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Chapter 6 notes
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Cellular Respiration: Release of the energy stored in food.
ATP: Useable form of energy
Glycolysis: first step in aerobic or anaerobic respiration.
Anaerobic: without oxygen
Aerobic: with oxygen
Oxidation: Reaction when an atom or molecule loses electrons
Reduction: Reaction when an atom or molecule gains electrons,
Fermentation: Glycolysis is followed by the conversion of pyruvic acid into some
end product with no further release of energy
 Kreb’s Cycle:Continuing series of reactions
 Electron Transport Chain: reaction within the mitochondrion that powers the
formation of ATP.
Energy
 Required by all living things for life processes
 Cells need a continuous supply of energy to stay alive
 Fuel to burn and supply this energy is in food (Carbs, most often)
 Burning of fuel results in heat and storage of chemical energy.
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Cellular Respiration
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Release of energy stored in food
Happens in plants and animals
Is essentially the opposite reaction from photosynthesis
Energy released during photosynthesis is “packaged” in the molecules of certain
compounds
 One such compound is called ATP
ATP (Adenosine Triphosphate)
 The useable form of energy
 Composition:
 1 molecule of adenine (nitrogenous base)
 1 molecule of ribose (5-carbon sugar)
 Together these are called adenosine
 3 phosphate groups (triphosphate)
An ATP Molecule
Function of ATP
 The function of ATP is energy storage
 The bond linking the last phosphate group is a high-energy bond
 When the third phosphate is removed, it can attach to another compound and
transfer the energy from that high-energy bond.
 This transfer of energy is phosphorylation
 Removing the third phosphate from ATP creates ADP (Adenosine diphosphate),
which is a lower-energy compound than ATP.
How is ATP made?
 During cellular respiration, food is broken down.
 The energy released in this process is used to attach a 3rd phosphate group to
ADP, creating ATP.
 From the energy released from the breakdown of one Glucose molecule, 36 ATP
molecules are formed
 ATP can then be used by any part of the cell that needs energy.
 Storing energy as ATP rather than using it all at once allows the cell to use energy
where it needs to; also, it would be too much energy to handle at once if this were
not done..
Formation of ATP
Hydrogen (Electron) Acceptors
 Recall: Oxidation and Reduction
 After complex carbs are broken down into glucose, glucose is broken down in a
biochemical pathway. Oxidation and reduction take place along the way.
 NAD (nicotinamide adenine dinucleotide) and FAD (flavine adenine
dinucleotide) are electron carriers (or acceptors)
 NAD and FAD c an each accept a pair of high-energy electrons and a proton,
becoming reduced.
 After accepting high-energy electrons, molecules gain energy temporarily
Glycolysis
 Occurs in cytoplasm of the cell
 Is the first step in both aerobic and anaerobic respiration
 In this step, glucose is split.
2 phosphate groups are bonded to a glucose molecule. This uses 2 molecules of
ATP.
 A group of chemical reactions break down the glucose molecule into 2 molecules
of pyruvic acid. This produces 4 molecules of ATP.
 The net result is thus 2 molecules of ATP for every glucose. Also, 2 molecules of
NADH are formed.
Fermentation
 In anaerobic respiration, glycolysis is followed by a conversion of pyruvic acid
into some end product with no further release of energy (no more ATP formed)
 This is called fermentation
 Examples: In plant cells, the end result is ethyl alcohol. In animal cells, it is lactic
acid.
 In fermentation, pyruvic acid acts as an electron acceptor. They get these
electrons from NADH, which is then ready as NAD to be used again.
Anaerobic or Aerobic?
Aerobic Respiration
 The use of oxygen in the breakdown of food substances allows the cell to release
far more energy.
 Aerobic respiration begins with glycolysis. The rest of the steps take place within
the mitochondria.
 Inside the mitochondrion, pyruvic acid breaks down into CO2 NADH, and a 2carbon compound. This compound, combined with coenzyme A, forms acetyl
CoA.
Krebs Cycle
 Named for Sir Hans Krebs
 Acetyl CoA begins the Krebs Cycle, which is a continuing series of reactions
 Each turn of the Krebs Cycle takes one molecule of Acetyl CoA and converts it to
2 molecules of CO2, 3 molecules of NADH, 1 molecule of FADH2.
 Only 1 molecule of ATP is produced by each turn.
Electron Transport Chain
 Most of the energy released by breaking down glucose comes through the electron
transport chain.
 This is a highly organized system of enzymes and coenzymes on the inner
membrane of the mitochondrion.
 NADH and FADH2 carry electrons into the chain and pass them from one
compound to another. Eventually, oxygen is the final acceptor.
 At various points, energy is given up and used to pump hydrogen ions across the
mitchondrial membrane.
 This creates an electrical gradient, which provides the energy to convert ADP to
ATP
 In glycolysis, one molecule of glucose forms 2 molecules of ATP.
 In the Krebs cycle, 2 more molecules of ATP are formed (1 for each pyruvic acid)
 In the Electron Transport Chain, 32 molecules of ATP are formed from each
glucose molecule.
 Therefore, each glucose molecule yields 36 ATP molecules.
 The net reaction is:
C6H12O6
+
6O2 →
6CO2 +
6H2O
+ Energy (36 ATP)
Aerobic and Anaerobic Exercise
 When you exercise at a slow enough pace that your blood can supply your
muscles with adequate oxygen, aerobic respiration takes place normally. This is
aerobic exercise.
 During prolonged or strenuous activity, the cells cannot get sufficient oxygen.
This is anaerobic exercise. This means that the electron transport chain cannot
work, as it needs oxygen. This shuts down the Krebs cycle.
 In this case, only glycolysis can take place. This results in a buildup of lactic
acid, which makes the muscle feel tired.
 After a period of rest, the muscle can get enough oxygen to convert lactic acid to
pyruvic acid and begin aerobic respiration again. This repays the oxygen debt.
Chapter 17 notes
Photosynthesis
 The transformation of sunlight energy into chemical energy
 Photosynthesis is used by green plants, and photoautotrophs
 When light strikes, some of the energy from photons is passed to one of the
electrons in the atom. In photosynthetic organisms, this energy is used to make
chemical bond energy
Chlorophylls
 The most important and abundant photosynthetic pigments
 There are two main types of chlorophyll: Chlorophyll a and Chlorophyll b.
 Chlorophyll reflects green light to the eye, making plants appear green.
Chlorophyll a
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The primary photosynthetic pigment
Directly involved in converting light energy to chemical energy
Normally hides the carotenes (orange) and xanthophylls (yellow) in leaves
Breaks down in the fall, so carotenes and xanthophylls are visible. This turns the
leaves different colours.
Chlorophyll b
 Along with carotenes and xanthophylls, absorbs light energy and transfer it to
chlorophyll a
 Presence of chlorophyll b and the others enables the leaf to absorb light from all
different parts of the spectrum.
Chloroplasts
 Site of photosynthesis
 Made from stacked thylakoids called grana.
 Stroma are regions in between grana
Photosynthesis
 The reactions that occur in the chloroplasts are divided into two types.
 These two types are called light-dependent reactions and light-independent
reactions.
Light-Dependent Reactions
 Begin when chloroplasts absorb light
 Use water, ADP, and NADP.
 Produce ATP and NADPH. These are used to power the light-independent
reactions.
 Also produce Oxygen. This oxygen is of no help to photosynthesis, but is a very
useful by-product.
 Take place in the membranes of the chloroplast.
Light-Independent Reactions (aka the Calvin Cycle)
 Named for Melvin Calvin
 Take place in the stroma of chloroplasts.
 Carbon Dioxide is taken in and used to form glucose. This is called Carbon
Fixation.
 Calvin Cycle is controlled by enzymes.
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Begins with a 5-C sugar called RuBP (ribulose biphosphate)
CO2 is taken in and reacts with RuBP
This forms Phosphoglycerate (PGA), a 3-C compound.
Using energy from NADPH and ATP, PGA is converted to PGAL
(Phosphogylceraldehyde)
 Some PGAL is then transformed into glucose (2 PGAL make one Glucose)
 Most of the PGAL is converted back to RuBP using ATP. This is then used in the
next Calvin Cycle.
What Affects Photosynthesis?
 Light intensity, temperature and availability of water and minerals.
 Higher light intensity = faster photosyntheis
 Temperature must be between 0 and 35 degrees Celsius.
 Shortage of water or minerals slows photosynthesis.
Photosynthesis vs Respiration
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Stores energy
Takes place in chloroplasts
Reactants are Carbon Dioxide and Water
Products are Glucose and Oxygen
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Releases energy
Takes place in mitochondria
Reactants are Glucose and Oxygen
Products are Carbon Dioxide and Water
Special Cases
 C4 Plants: Some plants use an extra step to fix CO2 into a 4-C compound before
it enters the Calvin Cycle. This allows for faster carbon fixation (e.g. Sugar cane
and corn).
 CAM Plants: Close their stomates during the day, but take in CO2 at night,
storing it until day to make glucose (e.g. desert cacti).
 Chemosynthetic Bacteria: Use the Calvin cycle to fix CO2 but use inorganic
substances, not ATP and NADPH.
 Heterotrophic Plants: Supplement photosynthesis with other nutrients.
C4 Plant: Sugar Cane