CCEA GCSE Biology - Denmour Boyd, James Napier 2017
Unit 2
Health, disease, defence mechanisms and treatments
Specification points
This chapter covers sections 2.6.1 to 2.6.19 (Double Award Science 2.6.1 to 2.6.15) of the specification. It is about communicable diseases, aseptic techniques, the body’s defence mechanisms, plant defence mechanisms, development of medicines, antibiotics, antibiotic resistant bacteria, vaccinations, non-communicable diseases, heart attacks, strokes and cancer.
Diseases can be described as being communicable or non-communicable.
A communicable disease is a disease that can be passed from one organism (person) to another. A non-communicable disease is a disease that is not passed from one organism (person) to another.
Health is defined as being free from communicable and non-communicable disease. If we are healthy, we are free from disease.
Being healthy is important to us and our families. Health is also very important to society. Very unhealthy people cannot work and need care. Billions of pounds are spent each year by the National Health Service (NHS) on keeping people as healthy as possible and on treating and looking after people who are ill.
Tip
When we talk about communicable and non-communicable diseases, we normally (but not always) mean diseases that can, or cannot, be passed from person to person.
Tip
The NHS spends money on the salaries of doctors and nurses and other staff, the upkeep of hospitals and health centres, and the drugs and medicines used to treat people.
Communicable diseases
Most communicable diseases are caused by microorganisms such as bacteria, viruses and fungi.
Table 13.1 shows some diseases caused by microorganisms and how they can be spread (what makes them communicable). The table also shows how they can be avoided or treated.
Tip
Communicable diseases are also described as infectious diseases.
Tip
The only non-human disease in Table 13.1 is potato blight. This is a disease that affects the potato and some other types of plant.
Figure 13.1 shows how the spray of moisture and particles spreads through the air when a woman sneezes. If she has a cold or the flu this is how ’droplet’ infection can occur.
The body’s defence mechanisms against communicable diseases
The human body is well adapted to protect us against infection. The body is very successful at preventing most microorganisms from gaining entry and it has very effective defences against those microorganisms that do enter.
Preventing microorganisms gaining entry
The skin itself is an excellent barrier to microorganisms. The openings in the body such as the nose and the respiratory system are protected by mucous membranes that trap the microorganisms and prevent them going any further. Clotting of blood is also important as a defence mechanism. It stops more blood escaping but it also acts as a barrier against infection.
If a microorganism does enter the body it is the blood system that usually helps combat the invader. The blood system is very effective in this role but we are often ill for a period of time before our defence system allows us to recover.
Antigens and antibodies
Invading microorganisms have chemicals on their surface that the body can recognise as being foreign. These chemicals are called antigens and they cause special white blood cells called lymphocytes to produce antibodies.
As Figure 13.2 shows, these antibodies have a shape that matches the shape of the antigens on the microorganisms. The antibodies join with the microorganisms (like a jigsaw puzzle) and cause them to clump together. Once clumped (or immobilised) they are easily destroyed by other white blood cells called phagocytes in a process known as phagocytosis.
As the antigens on a particular microorganism and the antibodies used to combat that microorganism are complementary in shape, it is possible to work out the shape of one from the other. Look at the examples shown in Figure 13.3.
Tip
Antibodies work in the blood (and other body fluids).
Phagocytosis in action
Some white blood cells move around in the blood and destroy microorganisms trapped by antibodies, or destroy them directly without antibody action. This type of white blood cell is called a phagocyte. Phagocytes surround the microorganisms and engulf (’eat’) them, as shown in Figure 13.4. Eventually chemicals (enzymes) inside the phagocyte digest the microorganisms and destroy them.
Tip
As a consequence of antibody action, the organisms causing disease cannot spread through the body and, in time, our symptoms of the illness reduce.
Primary and secondary responses
The antibody/antigen reaction described above is a typical response to being infected by a bacterium or a virus. The infected individual is often ill for a few days before the antibody numbers are high enough to provide immunity. This is described as the primary response. However, once infected, the body is able to produce memory lymphocytes that remain in the body for many years. This means that if infection by the same type of microorganism occurs again, the memory lymphocytes will be able to produce antibodies very fast to stop the individual catching the same disease again. This is known as the secondary response.
Tip
We are often unaware when the secondary response occurs, as we may not show symptoms (catch the disease).
Immunity
Individuals who are protected against a particular infection or disease are described as being immune to that disease. Most people will be immune to a number of diseases. If someone is immune this means that his or her antibody levels are high enough (or high enough levels can be produced quickly enough) to combat the microorganism should it gain entry to the body again.
Show you can
The antibodies we produce to combat flu are different to the antibodies we produce for the cold. Explain why.
There are two types of immunity.
Active immunity is where the body produces the antibodies used to combat the infectious microorganism. This type of immunity is slower acting but usually lasts for a very long time.
Passive immunity is when antibodies from another source (such as those produced by pharmaceutical companies) are injected into the body. These are fast acting but only last for a short period of time.
Tip
The microorganisms in vaccinations need to be dead or modified in some way, otherwise the vaccination would give you the disease you are trying to avoid!
Test yourself
1 What is a communicable disease?
2 Name two human diseases spread by droplet infection.
3 Name the two types of white blood cell that help defend against disease.
4 Give two features of passive immunity.
Vaccinations
Vaccinations involve the use of dead or modified pathogens (microorganisms which cause diseases) that are injected into the body. The dead or modified microorganisms still have the antigens on their surfaces that cause the body to produce antibodies at a high enough level to prevent the individual becoming ill later (to provide active immunity). Crucially, a vaccination leads to memory lymphocytes being produced that will bring about a rapid immune response if a further infection occurs.
Tip
The process of antibody action following vaccination is exactly the same as if you had caught the disease — the big difference is you don’t get ill first.
Sometimes we need more than one vaccination to make sure that we remain immune for a reasonable period of time. This is known as a follow-up booster vaccination. Figure 13.5 shows what happens following a vaccination that involves a booster.
Tip
The type of immunity produced by vaccinations is active as the antibodies are produced by the body.
You need to be able to interpret graphs showing the antibody levels typically produced in active and passive immunity. Examples of these are shown in the graphs in Figures 13.6, 13.7, and 13.8.
Figure 13.6 represents active immunity in action. The antibodies are produced by the body in response to infection. The relatively slow increase in antibody number is typical of the primary immune response — gaining immunity following infection by a type of microorganism for the first time.
However, in passive immunity the level of antibody increases rapidly but it quickly falls too (Figure 13.7).
The differences in the speed of the body producing antibodies following a first infection (primary response) and being reinfected by the same pathogen (secondary response) are shown in Figure 13.8.
Tip
The secondary response both produces antibodies more quickly and also produces many more antibodies than the primary response.
Test yourself
5 What is a booster injection?
6 Explain why booster injections are given.
Plant defence mechanisms
Plants can also be harmed by infectious microorganisms. However, like humans and other animals, they have a range of defences against infectious microorganisms. These defences can be structural or chemical.
Structural defences include waxy cuticles that prevent microorganisms from entering leaves and the thick cell walls that surround cells.
Show you can
Many types of plant pathogens are adapted to gaining entry to plants by entering through stomata. Suggest why.
Chemical defences involve plants producing chemicals that are harmful to infectious microorganisms. These antimicrobial chemicals can help defend against bacteria and/or fungi and/or viruses.
Chemicals in mint have been shown to have antimicrobial properties that will kill or restrict the growth of bacteria. This can be demonstrated by adding an aqueous mint extract to a Petri dish containing bacteria — see Procedure A on page 148. Similar effects have been demonstrated by digitalis, which is extracted from foxgloves. The digitalis is poisonous to insects, slugs and other animals that would otherwise feed on it.
As well as the human body defending against disease we can also produce drugs and medicines to help us do this. The development of drugs and medicines is covered in the next section.
The development of medicines
Medicines have been around for a very long time (although not the same type that we get from the pharmacist today). Medicines are substances that help us recover from illnesses or reduce discomfort or pain. Rubbing dock leaves on nettle stings to reduce pain is a very old remedy, as is the use of iodine to help heal cuts.
The discovery of medicines in earlier times was often by accident or chance. An example of this can be seen in one of the most famous medical discoveries of the last century — the discovery of penicillin. Penicillin is an antibiotic, a type of chemical produced by fungi that kills or prevents the growth of bacteria.
Penicillin
Penicillin was the first antibiotic to be developed. In 1928 Alexander Fleming was growing bacteria on agar plates and he noticed that one of his plates had become contaminated with mould (fungi). This is common when culturing bacteria unless great care is taken to avoid contamination.
The growth of mould did not surprise Fleming, but he was surprised when he noticed that the bacteria he was culturing did not grow well close to the edges of the mould. He concluded that the mould produced a substance that prevented the growth of the bacteria. As the fungus causing the contamination was called Penicillium, the antibacterial substance was called penicillin and the first antibiotic was developed.
Fleming carried out some work with his antibacterial substance on animals, but his progress was hindered because he was unable to produce a pure form of the substance. In the early 1940s, two other scientists, Florey and Chain, were able to isolate a pure form of penicillin and its large-scale production began. Penicillin has been in use since then but is now only one of a large number of antibiotics in use.
Making penicillin commercially
Penicillin and other drugs are made in very carefully controlled conditions that maximise productivity. The microbes that make the penicillin are grown in large biodigesters or fermenters that create the perfect conditions for fungal growth. Downstreaming (extraction, purification and packaging) is required following the production of the penicillin (as with insulin which was discussed in Chapter 10).
Figure 13.12 shows how a typical fermenter works and Figure 13.13 shows the commercial production of penicillin in the pharmaceutical industry.
New medicines are continually being developed and the development of new drugs has made the pharmaceutical industry a major contributor to developed economies today.
Making new medicines
The making of new medicines is a very long and expensive process. It involves a number of stages and is very tightly regulated by government agencies.
The development of medicines and drugs can be divided into two distinct stages: preclinical trials involve the stages before the drug is used on people and clinical trials involve the testing of drugs on people.
Preclinical trials
Preclinical trials involve the testing of drugs in laboratories on isolated cells and tissues and the use of animal testing, the two main stages that occur before testing on humans. Computer modelling is also used at this stage.
Early in the preclinical stage the testing of drugs on cells and tissues in laboratories takes place and is called in-vitro testing.
Tip
In-vitro testing is a very long term and expensive process as it is very much a ’trial and error’ process to see what works.
Tip
Some people are opposed to animal testing and hold demonstrations against it.
A later preclinical stage is animal testing. This allows scientists to check how well the drug works on entire living organisms before testing on humans.
Each type of preclinical testing has two main functions:
• to check if the drug is poisonous or harmful
• to check how effective the drug is (its efficacy).
Clinical trials
Clinical trials follow preclinical trials and only take place if preclinical trials show that the drug works and there are no harmful side effects.
In clinical trials the drug is tested on human volunteers. Initially the drug is tested on a very small number of healthy people but in due course much larger numbers are involved. Although volunteers can get a fee for taking part, some people are willing to act as volunteers as they think it is morally right to contribute to medical research even though there are risks.
Figure 13.15 shows a typical advert for volunteers for medical research.
Volunteer patients are also involved in clinical trials. This makes sense as if a new medicine or drug is tested on them, scientists can see how effective the drug is on the people who will actually use them in due course.
The clinical stage is used to determine the optimum dosage.
If the clinical trials prove successful, the drug or medicine can then be licensed for use.
Tip
Small numbers of volunteers are used at the start of clinical testing in case something goes wrong; very occasionally there are major problems with a drug that are not picked up in preclinical trials.
Peer review
It is very important that the development of new medicines and other scientific research is properly tested and validated. This is both to ensure that conclusions drawn from scientific investigations are correct and also that the whole process of scientific investigation is thorough.
The most common type of validation is peer review. This is where the new research and new discoveries are scrutinised by other scientists of at least equal standing to the investigator. The peer reviewers provide detailed feedback and suggest refinements where appropriate.
The results of scientific (including medical) advances are only ever published following peer review.
Tip
If you get a question about peer review on a GCSE Biology paper it will be about peer review in the context described opposite. It will not be about peer review in the classroom in which students sometimes review the work of other students!
Show you can
Outline the arguments for and against using animals in preclinical testing.
Test yourself
7 Give two functions of preclinical trials in the development of medicines.
8 What is the main function of clinical trials?
9 Describe the process of peer review.
Antibiotics
We have come across antibiotics earlier in Unit 2 when looking at natural selection in Chapter 12. Antibiotics, such as penicillin, are chemicals produced by fungi that are used against bacterial diseases to kill bacteria or reduce their growth.
Most people have had antibiotics at some time in their lives to defend against bacterial conditions such as septic throats or infected wounds in the skin. The effect of an antibiotic can be seen in Figure 13.16.
Antibiotics are not as specific as antibodies in that they are not designed to combat only one type of bacteria — they usually act against a range of bacteria and they act in a different way to antibodies. Antibiotics do not all act in the same way and, for this reason, a GP may not prescribe the same antibiotic when a patient is being treated for different infections.
Tip
Antibiotics cause harm to bacteria — they have no effect on viral diseases, such as colds and flu.
Antibiotic-resistant bacteria
Bacterial resistance to antibiotics was used as an example of natural selection in Chapter 12. Bacterial resistance to antibiotics is becoming a major problem and is making many antibiotics ineffective against various bacteria. The overuse of antibiotics is largely responsible and it is very important that antibiotics are only used when they are really necessary. The overuse of antibiotics has allowed many types of bacteria to become resistant to the main antibiotics, and so it is the mutated resistant forms that are now common.
Some bacteria have developed resistance to the extent that they are now referred to as ’superbugs’. They are responsible for a number of serious medical conditions. These superbugs, such as MRSA, are resistant to most types of antibiotic and can be a very serious problem in hospitals. The headline in Figure 13.17 is typical of many headlines that have appeared in the media in recent years.
There has been media speculation that the problem with superbugs is due to poor standards of hygiene in some hospitals, but is this really fair? There is no doubt that good hygiene is very important in preventing the spread of microbes in hospitals but other factors are important in allowing superbugs to flourish in this type of environment too. Patients in hospital often have weak immune systems and they may have wounds that allow microbes to enter the body easily. Another factor is that hospitals provide an ’antibiotic-rich’ environment where the microbes have every opportunity to come into contact with a range of antibiotics. This ensures that the non-resistant microbes are eliminated and a high proportion of the surviving microbes are antibiotic resistant.
There is no doubt that ’superbugs’ are extremely difficult to eradicate. Nonetheless, new measures in hospitals include increased levels of hygiene (such as the immediate cleaning of spillages of body fluids and the wearing of gloves) and greater care in the administering of antibiotics. Additionally, patients who contract a ’superbug’ are often isolated from other patients to reduce the possibility of infecting others.
Aseptic techniques
When working with bacteria and fungi in the laboratory, it is very important that great care is taken to avoid contamination and also the growth of unwanted, pathogenic (harmful) microorganisms. The procedures used to avoid this are referred to as aseptic techniques.
In a school environment there are important health and safety precautions that need to be used when growing or culturing microbes. These include:
• not eating or drinking in the laboratory
• wiping down lab benches with a disinfectant
• not culturing microbes at body temperature
• using sterile loops for transferring cultures
• flaming the necks of culture bottles to prevent contamination
• sterilising (using an autoclave) or disposing of all equipment after use
• washing hands thoroughly after each part of the experiment.
Tip
An autoclave is a type of pressure cooker that uses high pressure steam at 120 + °C to kill all living organisms. It sterilises agar dishes, culture media and other apparatus.
When culturing or transferring microorganisms it is important to use aseptic techniques as in the procedure described below.
The apparatus in Figure 13.18 is normally used when inoculating and plating bacteria in the laboratory. All the apparatus used, for example agar plates, should be sterilised and disposed of as indicated by your teacher. A typical sequence is:
1 Pass the metal loop through the flame of the Bunsen burner to sterilise it.
2 Allow the metal loop to cool, as if it is too hot it will kill any microorganisms that it comes into contact with.
3 Remove the lid of the culture bottle (A) and glide the loop over the surface of the agar without applying any pressure. This will ensure that the metal loop has bacteria from the culture bottle over its surface (inoculation).
4 You should ’sweep’ the neck of the bottle through the flame to destroy any airborne microbes. Replace the lid of the culture bottle to prevent contamination.
5 Spread the microbes over the surface of the agar in the Petri dish (B) by gently gliding the metal loop over the nutrient agar surface (plating). It is important to hold the Petri dish lid open at an angle rather than completely removing it, as this will reduce the chance of unwanted microbes from the air entering the dish.
6 The metal loop should then be heated again to a high temperature to ensure that any microbes remaining on the loop are destroyed.
7 The Petri dish should be taped in four places and then incubated in an oven at 25 °C. This temperature will allow the microorganisms to grow and form colonies but is below body temperature, meaning pathogenic microbes that could harm humans will not grow.
8 When carrying out the transfer it is important to work close to a Bunsen burner so that the Bunsen flame can kill microorganisms in the air.
Note: instead of using a metal loop it is possible to use sterile disposable plastic loops that do not require heating.
Tip
Nutrient agar is a type of agar enriched with minerals and nutrients essential for the growth of bacteria.
Tip
When incubating Petri dishes (agar plates) in an incubator it is important to store the taped dish upside down to avoid condensation dripping on to the culture.
Prescribed practical
Biology practical 2.3: Investigate the effect of different chemicals or antibiotic discs on the growth of bacteria
Possible procedure A (measuring the effect of different chemicals)
1 Add some mint leaves and a small amount of water to a mortar and grind using a pestle.
2 Soak a small disc of filter paper (approx. 1 cm2 diameter) in the aqueous plant extract.
3 Repeat this process using a different plant, e.g. wild garlic leaves.
4 Use a sterile spreader to add a bacterial culture to a pre-prepared Petri dish with nutrient agar.
5 Using sterile forceps, place the two plant discs on opposite sides of the Petri dish.
6 Tape the lid of the Petri dish in place.
7 Invert the Petri dish (to prevent condensation) and incubate for 48—72 hours at 25 °C.
8 Measure the radius/diameter of any clear zones around the two discs to compare the antibacterial properties of the chemicals in the two plant species.
Instead of using plant extracts the investigation could be completed using small pieces of filter paper soaked with a commercial products such as TCP or alcohol.
Possible procedure B (measuring the effect of different antibiotics)
1 Use a sterile spreader to add a bacterial culture to a pre-prepared Petri dish with nutrient agar.
2 Place a Mastring with several different antibiotics onto the agar (alternatively individual antibiotic discs of different types or strengths can be used).
3 Tape the lid of the Petri dish in place.
4 Invert the Petri dish (to prevent condensation) and incubate for 48—72 hours at 25 °C.
5 Measure the radius/diameter of any clear zone around each antibiotic to determine its effectiveness.
Sample results and questions
Figure 13.19 shows how bacterial growth is affected by four different antibiotics, A, B, C and D.
1 Which antibiotics were most and least effective in killing the bacteria?
The test was repeated a few months later using the same antibiotics on the same type of bacteria. The results are shown in Figure 13.20.
2 One conclusion from the second test was that the bacteria had become resistant. Use evidence from the diagrams to help explain this conclusion.
3 Apart from using the same bacteria and the same antibiotics, state two other things that would need to have been done to make the results valid (a fair test) when comparing the results.
Non-communicable diseases
Non-communicable diseases are diseases that are not passed from person to person — they are not infectious diseases.
Non-communicable diseases are usually a consequence of inheriting a combination of genes that predispose us to developing some conditions, for example cancer, or are due to lifestyle.
Many cancers and type 1 diabetes are non-communicable diseases in which those affected normally have a genetic predisposition to the condition.
Example
Women who have a mutated form of a particular gene (the BRCA1 gene) have around a 75% chance of developing breast cancer in their lifetime.
Lifestyle factors and non-communicable disease
Lifestyle factors that are linked to disease include a poor diet, lack of exercise, overexposure to the Sun and the misuse of drugs (smoking and drinking too much alcohol).
Diet and disease
Diet has a major effect on our health. There are a number of features of our diet which contribute to many people not being as healthy as they could be. As a population we are eating too much sugar and fat.
Eating too much of foods high in sugar and fat has two main effects on the body. It means that:
• the individual can become overweight and obesity can result
• the individual will not be getting a balanced diet and probably not enough fruit and vegetables, meaning that they miss out on essential vitamins and minerals.
Exercise and health
If the energy we use in exercise is less than the amount we eat then we run the risk of becoming overweight or obese. Lack of exercise and eating too much fat and sugar are the two main reasons why so many people are obese in the UK.
Exercise is good for the body in many ways and not just as a means of using energy. The right type of exercise can strengthen our bones, help our circulatory system and can even help our mood.
Overexposure to the Sun
Too much ultraviolet (UV) radiation from the Sun or sunbeds can cause skin cancer (Figure 13.22). The UV light can cause mutations in the skin that can lead to cancer.
Tip
Mutations are random changes to DNA, chromosomes or genes.
In the UK, the number of people getting skin cancer is rapidly rising but the possibility of getting it can be reduced by reducing the time spent in strong sun, covering up and using sun lotion.
Misuse of drugs — alcohol
Many people drink alcohol in moderation and are unlikely to suffer serious harm. However, many people, including many teenagers, drink too much alcohol and can cause harm to themselves and others.
Long-term excessive drinking of alcohol can damage the liver as well as many other parts of the body. Drinking heavily during pregnancy can cause serious damage to the foetus including brain damage (foetal alcohol syndrome).
Binge drinking is a particular problem. This occurs when a large amount of alcohol is drunk over a short period of time, for example, on one night out (Figure 13.23).
Misuse of drugs — tobacco
Smoking can seriously damage health, as summarised in Table 13.2.
Tip
Bronchitis can leave affected individuals struggling for oxygen as not enough may reach the alveoli due to the airways (bronchi and bronchioles) being constricted.
The introduction of smoking bans in many countries has proved very effective. It both encourages smokers to stop and significantly reduces the chances of people being affected by passive smoking. The use of E-cigarettes is enabling many people to stop smoking tobacco. However, not everyone is in favour of E-cigarettes as many contain nicotine and some people suggest that they encourage people to take up smoking tobacco.
Tip
Carbon monoxide combining with red blood cells reduces the number of red blood cells available to carry oxygen. This can result in a shortage of oxygen reaching the body tissues and therefore less oxygen available for respiration.
Test yourself
10 What is meant by a non-communicable disease?
11 Describe the link between overexposure to the Sun and skin cancer.
12 State one harmful effect of alcohol on the body.
13 State two harmful effects of tar (in tobacco smoke) on the body.
Show you can
Explain why people who smoke a lot of tobacco can have low levels of energy.
Heart attacks and strokes (cardiovascular diseases)
Heart disease is caused by cholesterol and other fatty substances being present at such high levels that they build up in the walls of the arteries. Over time this leads to a narrowing of the arteries, making it more difficult for blood to flow through them. This is particularly likely to happen in the very narrow coronary arteries that supply the heart, hence the term coronary heart disease (CHD).
Eventually a coronary artery may become so narrow that a blockage forms (a clot) and stops the blood from flowing in this particular artery, shown in Figure 13.24. This prevents the heart muscle that the artery serves from receiving oxygen and glucose. Respiration can no longer happen in these cells, causing them to die and the heart to stop beating. This is a heart attack.
If the blockage is in the brain, a stroke can result. Again, the cells deprived of oxygen and glucose die and the affected part of the brain stops functioning properly. This often causes paralysis of parts of the body.
Some of the main lifestyle factors that can increase the risk of having a heart attack or a stroke are included in Figure 13.25.
Adopting a healthy lifestyle (for example taking exercise and not smoking) can help reduce the risk of developing cardiovascular diseases. In recent decades, cardiovascular disease was often treated by surgery. Now there is a greater emphasis on other less invasive methods.
For example:
• Angioplasty and stents are often used to increase the space for blood in arteries. An angiograph is a medical imaging technique that allows doctors to see inside blood vessels. Dye is added to the blood through a thin tube that is inserted into a blood vessel that is close to the skin. The dye helps provide the contrast necessary when viewing the affected blood vessel. Balloon-like structures are used to hold the affected artery open for stents (small mesh like structures) to be inserted into the blood vessels to keep them open (see Figure 13.26).
• Drugs such as statins and aspirin can help protect against cardiovascular disease. Statins help reduce blood cholesterol and therefore the rate at which blood vessels can become clogged up with fatty deposits. Aspirin has similar effects. Low doses of aspirin are often given to people who have had a heart attack or stroke or are at risk of having one. The aspirin helps ’thin’ the blood and makes it less ’sticky’, therefore reducing the risk of a clot forming in the narrowed blood vessels and a heart attack or stroke occurring.
Some of the diseases covered in this section are closely linked. Consequently, many people who are affected by one condition (such as obesity) often suffer from one or more other conditions; obese people often develop cardiovascular disease and type 2 diabetes.
Test yourself
14 Give three lifestyle factors that can reduce the risk of having a heart attack.
15 Describe how stents can be used to treat someone with cardiovascular disease.
Show you can
Draw a flow chart to show how high cholesterol levels can lead to a heart attack.
Cancer
Cancer is uncontrolled cell division and this uncontrolled division can lead to the development of tumours.
There are two types of tumour:
• Benign tumours remain in one place and do not spread throughout the body. They may be surrounded by a distinct boundary or capsule (encapsulated).
• In malignant tumours groups of cancer cells may break off from the main (primary) tumour and spread around the body, where they can grow into other (secondary) tumours. Malignant tumours are less likely to have a distinct boundary or capsule around them. Malignant tumours are usually much more dangerous.
Tip
It is expected that around one in two people will get cancer at some point during their lives. Thankfully, the treatments are getting better all the time!
As with most of the non-communicable diseases discussed in this chapter, lifestyle choices can affect the risk of developing cancer.
In Northern Ireland girls in Year 9 are offered the HPV (human papilloma virus) vaccine. This vaccine helps protect against cervical cancer. The link between smoking and lung cancer is well known, as is the link between high levels of UV radiation and skin cancer.
It is very important to detect cancer early. If the cancer is detected early the tumour will be smaller and therefore likely to have caused less damage to the body. It is also very important to detect a malignant tumour before it spreads to other parts of the body.
Early detection often involves screening programmes. There are screening programmes for women for both breast and cervical cancer. In these screening programmes, commonly women of a certain age and/or with a particular medical history are invited periodically to a medical centre in order to identify if any cancerous cells are present. Everyone between the ages of 60 and 74 in Northern Ireland is given the opportunity to screen for bowel cancer. Some cancers are relatively easy to check by the individual. For example, testicular and skin cancer can often be spotted early by self-examination.
Cancer can be treated using surgery, radiotherapy and chemotherapy. Each of these methods is described below:
• Surgery — involves removing the cancer cells from the body. Surgery will be less effective if the cancer has spread throughout the body or the tumour is in an inaccessible part of the body.
• Radiotherapy — X-rays can be used to kill the cancer cells. Modern radiotherapy machines, Figure 13.28, are able to pinpoint the X-ray beams very accurately and target very small tumours. However, other normal cells are often affected as well because the X-rays have to pass through ’normal’ tissues before reaching tumours within the body.
• Chemotherapy — this involves using a drug or range of drugs to kill the cancer cells. As with most cancer treatments, there are a range of side effects with chemotherapy, including other (normal) cells being affected and hair loss. An advantage is that chemotherapy can kill cancer cells anywhere in the body.
Example
Radiotherapy is often used to treat men with prostate cancer. Typically men are given 37 sessions of radiotherapy (one each weekday for seven and a half weeks) to destroy the cancer cells in the prostate (and the surrounding area if it is thought the cancer has spread outside the prostate gland). Splitting the dose over 37 sessions means that on any one occasion smaller doses are used thus reducing the risk of side effects.
Tip
All forms of cancer treatment involve a balancing act between the benefits the treatment can bring and the risk of side effects.
A relevant new form of treatment for cancer is immunotherapy. This involves injecting antibodies into the body that attach to the cancer cells, allowing the body’s immune system to destroy them. Immunotherapy often involves special antibodies made in the laboratory that:
• attach specifically to antigens found only on the surface of cancer cells
• act as ’markers’ so that phagocytes and other white blood cells can locate and destroy them
• provide a targeted treatment with potentially reduced side effects compared with other treatments.
In general, immunology is a group of techniques used to stimulate the body’s immune system enabling it to help defend against disease.
Practice questions
1 a) Copy and complete Table 13.3 about communicable diseases and how they are spread.
(5 marks)
b) Describe how tuberculosis can be:
i) prevented
(1 mark)
ii) treated.
(1 mark)
2 The flu is a communicable virus disease that can make people ill for a number of days.
a) What is meant by the term communicable?
(1 mark)
b) Each year scientists make a vaccination against the flu. When they do this they have to predict which flu strain is likely to infect the most people. Some targeted groups such as the elderly and people with diabetes are now given the vaccination for free.
i) Suggest why elderly people are offered the flu vaccination.
(1 mark)
ii) Explain how the vaccination enables people to be immune to the disease.
(3 marks)
iii) Use the information provided to suggest why it is possible for someone who has been given the vaccination to still get the flu.
(1 mark)
3 a) Describe and explain two aseptic techniques followed when transferring bacteria from one agar plate to a second sterile agar plate.
(4 marks)
b) Why are Petri dishes containing microorganisms incubated at 25 ºC or lower?
(1 mark)
4 a) The graphs in Figure 13.29 show how the number of people smoking and the number of people diagnosed with lung cancer have changed over a 50 year period in a large city.
i) What is the evidence from the graphs to suggest that smoking is a cause of lung cancer?
(1 mark)
ii) What is the evidence that suggests that it takes a number of years for lung cancer to develop?
(1 mark)
b) i) Name the component in tobacco smoke that causes lung cancer.
(1 mark)
ii) Name one other harmful effect that this component causes.
(1 mark)
5 Figure 13.30 shows a cancer tumour.
a) State one difference between the cancer cells and the normal cells in the diagram.
(1 mark)
b) Give two pieces of evidence from the diagram that suggests that this is a malignant tumour.
(2 marks)
c) Explain why it is important to find and treat malignant tumours early in their development.
(2 marks)
d) Give one advantage and one disadvantage in using chemotherapy as a treatment for cancer.
(2 marks)