Bio7.Search for Better HealthU


Full text


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


but first, some definitions...

HSC Biology Topic 3


What is this topic about?

To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:






What is “Health”?

Health is a very difficult thing to define. A simple definition is that “Health is the absence of disease”.

The World Health Organization (WHO) has declared this definition as too simplistic and defines “health” as

... and NOT merely the absence of disease. Does this mean that

if you were physically fit, well-fed and sane, but having a bad hair day, (socially

dangerous) that you are not healthy? Despite the WHO’s definition, to really understand “Health”, you need to study “Disease”, and that’s

what this topic is really all about!

What is “Disease”?

Disease can be defined as

By this definition, a broken toe-nail might be a disease, but in this topic you will study some much more serious conditions...

The Different Types of Disease

Diseases can be simply classified as follows

“a state of complete physical, mental

and social well-bbeing”

“any condition that disturbs the

normal functioning of the body”


CCaauusseedd bbyy tthhee iinnvvaassiioonn ooff tthhee bbooddyy bbyy aa

ddiisseeaassee-ccaauussiinngg oorrggaanniissmm,, aa



Doo NNOOTT iinnvvoollvvee aa ppaatthhooggeenn,, aanndd ccaannnnoott bbee

ccoonnttaaggiioouuss.. M

Maayy bbee dduuee ttoo

Pathogens include: •• PPrriioonnss •• VViirruusseess •• BBaacctteerriiaa •• PPrroottoozzooaannss •• FFuunnggii •• MMaaccrroo-ppaarraassiitteess •• HHeerreeddiittyy ((iinnhheerriitteedd)) •• SSttrruuccttuurraall oorr m meettaabboolliicc mmaallffuunnccttiioonn •• LLiiffeessttyyllee ffaaccttoorrss •• EEnnvviirroonnmmeennttaall ffaaccttoorrss •• PPoooorr nnuuttrriittiioonn ... aanndd ootthheerr tthhiinnggss


Maannyy iinnffeeccttiioouuss ddiisseeaasseess aarree

Infectious Non-iinfectious


TThhiiss mmeeaannss tthhaatt yyoouu ccaann ccaattcchh tthhee ddiisseeaassee ffrroomm aannootthheerr iinnffeecctteedd ppeerrssoonn,, ffrroomm bbooddyy ccoonnttaacctt,, ffrroomm tthhee aaiirr,, ffrroomm ffoooodd aanndd

w waatteerr eettcc.. SSoommee ddiisseeaasseess ccaann bbee

iinnffeeccttiioouuss,, bbuutt nnoott ccoonnttaaggiioouuss..

SSoommee aarree ttrraannssmmiitttteedd bbyy aa


AA vveeccttoorr iiss aannootthheerr oorrggaanniissmm wwhhiicchh ttrraannssmmiittss

tthhee ppaatthhooggeenn ffrroomm oonnee ppeerrssoonn ttoo aannootthheerr.. FFoorr eexxaammppllee,, tthhee ppaatthhooggeenn


whhiicchh ccaauusseess MMaallaarriiaa iiss ccaarrrriieedd ffrroomm oonnee iinnffeecctteedd

ppeerrssoonn ttoo aannootthheerr bbyy m

moossqquuiittooeess.. TThhee mmoossqquuiittoo iiss tthhee vveeccttoorr ooff tthhee ddiisseeaassee..

Fleas (on rats) were the vector for

the “Black Death” in the Middle Ages.

Plague victims 14th century


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly



Some students find that memorising the OUTLINE of a topic helps them learn and remember the concepts and important facts. As you proceed through the topic, come back to

this page regularly to see how each bit fits the whole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

The History of our understanding of infectious disease 1st Line of Defence... the barriers Epidemiology The range of PATHOGENS 2nd Line of Defence... Non-sspecific Immunity Case Study of an Infectious Disease Inherited Disease Nutritional Deficiency Environmental Disease Use of Pesticides Genetic Engineering Quarantine










SSttrraatteeggiieess ttoo



Diisseeaassee iinn

PPllaannttss && AAnniim




Diisseeaasseess &&






Case Studies 3rd Line of Defence... Specific Immunity


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


Genes, Differentiation and Health

You began life as a single cell, and have since grown to be made up of billions of cells. Growth occurs by mitosis which produces genetically identical daughter cells, so every one of your billions of cells has exactly the same set of genes. However, not all your cells are the same... they have specialised for different functions; muscle cells, nerve cells, blood cells, and so on. If all your cells are genetically identical, how can they also specialise and be so different? The answer is that, in the embryo stage, your body underwent a process called differentiation. Every cell in your body contains in its

chromosomes, ALL the genes needed to

specify all your body parts, functions and traits. In each cell though, only some of the genes are “switched-on”. Muscle cells have switched on the genes for building muscle fibres, but have not switched on the genes for eye-colour, or production of saliva. Each specialised type of cell has switched on just those genes which allow it to carry out its function, and no others. Differentiation is essential for the correct functioning of your body, and therefore for health. If a muscle cell suddenly switched on the genes appropriate for a blood cell, it would no longer be functioning properly. This could cause a loss of body function, and therefore, a lack of good health.

Cleanliness is Next to Healthiness

Good health is not just about correct cell and body functioning. It was recognised in ancient times that cleanliness in water, food and personal hygiene would help prevent disease. At the time, the concept of “germs” was not understood.

You may have done laboratory work to grow microbes on “nutrient agar” in petri dishes. You probably discovered an amazing number and variety of microbes in our food and water, and throughout our whole environment.

When Good Guys Turn Bad

We are constantly surrounded by millions of microbes. Most of them are harmlessly going about their business and cause no problems. However, even “harmless” microbes can cause disease.

If, for example, people are careless with food storage then microbes can rapidly multiply within the food. If eaten, the food can cause “food poisoning” because of the waste products and toxins produced by the growing microbes. Many potentially dangerous microbes commonly live on the skin or in people’s throats and generally cause no disease because their population is small. However, if the person is weakened by stress, lack of food or illness, these “resident” microbes can suddenly multiply rapidly and cause a serious disease. So, quite apart from the B.O. and bad breath, it really is a good idea to wash yourself and clean your teeth!

Water from a river or lake may contain potentially dangerous microbes. This is why our water supplies are so carefully treated.

Treatment of Water Supplies

A typical Australian town or city obtains its water from the local rivers. Generally, before it reaches the consumer:

• the water sits for some time in a large reservoir. This allows time for much of the suspended matter (including microbes and the matter they are feeding on) to settle to the bottom.

• the water is filtered to remove any remaining suspended solids.

• the water is chlorinated to kill virtually all remaining microbes.

When is a Microbe a Pathogen?

Some of the “germs” around us are always “bad guys” and their only purpose and way of life involves invading a person’s body and causing disease.

Others are “harmless” organisms which normally go about their life without affecting people. However, many are opportunistic, and if presented with a chance to multiply in or on our body they will do so, and may cause a disease.

Any organism is a “pathogen”

if it causes a disease.


Fungi colonies PETRI DISH inoculated by touching with fingers Bacteria colonies


Copying is permitted according to the Site Licence Conditionsonly


We have only known about the role of pathogens (especially microscopic “germs”) as the cause of infectious diseases for about 150 years. Diseases were previously thought to be caused by “evil spirits” or were due to “bad air”, or similar ideas. The man recognised as the discoverer of the “Germ Theory of Disease” was:

Louise Pasteur


Pasteur came to suspect that infectious diseases were caused by microbes after proving that microscopic yeast was responsible for the fermentation involved in making beer and wine, and also showing that it was the growth of bacteria in wine that caused it to go sour.

His famous experiment of 1862 did 3 things: • disproved the generally-held idea of “spontaneous generation” of life, and helped establish “Cell Theory”.

• proved that decay was caused by air-borne microbes, and not just due to contact with air. • stimulated scientists to start looking for microbes that were causing diseases... and, of course, they found them!

You may have repeated Pasteur’s experiment in your laboratory work.

keep it simple science ®

HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science

EEaacchh ffllaasskk ccoonnttaaiinnss aa ““bbrrootthh””,, bbooiilleedd uunnttiill sstteerriilliizzeedd

CClloosseedd ffllaasskk rreemmaaiinnss sstteerriillee... nnoo

m miiccrroobbeess ggrrooww iinn iitt..


Oppeenn ffllaasskk ggrroowwss m

miiccrroobbeess && rroottss.. IItt wwaass bbeelliieevveedd

tthhee lliiffee ccaammee ssppoonnttaanneeoouussllyy

ffrroomm ccoonnttaacctt w wiitthh aaiirr..

TThhiiss ffllaasskk iiss ooppeenn ttoo tthhee aaiirr,, bbuutt tthhee ““ggoooosseenneecckk”” pprreevveennttss aaiirrbboorrnnee ssppoorreess

ggeettttiinngg ttoo tthhee bbrrootthh.. IItt rreemmaaiinneedd sstteerriillee,, aanndd

pprroovveedd ““ssppoonnttaanneeoouuss ggeenneerraattiioonn”” iiss wwrroonngg..

A Brief History of Our Understanding of Infectious Disease



Robert Koch


One of the scientists who followed up on Pasteur’s work was the German Robert Koch. He isolated the bacterium responsible for the serious disease anthrax, but more importantly he developed a general system for identifying a pathogen.

The problem is that there are always many different microbes present in the body of a person with a disease. It can be very difficult to be certain which one is causing the disease, and which are just “innocent by-standers”.

Koch developed a set of procedures to follow, which will definitely and scientifically identify the pathogen. These procedures are known as “Koch’s Postulates” and are still used today when previously unknown infectious diseases are discovered.

Historical Case Study: Understanding Malaria

Malaria is a tropical disease caused by a protozoan pathogen which is carried by a vector... the mosquito. The symptoms are attacks of shivering, fever, headaches, nausea and extreme tiredness. Without treatment, about 10% of patients die, but survivors keep having re-occurrence of symptoms, perhaps for many years.

The history of human attempts to understand it, and cure or prevent it, is a good example of how difficult this process can be.

The name “malaria” means in Italian “bad air” and it was believed since ancient times that it was caused by the smelly gases from swamps. In ancient Rome the occurrence of malaria was reduced by draining swamps. (The real connection to swamps was mosquitoes... but no-one thought of that)

After the work of Pasteur and Koch, a scientific search for a microscopic pathogen began. In 1880, Charles Laveran discovered a protozoan Plasmodium in the blood of malaria patients, but the method of transmission could not be found.

In 1898-9 Ronald Ross found the pathogen in mosquitoes and, using human volunteers, was able to prove the transmission of the disease via the mosquito vector. Throughout the 20th century many strategies were tried against the disease:

• Anti-malarial drugs, such as “Chloroquine”, seemed effective to cure the disease until the pathogen evolved resistance.

• Widespread spraying of swamps, forests and villages with insecticides to try to eradicate the mosquito vector may have reduced the incidence at times, but overall this strategy failed.

• All attempts to develop a vaccine against the pathogen have been unsuccessful, but research is still going on, and recent developments are promising. Malaria remains one of the world’s greatest health problems. Several hundred million people are affected by it, and 2-3 million die each year... mostly children.

Anopheles Mosquito Vector for Malaria


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


The Variety of Pathogens

There are 6 different categories of pathogen known to cause human diseases.


These are the larger, macroscopic parasites. Ectoparasites are those

which are parasites on the outside of the body, usually sucking blood. Examples are fleas, ticks, leeches, mites, lice, mosquitoes, and so on. Some can inject toxins while feeding, causing inflammation, allergic reactions and sometimes partial paralysis.

Generally, ectoparasites only become major threats to health if they are vectors for microscopic pathogens.

Endoparasites are those parasites which live inside the body. The most common pathogens are either flatworms (e.g. tapeworms and flukes) or roundworms.

Disease Example: Taeniasis

(Tapeworm disease)


Taenia saginata


Comment: Tapeworm lives in intestine. Can cause weight loss and abdominal pain.


Protozoans are single-celled organisms. The cell is animal-like; eucaryotic and lacking a

cell wall. Billions of protozoans live in swamps, rivers and oceans where they form

part of the “plankton” and are a vital link in the food chains. Only a few cause disease. Disease Example: Malaria




Comment: Mosquito vector.

Affects many millions of people.

Major health problem.


The Fungi include the various moulds and yeasts. Some are very useful (yeast for bread

& beer) or are eaten for food (mushrooms). Most fungi live in soil and are important as

decomposer organisms in nature. Only a few cause disease.

Disease Example: Tinea (Athlete’s foot) Pathogen:

Tinea pedis

(a mould-like fungus) Comment: Highly contagious. Feeds on

skin, causing itchy, smelly, flaking of feet.


Bacteria are an enormously varied group of single-celled, procaryotic organisms. The vast majority are decomposer organisms in soil and water environments,

or make their own food by photosynthesis or chemosynthesis.

Some, however, are disease pathogens and caused many of the great “plagues” of history, such as the “black death” of the Middle Ages.


In the 20th century, most of the serious bacterial diseases were brought under control

by the use of antibiotics and programs of mass immunization.

Disease Example: Tetanus


Clostridium tetani

(a rod-shaped bacterium) Comment:Detailed case-study in this section.

More pathogens next page...


Bacteria have very small cells, in many shapes

Rod Shaped Bacteria


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


The Variety of Pathogens



One of the great success stories of disease control in the 20th century was the discovery of the class of drugs called antibiotics. The first and most famous was Penicillin, first extracted from a mould fungus Penicillium, in 1928. Other

antibiotics were discovered in various fungi, and some have been synthesised chemically.

Antibiotics are selectively toxic to living cells. They kill or inhibit the cells of microbes such as bacteria, but do not harm human cells. Antibiotics are mainly effective against bacteria. Some will kill fungal pathogens (these are usually called “fungicides”) and others work against protozoans. It should be noted that antibiotics DO NOT work on viruses.

During the 20th century the use of antibiotics was responsible for helping to bring under control a range of diseases (mostly bacterial) which had been health problems for centuries... tuberculosis, leprosy, syphilis, pneumonia, cholera, to name just a few. For the first time in history, these serious diseases became curable, and some have been virtually eradicated.

Also, antibiotics are widely used to treat infection in minor wounds, sore throats, eye and ear infections, and so on. This speeds recovery from minor ailments and improves everyone’s quality of life. Antibiotics are frequently prescribed for those suffering viral infections also. This prevents “secondary infections” of bacterial disease that might strike a person weakened by the virus.

The Bugs Fight Back...

Antibiotic Resistance

Unfortunately, there is a down-side to the use of antibiotics; Natural Selection. Among the billions of individual pathogen cells there may be a few which have some natural resistance to an antibiotic. When the antibiotic kills all the others, the resistant cells survive and reproduce and evolution takes place. Many pathogens have evolved resistance to the older antibiotics and new ones need to be developed or discovered, in order to keep winning the war against the germs.

The danger is that, by using antibiotics, we have caused the evolution of resistant strains. This could lead to future epidemics of diseases that we cannot control.


Prions are a mysterious type of pathogen only discovered about 20 years ago and

still not fully understood. They are NOT living things, and are not cellular. Prions are proteins molecules which

reproduce themselves and cause infectious disease, especially of nerve tissue such as the brain. They seem to be

proteins that are folded and twisted into the wrong shape, and are able to cause more proteins to re-arrange to the wrong

shape, thus spreading from cell to cell and causing malfunctions to the brain.

Disease Example: CJD (Creutzfeldt-Jakob disease)

Pathogen: BSE prion

(causes “Mad Cow Disease” in cattle.) Comment: Incurable, 100% fatal, brain degeneration. Transmitted by eating nerve tissue from infected animals.


Viruses are all “bad guys”. Every virus is a pathogen which causes disease in some organism or other... plants, animals, even bacteria all suffer virus diseases. The lifestyle of every virus is to invade a living cell and “hijack” its genetic machinery. The cell is taken over

and forced to make more virus particles to infect more cells. Viruses are NOT cellular. Each is a very small capsule of

protein containing either DNA or RNA.

Many serious and common human diseases are caused by viruses, including AIDS, influenza (flu), measles, polio, rabies and the common cold. Some, such as polio, have been brought

under control by immunization programs.



Nuucclleeiicc aacciiddss

PPrrootteeiinn ccaappssuullee aanndd aattttaacchhmmeennttss ffoorr eenntteerriinngg hhoosstt cceellll


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


Case Study of an

Infectious Disease: Tetanus

Tetanus, also known as “Lock-jaw”, has been known since ancient times, but only understood since about 1890 when the cause

and method of infection was discovered. Since early in the 20th century it has

become curable and preventable by the use of immunization.

Host Response

The infected person’s defence mechanisms react in all the usual ways:

Inflammation of the wound, serves to partly seal off the infected area and raise the temperature to try to speed healing and inhibit heat-sensitive pathogens.

Phagocytes (white blood cells which “eat” bacteria) are attracted to the wound area and destroy bacteria and clean up dead tissue. However, they can only operate at the edges of the wound where conditions are aerobic. Further in, the C. tetani can be thriving in the anaerobic areas.

The immune system reacts to the exotoxin by beginning the process of producing an antibody to destroy the toxin molecules. However, this process may take weeks, and the disease is likely to kill the person well inside this time, if untreated.



Clostridium tetani


a rod-shaped bacterium.

This bacterium is common in soil, especially if there is a lot of animal manure, such as around

farmyards. The bacterium is anaerobic (lives where there is no oxygen) and normally feeds

on dead organic matter in the soil.

C. tetani produces heat-resistant spores

which can survive in soil for many years.

Major Symptoms

The tetanus exotoxin affects nerve cells causing them to keep “firing” when they shouldn’t. This stimulates muscles to go into

spasms and seizures.

Jaw and throat muscles are usually the first affected... hence “Lock-jaw”. High temperature, elevated blood pressure and

heart rate. Sudden, powerful and painful muscular seizures may be so strong as to break bones and tear muscles in the abdomen

and chest. Seizures can interrupt breathing, causing brain damage and suffocation. Untreated, between 30-60% of patients will die,

and survivors may take months to recover.

Prevention and Control

Tetanus is completely preventable by immunization. The vaccine contains tetanus “toxoid”; tetanus toxin which has been treated chemically to render it harmless, but it still sets off

the immune system to actively produce antibodies. Immunity lasts about 12 years, so “booster” shots are recommended every 10 years.

The world-wide death toll from tetanus is approximately 200,000 per year, but only a few hundred of these are in “developed” countries like Australia because of the immunization programs.

Virtually all Australian cases occur in older people who have forgotten to get a booster shot, or from self-tattooing, or drug-users using dirty needles.


• Antibiotics to kill bacteria in the wound.

• Surgical exploration and cleaning of the wound. • Treat spasms with muscle-relaxant drugs.

• The major treatment is the use of tetanus antitoxin. The “Antitoxin” is Tetanus Immune Globulin (TIG). Basically this is a concentrate of antibodies from a person (or other animal) who has developed immunity to tetanus. TIG binds to the tetanus toxin in the bloodstream so it becomes harmless and is destroyed by phagocyte cells.


The disease is not contagious. You cannot catch it from someone else.

The normal manner of infection is from a deep wound, such as when someone steps on a nail, but even being pricked by a plant thorn could be enough. The essential requirement is that the wound is deep enough to provide anaerobic conditions in dead tissue.

If spores of C. tetani enter the wound, they may germinate and the bacteria grow, feeding on the dead cells within the wound. If that’s all that happened, it would not be a serious problem, but C. tetani produces an “exotoxin” which happens to be one of the most potent nerve poisons ever discovered.


“Health” is a state of a)... ... “Disease” is any condition b)... Infectious disease is caused by a c)... If the disease can be caught from another infected person then it is said to be d)... Some infectious diseases are transmitted by another organism, called a e)...

“Differentiation” is the process by which body cells become f)... Every cell in a multicellular organism is genetically g)..., but differentiated cells have “switched on” different h)... in order to function correctly.

Microscopic organisms are found in every part of our environment. This is why it is essential to follow i)... procedures for storage of j)... and personal k)... Water supplies are routinely l)... and m)... to remove or kill microbes. Any organism can become a n)... if it causes o)...

The man most responsible for helping us understand the “Germ Theory of Disease” was p)... ...

Tetanus Case Study.

The pathogen is called v)... Tetanus w)... (is or is not) contagious. Transmission usually occurs by x)... ... The pathogen grows in y)... conditions in a wound, feeding on z)... It produces a powerful aa)... which affects ab)... cells.

The host reponses include inflammation, which attempts to ac)... Also, white cells called ad)... gather at the wound site. The immune system begins making ae)... but the disease progresses faster than this.

The major symptom is sudden, violent af)... which can break bones, and even interrupt ag)... leading to brain damage and suffocation.

Patients are treated with an antitoxin containing ah)... from an immune person or animal. Prevention of tetanus is achieved by ai)... This involves a “toxoid” which is aj)... Booster injections are needed every ak)... years. Antibiotics are especially effective against al)... but have no effect on am)... A modern problem is pathogens that have an)...


Copying is permitted according to the Site Licence Conditionsonly keep it simple science


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science


Worksheet 1 Basic Definitions & History

Fill in the blank spaces Name...

Worksheet 2 Pathogens & Disease

Name... His famous experiment of 1862 proved that decay was caused by q)... and not just due to r)... His work stimulated others to begin searching for microscopic pathogens. The great German scientist s)... discovered the bacteria which caused t)..., but more importantly he developed a set of procedures which allow u)... ... ...

Malaria is caused by a v)... pathogen, transmitted by a vector, the w)... The pathogen, called x)..., was discovered in patients’ blood in 1880. The link to mosquitoes was proven by y)... in 1898. Many strategies have been used against Malaria, including drugs such as z)... These were successful, but the pathogen has evolved aa)... to drugs in many places. Attempts to kill the mosquito vector have failed, and attempts to develop a ab)... have not yet succeeded. Malaria remains a major world health problem, killing ac)... people each year.

There are 6 different categories of pathogen:

Macro-parasites include the a)...-parasites which feed on the outside of the body, such as b)... These rarely cause any serious problems themselves, but can be c)... for other pathogens. Endoparasites live d)... the body. An example is e)... (tapeworm disease) caused by the flatworm f)... Fungi are responsible for some diseases of the skin, such as the highly contagious g)... caused by the fungus h)... (scientific name) i)... are single-celled, eucaryotic organisms. Not many cause disease, but Malaria, caused by various species of j)... is one of the world’s greatest health problems.

Bacteria are a varied group of k)... organisms with very l)... (size) cells of various shapes. They are responsible for many diseases including m)... caused by n)... Viruses are non-cellular. Each is a capsule of o)... containing p)... A virus invades living cells and forces the cell to q)... Examples of virus diseases include r)...and ...

s)... are non-cellular protein molecules which cause diseases of the t)... system. A human example is u)...


Multiple Choice


A disease could NOT ever be: A. infectious and contagious

B. hereditary and carried by a vector C. non-infectious and hereditary D. pathogenic and contagious


“Differentiation” occurs when cells become specialized because:

A. they contain different genetic information. B. they contain the same genes, but mutations


C. new combinations of genes have been produced by meiosis.

D. they follow different parts of the same total set of genes.


The scientist responsible for developing a system for positively identifying the pathogen responsible for a disease was:

A. Pasteur B. Laveran C. Koch D. Ross


A pathogen was described as:

“Non-cellular and microscopic. Composed of a protein capsule containing nucleic acid”

This pathogen is a: A. Fungus B. Bacteria C. Virus D. Prion 5.

The pathogen responsible for the disease Malaria, and its vector would be classified (respectively) as:

A. protozoan and insect.

B. bacterium and macro-parasite. C. insect and virus.

D. macro-parasite and bacterium.


Antibiotics are not an effective treatment for a disease caused by a:

A. fungus B. bacterium C. protozoan D. virus

Longer Response Questions

Mark values given are suggestions only, and are to give you an idea of how detailed an answer is appropriate. Answer on reverse if insufficient space. 7. (5 marks)

Write a brief definition for each of the following. a) Infectious disease b) Non-infectious disease c) Pathogen d) Contagious e) Vector 8. (3 marks)

It is essential for public health that water supplies are made as safe as possible. Outline the processes that are typically used to treat our water supplies.

9. (3 marks)

Give a brief account of the main strategies that have been made to control the disease malaria, commenting on the effectiveness of each.

10. (6 marks)

List the 6 categories of pathogen responsible for infectious disease. For each, name a disease caused by a pathogen of that type.

11. (8 marks)

For a named, infectious disease you have studied:

a) give the name of the pathogen b) describe the major symptoms

c) describe how the disease is transmitted d) describe the host response to the infection e) outline the treatment given to a patient with the disease

f) outline any measures to control & prevent the disease


Copying is permitted according to the Site Licence Conditionsonly keep it simple science


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly



Flushing Mechanisms

• Regular emptying of the bladder flushes microbes from the

bladder and urethra. • Production of tears, and regular

“blinking” wash and wipe microbes from the eyes.

Reflex Actions

Coughing and sneezing reflexes move dust, mucus and trapped pathogens, etc out of the breathing passageways.

Vomiting removes stomach contents that are making you nauseous, removing pathogens which have been swallowed.


The outside surface of skin is layers of dead, dry cells, virtually impossible for

microbes to penetrate.

It is a difficult environment for a pathogen to grow on (no water).

Skin constantly flakes off, carrying microbes away.

Your body is not defenceless against invading pathogens. You are equipped with 3 “lines” of defence:

The 1st Line of Defence:

Barriers to Invasion

There are a number of physical and chemical barriers which prevent most potential pathogens from entering your body. The most important ones are:


Mucous Membranes

Chemical Barriers & Secretions

Flushing Mechanisms & Reflexes such as the tears from the


eyes, contain an anti-bacterial

enzyme “Lysozyme”.

Chemical Barriers

Stomach is highly acidic. This kills most pathogens

that are swallowed with food, or in mucus. Urinary and reproductive

openings are mildly acidic... enough to inhibit

the growth of many microbes.


Living in, and on, the human body are many “friendly” microbes which share a symbiotic relationship with us. Some live in the intestines and manufacture vitamins for us. Others live on skin and mucous membranes where they normally act as competitors to potential pathogens. They keep the population in check by

out-competing the pathogens, or by creating chemical conditions that pathogens cannot tolerate.


The female reproductive system is largely protected by its normal microflora. Taking medications, such as antibiotics, can upset the normal balance. The yeast Candida albicans, which is always present in low numbers, can take advantage and multiply rapidly. This results in a disease called

“Thrush”, with symptoms of itching, a white discharge and general discomfort.

Mucous Membranes

These membranes line the natural body openings of mouth and throat, and the

urinary and reproductive tracts.

The mucous membranes secrete mucus, a sticky fluid

which traps pathogens. In some places the membranes are lined with cilia.

These are microscopic hairs which “beat” in a rhythmic

way to move mucus (and trapped pathogens) along

for disposal. For example, mucus in the

breathing tubes is moved upwards, until it can be swallowed into the acid


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


Antigens and the

Immune Response

Sooner or later, pathogens manage to get past the 1st line of defence and invade the body. Once the barriers are penetrated there are 2 more lines of defence to combat the pathogens, but first the body has to recognise that foreign cells or toxins are present. It is the special cells of your immune system which do this.

Each of your own body cells has on the outside of its cell membrane, special proteins and glycoproteins (combinations of carbohydrate with protein) which act as identification markers, proclaiming “SELF”. Your immune system constantly checks everywhere, but ignores anything labelled as “self”.

Any foreign cell, cell fragment, or even just a protein molecule or toxin will act as an “Antigen”. It will not be recognised as “self”, and therefore must be foreign. This will set off a range of defence responses by the immune system.

Organ Transplants and

“Tissue Rejection”

When a person receives an organ transplant such as a kidney transplant, the new organ is, of course, from another person. The cells will have different “marker” proteins on their cell membranes.

Therefore, the cells of the new organ will act as antigens and set off the immune responses. The immune system reacts to the new organ as if it were a foreign invader and attempts to kill it. The result is called “Tissue Rejection” and can quickly lead to the failure of the transplant. To try to prevent this happening, the transplant doctors:

• use only organs from donors who closely match the patient in their “tissue type”. This means their cell markers will be similar and will not act as antigens quite as strongly.

• treat the patient with “immuno-suppressant” drugs to reduce their immune response. Their immune system is partially shut-down and does not attack the transplant. However, this also makes the patient more vulnerable to pathogens and they must be protected from infection. ANTIGENS are chemicals

recognised as “NOT-SSELF” (such as proteins on foreign cells) which trigger the immune response






ERYTHROCYTES Red Blood Cells Carry oxygen

LEUCOCYTES White Blood Cells

Immune System BASOPHILS involved in inflammation B-CCELLS (2 types) produce Antibodies T-CCELLS (4 types) Kill infected body cells LYMPHOCYTES form the 3rd Line of Defence EOSINOPHILS NEUTROPHILS MACROPHAGES

These 3 types carry out “Phagocytosis” All these types are part of the

“2nd Line of Defence”

Notice that

there are

many different

kinds of

“white cells”


Copying is permitted according to the Site Licence Conditionsonly


When pathogens penetrate the 1st-Line barrier defences their antigens will rapidly set off counter-attack responses of the 2nd-Line of Defence. This is “non-specific”, meaning that the exact identity of the foreign invader does not matter... the response is the same.


Phagocytosis means literally “to eat cells” and that’s exactly what some of the white blood cells are designed to do. The Eosinophils,

Neutrophils and Macrophages are all

“phagocytes” and able to eat and destroy foreign cells such as invading bacteria.

The phagocyte cells detect the antigens of a foreign cell, recognise it as “not-self” and attack it.

Phagocyte cells are “shape-changers” and not only can they wrap around a pathogen to engulf it, they can also squeeze their way out of the bloodstream and move among the tissue cells. Whenever they encounter antigens that signal “NOT-SELF” they will carry out phagocytosis to destroy it.

When large numbers of phagocytes gather at a site of infection, they form “pus”. Pus is rather nasty stuff (it’s full of infectious pathogens) but is a healthy sign... it means your phagoctes are on the job!


Inflammation is the way the body reacts to any cell damage, such as a cut, abrasion, crushing or burn. When cells are damaged they release chemicals which the immune system recognises as a “distress” signal.

In response, the white bood cells called Basophils release the chemical histamine.

Effects of Histamine

• dilation (widening) of the blood capillaries around the injury site. This allows more blood to flow in, bringing more clotting factors and more phagocyte cells to destroy pathogens.

This also brings more body heat to the site. Heat can inhibit some pathogens, and speeds up all chemical reactions for faster repairs.

• capillaries to become more permeable,

allowing fluids to escape from blood into the tissues. This causes swelling. The extra fluid in the tissues brings more phagocytes to fight infections, and the extra pressure causes drainage of fluid into the Lymph System. This washes dead cell debris towards the lymph nodes for disposal, thus clearing the area for repairs to begin.

Features of an inflammed wound

• Hot and red, from extra blood & body heat • Swollen, from extra tissue fluid

• Pus formation, from millions of phagocytes

Cell Death... Apoptosis

Sometimes at an infection site, the tissue cells may become so thoroughly infected by viruses, or infiltrated by so many bacteria, that the best defence is to seal off the area and sacrifice all the body cells within.

Immune system cells can start the process of Apoptosis, in which cells are given a chemical instruction to “commit suicide”. The suicidal cell produces enzymes which chop the cell’s

DNA to pieces, the energy-producing

mitochondria swell and burst, and the cell self-destructs.

More importantly, special antigens appear on the cell membrane which attract phagocytes to destroy the cell, and its load of pathogens. In some cases, an infected site will be “walled-off” by a layer of cells forming a capsule or cyst, inside which all the cells have been ordered to suicide. This isolates an infection and stops it spreading. Later, the dead debris inside the cyst will be destroyed by phagocytes, and the tissue repaired.

keep it simple science ®

HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science


PPhhaaggooccyyttee CCeellll LLyyssoossoommeess ((ccoonnttaaiinn ddiiggeessttiivvee eennzzyymmeess)) BBaacctteerriiaall CCeellll PPhhaaggooccyyttee eenngguullffss ffoorreeiiggnn cceellll..

PPaatthhooggeenn wwrraappppeedd iinn aa m

meemmbbrraannee iinnssiiddee PPhhaaggooccyyttee.. LLyyssoossoommeess ffuussee wwiitthh tthhee

ppaacckkaaggee.. PPaatthhooggeenn ddeessttrrooyyeedd bbyy

llyyssoossoommeess cchheemmiiccaallss


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


The Lymphatic System

As the blood circulates through the tissues, some of the blood plasma always seeps out of the capillaries and bathes the cells in “tissue fluid”. The body is equipped with a system of “drains” to collect this fluid and return it to the blood. This drainage system is the Lymphatic System.

Lymph tubes form a one-way drainage system from all body

extremities, back to a point near the heart where tissue fluid is dumped back into a vein to re-join the blood. Tissue fluid is squeezed through

lymph vessels by the surrounding

muscles, and the tubes have valves to prevent back-flow. At various points along the lymph vessels there are special chambers called “lymph nodes”. These are important sites for the immune system to defend against disease.

If there is an infection in any body tissues, it is likely that pathogens will be carried along by the flow of lymph fluid.

The 3rd Line of Defence: Specific Immunity

The 3rd line of defence said to be “specific” because the lymphocyte cells are able to identify particular pathogens by their antigens and set up defences which will accurately target each one. The pathogen will be destroyed not only in the current infection, but in future infections as well...

you become immune to the disease.

The cells responsible are the white blood cells known as “T-lymphocytes” and “B-lymphocytes”. B-Lymphocytes produce protein molecules called “antibodies” which can “lock-on” to a foreign

antigen rather like an enzyme fitting its substrate... i.e. it is a “key-in-lock” situation, with each antigen needing a specific antibody to “fit” it.


are produced in bone marrow, but mature and multiply in the Thymus Gland (hence “T” cells).

“Cell-MMediated” Immune response. T-ccells attack body cells that are

infected by pathogens, or growing abnormally as cancers.


are produced and mature in bone marrow (hence “B” cells). Produce ANTIBODIES. “Antibody-MMediated” Immune response. Antibodies attack pathogens (and their toxins)

which are NOT inside body cells, but in the blood, lymph or tissue fluid.

The 3rd Line of Defence

To help you remember which is which, think of “B for Bomber”... B-ccells are

like bomber aircraft which drop bombs (antibodies) on the enemy without ever getting close to them. This could spread pathogens throughout the

body, but the lymph nodes generally prevent that. Lymph nodes contain many phagocytes to “eat” foreign cells, and also contain lymphocyte cells (below)

which are able to target specific pathogens and

destroy them. When fighting a serious infection the lymph nodes become swollen and painful. This is often a sign of infection and an indication of where it is. For example, swollen lymph nodes in one armpit indicate that an infection is travelling up the arm, possibly from an infection site in the hand. There are also several glands of the body which are associated with the lymphatic system, and have a role in body defences. These include the adenoids and tonsils, the thymus gland in the upper chest, and the spleen. All act as “reservoirs” for immune sytem cells. LYMPHATIC SYSTEM

sshhoowwiinngg ssoommee ooff tthhee ddrraaiinnaaggee

LLyymmpphh NNooddeess nneecckk aarrmmppiitt ggrrooiinn LLyymmpphh fflluuiidd rreettuurrnneedd ttoo bbllooooddssttrreeaamm nneeaarr hheeaarrtt D Drraaiinnaaggee ppaatttteerrnn ffrroomm aarrmm aanndd lleeggss

You also need to know about how T-cells and B-cells interact with each other, and how they destroy pathogens.

This is also described on the next page. There are 2 categories of B-cells,

and 4 categories of T-cell. Some details about these are


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science keep it simple science


Copying is permitted according to the Site Licence Conditionsonly


The 3rd Line of Defence LYMPHOCYTES B-CCells T-CCells Plasma Cells Produce Antibodies to fight the current infection Memory B-CCells Remain in the system to respond to future infections by the same pathogen Helper T-CCells Interact with Phagocytes to set off the specific immune responses Cytotoxic (Killer) T-CCells Attack body cells which are infected by pathogens Suppressor T-CCells Suppress the immune response (turn it off) after an infection is defeated Memory T-CCells Remain in the system to respond to future infections by the same pathogen



w W

Whhiittee BBlloooodd CCeellllss IInntteerraacctt w

wiitthh EEaacchh O


Step 1

Phagocyte Displays an Antigen A Phagocyte “eats” a pathogen. Part of the pathogen (an antigen) is displayed on MHC molecule. W WHHAATT IISS MMHHCC?? M

MHHCC ssttaannddss ffoorr ““MMaajjoorr HHiissttooccoommppaattiibbiilliittyy CCoommpplleexx””.. TThhiiss iiss aa ggllyyccoopprrootteeiinn mmoolleeccuullee wwhhiicchh aaccttss lliikkee

aann eegggg-ccuupp ttoo hhoolldd aann aannttiiggeenn oouutt ffoorr iinnssppeeccttiioonn bbyy aa llyymmpphhooccyyttee cceellll..

PPhhaaggooccyyttee CCeellll MMHHCC m moolleeccuullee AAnnttiiggeenn bbeeiinngg ddiissppllaayyeedd PPaatthhooggeenn hhaass bbeeeenn ddeessttrrooyyeedd Step 2

Antigen is “Inspected” by a Helper T-Cell Helper T-Cells will “dock”

with a phagocyte and “inspect” the antigen. The T-Cell

then releases chemical messages which stimulate the production of huge numbers of specific Plasma (B) Cells

and Cytotoxic (T) Cells, each “keyed” to

that specific antigen shape.

PPhhaaggooccyyttee CCeellll HHeellppeerrTT-CCeellll AAnnttiiggeenn M MHHCC TT-CCeellll rreecceeppttoorr Step 3 Killer T-CCells AAnnttiiggeenn rreecceeppttoorr IInnffeecctteedd bbooddyy cceellllss..

AAnnttiiggeennss aappppeeaarr oonn cceellll mmeemmbbrraanneess

TT-CCeellllss ““ddoocckk”” wwiitthh aannttiiggeennss oonn iinnffeecctteedd

bbooddyy cceellllss.. CCeellllss aarree kkiilllleedd bbyy bbeeiinngg

bbuurrsstt ooppeenn bbyy eennzzyymmeess ffrroomm TT-CCeellll

Chemical Signals stimulate production of millions of

specific Lymphocytes

Produce Antibodies Antibodies lock onto pathogens so they are neutralized and immobilized. Phagocytes then destroy them. Antibodies are proteins with a shape to fit antigens on each pathogen exactly Plasma B-CCells KKiilllleerr TT-CCeellllss


Copying is permitted according to the Site Licence Conditionsonly



Once a person has been infected by a particular pathogen and then recovers from the disease, the immune system stops producing T-Cells and B-Cells for that pathogen. (This is done by “Suppressor T-Cells”)

However, “Memory T-Cells” and “Memory B-Cells” remain in the system for years afterwards, possibly for life. If that same pathogen invades the body again, the 3rd Line of Defence is already primed and ready. It reacts rapidly with a flood of T-Cells and antibodies so that the pathogen is usually destroyed before any disease symptoms are produced. The person cannot be affected by that pathogen ever again... he or she is immune to that disease.

This is why many diseases, such as childhood measles, are only ever caught once. At the first infection it takes time for the immune system to begin producing specific lymphocytes, so the disease takes hold and symptoms appear. Later in life many re-infections with measle virus may occur, but the primed immune system destroys the pathogen so symptoms do not occur again.

The Success of Vaccination

It was mentioned in a previous section how the use of antibiotics was a tremendous step forward in our ability to cure certain infectious diseases. Even more important has been the prevention (always better than cure) of disease by programs of mass immunization by vaccination.


is a viral disease which, if untreated, has a high death rate and survivors are left disfigured and scarred for life. In the 1950’s smallpox was targetted by the World Health Organization as “public enemy No.1”. A world-wide effort of vaccination resulted in the disease being totally eliminated by 1977... the most outstanding success against any disease in history.

Poliomyelitis (“Polio”)

is a viral disease which results in paralysis of limbs, causing the victim to be disabled for life. It used to kill or cripple hundreds of Australian children every year.

Since the 1950’s, the use of polio vaccines (originally injected, now taken orally) has eliminated the disease from Australia, and almost from the world. The disease still occurs in a few African nations only.


is a disease caused by a highly contagious bacterium. It can lead to permanent nerve and heart problems, even when patients are cured of the infection. Therefore, prevention is definitely far better than cure.

In the 1920’s, several thousand Australian children died from Diphtheria, or were permanently weakened by it. Vaccination programs had virtually eliminated it by the 1970’s.

It is now compulsory in Australia for all children to be vaccinated against Diphtheria, Tetanus, Polio, and another one-time child-killer, “Whooping Cough”. Other diseases for which successful vaccination programs exist include Rubella, Hepatitis, Measles and Influenza.

keep it simple science ®

HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science However, some pathogens keep altering the “antigens” on their cell membranes or viral capsules. This means the memory lymphocytes from the previous infection are useless, and the immune system must “re-llearn” to recognise the pathogen. This is why diseases such as the common cold can be caught over and over again.

“Vaccination” comes from the Latin word

“vacca” which means “cow”.

Edward Jenner

(English, 18th century)

had noticed that milkmaids always caught a mild disease “cowpox” from the cows, but never suffered the deadly smallpox.

Jenner used pus from a cowpox sore to deliberately infect people with cowpox. This caused later immunity to smallpox. (We now know that the viruses are so similar that antibodies for one, work against the other). So, “vaccination” literally means “cow-aation”.


The problem with becoming immune to a disease the natural way is that a person has to actually suffer the disease in order to gain immunity. Vaccination is the process of deliberately putting antigens into a person’s body so that the immune system reacts, and the person becomes immune, but without danger from the actual disease. The “vaccine” might be injected, or taken orally, to introduce one of the following into the body:-Live pathogens that are “attenuated”... harmless strains of the pathogen which have been bred. Pathogens that have been killed by heat or chemicals.

Fragments of pathogens, such as part of the cell wall of a bacterium, or the capsule of a virus. A “toxoid”, which is a toxin molecule from the pathogen, but rendered harmless by some treatment.

The antigens in the vaccine set off the immune response, eventually giving the person immunity to that disease.


“Antigens” are chemicals which trigger

the o)... ...

Antigens are proteins which the body

recognizes as p)... After an

organ transplant, the patient’s immune

system must be q)...

by drugs, otherwise their immune

system will r)... the

transplanted organ. The immune system

is made up of a variety of types of white

blood cells, or s)...

The 2nd Line of Defence is

t)... (specific or non-specific).

Three types of leucocyte (called

u)..., ... and

...) carry out phagocytosis.

This is when the “phagocyte” cell

envelopes a foreign cell and digests it

with enzymes from the v)...


Another type of leucocyte called

w)... set off the

x)... response whenever

the body has suffered damage.

Basophils release the chemical

y)... which z)...

blood capillaries, resulting in swelling,

hotness and redness around the injured


Sometimes body cells can be given

instructions to “commit suicide”. This

process is called aa)...

The Lymphatic System is a system of

ab)... which return tissue

fluid to the blood. If an infection is

present, pathogens could rapidly spread

via the lymph tubes. To prevent this

there are “Lymph ac)...”

at various points such as the neck,

ad)...and ...

Each lymph node has many phagocytes

and lymphocytes to destroy any



Copying is permitted according to the Site Licence Conditionsonly keep it simple science


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science

Worksheet 4 Non-Specific Body Defences

Fill in the blank spaces Name...

The 1st Line of Defence are the

a)... to infection. The skin is

made of layers of b)...

cells which are very difficult for a

pathogen to c)...

d)... membranes line

the body openings. They secete

e)... which traps pathogens.

Some mucous membranes are lined

with f)... which beat

rhythmically to remove mucus and

trapped pathogens.

The g)... conditions of the stomach

are a h)... barrier which

kills microbes that are swallowed.

Emptying the i)... and

blinking the eyelids both serve to

“flush” microbes away. Tears also

contain an enzyme called

j)... which can kill

bacterial cells.

Reflex actions, such as k)...

or vomiting helps to remove microbes

that have been breathed in or


It is normal for the body to have many

“friendly” microbes living in and on it.

These are called the body’s

l)... These

organisms help control potential

pathogens by competing with them. If

there is an imbalance of microflora, a

m)... may result.

An example is the fungal disease called





Multiple Choice

1. An example of a “chemical barrier” to infection is:

A. mucus in your breathing tubes B. acid in your stomach

C. dead, dry skin cells

D. cilia in a mucous membrane 2. An “antigen” is:

A. a protein that can “lock-on” to a pathogen and neutralise it.

B. a chemical which can kill pathogen cells. C. a foreign protein which sets off an immune


D. a blood cell which releases antibodies. 3.

The white blood cells Eosinophils, Neutrophils and Macrophages are all:

A. phagocytes B. lymphocytes C. antibody producers

D. part of the “1st line of defence” 4. “Apoptosis” is the process of: A. programed cell “suicide”.

B. enveloping and “eating” a foreign cell. C. pus formation at a site of infection. D. red swelling of infected tissue. 5.

The diagram shows part of the A. Circulatory system.

B. Immune system C. Nervous system D. Lymphatic system

6. Antibodies are produced by: A. killer T-cells

B. basophils C. plasma cells D. phagocytes 7.

Before the “specific” immune response can be mounted by lymphocytes for the first time: A. killer T-cells need to “lock-on” to

infected body cells.

B. helper T-cells need to “inspect” an antigen presented by phagocytes.

C. memory B-cells need to activate antibody production.

D. antibodies need to combine with an antigen. 8.

Which of the following would NOT be suitable to use as a vaccine?

A. live, attenuated pathogens B. fragments of pathogen cells C. active toxin from a pathogen D. killed pathogen cells

Longer Response Questions

Answer on reverse if insufficient space. 9. (3 marks)

Describe the location and features of the body’s mucous membranes in helping to protect against disease.

10. (4 marks)

Explain how the natural “microflora” of the body help protect against disease and, using a named example, how an imbalance in the microflora can result in disease.

11. (4 marks)

One of the responses to infection or tissue damage is “inflammation”.

a) Name the type of leucocyte responsible for initiating inflammation.

b) Explain how the typical features of inflammation (namely hot, red and swollen tissue) are brought about.

12. (4 marks)

Compare and constrast “B-cells” and “T-cells” and their methods of attack against invading pathogens.

13. (4 marks)

There are 4 varieties of “T-lymphocytes”... “helper”, “killer”, “suppressor” and “memory” cells.

Briefly outline the function of each.

14. (5 marks)

a) Explain how vaccination can make a person immune to a disease, possibly for life, without them ever getting sick from that disease.

b) Name a previously serious disease which has been brought under control by vaccination.


Copying is permitted according to the Site Licence Conditionsonly keep it simple science


HSC Biology Topic 3 “Search for Better Health” copyright © 2005-22009 keep it simple science





Related subjects :