Video Transcript
In this video, we will explore the
key steps of the carbon cycle, how carbon is used in organisms, and we will have a
look at some chemical reactions occurring at the different stages of the carbon
cycle.
Carbon is the key element for life
for all organisms, both on land and in bodies of water such as oceans and
rivers. Most molecules found in living
organisms have carbon as the backbone element. Carbon in the backbone is bonded to
other elements like oxygen, hydrogen, sulfur, and nitrogen. These carbon-based molecules in all
living organisms include proteins, carbohydrates, lipids, DNA, and much more. Carbon is also an important
component of the atmosphere, found predominantly as carbon dioxide and also as some
other gases, for example, methane, CH4.
In the ground, carbon is found in
the form of limestone and fossils, as well as fossil fuels like coal, natural gas,
and oil. And in the bodies of water of the
earth, including oceans and rivers, carbon is found in the form of dissolved carbon
dioxide, carbonic acid, which is H2CO3, and bicarbonate ions, HCO3−. These three substances have a close
relationship. Carbon constantly cycles and
recycles through these living and nonliving factors in a cycle known as the carbon
cycle.
Let’s start the journey through the
carbon cycle with atmospheric carbon, which exists mostly in the form of carbon
dioxide gas. Carbon dioxide is absorbed by
plants and some bacteria on land and by plankton and algae in the oceans and
rivers. These organisms use carbon dioxide
along with water to produce organic, carbon-based compounds like simple
carbohydrates such as glucose during a process called photosynthesis. These simple compounds are then
converted to more complex compounds like proteins, lipids, et cetera. Energy from sunlight is used to
drive the photosynthesis reaction, and oxygen gas is also produced. The general photosynthesis equation
is 6CO2 plus 6H2O reacting together in the presence of sunlight to give glucose
C6H12O6 plus 6O2. Carbon in its various complex forms
in photosynthesizing plants and other producers can then enter food chains and food
webs when animals consume or eat plant matter. And so, carbon in its various forms
can move from animal to animal in this way.
All living organisms in the food
chains and food webs, including producers like plants themselves, undergo cellular
respiration and release carbon back to the atmosphere as carbon dioxide. The general equation for cellular
respiration in plants and animals is C6H12O6 plus 6O2 reacting to give 6CO2 plus
6H2O plus ATP. Respiration produces ATP, adenosine
triphosphate, a molecule used to transfer or deliver energy in living cells to drive
many cellular processes. So far, we have seen that plants
absorb carbon during photosynthesis and all organisms release carbon during
respiration.
Carbon can move from some animals
to the atmosphere as methane during food digestion or to the soil as waste products
such as manure and urine. Wastes in the soil from animals as
well as dead plant and animal organisms are broken down by decay organisms in the
soil in a process known as decomposition. Decomposition could be considered a
type of respiration because organic compounds and oxygen in the cells of the
decomposer organisms produce similar products to respiration. The general equation for
decomposition is organic compounds plus O2 reacting to give H2O plus CO2 plus
inorganic nutrients and energy.
The carbon dioxide gas produced
from the decay of rotting matter goes back into the atmosphere. And the inorganic nutrients
produced from decomposition include nitrates and phosphates, which go back into the
soil, and are used again by growing plants. Not all the carbon in dead decaying
organic matter is converted to carbon dioxide gas; some of it over long periods of
time and high pressure is converted to underground limestone deposits as well as
fossils and deposits of carbonaceous fossil fuels. Some of these fossil fuels include
coal, natural gas, and oil.
The fourth main key step in the
carbon cycle is a process called combustion. This part of the carbon cycle is
largely driven by human activity and the burning of fossil fuels. The emissions produced from the
burning of fossil fuels and factories and in vehicles releases carbon dioxide back
to the atmosphere. The equation for combustion is
similar to that for respiration and decomposition. The general equation is a fuel,
usually a fuel is made of carbon and hydrogen, plus O2 reacting to give CO2 plus H2O
and releases energy. Carbon dioxide and water are the
products of combustion when sufficient oxygen is present. However, CO or carbon monoxide is
also a possible carbon product produced from combustion when there is not sufficient
oxygen. Carbon monoxide is another form of
carbon in the carbon cycle.
Besides human-related combustion,
some natural processes release underground carbon to the atmosphere to land and to
oceans. These natural processes include
volcanic eruptions and emissions. When large quantities of land are
deforested and are not sustainably replanted, the balance of CO2 removal from the
atmosphere by photosynthesis may be influenced. This could lead to a variety of
environmental problems. These potential problems, such as
the greenhouse effect, are a topic for another video. Now, it’s time to practice some
problems and then summarize everything we have learnt.
What is the name given to an
organism that releases carbon dioxide into the atmosphere by breaking down dead
organic material? (A) Scavenger, (B) decomposer, (C)
composter, (D) carbon dioxider, or (E) decayer.
An organism that breaks down dead
organic material and releases carbon dioxide is part of one of the key steps in the
carbon cycle. The four main processes in the
carbon cycle are photosynthesis, respiration, decomposition, and combustion. In photosynthesis, carbon dioxide
is removed from the air. This happens in green plants,
algae, some bacteria, and phytoplankton. 6CO2 molecules react with six water
molecules, and sunlight energy is used to convert these into glucose, C6H12O6, and
six oxygen molecules.
The carbon from carbon dioxide in
the atmosphere is incorporated into organic molecules inside the plants. In the other three main processes
of the carbon cycle, carbon dioxide gas is released to the air. Their equations are very
similar. They all involve a carbon compound
reacting with oxygen to produce CO2 and water, as well as energy or molecules which
transfer energy. The question asks about the release
of carbon dioxide. So, we know the question is not
talking about photosynthesis, and we can eliminate it. The question asks about the
breaking down of dead organic material.
Let’s look at the remaining three
processes to see which one involves the breaking down of dead organic matter. Respiration is a process which
occurs in every living cell with a plant or animal. The purpose is to produce ATP
molecules from food, and ATP delivers energy to drive cellular processes. Decomposition occurs in decomposer
organisms. Decomposition is a type of
respiration where dead organic material is the food for the decomposer organism. Combustion, though it has a similar
equation to respiration and decomposition, is a human activity. Combustion is the burning of fuel,
such as fossil fuels, for example, coal, oil, and natural gas. So, we can see that an organism
that releases carbon dioxide by breaking down dead organic material is a
decomposer.
Match the equations to the
processes. A: CH4 plus 2O2 giving CO2 plus
2H2O, B: 6CO2 plus 6H2O giving C6H12O6 plus 6O2, C: C6H12O6 plus 6O2 giving 6CO2
plus 6H2O. And the possible processes are 1:
photosynthesis, 2: combustion, 3: respiration. The answer options are (A) A:3,
B:2, C:1; (B) A:2, B:3, C:1; (C) A:1, B:3, C:2; (D) A:1, B:2, C:3 ;or (E) A:2, B:1,
C:3.
In the four main processes of the
carbon cycle, photosynthesis is the only one which removes carbon dioxide from the
atmosphere. In producers such as green plants,
phytoplankton, some bacteria, and algae, carbon dioxide and water react together in
the presence of energy from sunlight to produce glucose and oxygen. Equation B and process 1 belong
together. The other three processes produce
carbon dioxide by very similar equations. The general equation for these
three processes is carbon compound plus oxygen forming carbon dioxide and water. In respiration, glucose reacts with
oxygen to produce carbon dioxide, water, and ATP. And this happens in every living
cell, both plant and animal. ATP is the molecule which transfers
or delivers energy to carry out cellular processes. We can see that equation C and the
process respiration belong together.
Combustion is the process of
burning of fuel in the presence of oxygen to produce carbon dioxide, water, and
energy. The equation in purple is a
specific example of a fuel burning and oxygen. Here, the fuel is methane gas,
CH4. This equation is the same as
equation A and matches or belongs to process 2, combustion. So, equation A belongs to process
2; equation B, process 1; and equation C, process 3. The last process in the carbon
cycle, decomposition, also produces carbon dioxide, water, and energy, as well as
inorganic nutrients which go back into the soil, for example, nitrates and
phosphates.
In this video, we learned that
carbon is the key or backbone element to molecules in all living organisms. We learned that carbon is found in
different forms or substances in organisms, in the atmosphere, in the soil and deep
underground, and in bodies of water such as oceans and rivers and that carbon in its
various forms cycles through these living and nonliving factors continuously. We learned that carbon as carbon
dioxide moves from the atmosphere into plants, phytoplankton, and algae during
photosynthesis and is converted into many other carbon products. And these organic compounds then
are transferred into animals in food webs when consumed or eaten.
We learned that carbon as carbon
dioxide moves from plants and animals and all living organisms back to the
atmosphere during respiration. We saw that carbon from dead
organisms moves back into the air as carbon dioxide and back into the soil through
waste products during decomposition. And we learned that when fossil
fuels are mined from the ground and burnt or combusted, that carbon returns back to
the atmosphere once again as carbon dioxide.
