Photosynthesis
vs. Respiration
Free Energy – ∆𝐺 = ∆𝐻 − 𝑇∆𝑆

Enthalpy (heat of reaction) is the amount of
energy released or absorbed during a chemical
reaction



Entropy is a measure of randomness, tendency
toward disorder






Symbol is ΔH
Think of it as energy needed
Symbol is ΔS
More disorder = more entropy
If reaction leads to more disorder, the entropy
change (ΔS) is positive, if it becomes more
ordered, ΔS is negative
Example: melting ice, condensing water, cleaning
your room (+,-,-)
Temperature – T measured in K (273 + ºC)
Free Energy – spontaneity of a reaction


Spontaneous - ∆𝐺 is negative
Not spontaneous - ∆𝐺 is positive. Would be
spontaneous if reversed.
Things in Common
 Both
photosynthesis and respiration make
ATP.
 Both involve, CO2, oxygen, sugar
(C6H12O6), and water (H2O)
 Almost all cells go through respiration
 ATP
transfers energy from the breakdown of food
molecules to cell functions.
– Energy is released when a phosphate group is removed.
– ADP is changed into ATP when a phosphate group is added.
phosphate removed
Organisms break down carbonbased molecules to produce ATP.
 Carbohydrates
are the molecules most commonl
broken down to make ATP.
– not stored in large amounts
– up to 36 ATP from one glucose
molecule
adenosine
triphosphate
tri=3
adenosine
di=2
diphosphate
 Fats
store the most energy.
– 80 percent of the energy in your body
– about 146 ATP from a triglyceride
• Proteins are least likely to be broken down to make ATP.
– amino acids not usually needed for energy
– about the same amount of energy as a carbohydrate

The light-dependent reactions capture energy from sunlight.
–
–
–
–
take place in thylakoids
water and sunlight are needed
chlorophyll absorbs energy
energy is transferred along thylakoid membrane then to lightindependent reactions
– oxygen is released
 The
light-independent reactions make sugars.
– take place in stroma (fluid outside the thylakoids)
– needs carbon dioxide from atmosphere
– use energy to build a sugar in a cycle of chemical reactions
 Photosystem
II captures and transfers energy.
– chlorophyll absorbs
energy from sunlight
– energized electrons enter
electron transport chain
– water molecules are split
– oxygen is released as
waste
– hydrogen ions are
transported across
thylakoid membrane
 Photosystem
I captures energy and produces energycarrying molecules.
– chlorophyll absorbs energy
from sunlight
– energized electrons are
used to make NADPH
– NADPH is transferred to lightindependent reactions
Summary of Light Dependent
Reactions
 Energy
is captured from the sun.
 Energy goes into electrons into the
electron transport chain.
 Water is broken down
 H+ ions are transported and form NADPH
 Flow of H+ ions through ATP synthase
makes ATP
 Electron Transport
Summary of Light
Independent Reactions
(Calvin Cycle)
 CO2
enters cycle
 ATP and NADPH from light-dependent
transfer energy
 1 3-carbon molecule made for every 3
CO2
 2 3-carbon molecules bonded to make
sugar
 Products – 6-carbon sugar, NADP+, and
ADP
A
molecule of glucose is formed as it stores some of
the energy captured from sunlight.
– carbon dioxide molecules enter the Calvin cycle (this is what has
sugar as an end product
– energy is added and carbon molecules are rearranged
– a high-energy three-carbon molecule leaves the cycle
o A molecule of glucose is formed as it stores some of the energy
captured from sunlight.

two three-carbon molecules bond to form a sugar
– remaining molecules stay in the cycle
Cellular respiration makes ATP by
breaking down sugars.
 Cellular
respiration is aerobic, or requires oxygen.
 Aerobic stages take place in mitochondria.
mitochondrion
animal cell
 Glycolysis
–
–
–
–
must take place first.
anaerobic process (does not require oxygen)
takes place in cytoplasm
splits glucose into two three-carbon molecules
produces two ATP molecules
Cellular respiration is like a mirror image
of photosynthesis.
 The
Krebs cycle transfers energy to an electron
transport chain.
Krebs Cycle


1
takes place in
mitochondrial matrix
breaks down three-carbon
molecules from glycolysis
– makes a small amount
of ATP
– releases carbon
dioxide
– transfers energycarrying molecules
mitochondrion
ATP
matrix (area enclosed
and
by inner membrane) 6CO
2
energy
3
energy from
glycolysis
and
6O2
2
inner membrane
ATP
and
6H2 O
4
• The electron transport chain produces a large amount of ATP.
– takes place in inner
membrane
– energy transferred to
electron transport chain
– oxygen enters process
– ATP produced
1
mitochondrion
matrix (area enclosed
and
by inner membrane) 6CO
2
energy
Electron Transport
3
energy from
glycolysis
and
6O2
– water released as a
waste product
ATP
2
inner membrane
ATP
and
6H2 O
4
The Krebs cycle is the first main part of
cellular respiration.
 Pyruvate
is broken
down before the Krebs
cycle.



carbon dioxide
released
NADH produced
coenzyme A (CoA)
bonds to two-carbon
molecule
 The
Krebs cycle produces energy-carrying molecules.
The electron transport chain is the
second main part of cellular
respiration.
 The
electron transport chain uses NADH and FADH2 to
make ATP.



high-energy electrons enter electron transport chain
energy is used to transport hydrogen ions across the inner
membrane
hydrogen ions
flow through a
channel in the
membrane
The electron transport chain is the
second main part of cellular
respiration.
o The electron transport chain uses NADH and FADH2 to make ATP.

The breakdown of one glucose molecule produces up to
36 molecules of ATP. (2 from glycolysis, 2 from Kreb, 32 from ETC)
– ATP synthase
produces ATP
– oxygen picks up
electrons and
hydrogen ions
– water is released as
a waste product
ATP Products of Cellular
Respiration including glycolysis
 Glycolysis
– uses 2 ATP and make 4 ATP.
Net gain of 2 ATP
 Kreb Cycle – 2 ATP, 8 NADH, 2 FADH2
 Electron Transport Chain – 32ATP
 Net gain – 36 ATP for every glucose
molecule.
Comparison of Photosynthesis
& Cellular Respiration
Photosynthesis
Cellular Respiration
Organelle for
process
Chloroplast
Mitochondrion
Reactants
CO2 and H2O
Sugars (C6H12O6) and
O2
Cycle of
chemical
reactions
Calvin cycle in
stroma of
chloroplasts builds
sugar molecules
Krebs cycle in matrix
of mitochondria
breaks down
carbon-based
molecules
Electron
Transport Chain
Proteins within
thylakoid
membrane
Proteins within inner
mitochondrial
membrane
Products
Sugars (C6H12O6)
and O2
CO2 and H2O
Fermentation allows glycolysis to
continue when oxygen is
unavailable.
 Fermentation


is an anaerobic process.
occurs when oxygen is not available for cellular
respiration
does not produce ATP
 Fermentation
allows glycolysis to continue making ATP
when oxygen is unavailable.
• NAD+ is recycled to glycolysis
• Lactic acid fermentation occurs in muscle cells.
– glycolysis splits glucose into two pyruvate molecules
– pyruvate and NADH enter fermentation
– energy from NADH converts pyruvate into lactic acid
– NADH is changed back into NAD+
 Fermentation
– yogurt
– cheese
– bread
is used in food production.
Project
 In
teams of 2, students will create a visual
representation (e.g., poster or PowerPoint)
to explain the interdependent
relationships of cellular respiration and
photosynthesis, and how the processes of
cellular respiration and photosynthesis
affect a runner in a marathon race.
 Students should use few words and focus
on using graphics to represent the cyclic
processes. Visual representations will be
peer and teacher reviewed.