Edexcel A2 Level Biology Unit 5 Topic 7 Processes

All processes in topic 7 unit 5 of edexcel biology course

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Preview of Edexcel A2 Level Biology Unit 5 Topic 7 Processes

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Topic 7: Process Details
Sliding Filament Theory:
1. Nerve impulses arrives at a neuromuscular junction.
2. Calcium ions are released from the sarcoplasmic reticulum.
3. Calcium ions diffuse through the sarcoplasm.
4. This initiates the movement of the protein filaments.
5. Calcium attaches to the troponin molecule causing it to move.
6. The tropomyosin on the actin filament shifts its position exposing the
myosin binding sites on the actin filaments.
7. Myosin heads bind with myosin binding sites on the actin filament forming
8. When the myosin head binds to the actin ADP and Pi on the myosin head
are released.
9. The myosin changes shape causing the myosin head to nod forward.
10. This movement results in the relative movement of the filaments, the
attached myosin moves over the myosin.
11. An ATP molecule binds to the myosin head causing the myosin head to
12. An ATPase on the myosin head hydrolyses the ATP forming ADP and Pi.
13. This hydrolysis causes a change in shape of the myosin head.
14. The myosin head returns to it's upright position and the cycle can start
1. Stores of glycogen are converted into a hexose sugar, glucose.
2. Glucose is stable and unreactive so energy from ATP is needed to start
the reactions.
3. Two phosphate groups are added to the glucose from 2 ATP molecules,
this increases the reactivity of the glucose.
4. The glucose is now split into 2 molecules of 3carbon compounds.
5. Each intermediate 3C sugar is oxidised producing pyruvate.
6. Two hydrogen atoms are removed during the reaction and taken up by the
coenzyme NAD.
7. Fate of hydrogen's and NAD is seen in the Krebs cycle and Electron
transport chain.
8. Glucose is at a higher energy level than the pyruvate and so on
conversion some energy becomes available for the direct creation of
9. Phosphate from intermediate compounds is transferred to ADP creating
ATP which is called Substrate Level Phosphorylation because the energy
for the formation of ATP comes from the substrates.
Link Reaction
1. Pyruvate is : decarboxylated (carbon dioxide released as a waste
product) ­ dehydrogenated ( two hydrogen's are removed and taken up
by the coenzyme NAD).
2. 2 carbon molecule combines with coenzyme A to form acetyl coenzyme.
3. 2 hydrogen atoms released are involved in ATP formation.

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Krebs Cycle
1. 2 carbon acetyl CoA combines with a 4carbon compound to create a
6carbon compound.
2. Two steps involve decarboxylation with the formation of carbon dioxide.
3. Four steps involve dehydrogenation, the removal of hydrogen atoms to
convert NAD to reduced NAD or FAD to reduced FAD.
4. One of the steps involves Substrate Level Phosphorylation with direct
synthesis of a single ATP.
5. This is a cycle known as the Krebs Cycle.
Electron Transport Chain
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The impulses spread upwards through the ventricle walls and cause
contraction of the ventricles.
6. Blood is squeezed into the arteries.
ECG Trace Explanation
P Wave: depolarisation of the atria, leading to atrial contraction.
PR Interval: the time taken for impulses to be conducted from the SAN
across the atria to the ventricles through AVN.
QRS Complex: the wave of depolarisation resulting in contraction of the
T Wave: repolarisation of the ventricles during heart's relaxation phase.
Nervous Control of Heart Rate
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Impulses are sent from the ventilation centre to stimulate the muscles
involved in breathing.
8. Chemoreceptors in the aorta and carotid artery are stimulated by
changes in pH resulting from changes in carbon dioxide concentration.
9. Chemoreceptors monitor the blood before it reaches the brain and send
impulses to the ventilation centre.
Peptide Hormones
1. Relatively small molecules, peptide hormones cannot pass through cell
membranes easily because they are charged.
2.…read more


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