Download Today`s Objective: SOL 3.d

Cellular Respiration
Energy for life’s activities
Overview of Cellular Respiration
The life processes of ALL organisms
require energy.
 The potential energy held in the bonds
of food molecules CANNOT be used
directly by the cell.
 Energy from food must be converted to
the ONLY energy source that cells can
use … ATP!

Review of ATP
Adenosine Triphosphate
 Result of the bonding of a free
phosphate w/free ADP molecule
 The bond between the phosphates is
where the actual energy is stored

Review of ATP, cont.

When the bond between the
phosphates is broken, energy is
released
Cellular Respiration Defined
Respiration is the process by which the
energy in the bonds of nutrients are
used to synthesize ATP.
 Respiration occurs continuously in all
cells of all organisms.
 The energy needed to synthesize ATP
comes from an organism’s food

Summary of Cell Respiration
ATP
ATP
cellular
respiration
cellular
respiration
energy
(out)
energy
(in)
energy
(out)
cell
cell
activities
activities
ADP + P
The whole process is an enzyme controlled reaction.
Aerobic Respiration

Aerobic Respiration – respiration with
oxygen
C6H12O6 + 6O2
6CO2 + 6H2O
energy
(to make ATP)
Aerobic Respiration, cont.


Happens in 2 stages:
Stage 1 – Glycolysis
glyco – glucose lysis – splitting
 In glycolysis, a glucose molecule is broken
into 2 pyruvic acids
 This requires the input of 2 ATP molecules as
activation energy

glucose
energy released
to make small
quantity of ATP
(2 molecules)
series of enzyme
controlled reactions
pyruvic acid
Glycolysis does not require oxygen
Aerobic Respiration, cont.



Stage 2 – Breakdown of pyruvic acid
The pyruvic acid made in glycolysis still
contains a lot of energy
It can only be broken down to release
the rest of the energy in the presence of
oxygen
pyruvic acid
series of enzyme
controlled reactions
energy released to
make large
quantity of ATP
(34 molecules)
carbon dioxide + water
Summary of ATP production


Stages 1 and 2 release all the chemical
energy in one molecule of glucose to
make a total of 36 molecules that can
be used by the organism
There is actually enough energy in a
glucose molecule to make ~90 ATP, but
the rest is lost as heat
ATP production – summary
glucose
2 ADP + 2 P =
2 ATP
pyruvic acid
~56 ATP
(heat)
carbon dioxide + water
34 ADP + 34 P =
34 ATP
The Mitochondrion
The Role of the Mitochondrion
In order for the cell to capture as much
energy as it possibly can from it’s food,
a series of controlled reactions requiring
the input of oxygen is necessary
 These reactions are directed by the
mitochondrion

The Role of the Mitochondrion, cont.
Glycolysis occurs in the cytosol
(cytoplasm) of the cell
 The aerobic reactions occur in the
mitochondria of the cell and are divided
into 2 stages

The Role of the Mitochondrion, cont.





Stage 1 – The Krebs (Citric Acid) Cycle
Discovered by Hans Krebs in 1937
Pyruvic acid is broken down into CO2 in
a series of energy-extracting reactions
The first compound formed in this series
of reactions is citric acid
This is the stage that is the source of all
the CO2 that you exhale
 The Krebs Cycle occurs in the matrix of the mitochondrion
Krebs
Cycle
The Role of the Mitochondrion, cont.




Stage 2 – The Electron Transport Chain
The Krebs Cycle generates many highenergy hydrogen atoms
Oxygen is added as an electron carrier
at this stage
When the oxygen binds with the
hydrogen, energy is released to form
ATP and water is made
 The electron transport chain occurs in the cristae of
the mitochondrion.
Electron
Transport
Chain
Anaerobic Respiration
Also called fermentation
 Happens in low/no oxygen conditions
 1 Glucose only partially broken down to
form waste products and 2 ATP

Anaerobic Pathways


Pathway 1- Lactic Acid Fermentation
Glucose  2 lactic acid + 2 ATP
– Happens in muscle cells when they run out
of oxygen
– Happens in bacteria that make yogurt,
cheese, dill pickles
glucose
glycolysis still
happens as it does
not require oxygen
pyruvic acid
in absence of oxygen
pyruvic acid is
turned into lactic
acid.
lactic acid
2 ADP + 2 P
2 ATP
Anaerobic Pathways, cont.

A build up of lactic acid produces muscle
fatigue
 This makes the muscles ache and contract
with less power
 A recovery period is needed; during this time
more O2 is taken in which converts lactic acid
back into pyruvic acid
 The volume of O2 needed is called oxygen
debt
Anaerobic Pathways, cont.



Pathway 2 – Alcoholic Fermentation
Glucose  2 ethanol + 2 CO2 + 2 ATP
process in which sugars are converted
into alcohol and carbon dioxide by the
action of various yeasts, molds, or
bacteria
glucose
2 ADP + 2 P
glycolysis still
happens, producing
2 ATP molecules
2 ATP
pyruvic acid
This time in absence of
oxygen, pyruvic acid is
turned into carbon
dioxide and ethanol
This is irreversible
ethanol + carbon dioxide
Comparing Aerobic & Anaerobic
Cellular Respiration Pathways
Aerobic (needs
oxygen)
Anaerobic
(no oxygen)
Occurs in:
Most organisms
Mostly yeast and
bacteria
1 glucose
makes:
6 CO2 + 6 H2O
Ethanol + CO2
Or
Lactic acid + CO2
Net ATP
production:
36
2
Adaptations for Respiration

Bacteria, protists & fungi
– Respiratory gases are exchanged by
diffusion

Plants
– Respiratory gases are exchanged through
leaves, stems, and roots
– Moves in and out of cells by diffusion but
leaves and stems also have openings to
the environment (stomata)
Adaptations for Respiration in
Animals

Techniques vary:
– Simple diffusion across cell membranes
– Diffusion across moist skin into a
circulatory system
– Openings to the environment that can be
flapped open and closed with a circulatory
system to transport gases
– Specialized respiratory structures (e.g.
lungs) to speed exchange of respiratory
gases