Video Transcript
In this video, we will learn about
the process of cellular respiration and how it provides energy for cells and
organisms. Then we’ll try some practice
questions. And finally, we’ll summarize what
we’ve learned.
You’re likely aware that our bodies
use the food that we eat to generate energy. Recall that your body consists of
many organ systems; each of which consists of many organs. Each organ is made of several
tissues, and tissues consist of many cells. The cells of your body look
something like this. And they contain several
organelles, which are subcellular structures specialized to carry out a specific
function. Do you know which organelle is
responsible for producing cellular energy? Absolutely, the mitochondria
produce cellular energy.
Our cells need energy to do work,
and that work is different depending on the cell. Muscle cells need energy to
contract and cause movement. Nerve cells need energy to carry
impulses throughout your body. And your white blood cells need
energy to fight off infections and keep you healthy. Cells need energy to carry out all
the essential functions that keep us alive. And the mitochondria provide the
energy that the cells need to do their jobs.
All living organisms use a form of
cellular respiration to break down nutrients to generate energy. Usually this energy is in the form
of a molecule called ATP, which we’re gonna discuss a little bit more next. If cellular respiration utilizes
oxygen, we call it aerobic respiration. And if cellular respiration does
not utilize oxygen, we refer to it as anaerobic respiration. An- is a prefix meaning not. For now, we’re gonna further
investigate aerobic respiration, and we’re gonna start with this molecule ATP. ATP stands for adenosine
triphosphate. It’s the molecule that provides the
energy for almost all cellular processes in almost all living things.
You may be interested to know that
adenosine triphosphate, or ATP, is composed of the nitrogen containing base adenine
and a ribose sugar, which is hopefully reminding you of the structure of a
nucleotide. However, instead of one phosphate
group like a nucleotide, ATP has three, which is the origin of the tri- in
triphosphate. ATP is an energy-rich molecule,
meaning that there’s lots of energy stored within its chemical bonds, especially
here between the second and third phosphate groups. So when our cells need energy to do
their work, they take a molecule of ATP and break off that last phosphate group,
freeing the energy stored in that high-energy chemical bond. The remaining molecule is called
ADP or adenosine diphosphate, di- being a prefix meaning two.
Well, our cells need lots of
energy, and it would take so much time and resources to make all of the ATP our
cells need from scratch. Instead, one molecule of ATP can be
recycled to ADP and back thousands of times. To provide power for cellular
processes, energy is released from ATP by breaking off a phosphate group, creating
ADP. That same ADP molecule can be
converted back into ATP by reattaching a phosphate group. This occurs through a complex set
of metabolic reactions known as cellular respiration. Cellular respiration is a chemical
reaction, so we’ll represent it with a chemical equation. You might’ve learned in chemistry
that the chemicals to the left of the arrow in a chemical reaction are the reactants
and the chemicals to the right of the arrow are the products.
Well, since what we’re discussing
is aerobic cellular respiration, we know that one of the reactants is oxygen. We also learned a little bit
earlier that cellular respiration is the process of cells breaking down nutrients
for energy. The nutrient that our cells
typically use for cellular respiration is glucose, a type of simple sugar. The oxygen and glucose are broken
down and rearranged into carbon dioxide and water, a process which releases energy
that’s used to generate ATP. A chemical reaction that releases
energy is called an exothermic reaction. In fact, some of the energy created
during cellular respiration is actually given off as heat. Also important to know is that
energy in this chemical equation is represented in parentheses or brackets. That’s because while energy is
released, it’s not technically a product of the chemical reaction.
Now that we’ve explored the
chemical equation for cellular respiration using words, we’ll go ahead and try to
look at it using the proper chemical symbols. The chemical symbol for oxygen is
O2 because there are two atoms of oxygen in every molecule of oxygen. The chemical symbol for glucose is
C6H12O6, and a molecule of glucose looks something like this. If you counted up the atoms in this
molecule, you would see that there are six atoms of carbon, 12 atoms of hydrogen,
and six atoms of oxygen. For the sake of simplicity, we’ll
represent the components of the glucose molecule like this. The chemical symbol for carbon
dioxide is CO2 because carbon dioxide contains one atom of carbon and two atoms of
oxygen. The chemical symbol for water is
H2O. Water contains two atoms of
hydrogen and one atom of oxygen.
So now we have represented our
cellular respiration equation using chemical symbols. But the number of atoms that we
have in our reactants is higher than the number we find in our products. In order for this to be a balanced
chemical equation, we need to have the same number of carbon, hydrogen, and oxygen
atoms in our reactants as we have in our products. In order to balance this chemical
equation, we’ll need to add some coefficients. So our balanced chemical equation
looks like this. It takes six molecules of oxygen
and one molecule of glucose to generate six molecules of carbon dioxide and six
molecules of water and to release the energy that our cells use to make ATP. Try counting up the atoms on each
side of this equation to make sure that we balanced it properly.
Before we move on to our practice
questions, let’s take a moment to look at how the process of breathing, also called
respiration, is related to the process of cellular respiration. Cellular respiration primarily
takes place within the mitochondria. Mitochondria are bean-shaped
organelles that possess a folded inner membrane and many types of enzymes to
facilitate the complex set of chemical reactions, which convert glucose and oxygen
into carbon dioxide, water, and energy, which is used to generate ATP, which powers
almost all of our cellular processes. Well, glucose is a sugar made from
the nutrients we get from our food or, in plant cells, glucose is a product of
photosynthesis. And the water in our bodies is
recycled and used for many different purposes. But what about the oxygen and the
carbon dioxide?
Well, you may have already
guessed. When we breathe in, oxygen from the
air enters our lungs. And from there it’s pumped through
the bloodstream to each of our cells, where the mitochondria use it to carry out
cellular respiration, producing carbon dioxide as a waste product, which enters the
blood and is pumped back to the lungs, where it’s removed from our bodies when we
exhale. And this is why the respiration
which occurs in our cells and the respiration which occurs in our lungs have the
same name.
This also helps to explain why
cells that are more active will have more mitochondria inside of them. For example, you could expect to
find more mitochondria in a muscle cell than in a skin cell. This also helps to explain why as
you do more physical activity, like exercise, your respiration rate or breathing
rate will increase. When you’re more physically active,
you need to breathe in more oxygen so that your cells can make more ATP to keep your
body moving.
Well, now that we’ve learned a
little bit about aerobic respiration, why don’t we try some practice questions
together?
Not including energy or ATP, state
the correct word equation for aerobic respiration.
This question is asking us to
recall the word equation for aerobic respiration. Since our final product will be a
word equation, while knowing the chemical symbols will come in handy, we’re not
going to include them in our final answer. Another thing we’ve been told not
to include is energy or ATP in this word equation. So while we know that they’re the
purpose of aerobic respiration, we’re gonna go ahead and leave them out of our
answer. Our final word equation should have
the reactants for aerobic respiration on the left side of an arrow and the products
on the right.
In order to answer this question,
let’s review what we know about aerobic respiration. Here, we see our busy biology
student. They are breathing, they’re eating
an apple as a healthy snack, and their heart is beating, pumping blood all
throughout their body. And all of these things are
essential to the process of aerobic respiration. Cellular respiration is the process
of breaking down nutrients for energy. And every living organism carries
out some form of cellular respiration. And the word aerobic means that
this is specifically a type of cellular respiration that uses oxygen. So we know that our reactants have
to include some type of nutrients as well as oxygen.
Let’s take a closer look at our
student and his cells. Our student receives their
nutrients from the food they eat. They’re broken down in the small
intestine and absorbed into the bloodstream, where they’re transported to our cells
primarily in the form of glucose. Our student also breathes in oxygen
from the air, which enters the lungs and is absorbed into the bloodstream, which
distributes it to the cells of our bodies. Recall that each cell contains
mitochondria, which are bean-shaped organelles that are the site of cellular
respiration. They possess a folded inner
membrane and several different types of enzymes that facilitate the complex
metabolic reactions that allow them to convert oxygen and glucose into carbon
dioxide and water and releasing energy that’s used to form ATP, which is a molecule
that powers almost all of our cells’ essential functions.
The water is largely recycled, but
the carbon dioxide diffuses out of the cells and back into the bloodstream, which
carries it back to the lungs, where it’s removed from our bodies when we exhale. So breathing takes in oxygen and
removes carbon dioxide, eating provides nutrients, especially glucose, and your
circulatory system, driven by your heart, carries all of these materials from place
to place, which allows our cells to make the ATP that provides the cellular energy
that they use to do their jobs. So in response to our question,
aerobic respiration is the process of converting oxygen and glucose into carbon
dioxide and water, which releases energy to power our cells.
Let’s try another practice
question.
Which of the following is correct
about cell activity and the number of mitochondria? (A) The more active the cell, the
lower the number of mitochondria. (B) There is no correlation between
the activity of the cell and the number of mitochondria it contains. Or (C) the more active the cell,
the higher the number of mitochondria.
This question is asking us to read
each of the statements and to choose the one that is correct or true about the
relationship between cell activity and the number of mitochondria. In order to visualize information
regarding relationships, it’s often helpful to sketch a little graph. We’ll let the 𝑥-axis represent
cell activity and the 𝑦-axis represent the number of mitochondria. Choice (A) states, the more active
the cell, the lower the number of mitochondria. So we can expect this graph to look
something like this. Choice (B) states that there’s no
correlation between cell activity and mitochondria number. So we might expect a graph of this
information to look like this. Choice (C) says the more active the
cell, the higher the number of mitochondria. So we can expect a graph of this
information to look something like this.
Well, what do we know about
mitochondria? Recall that mitochondria are
bean-shaped organelles found inside of almost all eukaryotic cells. Also recall that mitochondria are
the site of cellular respiration, a process that converts oxygen and glucose into
carbon dioxide and water, a process which releases energy. This energy is used to produce a
molecule called ATP, which is used to power almost all cellular activities or
functions. So if a cell is more active, it
would require more energy, which is generated in the mitochondria.
So as cellular activity increases,
you expect the cell’s need for energy to also increase. And since mitochondria produce
cellular energy through cellular respiration, it’s also reasonable to expect their
number to increase. So returning to our answer choices,
the statement that’s correct about the relationship between cell activity and the
number of mitochondria is the more active the cell, the higher the number of
mitochondria.
Let’s take just a moment to review
what we’ve learned in this video. We’ve learned that cellular
respiration is the process of breaking down nutrients to release energy and that
aerobic is a word that means using oxygen. So aerobic respiration is cellular
respiration that uses oxygen. We also learned about the chemical
equations that represent the complex metabolic processes that go into cellular
respiration. And we reviewed how your lungs and
mitochondria work together in this process to produce a molecule called ATP that’s
used to power almost all of our cells’ activities.
