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1.4.1 Why Do Living Organisms Need to Respire?
· Respiration is the process where energy stored in complex molecules is used to make ATP ­ occurs in living cells.
· Energy cannot be created or destroyed, just converted from one form to another. It is measured in joules/kilojoules and it
has many forms.
Why do we need Energy?
· All living organisms need energy to drive their biological processes ­ metabolism.
· Metabolic processes that need energy include:
­ ACTIVE TRANSPORT: moving ions/molecules across a membrane against a concentration gradient.
­ SECRETION: large molecules are exported by exocytosis.
­ REPLICATION: DNA + synthesis of organelles before a cell divides.
­ MOVEMENT: movement of flagella/cilia/muscle contraction.
· Some of the energy from catabolic reactions is released in the form of heat ­ useful as metabolic reactions are controlled by
enzymes so organisms need to maintain a suitable temperature.
Where does the Energy come from?
· Plants use sunlight energy (photoautotrophs) to make large molecules that contain chemical potential energy.
· ATP is a phosphorylated nucleotide ­ high-energy.
· Each molecule of ATP consists of adenosine + 3 phosphate groups.
· It can be hydrolysed to ADP and Pi.…read more

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1.4.2 The Stages of Respiration
· Respiration of glucose can be described in 4 stages:
· Happens in the cytoplasm of all cells.
· Doesn't need oxygen.
· Can take place in aerobic or anaerobic conditions.
· Glucose (6-carbon sugar) is broken down to 2 molecules of pyruvate (3-carbon compound).
The Link Reaction
· Happens in the matrix of mitochondria.
· Only takes place under aerobic conditions.
· Pyruvate is dehydrogenated and decarboxylated and converted to acetate.
Krebs Cycle
· Happens in the matrix of mitochondria.
· Only takes place under aerobic conditions.
· Acetate is decarboxylated and dehydrogenated.
Oxidative Phosphorylation
· Happens on the folded inner membranes (cristae) of mitochondria.
· Only takes place under aerobic conditions.
· ADP is phosphorylated to ATP.
· Under anaerobic conditions, pyruvate will be converted to ethanol or lactate.…read more

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1.4.2 Coenzymes
Why are Coenzymes needed?
· During glycolysis, the link reaction + Krebs cycle, hydrogen atoms are removed from substrate molecules in oxidation
reactions ­ these reactions are catalysed by dehydrogenase enzymes (not very efficient enzymes).
· Coenzymes are needed to help them carry out the oxidation reactions of respiration ­ the hydrogen atoms are combined
with coenzymes like NAD which carry the hydrogen atoms to the inner mitochondrial membranes ­ where oxidative
phosphorylation can occur.
· Made of 2 linked nucleotides.
· When a molecule of NAD has accepted 2 hydrogen atoms with their electrons, it is reduced.
· When it loses the electrons it is oxidised.
Coenzyme A (CoA)
· Its function is to carry ethanoate (acetate) groups from the link reaction onto the Krebs cycle.
Adenine Ribose
Coenzyme A
NAD…read more

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1.4.4 Structure + Function of Mitochondria
· Mitochondria are organelles found in eukaryote cells.
· All mitochondria have an inner + outer membrane (the envelope).
· The outer membrane is smooth and the inner membrane is folded into cristae (large SA).
· Between the 2 membranes is the intermembrane space.
· The matrix is enclosed by the inner membrane ­ semi-rigid and gel-like, contains proteins + lipids + looped DNA + ribosomes
+ enzymes.
· Metabolically active cells have more mitochondria ­ mitochondria can be moved around within cells by the cytoskeleton.
How does their Structure enable them to carry out their Functions?
· The matrix is where the link reaction + krebs cycle take place. It contains:
­ The enzymes that catalyse the stages of these reactions.
­ Molecules of NAD.
­ Mitochondrial DNA which codes for mitochondrial enzymes + other proteins.
­ Mitochondrial ribosomes where proteins are assembled.
· The outer membrane contains proteins that allow the passage of molecules like pyruvate.
· The inner membrane:
­ Has a different lipid composition from the outer membrane and is impermeable
to most small ions.
­ Is folded into cristae to give a large surface area.
­ Has many electron carriers and ATP synthase enzymes embedded in it.…read more

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1.4.3 Glycolysis
· Occurs in the cytoplasm of all cells that respire anaerobically and
aerobically. Glucose (6C)
Stage 1 ­ Phosphorylation
1. 1 ATP molecule is hydrolysed and the phosphate group released is ATP
attached to a glucose molecule.
2. Glucose 6-phosphate -> fructose 6-phosphate. Glucose 6-P
3. Another ATP is hydrolysed and the phosphate group released is attached
to fructose 6-phosphate = fructose 1,6-bisphosphate.
4. The energy from the hydrolysed ATP molecules turns this into hexose 1,6-
Fructose 6-P
· 2 molecules of ATP have been used for 1 molecule of glucose. ATP
Stage 2 ­ Splitting of Hexose 1,6-bisphosphate
1. The hexose 1,6-bisphosphate molecule is split into 2 molecules of triose Hexose 1,6 Bisphosphate
phosphate (TP).
Stage 3 ­ Oxidation of Triose Phosphate
1. 2 hydrogen atoms are removed from each TP molecule using
dehydrogenase enzymes to form 2 intermediate compounds. 2 x TP (3C)
2. These are aided by NAD which combines with the hydrogen atoms,
becoming reduced NAD. 2 Reduced
· 2 molecules of NAD are reduced per 1 molecule of glucose. 2 x Intermediate NAD
· 2 molecules of ATP are formed (substrate ­level phosphorylation). Compounds (3C)
Stage 4 ­ Conversion of TP to Pyruvate
1. Enzyme-catalysed reactions convert both TP intermediate compound into 2
molecules of pyruvate.
2 x Pyruvate (3C)
· 2 molecules of ADP are phosphorylated to 2 molecules of ATP.…read more

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