The Working Cell: Energy From Food
Sunlight Powers Life
There are 2 main types of organisms:
1. Autotrophs are organisms that make their own food from CO2 and
an energy source such as sunlight. Ex Plants, algae, and some
• Autotrophs are the producers b/c they produce their own food &
food for other organisms (they do NOT produce their own
There are 2 types of autotrophs:
• Photoautotrophs: organisms that use sunlight
(photosynthesis) to produce their own food (plants,
algae, and some bacteria).
• Chemoautotrophs: organisms that use inorganic
chemicals/compounds (chemosynthesis) to produce
their own food (bacteria).
Heterotrophs are organisms that
cannot produce their own and must
consume (eat other organisms);
therefore they are consumers. Ex
animals, fungi, and many unicellular
• All organisms perform some type of
– Conversion of sugar & O2 into usable
chemical energy (ATP)
– By-products are CO2 & H2O
• Kinetic energy: energy of motion
• Potential energy: stored energy
• Thermal energy: random molecular motion;
when transferred produces heat
• Chemical energy: form of potential energy
(macromolecules & ATP)
• Calorie: amount of energy needed to raise the
temp of 1 g of H2O by 1˚C; kilocalories = 1,000
• Cellular respiration is a slow ‘burn’ where heat
• Life depends on energy. Compounds that
store energy: ATP, NADPH, NADH, & FADH2.
• ATP= adenosine triphosphate is the energy
currency of the cell (cash of the cell; main
energy of the cell for chemical reactions)
• Every time a bond holding a phosphate group
(PO3) is broken energy is released; therefore
every time ATP losses a PO3, energy is
• ATP can be used for ALL types of cellular
ATP is constantly needed b/c
cells are constantly working.
ATP is continuously broken
down and recycled very
rapidly (used and remade).
• Cellular Respiration is the process of
breaking down glucose molecules
through a series of steps to release
– This produces ATP.
– Occurs in the mitochondria
• This can occur in the presence of O2
(aerobic respiration) or without O2
• Aerobic respiration produces 36 ATP molecules
whereas anaerobic respiration produces only 2
The overall equation of cellular respiration:
C6H12O6 + 6 O2
6CO2 + 6H2O + energy
• Metabolism: all of the cell’s chemical reactions
Mitochondria (Sing. Mitochondrion)
(outer & inner); both
involved in cellular
•Cristae: folds of
•Matrix: space within
the inner membrane
There are 3 Phases of Aerobic Respiration:
• Whether the organism is aerobic or
anaerobic, that organism will undergo
glycolysis. This is always the 1st step!
• Glucose is converted to pyruvate (a 3-C
compound) and 2 ATP are released.
• This occurs in the cytoplasm
• This occurs in 10 steps; 2 phases
• The final results are: 2 NADH, 2 ATP,
and 2 pyruvate
2. Krebs Cycle:
This is a.k.a. the citric acid cycle
Pyruvate is converted into acetyl-CoA and
CO2 is released
Acetyl-CoA enters the Krebs cycle
This occurs in the mitochondria (matrix)
2 ATP, NADH, and FADH2 are released.
For every glucose molecule, 2 pyruvate are
1 ATP is made for each pyruvate; therefore a
total of 2 ATP are made.
3. Electron Transport:
Both NADH and FADH2 enter the electron transport
This occurs in the mitochondria (cristae)
This is the only part that REQUIRES OXYGEN.
Prior to this ONLY 4 ATP have been made, yet a total
of 36 ATP can be made during aerobic respiration.
That means 32 ATP can be made here. This is the
cash cow of cellular respiration!
Energy is transferred from NADH and FADH2 to
Water is produced as a by-product as well as heat.
Anaerobic Respiration (w/o O2):
• Fermentation is the extraction of energy from
pyruvate without O2.
• Alcohol fermentation is the conversion of
pyruvate to CO2 and ethanol (yeast, a
unicellular fungi, performs this).
• Lactic acid fermentation is the conversion of
pyruvate to lactic acid during strenuous
exercise when there isn’t enough O2 (animal
muscle cells perform this).
– This is why muscles become fatigued and sore
after strenuous exercising.
• Calories are the amount of heat energy
needed to raise the temperature of 1 gram of
water 1 degree C.
– This is the energy contained in food substances.
This slide show was developed by Dana Halloran,
Cardinal Mooney High School, Sarasota, FL.
Used with her personal permission,
adapted and amended by Rosa Whiting,
Manatee School for the Arts, Palmetto, FL.