section
4.4
Overview of Cellular
Respiration
Teacher Notes and Answers
SECTION 4
Instant Replay
1.It means that it needs oxygen to happen.
2.6CO2 molecules and 6H2O molecules should be
circled.
Vocabulary Check
1.aerobic and anaerobic
2.glycolysis
3.Krebs cycle
4.cellular respiration
The Big Picture
5.mitochondria
6.reactants: C6H12O6 and 6O2, products: 6CO2 and
6H2O
7.the electron transport chain
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section
4.4
4B, 9B
Overview of Cellular
Respiration
Key Concept The overall process of cellular respiration converts sugar into
ATP using oxygen.
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Cellular respiration makes ATP by breaking down sugars.
You probably know that you need to breathe oxygen to survive. But
how does your body use that oxygen? That oxygen helps your body to
release chemical energy that is stored in sugars and other carbonbased molecules. The energy is released to produce ATP. This process
of using oxygen to produce ATP by breaking down carbon-based molecules is called cellular respiration. Cellular respiration makes most
of the ATP that a cell needs. Cellular respiration is an aerobic process.
Aerobic (air-OH-bihk) means that it needs oxygen to happen.
Cellular respiration takes place in mitochondria. These organelles
are sometimes called the cell’s “powerhouses” because this is where
most of the cell’s ATP is made. Mitochondria do not make ATP
directly from food. ATP is made through many chemical reactions.
Before cellular respiration can happen, food has to be broken down
into smaller molecules. Food gets broken down into smaller molecules like glucose. Then, glucose gets broken down. Remember that
glucose is a six-carbon sugar. Glycolysis (gly-KAHL-uh-sihs) breaks
glucose into two molecules that each have three carbons.
2
C C C C C C
glucose
ADP
2
ATP
Mitochondria (middle) are
found in both animal (top)
and plant (bottom) cells.
They make ATP through
cellular respiration.
C C C
C C C
2 three-carbon molecules
Glycolysis breaks glucose into 2 three-carbon molecules.
Glycolysis is an anaerobic process. Anaerobic means that it does not
need oxygen to happen. Glycolysis happens in the cell’s cytoplasm. The
three-carbon molecules from glycolysis then enter the mitochondria.
The products of glycolysis—the three-carbon molecules—enter the
mitochondria and are used in cellular respiration.
Why is cellular respiration called an aerobic process?
Interactive Reader
65
Cellular respiration is like a mirror image of photosynthesis.
COMPARING Processes
Photosynthesis
REACTANTS
light
energy
light
energy
CO2
Sugars (C6H12O6)
H2O
O2
Cellular Respiration
PRODUCTS
Sugars (C6H12O6)
H2O
O2
ATP,
heat
ATP,
energy
heat
energy
The products of photosynthesis—sugars and
O2 —are the reactants in cellular respiration.
Stage 2: Electron Transport Energy is moved through a chain of proteins and a large number of ATP molecules are made. Oxygen enters the
process here. The oxygen is used to make water molecules, which are
waste products.
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REACTANTS
CO2
Stage 1: Krebs cycle The molecules from glycolysis enter a series of
reactions called the Krebs cycle. The Krebs cycle produces a small
amount of ATP and other molecules that carry energy to the next part of
cellular respiration. It also makes carbon dioxide as a waste product.
66
PRODUCTS
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A mirror image is like an opposite—the same
thing, but in reverse. Cellular respiration and
photosynthesis are not really opposites, but it can
be helpful to think about them in that way. Photosynthesis makes sugars and cellular respiration
breaks down sugars. The chemical equations of the
two processes are basically opposites.
The structures of mitochondria and chloroplasts are very similar. Remember that part of
photosynthesis happens inside the stroma—
the fluid in the chloroplast—and part of photosynthesis happens inside the membrane of the thylakoid. Similarly, part of cellular respiration happens
in the fluid inside the mitochondria, called the
matrix. The other part of cellular respiration
happens in the inner membrane of the
mitochondria.
After glycolysis, the three-carbon molecules
enter the mitochondria and begin the process of
cellular respiration. There are two main parts of
cellular respiration:
overview of cellular respiration
STAGE 1: Krebs Cycle
1
Three-carbon molecules
from glycolysis enter
cellular respiration in
mitochondria.
mitochondrion
matrix (area enclosed
by inner membrane)
ATP
AND
2
energy
6CO2
Energy-carrying
molecules transfer
energy to Stage 2.
STAGE 2: Electron Transport
3
Energy-carrying molecules from
glycolysis and the Krebs cycle enter
Stage 2 of cellular respiration.
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inner membrane
ATP
energy from glycolysis
AND
AND
6H2O
6O2
4
ATP molecules are produced.
Heat and water are released
as waste products.
Up to 38 ATP molecules are made from the breakdown of one glucose
molecule. The equation for cellular respiration is shown below. You can
see that there are many arrows between the reactants—C6H12O6 and
6O2—and the products—6CO2 and 6H2O. These arrows are there to tell
you that there are many steps in the process. For example, the equation
for cellular respiration includes glycolysis. Many enzymes also play
important roles in the production of ATP.
C6H12O6 1 6O2
a sugar
oxygen
6CO2 1
carbon dioxide
6H2O
water
Interactive Reader
67
Follow the steps of cellular respiration shown on in the figure on the
previous page.
Circle the products of cellular respiration in the figure on the
previous page.
4.4 Vocabulary Check
cellular respiration
anaerobic
aerobic
Krebs cycle
glycolysis
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Which two terms are opposites?
2. Which term is a process that must happen in the cell’s cytoplasm
before cellular respiration?
3. Which term is a process that happens within the mitochondria as part
of cellular respiration?
C6H12O6 1 6O2
a sugar
4.4 oxygen
6CO2
1 6H2O
carbon dioxide
water
The Big Picture
5. In which organelle does cellular respiration take place?
6. What are the products and the reactants for cellular respiration?
7. Where is most of the ATP made during cellular respiration?
68
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4. Which term is the name for this chemical equation: