Did you know the average person burns around 1,800
calories of energy a day doing absolutely nothing? Yep, you heard that right. 1,800 calories doing
absolutely nothing. You'll probably burn twelve calories or so just from watching this video,
not to mention the energy you'll burn from taking notes, stretching, thinking about what's
for dinner. That's right, even thinking requires energy and yes, thinking about how thinking
costs you energy also costs you energy. Every living thing needs en
ergy to survive
and flourish, from microscopic bacteria thriving in underwater volcanoes to majestic
eagles soaring through the stratosphere. So, where do living things
get all this energy from, and more importantly, how is this energy
captured and used in a reliable way? In today's lesson, we'll explore this and more as
we describe three processes of cellular metabolism and explain how cells use each of these processes
to obtain and utilize energy. Let's get into it. Cellular metabolism i
s the set of chemical
reactions that occur in living organisms in order to maintain life. Remember, our
bodies strive for homeostasis, or, balance, and cellular metabolism, like cellular transport,
is essential for maintaining this balance. While cellular transport deals with moving
resources in and out of cells, cellular metabolism involves reactions that chemically change these
resources, allowing cells to capture and store energy that is essential for their survival. There
are three mai
n forms of cellular metabolism we will discuss today and they are photosynthesis,
cellular respiration, and fermentation. To understand how energy flows through living
things, we have to start with the source - the sun. The sun provides all of the energy needed to
sustain life on Earth. Sunlight enables the growth of vast jungles, towering redwood forests,
and sprawling grasslands, supporting life in countless ecosystems including deserts, mountains,
marshes, and tundras. It permeates our o
ceans, filtering energy into massive kelp forests
and coral reefs, which in turn provide food and sanctuary for many other living organisms. So,
if sunlight is the original source of energy, how do plants and other organisms capture the sun's
energy to make Earth's rich ecosystems possible? The sun's energy is captured in a process called
photosynthesis, which is a series of reactions occurring in the presence of sunlight that
create glucose, or, sugar. Photosynthesis occurs in specialized
organelles called chloroplasts,
which can only be found in some organisms such as plants, algae, and special types of bacteria.
The green color of this organelle and consequently most plants comes from the pigment chlorophyll,
which is used to absorb the energy from sunlight. Once light energy is absorbed, it sets off a chain
of reactions that is summarized by this equation: 6CO2 plus 6H2O plus sunlight
yields C6H12O6 plus 602. C6H12O6 is the chemical formula for glucose,
or, sugar, which
has six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.
Notice anything about our equation? If you count up all the carbons hydrogens
and oxygens on each side, they match. Plants can't create glucose, nature's miracle
food, out of nothing. The word photosynthesis comes from the words photo, meaning "light",
and synthesis, which means "put together". Plants and other photosynthesizing organisms
use chemical reactions to put together glucose, or, sugar, using water, carbon
dioxide
, and energy from sunlight, while producing oxygen as a waste product. Plants
use the glucose they make in a variety of ways, but the main purpose is to help them grow.
All plants on Earth, even this mighty redwood, start from humble beginnings such as seeds or
spores, and build themselves over time out of a starch called cellulose, which is basically a
ton of glucose chained together. Plants also use glucose to build additional sugars, starches, and
fats found in fruits, vegetables, seeds,
and nuts. Plant-eating organisms then eat these
resources, breaking them back down into glucose, giving rise to massive food webs. This glucose
is relied upon for food by almost every living thing that can't photosynthesize, so it's hard
to overstate the importance of this process. And that's not all. Trees and other
photosynthesizing organisms act as natural air filters, regulating the amount of
carbon in the atmosphere by taking carbon dioxide out of the air and replacing it with oxygen
gas,
which is a vital resource for many living things. In order to understand just how important oxygen
is, we'll need to talk about a process called cellular respiration. Cellular respiration is
a series of reactions occurring in the presence of oxygen by which glucose is broken down to
create ATP. ATP, or, adenosine triphosphate, is a molecule that stores and carries energy
within cells. Your cells are constantly spending ATP to survive and cellular respiration is their
way of replenishi
ng it so they don't run out. The term respiration means the act of breathing,
so you can think of cellular respiration as breathing at a cellular level. It is important
to understand that it is our individual cells that need oxygen gas specifically for this process
of creating ATP, which is why we breathe at all. Cellular respiration occurs in the
mitochondria, or, powerhouse, of the cell. It's worth noting that plants have mitochondria
and do in fact perform cellular respiration as well; t
hey just have the added benefit of making
all the glucose needed for this process in-house. To find out what other materials are involved,
let's take a look at the chemical equation for cellular respiration. C6H12O6 plus 602 yields 6CO2
plus 6H2O plus ATP. Remember, C6H12O6 is glucose. As you might notice, this equation for cellular
respiration is very similar to photosynthesis, just in reverse order and involving stored energy
as ATP instead of sunlight. With this process, organisms breath
e in oxygen and consume glucose
in order to produce stored energy while expelling water and carbon dioxide as waste products.
Carbon dioxide and water are then used by plants for photosynthesis to create glucose and oxygen,
repeating the cycle. In this way, photosynthesis and cellular respiration complement each other,
recycling each other's waste to maintain a healthy balance of resources on Earth, all while
keeping energy flowing through living things. Okay, we've now covered how organism
s capture
energy using oxygen. But what happens when oxygen isn't present? In this case, is it
possible for cells to make any energy at all? Well, actually they can, but it is not nearly as
efficient at creating ATP as cellular respiration. Fermentation is a chemical process occurring
without oxygen by which glucose is broken down to create ATP. The big difference between
cellular respiration and fermentation is that one cycle of cellular respiration generates a whopping
thirty-eight ATP m
olecules while fermentation only yields a measly two from the same amount
of glucose. And to add insult to injury, fermentation creates byproducts like ethyl
alcohol and lactic acid that clog up cells. The type of byproduct depends on the type of
fermentation. If you've ever exercised so hard that you struggle to breathe and felt that heavy,
achy feeling in your muscles, you know what lactic acid feels like. Your body performs lactic
acid fermentation when your lungs can't keep up with the
oxygen demands of your muscles,
or, there simply isn't any oxygen present. It's good to know our bodies have a backup
system in place, but fermentation is definitely not a good way for us to obtain energy in the
long term. Plants and other organisms can use fermentation as well, but typically only do so
when oxygen is scarce. However, some organisms only use fermentation to generate ATP. Bacteria,
such as lactobacillus, survive by using lactic acid fermentation. Yogurt and cheese are exampl
es
of food created from this fermentation process. Another example is yeast, which is a fungus
that ferments sugars and is responsible for making bread rise or puff up when baked. As you
can see, fermentation is important for a variety of organisms, either as a backup energy system or
a main source of energy. Additionally, organisms that perform fermentation also release CO2 as a
waste product, which helps plants photosynthesize. All right, we have now covered the basics of
cellular metabo
lism, which is how organisms use chemical reactions to maintain life. One of
these metabolic processes is photosynthesis, which harnesses the energy from sunlight to convert
carbon dioxide and water into glucose and oxygen. Another process is cellular respiration,
which uses the glucose and oxygen created by photosynthesis to create carbon dioxide, water,
and ATP, which is the energy currency of living things. Glucose can also be used to create ATP
through the process of fermentation, but t
his process is not nearly as efficient at creating ATP
as cellular respiration. In our next lesson, we'll dive deeper into cellular processes as we unravel
the mysteries of the cell cycle. Until then, I'm Caroline. And remember, life is full of wonders
so keep learning and don't ever stop wondering.
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