Cell Unit II: Respiration and
Photosynthesis
Themes:
The cell, Structure and Function,
Regulation, Evolution, Interaction
with the environment
Objectives for Respiration:
 Cellular Respiration and Metabolism are
catabolic
 Cells recycle ATP
 Respiration involves: Glycolysis, Krebs
Cycle and ETC
 Fermentation: Lactic Acid, Alcoholic
 Feedback Mechanisms control cellular
respiration
Root Words





Aero – air
An – not
Chemi – chemical
Glyco – sweet
Lysis - split
Cellular Respiration is:
Catabolic Pathway Exergonic- Products have
less energy than
reactants.
C6H12O6 & 6 O2
6 H2O & 6 CO2 & Energy (ATP)
(Same as combustion - example gasoline)
- G 686 KC/mole of Glucose (approx. 40%
efficient).
ENERGY FLOW AND
CHEMICAL RECYCLING IN
ECOSYSTEMS.
Chemicals are
recycled but energy
is not. Energy leaves
the system as heat
and must be put
back into the system
by sunlight.
RESPIRATION: is a series of REDOX REACTIONS.
(Reduction/Oxidation)
Oxidation -Loss of
electrons (H+) also the
reducing agent.
Reduction - Gain of
electrons (H+) also the
oxidizing agent.
LEO goes GER
L- Lose
E- Electron
O - Oxidation
G - Gain
E- Electron
O - Reduction
C6H12O6 & 6 O2
steps
enzymes
Undergoes
oxidation
Undergoes
reduction
(Reducing agent)
(Oxidizing agent)
6 CO2 & 6 H2O
Respiration &
Combustion release the
same amount of energy
(combustion releases it
faster)
REDOX EXAMPLE: with the use of coenzymes
GLUCOSE
Enzymes called Dehydrogenates
rip 2H+ off glucose in pairs (2 e & 2 p).
One proton goes into cell solution . The 2e & 1p
are picked up by coenzyme (NAD+) & forms
NADH. (Glucose is oxidixed & NAD+ is reduced.)
Respiration Lab - # 5
 We will be using Vernier Probes
SUBSTRATE-LEVEL
PHOSPHORYLATION
The enzyme takes a
substrate that has a
phosphate &
transfers it to an
ADP making it ATP.
EXAMPLES:
Pg. 163 reaction
# 7 & 10.
OXIDATIVE
PHOSPHORYLATION:
what is phosphorylation?
2H’S From Glucose
taken by NAD+ pass
their electrons
through the
Electron Transport
Chain (ETC)
releasing energy
that converts ADP
to ATP.
Each step of respiration is controlled by a different
enzyme. (Compare to next slide Fig. 9.16)
10 steps
8 steps
GLYCOLYSIS - 1ST 10 STEPS OF RESPIRATION:
Glucose(6 C’s) is split into 2 pyruvate molecules (each 2 C’s)
Each Pyruvate is an acid
Each step has a different enzyme.
This is anerobic respiration (without using O2)
Believed to be most ancient of metabolic processes since
it does not need O2; found in all eukaryote & prokaryote
cells. The enzymes are in cytosol not in the mitochondria.
ATP made only through substrate-level Phosphorylation.
(net gain is 2 ATP & 2 NADH)
REMEMBER- NAD+ to NADH (NAD+ reduced) so a
substrate went through oxidation.
Substrate phosphorylation yields only 4 ATP
Oxidative phosphorylation yields 34 ATP/ mole of Glucose.
FIG. 9.8.
Formation of 2
pyruvates; 2 ATP by
substrate -level
Phos. & 2 NADH.
(REDOX Reactions)
FIG. 9.9
This is
where the 6
carbon
molecule is
split into 2
3 carbon
molecules.
FIG. 9.9
Here is where 2 ATP are formed (sub-lev.
Phos.) and the net gain of 2 ATP, the final
product of Glycolysis is formed (pyruvate).
This is the step between the end of GLYCOLYSIS & the
beginning of the KREBS CYCLE.
Each Pyruvate loses a CO2 & NAD+ is reduced to NADH
and Coenzyme A is added to the molecule making
Moving from:
Cytosol to
the
mitochondria
This molecule enters
the KREBS CYCLE
KREBS CYCLE:Note the following:
(A) Where Acetyl
CoA comes into
reaction.
(B) Where CO2’s
are produced.
(C) Where
coenzymes FADH2
& NADH are
reduced.
(D) How # of
carbons change.
Pyruvate from
Glycolysis converted
into Acetyl CoA
2c
2c
2c
2 turns for each
glucose molecule
4c
6c
6c
4c
4c
Substrate level
Phos.here
4c
4c
5c
PARTS OF MITOCHONDRIA:
(A) Inner Mitochonrial Membrane
(B) Outer Mitochondrial Membrane
(C) Cytosol
(D) Mitochondrial Matrix
(E) Intermembrane Space
(F) Cristae increases surface
area.
F
ELECTRON TRANSPORT CHAIN (ETC)
(Located in the inner mitochondrial membrane)
The electrons of the H of NADH & FADH2 that
was reduced in Glycolysis & Krebs Cycle enter
the ETC.
The Proton of the hydrogen does not enter the
ETC.
The electron moves from one compound of ETC
to another. (oxidation/reduction)
Electrons release energy as they move from
compound to compound of the ETC.
Last compound of ETC releases electron which
joins with a proton to make (H) again.
When 2 electrons go through ETC we get 2H.
These join with metabolic oxygen to make
metabolic water.
***** O2 is to be the final electron
acceptor of electron of glucose.*****
Chemiosmosis: How the Mitochondrial membrane
couples ETC with Oxidative Phosphorylation
As NADH passes through the ETC, this energy is
used to pump H+ ions (protons) from M. Matrix
to Intermembrane space.(H+ not from H of NADH)
This causes
PROTON
MOTIVE
FORCE. (More
H+ in Internal
Membrane
Space than in
Membrane
Matrix.)
These H+ ions will “leak” back into the M.
Matrix through a protein complex (integral
proteins) and this will release enough energy to
join ADP with a (P) to make ATP.
IMPORTANT STATEMENT: Since most ATP
formed is from oxidative phosphorylation, ATP
yield in respiration needs a supply of O2.
Since O2 “pulls” electrons down the ETC then if
there is not enough Oxygen the ETC will stop
(and stop ATP formation).
FERMENTATION - is a process that some
cells can use to oxidize food and make ATP
without the use of O2.
FERMENTATION - anaerobic respiration bc it
is respiration without oxygen.
(Glycolysis is already anaerobic.)
Lactic Fermentation - Pyruvate can’t enter
Krebs Cycle since there is O2 available at the
end of the ETC. (All NADH’s are filled and have
no where to go). This process is done in human
muscle cells, fungi & bacteria.
2 Pyruvates are reduced to Lactate
(lactic acid) forming the production
of 2 ATP.
In Human muscle cells, this
causes muscle fatigue &
sometimes pain early in strenuous
exercise.
This is when sugar catabolism
for ATP outpaces muscle’s supply
of O2 in the blood.
Sometimes called O2 debt
ALCOHOL FERMENTATION –Note this is similar
to Lactic Fermentation, except CO2 is given off
and 2 pyruvates are reduced to Ethanol (Ethyl
alcohol.) (2 ATP again).This is substrate-level
phosphorylation.
This process happens
in yeast and makes
alcohol and in bread
the CO2 causes bread
to rise.
Many bacteria also
carry out this process.
Objectives for Photosynthesis:
 Plants & other Autotrophs are producers
 Site of photosynthesis – chloroplasts
 Light reactions and Calvin Cycle – convert
light energy to chemical energy
 Alternative mechanisms in hot, dry
environments
Root Words
Auto –
 - Troph
Chloro –
- phyll
Electro –
Magnet –
Hetero –
Meso –
Photo -
SUMMARY REACTION:
6 CO2 & 6H2O
C6H12O6 & 6 O2
PHOTOSYNTHESIS AS A REDOX REACTION:
Respiration - energy released from glucose when
electrons that came from H are transported by
carriers (ETC) to O2 forming H2O. Electrons
lose energy as O2 pulls them down the ETC and
mitochondria use this energy to make ATP.
Photosynthesis - reverses flow of electrons.
Water is split & electrons are transferred
along with H ions from water to CO2 reducing
it to sugar. The required energy is provided by
light.
TYPES OF FEEDERS IN A BIOSPHERE:
Autotrophs – “self-feeders” -green plants
(AKA producers.) Make organic compounds with
light.
PLANTS are Photoautotrophs.
Chemoautotroph - produce organic compounds
without the use of light. Some Bacteria, think
Deep Sea thermal vents
Heterotrophs – “Other feeders” Can’t make
their own food.
Decomposers: are Heterotrophs that consume
the remains of dead organisms. (Detritivores)
Sites of Photosynthesis
LIGHT REACTION (1st steps) – within Thylakoid
membrane.
DARK REACTION ( Calvin Cycle ) - (2nd steps) –
within Stroma.
ETC in the
Thylakoid
membrane
will also be
involved in
chemiosmosis
Fig. 10.4 OVERVIEW OF PHOTOSYNTHESIS.
(Entire process happens in the chloroplast.)
NOTE:
H2O is used &
releases O2
ATP &
NADPH is
made in
Light
reaction &
used in
Calvin
Cycle.
LIGHT & PHOTOSYNTHESIS: (Fig. 10.5)
Light “acts” as though it was particles, even
though it is not.
The packets of energy in light are called
“photons”.
NOTE: Energy in light is inversely proportioned
to it’s wavelength.
Higher
wavelength =
Lower
energy &
vice versa.
EXICITED/“ENERGIZED” ATOMS OF CHLOROPHYLL a
(A) Certain atoms within chlorophyll absorb a “photon” from light
& move from ground state to a higher level. (This means that
atom now has more potential energy.)(B)
REMEMBER:
energy).
Orbits AKA energy levels (further e- is from nucleus = more
(C) Atom stays in
this “excited” state
for a billionth of a
second, then return
to ground state &
release their energy.
Sometimes
electrons
picked up by
NADP+
Photoexcitation of a Chlorophyll a Molecule.
Same as last slide. Note e- moving from
ground to excited state by photon of light.
Excited photon
releases
energy(heat) &
photon returns
to ground
state.
Note: the pigments of chlorophyll absorb blue &
red light which are the most effective in
photosynthesis. Pigments reflect green light (the
least effective in photosynthesis).
Chlorophyll a is green
(participates directly in
the light reaction converts
solar to chemical energy.)
Chlorophyll b is
accessory pigment & is
yellow-green.
Carotene and Xanthophyll
are accessory pigments
that are shades of yellow
& orange.
Chromatography Lab - #4
Spinach Lab Variation
ABSORBANCE SPECTRA - Note the wavelengths
at which each pigment is absorbed.
NOTE: Green part of spectrum not useful for
photosynthesis. Notice other colors which are
useful for photosynthesis
Light
absorption
verses
wavelength.
Experiment Demonstrating the Action Spectrum
for Photosynthesis
(A) Algae illuminated with light that had been
passed through a prism (to get the spectrum of
light).
(B) Aerobic bacteria were put with algae. They
would go to O2 source.
(C) Bacteria went to
where Photosynthesis
would release O2.
(where red & blue
light are) SAME
PATTERN AS
ACTION SPECTRUM.
HOW A PHOTOSYSTEM HARVESTS LIGHT
Photosystems are a complex of proteins & other
molecules.
A photon hits a pigment molecule, the energy is
passed from molecule to molecule until it reaches the
reaction center of chlorophyll.
Here, the energy
drives a Redox
reaction.
Excited e- from
reaction center of
chlorophyll is
captured by primary
e- acceptors.
Photosystem I :
Chlorophyll a reaction center called P700 because the
pigment is best absorbed by a wavelength of light at
700 nm
Photosystem II:
Chlorophyll a reaction center called P680 because the
pigment is best absorbed by a wavelength of light at
680 nm.
Both chlorophyll a’s are identical but different proteins
present in each cause the chlorophyll a to have different
light- absorbing properties.
Both photosystems are involved in Noncyclic
Electron flow but Photosystem I is involved in
Cyclic Electron Flow.
NONCYCLIC ELECTRON FLOW:
REMEMBER: how a photosystem harvests light !!! This
is happening in the Thylakoid membrane.
NOTE: O2
lost from
water is
released by
Photo.
Enzyme
extracts
electrons from
water
replacing
electrons lost
from P680.
Photophosphorylation
(noncyclic)
CYCLIC ELECTRON FLOW: Everything in black
does NOT take place.
This uses Photosystem I not Photosystem II.
The ATP produced is from cyclic
photophosphorylation.
NOTE:
There is no
NADPH
produced & no
release of
O2.
Chemiosmosis in
both mitochondria
& Chloroplast.
(which both occur
in plants.)
NOTE: Same
process except
performed in
different parts
of the cell.
Stroma
The 2 Photosystems & how they relate to the
ETC & Chemiosmosis.
NOTE: Both
light
reaction &
the Calvin
Cycle stop
after dark.
Photosyn.
does not
occur at
night!
THE CALVIN CYCLE: (AKA Dark Reaction or
Light Independent Reaction)
Most abundant
protein on the
earth
(A) Uses ATP & NADPH
made during the light
reaction for energy &
recycled back to the light
reaction as ADP &
NADP+.
(B) CO2 enters & leaves
in the form of sugar.
(C) Rubisco (also called
ribulose biphosphate
carboxylase) is the most
important enzyme used in
the 1st step.
3 cycles to
make 1 glucose
molecule
Major
compound
produced.
PHOTORESPIRATION & THE CALVIN CYCLE
1) Calvin Cycle is 1st fixation of CO2 with
RuBP(ribulose biphosphate)
2) Plants discussed so far are C3 Plants since
CO2 is fixed with a 3 carbon compound.
(A) Hot dry day - stomata close - thus CO2 intake
stops.
(B) Plants use up CO2 starving the Calvin Cycle.
(C) Rubisco will now accept O2 in place of CO2 &
this is added to the Calvin Cycle.
(D) 2 carbon compound formed & exported to
mitochondria to be broken down.
(E) Photorespiration now takes place -this makes
no ATP thus decreases photosynthesis output.
C4 PLANTS: (called this because they fix CO2 into
a 4 carbon compound.) CO2 fixed in the mesophyll
cells but the Calvin Cycle takes place in the
Bundle-sheath cells.
An enzyme called PEP carboxylase adds CO2 to a
substrate called PEP.
PEP carboxylase has a
higher affinity for
CO2 than RuBP
carboxylase (rubisco)
New 4 C compound
exported to the
bundle-sheath cells
(through
plasmodesmata.)
4 carbon compound (Malate) releases CO2 which is
re-assimilated into organic material by Rubisco in
the Calvin Cycle.
What really happens - this keeps CO2
concentration high enough in bundle-sheath cells
to allow Rubisco to accept CO2 rather than O2.
This minimizes
photorespiration
and enhances
photosynthesis.
Important plants
such as sugarcane
& corn are C4
Plants.
CAM PLANTS: (in water storage plants such as
cacti & pineapples called succulents.) ARID
CONDITIONS.
Open stomata during the night & close them
during the day. (reverse of other plants).
1) This helps desert plants conserve water, but
CO2 can’t enter the leaves.
2) CO2 is fixed in organic acids during the
night in vacuoles when stomata are closed.
3) During the day, light reaction supplies ATP &
NADPH for the Calvin Cycle. CO2 is released
from organic acids to be used to make sugar.
Fig. 10.19 A REVIEW OF PHOTOSYNTHESIS.