B1a Fit for life

RespirationAll the energy that our bodies use is provided byrespiration. Respiration is a chemical reactionthat takes place inside every body cell. Thisreaction releases energy from glucose. The energycan then be used by the cell for whatever isneeded. For example, if it is a muscle cell, it canuse the energy for contracting (getting shorter). Ifit is a cell in the digestive system, it can use it formaking enzymes. If it is a nerve cell, it can use itfor sending electrical impulses to the brain.

Each cell must release its own energy, so everyliving cell respires.

Aerobic respirationWhen cells get enough oxygen, they respireaerobically. In aerobic respiration, glucose reacts with oxygen. The word equation for thisreaction is:

glucose + oxygen → carbon dioxide + water

This is an example of a metabolic reaction. Ametabolic reaction is a chemical reaction thattakes place inside a living organism.

High altitude, low oxygen

Up on top of the world, in the high Himalayas, oxygenis hard to come by. At Everest Base Camp, a height of5240 metres above sea level, the air is much thinnerthan at the kinds of altitudes where people usuallylive. However fit a person is, they struggle to getenough oxygen into their body.

Reinhold Meissner and Peter Habeler were the firstpeople to climb Everest without breathing any oxygenfrom a cylinder. Meissner wrote:

‘Now, at a height of 8800 metres, we can no longerkeep on our feet while we rest. We crumple to ourknees, clutching our axes ... Breathing becomes such astrenuous business that we scarcely have the strengthto go on. Every ten or fifteen steps we collapse intothe snow to rest, then crawl on again. My mind seemsalmost to have ceased to function ... I crawl, I cough,but I am drawn on.’ Figure 1a.1 At high altitude.

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SAQ1 This is the word equation for another metabolic

reaction:

carbon dioxide + water → glucose + oxygen

What is this reaction? Where does it take place?

This is the balanced symbol equation for aerobicrespiration:

C6H12O6 + 6O2 → 6H2O + 6CO2

In this process, glucose is oxidised. In many ways,aerobic respiration is similar to combustion(burning) – a fuel (glucose) reacts with oxygenand energy is released. However, burning cannotbe allowed to happen in a cell because a rapidtemperature rise would destroy the proteins andother molecules in the cell.

In a living cell, the oxidation of the glucosetakes place in a series of small, carefully controlledsteps. The energy is released gradually, not all atonce as happens during burning.

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SAQ2 Write down two similarities between aerobic

respiration and combustion.

3 Write down two differences between aerobicrespiration and combustion.

Anaerobic respirationCells are also able to release energy from glucosewithout using oxygen. This process is calledanaerobic respiration. The glucose is brokendown to produce lactic acid:

glucose → lactic acid

Anaerobic respiration is not very efficient. Thatmeans that you don’t get as much energy from acertain amount of glucose as you would withaerobic respiration. This is because anaerobicrespiration does not break down the glucosecompletely. It is really a ‘last resort’ for cells whentheir oxygen supply runs out but they still needto use energy.

Imagine you are running fast. Your leg musclesare working flat out. Your heart rate has increasedand so has your breathing rate, to supply oxygenat a much faster rate than usual to the muscles.But their best efforts are not enough and yourmuscles need more energy than they can releasethrough aerobic respiration. So they use anaerobicrespiration as well.

The lactic acid that is made in anaerobicrespiration is toxic (harmful) to cells. As itaccumulates (builds up) in your muscle cells, theybegin to hurt. If a lot of lactic acid accumulates inthem, they can no longer carry out anaerobicrespiration. You have reached your limit; nomatter how much you want to keep on runningfast your muscles simply cannot do it.

The lactic acid made during anaerobicrespiration diffuses out of the cells where it ismade and into the blood. It is carried to the liver.This is helped by the rapid beating of the heart,which keeps blood moving swiftly through thearteries and veins.

When you stop running, you keep on breathinghard so you are still getting lots of oxygen intothe body. Some of this oxygen is used by the livercells to break down the lactic acid. You keep onbreathing faster and deeper than usual until allthe lactic acid has been broken down. The extraoxygen that you need to do this is called youroxygen debt.

2 Fit for life

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Figure 1a.2 A top-class sprinter may not breathe at all duringthe 10–11 seconds of a 100 m race but relies heavily onanaerobic respiration.

Aerobic respiration Anaerobic respiration

Similarity

energy released by energy released bybreakdown of glucose breakdown of glucose

Differences

uses oxygen does not use oxygen

no lactic acid made lactic acid made

carbon dioxide and no carbon dioxide orwater made water made

releases a large amount releases a small amountof energy of energy

Table 1a.1 A comparison between aerobic and anaerobicrespiration in humans.

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Keeping fit

Fit for life 3

Fatigue

In June 2005, Centre Court at Wimbledon wasbrought alight by a young Scottish tennis player whohad seemingly appeared from nowhere. 18-year-oldAndrew Murray took the first two sets from DavidNalbandian, playing brilliant tennis. But as they wentinto the third set, Andrew began to suffer frommuscle cramp and fatigue. He had all the tennisknow-how and ability, all the agility, flexibility andspeed. But he lacked the stamina to take a world-classplayer to the end of a five-set match. Nalbandian tookthe last three sets and the match.

Andrew went away from Wimbledon knowing thathe had the ability to get into the top ten in the world.His priority was to work on his physical fitness,training his heart, lungs and muscles so that theywork together to supply his legs with the energy thatthey need to keep going to the end of a hard-fought match. Figure 1a.3 Andrew Murray playing David Nalbandian.

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H produce. For example, the strength of the handand arm muscles can be measured with aninstrument where you squeeze as hard as youcan on a hand-grip monitor, which gives you areadout of the force you have generated.

● Stamina is how long you can keep going with aparticular exercise. You could measure howlong you can keep running at a particularspeed or how many press-ups you can dowithout a break.

● Flexibility is how easily and how far your jointscan allow you to bend. For example, you could doa sit-and-reach test, in which you sit on the floorwith your legs straight in front of you and thenmeasure how far you can reach with your arms.

● Agility is how quickly and easily you can turnand twist while you are moving. One test foragility is called the ‘hexagonal obstacle’ test.You stand in the centre of a hexagon with 66 cmsides, marked out on the floor. You then have tojump as quickly as possible from the centre overone side, back to the centre and over anotherside, and so on all around the hexagon.

Andrew may not have been fit enough to getthrough a gruellingly long and tough match buthe is probably much fitter than almost everyone inyour class. Most of us don’t need to be fit enoughto play five sets of hard tennis on a hot day. Butbeing fit is a good thing to aim for. It makes youfeel good and helps your general health. It won’tstop you from getting infectious diseases such ascolds and flu, but it does help you to enjoyphysical activity. And that can improve yourhealth, because it can make it less likely that youwill suffer from heart disease when you are older.

Measuring fitnessIf you ask a trainer at a gym to devise a fitnessprogramme for you, they will probably want tostart off by measuring your fitness. There aremany different aspects of fitness that can bemeasured and lots of different ways of measuringthem. Here are a few examples.● Strength of a particular set of muscles can be

measured by making them work as hard asthey can and measuring the force they

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● Speed is how fast you can run. You canmeasure this on a treadmill.

● Cardiovascular efficiency is how well your heartmanages to supply oxygen to your muscles. Thereare a great many ways of measuring this. Onemethod is to measure VO2 max. This is short for‘maximum volume of oxygen’. VO2 max is themaximum rate at which your muscles can useoxygen before they have to go over to anaerobicrespiration (because the oxygen has run out). Thebetter your heart and blood are at getting oxygento your muscles, the higher your VO2 max.Cardiovascular efficiency affects your stamina.

SAQ4 Which of the above types of fitness do you think

let Andrew Murray down in his five-set matchagainst David Nalbandian?

5 Choose two of the methods described aboveand discuss how useful they are in givinginformation about someone’s fitness.

Blood pressureYour heart is made of cardiac muscle, a kind ofmuscle that naturally contracts and relaxesrhythmically, all the time. Each time it contracts,it squeezes inwards on the blood inside the heart,increasing its pressure and squirting it out of the

heart into the big arteries that carry the blood toother parts of the body.

You can feel this blood pressure when you takeyour pulse. If you hold two fingers gently over thetendon on the inside of your wrist, or at the frontof your neck, you can feel the arteries expandingand recoiling every time the heart beats. Thearteries have thick walls with a lot of elastic tissuein them. This allows them to be stretchedoutwards by the surge of high-pressure blood eachtime the heart contracts, and then recoil back totheir normal diameter when the heart relaxes.

4 Fit for life

Figure 1a.4 Measuring stamina. Figure 1a.5 Measuring flexibility.

Figure 1a.6 Measuring blood pressure.

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If you have your blood pressure measured, youwill be told two numbers. The first is the highestpressure that blood in the big arteries in your arm reaches. This happens when the heart iscontracting and it is called the systolic pressure.When the heart relaxes, the pressure in the arteriesdrops and this is called the diastolic pressure.

In science, pressure is measured in units calledpascals. In medicine, though, doctors still use oldunits for measuring pressure. They aremillimetres of mercury, written as mmHg forshort. This refers to the height that a particularpressure can push a column of mercury up atube. Now we have digital blood pressure meters,but many doctors still use tubes of mercury tomeasure blood pressure.

What affects blood pressure?A good blood pressure for a 16-year-old to have issomewhere around 120 over 80. This means thatyour systolic pressure is 120 mmHg and yourdiastolic pressure is 80 mmHg.

So what affects your blood pressure? We all varya bit from each other, just naturally, but there areseveral things that definitely have an effect.

As you age, your blood pressure will probablyincrease a bit. By the time you are 60, it is fairlynormal to have a blood pressure of around 135over 89.

Blood pressure is also affected by diet. A dietcontaining a lot of salt can increase your bloodpressure. This is because the high concentrationof salt in your blood means that the kidneys haveto allow there to be a lot of water in the blood, todilute the salt. So you have a greater volume ofblood squeezed inside your blood vessels,increasing the pressure.

It is also affected by the amount of exercisethat you do. While you are exercising, the heartbeats harder and faster and your blood pressureincreases. When you relax, the pressure goesdown to normal. If you exercise regularly, yourresting blood pressure will probably be lowerthan if you are unfit.

Your weight is also important. Overweightpeople tend to have higher blood pressure thanpeople of normal weight.

Alcohol affects blood pressure. Regularlydrinking large amounts of alcohol increases blood pressure. We don’t really understand whythis happens.

Stress is yet another factor that increases bloodpressure. Some stress is good for you – it meansthat you have challenges in your life and canmake your life more interesting and rewarding.But some kinds of stress – the kinds you can’tcontrol or escape from – are not good, especiallyif they go on for a long time. Stress can haveseveral damaging effects on your body, includingincreasing your blood pressure.

High and low blood pressureHigh blood pressure can cause considerable harmto the circulatory system and to other organs.● It puts extra strain on the heart, which can

increase the likelihood of burst blood vessels. Ifthis happens in the brain then part of the brainmay be damaged – either because the leakedblood builds up and presses dangerously on the

Fit for life 5

Figure 1a.7 Stress can cause an increase in blood pressure.

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6 Fit for life

brain tissue, killing brain cells, or because theburst vessel no longer supplies oxygen to thebrain cells, so they die. This is called a stroke.

● It can damage the kidneys. Blood pressure is alittle higher in the kidneys than in other partsof the body. This helps them to filter the bloodefficiently. But if the blood pressure is highalready then the extra-high pressure in thekidneys can damage them. Kidney failure ismuch more common in people who have highblood pressure.Although most people know that high blood

pressure is a health risk, not so many ever thinkabout low blood pressure. But this is dangeroustoo. If you have low blood pressure then bloodisn’t moving through your blood vessels as fast asit should. So, for example, less oxygen gets carriedto your brain and you may get dizzy spells orfaint, especially when you stand up quickly aftersitting down. Poor blood circulation means thatyour fingers and toes may not get enough bloodto them, which can harm the cells.

SAQ6 If someone has high blood pressure, do you

think a high diastolic or a high systolic pressureis the more dangerous? Explain your answer.

7 Explain fully why low blood pressure can makesomeone faint.

Figure 1a.8 This is a scan of the brain of someone who has hada stroke. The orangey-red area shows where blood has floodedinto the brain tissue.

Summary

You should be able to:

◆ describe how energy is released from

glucose in aerobic respiration and in

anaerobic respiration, and write the

word equations

◆ write the balanced equation for aerobic

respiration

◆ explain why your heart beats faster, and

you breathe faster, when you are

exercising

◆ explain how lactic acid is removed as

you recover from exercise

◆ describe what is meant by diastolic and

systolic blood pressure, and know that

they are measured in mmHg

◆ know that diet, age, exercise, weight

and alcohol intake affect blood pressure

◆ explain the consequences of high blood

pressure

◆ explain the difference between being fit

and being healthy

◆ describe some ways of measuring

fitness

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Fit for life 7

Questions

1 Copy and complete these sentences to compare aerobic and anaerobic respiration.

a Anaerobic respiration releases ....................... energy than aerobic respiration.

b Anaerobic respiration makes ............................. acid.

c Carbon dioxide is made in .......................... respiration but not in ......................... respiration.

2 Jenny is told her blood pressure is 160 over 90.

a Which number is her diastolic pressure and which is her systolic pressure?

b What are the units her blood pressure was measured in? Choose from: pascals, millimetres of

mercury, newtons, joules.

c Jenny’s blood pressure is too high. Suggest two changes she could make to her lifestyle that

might bring her blood pressure down.

3 The graph shows the percentage of men and women in different age groups who had high blood

pressure in 2003.

a Describe the relationship between age and high blood pressure.

b Describe the relationship between a person’s sex and their risk of having high blood pressure.

c Explain why high blood pressure is dangerous.

90

80

70

60

50

40

30

20

10

0

75 & over16–24 25–34 35–44 45–54 55–64 65–74

Men

Women

Per

cent

age

with

hig

h bl

ood

pres

sure

Age group

Figure 1a.9 Prevalence of high blood pressure by sex and age, 2003, England.

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