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IB BIOLOGY: Respiration Notes
Draw and annotate a molecule of ATP to show how it stores and releases energy.
Contrast oxidation and reduction from the perspectives of (a) the gain or loss of
electrons from an element, and (b) gaining oxygen or losing hydrogen.
Oxidation involves the loss of electrons from an element, whereas reduction involves the
gain of electrons and that oxidation frequently involves gaining oxygen or losing
hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen.
OIL RIG: Oxidation Involves Loss of Hydrogen, Reduction Involves Gain in Hydrogen.
Define cell respiration.
• Respiration is the controlled release of energy from organic compounds in cells to
form ATP.
Write the summary equation for cellular respiration.
Identify two components of the cell in which respiration takes place.
Glycolysis takes place in the cytoplasm (cytosol), while the citric acid (Krebs) cycle and
oxidative phosphorylation take place within the mitochondria.
Distinguish between aerobic and anaerobic in terms of cell respiration.
• Aerobic Cellular Respiration: A series of chemical reactions (biochemical
pathways) that produces ATP from glucose and oxygen.
• Anaerobic Cellular Respiration: A series of chemical reactions where pyruvate
is converted in the cytoplasm to produces small amounts of ATP without oxygen.
o Occurs in cytoplasm of cell
o Two types
 Alcohol fermentation: pyruvate is converted in the cytoplasm
into ethanol, carbon dioxide and energy, with no further yield of
ATP. Occurs in bacteria.

Lactic acid fermentation: Produces lactic acid and energy.
Occurs in humans (or anything with muscles).
Diagram of anaerobic respiration
Phosphorylation:
The process of joining a phosphate group to a molecule
1. Substrate-level phosphorylation
• Producing ATP by adding a phosphate molecule to ADP from a carbon (organic)
substrate molecule
• This method doesn’t produce very much ATP (2-4)
2. Oxidative Phosphorylation
• Producing ATP in the electron transport chain by adding inorganic molecules to
ADP
• This produces a lot of ATP (34-38)
Outline the process of glycolysis, including phosphorylation, lysis, oxidation and
ATP formation (see diagram below).
Step 1 - Glucose is phosphorylated. Two phosphate groups are added to glucose to form
hexose biphosphate. These two phosphate groups are provided by two molecules of ATP.
Step 2 - Lysis of hexose biphosphate: splits into two molecules of triose phosphate.
Step 3 - Each triose phosphate molecules is oxidized. Two atoms of hydrogen are
removed from each molecule. The energy released by the oxidation is used to add another
phosphate group to each molecule. This will result in two 3-carbon compounds, each
carrying two phosphate groups. NAD+ is the hydrogen carrier that accepts the hydrogen
atoms lost from each triose phosphate molecule.
Step 4 - Two pyruvate molecules are formed by removing two phosphate groups from
each molecule. These phosphate groups are given to ADP molecules and form ATP.
Draw and label a diagram showing the structure on mitochondrion as seen in a
TEM image. Include the inner and outer mitochondrial membranes, matrix, and
ribosomes, as well as a scale bar.
Mitochondrion Size: 0.5 micrometers - 10 micrometers
KEY
A: Matrix
• site for Krebs' cycle (contains necessary enzymes for reactions)
• link reaction
• ATP synthesis
B: Inner Membrane
• site of oxidative phosphorylation
• electron transport chain
• increased surface area
• ATP synthesis
C: Intermembrane Space
• H+ / proton build up
Explain the relationship between the structure of the mitochondrion and its
function.
Having two membranes allows compartmentalization and accumulation of protons
(hydrogen ions) during chemiosmosis
Having a folded inner membrane (cristae) forms a large surface area and increases the
length available to the electron transport chain, therefore maximizing ATP production
during chemiosmosis
The fluid matrix containing enzymes of the Krebs cycle.
Explain oxidative phosphorylation in terms of chemiosmosis.
Electrons are given to proton pumps that are embedded in the membrane between the
matrix and inner membrane/cristae of the mitochondrion. The pumps are reduced, giving
them energy to pump protons into the inner membrane space. The electrons are
transferred along a chain of pumps, continuously losing energy. The proton pumps create
a high concentration gradient of protons (H+) inside the inter membrane space. Thus,
protons diffuse back into the matrix through facilitated diffusion of ATP synthase
(channel protein and enzyme). As the protons pass along this protein channel, the kinetic
energy of the protons causes the ATP synthase molecule to turn slightly, exposing active
sites that create ATP by binding ADP with inorganic phosphate molecules. The result is
36 ATP produced by oxidative phosphorylation.
Explain aerobic respiration including the link reaction, the Krebs cycle, the role of
NADH +H+, the electron transport chain and the role of oxygen.
In aerobic respiration (in mitochondria in eukaryotes), each pyruvate is decarboxylated
(CO2 removed). The remaining two-carbon molecule (acetyl group) reacts with reduced
coenzyme A, and, at the same time, one NADH + H+ is formed. This is known as the
link reaction. Acetyl CoA then enters the Krebs Cycle where FAD / NAD+ accepts
hydrogen and a high-energy electron to form NADH / FADH2. These electron carriers
(FADH2 / NADH) donate electrons to electron transport chain. These electrons transfer
their energy to member proteins (proton pumps) and actively pump protons (hydrogen
ions) across inner membrane. Oxygen is the final electron acceptor and produces water as
a “waste product”. In the final step, Chemiosmosis, protons build up (making a proton
gradient) in the inter-membrane space of the mitochondrion. This gradient potential is
then turned into ATP as protons flow into matrix of mitochondrion through ATPase /
ATP synthase.
Describe the central role of acetyl CoA in carbohydrate and fat metabolism.
Both carbohydrate and fat metabolism is accomplished by splitting the molecules into 2
carbon structures. These structures are then attached to Coenzyme A, creating Acetyl
CoA and allowing the molecules to pass into the inner matrix of the mitochondrion in
order to complete the Krebs Cycle and chemiosmosis.
Draw the complete steps for the Krebs cycle.
The krebs cycle is an example of a metabolic cycle. Each step in the cycle requires
enzymes to reduce the activation energy. The reactions all take place in the matrix of the
mitochondria and are usually represented as a circular diagram. Try to overcome the idea
that the molecules are going in a circle but more that this reaction is taking place within
the confined space of the matrix where each intermediate becomes the substrate for the
next step.
Alternative Summary of Krebs Cycle
(a) Pyruvate (3C)
(b) Link reaction
(c) C4 + C2= C6
(d) Recycling of CoA
(e) Decarboxylation C6 to C5 and the reduction of NAD
(f) Decarboxylation C5 to C4 and the reduction of NAD
(g) C4 to C4 with the reduction of coenzymes FAD and NAD. ATP is made directly.
(h) C4 to C4 acceptor
This cycle follows one acetyl group.
Each glucose that enters glycolysis will produce 2 acetyl groups.
Annotate the diagram below with the stages of the electron transport chain and
oxidative phosphorylation, including the generation of a H+ concentration gradient
in the inter-membrane space, movement of electrons, oxidative phosphorylation by
ATP synthase, use of O2 as the terminal electron acceptor.