Chapter 4
Cellular Processes
Cellular Energy
Cells Use Energy
• Maintain homeostasis
• To perform all cellular processes
• To make energy-storing molecules
When they stop using energy,
they are dead
Energy Relationships
• Energy is a one time commodity –
every time it is used some escapes
and becomes unusable
• More energy is needed to build an
energy-storing molecule than is
stored in the molecule.
How do organisms
obtain their food?
• Autotrophs
– “auto” = self
– “troph” = nourishment
• Heterotrophs
– “hetero” = others
Autotrophs
• Make their own food
– They capture light energy
and convert it into sugar
– Ex: plants, algae, and
some bacteria.
Heterotrophs
• Depend on other organisms
for their energy source
– Ex: humans, animals, fungi,
and most bacteria.
ATP – Adenosine
Triphosphate
• Most energy sources (fats,
carbohydrates) are large and must be
broken down into smaller units (sugar –
glucose)
• ATP stores energy in a usable form for all
living organisms
• The bonds between the three phosphate
groups are unstable high-energy covalent
bonds
ATP
Energy Production
• When the bonds are broken, a large
amount of energy is released (an
exothermic reaction) and is available for
use in any cellular function that requires
energy (an endothermic reaction).
• ATP  ADP + P + Energy
ATP
adenosine triphosphate
Adenosine
1
2
Phosphates
3
ATP Production
• ADP and P can be reused to form ATP
with the proper enzymes and adequate
supply of energy
• ADP + P + Energy  ATP
ADP
adenosine diphosphate
Adenosine
1
2
Phosphates
ATP-ADP Cycle
4A – 2
PHOTOSYNTHESIS
The process of taking
light energy and
converting it into stored
chemical energy
sun
The
is the source
of energy for living things!
Photosynthesis Reaction
• Reaction converting light energy
into stored chemical energy
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
(Carbon
dioxide)
(water)
(glucose)
(oxygen)
• Green plants and algae perform this
energy transformation in large enough
quantities to provide stored chemical
energy for most living organisms
Photosynthesis is
important because…
1) It converts solar
energy into
usable chemical
energy
2) It produces
oxygen
Light Absorption
• Different wavelengths of
visible light are seen by the
human eye as different
colors.
• The color we see is actually
the color reflected.
Chlorophyll a
• Primary catalyst of
photosynthesis
• Green pigment in the grana
of chloroplasts
• Becomes activated by light
energy
Chlorophyll a
• Chlorophyll a is a blue green
pigment – it reflects the
blues and greens and
absorbs the reds and violets
Chlorophyll b
• Is a yellow green pigment – that
absorbs some of the same pigments as
chlorophyll a as well as some of the
blues not absorbed by chlorophyll a and
reflects some of the yellow greens that
chlorophyll a absorbs
Absorption Spectrum
The Process of
Photosynthesis
The Light-Dependent Phase
• Requires sunlight and water
• Occurs in the grana of the
chloroplast
• Produces: Oxygen , ATP and
NADPH (electron carrier that stores energy
for later use)
Photosynthesis: The
Process
Light-Independent Phase
• Light is NOT required
• Occurs in the stroma of the chloroplast
• Also called:“Dark phase,” “synthetic phase,”
“Calvin cycle,” “carbon fixation cycle”
• Is dependent upon the products of the
light phase (ATP and NADPH) and CO2
from the atmosphere
Conditions for
Photosynthesis
• Proper wavelengths of light
• Sufficient absorption of
carbon dioxide
• Proper temperatures
• Proper amount of water
Chemosynthesis:
Other autotrophs
• A few bacteria use
inorganic chemicals (i.e.
ammonia or sulfur) to
obtain energy
• Ex. Symbiotic bacteria in
tubeworms in hydrothermal
vents convert chemical
energy in sulfur into usable
energy
Cellular
Respiration
Cellular
Respiration
The breakdown of a
food substance into
usable cellular energy
in the form of ATP
Summary
Kinetic energy (sun)
stored chemical energy
(C6H12O6)
= photosynthesis
Summary
stored chemical energy
(C6H12O6)
ready-to-use chemical energy
(
)
= cellular respiration
Cellular Respiration
• Aerobic
– Requires oxygen, is the opposite
of photosynthesis, combines
oxygen with sugar to release
energy, carbon dioxide and water
• Anaerobic
– Does not require oxygen
Aerobic Cellular
Respiration
Aerobic Cellular
Respiration
C6H12O6 + O2
H2O + CO2 + energy
(ATP)
The Process of
Cellular Respiration
• Glycolysis
• Citric Acid Cycle (Krebs Cycle)
• Hydrogen and Electron Transport
System
Glycolysis
• All types of cellular
respiration begin with
glycolysis.
• Does not require oxygen
• Occurs in the cytoplasm
Glycolysis
• Breakdown of glucose into
pyruvic acid, H+, and
electrons
• 2 net ATP
Aerobic Cellular
Respiration
The products from glycolysis are sent
to the mitochondria.
Aerobic Cellular
Respiration
1. Citric Acid Cycle (Krebs
Cycle) = Pyruvic acid is
broken down into citric acid.
− Pyruvic acid  Acetyl
CoA
− Acetyl CoA  Citric acid
Aerobic Cellular
Respiration
2. Hydrogen and Electron
Transport System
− Occurs in the cristae of
the mitochondria
Aerobic Cellular
Respiration
2. Hydrogen and Electron
Transport System
− At the end of the chain, H
combines with oxygen to
form water.
− Oxygen is the rate-limiting
factor.
Energy Facts
• Aerobic Cellular Respiration
results in the net gain of 36
ATP molecules.
+ & eH
Citric Acid transport
Glycolysis
Cycle
system
Location Cytoplasm
Mitochondria Mitochondria
(matrix)
(cristae)
Glucose
Pyruvic
acid
H+; e-
Pyruvic
Products acid; H+;
e-
CO2; H+;
e-
ATP;
water
Reactants
ATP
2 net
2 net
32
Anaerobic
Respiration
• Breakdown of food (glucose)
without oxygen
• “Cellular fermentation”
2 Types of Fermentation
1) Alcoholic fermentation – pyruvic acid +
NADH  alcohol + CO2 + NAD+
Ex: yeast
2) Lactic Acid fermentation – pyruvic acid
+ NADH  lactic acid + NAD+
Ex: produced in your muscles during
rapid exercise when the body cannot
supply enough oxygen to the tissue
Energy Facts
• Cellular fermentation
supplies no ATP energy
beyond glycolysis.
Energy Facts
• Cellular fermentation
supplies no ATP energy
beyond glycolysis.
• Cellular fermentation results
in the net gain of 2 ATP
molecules.
Cellular Respiration
Comparison of Photosynthesis and
Cellular Respiration
Function
Energy Capture
Energy release
Location
Chloroplasts
Mitochondria
Reactants Carbon dioxide
and water
Glucose and oxygen
Products
Carbon dioxide and water
Glucose and
Oxygen
Equations 6CO2 + 6H2O +
energy 
C6H12O6 + 6O2
6O2 + C6H12O6  6CO2 +
6H2O + energy
Match the following:
____1. Organisms that make their own food
A. Chloroplasts
____2. Site of photosynthesis
B. Aneorobic
____3.Process occurs in a mitochondrion
C. Aerobic
____4. C6H12O6
D. Glucose
____5. Process does not require oxygen
E. ATP
____6. Process requires oxygen
F. Kreb’s cycle
____7. Adenosine diphosphate
G. Glycolysis
____8. Energy storing molecule
H. Energy
____9. The anaerobic process of splitting glucose and forming two
molecules of pyruvic acid
I. ADP
____10. The ability to do work
J. Autotrophs
WORD BANK
2 ATP
2 ATP
36 ATP
6 NADH
2 FADH
Electron transport chain
Mitochondrion
Cytoplasm
Fermentation
Glycolysis
Glucose
Pyruvate
Lactic acid
Kreb's Cycle