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Edexcel Categories Archives: Add Topic 7

5.7.14 – Whether the use by athletes of performance enhancing substances is morally and ethically acceptable.

Why should we allow use of drugs;

 

  • Gives people a chance to be as good as their potential allows
  • Removes “unfair” genetic advantages
  • Controlled use of drugs is less risky
  • People should have the right of choice
  • Legalising drugs makes their distribution controllable (no use by under- age, infirm etc)

Arguments for not using drugs;

 

  • Dangerous (obviously)
  • May be pushed onto athletes by trainers
  • Effects are permanent
  • Not used under doctor’s supervision
  • Often cut with other drugs
  • Exposes athletes to criminals (danger of using other drugs)

The list goes on, just think for yourself in the context of the question. You can argue the toss either way, but make sure you can back up your opinion with some sensible, logical arguments.

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5.7.13 – How medical technology, including the use of key-hole surgery and prostheses, is enabling those with injuries and disabilities to participate in sports

Key-hole surgery is a technique which allows doctors to conduct surgery with the minimum possible damage to the patient. The surgeon makes a small incision (a “key-hole”) and uses a fibre-optic camera to view the damaged area. If required, the surgeon can make a second incision and use a number of small, remote operated tools to repair the damage. Because the incisions are small and only the damaged area is targeted, the patient recovers quickly. There is also less chance of infection.

Unfortunately, the procedure requires a high degree of training, expensive equipment and can only be used on certain types of surgery.

Prosthetics allow people with amputations to participate in many activities, including sports.

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5.7.12 – Possible disadvantages of exercising too much (wear and tear on joints, suppression of the immune system) and exercising too little (increased risk of obesity, CHD and diabetes)

 

 

 A moderate level of exercise improves health & well-being.

However, over-training can result in  the opposite effect. This is the phenomenon known as “burn-out”

 

 

Positive effects of exercise include;

 

  1. Increased BMR
  2. Decreased blood pressure
  3. Increased HDL
  4. Decreased LDL
  5. Maintaining healthy BMI
  6. Decreased risk of diabetes
  7. Increased bone density
  8. Improved well being
  9. Decreased adrenaline levels
  10. Less stress
  11. Decreased risk of CHD
  12. Moderate exercise increases levels of Natural Killer cells, which secrete apoptosis-inducing chemicals in response to non-specific viral or cancerous threat

Negative effects of exercise (over-training) include;

 

  1. Decreased levels of Natural Killer Cells, Phagoctyes and B & T Cells. This decreses immune
  2. Increased muscle inflammation
  3. Muscle tears and sprains
  4. Increased adrenaline levels
  5. Increased cortisol levels, which also decreases the immune response
  6. Increased stress
  7. Damaged cartilage
  8. Tendinitis
  9. Ligament damage
  10. Swollen bursae.
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5.7.12 – The concept of homeostasis and its importance in maintaining the body in a state of dynamic equilibrium during exercise as exemplified by thermoregulation, including the role of the heat loss, heat gain centres and mechanisms for controlled body temperature

See 4.6.11 for mechanisms of thermoregulation.

The thermoregulatory process (and most homeostatic systems) are controlled by negative feedback processes. If a system changes, it is detected, a homeostatic response is activated, which aims to return the system to its original level. Negative feedback, therefore, holds systems at a set point, in this case 37.5˚C.

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5.7.10 & 5.7.11 – Why some animals are better at short bursts of high intensity exercise while others are better at long periods of continuous activity, the structural, and the physiological, differences between fast and slow twitch muscle fibres

Sprinters need lots of fast twitch muscle, joggers need slow twitch. Therefore, the muscle type of a cheetah or a gazelle will be predominantly fast twitch, whereas the muscle of a camel or an elephant will be predominantly slow twitch.

Muscle type in humans is predominantly one or the other due to inherited alleles. However, different training programmes can cause the % of either type to change slightly.

 

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5.7.9 – How to investigate the effects of exercise on tidal volume and breathing rate

A spirometer is used to plot breathing patterns

 

Vital Capacity: The maximum amount of air a person can exhale   after inhaling the maximum possible volume of air

Tidal Volume: The volume of air inhaled & exhaled in one breath

Basal Metabolic Rate: The rate of respiration

The spirometer can be used to plot VC and TV directly. BMR can be worked out if a CO2 scrubber is used. The spirometer has fixed volume and is filled with 100% O2 before the experiment begins. As the person respires, O2 is replaced proportionally with CO2. The total volume should stay constant. However, if CO2 is removed, the total volume will slowly fall as O2 is used. The rate at which the volume decreases is proportionaly to BMR.

You are not expected to know how the spirometer works… although its not very difficult to understand.

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5.7.3 – Explain how phosphorylation of ATP requires energy and how dephosphorylation of ATP provides an immediate supply of energy for biological processes

 

Adenosine TriPhosphate (ATP) is made from three components;

 

  • Ribose (the same sugar that forms the basis of DNA).
  • A base (a group consisting of linked rings of carbon and nitrogen atoms); in this case the base is adenine.
  • Up to 3 phosphate These phosphates are the key to the activity of ATP

The energy used in all cellular reactions comes from ATP. By breaking the 3rd phosphate from the ATP molecule energy is released, which can be used to power intracellular reactions. The ATP is then regenerated by recombining the phosphate and ADP in respiration (or another process e.g. photosynthesis).

 

The recycling of ATP is crucial for life. For example a runner uses ~84kg of ATP in a marathon (more than their total body weight), yet there are only 50g of ATP     in the

 

entire body! This means each that each molecule of ATP has been recycled 1676 times during the race!

HOW THE ENERGY IN ATP IS LIBERATED:

Normally, as soon as ATP has been converted into ADP + Pi it is converted back into ATP using energy from respiration. However, during exercise ADP may be converted into AMP or even Adenosine to provide energy.

RESPIRATION

Respiration: a process in which the chemical bond energy in glucose molecules is used to convert 38 ADP molecules into 38 ATP molecules. Oxygen is required and Carbon Dioxide and Water are produced as waste products.

Respiration occurs in 4 distinct steps;

RESPIRATION: STEP 1 – GLYCOLYSIS

Glycolysis takes place in the cytoplasm of a cell

In Glycolysis a Glucose molecule (6C) is split into 2 molecules of Glyceraldehyde Phosphate (3C).  2ATPs are required for this to happen.

Then, each 3C Glyceraldehyde Phosphate molecule is converted into a 3C Pyruvate molecule. In the process of converting one Glyceraldehyde Phosphate to one Pyruvate, enough energy is released to convert one NAD molecules into one NADH molecules and also to make two ATP molecules.

Overall; 4ATP are made, 2NADH are made and 2ATPs are used.

Net gain: 2ATP and 2NADH

In anaerobic conditions [H+] rises in the mitochondria as there are no available oxygen molecules to mop it up with and form water. This leads to saturation of the electron transport chain and a build-up of NADH and FADH2. This means [NAD] falls, which stops the Krebs’ Cycle. Acetyl CoA levels build-up, [CoA] falls and the Link Reaction stops. Pyruvate levels start to rise…

Muscle cells turn pyruvate into lactate to stop rising [pyruvate] from stopping Glycolysis (remember, enzyme controlled reactions are reversible and depend on [reactants] and [products]).

In the liver the lactate is converted back into pyruvate. This requires oxygen, which is the basis of the “Oxygen Debt”

 

RESPIRATION: STEP 2 – LINK REACTION

Link Reaction takes place in the matrix of the mitochondria

In the Link Reaction a Pyruvate molecule (3C) is split into a 2C molecule and a CO2. The 2C molecule is attached to a CoA enzyme, forming Acteyl CoA.

Remember, two molecules of Pyruvate were made at the end of Glycolysis,  therefore the Link Reaction happens twice.

Overall; 2NADH and 2 CO2 are made. Net gain: 2NADH

RESPIRATION: STEP 3 – KREBS’ CYCLE

2 NADH are made (4 overall)                  1 ATP is made (2 overall)

1 FADH2  is made (2 overall)                             2 CO2  are made (4 overall)

Krebs’ Cycle takes place in the matrix of the mitochondria

In the Krebs’ Cycle the Acetyl CoA gives its 2C atoms to a 4C molecule (Oxaloacetate) forming an unstable 6C molecule (Citric Acid). The 6C molecule breaks down into a  4C compound (Succinyl – CoA) releasing enough energy to make one NADH. The two spare C atoms are released as two CO2 molecules.

Succinyl – CoA is converted back into Oxaloacetate and this releases enough energy to make one NADH, one FADH2 and one ATP. The Oxaloacetate can then be used in the cycle again.

Remember, two molecules of Acetyl CoA were made at the end of the Link Reaction, therefore the Krebs’ Cycle happens twice.

Overall; 4NADH, 2FADH2, 2CO2  and 2ATP are made.

 

RESPIRATION: STEP 4 – OXIDATIVE PHOSPHORYLATION

Oxidative Phosphorylation uses the NADH and FADH2 produced in the previous steps of respiration to make ATP. Each NADH makes 3ATP and each FADH2 makes 2 ATP.

Oxidative Phosphorylation takes place using enzymes embedded in the inner membrane of cristae of the mitochondria

Hydrogen atoms from the NADH and the reduced FADH2 are passed onto 2 the first 2 enzymes of the Electron Transport Chain. These enzymes are Hydrogen Carriers and they accept the H atoms from the NADH and the FADH2.

Electrons, which made up the chemical bond between the hydrogen atoms and the NADH / FADH2 are passed onto 3 Electron Carrier enzymes further down  the  Electron Transport Chain.

At the end of the Electron Transport Chain, the electrons are recombined with the H+ atoms and oxygen, to form water. This is the only, but crucial, part of respiration to involve oxygen.

NADH starts at the first Hydrogen Carrier and has enough energy to phosphorylate 3ADP. FADH2 has less energy and starts at the second Hydrogen Carrier, it generates 2 ATPs

Where does the 38 ATP come from?

 

Glycolysis produces;

 

Link Reaction produces;

2ATP2NADH

 

2NADH

Kreb’s Cycle produces;2ATP6NADH2 FADH2
Total4 ATP10NADH2 FADH2

 

Each NADH produces 3ATP \ total production is 30ATP from NADH

Each FADH2 produces 2ATP \ total production is 4ATP from FADH2

Grand Total         4ATP     +      30ATP  +       4ATP    = 38ATP

Chemiosmosis of H+ ions from the mitochondrial envelope into the matrix through ATP Synthetase proteins is what actually generates the ATP in respiration.

 

 

 

The electron transport chain uses the process of chemiosmosis (the diffusion of ions across a membrane). H+ ions are actively pumped into the mitochondrial envelope. This is done by the proteins in the electron transport chain, using the energy stored in NADH and FADH2.

The [H+] builds up to very high levels in the envelope. However, H+ cannot escape because it is charged (hydrophilic) and therefore cannot move through the phospholipid bilayer in the envelope membranes.

Special proteins called ATP Synthetase do allow H+ to pass through them and escape into the mitochondrial matrix. Whenever an H+ ion moves through the ATP Synthetase protein an ADP is phosphorylated by the ATP Synthetase.

 

In summary;

 

  1. NADH and FADH2 contain stored chemical energy.
  2. The energy is used to pump H+ into the mitochondrial membrane against the concentration
  3. H+ trapped in one place represents a store of potential
  4. H+ ions leave the envelope through ATP Synthetase
  5. The potential energy of the H+ is used to phosphorylate ATP as the H+ moves out of the envelope.
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5.7.2 – Explain the contraction of skeletal muscle in terms of the sliding filament theory (including the role of actin, myosin, troponin, tropomyosin, Ca2+, ATP).

Muscles are made from muscle fibres arranged into bundles. Each fibre is made from bundles of myofibrils, which are extremely long, cylindrical muscle cells.

The functional unit of contraction is the sarcomere. Muscle cells contain many sarcomeres arranged in parallel. The muscle cell takes on a characteristic banded appearance because of the regular arrangement of the sarcomeres. This is called striation.


A sacromere. Note the striated appearance of the muscle

The sarcomere contains overlapping actin and myosin. The myosin is often called the thick filament because the myosin heads make it appear thick. The actin is, therefore, the thin filament

 The process by which the thin filaments are pulled in towards each other by the myosin is called

cross-bridge cycling. It is how muscles contract.

CROSS-BRIDGE CYCLING:

  1. A nerve impulse arrives at the neuromuscular junction.
  2. The muscle cell is depolarized.
  3. Ca2+ is released from the sarcoplasmic reticulum inside muscle cells.
  4. Ca2+ bids to Troponin protein in the thin
  5. Troponin protein and Tropomyosin protein move position in the thin filament.
  6. Myosin binding sites are exposed on the thin
  7. Myosin heads of the thick filament stick to
  8. ATP (already bound to the myosin head) is hydrolysed causing the myosin head to pivot forwards in the
  9. As the head pivots the thick filament moves across the thin filament – muscle contraction
  10. ADP diffuses away from the myosin head leaving the ATP-binding site empty.
  11. New ATP binds & the myosin head & causes the myosin head to detach from the
  12. The myosin head re-cocks.
  13. The head rebinds further up the myosin.
  1. Repeat stages 7 to 13 until the [Ca2+] falls too low, when contraction
Key Point: ATP is required to release myosin  from  actin. If ATP levels drop (assuming Ca2+ is present) the myosin stays attached to the actin and the  muscle  stays permanently contracted. This is what causes rigor mortis

 

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