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HSC Biology Topic 3
THE SEARCH FOR BETTER HEALTH
What is this topic about? To keep it as simple as possible, (K.I.S.S.) this topic involves the study of: 1. INFECTIOUS DISEASES & PATHOGENS 2. BODY DEFENCES AGAINST DISEASE 3. NON-INFECTIOUS DISEASES 4. STRATEGIES TO PREVENT DISEASE IN PLANTS & ANIMALS
but first, some definitions... The Different Types of Disease
What is “Health”?
Diseases can be simply classified as follows
Health is a very difficult thing to define. A simple definition is that “Health is the absence of disease”.
DISEASES
The World Health Organization (WHO) has declared this definition as too simplistic and defines “health” as
“a state of complete physical, mental and social well-b being”
Infectious
Non-iinfectious
Caused by the invasion of the body by a diseasecausing organism, a
Do NOT involve a pathogen, and cannot be contagious. May be due to
“Pa athogen”
... and NOT merely the absence of disease.
Pathogens include:
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?
• • • • • •
What is “Disease”? Disease can be defined as
Contagious This means that you can catch the disease from another infected person, from body contact, from the air, from food and water etc.
For example, the pathogen which causes Malaria is carried from one infected person to another by mosquitoes. The mosquito is the vector of the disease.
Fleas (on rats) were the vector for the “Black Death” in the Middle Ages.
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Vector
A vector is another organism which transmits the pathogen from one person to another.
Some diseases can be infectious, but not contagious.
“any condition that disturbs the normal functioning of the body”
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... and other things
Some are transmitted by a Many infectious diseases are
Despite the WHO’s definition, to really understand “Health”, you need to study “Disease”, and that’s what this topic is really all about!
By this definition, a broken toe-nail might be a disease, but in this topic you will study some much more serious conditions...
Prions Viruses Bacteria Protozoans Fungi Macro-p parasites
• Heredity (inherited) • Structural or metabolic malfunction • Lifestyle factors • Environmental factors • Poor nutrition
Plague victims 14th century
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CONCEPT DIAGRAM (“Mind Map”) OF TOPIC 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
The range of PATHOGENS
1st Line of Defence... the barriers
Case Study of an Infectious Disease
Infectious Diseases & Pathogens
2nd Line of Defence... Non-s specific Immunity
Body Defences Against Disease
THE SEARCH FOR BETTER HEALTH
3rd Line of Defence... Specific Immunity
NonInfectious Diseases
Strategies to Prevent Disease in Plants & Animals
Epidemiology Case Studies
Nutritional Deficiency
Quarantine Genetic Engineering HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
Environmental Disease
Inherited Disease
Use of Pesticides
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1. INFECTIOUS DISEASES & PATHOGENS Genes, Differentiation and Health
When Good Guys Turn Bad
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.
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.
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.
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!
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.
Water from a river or lake may contain potentially dangerous microbes. This is why our water supplies are so carefully treated.
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.
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.
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.
• the water is filtered to remove any remaining suspended solids. • the water is chlorinated to kill virtually all remaining microbes.
You may have done laboratory work to grow microbes on “nutrient agar” in petri dishes.
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.
You probably discovered an amazing number and variety of microbes in our food and water, and throughout our whole environment. PETRI DISH inoculated by touching with fingers
Fungi colonies
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.
Bacteria colonies HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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A Brief History of Our Understanding of Infectious Disease 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:
Pasteur’s Experiment
Closed flask remains sterile... no microbes grow in it.
Louise Pasteur (1822-1895) 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.
Each flask contains a “broth”, boiled until sterilized
Open flask grows microbes & rots. It was believed the life came spontaneously from contact with air.
This flask is open to the air, but the “gooseneck” prevents airborne spores getting to the broth. It remained sterile, and proved “spontaneous generation” is wrong.
Robert Koch (1843-1910) 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.
His famous experiment of 1862 did 3 things: • disproved the generally-held idea of “spontaneous generation” of life, and helped establish “Cell Theory”.
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”.
• 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!
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.
You may have repeated Pasteur’s experiment in your laboratory work.
Historical Case Study: Understanding Malaria 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:
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.
• Anti-malarial drugs, such as “Chloroquine”, seemed effective to cure the disease until the pathogen evolved Anopheles Mosquito resistance.
The history of human attempts to understand it, and cure or prevent it, is a good example of how difficult this process can be.
Vector for Malaria
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.
• 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.
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)
• All attempts to develop a vaccine against the pathogen have been unsuccessful, but research is still going on, and recent developments are promising.
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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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. 4
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The Variety of Pathogens There are 6 different categories of pathogen known to cause human diseases.
Fungi
Macro-Parasites
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.
These are the larger, macroscopic parasites. Ectoparasites are those which are parasites on the outside of the body, usually sucking blood. Examples are fleas, Tick 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.
Disease Example: Tinea (Athlete’s foot) Pathogen: Tinea pedis (a mould-like fungus) Comment:
Protozoans 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.
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: Pathogen:
Disease Example: Malaria Pathogen: Plasmodium species
Taeniasis (Tapeworm disease)
Comment:
Taenia saginata (tapeworm)
Comment:
Highly contagious. Feeds on skin, causing itchy, smelly, flaking of feet.
Tapeworm lives in intestine. Can cause weight loss and abdominal pain.
Mosquito vector. Affects many millions of people. Major health problem.
More pathogens next page...
Bacteria 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. VARIETY OF BACTERIA Bacteria have very small cells, in many shapes
In the 20th century, most of the serious bacterial diseases were brought under control by the use of antibiotics and programs of mass immunization.
Rod Shaped Bacteria
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Disease Example: Tetanus Pathogen: Clostridium tetani (a rod-shaped bacterium) Comment:Detailed case-study in this section.
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The Variety of Pathogens
Prions
Continued
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.
Viruses 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. FLU VIRUS
Nucleic acids
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)
RABIES VIRUS
Pathogen: BSE prion (causes “Mad Cow Disease” in cattle.) Comment: Incurable, 100% fatal, brain degeneration. Transmitted by eating nerve tissue from infected animals. Protein capsule and attachments for entering host cell
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.
Antibiotics 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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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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.
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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.
Cause Pathogen:
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.
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.
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.
C. tetani produces heat-resistant spores which can survive in soil for many years.
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.
Transmission 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. In the human body it is life-threatening!
Untreated, between 30-60% of patients will die, and survivors may take months to recover.
Treatment • 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.
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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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Worksheet 1
Basic Definitions & History
Fill in the blank spaces
Name....................................
“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)...........................
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).......................... ..................... .....................................
“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.
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.
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)..................... .............................
COMPLETED WORKSHEETS BECOME SECTION SUMMARIES
Worksheet 2 Pathogens & Disease
Name....................................
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).......................................
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.
Fungi are responsible for some diseases of the skin, such as the highly contagious g)...................... caused by the fungus h)........................................... (scientific name)
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.
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.
The major symptom is sudden, violent af)........................ which can break bones, and even interrupt ag).......................... leading to brain damage and suffocation.
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)................................
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.
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 ..........................
Antibiotics are especially effective against al)........................... but have no effect on am)........................ A modern problem is pathogens that have an)......................................................
s)...................... are non-cellular protein molecules which cause diseases of the t)................................. system. A human example is u)................................ HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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Worksheet 3 Test Questions Multiple Choice
section 1
Name....................................
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.
1. 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
7. (5 marks) Write a brief definition for each of the following. a) Infectious disease b) Non-infectious disease
2. “Differentiation” occurs when cells become specialized because: A. they contain different genetic information. B. they contain the same genes, but mutations occur. C. new combinations of genes have been produced by meiosis. D. they follow different parts of the same total set of genes.
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.
3. 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
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.
4. 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
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.
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.
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
6. Antibiotics are not an effective treatment for a disease caused by a: A. fungus B. bacterium C. protozoan D. virus
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2. BODY DEFENCES AGAINST DISEASE Your body is not defenceless against invading pathogens. You are equipped with 3 “lines” of defence:
Skin The outside surface of skin is layers of dead, dry cells, virtually impossible for microbes to penetrate.
The 1st Line of Defence: Barriers to Invasion
It is a difficult environment for a pathogen to grow on (no water). Skin constantly flakes off, carrying microbes away.
There are a number of physical and chemical barriers which prevent most potential pathogens from entering your body. The most important ones are: Skin Mucous Membranes Chemical Barriers & Secretions Flushing Mechanisms & Reflexes
Secretions such as the tears from the eyes, contain an anti-bacterial enzyme “Lysozyme”.
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.
Chemical Barriers Stomach is highly acidic. This kills most pathogens that are swallowed with food, or in mucus.
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 of the stomach.
Urinary and reproductive openings are mildly acidic... enough to inhibit the growth of many microbes.
Flushing Mechanisms
Reflex Actions Coughing and sneezing reflexes move dust, mucus and trapped pathogens, etc out of the breathing passageways.
• 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.
Vomiting removes stomach contents that are making you nauseous, removing pathogens which have been swallowed.
MICROFLORA 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 outcompeting the pathogens, or by creating chemical conditions that pathogens cannot tolerate.
MICROFLORA IMBALANCE CAN LEAD TO DISEASE 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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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Antigens and the Immune Response
Organ Transplants and “Tissue Rejection”
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.
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.
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”.
To try to prevent this happening, the transplant doctors:
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.
• 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-S SELF” (such as proteins on foreign cells) which trigger the immune response
BEFORE STUDYING THE IMMUNE SYSTEM YOU NEED TO KNOW MORE ABOUT BLOOD CELLS
BLOOD CELLS
ERYTHROCYTES Red Blood Cells Carry oxygen
BASOPHILS involved in inflammation
Notice that there are many different kinds of “white cells”
LEUCOCYTES White Blood Cells Immune System
EOSINOPHILS
LYMPHOCYTES form the 3rd Line of Defence
NEUTROPHILS
MACROPHAGES These 3 types carry out “Phagocytosis” B-C CELLS (2 types) produce Antibodies
All these types are part of the “2nd Line of Defence”
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T-C CELLS (4 types) Kill infected body cells
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The 2nd Line of Defence: Non-Specific Immune Responses When pathogens penetrate the 1st-Line barrier Inflammation 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.
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.
Phagocytosis
In response, the white bood cells called Basophils release the chemical histamine.
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.
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.
The phagocyte cells detect the antigens of a foreign cell, recognise it as “not-self” and attack it.
This also brings more body heat to the site. Heat can inhibit some pathogens, and speeds up all chemical reactions for faster repairs.
PHAGOCYTOSIS Phagocyte Cell
• 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.
Phagocyte engulfs foreign cell.
Bacterial Cell Lysosomes (contain digestive enzymes)
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 Pathogen destroyed by lysosomes chemicals
Pathogen wrapped in a membrane inside Phagocyte. Lysosomes fuse with the package.
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 selfdestructs.
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.
More importantly, special antigens appear on the cell membrane which attract phagocytes to destroy the cell, and its load of pathogens.
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!
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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.
In some cases, an infected site will be “walledoff” 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. 12
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The Lymphatic System
This could spread pathogens throughout the body, but the lymph nodes generally prevent that. As the blood circulates through the LYMPHATIC SYSTEM Lymph nodes contain many tissues, some of the blood plasma always showing some of the drainage phagocytes to “eat” foreign seeps out of the capillaries and bathes cells, and also contain the cells in “tissue fluid”. The body is lymphocyte cells (below) equipped with a system of “drains” Lymph fluid returned to which are able to target to collect this fluid and return it to Lymph Nodes bloodstream specific pathogens and the blood. This drainage system is neck near heart destroy them. the Lymphatic System. armpit
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.
Lymph tubes form a one-way groin 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 Drainage pattern lymph vessels from arm and legs by the surrounding muscles, and the tubes have valves to prevent back-flow.
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.
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.
The 3rd Line of Defence T-L LYMPHOCYTES are produced in bone marrow, but mature and multiply in the Thymus Gland (hence “T” cells). “Cell-M Mediated” Immune response. T-c cells attack body cells that are infected by pathogens, or growing abnormally as cancers.
To help you remember which is which, think of “B for Bomber”... B-c cells are like bomber aircraft which drop bombs (antibodies) on the enemy without ever getting close to them. B-L LYMPHOCYTES are produced and mature in bone marrow (hence “B” cells). Produce ANTIBODIES. “Antibody-M Mediated” Immune response. Antibodies attack pathogens (and their toxins) which are NOT inside body cells, but in the blood, lymph or tissue fluid.
There are 2 categories of B-cells, and 4 categories of T-cell. Some details about these are shown on the next page.
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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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The 3rd Line of Defence LYMPHOCYTES
T-C Cells
B-C Cells
Plasma Cells
Memory B-C Cells
Produce Antibodies to fight the current infection
Remain in the system to respond to future infections by the same pathogen
Helper T-C Cells Interact with Phagocytes to set off the specific immune responses
Cytotoxic (Killer) T-C Cells Attack body cells which are infected by pathogens
Suppressor T-C Cells Suppress the immune response (turn it off) after an infection is defeated
Memory T-C Cells Remain in the system to respond to future infections by the same pathogen
How White Blood Cells Interact with Each Other Step 2 Antigen is “Inspected” by a Helper T-Cell
Step 1 Phagocyte Displays an Antigen
Helper
A Phagocyte “eats” a pathogen. Part of the pathogen (an antigen) is displayed on MHC molecule.
Phagocyte Cell
Pathogen has been destroyed
T-C Cell Helper T-Cells will “dock” Phagocyte Cell with a phagocyte and “inspect” Antigen the antigen. The T-Cell then releases chemical messages which stimulate the production of huge numbers of specific MHC T-C Cell Plasma (B) Cells receptor and Cytotoxic (T) Cells, each “keyed” to Step 3 that specific antigen shape.
MHC molecule
Antigen being displayed
WHAT IS MHC? MHC stands for “Major Histocompatibility Complex”. This is a glycoprotein molecule which acts like
Killer T-C Cells
an egg-c cup to hold an antigen out for inspection by a lymphocyte cell. Infected body cells. Antigens appear on cell membranes
Plasma B-C Cells
Killer T-C Cells
T-C Cells “dock” with antigens on infected body cells. Cells are killed by being burst open by enzymes Cell from T-C
Chemical Signals stimulate production of millions of specific Lymphocytes
Antigen receptor
Antibodies are proteins with a shape to fit antigens on each pathogen exactly
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Produce Antibodies Antibodies lock onto pathogens so they are neutralized and immobilized. Phagocytes then destroy them.
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Immunity 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. 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 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. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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.
Smallpox 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.
Diphtheria
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.
“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-a ation”.
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Worksheet 4 Non-Specific Body Defences Fill in the blank spaces
Name....................................
“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 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 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)......................... (organelle)
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.
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 site.
Reflex actions, such as k)....................... or vomiting helps to remove microbes that have been breathed in or swallowed. 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 n)............................................
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 pathogens.
WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES
WORKSHEET 6
COVERS THE IMMUNE SYSTEM & VACCINATION
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Worksheet 5 Test Questions
section 2
Name....................................
Multiple Choice
Longer Response Questions
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
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.
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 response. D. a blood cell which releases antibodies.
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.
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”
11. (4 marks) One of the responses to infection or tissue damage is “inflammation”. a) Name the type of leucocyte responsible for initiating inflammation.
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.
b) Explain how the typical features of inflammation (namely hot, red and swollen tissue) are brought about.
5. The diagram shows part of the A. Circulatory system. B. Immune system C. Nervous system D. Lymphatic system
12. (4 marks) Compare and constrast “B-cells” and “T-cells” and their methods of attack against invading pathogens.
6. Antibodies are produced by: A. killer T-cells B. basophils C. plasma cells D. phagocytes
13. (4 marks) There are 4 varieties of “T-lymphocytes”... “helper”, “killer”, “suppressor” and “memory” cells. Briefly outline the function of each.
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.
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.
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 HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
b) Name a previously serious disease which has been brought under control by vaccination. 17
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3. NON-INFECTIOUS DISEASES Epidemiology Epidemiology is the study of the occurrence of diseases. It is very much about collecting data and analysing it statistically to look for patterns and correlations between the incidence of disease and the many factors that may be involved in the cause(s) and the spread of disease. The data collected by epidemiologists includes information from:
Case Study Epidemiology of Lung Cancer Now that many infectious diseases are more or less under control, the major causes of death in our society are heart disease and cancer. In the USA in 1996, of all the many deaths by cancer, those due to lung cancer amounted to 25% in men and 14% in women. Epidemiology has now established beyond doubt that there is a very strong link between lung cancer and smoking.
Hospitals and health-c care workers who Government studies such as report on their the national census, which patients and the measures the size and age treatments given. distribution of the population, where people live, what they do for a living and so on. Case studies of particular diseases, in which detailed information is gathered about those people suffering the disease, and compared to a “control group” of similar people without the disease.
The correlation between smoking and a number of health problems, including lung cancer, was suggested by epidemiology data as early as the 1950’s. The powerful and influencial tobacco companies were able to argue that... ...“correlation doesn’t prove causation”
The results of an epidemiological study might include:
This is quite true. Just because 2 things occur together doesn’t prove that one causes the other. As the ancient Romans knew, malaria is more common around swamps. They thought it was the “bad air”. Now we know it’s because of the mosquito vector breeding in the swamps.
Identifying that a new disease has appeared. Identifying the possible causes or risk factors of a disease.
Discovering that an existing disease has changed in its occurrence.
Assessment of the effectiveness of public health systems and vaccination programs.
Such findings allow health authorities and governments to plan and allocate resources to better meet the health needs of a community. For example, epidemiology results might point out the need for a new hospital to be built in a certain place, or for a law to be made to ban the advertising of products that endanger health, such as tobacco products. A classic example which shows the value of epidemiology is the case of the drug thalidomide. In the 1960’s this drug was commonly prescribed to pregnant women to prevent “morning sickness”. Throughout history there have always been some children born with deformities, and no-one noticed that there had been a slight increase in these cases. However, an epidemiology study revealed a correlation between the use of thalidomide and an increased risk of babies being born without arms or legs. The drug was quickly banned, saving many more people from its terrible effects. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
Throughout the 1970’s and 1980’s the epidemiology studies kept collecting data and compiling evidence showing that smoking was linked to lung cancer. Experiments to try to prove the causation were done too. For example, thousands of laboratory rats were forced to breathe tobacco smoke for long periods of time and the incidence of lung cancer compared with “non-smoking” rats. Eventually the evidence became overwhelming: • Annual deaths from lung cancer are about 5 times higheramong smokers than non-smokers. • Quitting smoking immediately begins reducing the chance of developing lung cancer • Since the banning of tobacco advertising and public awareness programs, the percentage of smokers in the population has declined. The incidence of lung cancer (and other smokingrelated problems) has declined exactly in parallel. 18
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Case Studies of Non-Infectious Diseases An Inherited Disease A Nutritional Deficiency Disease Haemophilia Scurvy
Occurrence Haemophilia occurs in males only, at a rate of 1 in every 5,000 male births.
Occurrence In modern Australian society, scurvy is virtually non-existant because of the generally high quality diet available. (We eat too much... but that’s another story.)
Symptoms The person’s blood lacks certain blood “factors” involved in blood clotting, so their body is unable to stop the bleeding from minor injuries. Even gentle activity can cause minor bleeds at joints and in muscles.
In history, scurvy was a significant disease, especially on long sea voyages. A British report in 1600 indicated that 10,000 sailors had died of scurvy in the previous 20 years.
With haemophilia, there is continued internal bleeding, extreme pain in joints, and this leads to joint damage and disability. Untreated, it is usually fatal during childhood.
Symptoms The main protein of skin, bone and hair is “collagen”. In scurvy, the collagen cannot be made properly by the body, so • hair falls out • skin erupts, flakes and discolours • teeth loosen and fall out • blood capillaries leak blood, so bruising spots appear all over the body
Cause Haemophilia is caused by a recessive, sexlinked gene. The recessive gene is carried on the “X” chromosome and so is inherited more commonly in males than females.
Cause
In fact, it is virtually unknown in females because to have haemophilia a female must be the daughter of a haemophiliac father. Until recently no haemophiliac males survived long enough to father children.
Lack of Vitamin C in the diet. Vitamin C is found in citrus fruits such as oranges, and in some vegetables such as tomatoes. The enzyme responsible for a critical step in making collagen requires ascorbic acid (vitamin C) for its correct functioning.
Treatment/Management Modern treatment allows haemophilia sufferers to lead a fairly normal life. Treatment involves 23 injections per week of blood clotting factors extracted from donated blood.
Treatment/Management A balanced diet including fresh fruits and vegetables, will prevent scurvy.
An Environmental Disease: Melanoma Cause (cont) Exposure to UV damages skin cells, causes mutations in the DNA and greatly increases the risk of a melanoma developing.
Occurrence Melanoma is the 3rd or 4th most common cancer in Australia, and approximately 2,000 Australians die from it each year. Between 1950 and 1990 its occurrence tripled, and Australia has the highest incidence of melanoma in the world, per capita.
It can also be considered a “lifestyle disease” since its occurrence is related to outdoor lifestyles, and activities such as sunbaking. People with fair skin are more at risk.
Symptoms Dark, irregular-shaped moles appear on the skin. These may become raised, and later bleed and become ulcerated. This “primary” tumour may shed cells which can spread in the blood and establish “secondary” tumours in vital organs such as lungs, kidneys, liver or brain.
Treatment/Management The primary tumour can be removed by surgery. Secondary tumours are treated by surgery, radiation therapy and anti-cancer drugs. Early detection greatly increases the chances of survival.
Cause Melanoma is classed as an “environmental disease” because its major cause is a factor of the Australian environment... ultra violet (UV) rays from the Sun.
Prevention (always the preferred strategy) includes avoiding skin exposure to the Sun by the use of protective clothing, and sunscreen lotions, and changing lifestyle by avoiding deliberate sunbaking.
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4. STRATEGIES TO PREVENT DISEASE IN PLANTS & ANIMALS Plant and Animal Diseases
Quarantine Even in ancient times, people understood the principle of quarantine... for example, people suffering the disease leprosy, were isolated in “leper colonies” to prevent the disease spreading through a community.
Plants and animals suffer from diseases caused by the same range of pathogens as do humans. In addition, plants suffer a lot of damage from herbivorous animals feeding on them, especially from insects.
In modern Australia, quarantine is a major strategy used to prevent the entry and spread of a variety of plant and animal diseases and pests which could have devastating effects on our agricultural and pastoral industries.
In your practical work you may have examined plant shoots and leaves and gathered evidence of pathogens and insect damage. Leaf damage from a “leaf miner” insect
QUARANTINED
Fungal disease
People who wish to bring in live animals, such as pets or racehorses, must go through lengthy and expensive procedures to ensure the animal is not carrying a disease. The animal will be quarantined... placed in isolation for possibly several weeks, and regularly examined by a veterinarian for any signs of disease.
Leaf Galls A common sign of disease in many plants is the growth of a “gall” in the plant tissue. A gall is the plant’s response to an infection or irritation caused by a microscopic pathogen or macroparasite.
People entering from certain “risky” parts of the world must show proof of vaccination against some diseases, or else they too will be quarantined until it is proven they are not carrying an excluded pathogen.
The plant grows layers of tough, woody tissue around the infection site in an attempt to “walloff” the pathogen and prevent the infection spreading.
The Success of Quarantine The fact that Australia has remained totally free of certain human, plant and animal diseases is evidence of the effectiveness of our quarantine system. Australia is free of:
Disease and Pest Control Australia’s agricultural industry not only supplies us with most of our food, but is a major part of the nation’s economy.
• Foot-and-Mouth disease which could devastate sheep & cattle herds. • Malaria and Rabies. (serious human diseases) • Sorghum Downy Mildew, a fungal pathogen with potential to destroy many cereal crops and native grasses... and many others.
Disease, or insect pests in crops, could have a devastating effect on this industry. Therefore, our governments and industry organizations use a variety of strategies to control disease and agricultural pests. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
The government agency responsible is the Australian Quarantine Inspection Service (AQIS). Every airport and other point of entry for people and goods into Australia is under AQIS scrutiny. Tourists may not bring plant seeds, fresh foods, animal skins or soil (even muddy boots) in from another country.
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Use of Pesticides
Genetic Engineering for Disease & Pest Resistance
A “pest” species is any plant or animal that we find troublesome or destructive to our agriculture and animal husbandry.
Genetic Engineering (GE) is the process of altering the genetic make-up of a species. Many of the modern developments in GE are aimed at modifying our crops and animal herds to make them resistant to various diseases or pests so that usage of pesticide chemicals can be reduced or eliminated.
In the 20th century many “pesticides” were developed in an attempt to control pest species. In general terms, a “pesticide” is a chemical which can kill a pest species without serious harm to the plant crop or animals we wish to protect.
Case Study: Cotton Bollworm (Heliothis caterpillar)
Pesticides Insecticides kill insects.
The original was DDT
Herbicides kill plant “weeds” The best known is “Roundup”
This insect pest chews holes in cotton, maize, tomatoes and peanut crops. As well as this damage itself, the crop becomes more prone to fungal disease.
Fungicides kill fungal pathogens
Insecticides are not the answer, because Heliothis has evolved resistance, and many natural enemies and predators of Heliothis are killed by sprays.
Dips & Drenches are given or applied to animals to kill macro-p parasites such as worms & ticks
GE Strategy No.1
Originally, the pesticides were thought to be “magic bullets” which would keep pest species under control. This attitude has changed, as many pesticides either lose their effectiveness, or create environmental problems. Pests Develop Resistance
Scientists have transferred a gene from a bacterium into cotton plants. The gene is for the production of a toxin, which is lethal to the caterpillar if eaten.
Human Toxicity Pesticides pose a danger to the humans who use them. Residues of pesticides may be present in foods and pose a threat to consumers
In almost every case of a pesticide, the pest species show a tendency to develop resistance. This is Natural Selection in action, resulting in Pesticides are Indiscriminant the evolution of resistant pests. Insecticides, for example, kill any insects, not just the “target” pest species. This Environmental Pollution creates even worse pest Pesticides can wash into rivers and enter natural problems because the food chains. Fish are natural competitors and killed by insectides. DDT predators of the pest are had severe impacts on the reproduction in many bird killed too.
GE Strategy No.2 Research is being done with a virus which specifically infects Heliothis caterpillars only, and will not infect other species.
The virus already causes a disease in the caterpillar, but scientists are developing ways Since cotton is not to genetically alter the virus to include a gene for a lethal toxin. a human food, and the toxin is only produced by The idea is to produce billions of GE viruses and then deliver the leaf cells in them in a spray to crops that the plant, the have a Heliothis infestation. No presence of the other species would be bacterial toxin is affected. not a problem for humans.
species.
It is now realised that, although many pesticides have been effective, it is better in many cases to look for alternative ways to deal with pests... once again the principle is all about prevention and avoidance, rather than cure. Two important strategies are:
In the field of human disease control, the emphasis has shifted from treatment and cure, towards prevention. While antibiotics still have their value as treatment drugs, the great success story of human health has been mass vaccination to prevent millions of people ever getting certain diseases.
• Biological Controls... using natural predators and pathogens to control a pest, and • Genetic Engineering...
The same trend, from treatment towards prevention, is occurring with plant and animal diseases, and pest control.
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Worksheet 6
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Immune System & Vaccination
Fill in the blank spaces
Name....................................
There are 2 sub-categories of B-cell: i)............................ cells produce proteins called j)....................................... These are able to bind to a specific antigen (rather like the lock-andkey system with enzymes and substrates).
The 3rd Line of Defence is a)............................... (specific/non-specific) immunity, meaning that this system “targets” each antigen specifically. The white blood cells involved are called b).................................. and are of 2 main types called c)..........-cells and .........-cells.
By surrounding the antigen, antibodies neutralize it and attract k).................................... which “eat” and destroy it. l)............................... B-cells remain in the system to respond to future attacks by the same pathogen.
T-cells have 4 sub-categories as follows: Helper T-cells interact with phagocytes to “learn” about a new d)................................... and then send chemical signals to cause the production of millions of “specifically targetted” lymphocytes.
Once a disease pathogen has been defeated, the m).............................. lymphocytes remain on guard, ready to respond to future infection by the same pathogen. This means the person is n)....................... to that disease, because the pathogen will be destroyed before any symptoms occur.
e)......................... (killer) T-cells can recognise body cells which are infected with a pathogen and kill the cell by bursting its cell f)............................ with enzymes.
o)............................ is an artificial method of making people immune to a disease. The “vaccine” contains p)........................... to set off the immune response, without causing the disease. Programs of mass vaccination have been very successful against some diseases. For example, q)........................... has been totally eradicated, diseases such as r).......................... and ............................. are virtually non-existant.
Suppressor T-cells g).................................... the immune response after an infection has been defeated. h)........................ T-cells remain in the system to respond to future attacks by the same pathogen.
Worksheet 7 Non-Infectious Diseases Fill in the blank spaces
Name....................................
It is caused by a recessive gene carried on the p).............. chromosome, so it is said to be q)...............-linked. The disease was invariably fatal in the past, but modern treatments involve the injection of r).............................................. from donated blood.
Epidemiology is the study of the a)........................ of diseases. By collecting and b)......................... data, the patterns and c)........................... between various factors can be used to identify disease risks and assess the effectiveness of d)................................ programs. These findings help health authorities and governments make decisions and laws about community health, such as banning advertising for e)......................................
Scurvy is an example of a s).................................. deficiency disease. It is due to a lack of t)............................ in the diet and used to be a significant risk during u).......................... ................... with no supplies of fresh fruit available. Symptoms include hair and teeth v)............................, and skin eruptions and bruising due to leaking of blood from w)..........................................
Epidemiology has established the link between f)............................. and smoking. The death rate from lung cancer among smokers is g)................. (number) times higher than among nonsmokers. Since the ban on tobacco advertising, and h)........................... programs, the percentage of smokers has i)........................ and so has the j)......................... of lung cancer.
Melanoma is a very dangerous form of x)................... cancer. It can be classed as an “Environmental Disease” since a major causative factor is exposure to y)......................... rays from the Sun. Approximately z)...................... (number) of Australians die from melanoma each year. This is the aa)............................. rate in the world, on a per capita basis.
Haemophilia is an example of an k)............................ disease. Its occurrence is in l)....................... only, at a rate of 1 case every m)............. (number) male births. The disease causes internal n)......................... due to the lack of o)................................... factors in the blood. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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Worksheet 8 Strategies for Plant & Animal Diseases Fill in the blank spaces
Name....................................
Inspection of plant foliage often reveals a)........................... due to pathogens and insects. A “gall” is a plant’s response to b)......................... or irritation. A gall is a capsule of woody tissue that grows around an infection site in an attempt to c).....................................................................
Fungicides for n)............................., and Dips and Drenches to kill o)............................... in animals. It is now realised that pesticides are not as wonderful as once thought, because: • pests develop p).......................................... • pesticides are a toxic risk to q)............................ • insecticides are indiscriminate, killing not only pests, but r)........................................ as well. • pesticides can pollute the s)............................... and affect other life forms such as fish or birds.
The importance and economic value of our agriculture demands strategies to combat disease and pest species. A major stategy is d)................................. which means to isolate potential sources of infection, to prevent their entry and spread. The government agency responsible is called e).................... (abbreviation) and it checks all people and goods entering Australia. Prohibited goods include f).................................., ................................ and ......................................... Animals, such as pets or livestock, must be placed in g)......................................... for several weeks and examined and tested to ensure they are not harbouring h)..................................
One alternative to pesticides is t)........................................... For example, the pest caterpillar u)............................... attacks cotton, maize, tomato and peanut crops and is one of Australia’s worst agricultural pests. Two different G.E. strategies are being researched and tested to control this pest. One involves inserting genes from a v)............................... into cotton plants so they produce a w)............................... which kills any insect that eats it. Another strategy involves genetically modifying a x)......................... which attacks only the caterpillar. The virus will be genetically modified to produce a fast-acting y)............................. to kill the caterpillars rapidly.
Our quarantine system has been successful at keeping Australia free from animal disease such as i)............................., human diseases like j)................................. and .............................. and plant diseases such as k).......................................
As for human disease control, the emphasis has shifted from z)................................. diseases/pests towards aa)............................. them occurring.
“Pesticides” include l)............................ to kill insects, m)....................... to kill weeds,
Worksheet 9 Test Questions
sections 3 & 4
Name....................................
Multiple Choice
Longer Response Questions
1. The results from an Epidemiology study would probably NOT be useful for: A. experiments to extract an antibiotic from a fungus. B. assessing a vaccination program. C. identifying risks of an environmental disease. D. discovering the appearance of a new disease.
5. (3 marks) Outline some of the epidemiological correlations that point to the link between smoking and lung cancer. 6. (4 marks) You have studied an hereditary disease. Name the disease you studied and describe: a) the occurrence a) the symptoms b) the cause c) the treatment or management ... of the disease.
2. The disease which has risk factors of an environmental and lifestyle nature is: A. malaria . B. melanoma C. scurvy D. haemophilia 3. The effectiveness of Australia’s quarantine system can be seen by the: A. amount of prohibited articles seized at airports. B. difficulty of bringing a pet animal into Australia. C. small number of tourists with diseases. D. absence of certain diseases and pests in Australia.
7. (5 marks) a) Briefly discuss reasons why the widespread use of pesticides against agricultural pest species and diseases is no longer considered as the best strategy for control.
4. Using pesticides against agricultural pests is similar in principle to the use (in human medicine) of: A. vaccination B. quarantine C. epidemiology D. antibiotics HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
b) Using a named example of a pest species, outline an alternative strategy involving Genetic Engineering. 23
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CONCEPT DIAGRAM (“Mind Map”) OF TOPIC Some students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts and important facts. Practise on this blank version.
THE SEARCH FOR BETTER HEALTH
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Answer Section
8. • Water typically sits in reservoir which allows a lot of suspended matter, and pathogens, to settle out. • It is often filtered to remove remaining suspended solids. • It is chlorinated to kill any pathogens.
Worksheet 1 a) complete physical, mental and social well-being. b) which disturbs the normal functioning of the body. c) pathogen d) contagious e) vector f) specialised g) identical h) genes i) correct hygienic j) food k) hygiene/cleanliness l) filtered m) chlorinated n) pathogen o) disease p) Louis Pasteur q) microbes r) contact with air s) Robert Koch t) anthrax u) the pathogen of a disease to be identified v) protozoan w) (Anopheles) mosquito x) Plasmodium y) Ronald Ross z) chloroquine aa) resistance ab) vaccine ac) 2-3 million
9. • Anti-malarial drugs (such as Chloroquine) were successful treatments, but the parasite has now developed resistance. • Attempts to eradicate the mosquito vector using insecticides lowered the incidence of malaria at times, but overall this strategy failed. • All attempts so far, to develop a vaccine have failed. 10. Macro-parasites eg Taeniasis (Tapeworm disease) Fungi eg Tinea Protozoa eg Malaria Bacteria eg Tetanus Viruses eg AIDS Prions eg CJD (Creutzfeldt-Jacob disease)
Worksheet 2 a) macroscopic b) leeches/ticks/lice c) vectors d) inside e) Taeniasis f) Taenia saginata g) Tinea h) Tinea pedis i) Protozoa j) Plasmodium k) procaryotic l) small m) Tetanus n) Clostridium tetani o) protein p) nucleic acid (DNA or RNA) q) make new viruses r) AIDS, ‘flu, measles, etc s) Prions t) nervous u) CJD (Creutzfeldt-Jakob disease)
11. Disease: Tetanus a) Clostridium tetani (bacterium) b) Violent, painful muscle spasms, which can interrupt breathing. c) Pathogen enters a deep wound, such as stepping on a nail. Disease is NOT contagious. d) Normal responses: inflammation around wound, immune system begins to respond to tetanus toxin, but progress of the untreated disease is too fast for immune system to cope. e) Muscle-relaxant drugs to treat spasms. Antibiotics to kill bacteria. Clean wound surgically. Administer Tetanus antitoxin, which is antibodies from an immune person or animal. f) Vaccination with tetanus “toxoid” gives immunity and is 100% effective at preventing disease.
v) Clostridium tetani w) is not x) a deep wound y) anaerobic z) dead tissue aa) toxin ab) nerve ac) seal off/ inhibit pathogens ad) phagocytes ae) antibodies af) muscular seizures ag) breathing ah) antibodies ai) vaccination aj) tetanus toxin, made harmless by chemical treatment ak) 10 al) bacteria am) viruses an) antibiotic resistance
Worksheet 4 a) barriers b) dead, dry c) penetrate. d) Mucous e) mucus f) cilia g) acid h) chemical i) bladder j) lysozyme k) coughing l) microflora m) disease n) Thrush o) immune response p) foreign q) suppressed r) reject / attack s) leucocytes t) non-specific u) eosinophils, neutrophils & macrophages v) lysosome w) basophils x) inflammation y) histamine z)dilates aa) apoptosis ab) tubes/vessels/“drains” ac)nodes ad) armpits & groin
Worksheet 3 1. B
2. D
3. C
4. C
5. A
6. D
7. a) Disease caused by a pathogen. b) Disease that does not involve a pathogen. c) An organism which invades the body and disturbs the normal functioning of it. d) A disease which can be “caught” by transmission from an infected person. e) An organism (usually animal) which carries a pathogen from one host to another. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
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13. (cont) “Killer T-cells” are able to identify and “lock-on” to body cells which are infected with a specific pathogen, such as a virus. They destroy the cell by bursting its membrane with enzymes.
Workskeet 5 1. B 5. D
2. C 6. C
3. A 7. B
4. A 8. C
9. Mucous membranes line all the body openings at mouth, nose, throat and reproductive and digestive openings. Membranes produce mucus, a thick fluid wich traps dust and microbes. In some places (eg trachea) there are microscopic hairs (“cilia”) which beat rhythmically to move mucus along for removal.
“Suppressor” T- cells turn off the response after a pathogen has been defeated. “Memory” cells remain in circulation, possibly for life, ready to quickly re-activate the immune system against future invasions by that specific pathogen. 14. a) Vaccination is the process of introducing into a person’s body an antigen which will set off the immune response without making the person ill.
10. The skin, mouth, digestive and reproductive tracts all have a natural population of microbes living there, many in a mutualistic relationship. They control potential pathogens by outcompeting them, or by creating conditions that the pathogens cannot tolerate.
For example, a vaccine might contain harmless, killed bacteria. This will set off the immune response so that future infection by the living bacterial pathogen will be destroyed before symptoms appear. The person is “immune” to that pathogen.
If this natural “microflora” population becomes unbalanced or damaged, an opportunistic pathogen may multiply and cause disease. An example is the yeast Candida albicans which is usually present in the female reproductive tract, but kept under control by the microflora. An outbreak of Candida results in the disease “Thrush”.
Worksheet 6 a) specific c) B-cells & T-cells e) cytotoxic g) suppress i) Plasma k) phagocytes m) memory o) Vaccination q) Smallpox
11. a) Basophils b) Basophils release Histamine which causes: • dilation of blood capillaries; more blood and body heat flows to area... hence hot and red • capillaries become more porous, so more plasma leaks out causing swelling.
Worksheet 7
12. Comparison (similarities): T-cells and B-cells are both lymphocytes which can defend against specific pathogens.
a) occurrence b) analysing c) correlations d) public health e) tobacco products (or other dangerous products) f) lung cancer g) 5 h) public awareness i) declined j) incidence k) inherited l) males m) 5,000 n) bleeding o) clotting p) X q) sex r) clotting factors s) nutritional t) vitamin C u) long sea voyages v) loss w) capillaries x) skin y) ultra-violet z) 2,000 aa) highest
Contrast (differences): B-cells produce antibodies; proteins which “lock-on” to antigens and neutralize pathogens/toxins which are free in bloodstream or tissues. Neutralized pathogens are then destroyed by phagocytes. T-cells are able to recognise body cells that are infected by a pathogen (eg has a virus multiplying inside it) and kill the cell by bursting its membrane with enzymes. 13. “Helper” T-cells interact with phagocytes which “present” a new antigen to them. Helper cells then send chemical signals which cause the cloning and rapid production of millions of lymphocytes able to “target” that specific antigen. HSC Biology Topic 3 “Search for Better Health” copyright © 2005-2 2009 keep it simple science www.keepitsimplescience.com.au
b) lymphocytes d) antigens f) membrane h) Memory j) antibodies l) Memory n)immune p) antigens r) Polio & Diphtheria
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6. Haemophilia a) Occurs in males only, at the rate of 1 per 5,000 male births. b) The blood fails to clot properly, so any activity can result in internal bleeding into joints, bruising etc. This leads to painful joint damage and disability. If untreated, it is usually fatal in childhood. c) Inheritance of a recessive gene, carried on the X-chromosome. This means it is “sex-linked” and appears in males much more commonly than females. d) Clotting factors extracted from donated blood are injected 2-3 times per week. This allows the patient to lead a relatively normal life, but gentle exercise and injury avoidance are important.
Worksheet 8 a) damage b) infection/ a pathogen c) prevent the infection spreading d) quarantine e) AQIS f) plants, fresh food, soil g) quarantine h) pathogens i) Foot-and-Mouth j) Malaria & Rabies k) Sorghum Downy Mildew l) insecticides m) herbicides n) fungi o) macro-parasites p) resistance q) humans r) their predators t) Genetic Engineering u) Heliothis v) bacterium w) a toxin x) virus y) toxin z) treating/killing aa) preventing
7. a) • many pests have developed resistance to the pesticide. • pesticides pose a toxic threat to humans who use them, and to consumers. • Some pesticides cause environmental problems, such as the widespread effects of insecticide DDT on bird reproduction up until the 1970’s.
Worksheet 9 1. A
2. B
3. D
4. D
5. The data shows that the chances of contracting lung cancer are about 5 times higher among smokers than among non-smokers. The incidence of lung cancer among exsmokers shows a steady decline against the time since they quit.
b) The Heliothis caterpillar is a major pest in cotton crops, but is now resistant to insecticides.
The incidence of lung cancer in society has shown a decline exactly in parallel with the decline in the number of smokers, brought about by the ban on tobacco advertising, and public awareness programs.
Scientists have genetically engineered cotton plants by inserting into their chromosomes a bacterial gene which causes the production of a toxin. The cotton plant produces toxin which kills any insects which eat the crop, eliminating the need to spray pesticides.
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