Objective C (continued)
Objectives
• Write and explain the chemical formula for cellular
respiration.
• Compare photosynthesis with cellular respiration.
• Describe the results of fermentation and understand
when fermentation is needed.
• Where does the energy captured at the beginning of
photosynthesis originate from?
• What is the form of chemical energy produced by
photosynthesis?
Cellular Respiration
 How does the food you eat provide energy?
When you need a quick boost of energy, you might reach for
an apple or a candy bar. Although foods with sugars can give
you a quick boost of energy, they cannot be used for energy
directly by your cells. Energy is simply stored in these foods.
 Through the process of cellular respiration, the energy in
food is converted into energy that can be used by the
body's cells.
 Glucose and O2 is converted into ATP and CO2 and H2O.
 ATP is the molecule that provides energy for your cells to
perform work.
 Cellular respiration a process that converts one type of
chemical energy, the energy stored in sugar, into another
type, ATP.
Overview of Cellular Respiration
 Most often, cellular respiration proceeds by breaking down
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glucose into carbon dioxide and water. As this breakdown of
glucose occurs, energy is released.
The process of cellular respiration includes the conversion of this
stored energy into ATP.
This exchange of carbon dioxide and oxygen in all the organisms
that use photosynthesis and/or cellular respiration worldwide,
helps to keep atmospheric oxygen and carbon dioxide at
somewhat stable levels.
Glucose is broken down slowly so that cells convert as much
sugar as possible into the usable form of energy, ATP.
Some energy is lost in the process in the form of heat.
When one molecule of glucose is broken down, it can be
converted to a net total of 36 or 38 molecules of ATP.
Cellular respiration can be divided
into three phases.
Glycolysis: the breakdown of glucose.
2. The Krebs Cycle (citric acid cycle): the formation of
electron carriers.
3. The electron transport chain: use of oxygen to make
ATP.
In eukaryotic cells, the first phase takes place in the
cytoplasm of the cell, while the other phases are carried
out in the mitochondria.
1.
Mitochondria
 This organelle is known as the “powerhouse” of the cell
because this is the organelle where the ATP that
powers the cell is produced.
st
1
step - Glycolysis
 During glycolysis, glucose is converted into Pyruvate
and energy.
 After glycolysis, the pyruvate can go down several
different paths.
 If there is oxygen available, the pyruvate moves inside
the mitochondrion to produce more ATP during
further break-down stages.
 In the absence of oxygen, the fermentation process
begins.
nd
2
step – The Krebs Cycle
 Inside the Mitochondria if oxygen is available, the next
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step of cellular respiration is moving the pyruvate into
the mitochondria.
The mitochondria’s unique shape makes it possible to
carry out the Krebs Cycle.
The Krebs cycle starts with pyruvic acid (pyruvate) and
produces energy.
Within the mitochondria the Krebs Cycle or citric acid
cycle occurs.
The citric acid cycle is a series of steps that produce
Carbon dioxide, ATP, NADH and FADH2.
rd
3
step – The Electron Transport
Chain
The Electron Transport
Chain takes place in the
Mitochondria and
changes NADH and
FADH into ATP. What is
the final product of the
ETC?
 During this energy conversion oxygen, which is necessary,
combines with hydrogens and becomes water.
 That is the key reason why this process only occurs in the
presence of oxygen.
 This is known as aerobic respiration.
 The Electron Transport Chain takes place in the
Mitochondria and changes NADH and FADH in to ATP.
However, there is not always enough oxygen present for
aerobic respiration to occur. In this case, the next step after
glycolysis will be fermentation instead of the citric acid cycle.
 What is the final product of the ETC?
Fermentation
 Sometimes cellular respiration is anaerobic, occurring
in the absence of oxygen.
In the process of fermentation, the NAD+ is
recycled so that is can be reused in the glycolysis
process.
 No additional ATP is produced during fermentation.
 Yeasts (single-celled eukaryotic organisms) carry on
alcoholic fermentation in the absence of oxygen,
making ethyl alcohol and carbon dioxide.
 Animals and some bacteria and fungi carry out lactic
acid fermentation.
Why do your muscles get sore after vigorous exercise?
What is the purpose of fermentation?
Lactate (lactic acid) is a waste
product of lactic acid fermentation.
 Our muscles undergo lactic acid fermentation during
strenuous exercise, when oxygen cannot be delivered to
the muscles quickly enough.
 The buildup of lactate is what makes your muscles sore
after vigorous exercise.
 Bacteria that produce lactate are used to make cheese
and yogurt.
 Tooth decay is also accelerated by lactate from the
bacteria that use the sugars in your mouth.
In all these types of fermentation, the goal is the
same: to recycle NAD+ for glycolysis.
Products of fermentation include cheese (lactic acid
fermentation) and wine (alcoholic fermentation).
• Alcoholic fermentation is central to bread
baking.
• The carbon dioxide bubbles allow the
bread to rise, and the alcohol evaporates.
• In wine making, the sugars of grapes are
fermented to produce the wine.
Summary
 Cellular respiration is the breakdown of glucose to
release energy in the form of ATP.
 Glycolysis, the conversion of glucose into two 3-carbon
pyruvate molecules, is the first step of cellular
respiration.
 If oxygen is available, the pyruvate enters the
mitochondria and goes through a series of reactions,
including the citric acid cycle, to produce more ATP.
 If oxygen is not available, the pyruvate is reduced
during the process of fermentation to free up more
NAD+ for glycolysis, and there is no net gain of ATP.
Review Questions
1.
2.
3.
4.
5.
6.
What are the products of alcoholic fermentation?
What is the metabolic process where glucose is
ultimately converted to two molecules of pyruvate?
What is the purpose of fermentation?
Where does the citric acid cycle take place?
Write the chemical reaction for the overall process of
cellular respiration.
Which is more efficient, aerobic or anaerobic cellular
respiration?
Vocabulary
• ATP
• Chlorophyll
• Photosynthesis
• Cellular
Respiration
• Homeostasis
• Fermentation
• Anaerobic
respiration
• Aerobic respiration
Points to Consider
Now that we know how the cell gets its energy, we are
going to turn our attention to cell division. Cell
division is a highly regulated process.
2. What do you think could happen if your cells divide
uncontrollably?
3. When new life is formed, do you think it receives all
the DNA of the mother and the father?
4. Why do you think you might need new cells
throughout your life?
1.