Carbon and Nitrogen Cycles


Captions are on! Turn off by clicking CC button at bottom right. Follow us on Twitter (@AmoebaSisters) and Facebook! So last weekend, my family bought something
pretty cool. Something we’re sure you’ve always wanted. No, it’s not a pony. It’s a rotating compost bin! Yeah! It’s for compost and it rotates. Which is going to be so awesome because the
rotating part, that allows it to get aeration. You may already know about compost. It’s where biodegradable things can decompose
and the whole idea is—after decomposing, the result is this nutrient rich organic material
that you can provide your plants with. So I’m thinking after a while of adding
leaves, banana peels, grass clippings, twigs, overripe fruit…ok I could keep going but
I won’t…after all these items break down and decompose, I’m hoping to get some nutrient
rich material for my plants. So why am I even talking about this? Well there are two major things that compost
supplies plants with that are so important—carbon and nitrogen. We’re going to spend some type talking about
these 2 elements—and their cycles—because both are so important for life. With so many incredible elements on the Periodic
table, we don’t know if it’s really fair to have a favorite. But we do. It’s carbon. Sorry nitrogen, you’re cool too. But why the love for carbon? Well, we really love how versatile it is. In one form it could make up your pencil led—which
isn’t really lead at all, it’s graphite. It’s a form of carbon. In another form, carbon can make up one of
the hardest substances, diamond. The big 4 biomolecules—carbohydrates, lipids,
proteins, and nucleic acids—they all have carbon. In fact, molecules that contain carbon are
known to be organic molecules. Organic chemistry is a branch of science that
studies the interactions of molecules that contain carbon! Just look at this carbon atom. Ahh, just look at it. It has 4 valence electrons. Carbon has the ability to form tons of compounds. Carbon is often known as a building block
in life for this reason. Now that we understand how important carbon
is, let’s make sure we understand how we get carbon. That means we need to take a look at how carbon
can cycle. First it’s important to understand that
there are carbon reservoirs and that the carbon cycle is really an exchange of carbon among
these reservoirs. Reservoirs being where carbon is basically
hanging out. So here are some major examples of where carbon
is found: Carbon is dissolved in the ocean. It is in rocks and fossil fuels. It is in living organisms. It can be in the atmosphere. So the idea is to understand that carbon cycles
among these reservoirs. Now our time is limited…let’s take a look
at one pathway. Consider carbon dioxide in the atmosphere. It is taken in by organisms that perform photosynthesis. This may be plants, like land plants. It may be algae in oceans or lakes. The carbon becomes a part of that photosynthetic
organism. If the photosynthetic organism is eaten by
an animal, it becomes a part of that animal too. And the animals that eat that animal. Both the plants and animals do cellular respiration
which releases carbon dioxide. When the plants and animals die, the carbon
from their bodies can be stored in sediment over a long period of time—after a very
long time, they can even be converted into a fossil fuels. The burning of fossil fuels produces a lot
of carbon dioxide—and this has also led to the concern of excessive carbon dioxide
in the atmosphere. Carbon dioxide is a ‘greenhouse gas’ which
means that it can trap heat in the atmosphere——-so too much carbon dioxide—-is not a good thing. So what about nitrogen? Nitrogen is a critical element in amino acids,
which are the monomers of proteins—-and an element of nucleotides, which are the monomers
of nucleic acids. And if you remember from our biomolecule video,
proteins and nucleic acids are two very important biomolecules for life. Nitrogen is kind of a big deal in the atmosphere
considering it’s the primary gas in the atmosphere. The thing about nitrogen is that it is much
more useful to organisms when fixed into other, more usable forms. Nitrogen can be fixed by bacteria which could
be living in the soil or even in the roots of some types of plants where the bacteria
live in symbiotic harmony inside the roots—meaning the bacteria get a home in the plant root
and the plants get the benefit of fixed nitrogen. Once again, we’re just looking at one pathway
here in the nitrogen cycle so keep in mind this is just one way for nitrogen to cycle. Ok so let’s take a look at this nitrogen
in the atmosphere. Consider the types of plants that have nitrogen
fixing bacteria living in their roots—the nitrogen is fixed by those bacteria into a
form of nitrogen known as ammonia and ammonium. Nitrifying bacteria in the soil can convert
the ammonium to nitrates and nitrites, forms of nitrogen that plants can also easily use
and assimilate. Then animals can eat those plants and obtain
nitrogen. When both plants and animals decompose, decomposers
return ammonia to the soil in a process called ammonification where it could be reused again. But not all of the nitrates and nitrites get
assimilated by plants, eaten by animals, and then converted back into ammonia. There are also another type of bacteria in
the soil…drumroll….denitrifying bacteria! Denitrifying bacteria in the soil can convert
nitrates and nitrites back into atmospheric nitrogen gas. Again this is one example of nitrogen cycling
through, but keep in mind that this happens in both aquatic and terrestrial environments
and there are other ways for nitrogen to be fixed and cycle. You know how we mentioned that too much carbon
dioxide can be problematic? You want a balance in these cycles. There’s a balance for the nitrogen cycle
too and nitrogen pollution can be problematic. Consider plant fertilizer. Plants love it. It contains a form of nitrogen. Well, if it’s not used responsibly, the
excess nitrogen in fertilizing crops can drain into bodies of water. One reason this could be harmful is that it
will basically cause an aquatic producer heyday! All of the algae and water plants now have
this crazy load of nitrogen for growth. That might sound like a good thing but all
this producer excessive growth is messy—it can block light to the water and when they
die and decompose, all that decomposing uses up a lot of dissolved oxygen in the water
which can be harmful to aquatic life. Phew! You know, this recycling of carbon and nitrogen
is pretty remarkable. Just think—you could contain a carbon atom
that was once part of…a dinosaur! Because of all this recycling. The carbon and nitrogen cycle—just another
beautiful thing connecting all of us. Well I better get back to my compost. That’s it for the amoeba sisters and we
remind you to stay curious!

42 thoughts on “Carbon and Nitrogen Cycles

Leave a Reply

Your email address will not be published. Required fields are marked *