems, then notice that we have these set of arrows that are number 2, 3, and 4, which correspond with the numbers 2, 3, and 4 that we have over here in the terrestrial ecosystem.

They represent assimilation, consumption, and decomposition. These dissolved phosphates can be assimilated via primary producers such as phytoplankton, then they can be consumed and make their way up the food chain to other organisms such as fish. Then eventually these organisms will die and decompose, and the decomposition process returns the phosphates back to the water. Once these phosphates are in the water, they can undergo a process known as sedimentation, which can reform the rocks, those phosphate containing rocks. These phosphate containing rocks can be re-exposed to the atmosphere via geologic uplift, which can change the shape of the surface of the earth. And again, reexpose those rocks to the atmosphere to complete this cycle.

This here concludes our lesson on the phosphorus cycle, and moving forward, we'll be able to apply these concepts and problems. So I'll see you all in our next video.

Biogeochemical Cycles Example 4

So here we have an example problem that says to complete the phosphorus cycle diagram down below right here by matching the following terms in this word bank to the correct number in the diagram. It says that not all answer options will be used. Recall from our last lesson video that the largest reservoir of phosphorus are phosphorus-containing rocks. It makes sense to start this diagram off here with number 1 with those phosphorus-containing rocks. That is going to be the word that goes into that position.

So for number 1 down below, we can put in 'rock' and then we can cross off 'rock' from the list above. Now, we know that the process of weathering can release the phosphates from those phosphate-containing rocks. So, number 2 here is going to be 'weathering', and we can go ahead and fill in 'weathering' into number 2 down below. Then we can cross off 'weathering' from the list in the word bank. Once the phosphates have been released through weathering, they can make their way into the soil and into freshwater.

From there, the phosphates can be assimilated into organisms, into biomass. Notice that we can return the phosphates back to soil and freshwater from the biomass through the process of decomposition. So this next arrow, number 3, is going to be 'decomposition', allowing the phosphates to return from the biomass back to the soil and or the freshwater. We can go ahead and put 'decomposition' here for number 3 and then cross it off the list from above. As you can see, from the freshwater, the phosphates can run off and end up in the ocean.

So number 4 here is going to be 'ocean', and we can go ahead and fill that in down below. Once the phosphates are in the ocean, then they can begin to sediment back into the rocks. That returns us back to number 1, which again is the 'rock'. This here completes this example problem, and I'll see you all in our next video.

Which of the following statements is true?

• A. Unlike nitrogen, carbon, and water, the atmosphere is not a significant reservoir of phosphorus.
• B. Sedimentary rock is one of the largest reservoirs of phosphorus.
• C. Phosphorus is essential to ecosystems as it’s a major component of nucleic acids & ATP.
• D. All of the above are true.