Energy in Living Organisms:
Cellular Respiration
Review: Autotrophs
 Autotrophs get their
energy from the sun.
 Convert light energy
into stored chemical
energy (glucose) via
photosynthesis.
Review: Heterotrophs
 Heterotrophs get
their energy from the
autotrophs.
 Convert stored
chemical energy
(glucose) into usable
chemical energy
(ATP).
 This process is called
cellular respiration.
Cellular Respiration (aerobic)
 Process by which glucose (C6H12O6) is
broken down to release energy for making
ATP, another form of chemical energy.
What is ATP?
 Energy used by all cells!
 Adenosine Triphosphate
 Organic molecule containing high-
energy Phosphate bonds
How does ATP supply us with energy?
 By breaking the high- energy bonds
between the last two phosphates in ATP!
How?
 Hydrolysis! (adding H2O)
Aerobic Respiration – Equation
C6H12O6 + 6 O2
food
oxygen
(glucose, a carbohydrate)
6 H2O + 6 CO2 + 36 ATP
water
carbon
dioxide
A Huge Theme in Biology…
Interdependence!
Photosynthesis:
6 H2O + 6 CO2 + energy (sun) → C6H12O6 + 6 O2
Aerobic Cellular Respiration:
C6H12O6 + 6 O2 → 6 H2O + 6 CO2 + energy (ATP)
Why ATP? An analogy to money…
 Glucose in our food is a great source of energy! ($100 bill)
 However, individual cell processes may only require a small
amount of energy ($1 bill)
 Analogy: most vending machines do not accept $100 bills!
We need a smaller form of “currency” for these processes.
 ATP (adenosine triphosphate) is this important cellular
“currency” for life.
 ATP releases more appropriate amounts of energy for the
individual cellular processes that require energy.
The BIG Question is…
Do only animals respire?
Or do plants respire too?
 Only plants perform photosynthesis
 Plants AND animals perform cellular
respiration!
(Can you explain why??)
Steps of Cell Respiration
Stage
Occurs in the…
Glycolysis
Cytoplasm
Krebs Cycle
Matrix of mitochondria
Electron Transport Chain Mitochondrial membrane
Glycolysis
BIG IDEA: Splits glucose into 2 three-carbon
molecules called pyruvate!
 Anaerobic – doesn’t require oxygen!
 Releases CO2
 Net production of 2 ATP
– Takes 2 ATP to get started, produces 4 ATP  overall
gain of 2 ATP!
Krebs Cycle
 Aerobic – requires oxygen!
 Produces 2 ATP
Summary: Produces 2 ATP, NADH & FADH2, CO2
The Electron Transport Chain
 32-34 ATP are produced!
 Aerobic – requires oxygen
 H2O is also produced
Significant ATP Production
 Aerobic cellular respiration releases energy
SLOWLY, using oxygen to convert ONE
molecule of glucose to 36 ATP!
It’s a good thing too! Each cell uses 1-2 BILLION
ATP per minute!
But…
 What happens when cells don’t have enough oxygen?
 Some organisms live in an oxygen-free environment.
How do they get their energy?
Cellular Respiration (anaerobic)
 Anaerobic respiration is also called
fermentation  the process by which
energy is released from glucose when
oxygen is NOT available.
 Allows organisms to continue to produce
energy until oxygen is available.
 However, this process only releases 2 ATP
per molecule of glucose.
Fermentation
 Anaerobic way of converting energy for yeast and
other microorganisms
 Glucose broken down to produce alcohol, CO2
and energy (ATP)
 C6H12O6  ethanol + CO2 + 2 ATP
 EX: baking bread with yeast
Fermentation - Bread
 Source of sugar?
 DOUGH! (sugar and/or flour)
 Yeast use up the O2 and ferment sugar
 Produce CO2, which is trapped within
tiny bubbles & results in the dough rising
 Produce ethanol, which evaporates in the
baking process
Lactic Acid Fermentation
 Anaerobic way of converting energy in
animal cells and some microorganisms
 Glucose broken down to produce lactic
acid, CO2 and energy (ATP)
 C6H12O6  lactic acid + CO2 + 2 ATP
 EX: muscle cells during strenuous exercise
(causes the “burn”) fermenting cheese,
yogurt, sour cream
Comparing ATP Production
 First, your body breaks down glucose through
aerobic respiration to produce 36 ATP per
glucose molecule; however, this is a slow
process.
 When muscle cells cannot get enough O2
they break down glucose through lactic acid
fermentation to produce 2 ATP per
glucose…
 Therefore, AEROBIC RESPIRATION is
much more efficient in terms of ATP
production –
36 ATP compared to 2
Aerobic Training
 Ex: long runs, biking, swimming
 Can increase the size and number of
mitochondria in muscle cells
 Can increase the delivery of O2 to muscles
by improving the heart and lungs
Anaerobic Training
 Ex: sprints, strides,
quick bursts of energy
 Increase the glycogen levels in the
muscles
 Increase body’s tolerance to lactic acid