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Biology 20
Unit III – Chapter 5 Tannant
Unit 3 – Photosynthesis and Cellular Respiration
Preparation:
Plant Cells and Organelles
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Unit III – Chapter 5 Tannant
Animal Cells and Organelles
Structure and Function of Cell Membranes
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Protein molecules in a cell membrane acting as channels (passive transport) or active
pumps (active transport)
The active transport processes of endocytosis and exocytosis.
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Section 5.1 – Matter and Energy Pathways in Living Systems
Photosynthesis

Cellular Respiration
Captures
Solar Energy
Releases
Chemical Energy
Chloroplasts
Mitochondria
Only in Plant cells
Both plant and animal cells
ATP and Cellular Activity
- Chemical energy used by cells is in the form of ATP (adenosine triphosphate)
There are other high energy chemicals, but ATP is the most common.
o ATP is a useful energy molecule because it can be broken down and reformed
very quickly (oxidation-reduction process...or linked catabolic-anabolic
Adenosine Triphosphate
Adenosine Diphosphate
Adenosine – P ~ P ~ P
Adenosine – P ~ P
chemical reactions)
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Unit III – Chapter 5 Tannant
The energy of the third phosphate bond is key to the action of ATP.
o When the phosphate bond breaks, energy is released  and transferred to other
chemicals involved in cellular activity.
 This forms ADP, a lower energy molecule.
o ADP can be regenerated when phosphate is added to ADP.
Chloroplasts
- Membrane bound organelles containing the pigment chlorophyll
o Contain 2 surrounding membranes
 Outer membrane
 Inner membrane
o Also contain
 Fluid – in the inner space of a chloroplast (Stroma)
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Concentrated mix of proteins and other chemicals needed to
synthesize carbohydrates.
Thylakoid membrane – a third membrane inside the stroma
 Interconnected, flattened sacs (thylakoids)
 May be stacked into columns called grana
 Chlorophyll is located in (embedded in) the thylakoid membranes.
Mitochondria
- Site of cellular respiration
- Organelles found in all eukaryotes
- Smaller than chloroplasts
- Membrane bound organelles
o Contain 2 membranes
 Outer membrane
 Inner membrane – highly folded layer
 Folds are called – cristae
 Cristae provide a large surface area for the production of ATP
o Also contain
 Fluid filled inner space – matrix
 Contains proteins and other chemicals needed to break down
carbohydrates
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Metabolic Pathways for Cellular Reactions
- Chemical reactions inside living organisms often cannot occur in the same manner
they would in a lab.
 Reactions in living organisms cannot release too much heat or absorb too
much heat or the reactions would kill the organism
o Therefore, chemical reactions in living organisms are broken down into a series of
smaller reactions that occur in a specific order.
 The end product of one small reaction is the reactant for the next.
 Each smaller reaction is controlled by biological catalysts called –
enzymes
 Energy can be stored or released from ATP at each smaller reaction, so
that there is no overwhelming exothermic or endothermic event.
o The step-by-step sequence of smaller chemical reactions are called – metabolic
pathways.
Enzymes Catalyze Cellular Metabolism and Energy Production
Metabolism – all the chemical reactions that occur within a cell to support life functions
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Catabolic reactions  to break down reactants into smaller, usually lower-energy
products.
o Energy is released – exothermic
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Anabolic reactions  synthesize (form) larger products from smaller reactants.
o Energy is absorbed – endothermic
o Energy usually from ATP
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Catalysts – Enzymes
 To speed up reactions you can add heat (which is not practical in living
organisms) or you can use a catalyst
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
A substance that speeds up a reaction (reducing activation energy) without
being used up in the reaction itself.
Enzymes are protein molecules with highly specific shapes
 Enzymes can change their shape depending upon environmental
conditions and what chemicals it is reacting with
 The shape determines its function
 Chemical reactants ‘fit’ into regions of the enzyme (like a lock
holds a shape that a key can fit into)
 The enzyme ‘holds’ the chemical reactants together in the ideal
configuration for the reaction to occur
Linking Reactions through Oxidation and Reduction
Oxidation – when an atom or molecule loses electrons
- Remember, electrons are never ‘lost’...they only join up with other
atoms/molecules
- Therefore all oxidation-reduction reactions are coupled...they cannot
occur without each other.
- Often called redox reactions (reduction-oxidation)
Reduction – when an atom or molecule gains electrons
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In any chemical reaction between 2 compounds, one compound loses
electrons (is oxidized) and the other gains those electrons (is reduced).
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The chemical that is oxidized CAUSES the other to be reduced, and so
is called the Reducing Agent
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The chemical that is reduced CAUSES the other to be oxidized, and so
is called the Oxidizing Agent
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Section 5.2 – Photosynthesis Stores Energy in Organic Compounds
Photosynthesis Overall (Net) Reaction
6 CO2 + 6 H2O + sunlight + chloroplasts  C6H12O6 + O2
Glucose
- Glucose is converted to
 Cellulose (wood fibres)
 Other sugars (fructose, etc)
 Starch (long chains of carbohydrates for storage)

Glycoproteins – sugars combined with proteins
 Found on cell membranes and involved with cell ID
and immune system functioning
The Process of Photosynthesis
- The arrow in the overall photosynthesis equation represents over 100
step-by-step chemical reactions in the metabolic pathway
- Photosynthesis
- 2 steps
o Photo  light capturing (light dependent reaction)
 Trapped light energy is used to generate 2 high energy
compounds (ATP and NADPH)
o Synthesis  producing carbohydrates (light-independent
reaction
 The ATP and NADPH are used to reduce CO2 to make
glucose.
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Light Dependent Reactions
Photosystems – clusters of
pigments (chlorophyll and
others)
Pigments in the thylakoid
membrane absorb light energy
Chlorophyll – reflects green
light but absorbs red and blue
light.
Pigments – compounds that
absorb some wavelengths of
light and reflect others. (The
reflected light waves give the
pigment its colour.)
Beta-carotene (carotenoids) –
absorb blue and green light, but
reflect yellow, orange, and red.
Light energy striking the
pigment causes electrons to
move  the electrons are
passed to other chemicals.
Absorption Spectrum – a graph that shows the relative amounts of light of different colours that
a compound absorbs.
Action Spectrum – shows the relative effectiveness of different wavelengths of light for
promoting photosynthesis  determined by the rate of oxygen produced from photosynthesis.
The Metabolic Pathway of the Light Dependent Photosynthesis Reaction
Photosystems – the clusters of pigments (chlorophyll and others) embedded in the thylakoid
membrane.
- Named according to the order of
discovery
o Photosystem II (PSII) – first in
the sequence of photosynthesis.
o Photosystem I (PSI) – second in
the sequence of photosynthesis.
- Present in the photosystems
 One dozen or more
chlorophyll molecules
 A few carotenoid
molecules
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An electron acceptor molecule (the reaction centre)
Example: Consider the photosystems like radio antennas...they collect the light and pass the electric
current on to the station.
Electron Transport System
- A series of electron-carrying molecules
- With each transfer along the system the electron releases a small amount of energy.
 This energy is used to push hydrogen ions from the stoma  across the
thylakoid membrane  into the thylakoid space.
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Steps of the light dependent reaction:
1. Light strikes the photosystem II
2. An electron in the photosystem reaction centre is ‘excited’.
3. The electron is passed to an electron-accepting molecule.
a. Gain electron = reduced = has greater energy
4. The reaction centre in the photosystem is now missing an electron – which has to be
replaced before more light can be absorbed.
a. Water molecule is split  2 H+ and O2- and one electron, which is taken in
by the photosystem to replace the missing electron.
b. The oxygen released is eventually released as oxygen gas by the plant.
5. From the electron acceptor the electron is passed to the electron transport system.
a. The hydrogen ions [H+] from the water molecule are pushed into the
thylakoid.
b. Results in a greater concentration of hydrogen inside the membrane. This
creates a potential energy situation = stored energy
c. This energy will be used to generate ATP
i. ADP + Pfree phosphate group + energyfrom [H+] gradient  ATP
6. While the above steps take place, photosystem I also absorbs light energy.
a. Energy transferred to a reaction centre
b. Electron becomes excited
c. Electron passed to electron acceptor
i. Missing electron from reaction centre is replaced by electron from the
end of photosystem II transport chain.
d. Electron passed from electron acceptor to electron transport chain
i. The electron reduces NADP+ to NADPH
ii. NADPH is a high energy reducing agent that will be used in the lightindependent reactions.
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Making ATP: Chemiosmosis
When H+ ions are forced inside the thylakoid they cannot diffuse back (membrane is
impermeable to them)
An enzyme embedded in the thylakoid membrane called ATP Synthase (which is
linked to an enzyme that bonds free phosphate groups to ADP) allows the H+ ions to
fall back down the concentration gradient and move outside of thylakoid.
 Links the movement of H+ ions to the formation of ATP.
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Biomimicry – scientists are looking at mimicking the chemical processes of photosynthesis to
find ways of utilizing solar energy more efficiently.
The Metabolic Pathway of the Light-Independent Photosynthesis Reactions
Once there is enough NADPH and ATP in the stroma – the molecules can be used to
synthesize glucose (whether light is present or not)  Called the Calvin-Benson Cycle
(or the Carbon-Fixing Cycle)
1. Fixing CO2
a. The carbon atom from CO2 is chemically bonded to a pre-existing molecule in the
stroma (Ribulose Bisphosphate – RuBP...a 5-Carbon molecule)
b. Produces a 6-carbon (unstable) compound
i. Immediately breaks into two 3-Carbon compounds
c. Summary so far: CO2 + RuBP  unstable C6  2 C3
2. Reduction
a. C3 molecules are low energy compounds.
i. They are activated by ATP (phosphorylation = add phosphate from ATP
to the carbon molecules)
ii. Once activated (phosphorylated) they are reduced by NADPH
b. After phosphorylation and reduction, the resulting molecules are PGAL
(glyceraldehyde-3-phosphate)
i. Some PGAL molecules leave the calvin-benson cycle to make glucose.
ii. Remaining PGAL molecules move to the third stage of the calvin-benson
cycle
3. Replacing RuBP
a. Most of the PGAL molecules, in combination with ATP, are chemically
rearranged to make RuBP (C5)
4. The Calvin-Benson Cycle must occur 6 times in order to synthesize one molecule of
glucose
a. Of the 12 PGAL molecules made, 10 are used to remake RuBP and 2 are used for
glucose
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Section 5.3 – Cellular Respiration Releases Energy from Organic Compounds
Cellar Respiration – the step-by-step process of releasing energy from organic (carbon-based)
compounds and storing that energy in high-energy chemical compounds like ATP.
C6H12O6 + 6 O2 + mitochondria  6 CO2 + 6 H2O + heat + ATP energy
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Glucose is oxidized to carbon dioxide.
o Electrons (and H+ ions) are removed from glucose
Three Pathways for Energy Release
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Different species release energy from food in different ways.
1. Aerobic Cellular Respiration
a. Oxic – containing oxygen – conditions
b. Oxygen is required to produce ATP
c. Animals, plants, and many types of fungi, protists, and bacteria are aerobic
2. Anaerobic Cellular Respiration
a. Anoxic – no oxygen – conditions
b. Oxygen is not required for ATP production
c. In fact, oxygen may be lethal
d. Bacteria, and members of the archaea domain, and chemosynthetic organisms,
and some nitrogen-fixing bacteria
3. Fermentation
a. An anaerobic process performed by yeasts and some bacteria
i. Lactobacillus bulgaricus – bacteria causing milk to sour
b. Fermentation can also occur in the muscle cells of aerobic organisms – forms
lactic acid by-product
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Aerobic Cellular Respiration
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Oxidation reaction in which a series of enzyme-catalyzed reactions transfer electrons
from high-energy molecules (glucose) to oxygen, releasing energy (ATP)
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Cellular respiration begins with glycolysis  in the cell cytoplasm
 Glycolysis is an anaerobic process and generates only a small amount of
ATP
 Glycolysis = lysis of glucose = breakdown of glucose
 Occurs in all living cells
 Produces Pyruvate, a high-energy molecule
 If no oxygen is available, pyruvate will proceed to fermentation
With sufficient oxygen, pyruvate enters the mitochondria and undergoes a series of
preparatory reactions and then undergoes the Krebs Cycle
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Kerb’s Cycle
 A step-by-step process of transforming pyruvate into NADH and FADH2
(reducing agents)
 NADH and FADHH supply electrons to an electron transport system that
produces a large amount of ATP
 Water is the final end-product
Glycolysis – Inside the Cytoplasm
1. Glucose (C6) is split into two Pyruvate (C3 ) molecules
a. ATP is required for this process- glucose must be phosphorylated before it can
split
b. Several more chemical reaction steps occur
i. 4 ATP are synthesized (Carbon compounds are dephosphorylated and
ADP is phosphorylated)
ii. NAD+ (nicotinamide adenine dinucleotide) is reduced (gain electron and
H) to NADH.
c. Summary:
i. 2 ATP used
ii. 4 ATP synthesized
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iii. NADH synthesized
iv. Pyruvate is produced
Inside the Mitochondria – Kreb’s Cycle Preparation
2. Pyruvate loses a carbon (as CO2) to form a C2 molecule called acetate
3. The remaining C2 molecule joins with a molecule of Coenzyme A (CoA) to form acetyl
CoA
a. the CoA molecule acts like a ‘tow truck’ to tow the acetyl group to the Krebs
Cycle
4. Another NAD+  NADH is formed
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Inside the Mitochondria – The Kreb’s Cycle
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The Kreb’s cycle is also called the Citric Acid Cycle
It is a cycle because the last compound (C4) must be regenerated
During one complete cycle
 A C2 group (acetyl) is
added to the C4 molecule
 2 carbons are fully
oxidized and released as
CO2
 Energy released from the
oxidization of Carbon is
transformed into
reducing agents
 NADH and
FADHH (flavin
adenine
dinucleotide)
 ATP is also
generated
The majority of ATP produced is in
the electron transport system
(similar to the ones in photosynthesis)
 High energy electrons are passed to a chain of electron-carrying molecules
 Found on the inner membrane of the mitochondria
 As electrons are passed from one carrier to another, small amounts
of energy are released
 This energy is used to pump H+ ions across the membrane from
the matrix to the inter-membrane space (between the inner and
outer mitochondrial membranes)
 The build up of H+ ions creates a hydrogen ion concentration
gradient
o The ions diffuse back across the membrane though
channels (ATP Synthase)
o As H+ ions move, ATP is formed from ADP
(Chemiosmosis)
 Oxygen is the final electron acceptor in the transport system
o The oxygen accepts both electrons and hydrogen ions 
water
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Anaerobic Cellular Respiration
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Since oxygen cannot act as the final electron acceptor, other inorganic chemical
compounds like nitrates, sulphates, or carbon dioxide take that role.
Depending upon the final electron acceptor, final products of anaerobic respiration
may be free nitrogen (N2), sulphur (S2), nitrite, or methane.
Fermentation
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Not only does not require oxygen, but does not have an electron transport system
Reactions occur in the cytoplasm of the cell
There are many types of fermentation
 Lactate fermentation – muscle cells under oxygen debt
 Ethanol fermentation – yeasts able to function aerobically and
anaerobically
 Products vary depending upon the conditions
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Table 5.2 Selected Fermentation Products and their Uses
Products of
Possible Sources
Fermentation
Acetic Acid
Uses
Bacteria:
Sours beer;
Leuconostoc sp.
Produces vinegar
Acetobacter xylenam
Diacetyl
Bacteria:
Streptococcus diacetialactis
Lactic Acid (Lactate)
Bacteria:
Lactobacillus bulgaricus
Propionic acid + CO2
Bacteria:
Proprionibacterium shermani
Provides fragrance and flavour
to buttermilk
Aids in changing milk to
yogurt
Produces the “eyes” (holes)
and flavour of Swiss cheese
Ethanol Fermentation and use in Fuels.
- Ethanol is a waste product and toxic to the bacteria that produce it.
- Ethanol is produced from the fermentation of corn and wheat
 This is a food source – is it ethical to use food to power cars and industry?
 When ethanol burns it still releases carbon dioxide – is this a viable
alternative fuel then?
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
Ethanol does burn cleaner than other fossil fuels – this means is does not
release potentially harmful volatile organic compounds (VOC’s) into the
atmosphere, it does not contribute to smog, and reduces the amount of
carbon monoxide in car exhaust. Is this enough benefit to support its use?
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