Cellular Respiration

1. 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
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 carbon-
based molecules. The energy is released to produce ATP. This process
of using oxygen to produce ATP by breaking down carbon-based mol-
ecules 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 mol-
ecules 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.
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?
Glycolysis breaks glucose into 2 three-carbon molecules.
C C C C C C
C C C
C C C
2 ADP 2 ATP
glucose 2 three-carbon molecules
Overview of Cellular
Respiration
Key Concept The overall process of cellular respiration converts sugar into
ATP using oxygen.
Mitochondria (middle) are
found in both animal (top)
and plant (bottom) cells.
They make ATP through
cellular respiration.
65
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Cellular respiration is like a mirror image
of photosynthesis.
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. Photo-
synthesis makes sugars and cellular respiration
breaks down sugars. The chemical equations of the
two processes are basically opposites.
The structures of mitochondria and chloro-
plasts are very similar. Remember that part of
photosynthesis happens inside the stroma—
the fluid in the chloroplast—and part of photosyn-
thesis happens inside the membrane of the thyla-
koid. 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:
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.
Stage 2: Electron Transport Energy is moved through a chain of pro-
teins 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.
COMPARING Processes
Photosynthesis
Cellular Respiration
The products of photosynthesis—sugars and
O2—are the reactants in cellular respiration.
light
energy
ATP,
heat
energy
light
energy
ATP,
heat
energy
REACTANTS
PRODUCTS
Sugars (C6H12O6)
O2
CO2
H2O
REACTANTS PRODUCTS
CO2
H2O
Sugars (C6H12O6)
O2
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overview of cellular respiration
6H2O
6O2
1
2
3
4
STAGE 2: Electron Transport
STAGE 1: Krebs Cycle
Three-carbon molecules
from glycolysis enter
cellular respiration in
mitochondria.
Energy-carrying molecules from
glycolysis and the Krebs cycle enter
Stage 2 of cellular respiration.
ATP molecules are produced.
Heat and water are released
as waste products.
ATP
ATP
6CO2
mitochondrion
energy
AND
AND
AND
Energy-carrying
molecules transfer
energy to Stage 2.
matrix (area enclosed
by inner membrane)
inner membrane
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 6CO2 1 6H2O
a sugar oxygen carbon dioxide water
energy from glycolysis
67
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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.
cellular respiration anaerobic
aerobic Krebs cycle
glycolysis
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?
4. Which term is the name for this chemical equation:
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?
4.4 Vocabulary Check
Go back and highlight
each sentence that
has a vocabulary
word in bold.
Mark It Up
C6H12O6 1 6O2 6CO2 1 6H2O
a sugar oxygen carbon dioxide water
4.4 The Big Picture
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