Topic 7 Biology SNAB Revision

Topic 7 Snab Biology A2

  • Created by: Becky
  • Created on: 18-04-12 21:03


Muscle movement involves skeletal muscles, tendons, ligaments and joints.

  • Skeletal muscleis the type of muscleyou use to move. They areattached to the bones by tendons. 
  • Ligaments attach bones to other bones, to hold them together.
  • Skeletal musclescontract and relaxto move bones at a joint.

1. The bones on your lower arm are attached to a biceps muscle and a     triceps muscle by a tendon.
2. The biceps and triceps work together to move your arm, as one             contracts, the other relaxes. (antagonistic pair)

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  • Made up of large bundles of long cells called muscle fibres.
  • The cell membrane of muscle fibre cells is the sarcolemma.
  • Bits of the sarcolemma fold inwards and stick in the sarcoplasm. These folds are called Transverse tubules, and help spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre.
  • A network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm, storing and releasing calcium ions needed for muscle contraction.
  • Lots of mitochondria to provide ATP for muscle contractions.
  • Multinucleate
  • They have long, cylindrical organelles called myofibrils,  proteins, highly specialised for contraction.
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1) Contain bundles of thick and thin myofilaments that move past each other to make muscles contract.

  • Thick myofilaments are made of the protein myosin
  • Thin myofilaments are made of the protein actin

2) If you look at a myofibril under an electron microscope, alternating pattern of     light and dark bands.

  • Dark bands contain the Thick myosin filaments and some overlapping thin actin filaments
  • Light bands contain thin actin filaments only
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  • Made up of many short units called sacromeres
  • The ends of each sacromere are marked with a Z-line.
  • In the middle of each sacromere is an M-line.
    The M-line is the middle of the myosin filaments.
  • Around the M-line is the H-zone. The H-zone only contains myosin filaments.
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When a nerve impulse arrives at a neuromuscular junction, Calcium ions (Ca2+) are released from the sarcoplasmic reticulum. The calcium ions diffuse through the sarcoplasm which initiates the movement of protein filaments as follows:

  • Ca2+ attaches to the troponin molecule, causing it to move.
  • As a result, the tropomyosin on the actin filament shifts its position, exposing myosin binding sites on the actin filaments.
  • Myosin heads bind with myosin binding sites on the actin filament, forming cross-bridges.
  • When the myosin head binds to the actin, ADP and Pi on the myosin head are released.
  • The myosin changes shape, causing the myosin head to nod forward. This movement results in the relative movement of the filaments; the attached actin moves over the myosin. 


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  • An ATP molecule binds to the myosin head, causing the myosin head to detach.
  • An ATPase on the myosin head hydrolyses the ATP, forming ADP and Pi.
  • This hydrolysis causes a change in the shape of the myosin head. It returns to its upright position enabling the cycle to start again.

The collective bending of many myosin heads combines to move the actin filaments relative to the myosin filament. This results in muscle contraction.

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Skeletal Muscles are made of Slow and Fast Twitch Muscle Fibres


Red (a lot of myoglobin, a red protein stores oxygen)

Many mitochondria

Little sarcoplasmic reticulum

Low glycogen content

Numerous capillaries

Fatigue resistant

Use for posture

Good for endurance

Contract slowly

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White (little myoglobin, a red protein stores oxygen)

Few mitochondria

Extensive sarcoplasmic reticulum

High glycogen content

Few capillaries

Fatigue quickly

Use for fast movement

Good for short bursts

Contract very quickly

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Aerobic respiration releases energy.

  • a large amount of energy is released by splitting glucose into
     + CO2 = released as a waste product
     + H2 = combines with atmospheric O2 producing H20
  • The energy release is used to phosphorylate ADP to ATP, providing energy for all the biological processes in a cell.
  • 4 stages - glycolysis, link reaction, krebs cycle, oxidative phosphorylation 
  • First 3 stages are a series of reactions, final stage uses the products from these reactions to produce loads of ATP.
  • The first stage happens in the cytoplasm of cells
  • The other three take place in the mitochondria.
  • Coenzymes are used in respiration
    - NAD and FAD transfer hydrogen from one molecule to another,                 can reduce or oxidise a molecule. 
    - Coenzyme A transfers acetate between molecules.
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Involves splitting 1 molecule of glucose, 6C into 2 smaller molecules of pyruvate 3C

Anaerobic process

Stage 1) Phosphorylation

  • Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP.
  • This creates 2 molecules of triose phosphate (TP) and 2 molecules of ADP.

Stage 2) Oxidation

  • TP is oxidised (loses hydrogen), forming 2 molecules of pyruvate
  • NAD collects the hydrogen ions, forming 2 reduced NAD
  • 4 ATP are produced, but 2 were used up in stage 1, so theres a net gain of 2 ATP.
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Takes place in the mitochondrial matrix

  • Pyruvate is decarboxylated (carbon is removed) - one carbon is removed from pyruvate in the form of CO2
  • NAD is reduced. Collects a hydrogen from pyruvate, changing the pyruvate into acetate
  • Acetate is combined with coenzyme A (CoA) to form Acetyl coenzyme A
  • No ATP produced in this reaction.

2 pyruvate molecules are made for every glucose molecule that enters glycolysis. This means that the link reaction and the krebs cycle happen twice for every glucose molecule. So for each glucose molecule:

  • 2 molecules of acetyl coenzyme A go into krebs cycle
  • 2 CO2 molecules are released as a waste product
  • 2 molecules of reduced NAD are formed and go to the last stage, oxidative phosphorylation
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  • Involves a series of oxidation-reduction reactions
  • Takes place in the matrix of mitochondria
  • Each of these reactions is controlled by a specific intracellular enzyme
  • Cycle happens once every pyruvate molecule, so goes round twice for every glucose molecule.

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  • Acetyl CoA combines with a 4 Carbon compound to create one with 6 Carbons.
  • Coenzyme A goes back to the link reaction to be used again


  • The 6C molecule is converted into a 5C molecule.
  • Decarboxylation occurs where CO2 is removed.
  • Dehydrogenation also occurs - where hydrogen is removed.
  • The hydrogen is used to produce reduced NAD from NAD.


  • The 5C molecule is then converted into a 4C molecule.
  • Decarboxylation and dehydrogenation occur producing one molecule of reduced FAD and two reduced NAD.
  • ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. When a phosphate group is directly transferred from one molecule to another it's called substrate-level phosphorylation.
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Some of the products of the Krebs Cycle are reused, released or used in the next stage...

  • 1 coenzyme A - reused in next link reaction
  • 4 carbon molecule - regenerated for use in next krebs cycle
  • 2 CO2 - released as waste product
  • 1 ATP - used for energy
  • 3 reduced NAD - To oxidative Phosphorylation
  • 1 reduced FAD - To oxidative Phosphorylation
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  • The process where energy carried by electrons, from reduced coenzymes (reduced NAD/FAD), is used to make ATP.
  • Oxidative phosphorylation involves 2 processes
      -- the electron transport chain
      -- chemiosmosis 

Oxidation cont. next page

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  • Hydrogen atoms are released from reduced NAD and reduced FAD as they're oxidised to NAD and FAD. The H atoms split into protons (H+) and electrons (e-)
  • The electrons move along the electron transport chain (made up of 3 carriers) losing energy at each carrier.
  • The energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space.
  • The concentration of protons is now higher in the intermembrane space than the mitochondrial matrix, forming an electrochemical gradient. (concentration gradient of ions).
  • Protons move down the electrochemical gradient, back into the mitochondrial matrix, via ATP synthase. This movement drives the synthesis of ATP from ADP and inorganic phosphate (Pi)
  • The movement of H+ ions across a membrane, which generates ATP is called chemiosmosis.
  • In the mitochondrial matrix at the end of the transport chain, the protons, electrons and O2 (from the blood) combine to form water. Oxygen is said to be the final electron acceptor.
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The volume of oxygen taken up or the volume of carbon dioxide produced indicates the rate of respiration.

  • Each tube contains potassium hydroxide solution (KOH) or soda lime, which absorbs CO2.
  • The control tube is set up in exactly the same way as the test tube, but without the woodlice, to make sure the results are only due to the woodlice respiring.
  • The syringe is used to set the fluid in the manometer to a known level.
  • The apparatus is left for a set period of time (e.g. 20 minutes)
  • During that time, there'll be a decrease in the volume of the air in the test tube, due to oxygen consumption by the woodlice. (the CO2 is absorbed by potassium hydroxide)
  • The decrease in the volume of the air will reduce the pressure in the test tube and cause the coloured liquid in the manometer to move towards the test tube.
  • The distance moved by the liquid in a given time is measured. This value can be to calculate the volume of oxygen taken in by the woodlice per minute.
  • Any variables that can affect the results are controlled, e.g. temp, volume of KOH
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It doesn't use oxygen. It doesn't involve the link reaction, the Krebs cycle or oxidative phosphorylation.

Lactate Fermention
 - one type of anaerobic respiration, occurs in animals and produces lactate

  • Glucose is converted to pyruvate via glycosis.
  • Reduced NAD (from glycosis) transfers hydrogen to pyruvate to form lactate and NAD.
  • NAD can then be reused in glycosis.

 - The production of lactate regenerates NAD. Meaning glycosis can continue even when there isn't much oxygen, so small amount of ATP can be produced to keep some biological processes going.

Breaking down lactic acid
- After a period of anaerobic respiration lactic acid builds up.  

  • Cells can convert the lactic acid back to pyruvate, which then re-enters in aerobic respiration at the Krebs cycle.
  • Liver cells can convert the lactic acid back to glucose, which can then be respired or stored.
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Cardiac Muscle Controls the Regular Beating of the

Cardiac muscle is myogenic - contracts/relaxes without recieving signals from neurones.

  • Electrical impulses from the Sinoatrial node (SAN) spreads across the atria walls, causing contraction.
  • Impulses pass to the ventricles via the atrioventricular node (AVN).
  • But there's a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.
  • After this delay, the signal reaches the Purkyne fibres. These are large unspecialised muscle fibres that conduct impulses rapidly to the apex (tip) of the ventricles. There are right and left bundles of fibres, collectively called the bundle of His.  
  • Impulses pass down the Purkyne fibres into the inner cells of the ventricles, and spreads through the entire ventricles.
  • The impulses spread up through the ventricle walls causing contraction from the apex upwards towards the atria. This produces a wave of contraction moving up the ventricles, pushing the blood into the aorta and pulmonary artery. 
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A machine that records the electrical acivity of the heart. 

  • The heart muscle depolarises (loses electrical charge) when it contracts and repolarises (regains charge) when it relaxes.
  • The trace is called an electrocardiogram, ECG.

1)The P wave is caused by contraction (depolarisation) of the atria.
2)The main peak of the heartbeat, together with the dips and the side is the QRS complex, caused by contraction (depolarisation) of the ventricles.
3)The T wave is due to relaxation (repolarisation) of the ventricles. 
4)The PR interval is the time taken for impulses to be conducted from the SAN across the atria to the ventricles, through the AVN. 

Heart rate calculation
work out how many squares represent 1 second, and how many in 1 minute.

number of squares between QRS complex X the length in seconds of a square

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ECG to diagnose heart problems

Tachycardia - Increased heart rate, sign of heart failure. Heart can't pump blood efficiently, so heart rate increases to ensure enough blood is pumped.

Problems with the AVN - The ventricles are contracting but the ventricles are not. (some P waves not followed by a QRS complex).

Fibrillation - Irregular heart beat. Both the atria and the ventricles have lost their rhythm and stopped contracting properly. 

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Breathing Rate and Heart Rate Increase When you Ex

When you exercise:-

  • Muscles contract more frequently
    - Means they use more energy
  • To replace this energy, your body needs to do more aerobic respiration
    - Needs to take in more oxygen and breathe out more CO2, your body does this by.... 

1) Increasing breathing rate and depth - obtain more oxygen and get rid of more         carbon dioxide

2) Increasing heart rate - to deliver oxygen (and glucose) to the muscles faster and remove extra CO2 produced by the increased rate of respiration in muscle cells

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MEDULLA controls Breathing rate

The ventilation centre in the medulla controls breathing.


  • The ventilation centre sends nerve impulses every 2-3 seconds to the external intercostal and diaphragm muscles. 
  • Both these sets of muscles contract causing inhalation


  • As lungs inflate, strech receptors in the bronchioles are stimulated. The stretch receptors send inhibitory inpulses back to the ventilation centre.
  • As a consequence, impulses to the muscle stop and relax, stopping inhalation and allowing exhalation.
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exercise triggers increase in breathing rate by de

  • During exercise, CO2 level in the blood increases, this decreases the pH of the blood.
  • Chemoreceptors (receptors that sense chemicals) in the medulla, aortic bodies and carotid bodies that are sensitive to changes in blood pH.
  • If the chemoreceptors detect a decrease in blood pH, they send nerve impulses to the medulla, which send more frequent nerve impulses to the intercostal muscles and diaphragm, increasing the rate and depth of breathing.
  • This causes gaseous exchange to speed up - the CO2 level drops and extra O2 is supplied for the muscles.
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Nervous control of heart rate

Heart rate is under control of the cardiovascular control centre located in the medulla.

Decreased blood pH causes increase in heart rate

  • A decrease in blood pH (caused by an increase in CO2) is detected by chemoreceptors.
  • Chemoreceptors send nerve impulses to the medulla
  • Medulla sends nerve impules to the SAN to increase heart rate

Increased blood pressure causes a decrease in heart rate

  • Pressure receptors in the aorta wall and in the carotid sinuses detect changes in blood pressure
  • If pressure is too high, pressure receptors send nerve impulses to the cardiovascular centre, which sends nerve impulses to the SAN to slow down heart rate
  • If pressure is too low,  pressure receptors send nerve impulses to the cardiovascular centre, which sends nerve impulses to the SAN to speed up heart rate
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Cardiac Output

The total volume of blood pumped by a ventricle every minute

Cardiac Output (cm3/min) = heart rate (beats per minute) x stroke volume (cm3)

(Stroke volume = the volume of blood pumped by one ventricle each time it contracts)

So cardiac output increases during exercise because heart rate increases

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Ventilation Rate

  • Tidal volume - the volume of air in each breath, usually about 0.4dm3
  • Breathing rate - how many breaths are taken, usually in a minute
  • Ventilation Rate - the volume of air breathed in or out, usually in a minute

(dm3 = decimetres cubed, sames as litres)

ventilation rate = tidal volume x breathing rate

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A machine that can give readings of tidal volume and breathing rate.

1) has oxygen filled chamber with moveable lid

2) A person breathes through a tube connected to the oxygen chamber

3) As the person breathes in, the lid of the chamber moves down. When they breathe out, moves up.

4) These movements are recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace

5) the soda lime in the tube the person breathes into absorbs carbon dioxide

Can be used to investigate the effects of exercise

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Maintainance of a constant internal environment

Negative Feedback

  • Homeostatic systems involve recpetors, a communication system and effectors
  • Receptors detect when a level is too high or too low, and the info is communicated via the nervous or hormonal system to effectors
  • The effectors counteract the change - bringing levels back to normal
  • The mechansim that restores the level to normal is called a negative feedback mechanism - helps keep things around normal level
  • NF only works within certain limits - if change is too big, may not be able to counteract
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Hypothalamus controls body temperature in mammals

  • The hypothalamus recieves information about temperature from thermoreceptors (temp receptors)
  • Thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors (muscles and glands)
  • The effectors respond to restore the body temperature back to normal
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(page 67 diagram.. draw!)

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Hormones switch genes on to help regulate temperat

  • In a cell there are proteins called transcription factors that control the transcription of genes.
  • Transcription factors (TF) bind to the DNA sites near the start of genes and increase or decrease the rate of transcription. Factors that increase the rate are activators and those who decrease the rate are called repressoers
  • Hormones can bind to some transcription factors to change body temperature:-

1) At normal body temp, the thyroid hormone receptor (a TF) binds to DNA at the start of a gene.

2) This decreases the transcription of a gene coding for a protein that increases metabolic rate

3) At cold temperatures thyroxine is released, which binds to the thyroid hormone receptor, causing it to act as an activator

4) The transcription rate increases, producing more protein. The protein increases metabolic rate, causing an increase in body temperature.

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Keyhole surgury
-- Way of doing surgury without making a large incision in the skin

-- Small incision, insert a tiny video camera and specialised medical instruments

Advantages of keyhole surgury

  • Lose less blood and less scarring, because of smaller incision
  • Less pain, recover quicker because less damage is done to the body
  • Easier for patient to return to normal activites, hospital stay is shorter 
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  • Can be used to replace whole limbs or parts of limbs
  • Some include electronic devices that operate the prostheses by picking up information sent by the nervous system
  • Make it possible for people with some disabilities to participate in sport
  • Also make it possible for people who have certain injuries to play sport again
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Performance-Enhancing Drugs

  • Anabolic steroids - Increase strength, speed and stamina by increasing muscle size and allowing athletes to train harder. Increase aggression. 
  • Stimulants - Speed up reactions, reduce fatigue and increase aggression
  • Narcotic analgesics - Reduce pain, so injuries don't affect performance

Arguments AGAINST using P-E drugs

  • some are illegal
  • competitions become unfair
  • serious health risks
  • athletes may not be fully informed of health risks

Arguments FOR using P-E drugs

  • Own decision
  • Drug-free sport isnt really fair anyway - access to different training facilities etc.
  • Athletes that want to compete at a higher level may only be able to by using them
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