1. Unit 3
Revision

2. Pathogens and types of diseases
What are pathogens?
Pathogens are microorganisms that cause infectious disease.
Pathogens may be viruses, bacteria, protists or fungi.
Communicable diseases are diseases that are caused by pathogens, they can be passed on/spread.
Non-communicable diseases are diseases such as diabetes, heart disease and cancer. They are caused by other factors such as radiation or lifestyle.
The spread of diseases can be reduced or prevented by:
simple hygiene measures
destroying vectors
isolation of infected individuals
vaccination.
How do pathogens spread?
They may infect plants or animals and can be spread by …
- direct contact,
- by water or
- by air
- by vectors (animals usually insects that spread disease)
- contaminated food
What is the difference between an epidemic and a pandemic?
Epidemic – When a disease spreads rapidly to many people.
Pandemic – When a disease spreads globally.

3. Pathogens and types of diseases - Questions
Communicable disease - questions
What does Communicable disease mean?
What is the other type of disease? Explain its meaning.
What is a pathogen?
Give 4 examples of pathogens.
How do bacteria cause disease?
How do viruses cause disease?
Give 4 ways in which pathogens spread?
How can the spread of diseases can be reduced or prevented?
What is the difference between an epidemic and a pandemic?

4. Pathogens - read the next 4 pages and then fill in the table on slide 8
Summary
Our bodies provide an excellent environment for many microbes which can make us ill once they are inside us. Our bodies need to stop most microbes getting in and deal with any microbes which do get in. Vaccination can be used to prevent infection.
Pathogens
Microorganisms that cause infectious disease are called pathogens.
Disease occurs when large numbers of pathogenic micro-organisms enter the body.
Bacteria
Not all bacteria are pathogens.
Pathogenic bacteria reproduce rapidly inside the body and may produce poisons (toxins) which make us feel ill.
Example: E.coli produces toxins that cause fever symptoms when we have food poisoning.
Viruses
Viruses are much smaller than bacteria.
All viruses are pathogens.
Viruses also produce toxins and they damage the cells in which they reproduce, leading to illness.
Viruses replicate by invading cells, reproducing inside them and bursting them.
This causes damage to tissues, leading to illness.
Examples:
HIV damages white blood cells, reducing immunity and leading to AIDS.
Influenza virus causes aches and fever symptoms.

5. Viral diseases
Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. Symptoms - it gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.
Transmission from plant to plant
TMV is very easily transmitted when an infected leaf rubs against a leaf of a healthy plant, by contaminated tools, and occasionally by workers whose hands become contaminated with TMV after smoking cigarettes. The virus can also contaminate seed coats, and the plants germinating from these seeds can become infected.
Treatment is to prevent the spread – e.g. cleaning tools.
Measles is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are treated by vaccinations against measles. Transmission - The measles virus is spread by inhalation of droplets from sneezes and coughs.
HIV initially causes flu-like symptoms. Once diagnosed HIV is treated with anti-viral drugs, this slows the replication of the virus, but cannot stop it.. Eventually the virus enters the lymph nodes and attacks the body’s immune system cells resulting in the development of AIDS. AIDS is when the body’s immune system is no longer able to deal with other infections or cancers.
Symptoms of AIDS include
Weight loss
Fatigue
Diarrhoea
Night sweats
Thrush
Rapidly progresses to the final stage
Dementia
Cancers (Kaposi’s sarcoma)
Death
HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.

6. Bacterial diseases Fungal diseases
Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.
Rose black spot is a fungal disease.
Symptoms
Purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced.
Transmission
It is spread in the environment by water or wind.
Treatment
Rose black spot can be treated
by using fungicides and/or removing and destroying the affected leaves.
Salmonella food poisoning is caused by bacteria. Transmission is due to bacteria eaten in food, or on food prepared in unhygienic conditions. In the UK, poultry are vaccinated against Salmonella to control the spread.
Symptoms - Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the
toxins they secrete.
Treatment.
If you have salmonella and a healthy immune system, your doctor may let the infection pass without giving any medicines. For serious infections antibiotics can also be prescribed.
Pain killers can be used to reduce temperature and relieve cramping. As with any infection that causes diarrhea, it's important to drink plenty of liquids to avoid dehydration.

7. Protist diseases - malaria
Most at risk are…
Infants
Children under 5
Pregnant women
Those who are HIV positive
- because all of these have weak immune systems
The pathogens that cause malaria are protists.
What is Malaria?
It is a disease caused by a single celled parasite called Plasmodium.
The malarial protist has a life cycle that includes the mosquito.
symptoms …
Malaria causes recurrent episodes of fever and can be fatal.
Chills
Fever
Exhausting sweats
Headache
Muscle aches
Tiredness
Transmission is by a vector – in this case mosquitoes.
The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten.
Prevention…
Nets are hung over beds, to prevent night-time mosquito bites. Since mosquitoes do most of their biting at night, nets can reduce malaria transmission by as much as 90% in areas with high usage. They are impregnated with a long-lasting insecticide to both kill and repel mosquitoes.
Habitat Reduction involves reducing mosquito breeding by draining the standing water in which their eggs hatch. Mosquitoes can lay eggs in very small amounts of water, so removing stagnant water from locations like old tires, mud puddles, or deep holes can cut down on transmission. Mosquitoes lay their eggs in so many locations, however, that habitat reduction is effective only on a household level, not a national level.
Indoor Residual Spraying (IRS) is exactly what it sounds like. The inside walls and other surface in houses are sprayed with pesticides designed to last for a long time. IRS does not prevent the mosquitoes from biting, but it kills them afterward, when they land on household surfaces, and stops mosquito reproduction and malaria transmission. To be effective, IRS must be applied to at least 70% of households in an area.
Drugs - Preventative treatment is provided to the two groups most at risk for death from malaria, pregnant women and infants. They get either steady or intermittent doses of the same drugs that treat malaria. It cannot keep them from becoming infected, but it will eliminate the malaria parasites that cause symptoms.
Life cycle of Plasmodium
First of all, a mosquito bites a human who is infected with malaria.
It sucks up human blood containing the Plasmodium parasite.
Plasmodium parasites reproduce and travel to the mosquitoes salivary glands.
When the mosquito bites another human, the parasites are injected into the new victim and travel to the liver causing liver damage. They then infect red blood cells. The parasite bursts the red blood cells (causing raging fever and exhausting sweats) releasing even more parasites. The parasites remain in the blood ready to be ingested when a female mosquito lands to feed.
If the victim is bitten by a mosquito during this phase, the mosquito will pick up the parasites and the whole cycle may start again ….

8. Name of disease Type of pathogen Symptoms Treatments Salmonella
Transmission/ how to prevent spread
Symptoms
Treatments
Salmonella
bacteria
Gonorrhoea
Rose black spot
Malaria
TMV (tobacco mosaic virus)
HIV
Measles

9. Human defence systems - 1
Bacteria and viruses (pathogens) have antigens on their outer cell surface; this makes it recognisable to our body that they are invaders and don’t belong.
Pathogens are recognised by the body due to their antigens and also by the fact that the body cells under attack release chemicals, such as histamine.
The immune system is split into non-specific and specific defence systems.
Non-specific defence systems of the human body involves barrier defence and inflammation and phagocytosis. This is fast acting and does not distinguish one pathogen from another.
Barrier defences
The human body defends itself against the
entry of pathogens.
• The skin is a barrier and produces antimicrobial secretions.
• The nose traps particles which may contain pathogens.
• The trachea and bronchi secrete mucus which traps pathogens and cilia waft the mucus to the back of the throat where it is
swallowed.
• The stomach produces acid which kills the majority of pathogens which enter via the
mouth.
If a pathogen manages to get through the barrier defences and enters the body the immune system tries to destroy the pathogen.
White blood cells help to defend against
pathogens by:
phagocytosis
antibody production
antitoxin production.
The immune system
The immune system defends our bodies against invading pathogens. The immune system consists of many different types of white blood cells. The two main types are
Phagocytes – these carry out phagocytosis
Lymphocytes – these make antibodies and antitoxins.

10. Human defence systems - 2
1. Phagocytosis – by phagocytes
If a pathogen manages to get through the barrier defences and enters the body the immune system tries to destroy the pathogen.
White blood cells help to defend against
pathogens by:
phagocytosis
antibody production
antitoxin production.
3. Antitoxin production - by lymphocytes
Antitoxins are made by lymphocytes. They neutralise any toxins the bacteria have produced which are making us feel ill.
2. Antibody production - by lymphocytes
Lymphocytes are SPECIFIC – they only recognise one specific pathogen (by the ANTIGENS on the pathogen).
Lymphocytes release ANTIBODIES – proteins that fit the antigens on the pathogen.
Antibodies can either kill the pathogen themselves or ‘label’ the pathogen to be ingested by a phagocyte.
Antibodies can work in 2 ways – Punching holes in microbes Or 2. sticking them together so they can’t move and they can be engulfed by phagocytes

11. Human defence systems - 3
Immunity and vaccinations
Natural Immunity – by a natural infection
The first time a pathogen invades our immune system a specific white blood cell comes across the pathogen, it will make an antibody to match that microbe’s antigen. The antibodies will coat the pathogen and kill it or make it easier to find by phagocytes. Memory cells are made and circulate in the blood for many years, so that if the pathogen enters a second time they make more antibodies faster. This means that the pathogen will be killed before it causes disease.
Herd immunity occurs when the vaccination of a significant portion of a population provides a measure of protection for individuals who have not developed immunity.
It arises when a high percentage of the population is protected through vaccination against a virus or bacteria, making it difficult for a disease to spread because there are so few susceptible people left to infect.

12. Human defence systems - questions How do we deal with disease?
Defence Mechanisms
What prevents pathogens entering the body?
White blood cells are part of the ____________________ what three things do they do to defend the body? 1. 2. 3.
How do we deal with disease?
You will need to be able to explain what a graph is showing you. Practice with this one.
Immunity
Describe how a natural infection causes immunity.
What is used to make a vaccine?
What can vaccines protect against?
How do vaccines work?
What is an antigen?
What is an antibody?
How can antibodies kill pathogens?
What do memory cells do?
What is the difference between antibodies and antitoxins?
Advantages of vaccination
Disadvantages of vaccination
Why is it necessary to continue to develop new vaccinations and medicines? 12

13. Antibiotics and painkillers
Alexander Fleming discovered antibiotics by accident. His lab was often a mess, however, this proved to be very fortunate. In 1928, Fleming was tidying his lab and came across a pile of petri dishes, which contained bacteria that he had forgotten he had been growing. Before placing the petri dishes into cleaning fluid, Fleming decided to take a look at them. One in particular made him stop and think. On closer examination, he realised that mould was growing on it. In itself this was nothing unusual but, on this particular sample, all around the mould the bacteria he had been growing was dead.
 Fleming wondered if it was the mould, a strain called Penicillium notatum, that had killed the bacteria. Fleming knew that he needed to test his prediction and, therefore, set up a control experiment. The experiment consisted of a petri dish, which contained the mould and bacteria, and one that did not. When he came back to look at the petri dishes, he observed that the bacteria around the mould were dead but that they continued to grow in the petri dish that did not contain the mould. He concluded that his prediction must be right.
Using drugs to treat disease
Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics.
The use of antibiotics has greatly reduced deaths from infectious bacterial diseases.
However, the overuse and misuse of antibiotics has caused some strains of bacteria to become resistant to antibiotics. This is of great concern, as if it is not slowed people will begin to die of bacterial infections again.
Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells.
It is difficult to develop drugs which kill viruses without also damaging the body’s tissues.
Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogens.
Traditionally drugs were extracted from plants and microorganisms.
• The heart drug digitalis originates from foxgloves.
• The painkiller aspirin originates from willow.
• Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.
Testing new drugs
New medical drugs have to be tested and trialled before being used to check that they are safe and effective.
New drugs are extensively tested for toxicity, efficacy and dose.
Preclinical testing is done in a laboratory using cells, tissues and live animals.
Clinical trials use healthy volunteers and patients.
• Very low doses of the drug are given at the start of the clinical trial.
• If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.
• In double blind trials, some patients are given a placebo, which does not contain the drug.
• Patients are allocated randomly to groups so that neither the doctors nor the patients know who has received a placebo and who has received the drug until the trial is complete. This is useful so researchers can compare the group taking the drug to a control group (without the drug). This helps them to decide if any differences are due to the drug.
Antibiotic resistance
Overuse and inappropriate use of antibiotics has increased the rate of development of antibiotic resistant strains of bacteria.
Pathogenic bacteria mutate, producing resistant strains.
Antibiotics kill individual pathogens of the non-resistant strain, the resistant ones survive and reproduce, passing on their resistance to their offspring, so the population of the resistant strain increases.
Many strains of bacteria, including MRSA, have developed resistance to antibiotics as a result of natural selection.
What can be done?
Doctor’s should only prescribe antibiotics when necessary – and not for viruses.
It is important that if you are prescribed antibiotics you take the whole course.
A lot of people will stop taking the antibiotic when they feel better.
If you do this, you leave a few bacteria inside your body.
These will reproduce, increasing the chance of some developing resistance.
Scientists are trying to develop new versions of the antibiotics.
Some antibiotics are developed but not used – just in case 13

14. Antibiotics and painkillers
Who discovered the first antibiotic?
What did he see that made him think that the mould made an antibacterial substance?
Using drugs to treat disease
What type of pathogen do antibiotics kill?
Explain the statement “It is important that specific bacteria should be treated by specific antibiotics.”
Why cant antibiotics be used to treat flu?
Why are viruses difficult to kill?
Why is it difficult to develop drugs that kill viruses?
What do painkillers do?
Name two painkillers.
What are the disadvantages of painkillers?
Traditionally drugs were extracted from plants and microorganisms.
Give two examples of drugs extracted from plants. 1 2
Testing new drugs
What are the three main things that drugs are tested for before they are used on patients?
What are drugs tested on before people?
List the stages of testing that follows on people. Explain each stage.
What is a double blind trial?
Why do researchers carry out double blind trials?
What is a placebo?
Antibiotic resistance
What has caused the swift development of antibiotic resistance?
How do bacteria become resistant to antibiotics?
How doe the population of resistant strains increase?
Name a resistant strain of bacteria.
What can be done?
Describe how we can slow the development of resistance. 14

15. A reminder – how to grow microbes
Growing Microoganisms cont.
The agar solidifies when left to cool.
Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms
Inoculating loops are used to transfer microorganisms to the media.
These must be sterilised by passing them through a flame:
The lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture.
In school and college laboratories, cultures should be incubated at a maximum temperature of 25oC.
This greatly reduces the likelihood of growth of pathogens that might be harmful to humans.
In industrial conditions higher temperatures can produce more rapid growth. 40oC would produce the maximum amount of growth without killing the bacteria.
Growing Microoganisms
Microorganisms = organisms that can only be viewed with a microscope.
Eg bacteria, viruses and fungi.
Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.
It is important that the culture is not contaminated with other microorganisms that may compete for nutrients or produce toxins.
Careful procedures are required to prevent potentially pathogenic microorganisms being released into the environment.
Culturing microorganisms
To study microorganisms, they need to be cultured.
They need to be provided with the conditions they need to reproduce quickly:
Nutrients
Warmth
Moisture
Bacteria and fungi can be grown in special media called agar.
This provides them with:
Carbohydrate
Protein or amino acids
Water
When agar is heated up it is liquid.
It can be poured into a Petri dish.
A circular plastic or glass dish with a lid:

16. Monoclonal antibodies – triple award only
What are monoclonal antibodies?
Polyclonal antibodies are a collection of many different types of antibodies
Monoclonal antibodies are a collection of a single type of antibody that is isolated and cloned.
How are monoclonal antibodies made?
B lymphocytes are the cells that produce antibodies.
A lymphocyte can divide several times to make clones of itself. But once it starts to make antibodies, it becomes a B lymphocyte and can’t divide anymore .
To get round this problem in a laboratory, a B lymphocyte is fused with a cancer cell (tumour cell). This creates a hybridoma. Tumour cells are long-lived and divide outside the body.
Making Monoclonal Antibodies
B lymphocytes are extracted from mice.
B lymphocytes are short-lived and do not divide outside the body, to enable them to divide and produce antibodies they are fused with tumour cells.
Tumour cells are long-lived and divide outside the body.
If B lymphocytes are fused with tumour cells a cell called a hybridoma is produced. These cells are long-lived cells that can divide outside the body and produce antibodies.
Detergent is added to a mixture of mouse B-lymphocytes and tumour cells to break down cell-surface membranes of both cells to help them fuse.
Once produced the hybridoma cells divide so there are lots of clones. All of the clones make the same type of antibody. These antibodies have come from cells cloned from a single cell and are called monoclonal antibodies. The antibodies produced are identical and can be used in several ways
Monoclonal antibodies have to be made in living cells because antibody proteins are far too complicated to be synthesised chemically in the laboratory.
What are Monoclonal antibodies used for?
Monoclonal antibodies have a wide range of applications:
Used in pregnancy testing kits
Used to treat cancer
Diagnostic tools for AIDS

17. Monoclonal antibodies – triple award only
Monoclonal antibodies are used in pregnancy tests
hCG hormone is detected during a pregnancy test. hCG hormone is found in pregnant women’s urine.
Antibodies for hCG are bound to a coloured bead (blue)
When urine is applied to the specified area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
Urine then moves up the stick to the test strip carrying any beads with it
The test strip contains antibodies to hCG that are stuck in place
The strip turns blue if hCG is present because the immobilised antibody binds to any hCG. If no hCG is present, the beads will pass through the test area without binding to anything, and so it won’t go blue.
If you are still unclear watch this video!
The development of monoclonal antibodies has provided society with the power and opportunity to treat diseases. However with this power and opportunity comes responsibility. The use of monoclonal antibodies raises some ethical issues.
Production involves the use of mice. These mice are used to produce both antibodies and tumour cells. The production of tumour cells involves deliberately inducing cancer in mice. Despite specific guidelines drawn up to minimise any suffering, some people still have reservations about using animals in this way.
Humanising Monoclonal Antibodies
Antibodies made from mouse cells can trigger an immune response in a patient.
Recent techniques use genetic engineering to ‘humanise’ hybridomas – replacing much of the antibody with the corresponding human antibody structure to prevent causing a harmful immune response in patients.
To eliminate the need for humanisation of the antibody, transgenic mice can be used. In this case, a human gene is placed in the mice to that they can produce human antibodies rather than mouse antibodies. This raises the whole debate surrounding the ethics of genetic engineering.
Monoclonal antibodies have been used successfully to treat a number of diseases, including cancer and diabetes, saving many lives. There have also been some deaths associated with their use in the treatment of multiple sclerosis.
Testing for the safety of new drugs presents certain dangers. In march 2006, six healthy volunteers took part in the trial of new monoclonal antibody (TGN1412) in London. Within minutes they suffered multiple organ failure, probably as a result of T cells overproducing chemicals that stimulate an immune response or attacking the body tissues. All the volunteers survived, but it raises issues about the conduct of drug trials.
The potential advantages of using monoclonal antibodies in the treatment of cancer are great because monoclonal antibodies only bind to the specific cancer cells that need treatment. Healthy cells are not affected at all. In contrast conventional drug treatment is carried all around the body in the blood and can have a devastating effect on healthy cells as well as cancer cells. Radiotherapy treatment is targeted on the area of the body affected by the cancer but still usually affects the healthy tissue in the area as well.
However monoclonal antibodies create more side effects than expected. Doctors and scientists thought they would act like a 'magic bullet' affecting only the diseased tissue. It hasn't quite worked out like that and monoclonal antibodies are not yet as widely used or as successful as everyone hoped.
Society must use the issues raised here, combined with current scientific knowledge about monoclonal antibodies, to make decisions about their production and use. We must balance the advantages that a new medicine provides with the dangers that its production and use might bring. Only then can we make informed decisions at an individual, local, national, and global level about the ethical use of drugs such as monoclonal antibodies.
Monoclonal antibodies are used in targeting cancer cells
Different cells in the body have different surface antigens
Cancer cells have antigens called tumour markers that are not found on normal body cells.
Monoclonal antibodies can be made that will bind to the tumour markers.
Anti-cancer drugs can also be attached to the antibodies
When antibodies come into contact with the cancer cells they will bind to the tumour markers
This results in the drug accumulating in the body where there are cancer cells.
Therefore the side effects of an antibody-based drug are lower then other drugs because they accumulate near specific cells.

18. Monoclonal antibodies – questions
What are monoclonal antibodies?
How are they different from polyclonal antibodies?
What is a B lymphocyte?
Why can’t B lymphocytes be used to make monoclonal antibodies?
Why do monoclonal antibodies have to be made in living cells?
How is a hybridoma created?
List four ways monoclonal antibodies can be used in science and medicine.
Why are cells from cancer tumours used to fuse with the B cells?
Why is detergent added to the mixture of B cells and tumour cells?
Create a table listing the advantages and disadvantages of using monoclonal antibodies.
List the ethical concerns surrounding the production of monoclonal antibodies.
List the ethical concerns surrounding the use of monoclonal antibodies.