Part One of B1 sample book AQA GCSE Biology Student Book

19 Pages·2010·13.55 MB·English

by  Mr Services User

Contents
Assess yourself questions 70 Plant oils, Earth and atmosphere P1 4.2 Comparing power stations 222
P1 4.3 Electricity from renewable resources 224
6 Variation
5 Chemicals from alkenes
P1 4.4 Renewables and the environment 226
B1 6.1 Gene basics 72
Introduction iii C1 5.1 Cracking 148
P1 4.5 Electricity distribution and voltage 228
B1 6.2 Diff erent types of reproduction 74
How to use this book iv C1 5.2 Polymers 150
P1 4.6 Meeting the demand 230
B1 6.3 Cloning plants and animals 76
How science works viii C1 5.3 New uses from polymers 152
B1 6.4 Modifying the genetic code 78 Investigative skills assessment 232
C1 5.4 Disposing of polymers 154
B1 6.5 Making choices about GM crops 80 Assess yourself questions 234
B1 C1 5.5 Ethanol production 156
GradeStudio – Achieve an A* 236
7 Evolution
6 Using plant oils
How organisms work
B1 7.1 Evolution of life 82 Waves and the Universe
C1 6.1 Vegetable oils and biodiesel] 158
1 Healthy bodies B1 7.2 Evolution of natural selection 84
C1 6.2 Emulsions 160
5 Waves
B1 1.1 Diet and exercise 4 B1 7.3 The development of a theory 86
C1 6.3 Hardening vegetable oils 162
P1 5.1 What is a wave? 240
B1 1.2 Slimming plans 6 Investigative skills assessment 88 C1 6.4 Oils and fats in our diet 164
P1 5.2 Measuring waves 242
B1 1.3 Pathogens 8 Assess yourself questions 90
Assess yourself questions 166 P1 5.3 Wave behaviour 244
B1 1.4 Defence against disease 10 GradeStudio – Achieve an A* 92
P1 5.4 Electromagnetic waves 246
B1 1.5 Treating and preventing disease 12 Examination-style questions 94 7 The Earth and atmosphere
P1 5.5 Radio waves and microwaves 248
B1 1.6 Controlling infection 14 C1 7.1 The structure of the Earth 168
P1 5.6 Mobile phones 250
B1 1.7 Vaccination programmes 16 C1 C1 7.2 Continental drift 170
P1 5.7 Making light work 252
B1 1.8 Keeping things sterile 18 C1 7.3 The atmosphere today 172
P1 5.8 Light and Infrared 254
The Earth provides C1 7.4 The changing atmosphere 174
2 Coordination and control P1 5.9 Sound 256
C1 7.5 Carbon dioxide and global warming 176
B1 2.1 The nervous system 20 1 Fundamental ideas in chemistry
Assess yourself questions 258
B1 2.2 Controlling our internal environment 22 C1 1.1 What are materials made of? 100 Investigative skills assessment 178
B1 2.3 Controlling pregnancy 24 C1 1.2 Electrons rule chemistry 102 Assess yourself questions 180 6 Red shift
B1 2.4 Evaluating the benefi ts of fertility treatment 26 C1 1.3 Electrons and the Periodic Table 104 GradeStudio – Achieve an A* 182 P1 6.1 The Doppler eff ect 260
B1 2.5 Plant responses 28 C1 1.4 A closer look at groups 1 and 0 106 Examination-style questions 184 P1 6.2 The expanding universe 262
B1 2.6 Using plant hormones 30 P1 6.3 The Big Bang theory 264
2 Rock and building materials
P1
Assess yourself questions 32 C1 2.1 Earth provides 108 Investigative skills assessment 266
Assess yourself questions 268
3 Drugs: use and abuse C1 2.2 Limestone chemistry 110 Energy
GradeStudio – Achieve an A* 270
C1 2.3 New materials from limestone 112
B1 3.1 Developing new drugs 34
1 Heat Examination-style questions 272
C1 2.4 New rocks from old 114
B1 3.2 Recreational drugs 36
P1 1.1 Infrared radiation 192
B1 3.3 Establishing links 38 3 Metals from rocks GGlloossssaarryy
P1 1.2 Kinetic theory 194
B1 3.4 Steroids and athletics 40 C1 3.1 Digging up the ore 116 IInnddeexx
P1 1.3 Conduction 196
C1 3.2 Metal from the ore 118
Investigative skills assessment 42 P1 1.4 Convection 198
C1 3.3 Developing new methods of extraction 120
Assess yourself questions 44 P1 1.5 How fast can energy be transferred by heating 200
C1 3.4 Finite resources 122
GradeStudio – Achieve an A* 46 P1 1.6 Heating buildings 202
C1 3.5 Heavyweight and lightweight metals 124
P1 1.7 Specifi c heat capacities 204
Environment and evolution
C1 3.6 Improving metals 126
2 Energy and effi ciency
4 Interdependence and adaptation Assess yourself questions 128
P1 2.1 Energy transfers 206
B1 4.1 Plant adaptations 50
4 Fuels from oil P1 2.2 Effi ciency and Sankey diagrams 208
B1 4.2 Animal adaptations 52
C1 4.1 Alkanes 130 P1 2.3 Reducing energy consumption 210
B1 4.3 Surviving the presence of others 54
C1 4.2 Separating crude oil 132
Assess yourself questions 212
B1 4.4 Extreme microorganisms 56
C1 4.3 Burning fuels 134
B1 4.5 The eff ect of changing environments 58 3 Electrical devices
C1 4.4 Problem fuels 136
B1 4.6 Pollution indicators 60 P1 3.1 Electrical energy 214
C1 4.5 Better fuels 138
P1 3.2 Paying for electricity 216
5 Energy
Investigative skills assessment 140
P1 3.3 Using diff erent devices 218
B1 5.1 Energy in biomass 62
Assess yourself questions 142
B1 5.2 Natural recycling 64 4 Generating electricity
GradeStudio – Achieve an A* 144
B1 5.3 Recycling issues 66 P1 4.1 Power stations 220
B1 5.4 The carbon cycle 68
vvii Proof copy – subject to Ofqual accreditation of the AQA specification. vviiii
B1 1.1 Diet and exercise
Your body uses some of its fat stores to replace the energy that it uses. Exercise
increases the proportion of muscle to fat in the body, which in turn increases
Changing lifestyles
Learning objectives metabolic rate.
The newspaper article in Figure 1 shows how medical experts are worried
•
explain why we need a healthy diet Everybody has a diff erent metabolic rate. It depends on many factors including
about the eff ects of poor diet and lack of exercise on young people. Experts are
•
describe what is meant by metabolic rate inheritance and how you live your life. Your metabolic rate decreases with age.
warning that many children are overweight or obese and therefore have more
•
interpret information about how
chance of developing serious health problems in later life.
metabolic rate and exercise are related to
fi tness b Medical 90
• explain how inherited factors aff ect our Science skills BRITISH CHILDREN TOP LEAGUE FOR Science skills experts p 80 Key Boys Girls
health recommend ou 70
• evaluate information about the eff ect of UNHEALTHY LIVING that young people carry out at least e gr 60
g
food on health 60 minutes of moderate exercise of a 50
• evaluate information about the eff ect of The largest study of youth health reveals that British every day. What percentage of e 40
g
lifestyle on development of disease. cvhegildetraebnl elisv.e on sugary snacks and almost no fruit and 15-year-old boys achieve this nta 30
The World Health Organisation report, based on surveys recommendation? erce 20
of more than 160 000 children in 35 countries, found that the P 10
c Suggest a reason for the change
dietary habits of Britain’s young were among the worst. 0
Taking it further Doctors recommend at least five portions of vegetables in activity levels among girls as 10 11 12 13 14 15
daily for a healthy diet. More than two-thirds of children aged they get older. Age/years
Insulin controls the amount of 11–15 admitted that they did not eat even a single portion of Figure 3 Percentage of young people taking part
glucose in the blood. In one form of vegetables a day. A third of 11-year-olds drank at least one in at least 60 minutes of physical activity a day.
sugary drink a day, as well as eating sweets and chocolate
diabetes, type 2 diabetes, the body
every day. Snacks and sugary drinks are high energy foods.
still makes insulin, but needs more Poor diet and increasingly inactive lifestyles are blamed
than it produces, or cannot use insulin Figure 1 for a massive increase in the number of people who are Blood cholesterol level
Unhealthy children. overweight.
properly. Type 2 diabetes is much
Cholesterol is a fatty substance transported by the blood. We all need some Does your work aff ect your metabolic rate?
more common than type 1 diabetes a Use information from the newspaper article to explain why poor diet and
cholesterol to keep our body cells functioning normally. Blood cholesterol level
(in which no insulin is produced). inactive lifestyles are blamed for the increase in obesity.
depends on the amount of fat in the diet. It is also aff ected by inheritance. People
It usually develops in people over
with high blood cholesterol levels are at increased risk of developing diseases of Examiner feedback
the age of 40. The risk of developing
You are what you eat the heart and blood vessels.
diabetes increases with body mass;
Examination questions are likely to
it is three times more common in The amount and type of food that you eat has a major eff ect on your health.
provide data that you will be asked to
people who are 10 kg overweight. Carbohydrates and fats in your food provide the energy you need to stay alive Practical comment upon or evaluate.
However, type 2 diabetes is now being and be active. Food also provides the proteins, vitamins and minerals your
reported in children, all of whom so body uses to grow and to replace damaged cells and tissues. By eating a varied You can compare the energy
far have been overweight. diet you are more likely to get everything you need to keep your body healthy. values of diff erent foods by thermometer
burning them under a beaker of
Malnutrition happens when you eat the wrong amount of each type of nutrient; water as shown in Figure 4. The stirrer Questions
either too much or too little. Defi ciency diseases can occur when the body rise in the temperature of the
1 Give the function in the diet of:
doesn’t get enough of a certain vitamin or mineral. These diseases are avoided water is measured for each food.
(a) fat (b) minerals.
by eating the right kinds of food. Figure 2 shows the types and proportions of The greater the temperature rise,
diff erent foods that make up a healthy balanced diet. the greater the energy content of 2 What is meant by defi ciency
the food. clamp disease?
Metabolism 3 Give two factors which aff ect
d Give two variables that should
The more exercise you do, the more energy you need. Many chemical reactions be controlled in this experiment blood cholesterol level.
calorimeter
take place in your body. These reactions release the energy from food. Your 4 What is meant by metabolic
metabolic rate is the speed at which your body uses that energy. rate?
water
Figure 2 These are the proportions of diff erent
5 List the factors that aff ect
foods that make up a balanced diet. Does this Even when you are resting, you need energy to keep your heart beating and for
metabolic rate.
match the food that you eat? breathing and digestion. The rate at which you use energy when you are resting
is called your resting or basal metabolic rate. Figure 4 Comparing the 66 EExxppllaaiinn tthhee rreellaattiioonnsshhiipp
energy values of foods using bbeettwweeeenn ddiieett,, mmeettaabboolliicc rraattee
The higher your metabolic rate, the more energy you use. As you exercise your
a calorimeter. food aanndd bbooddyy mmaassss.. A*
body builds up muscle tissue. Regular exercise also increases your metabolic rate.
4 Proof copy – subject to Ofqual accreditation of the AQA specification. Healthy bodies 5
B1 1.2 Slimming plans
Figure 2 shows some of the data from the study. h 5 Atkins diet
Learning objectives Do you believe what you read? b Which variables were controlled in the study? mont 4 WSliemig-Fhat sWtatchers
• evaluate claims made by slimming Ptheeompl elo isne t whee iUgKh ts. pend around £2 billion a year on products that claim to help cth eW wheaitg fheta-tlousres porfo tghrea mstumdeys m? ade it a ‘fair test’ between ss kg/ 23 Rcoonsetrmola gryro Cuopnley
• programmes d Which was the most eff ective programme in the ht lo 1
analyse and evaluate claims made for Currently, manufacturers are not compelled by law to prove that their products g
slimming programmes and products. work and can make claims that are unsupported by evidence. fi rst two months? Wei 0
�1
e How did the four programmes compare over 1 2 3 4 5 6
The advert in Figure 1 shows how a fi ctitious company tries to get people to
the six months? Time/months
buy their slimming product as a way of losing mass. The advert tries to convince
New Slimcredible contains 100% natural Figure 2 Results from the diet trial.
ingredients that amazingly: you that this product works. Many companies use adverts like this. The claims
• burn fat made in the adverts are rarely based on scientifi c evidence but rather on hearsay.
• block hunger pangs from Science in action Examiner feedback
Having an understanding of how evidence is used to provide reliable results
reaching your brain
• boost your concentration enables you to question what you read and to make informed decisions. Only one slimming pill, orlistat, has been approved by the NHS. Examination questions will be
• speed up your metabolism. based upon the evaluation of data
Medical experts say that there is only one way to lose weight, which is to eat Orlistat works by inhibiting enzymes that digest fat. Nearly a third of the fat that
Using Slimcredible, you can you eat is not digested if you take orlistat. The undigested fat is passed out with against the claims made for various
healthy foods and keep energy intake below energy use. Exercise increases the
lose up to one dress size in just two weeks! products. Remember to look at
your faeces. Studies have shown that orlistat, plus a mass-reducing diet and
amount of energy used by the body.
Our unique formula contains a blend of the data carefully and not jump to
exercise, causes more mass loss than a mass-reducing diet and exercise alone.
guarana, lemongrass, green tea, Garcinia
conclusions based on what you think
Some people lose 10% or more of their body mass within six months with the
cambogiam, L-carnitine and the Acai berry. Adverts showing photographs of a person before and you know.
help of orlistat. In others, it is less eff ective.
Years of scientific studies have shown that Science skills
after losing weight by using a slimming product used to
this combination of organic ingredients,
be common. This type of advertising has now been
amino acids and the renowned Brazilian
superfood the Acai berry massively boost banned. Questions
your weight loss power.
a Suggest reasons why the evidence in this kind of advert should be regarded as
1 Explain as fully as you can how a slimming programme such as the Rosemary Conley plan might help a person to
Figure 1 Can you trust all adverts? unreliable.
lose mass.
22 LLooookk aatt tthhee ffoouurr ddiieettss iinn FFiigguurree 33..
Slimming drugs warning
((aa)) CCoommppaarree tthhee wwaayyss iinn wwhhiicchh tthhee ffoouurr ddiieettss aarree iinntteennddeedd ttoo mmaakkee yyoouu lloossee mmaassss.. ((bb)) WWhhiicchh ddiieett ddoo yyoouu tthhiinnkk
Examiner feedback Trading standards offi cials investigated a variety of slimming products off ered iiss lliikkeellyy ttoo bbee mmoosstt eeffff eeccttiivvee?? GGiivvee rreeaassoonnss.. ((cc)) WWhhiicchh ddiieett sseeeemmss ttoo bbee lleeaasstt ccrreeddiibbllee?? GGiivvee tthhee rreeaassoonn((ss)) ffoorr yyoouurr
for sale over the Internet. They found that three-quarters of the products tested aannsswweerr..
Information aimed at consumers
made false claims. Most companies could not provide reliable evidence to back Weight Watchers
almost always uses the term ‘weight’, Atkins Diet
bcourtr eecxta mte rqmu ‘emstaiossn’.s refer to the ua•••Hb peotpa ata ulhiptlblthers lotie rethtd hxwseuap itercthe itpagra ttlrhtlshoo te adw-wnltuoa a bpcsrbuntsels r oec:tn lhptashali efmtea ti tsbfo .wao Tl odhphsyireleo est doe wp u abeecriougetp r honsltore fwa maa tdrie tebih e oeaotffs u opltehtrr eeode pg ifceo.rltaoaimnidmg miss o edtrh isegaoxetue scnrtocedmidssi pntoagon igeso omda tkoe 1••• •••S • s YYYeiYItIYtfto oco o s oiymouustuuoua n sroiadgu g tdsbrnaorethe oasrlnby tvtrod ’o ataitenny gdlteas lgoelyytaoo atep (iasds anaaelr lfasotdnostt m etmy waayer r afo eilovarnoguduri stnceer i 2oto (g byc,m0 uf ovaoi wtpgeerud bmlag areyoo ttek i,fuoehg t ifcdrafsiyhs aebnwadthrs tlebrb,ee a ufypoeseitsrp hokegos. s utyiirunt). dlsbnt rtrgrtaoyeiltl, ya beyecd rogeoe. uaggaTc skhesh) tni dsoa d osnptatrwd oiylco nr.fkesa smi.tn sygu o(o suwcirlles eb,i gbtoihsudstty.ut eienr,t oe ttch.)i.nking • • • ••p ‘Y nY wdEaEUroooaaomaesutucygcie go h.g hcrcshue oa apfastnn oneo swtp o .rmv eosodaeaofeit rnt incfe s tatah thsigtn se-oe,i byrvsfn sitteaebach’ stnterri eoenag pda gepam o wt snoa.iyendesisnat e tlesstoek sunbnm wrteagea.rsi rgtaaeghysnde ody itot ot fdnhcouoi erst dn rhct otuh ea se isn s.
be true, it probably isn’t good for you and isn’t true. • This gives you your maximum carbohydrate limit.
• You must stay under that limit to carry on losing weight.
Cabbage Soup Diet
Diet Trials was a study organised by the BBC and a group of scientists. Slim-Fast Diet • Take a large white cabbage and slice it up.
Science skills The study compared four popular commercial weight-loss programmes with a control group. Put it in a pan and cover it with water. Boil it
• the Slim-Fast plan: a mTheea ld rieeptsl awceemre:ent approach ••• YYSlooimuu -tcFaaaknse te tiawst aoa smS loiemfatel--Fnrae aspstl asschixea mtkiemesne ftso dar i bdertae.ya tkofa asvt oaindd h fiogrh lsu anncdh. lows. •• uYItno istui llc oiatw nb ieenca ofta mats be msu tua hcshiog fchta pibnub lfapibg. reSe es.aosuopn a tso y toaust leik.e.
• • You have a normal dinner. • You can combine the soup with any fruit or
Weight Watchers’ Pure Points programme: an energy-controlled diet with weekly group meetings • Each Slim-Fast meal replacement is around 240 calories and with the meal you vegetable you like (except for corn, beans,
• Dr Atkins’ New Diet: a self-monitored low-carbohydrate eating plan • Sshlimou-lFda snto sth gaok eosv ceor n1t2a0in0 caadldoeride sv.itamins and minerals, essential fatty acids and • pYeoaus o annldy sbtaicnka tnoa sth).is diet for 7 days then
• Rosemary Conley’s Eat Yourself Slim diet and fi tness plan: a low-fat diet and a weekly group exercise class. proteins. move onto a longer term dieting plan.
300 overweight people matched for age, sex and mass were randomly divided into the fi ve groups for the study. Figure 3 There are many approaches to dieting. A*
6 Proof copy – subject to Ofqual accreditation of the AQA specification. Healthy bodies 7
B1 1.3 Pathogens
before delivering a baby. When he got them to wash their hands in a chlorinated
hand wash before delivering babies, fewer women died. He concluded that
Transmitting infections
Learning objectives something was carried by the doctors from the dead bodies to the women.
Up to 5000 people die each year from infections picked up in hospitals in
•
explain what causes infectious disease and
England. The problem actually aff ects 100 000 people and costs the NHS a The discovery of pathogens
how diseases are spread
• thousand million pounds. It is thought that deadly infections are spread because Louis Pasteur and Joseph Lister studied ‘objects’ that became called
explain how pathogens cause disease
• hygiene rules are broken. For example doctors and nurses do not always wash ‘microorganisms’. Pasteur proved that there were ‘germs’ in the air and that they
describe the contribution made by
their hands or use hand gel between treating patients.
Semmelweiss to controlling infection in carried infection and disease. Lister developed a special soap called carbolic
hospitals today. A senior nursing offi cer said: ‘Levels of cleanliness have deteriorated in recent years. soap. He insisted that all medical instruments, dressings and even surgeons
I have seen dust under beds, cotton wool buds on the fl oor and dirty needles should be cleaned with it before any operation. More of Lister’s patients stayed Bacteria.
dumped in discarded meal trays. There are guidelines about changing the curtains healthy than those of other surgeons.
around beds, cleaning fl oors and cleaning bathrooms but these are often ignored.’
Chemicals that are used to clean wounds or get rid of sores, such as nappy rash,
Potentially fatal infections are carried in dust mites and a study has shown are called antiseptics. Chemicals that are used to clean work surfaces and other
that improving ward cleanliness can reduce infections. Hospitals now employ places where pathogens might be found are called disinfectants.
infection control specialists to reduce the number of infections.
Semmelweiss showed that keeping things clean helps to stop the spread of
pathogens. We call this hygiene. Hygiene is about keeping things clean to reduce
Ignaz Semmelweiss
the risk of disease. Washing removes the dirt and grease that pathogens stick to
Microorganisms are the tiny living things that can only be seen using a
and use as a source of energy to multiply.
microscope. They are everywhere, including in the food you eat and in you.
Microorganisms that cause illness or disease are types of pathogens. Microorganisms
Ignaz Semmelweiss was a doctor in the mid-1800s. He wondered why so many Pathogens are the ‘germs’ identifi ed by Semmelweiss, Pasteur and Lister. Two of Viruses.
women died of ‘childbed fever’ soon after giving birth. He also noticed that the main types are:
• Examiner feedback
student doctors carrying out work on dead bodies did not wash their hands bacteria – cause cholera, boils, MRSA, typhoid, tuberculosis
The standard of hygiene in hospitals needs to be • Do not use the term ‘germ’ in answers.
viruses – cause warts, herpes, polio, fl u, mumps, measles, smallpox.
high to avoid infections spreading. Think about
The general term to use is pathogen.
ways hygiene can be improved in hospitals.
a What was Semmelweiss’ observation? Spreading disease If you use the terms ‘bacteria’ or ‘virus’,
Science skills
make sure that they correctly apply to
b What was his hypothesis? Bacteria and viruses can pass from one person to another. This is how some
the disease in the question.
diseases spread and aff ect many people. You can become infected by pathogens
The table shows Semmelweiss’ original data.
in the air you breathe, the food you eat, the liquids you drink, and by touching
c Why did Semmelweiss calculate the percentage of deaths on each ward rather
someone. By making sure that your environment is clean, you lessen the chance Questions
than relying on the number of deaths?
that you will become infected.
d What conclusions can be drawn from this data? 1 What is a pathogen?
2 Name two types of pathogen.
Taking it further Hospital Number of Number of Deaths
Year span
ward deaths patients (%) 3 Give two ways in which
Bacterial cells do not have a nucleus pathogens pass from one
like animal and plant cells. Instead 1833–1838 (same Ward 1 1505 23 509 6.4 person to another.
number of doctors
the genes are found in a looped
and midwives in 4 Explain the diff erence between
chromosome and in plasmids, small each ward) Ward 2 731 13 097 5.81
an antiseptic and a disinfectant.
seperate rings of genetic material.
Plasmids are used by genetic 1839–1847 (medical Ward 1 1989 20 204 9.84 5 Explain fully why it is important
students and to wash your hands after
engineers to transfer genes into both
doctors in ward 1; visiting the toilet.
animal and plant cells. midwives in ward 2) Ward 2 691 17 791 2.18
66 WWrriittee aa hhyyggiieennee mmeemmoo wwiitthh
1100 bbuulllleett ppooiinnttss ffoorr hhoossppiittaall
1848–1859 Ward 1 1712 47 938 3.57
ssttaaffff .. BBaassee yyoouurr mmeemmoo oonn
(chlorinated hand
wash used) Ward 2 1248 40 770 3.06 tthhee sscciieennttiififi cc pprriinncciipplleess tthhaatt
SSeemmmmeellwweeiissss aapppplliieedd ttoo hhiiss
Figure 1 Semmelweiss’s original data. wwoorrkk.. A*
Passing on pathogens.
8 Proof copy – subject to Ofqual accreditation of the AQA specification. Healthy bodies 9
B1 1.4 Defence against disease
Some measles viruses Your white blood cells make The antibodies attack the measles
get into your body. antibodies and memory cells viruses, and kill them.
Immunity for the measles virus.
Learning objectives
This boy has a condition known
•
describe how pathogens make us ill
as SCID, also called ‘bubble boy’ antibodies
•
explain how white blood cells protect us
disease. He would not survive
against pathogens
• outside of his ‘bubble’ because he
explain how we become immune to
has no natural defence against If the measles virus gets into your body again,
pathogens.
pathogens; he is not immune to your memory cells know what kind of
antibody to make straight away.
them.
Bacteria and viruses make you ill
Examiner feedback by releasing poisonous chemicals white blood cell
called toxins or proventing your
You do not need to know the Figure 2 Some white blood cells release antibodies, which destroy pathogens.
cells from working properly. You
structure of either a bacterium or
might get symptoms such as a
a virus, but you must know that Life-long protection
headache, fever or feeling sick.
antibiotics do not aff ect viruses.
Once your white blood cells have destroyed a type of pathogen, you are unlikely
Once bacteria are inside you, they to develop the same disease again. This is because your white blood cells will
A boy in a bubble.
can multiply rapidly, doubling in recognise the pathogen the next time it invades your body and produce the
Taking it further number about every 20 minutes. Viruses multiply by entering the cells in your right antibodies very quickly to kill the pathogen before it can aff ect you. This
body. They use the chemicals inside the cell to make copies of themselves. The makes you immune to the disease.
Your blood group is determined by new viruses burst out of the cell ready to invade other body cells. This damages
the molecules present in the surface
or even destroys the cell.
Figure 3 shows what happens when
of your red blood cells. If you have
Science skills 6
someone is infected by a particular
type A blood, you have antibodies Cells to fi ght pathogens
pathogen. The graph also shows what
against the molecules of type B. So, if Your body has diff erent ways of protecting itself against pathogens. White blood happens when the person is infected a second time by the nnits 5
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md
blood type O, and if they have both, white blood cell pathogen after the second infection. Aoo 1
you are type AB. bl
c Suggest why the person did not become ill after the
0
For blood transfusions, people with second infection. 0 1 2 3 4 5 6 7 8 9 10 11 12 13
group O blood are said to be universal Figure 3 The immune response. Time/weeks
donors and people with group
AB blood are said to be universal Questions
Science in action
recipients. Explain why.
1 (a) Classify the following as B, caused by bacteria, or V, caused by viruses:
The white blood cell ...and then Antibodies are not all useful. Some
chicken pox, measles, tuberculosis, mumps, rubella, dysentery,
surrounds the pathogen... digests it. antibodies produced by a pregnant
smallpox, cholera, polio, infl uenza. (b) Which of these have you had?
woman can cause problems for
Figure 1 Some white blood cells ingest and destroy pathogens. (c) Which of these have you had only once? (d) Which have you had
her unborn baby. These antibodies
Examiner feedback more than once? (e) Which are you not immune to?
Other white blood cells release chemicals called antibodies which destroy destroy the baby’s red blood cells.
2 What is meant by immunity?
Make sure that you are quite clear about pathogens. Antibodies can only destroy a particular bacterium or virus, so In severe cases the baby is given a
3 What is meant by symptom?
the diff erence between an antibody white blood cells learn to make many diff erent types of antibody. For example, blood transfusion before birth. All
4 Explain the diff erence between antibody and antitoxin.
and an antitoxin. You may come across when a fl u virus enters the body, antibodies are made that destroy the fl u virus. pregnant mothers are screened for
5 Describe the ways in which pathogens make us feel ill.
the term ‘antigen’ in your studies. This production of these antibodies so that
After the virus has been destroyed, fl u antibodies remain in the blood and act
6 Describe the ways in which white blood cells protect us against pathogens.
term will not appear in the examination. the problem can be anticipated and
quickly if the same pathogen enters in the future. White blood cells also produce
Do not use the term unless you fully 77 WWrriittee aa ppaarraaggrraapphh ttoo eexxppllaaiinn ffuullllyy wwhhyy yyoouu ddoo nnoott uussuuaallllyy ssuuffff eerr ffrroomm aa dealt with.
antitoxins. These are chemicals that prevent the toxins made by pathogens from
understand what it means. ppaarrttiiccuullaarr iinnffeeccttiioouuss ddiisseeaassee mmoorree tthhaann oonnccee..
poisoning your body. A*
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B1 1.5 Treating and preventing
Because the pathogen is weak or inactive, the vaccine does not make you ill,
disease but your white blood cells still produce antibodies to destroy the pathogen. This
makes you immune to future infection by the pathogen. Your white blood cells
will recognise the pathogen if it gets into your body and respond by quickly
Feeling ill producing antibodies. The pathogen does not get a chance to reproduce enough
Learning objectives
• If you have a sore throat you might take throat lozenges to reduce the pain. to make you ill.
explain how diseases are treated using
The sore throat is a symptom caused by a pathogen that has infected your
medicines and antibiotics Weak or dead microbes are Antibodies are
• body. This medicine helps to relieve the symptom but it will not kill the injected into the body. produced which
explain how vaccination make us immune
destroy the
pathogen.
to pathogens microbes and White blood cells can
• quickly produce
evaluate data relating to the success of their toxins.
Killing bacteria antibodies if this
vaccination campaigns.
pathogen enters the
Antibiotics are medicines that help to cure diseases caused by bacteria. body again.
You take antibiotics to kill bacteria that get inside your body. Doctors use many
diff erent antibiotics to treat people. Penicillin was the fi rst antibiotic to be
discovered.
Antibiotics can’t kill viruses. Because viruses live and reproduce inside body cells,
it is diffi cult to develop medicines that kill viruses without damaging body cells Figure 2 How vaccination works.
and tissues.
antibiotic P antibiotic S The level of antibody in the blood
Science skills
after some vaccinations does 6
not get high enough to give
protection. In this case, a second, or booster, injection 5
s second injection
oThf eva gcrcaipnhe ash feoww sw teheek lse voer lm oof annthtisb loadteier sis i nn eae pdeerdso. n’s ody inary unit 4 of vaccine (booster)
bvalococidn efo.llowing a fi rst and second injection of a of antibm/arbitr 3 foirf svta icncjeincetion
a What was the diff erence in arbitrary units in the mount dstrea 2 immlevuenlity
level of antibody between the fi rst and second Aoo
injection? bl
1
b Explain why the person became immune after the
antibiotic T bacteria
How will this throat lozenge help? Which antibiotic is most eff ective? second injection but not the fi rst. 0
Figure 1 Finding out which antibiotic works best. 0 1 2 3 4 5 6 7 8 9 10 11 12 13
Time/weeks
Figure 3 Booster injections.
The eff ect of diff erent antibiotics on bacteria can be measured in the laboratory.
This is done by using small discs of paper containing antibiotics. The discs are
placed in a dish containing bacteria growing on a gel. The photograph shows Questions Examiner feedback
the eff ect of three antibiotics. The clear zone that forms around each disc is
1 What symptoms might you have if you catch a cold? It is important that you understand
where bacteria have been killed. Figure 1 shows the results of testing three other
2 What is the most common type of medicine that is not on these two why viruses cannot be killed by
antibiotics. Gel test are useful, but the body is more complicated than a gel. The
pages that is used to treat the symptoms of an infectious disease? antibiotics.
results in the body may be diff erent.
3 Which antibiotic in Figure 1 – P, S or T – works best against this
bacterium?
A quick jab
4 Explain why antibiotics can be used to treat bacterial infections but not
Immunity to a disease can be gained without ever having had the disease. A
viral infections.
newborn baby receives antibodies from its mother in the fi rst few days that it
5 Rubella is a pathogen that can pass across the placenta. Why is it
feeds on her milk. When you were a young child you were probably immunised
important that girls are vaccinated against rubella?
to protect you from very harmful diseases, such as whooping cough, measles
66 EExxppllaaiinn hhooww vvaacccciinnaattiioonn pprrootteeccttss yyoouu aaggaaiinnsstt aa ddiisseeaassee,, bbuutt ddooeess nnoott
and polio. Immunisation (vaccination) usually involves injecting or swallowing
ccaauussee yyoouu ttoo ddeevveelloopp tthhee ddiisseeaassee.. A*
a vaccine containing small amounts of a dead or weak form of the pathogen.
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B1 1.6 Controlling infection
a Describe the trend in the number of 1800
Antibiotic resistance Science skills Underlying cause
Learning objectives deaths from MRSA. 1600
Mentions
• 1400
explain how strains of bacteria can HOSPITAL SUPERBUG KILLS BABY b Suggest an explanation for the large increase in aths 1200
develop resistance to antibiotics e
d
• explain the consequences of the overuse the number of death certifi cates where MRSA of 1000
was ‘mentioned’. er 800
of antibiotics and of mutations of bacteria A one-day-old baby b
m 600
and viruses boy was killed by u
N
• describe how epidemics and pandemics the hospital 400
200
occur. superbug MRSA.
Baby Luke was 0
1993 1995 1997 1999 2001 2003 2005 2007
only 36 hours old
Figure 3 Deaths from MRSA in the UK. Year
Taking it further when he died.
Luke was born
Bacteria may develop antibiotic showing no signs Preventing more superbugs
resistance in several ways. These of bad health, but
To prevent more and more types of bacteria becoming resistant, it is important
include mutating to: within a day he
to avoid overusing antibiotics. This is why antibiotics are not used to treat non-
• became ill.
deactivate the antibiotic before it
serious infections like a sore throat. Doctors should only prescribe an antibiotic
reaches the inside of the bacterial
to treat a serious disease. By avoiding overusing antibiotics, you increase the
cell
likelihood that they will work when you really do need them.
• Figure 1 Newspaper article about a hospital ‘superbug’.
pump antibiotic out of the bacterial
cell Bacteria grow and divide every 20 minutes. Each new bacterium is exactly the Changing viruses
•
alter the protein on the bacterial same as the one it came from. Sometimes a bacterium is produced that is slightly Flu, or infl uenza, is a viral disease that aff ects many people every year. Most
cell so that the antibiotic cannot diff erent to the others. This is called a mutation. people recover within one–two weeks, but fl u can cause serious illness and
recognise the cell death, especially in very young children and old people. Flu viruses are always
• The mutation might result in the bacteria being resistant to existing antibiotics,
produce enzymes to destroy the mutating, producing new strains. Because the new strain is so diff erent, people
so that the bacteria are no longer killed by antibiotics. When an antibiotic is used,
antibiotic. will have no immunity to it. This allows the new strain to cause more serious
the non-resistant bacteria are killed but a small number of resistant bacteria
illness and to spread quickly from person to person.
remain. The resistant bacteria survive and reproduce. Continued use of the
When an outbreak of fl u aff ects thousands of people in a country it is called a
antibiotic causes the number of resistant bacteria to increase. This is an example
fl u epidemic. Sometimes fl u spreads very rapidly around the world, aff ecting
of natural selection (see lesson B1 7.2).
people in many countries. This is called pandemic fl u. In 2009 a pandemic fl u
You should always complete a course of antibiotics, even if you start to feel called ‘swine fl u’ developed. The UK government organised vaccination for all Figure 4 An old NHS advert.
better. If you do not complete a course of antibiotics, it is likely that some vulnerable people and stockpiled millions of doses of Tamifl u, an antiviral drug.
bacteria will survive. You could become ill again and need a second treatment
Figure 2 A mutation sometimes occurs when Examiner feedback Science in action
course. There would be more chance of resistant bacteria developing.
bacteria reproduce.
Scientists are continually developing new antibiotics to replace those that are no It is important that you are clear about the diff erence between an epidemic and a Tamifl u belongs to a family of drugs
pandemic. known as neuraminidase inhibitors.
longer eff ective.
These drugs prevent viruses spreading
Questions from cell to cell. When a virus enters
Superbugs
a cell it uses the cell’s materials to
Methicillin-resistant Staphylococcus aureus (MRSA) is a variety of S. aureus that is 1 What is MRSA? make multiple copies of itself. It
resistant to methicillin and most of the other antibiotics that are usually used to 2 Name the process that produces antibiotic-resistant strains of pathogens. also directs the cell to produce an
treat bacterial infections. MRSA is responsible for hundreds of deaths of hospital 3 Explain why patients are advised to always complete a course of antibiotics. enzyme that will cut through the
cell membrane to release the new
patients every year in the UK. 4 Explain why antibiotics are not used to cure viral infections.
viruses. Neuraminidase inhibitors
5 Suggest why antiviral drugs are only used to treat the most dangerous
Patients who die with MRSA are usually patients who were already very ill. It is block the action of this enzyme. So
infections.
often their existing illness, rather than MRSA, that is given as the cause of death they do not kill the virus but they
6 Explain why the ‘swine fl u’ virus spread rapidly around the world.
on the death certifi cate. In these cases, MRSA is only ‘mentioned’ on the death do stop it spreading from cell to cell.
7 Explain in terms of natural selection why doctors should not
certifi cate. White blood cells will then eventually
Dr Semmelweiss’s recommendations over-prescribe antibiotics. A* develop antibodies to kill the virus.
(lesson B1 1.3) two centuries on. All UK hospitals now have campaigns to prevent the spread of MRSA.
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B1 1.7 Vaccination programmes
c Explain why two major outbreaks of
Immunisation programmes Science skills g 100 100d
Learning objectives whooping cough occurred in 1982 n e
pi 90 90 at
• edvisaalduvaaten ttahgee asd ovfa bnetiangge vs aacncdin ated against Icmommmunoinsa itnio cnh ipldrorevnid. eAsn p erxoatemcptiloen i sa tghaein MstM seRv vearaccl idniese, aa sceosm thbaint eudse vda ctoci bnee tvhearyt d Describe the relationashnidp 1b9e8t6w.een the percentage of of whoousands 678000 Key 678000 n vaccing cough
a particular disease. mtdhisaeeksaees sde yi tsooeu asrso bemos deisoy c ndaeeu vwseehldoo bp iy si m na omvti ruiumnsim ttyhu atnot e ims. eeaassilleys s, pmreuamdp fsro amnd s orumbeeollna.e E wacithh o tfh e cchouildgrhe nc abseeisn sgin vcaec c1i9n9a0te.d and the number of whooping ber of cases cough/tho 23450000 PvNwaeohcr.o ccooeifn pncaitantasegged sec ooufgh 23450000 ge of childrenst whoopin
Vaccines such as MMR have saved millions of children from illness and even Num 100 100 entaagai
c
death. Before a measles vaccine was available, an average of approximately Figure 2 What caused whooping 1980198219841986198819901992199419961998 Per
250 000 children developed measles and 85 children died every year, and many cough epidemics in the 1980s? Year
others suff ered severe symptoms.
Route to A* A* If enough people in a community are immunised against certain diseases, then The MMR controversy Examiner feedback
it is more diffi cult for that disease to get passed between those who aren’t In 1998, many parents panicked and vaccination rates dropped
AAbboouutt 8855%% ooff UUKK cchhiillddrreenn hhaavvee bbeeeenn In examination questions asking you to evaluate,
vaccinated against measles. The World immunised. This is because most people who come into contact with the carrier rapidly after a doctor claimed that the MMR vaccine might make sure that you give your view and that it is
Health Organisation has set a target are immunised, so the disease is less prevalent in the population, and therefore trigger autism. However, the claim was based on a study of supported by the evidence in the article(s).
of 95%. Explain why it is important to even those who are not immunised are less likely to get it. Medical experts only 12 children. Soon the vaccine was being blamed for the
reach the World Health Organisation recommend that at least 90% of the population should be vaccinated to prevent apparent rise in autism in California. In some parts of the UK, the
target. epidemics of a disease. proportion of children receiving the MMR vaccine had dropped Questions
to 60% by 2005. This led to a rise in measles outbreaks and fears
1 What is contained in the MMR vaccine?
a What was the maximum number of cases of measles of an epidemic. Since then, other studies have failed to show any
Science skills 2 What does MMR stand for?
in any one year before a vaccine against the disease was link between autism and MMR. By 2010 the percentage receiving
3 Why is it important to be vaccinated against
introduced? the MMR vaccine had risen to 98%.
the three diseases?
b What was the maximum number of cases of measles in any one year after the
Society needs people to be immunised but individual parents
4 Why have some parents stopped their
introduction of the measles vaccine?
can easily be scared off by the risk that their child might react children having the MMR vaccine?
measles
withnds 800 vasctcainrtaetdion ncoemgaptliivcealtye tdo b tehcea vuascec pinaer.e Bnatsla anrcei nthgi nrikskin fga cotnolrys oisf mthaedire c mhioldre, 55 HHEExxooppwwllaa wwiinnoo yyuuoolldduu rryy aaoonnuuss aawwddeevvrrii..ssee tthheessee ppaarreennttss?? A*
ple usa 600 MMR whereas governments are looking at society as a whole.
oo
eh vaccination
er of pes/in t 400 started Is there a link between MMR and autism?
bsl 200 Science skills
mea The California data was used by opponents of the MMR vaccine. At fi rst glance it appears to show that
um
Examiner feedback N 0 an increase in autism is linked to the MMR vaccine. In fact it shows all people registered as having autism
1950 1960 1970 1980 1990
in a single year, 1991, plotted by year of birth. The data also do not take into account increases in population in California, nor
Year
Many examinations give data about improved diagnostic measures.
the number of cases of disease and Figure 1 The graph shows the eff ectiveness of the immunisation programme
The Yokohama graph shows the number of cases of autism before and after the MMR vaccine was withdrawn.
percentage vaccination. against measles.
Autism without regression
The data will often have two diff erent ns California graph Yokohama study Autism with regression
yayoRfo-onefar usmd xawrainssetee dmasrlc faatb awhngleeedairts i hqtn.t ohT usta etheg k iesidfevt yi ikefftoo ei emnauyrrs eget aton urobe tmt e fhyaafe-eosmank rxteetiwilss diya obs ort cioosusaete lhte s s . CCiakwllnihnlholdi eolb dnscoasrhpbeceoinisenek. gwsWirn unhcghnoo, o dua moaegrbpareh iko no nninngoeueg tec t oydvit eua vthacgoaarch rbiocnd ielsac dt taao.ie dnM ddbmeio rsaeiresrteaeta te tshmhdeea utt.n ohTc ahhhht eaom c lsdfaop itnsrhiet ecea aal lisb ukaeaesn becldya il enotmso n ba udgenne byvdv oeneeurrleyo teo spsdn e os eirfen i yocrtieoeuoanusur sga soih nvleiddn cgwcaa irnteh . Number of enrolled persowith autism in Californiain 1991 432156000000000000196019631966196919721975MMR STARTS19781981198419871990 Number diagnosedwith autism byage 7/10 000 11228460000000198819891MMR STARTS990199119921993MMR STOPS199419951996
evaluate such data. Conclude your In the 1970s, parents were concerned about possible side eff ects of the Year of birth Year of birth
answer with a reasoned conclusion. Figure 3 The graphs show data from two studies.
whooping cough vaccine and fewer children were vaccinated against whooping
It is not suffi cient to write ‘I think the
cough. As a result, major outbreaks of whooping cough occurred, with
pros outweigh the cons’. e Do the data in the two graphs indicate a link between the MMR vaccine and autism? Give the reasons for your answer.
thousands of children being taken into hospital.
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B1 1.8 Keeping things sterile
Safety fi rst
You must wash your hands before and after working with microorganisms. A
Growing bacteria
Learning objectives
clean, cleared working surface is also essential. Hair should be tied back, broken
Like all living organisms, bacteria and fungi need nutrients to grow and
•
explain why you need uncontaminated skin covered with a plaster and hand-to-face contact avoided while culturing
reproduce. In the laboratory, nutrients are often supplied to the microorganisms,
cultures of microorganisms to study the microbes. Work is carried out near the upward draught from a lighted Bunsen
also known as microbes, in a gel called agar. Agar is called a growth medium or
eff ects of diff erent treatments on them burner. The upward movement of air around the burner minimises the risk of
• culture medium. It melts at 98 °C and, as a liquid, it can be poured into plastic or
describe how apparatus is sterilised and airborne microbes falling onto culture plates.
glass Petri dishes. It solidifi es at about 44 °C. Microbes cannot digest agar, so it is
how this achieves pure cultures
• not used up as they grow.
explain how to inoculate a culture Inoculation
medium. Besides nutrients, many microbes need a temperature between 25 °C and 45 °C Inoculation is the process of transferring microbes to the culture medium. For
to grow. In school laboratories, the Petri dishes are put into a cabinet, or an solid agar, a wire inoculating loop is used. It is fi rst sterilised by holding it in a
incubator, set at a maximum temperature of 25 °C. Pathogens could accidentally Bunsen burner fl ame. After cooling the loop for ten seconds, near the Bunsen
be present in the culture dishes, so keeping the temperature at a maximum of burner, the microbes can be picked up from the pure culture and transferred to
25 °C minimises health risks from them, as they will grow much less well at lower the sterile agar by gently sweeping the loop back and forth over the surface.
temperatures.
upward draught
Why do we need to keep things sterile?
McCartney
inoculating loop
The air, the surfaces around you, your skin and clothes all have microorganisms bottle
on them. If you culture microorganisms in the laboratory, it involves growing Petri dish lid
Bunsen
Why are masks and gowns used in an operating very large numbers of bacterial cells. If safety procedures are not followed, you burner sterile agar McCartney
theatre? may accidentally introduce a harmful microbe into a harmless strain that you are Petri dish base bottle agar
slope
growing. This would multiply rapidly, just as the harmless microbes do, and
Examiner feedback would be a greater health risk than if it were a single cell. Sterile or aseptic
1 Pour the plate. 2 Sterilise the inoculating 3 Collect the microbes
techniques must therefore be used to prepare uncontaminated cultures.
This topic is where your loop in a flame. from the pure culture.
understanding of safety techniques Glassware and culture media are sterilised in an autoclave using pressurised upward draught
is most likely to be tested. Make sure
steam at a temperature of 121 °C for 15 minutes.
you can explain the reasons for safety
techniques, such as sterilisation,
maximum incubation temperature,
personal hygiene and disposal of used
cultures.
4 Inoculate the Petri dish by sweeping the loop back and 5 Write the details on the base
forth across the agar surface, with the lid held at an angle. of the sealed Petri dish.
Taking it further
Figure 1 The process of inoculation.
Like animals, most bacteria possess no
Before incubation the Petri dishes are sealed with adhesive tape to prevent
chlorophyll, so they cannot produce
contamination from airborne bacteria. After 24–72 hours, when the results have
their own food. They cannot eat solid
been noted, the cultures are autoclaved by a technician before disposal.
food and have to absorb nutrients
through their cell membranes. Like
Questions
all other living organisms, bacteria
use carbohydrates, such as sugars, 1 Give three ways in which microbiological equipment 5 Explain why the wire loop needs to be cooled before
as an energy source and to produce and media can be sterilised. picking up the microbes.
new cells. Some bacteria need only
2 What is meant by ‘aseptic’? 6 Suggest why the lid of the Petri dish is not removed
sugar and mineral ions such as nitrate,
completely when introducing the microorganisms.
potassium and phosphate, which 3 Give three personal safety precautions that should be
7 Describe what you should do with your successful
they use to produce proteins. Other The type of autoclave used in most schools. taken when experimenting with microorganisms.
culture after an experiment.
bacteria, particularly pathogenic
The high temperature needed to kill microbes melts plastic, so Petri dishes and 4 Describe what would happen if a single cell of a
bacteria, have to obtain proteins and 88 EEExxxppplllaaaiiinnn wwwhhhyyy aaagggaaarrr iiisss sssuuuiiitttaaabbbllleee aaasss aaa cccuuullltttuuurrreee mmmeeedddiiiuuummm fffooorrr
disposable instruments are sterilised by ultraviolet or ionising radiation. This is pathogen entered a culture dish.
vitamins from external sources. ggrroowwiinngg bbaacctteerriiaa.. A*
done commercially. Petri dishes remain sterile inside until the lid is opened.
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B1 2.1 The nervous system
Neurones are not joined to each other. There is a small gap between them
relay neurone
called a synapse. When an impulse reaches the end of a neurone, a chemical is
The nervous system
Learning objectives released. This travels across the gap, and starts an impulse in the next neurone. sensory neurone
The diff erence between winning and losing a race might be down to how quickly
• This means the message can only travel in one direction (see Figure 1).
describe the receptors that detect
you start. It is all about reaction time. This is the time between hearing the gun
diff erent stimuli
• and reacting to it. Refl ex actions
explain how your nervous system enables
you to react to your surroundings and The nervous system is made up of three main parts: the brain, the spinal cord When pain is detected by a sensory receptor in your fi nger, it sends an impulse
coordinates your behaviour and neurones, or nerve cells. along a sensory neurone to a relay neurone in your spinal cord. The relay
chemical released by the sensory
• describe a refl ex action neurone sends an impulse in an arc via a motor neurone to an eff ector, a muscle,
neurone
• analyse a response in terms of stimulus, It has receptors in the: which contracts, pulling your hand away. This is called a refl ex action. It is
• Figure 1 Chemicals released by a sensory
eyes that are sensitive to light
receptor, eff ector and response. automatic and very quick (see Figure 2). There are other types of refl ex actions neurone travel across the synapse to the relay
•
ears that are sensitive to sound and to changes in position, thus enabling us to such as coughing and blinking. These are needed to protect us from being hurt neurone.
keep our balance or from damage to our tissues, e.g. foreign bodies in airways or eyes.
• Examiner feedback
tongue and in the nose that are sensitive to chemicals and enable us to taste
spinal cord
and smell You should practise looking at diff erent
• synapse
skin that are sensitive to touch, pressure, pain and to temperature changes. diagrams of the refl ex arc and working
out what is happening in each part.
sensory neurone
Design an
Science skills
experiment to
measure the
relay neurone
width of the pupil under diff erent light
motor neurone intensities. Remember you must not
sensory receptor –
nerve endings in skin touch the surface of the eye.
Waiting for the starting signal. muscle in arm
a What are the independent, the
stimulus
dependent and the control variables?
b Explain what you will do to make sure
Figure 2 The refl ex arc.
your experiment produces reliable results.
Questions
The nervous system.
1 Identify six stimuli that you respond to and state where in the body the receptors for these are located.
Receptors are cells that detect stimuli or changes in the environment. Each 2 Some people suff er from a disease called motor
receptor cell, e.g. light receptor cells in the eye, like all animal cells, contains a neurone disease. (a) Suggest which part of the receptors that are very
Route to A* A* nucleus and cytoplasm surrounded by a cell membrane. nervous system it aff ects. (b) What will people with sensitive to the muscle quadriceps – effector muscle
being stretched suddenly
knee cap
this disease have diffi culty doing?
SSoommee ddrruuggss aarree uusseedd iinn mmeeddiicciinnee Information from receptors, e.g. in your nose if you smell something burning,
3 Coughing, sneezing and blinking are examples of
because they aff ect refl ex pathways. passes along neurones to the brain. The information passes along the neurones sensory neurone
refl ex actions. (a) Identify what part of the body
• The drug curare prevents muscles as signals called impulses. The brain then coordinates the response by sending each refl ex action protects. (b) Identify the receptor
from contracting, thereby making information to the appropriate organs. in each refl ex action. (c) Identify the eff ector in each tendon
synapse
surgery easier. At what place in a refl ex action. hamstrings
There are three types of neurone:
refl ex action does curare probably motor
• 4 People taking part in motor sports wear head, neck
sensory neurones carry impulses from the receptor to the spinal cord neurone
act?
and back protection. Why is it important to protect
• •
Dentists inject the drug procaine relay neurones carry impulses through the spinal cord and up to the brain each of these areas? spinal cord
into gums so that they can drill and from the brain back along the spinal cord Figure 3 The knee-jerk refl ex.
5 Suggest how a sprinter might improve his reaction time.
into teeth without causing pain. •
motor neurones take impulses from the spinal cord to an eff ector. 66 TThhee ddiiaaggrraamm sshhoowwss tthhee kknneeee--jjeerrkk rreeflfl eexx.. WWhheenn tthhee
What is the most probable reason
lleegg iiss ttaappppeedd wwiitthh aa hhaammmmeerr jjuusstt bbeellooww tthhee kknneeee,, tthhee
for procaine preventing pain? An eff ector can be a muscle that is made to contract, or a gland that secretes a
lleegg ssttrraaiigghhtteennss.. DDeessccrriibbee ffuullllyy tthhee sseeqquueennccee ooff eevveennttss iinn tthhiiss rreeflfl eexx aarrcc.. A*
chemical, for example a hormone.
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