Summary AQA Biology A Level Revision - Respiration - Unit 12
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Course
Unit 1 BIOL1 - Biology and disease (7402)
Institution
AQA
Book
AQA Biology A Level Student Book
These revision notes provide an in depth summary of this specific chapter of AQA Biology in the A Level Specification -
Very comprehensive notes and enabled me to achieve an A* in my A Level Biology exams.
- Glucose from photosynthesis cannot be used directly by cells as a source of energy
o Instead, cells use ATP as their immediate energy source
- The formation of ATP from the break down of glucose takes place during the process
of cellular respiration
- There are 2 different forms of cellular respiration depending on whether Oxygen is
available:
o Aerobic respiration – requires oxygen. Produced CO2, water and ATP
o Anaerobic respiration – takes place in the absence of oxygen and produces
lactate (in animals) or ethanol and carbon dioxide (in plants and fungi) but only
a little ATP in both cases
- Aerobic respiration can divided into four stages:
1. Glycolysis – the splitting of the 6-C glucose molecule into two 3-C pyruvate
molecules
2. Link reaction – the 3-C pyruvate molecules enter into a series of reaction which lead
to the formation of acetylcoenzyme A, a 2-C molecule
3. Krebs cycle – the introduction of acetylcoenzyme A into a cycle of oxidation-reduction
reactions that yield some ATP and a large quantity of reduced NAD and FAD,
released from the Krebs cycle to synthesis ATP with water produced as a by-product
4. Oxidative phosphorylation – the use of the electrons, associated with reduced NAD
and FAD, released from the Krebs cycle to synthesise ATP with water produces as a
by-product
- Glycolysis is the initial stage of both aerobic and anaerobic respiration
o Occurs in cytoplasm of all living cells and is the process by which a hexose
sugar, usually glucose, is split into two molecules of the molecule pyruvate
- Although there are a number of smaller enzyme-controlled reactions in glycolysis
- These can be grouped into 4 stages
1. Phosphorylation of glucose to glucose phosphate
- Before it can be split into two, glucose must firt be made more reactive by the
addition of two phosphate molecules by phosphorylation
- Phosphate moelcules come from the hydrolysis of 2 ATP to ADP
- This provides the energy to activate glucose and lowers the activation energy for
the enzyme-controlled reactions that follow
2. Splitting of the phosphorylated glucose
- Each glucose molecule is split into two 3-C molecules known as triose phosphate
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