Biology A2 edexcel topic 7: Run for your life

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Topic 7: Run for your life:
7.1 Cellular respiration
Respiration = The chemical process of releasing energy from organic compounds (respiratory
substrates) such as glucose through oxidation. The energy released is used to combine ADP
with inorganic phosphate to make ATP (energy). Respiration is a long series of
enzyme-controlled reactions.
Aerobic respiration: Requires oxygen to fully oxidise the organic molecule. This
releases a lot of energy
Anaerobic respiration: The breakdown of the molecule without oxygen. This
releases much less energy.
ATP carries energy around the cell to where it is needed by diffusion. It is a molecule made
from the nucleotide base adenine and 3 phosphate groups.
ATP is synthesised from ADP and Pi from an energy releasing reaction, such as the
breakdown of glucose in respiration. The energy is stored as chemical energy in the
phosphate bond. The enzyme ATPase catalyses the reaction.
When energy is required by a cell, ATP is broken back down into ADP and Pi, releasing
energy from the phosphate bond. ATPase catalyses this reaction. The more ATPs used, the
more energy is released.
In aerobic respiration, energy is released by splitting glucose into carbon dioxide (released
as a water product) and hydrogen (combines with oxygen to produce water). For aerobic
respiration to occur, the cells must have mitochondria. The energy is used to phosphorylate
ADP to ATP, providing energy for biological processes in a cell.
Aerobic respiration involves:
Glycolysis ­ splitting of sugar to form pyruvate ­ in cytoplasm
Link reaction ­ mitochondrial matrix
Krebs cycle ­ removal of hydrogen from pyruvate ­ mitochondrial matrix
Electron transport chain/oxidative phosphorylation ­ using hydrogen to produce
ATP ­ inner mitochondrial membrane
Glycolysis:
Glycolysis is the first stage of respiration and occurs in the cytoplasm. Glycolysis makes
pyruvate (3C) from glucose (6C). Glycolysis is the first stage in both anaerobic and aerobic
respiration and doesn't require oxygen to take place.
1. Glycogen in muscle or liver converted to glucose
2. A glucose molecule is phosphorylated as 2 ATPs donate phosphate to it. This
produces 2ADP and 2 molecules of a 6C molecule
3. The 6C molecule is reactive and so splits into 2 3C phosphates
4. Hydrogen is removed (oxidised) and taken up by 2 NADs which become reduced.
2ATPs are made as phosphate groups are added to ADP (substrate-level
phosphorylation). This forms 2 molecules of 3C pyruvate
Overall, 2 ATP are used and 4 are made from one glucose molecule - net gain of 2ATP.
Link reaction:

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If oxygen is available, the pyruvate moves to the mitochondrial matrix, where the link
reaction and Krebs cycle occurs. The link reaction converts pyruvate into acetyl CoA. The link
reaction does not produce any ATP.…read more

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The electrons are passed along the electron transport chain, on the
inner membrane of the mitochondria.
As they move along the chain in a series of redox reactions, they lose energy which is used
to transport hydrogen ions from the mitochondrial matrix across the inner membrane and
into the intermembrane space. This causes a high concentration of hydrogen ions in this
space, forming an electrochemical gradient. The hydrogen ions diffuse back into the matrix
through protein channels in stalked particles, working as ATPases.…read more

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Anaerobic respiration
If oxygen is not available, the link reaction and Krebs cycle stop and oxidative
phosphorylation cannot occur as there is no final electron acceptor. Glycolysis can still
continue as long as the pyruvate can be removed and the reduced NAD can be converted
back to NAD. This does not produce as much energy, the net yield is 2 ATP per glucose
molecule.
In animals this is done by converting pyruvate to lactate (lactate fermentation) in the
cytoplasm.…read more

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The rate of oxygen uptake is measured using a respirometer. Organisms (woodlice) are
placed into a tube and the same mass of a non-living material is placed in the other. Soda
lime (or potassium hydroxide/KOH solution) in each tube absorbs the carbon dioxide.
Cotton wool prevents contact of the soda lime with the organisms. A syringe is used to set
the coloured fluid into the manometer at a known level and flows into the capillary tube
without air bubbles to give the same quantity.…read more

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Link reaction: Turns pyruvate into acetyl coA for the Krebs cycle by releasing carbon
dioxide and 2 hydrogens.
Decarboxylation: Carbon dioxide is released as a waste product
Dehydrogenation: Hydrogens removed and taken up by coenzymes
Acetyl coA: First step in Krebs cycle, last step in the link reaction
Krebs cycle: A cycle that starts with acetyl coA and produces 2 carbon dioxide, 1
ATP, 3 reduced NAD and 1 reduced FAD
Electron transport chain: Produces the most of ATP for a cell.…read more

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Muscle fibres are made of myofibrils, which are made of many short units called sarcomeres.
The ends of sarcomeres have a Z line and the middle has an M line (attachment for myosin).
They contain bundles of protein filaments (myofilaments) called actin and myosin which
move past each other to make muscles contract.…read more

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Low levels of creatine phosphate High levels of creatine phosphate
Less sarcoplasmic reticulum More sarcoplasmic reticulum
Relatively narrow so oxygen can diffuse Relatively wide
rapidly
The sliding filament theory
Muscle contraction works as actin and myosin filaments slide between each other, causing
the sarcomeres to become shorter, shortening the whole muscle fibre.
1. A nerve impulse (action potential) arrives at the neuromuscular junction and
depolarises the sarcolemma
2.…read more

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The triceps are the extensor
muscle, causing the arm to straighten when it contracts. As the arm bends, the biceps
contract and the triceps relaxes, although it may contract slightly to control the movement.
Muscles can only pull they cannot push, two work together for movement, they are
antagonistic muscle pairs. When one muscle is contracting, the other is relaxing.
Keywords
Flex: When muscles contract to bend joints
Extend: When muscles relax to straighten joints
Flexor: A muscle that contracts to flex a muscle e.g.…read more

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Sarcoplasm: Cytoplasm of a muscle cell
7.3 The heart, energy and exercise
Controlling the heart
The heart is myogenic ­ it contracts and relaxes automatically without stimulation from
nerves to pump blood around the body. It is specific and made of specialised tissue called
cardiac muscle. Rhythmic contraction of the cardiac muscle is coordinated through
electrical impulses passing through the cardiac tissue.
In the right atrium wall, muscle tissue is present called the sinoatrial node (SAN) which acts
as a pacemaker.…read more

Comments

Tilly - Team GR

So detailed and helpful. Thanks :)

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