If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:7:55

Biogeochemical cycles overview

Video transcript

talk a little bit about biogeochemical cycles and the term biogeochemical sounds very fancy but really these are just cycles that involve different molecules that are essential for life and how they circulate through an ecosystem and really how they circulate through the entire through an entire biosphere and the molecules that we care about and molecules they could consist of one element or multiple elements they are things like well water molecules h2o oxygen and hydrogen make up a lot of living a lot of living creatures a lot of biomass and and water is just an essential element that is involved in life as we know it we're also going to be talking about carbon and carbon takes on many forms when we think about biogeochemical cycles there's carbon dioxide in the air there's a lot of carbon inorganic molecules that form up most of the mass of life as we know it and then there's actors that maybe don't get as much attention there are things like nitrogen and of course you have characters like characters like phosphorus and you might say okay I get that most organic molecules are made up of a bunch of carbons and hydrogen's and every now and then oxygens but what about nitrogen's and what about phosphorous and remember your DNA deoxyribonucleic acid we're talking about nitrogenous bases your Adnan's and guanine and all of these things that we talked about in DNA they involve nitrogen and there's other biomolecules amino acids proteins amino acids which make up proteins that involve nitrogen phosphorus ATP the the identity tri phosphate it's essential it's an in that in that core biomolecule it's also in the backbone of DNA so these are all essential elements for life and the key thing is is that they all get recycled through biogeochemical cycles so they are all recycled we talked about how an ecosystem energy flows it might start with light energy from the Sun and then over time as it's transferred from one form to another as it flows one form to another it gets dissipated as heat but the matter the elements the molecules here this is recycled it was originally formed I mean there's a few meteorites that hit every now and then but the foot most part most of the matter around us was here at the dawn of when the earth was first formed it was first created in the in the inside due to fusion reactions of stars billions and billions and billions of years ago so all of life everything that we've seen so so far in the history of Earth for the most part is just the same elements and the same molecules that have been recycled over and over and over again and so when we think about biogeochemical cycles we will think about things like if we're talking about h2o we're going to think about the water cycle water cycle and we have a whole video on that but in vist the short version of it is you could have water actually stored into multiple different ways some of it can evaporate as water vapor eventually it condenses in the form of clouds and then it can rain back down and along the way you can have animals get access especially to the fresh water and make that part of the actual living organisms you actually also have living organs that view the water as part of their ecosystem but we go into some depth in another video you'll also hear people talk about if we're talking about carbon the carbon cycle the carbon cycle and just as a very high-level overview of the carbon cycle so let's say that's the ground let's say that this is a plant right over here it's a primary producer an autotroph we talked about that in our ecosystem video so let me draw a leaf here this is a plant that is growing what it's doing while it takes light energy so it gets light energy from the Sun so that's the light energy right over there and it uses that light energy to fix carbon the carbon that is making up this plant it's just not emerging out of nowhere it's being recycled it's being recycled from carbon molecules that are in the air so the carbon molecules in the air they are going to be or the carbon in the air it's going to be in molecular form in terms it's going to be carbon dioxide so that over there is co2 and so the plant uses that light energy and that gaseous that co2 gas and it's able to fix the carbon to construct it so it looks like that plant is just growing it's not clear where all that mass is coming from but it literally is coming from the air and it might be able to get it might get a few of the nutrients especially things like nitrogen phosphorus from the ground and that's where we could go into the whole nitrogen and phosphorous cycles but then once these plants fix all of this carbon some of it it gets stored in the biomass sometimes the plant dies and then it gets buried and then with enough pressure it can turn into hydrocarbons so hydrocarbons when you fuel your car it's really it's really energy stored by dead plants a long long time ago that got buried and put into that form but it was essentially plants through photosynthesis that first store that energy but then of course and we talked about this you can have animals that eat those plants so let me draw an animal that is eating it so that looks like an animal well that one looks like something that likes to eat more than just plants so this is weed right like it's like an alligator chicken looking thing well that's close enough well you get the idea what it eats that plant it's using some of that carbon that was fixed originally by that plant for its own biomass but also as it as it metabolizes the some of it is that it will use that the the bond the energy stored in those chemical bonds to to live and grow and move about and as it does that it will it will exhale the co2 so that the co2 goes back into the environment and this is a huge oversimplification of the carbon cycle but this is the general idea and eventually this thing might die or might get eaten by other other consumers and then you have the decomposers down here who could further make use of those chemical bonds that the primary producer first created using that light energy let me deke um decomposers right over here and they might also as they consume that release more co2 which will eventually then get fixed again by a primary producer and there's similar cycles for nitrogen and phosphorus these often involving bacteria to fix the nitrogen in the phosphorus from the air to make it available as nutrients in the soil for some of the primary producers in say the carbon cycle and nitrogen doesn't get a lot of attention but this is actually the most common gas in our atmosphere so it's all around you right now even while we're breathing we are breathing a lot of nitrogen although it doesn't play as strong of a role as say oxygen and the oxygen in the air is going to be molecular oxygen so I could also write oh - right over here or as we breathe out carbon dioxide so I could write see co2 co2 right over there but hopefully this gives you a sense of how matter is recycled as energy is flowing through ecosystems including the largest ecosystem on earth which is earth as a biosphere you have matter being constantly recycled and the the cycle of that matter we call biogeochemical cycles I think I just said the word cycle a lot
Biology is brought to you with support from the Amgen Foundation