EdexcelA2BiologyRG_9781846905995_pg44_58_web

7/31/2019 EdexcelA2BiologyRG_9781846905995_pg44_58_web

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Muscles and movement

44

Unit 5: Exercise and Coordination5

Green Book 7.2 Orange Book 7.1

Muscles, joints and movementBones can move in relation to one another atjoints. Dierent types o joint allow

dierent degrees o movement. Ligaments are made o elastic connective tissue.They hold bones together and restrict the amount o movement possible at a joint.Tendons are cords o non-elastic fbrous tissue that anchor muscles to bones.

bone

cartilage

Skeletal muscles are those attached to bones and are normally arranged inantagonistic pairs. This means that there are pairs o muscles which pull in opposite

directions. Flexors contract to flex, or bend a joint, e.g. biceps in the arm; extensorscontract to extend, or straighten a joint, e.g. triceps in the arm.

Each skeletal muscle is a bundle o millions o muscle cells called fbres. Each musclecell may be several centimetres long and contains several nuclei. It contains manymyofibrils which are made up o the fbrous proteins actin (thin flaments) andmyosin (thick flaments). The cell surace membrane o a muscle cell is known as thesarcolemma. The sarcoplasmic reticulum is a specialised endoplasmic reticulumwhich can store and release calcium ions. The cytoplasm inside a muscle cell is calledthe sarcoplasm. The specialised synapse (see page 63, Topic 8) between neuronesand muscle cells is called the neuromuscular junction.

The sliding filament theory of musclecontraction

emember that muscles cant

tretch themselves. It is the pull

reated by the contraction of the

ntagonistic muscle that stretches a

muscle when it is in a relaxed state.

he prefix myo- refers to musclend sarco- to flesh (i.e. muscle) so

pecialist terms starting with myo-

r sarco- will refer to structures

within muscles.

A typical synovial joint.

The arrangement o actin and myosin

flaments in a sarcomere when relaxed

(A) and contracted (B).

A

B

one sarcomere

myosin actin

The unctional unit o a musclefbre is called a sarcomere.When the muscle contractsthe thin actin flaments movebetween the thick myosinflaments, shortening the lengtho the sarcomere and thereoreshortening the length o themuscle.


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Myosin flaments have flexible heads that can change their orientation, bind to actinand hydrolyse ATP (using ATPase). Actin flaments are associated with two otherproteins, troponin and tropomyosin, that control the binding o the myosin heads tothe actin flaments.

When a nerve impulse arrives at a neuromuscular junction, calcium ions are releasedrom the sarcoplasmic reticulum and the ollowing events take place that lead to the

contraction o the muscle.

45

Topic 7: Run for your life 5


Q1 Give one reason why ast-twitch muscles are more likely to get tired asterthan slow-twitch muscles.

Q2 Describe the role o ATP in muscle contraction.

Q3 Explain why muscles are arranged in antagonistic pairs.

Ca2+

Ca2+ binding site

actin

tropomyosintroponin

Myosinbinding sitesblocked bytropomyosin.Myosin headcannot bind

myosin

binding site

Myosin headreturns touprightposition.

ATPase causesATP hydrolysis

ADP and Pireleased

ATP binds

Ca2+

ADPP

i

ADPP

i

Ca2+Ca2+

Ca2+

Ca2+

ADP + PiADP + Pi

Ca2+

Ca2+Ca2+Ca

2+

Ca2+

Ca2+ attaches totroponin (on theactin) causing itto move togetherwith the threadsof tropomyosin.

Myosin bindingsites on the actinare exposed somyosin formscross-bridges withthe actin filament.

The myosin headsrelease the ADPand Pi and changeshape as a result =

the power stroke.

ATP bindsto the myosinhead causingit to detachfrom the actin.

AtDPP

i

AtDPP

i

AtDPP

i

AtDPP

i

ATPATP

The sliding flament theory o muscle contraction.

Characteristics of fast-twitch and

slow-twitch muscle fibres

Slow-twitch Fast-twitch

specialised or slower, sustained contraction

and can cope with long periods o exercise

specialised to produce rapid, intense

contractions in short bursts

many mitochondria ATP comes rom aerobicrespiration (electron transport chain) ew mitochondria ATP comes romanaerobic respiration (glycolysis)

lots o myoglobin (dark red pigment) to store

O2 and lots o capillaries to supply O2. This

gives the muscle a dark colour

little myoglobin and ew capillaries. The

muscle has a light colour

atigue resistant atigue quickly

low glycogen content high glycogen content

low levels o creatine phosphate high levels o creatine phosphate


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Energy and the role of ATP in respiration

46



All living organisms have to respire. There are two dierent ways in which they do this aerobic respiration (using oxygen) and anaerobic respiration (without oxygen).Both o these processes make the energy stored in glucose available in the orm o

ATP, to power metabolic reactions.

Aerobic respiration

glucose + oxygen carbon dioxide + water + energy

C6H12O6 + 6O2 6CO2 + 6H2O + ~30 ATP

Anaerobic respiration

glucose lactic acid + energy

C6H12O6 2C3H6O3 + 2 ATP

The structure and function of ATPATP (adenosine triphosphate) is the cells energy currency. Energy is required to add athird phosphate bond to ADP to create ATP. When this bond is broken by hydrolysis,the energy released can be used in energy-requiring processes taking place within thecell.

The breakdown of glucose in glycolysisStarting with one glucose molecule, glycolysis produces two molecules o pyruvate,two molecules o reduced NAD and a net gain o two molecules o ATP. Glycolysistakes place within the cytoplasm o cells.

emember that the formation of ATP

an example of a condensation

eaction, the reverse of which is

ydrolysis:

ATP + H2O ADP + Pi + energy

46

member that energy cannot

created or destroyed, but can

ange from one form into another

o never refer to energy being

oduced or used.

lycolysis means sugar splitting.

lyco = sugar, lysis = splitting.

ydrolysis means splitting using

water. Hydro = water.

glycolysis

glucose (hexose) (6C)ATP

2ATP

2NAD

2 reduced NAD

2ATP

2H

ATP

hexose phosphate (6C)

hexose bisphosphate (6C)

phosphorylation

2 molecules of triose phosphate (3C)

intermediates

2 molecules of pyruvate (3C)

Anaerobic respirationGlycolysis does not need molecular oxygen (O2). However, or glycolysis to continue, aconstant supply o NAD is required. In aerobic respiration the NAD is produced by theelectron transport chain. The reduced NAD must be oxidised to NAD. During anaerobicrespiration, NAD must come rom elsewhere. In animals, pyruvate rom glycolysis isreduced to give lactate, NAD is ormed and can keep glycolysis going.

The main stages o

glycolysis.


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Anaerobic respiration allows animals to make a small amounto ATP. It is an inefcient process but it is rapid and can supplymuscles with ATP when oxygen is not being delivered quicklyenough to cells.

Lactate orms lactic acid in solution which lowers the pH. Thiscan inhibit enzymes and, i allowed to build up, it can cause

muscle cramp. Once aerobic respiration resumes most lactateis converted back to pyruvate. It is oxidised via the Krebs cycleinto carbon dioxide and water. The extra oxygen required orthis process is called the oxygen debt.

Q1 Suggest ourexamples o biological processes that require the use o ATP.

Q2 Compare the role o ATP with glycogen.

Q3 Describe the role o NAD in anaerobic respiration.

small organisms

screw clip

experimental tube

gauze

KOH solution

absorbs carbon

dioxide

manometer tube

containing colouredfluid

KOH solution

three-way tap

1 cm3 syringe

47



The rate o aerobic respiration can be determined using a respirometer by measuringthe rate o oxygen absorbed by small organisms. Any CO2 produced is absorbedby the potassium hydroxide (KOH) solution, so that any oxygen absorbed by theorganisms results in the fluid in the manometer tube moving towards the organism(see arrow on diagram). The tube on the right-hand side compensates or any changesin pressure or temperature within the apparatus.

A respirometer

Dont forget the importance of

including something to absorb the

CO2 or the respirometer reading will

not change during aerobic respiration

of carbohydrates because the same

volume of gas is produced (6CO2) as

is absorbed by the organism (6O2) per

glucose molecule respired.

Q1 Draw the main stages of

glycolysis alongside the main

stages of the light-independentreactions of photosynthesis.

Use these diagrams to identify

the similarities and differences

between the two processes.

Thinking Task

pyruvate lactate

glucose

2ADP

+2Pi

2ATP

2H

2H

lactate pathway

reduced NAD NAD

Anaerobic respiration in animals.

Investigating the rate of respiration using

a respirometer

Build Better Answers

Remember that in the A2 Biology exams

you may be asked to:

bring together scientific knowledge

and understanding from different

areas

apply knowledge and understanding

of more than one area to a

particular situation or context

use knowledge and understanding

of principles and concepts in

planning experimental and

investigative work and in theanalysis and evaluation of data.

The respiration topic is a common

choice for such synoptic questions

because the process links to many other

areas such as photosynthesis, food

chains and muscle contraction.


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Krebs cycle and the electron transport chain

48



In aerobic respiration, the pyruvate (rom glycolysis) is completely oxidised into carbondioxide and water using oxygen.

Aerobic respiration takes place in two stages:

First pyruvate is oxidised into carbon dioxide and hydrogen (accepted by thecoenzymes NAD and FAD). This takes place in the matrix o the mitochondriaand involves the Krebs cycle.

In the second stage, most o the ATP generated in aerobic respiration is synthesisedby oxidative phosphorylation associated with the electron transport chain.This involves chemiosmosis and the enzyme ATPase. It takes place on the cristae(inner membranes) o the mitochondria.

Preparation for the Krebs cycle

(the link reaction)In aerobic respiration each pyruvate molecule coming rom glycolysis in the cellscytoplasm enters the matrix o the mitochondrion. It is converted rom pyruvate (3C)to an acetyl (2C) group. This involves the loss o CO2 (decarboxylation) and hydrogen(dehydrogenation) generating reduced NAD. The acetyl group is carried by coenzymeA as acetyl coenzyme A.

The Krebs cycleThe Krebs cycle occurs in the matrix o the mitochondria. The main purpose o thecycle is to supply a continuous flow o hydrogen (and thereore electrons) to theelectron transport chain or use in the synthesis o ATP by oxidative phosphorylation.

reduced NAD

reduced NAD

reduced NAD

cytoplasm

mitochondrial membrane

mitochondrial matrix

pyruvate (3C)

NAD

NADNAD

NAD

CO2

reduced NAD

CO2

CO2

acetylcoenzyme A (2C)

4Ccompound

6Ccompound

Krebs cycle

reduced FAD

FAD

5Ccompound

Note that all the reducedhydrogen acceptors channel

hydrogen through therespiratory chain to

produce ATP.

ATP

Many of the reactions involved in

espiration are redox reactions

where one substrate is oxidised

nd another is reduced. When

molecule is oxidised, it either

oses hydrogen or one or more

lectrons are lost. A molecule that

ains electrons or hydrogen is

educed. One way of remembering

his is to think of OILRIG (oxidation

loss, reduction is gain). When

molecule gains hydrogen it is

educed, and the molecule thatoses the hydrogen is oxidised. For

xample: pyruvate acetyl + 2H (is

xidation);

AD + 2H reduced NAD (is

eduction).

The reactions involved in the breakdown o pyruvate in aerobic respiration.

ou do not need to know the names

f the intermediate compounds of

he Krebs cycle for the exam, but

ou are expected to appreciate

hat aerobic respiration is a many-

tepped process with each step

ontrolled and catalysed by a

pecific intracellular enzyme.


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Q1 Describe what happens to the carbon and hydrogen atoms rom a glucosemolecule in aerobic respiration.

Q2 Explain what oxidative phosphorylation means.

Q3 Explain why the electron transport chain and the Krebs cycle would stop ithere was no oxygen.

Q1 Sketch a simple diagram of a cell

and mitochondria and outline

where the main steps in aerobic

respiration take place.

Thinking Task

Each molecule o the 2-carbon acetyl coenzyme A rom the link reaction is used to generate: three molecules o reduced NAD one molecule o reduced FAD two molecules o CO2 one molecule o ATP by substrate-level phosphorylation (synthesised directly

rom the energy released by reorganising chemical bonds) one molecule o a 4-carbon compound, which is regenerated to accept an acetyl

group and start the cycle again.Note that or each glucose molecule entering glycolysis two acetyl groups are ormed,so the Krebs cycle will turn twice (i.e. producing two ATP and six reduced NAD, etc.)

Oxidative phosphorylation, chemiosmosis

and the electron transport chainMost o the ATP generated in aerobic respiration is synthesised by the electrontransport chain.

1 Reduced coenzyme

carries H+ and electron

to electron transport

chain on inner

mitochondrial membrane.

intermembrane

space

inner mitochondrial

membrane

mitochondrial

matrix

reduced NAD NAD

2e

electron

carrier

electron

carrier

electron

carrier

ADP + Pi ATP

ATPase on

stalked particle

2H+

H+ H+ H+

H20

02

2 Electrons pass from one electron carrier to

the next in a series of redox reactions; the

carrier is reduced when it receives the electrons

and oxidised when it passes them on.

3 Protons (H+) move across the

inner mitochondrial membrane

creating high H+ concentrations

in the intermembrane space.

4 H+ diffuse back into the

mitochondrial matrix down

the electrochemical gradient.

5 H+ diffusion

allows ATPase to

catalyse ATP synthesis.

6 Electrons and H+ ions

recombine to form hydrogen

atoms which then combine

with oxygen to create water.If the supply of oxygen stops,

the electron transport chain

and ATP synthesis also stop.

1

2

3 4

5

6

12

The electron transport chain and chemiosmosis result in ATP synthesis by oxidative phosphorylation.

The majority o ATP generated by aerobic respiration comes rom the activity o theelectron transport chain in the inner membrane o the mitochondria (cristae).

The overall reaction o aerobic respiration can be summarised as the splitting andoxidation o a respiratory substrate (e.g. glucose) to release carbon dioxide as a wasteproduct, ollowed by the reuniting o hydrogen with oxygen to release a large amounto energy in the orm o ATP.


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The heart, energy and exercise


50 Green Book 7.3 Orange Book 7.3

The control of the cardiac cycleThe impulse to contract originates within the heart itsel rom the sinoatrial node the

heart is said to be myogenic.

Ater contracting (systole), the cardiac muscle then relaxes or a period calleddiastole when the blood returning rom the veins flls the atria.

Measuring electrical changes in the heartElectrical currents caused by the spread o the electrical impulse (wave odepolarisation) during the cardiac cycle can be detected with an electrocardiogram(ECG).

I disease disrupts the hearts normal conduction pathways changes will occur in theECG pattern which can be used or diagnosis o cardiovascular disease.

ou can calculate the heart rate

sing an ECG by measuring the timeterval between one P wave and

he next one (a complete cardiac

ycle) and then working out how

many occur in 1 minute.

RA

2

1

4

3

4

LA

LV

RV

sinoatrial node (SAN)

atrioventricularnode (AVN)

non-conducting layerin heart wall betweenatria and ventricles

Purkyne fibresThe route taken by electrical impulses across

the heart during the cardiac cycle.

P wave T wave

ST segment

PR interval

1 sQRS complex

R

SQ

A normal ECG pattern in a healthy heart.

Regulation of cardiac outputBlood is pumped around the body to supply O2 and remove CO2 rom respiringtissues. How much is pumped in a minute (cardiac output) depends on two actors:how quickly the heart is beating (heart rate) and the volume o blood leaving the letventricle with each beat (stroke volume).

cardiac output (dm3min1) = stroke volume (dm3) heart rate (min1)

1 Electrical impulses from theSAN spread across the atriawalls, causing contraction.This is called atrial systole.

2 Impulses pass to theventricles via the AVN aftera short delay to allow timefor the atria to finishcontracting.

3

4

3 Impulses pass down the Purkynefibres to the heart apex.

4 The impulses spread up through

the ventricle walls causingcontraction from the apex upwards.Blood is squeezed into the arteries.This is ventricular systole.

The P wave is thetime o atrial systole.

The QRS complexis the time oventricular systole.

The T wave is causedby repolarisation othe ventricles duringdiastole.


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The heart rate can be aected by hormones (e.g. adrenaline) and nervous control. Thecardiovascular control centre in the medulla o the brain controls the sinoatrialnode via nerves. The sympathetic nerve speeds up the heart rate in response to allsin pH in the blood due to CO2 and lactate levels rising, increases in temperature andmechanical activity in joints.

Impulses carried by the vagus nerve (parasympathetic) slow down the heart rate

when the demand or O2 and removal o CO2 reduces.

Regulation of ventilation rateThe rate at which someone breathes is called the ventilation rate. This is otenexpressed as the volume o air breathed per minute (the minute ventilation). Thevolume o air breathed in or out o the lungs per breath is called the tidal volume.The maximum volume o air that can be orcibly exhaled ater a maximal intake o airis called the vital capacity.

ventilation rate = tidal volume number of breaths per minute

The ventilation centre in the medulla controls the rate and depth o breathing

in response to impulses rom chemoreceptors in the medulla and arteries whichdetect the pH and concentration o CO2 in the blood. Impulses are sent rom theventilation centre to stimulate the muscles involved in breathing. A small increase inCO2 concentration causes a large increase in ventilation. It also increases in responseto impulses rom the motor cortex and rom stretch receptors in tendons and musclesinvolved in movement. We also have voluntary control over breathing.

Measuring lung volumes using a spirometerA person using a spirometer breathes in and out o an airtight chamber causing it tomove up and down and leaving a trace on a revolving drum (kymograph).

Volume/dm

3

8

7

6

Time (6 cm = 1 minute)

vital

capacity

A

B

tidalvolume

5

A spirometer trace showing quiet breathing with one maximal breath in and out.

You can calculate the volume

of O2 absorbed in a given time

by measuring the differences

in volume between the troughs

labelled A and B in the diagramand dividing by the time between

A and B.

Q1 I someone takes 11 breaths per minute with an average tidal volume o0.45 dm3 calculate their ventilation rate.

Q2 Sketch what you would expect an ECG trace to look like i a patientsuered rom ventricular fbrillation. (This is rapid and uncontrolledcontractions in the ventricles sometimes caused by a patch o damagedtissue in the ventricle acting as a pacemaker.)

Q3 Suggest what might happen to the heart rate i the connection betweenthe sinoatrial node and the vagus and sympathetic nerves was cut.

Q1 Summarise and explain the

effects of exercise on both heart

and ventilation rate.

Thinking Task

SAFETY!

A canister o soda lime

can be used to remove theCO2 rom the exhaled airto measure the volumeo O2 absorbed by theperson ater exercise, but itis important to rememberthat the chamber must beflled with medical gradeO2 beore starting i this isto be attempted.


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Homeostasis


52 Green Book 7.3 Orange Book 7.4

Homeostasis is the maintenance o a stable internal environment, within a narrowlimit, o the optimum conditions needed by cells so they can unction properly. Ahomeostatic system thereore requires:

receptors to detect the change away rom the norm value (stimulus) a control mechanism that can respond to the inormation. The control mechanismuses the nervous system or hormones to switch effectors on or o

effectors to bring about the response (usually to counteract the eect o the initialchange). Muscles and glands are eectors.

input receptors control mechanism eectors output

eedback

Negative feedback helps to keep the internal environment constant. A change inthe internal environment will trigger a response that counteracts the change, e.g. arise in temperature causes a response that will lower body temperature. For negativeeedback to occur, there must be a norm value or set point, e.g. 37.5 C or corebody temperature.

egative feedback is the key

o understanding homeostatic

esponses. Just remember if one

hing goes up, the body responds to

ring it back down, or vice versa. To

o this you need receptors, a norm

alue, a control centre (often part of

he brain like the hypothalamus) and

ome effectors to bring about theesponse.

Homeostasis and exerciseWe have already seen that the body responds to the demands o exercise by increasingcardiac output and ventilation rate under the control o centres in the medulla (seepage 51 The heart, energy and exercise). Not only does the increased respirationrate during exercise produce a lot o CO2 and/or lactate, but the energy transers alsorelease a lot o heat energy. This can be enough or a 1 C rise in body temperatureevery 510 minutes i we cant disperse the heat away rom the body.

The control o core body temperature through negative eedback is calledthermoregulation. Thermoreceptors in the skin detect changes in temperature. Inaddition thermoreceptors in the hypothalamus (in the brain) can detect changes in thecore blood temperature. I a rise in temperature is detected above the norm value theheat loss centre in the hypothalamus will stimulate eectors to increase heat loss romthe body usually through the skin.

A Conditions controlled by homeostasis fluctuate around the norm value.

norm value

(set point)

rise above

norm

fall below

norm

change from

norm detected

effectors act to

return the condition

to the set point

Timenorm value

B The condition is controlled by negative feedback.

A summary o the role o negative eedback in maintaining body systems within narrow limits.


10/1553



Q1 Using your revision in this

section and pages 45, 50 and 51

explain why some animals are

adapted to short bursts of fast or

powerful exercise, while others

are adapted to long periods of

continuous exercise.

Thinking Task

Q1 Explain what is meant by the term negative eedback.

Q2 Suggest what the consequences might be i you were unable to lose heatrom the body during exercise.

Q3 Describe the bodys likely responses to the core temperature droppingbelow 37 C.

set point

(norm)

detected

by receptors

effectors

react

effectors

react

detected by

receptors

set point

(norm)

set point

(norm)

heat loss

centre in

hypothalamus

heat gain

centre in

hypothalamus

send

impulses

sends

impulses

send

impulses

sends

impulses

temperature risestemperature falls

temperature fallstemperature rises

Negative eedback in thermoregulation.

Above or below certain temperatures homeostasis ails (e.g. because thehypothalamus may be damaged). Instead, positive eedback may occur resulting in ahigh temperature continuing to rise or a low temperature alling still urther. This canresult in hyperthermia or hypothermia and may lead to death.

Medical technology to enable those withinjuries and disabilities to participate in sportThe development o keyhole surgery using fbre optics has made it possible orsurgeons to repair damaged joints (including torn cruciate ligaments in the knee) withprecision and minimal damage. This is because only a small incision (cut) is needed sothere is less bleeding and damage to the joint, and recovery is much quicker.

A prosthesis is an artifcial body part designed to regain some degree o normalunction or appearance. The design o prostheses has improved signifcantly and manydisabled athletes are now able to compete at a very high level, e.g. with dynamicresponse eet that can literally provide them with a spring in their step. Damaged

joints (such as knee joints) can also now be repaired with small prosthetic implantsto replace the damaged ends o bones, reeing the patient rom a lie o pain andrestoring ull mobility.

Heat loss centre

Stimulates:

Inhibits:

skin (dilates capillaries in

skin)

hairs lie flat)

Heat gain centre

Stimulates:

Inhibits:

constrict

contract


11/15

Health, exercise and sport


54 Green Book 7.4 Orange Book 7.5, 7.6

The possible effects of too little exerciseThere are many benefts to regular moderate exercise. Here are a ew possible eects

o a lack o exercise over a prolonged period o time: reduced physical endurance, lung capacity, stroke volume and maximum heart rate increased resting heart rate, blood pressure and storage o at in the body increased risk o coronary heart disease, type II diabetes, some cancers, weight

gain and obesity impaired immune response due to lack o natural killer cells increased levels o LDL (bad cholesterol) and reduced levels o HDL (good cholesterol) reduced bone density, thereore increased risk o osteoporosis.

The possible effects of too much exerciseOvertraining can lead to symptoms such as immune suppression and increased wearand tear on joints. It can also result in chronic atigue and poor athletic perormance.

Too much exercise generally may also increase the amount o wear and tear onjoints. Damage to cartilage in synovial joints can lead to inflammation and a orm oarthritis. Ligaments can also be damaged. Bursae (fluid-flled sacs) that cushion parts othe joint can become inflamed and tender.

There is also some evidence o a correlation between intense exercise and the risko inection such as colds and sore throats. This could be caused by an increasedexposure to pathogens, or a suppression of the immune system. There is someevidence that the number and activity o some cells o the immune system may bedecreased while the body recovers ater vigorous exercise. It may also be the case thatdamage to muscles during exercise and the release o hormones such as adrenaline

may cause an inflammatory response which could also suppress the immune system.

Some ethical positions relating to the use

of performance-enhancing substances

by athletesSome athletes will do anything they can, in the pursuit o excellence. This mightinclude the use o illegal perormance-enhancing substances. Others may eel theyneed to ollow suit because they dont want to be at a disadvantage. This has been asubject or debate in the sporting world or many years.

These ethical rameworks can be used when considering both sides o the argument:

rights and duties maximising the amount o good in the world making decisions or yoursel leading a virtuous lie.

For example, doping in sport could be considered notacceptable because athleteshave a right to air competition, but could equally be considered acceptable becauseathletes have the right to exercise autonomy, or example to choose to achieve their bestperormance, and also have a duty to any sponsor they may have.

Remember that in order to maintain that something is ethically acceptable or not, youmust provide a reasonable explanation as to why that is the case.

Ethical absolutists see things as very clear cut. They would take one o two positions:1 It is never acceptable or athletes to use perormance-enhancing substances (even i

they are legal), or2 it is always acceptable or athletes to use any substance available to them to

compete more eectively, even i there are associated risks to their health.

Ethical relativists would realise that people and circumstances may be dierent, e.g: It is wrong or athletes to use perormance-enhancing substances, but there may be

some cases and circumstances where it is acceptable.

ust because two things are

bserved to happen, it doesnt

mean they are connected. In

articular it doesnt mean that one

aused the other. A correlation

oes not necessarily mean a

onnection. If there appears to

e a strong correlation between

wo factors, a causal link is more

kely if you can provide a biologicalxplanation for why one factor

will affect the other, especially

there arent many other likely

actors or explanations available.

or example, there is a positive

orrelation between the number

f shark attacks and the number of

ce creams sold at a beach. There

s no biological explanation for this

orrelation, so there is no direct

ausal link. In contrast it is thought

hat there is a causal link between

he number of cigarettes smoked

nd the number of deaths due toung cancer, because there is a

trong correlation and a biological

xplanation about why smoking

ould cause lung cancer.

emember that exam questions

this unit may refer back to any

ther topics from the A level biology

ourse, so now would be a good

me to check your notes about the

ells involved in the specific and

on-specific immune system (page

3, Unit 4).


12/1555


Green Book 7.4 Orange Book 7.5, 7.6

How can drugs affect your genes?Some drugs such as anabolic steroids are closely related to natural steroid hormones.They can pass directly through cell membranes and be carried into the nucleus boundto a receptor molecule. These hormone/receptor complexes act as transcriptionfactors. They bind to the promoter region o a gene allowing RNA polymeraseto start transcription. As a result more protein synthesis takes place in the cells.

For example testosterone increases protein synthesis in muscle cells, increasing thesize and strength o the muscle tissue. Peptide hormones do not enter cells directly,but they bind with receptors on the cell surace membrane. This starts a processthat results in the activation o a transcription actor within the nucleus. For exampleerythropoietin (EPO) stimulates the production o red blood cells. This means that theblood can carry more oxygen which is an advantage or an athlete.

Q1 Describe why a lack o exercise may lead to an increased risk o coronaryheart disease.

Q2 Explain why a lack o T helper cells may increase the risk o an athletesuering rom a sore throat.

Q3 Outline the role o transcription actors in the control o gene expression.

DNA transcription is controlled by transcription actors.

Q1 Even if all performance-

enhancing substances were

formally banned, would we ever

have a level playing field for

athletes?

Thinking Task

Genes are switched on bysuccessful formation andattachment of thetranscription initiationcomplex to the promoterregion.

Genes remain switchedoff by failure of thetranscription initiationcomplex to form andattach to the promoterregion. This is due tothe absence of proteintranscription factor(s) orthe action of repressormolecules.

transcriptioninitiation complex

RNA synthesis

transcription factors

RNA polymerase

gene

DNA

promoter region site for RNA polymerase attachment


13/15

Topic 7 Run for your life checklist


56

By the end o this topic you should be able to:

Revision spread Checkpoints Spec.

point

Revised Practice exam

questions

Muscles and

movement

Describe the structure o a muscle fbre and explain

the dierences between ast and slow twitch

muscle fbres.

LO2

Explain how skeletal muscle contracts using the sliding

flament theory.

LO3

Recall the way in which muscles, tendons, the

skeleton and ligaments interact to allow movement.

LO4

Energy and the

role o ATP

Describe aerobic respiration as splitting o glucose to

release carbon dioxide, water and energy.

LO5

Describe a practical to investigate rate o respiration. LO6

Recall what ATP is and how it supplies energy or cells. LO7

Describe the roles o glycolysis in both aerobic and

anaerobic respiration. You do not need to know all

the stages but you do need to know that glucose is

phosphorylated and ATP, reduced NAD and pyruvate

are produced.

LO8

Explain what happens to lactate ater you stop

exercising.

LO11

The Krebs cycle

and the electron

transport chain

Describe how the Krebs cycle produces carbon

dioxide, ATP, reduced NAD and reduced FAD. You

should also understand that respiration has lots o

enzyme-controlled steps.

LO9

Describe how ATP is made by oxidative

phosphorylation in the electron transport chain

including the roles o chemiosmosis and ATPase.

LO10

The heart, energy

and exercise

Understand that cardiac muscle is myogenic and

describe how electrical activity in the heart allows it to

beat. You should also know how ECGs can be used.

LO12

Explain that tissues need rapid delivery o oxygen and

removal o carbon dioxide during exercise and that

changes in ventilation and cardiac output allow this to

happen. You should understand how heart rate and

ventilation rate are controlled.

LO13

Describe how to use data rom spirometer traces to

investigate the eects o exercise.

LO14

Homeostasis Explain the principle o negative eedback. LO15

Discuss the concept o homeostasis and how it

maintains the body during exercise, including

controlling body temperature.

LO16

Health, exercise

and sport

Explain how genes can be switched on and o by

DNA transcription actors including hormones.

LO17

Analyse and interpret data on the possible dangers o

exercising too little and too much. You should also be

able to talk about correlation and cause.

LO18

Explain how medical technology helps people with

injuries or disabilities to take part in sport.

LO19

Outline the ethics o using perormance-enhancing

substances.

LO20


14/1557


1 Animals that are predators often show bursts of very fast movement. Their prey tend to be able to carry out sustained movement over

longer periods of time. Close examination shows that the muscles of predator and prey show a different composition of fast- and slow-

twitch fibres.

(a) (i) Outline the differences between fast- and slow-twitch muscle fibres. (2)

(ii) State whether predator or prey would show a higher proportion of slow-twitch fibres. (1)

(iii) Discuss why predators show different proportions of fast- and slow-twitch muscle fibres from their prey. (2)

Examiner tip

If you are asked for the differences, make sure you refer to both or use a comparative word, e.g. more.

Student answer Examiner comments

(a) (i) Slow-twitch muscle fibres have more mitochondria and

more capillaries supplying oxygen than fast twitch fibres.

(ii) Prey.

(iii) Predators are likely to have more fast-twitch than slow-twitch fibres, in comparison to their prey. This is because

predators tend to be fast and powerful over short distances

to catch and kill their prey and therefore use anaerobic

respiration to release ATP quickly.

This is a good response because not only does it provide a likely

comparison, it also provides a clear and plausible explanation.

(b) During fast movement, lactate builds up in the muscles of a predator, such as a cheetah. Explain what happens to this

lactate after the chase has ended. (3)


Lactate diffuses from the muscle into the blood where it is carried

away from the muscle to prevent cramp.

This response is a correct but only partial explanation. It explains

how the lactate is moved away from the muscle, but not how it is

removed from the body.

Lactate is oxidised back into pyruvate using NAD that has been

oxidised in the electron transport chain using oxygen. The extra

oxygen needed is the oxygen debt.

This response will gain maximum marks because it provides

a chemical explanation of the fate of the lactate, clearly

demonstrating an understanding of both aerobic and anaerobic

respiration, as well as recognition of the need for extra oxygen.

(c) During the chase, the core body temperature of both predator and prey rises. Describe how changes in blood circulation help to return

their core body temperatures to normal. (3)

Examiner tip

In longer questions like this try to be clear on writing cause and effect. Where possible use key terms and concepts from your course as part

of your description as you will often receive credit for these. However, the terms need to be in the correct context you will not gain marksfor lists of random terms that do not demonstrate your understanding of what they mean.


An increase in core temperature causes vasodilation so that more

heat is lost from the skin.

This response would only score 1 mark for the recognition that more

heat would be lost from the skin. The reference to vasodilation is

not enough as it does not describe what change occurs to the blood

circulation.

This is an example of homeostasis using a negative feedback

mechanism. Changes to the core temperature are detected by

thermoreceptors in the hypothalamus which send nerve impulses to

arterioles in the skin. This causes vasodilation resulting in increasedblood flow to the skin.

This response is better because it includes key terms and structures

in the correct context of how the change is caused (homeostasis,

negative feedback, hypothalamus). It also clearly describes the

effect of vasodilation on the blood circulation.

(Edexcel GCE Biology (Salters-Nuffield) Advanced Unit 5 June 2008.)

Build Better Answers


15/15

Practice questions


1 (a) Name the region o the human brain involved in control o heart rate. (1)

(b) Heart rate increases during exercise. Explain the mechanisms involved incontrolling this increase in heart rate. (4)

Total 5 marks(Edexcel GCE Biology (Salters-Nufeld) Advanced Unit 5 June 2007)

2 Doing too little exercise can lead to health problems, but too much exercise canalso be harmul. Discuss the benefts and potential dangers o exercisein humans. (6)

Total 6 marks(Edexcel GCE Biology (Salters-Nufeld) Advanced Unit 5 June 2007)

3 The table below reers to three major stages o aerobic respiration and the productso each stage. Copy and complete the table by inserting the part o the cell inwhich the stage occurs and two products in the blank spaces.

H zoneactin

Fully relaxed sarcomere

myosin

H zone

Partially contracted sarcomere

Stage Part of cell in which it occurs Two products

glycolysis

Krebs cycle matrix o mitochondrion

electron transport chain ATP and water

(4) Total 4 marks

(Edexcel GCE Biology Advanced Unit 4 paper 3 June 2007)

4 The diagrams show one sarcomere in its ully relaxed state and when it ispartially contracted.

(a) Calculate the percentage change in width o the H zone when the sarcomereis partially contracted. Show your working. (3)

(b) During the contraction o this sarcomere, the myosin flaments pull the actin

flaments towards the centre o the sarcomere. Explain how this isbrought about. (4)

Total 7 marks (Edexcel GCE Biology Advanced Unit 4 paper 3 June 2007)

5 The diagram showsthe ways in which therespiratory system anddierent parts o thebrain interact witheach other toregulate breathing.

Cerebralhemispheres

Respiratorycentres in the

pons and medulla

Diaphragm muscles andstretch receptors

Intercostal muscles andstretch receptors

Chemoreceptors

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