GCSE Biology: Infection and Response

Communicable/infectious diseases

• Can be spread from person to person e.g. measles

How are communicable diseases spread?

By pathogens such as bacteria, viruses, protists and fungi.

Non-communicable disease

Cannot be spread from person to person e.g. coronary heart disease.

What are pathogens?

Microorganisms that cause infectious disease

• May be viruses, bacteria, protists and fungi

What may pathogens infect?

Plants and animals.

How can pathogens be spread?

• Direct contact (HIV)

• Water (cholera)

• Air/water droplets (influenza)

What is health?

State of physical and mental well-being

What can ill health be caused by?

• Communicable diseases

• Non-communicable diseases

• High levels of stress

• Other life situations e.g. working with harmful chemicals

How do bacteria make us ill?

• Because bacteria reproduce very rapidly, once inside the body.

• Bacteria can release harmful chemicals called toxins that damage tissues and make us feel ill.

How do viruses make us feel ill?

• Viruses invade a host cell. They then live and reproduce inside the host cells, causing cell damage (e.g. when virus leaves the cell, it can cause the cell to burst open and die).

How can we reduce the spread of pathogens?

• Washing your hands regularly

• Providing people with clean drinking water

• Using a condom during sexual intercourse

• Isolating infected patients

• Vaccination

Give examples of viral diseases

• Measles

• HIV

• TMV

What are measles?

A highly infectious viral disease that can be fatal if complications arise.

These complications can cause damage to the breathing system and the brain.

Because of this most children are vaccinated against measles when they are very young.

What are the symptoms for measles?

• Fever (usually first symptom)

• Red skin rash (usually after 3 days)

How are measles spread?

By inhalation of droplets from sneezes and coughs of infected person. (air)

What are the symptoms of HIV?

• Flu-like illness (first symptom and usually disappears after one or two weeks).

• Unless successfully controlled with antiretroviral drugs, the virus attacks the body’s immune system.

• Symptoms of damaged immune system- joint pain, muscle pain, swollen glands.

  Over time the immune system becomes severely damaged and when late stage HIV or AIDS occurs it becomes so badly damaged that it cannot deal with other infections or cancers (so now the patient can easily contract other infections and they can also develop cancer).

How can people with HIV be treated?

• With antiretroviral drugs- This stops the virus from multiplying inside the patient so the virus does not damage the patient’s immune system

• Patients who take antiretroviral drugs do not go on to develop late stage HIV/ AIDS and they can lead a normal life expectancy.

• Antiretroviral drugs are not a cure for HIV or AIDS. The patients must take these drugs for the rest of their life.

How is HIV spread?

Through the exchange of fluids between humans.

• This can spread by unprotected sexual intercourse

• This can be spread when drug users share infected needles. Blood containing HIV can pass in the needle from one person to another.

Examples of bacterial diseases

• Salmonella food poisoning

• Gonorrhoea

What can be killed by antibiotics?

Bacteria

What is salmonella food poisoning?

A bacterial disease spread by the ingestion of infected food

(food prepared in unhygienic conditions).

What are the symptoms of salmonella food poisoning?

• Fever

• Abdominal cramps

Where can salmonella bacteria often be found?

In poultry such as chicken.

How is the spread of salmonella controlled in the UK?

All chicken are vaccinated against salmonella. This controls the spread of the disease.

What is gonorrhoea?

A sexually transmitted disease

Symptoms of Gonorrhoea

• Thick yellow/green discharge from the penis or the vagina.

• Pain when urinating

How was gonorrhoea previously treated?

Using the antibiotic penicillin.

However now antibiotic resistant strains of bacteria are common.

How to stop the spread of gonorrhoea?

• Using a condom during sexual intercourse-stops the bacteria from flowing person to person.

• People who have unprotected sex should be tested for gonorrhoea- if they have it they can be treated with antibiotics to kill the bacteria before passing it on to someone else.

Example of protist disease

Malaria

What is malaria?

Malaria is a communicable disease spread by the malaria pathogen (which is a protist).

It can be fatal.

What are the symptoms of malaria

Recurrent episodes of fever

Life cycle of malaria.

• Mosquito bites someone infected with malaria

• The malaria pathogen then passes into the mosquito.

• The mosquito now bites a different person and passes the malaria pathogen to them.

What do scientists call the mosquito?

A vector- because it carries the malaria pathogen from one person to another person.

How to reduce the spread of malaria?

• Prevent the vector from breeding- mosquitos breed in still water

  • so we need to find areas of still water and drain them

  • spray area of still water with insecticide which kills mosquitos.

• Prevent the mosquitos from biting humans- sleep under a mosquito net because the mosquitos can’t get through and bite whoever is sleeping.

  • Can also spray the mosquito net with insecticide so that the mosquitos that land on it die.

What is the job of the non-specific defence system?

To prevent pathogens from entering the human body.

What are the 4 main parts of the human defence system?

• Skin

• Nose

• Trachea and bronchi

• Stomach

How does the skin defend us against pathogens?

• The skin forms a protective layer covering the body.

• The outer layer of the skin consists of dead cells, making it difficult for pathogens to penetrate.

• The skin also produces an oily substance called sebum, which can kill bacteria.

• When skin is damaged, it could allow pathogens to enter the body, so the skin scabs over to prevent this.

• (sometimes this doesn’t work and pathogens enter the body)

How does the nose defend us against pathogens?

• The nose has hair and mucus, which can trap pathogens before they enter the breathing system.

• Sometimes pathogens do make it past the nose and head for the lungs.

• (sometimes this doesn’t work and pathogens enter the body)

How do the trachea and bronchi defend us against pathogens?

• Sometimes pathogens do make it past the nose and head for the lungs.

• The trachea and bronchi are covered with tiny hairs called cilia, which are covered in mucus and can trap pathogens.

• The cilia then wafts the mucus upwards towards the throat where it is swallowed into the stomach.

• (sometimes this doesn’t work and pathogens enter the body)

How does the stomach defend us against pathogens?

• The cilia then wafts the mucus upwards towards the throat where it is swallowed into the stomach.

• The stomach contains hydrochloric acid which kills pathogens before they can make their way further down into the digestive system.

• (sometimes this doesn’t work and pathogens enter the body)

What does the immune system do?

• Destroy pathogens and any toxins they produce.

• Protects us in case the same type of pathogen invades us again

What do white blood cells do?

The immune system contains white blood cells which have 3 main functions

• White blood cells can ingest and destroy pathogens in a process called phagocytosis.

• White blood cells can destroy pathogens by making antibodies.

• White blood cells produce antitoxins, which stick to toxin molecules (produced by bacteria) and prevent them from damaging cells.

Describe phagocytosis

1. The white blood cell detects chemicals released from the pathogens and goes towards it.

2. The white blood cell then ingests/takes in the pathogens.

3. Then the white blood cell uses enzymes to destroy the pathogens.

Describe how white blood cells destroy pathogens by creating antibodies

1. Every invading pathogen has unique molecules, called antigens, on it’s surface. When some types of white blood cells come across a foreign antigen (one they don’t recognise), they will start to produce proteins called antibodies.

2. The antibodies lock onto the pathogen so that they can be destroyed. The antibodies produced are specific to that type of antigen.

3. Antibodies are then produces rapidly and carried around the body to find all similar bacteria or viruses.

4. Antibodies can remain in the blood for a very long time- so they can protect us if we get infected again with the same pathogen.

What is TMV?

A widespread plant pathogen affecting many species of plants including tomatoes. It causes the leaves to discolour in a mosaic pattern, which affects the growth of the plant, due to the lack of photosynthesis.

Example of fungal disease

• Rose black spot

What is rose black spot?

A fungal disease where 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.

How is rose black spot spread?

By water or by wind

How can the spread of rose black spot be reduced?

• Spray the plants with fungicides

• Remove infected leaves and destroy them.

How can vaccination prevent illness in an individual?

• Vaccination involves introducing small quantities of dead or inactive forms of pathogens into the body.

• (Because the pathogen is dead or inactive it cannot lead to disease in the patient.)

• This stimulates the white blood cells to produce antibodies against the dead or inactive pathogen.

• At the same time, the white blood cell divide by mitosis to produce lots of copies of itself.

• These copies can stay in the blood for decades, meaning that if the same pathogen now enters the body, even years later, the white blood cells can produce the correct antibodies quickly which prevents infection and illness in an individual.

How can vaccinations prevent the spread of pathogens in a population?

If people are vaccinated then they’re protected from certain diseases.

As a result, unvaccinated people are also protected because it’s far less likely for them to catch the disease because majority of the population are vaccinated so it’s less likely for the pathogen to be spread onto the unvaccinated people.

Scientists call this herd immunity

What did scientists discover around the 1940s?

The first antibiotic-penicillin

What can antibiotics be used against?

Bacterial diseases

What do antibiotics do?

Kill infective bacteria inside the human body without harming the body cells

What is antibiotic resistance?

When an antibiotic is no longer effective because the bacteria has evolved and can’t be killed by the antibiotic.

What causes antibiotic resistance?

Overusing an antibiotic

What do specific bacteria require in order to be killed?

Specific antibiotics

What can antibiotics not kill?

Viral infections/ viruses

What do painkillers do?

Treat the symptoms of disease but do not kill pathogens

Why is it difficult to develop drugs that kill viruses without also damaging the body’s tissues?

Because viruses live and reproduce inside human cells.

What were drugs traditionally extracted from?

Traditionally drugs were extracted from plants and microorganisms.

• The heart drug digitalis originates from foxgloves.

• The painkiller aspirin originates from willow.

• Penicillin was discovered by Alexander Fleming from the Penicillium mould.

Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.

Why are new medical drugs tested and trialled before use?

To check that they are safe and effective.

What are new medical drugs tested for before use?

• Toxicity- checking whether it is safe for humans

• Efficacy- check whether it treats the disease we’re looking at

• Dose- figuring out the best dose of the drug

What is preclinical testing carried out on?

Preclinical testing is carried out on cells, tissues and on live animals

Why is preclinical testing not carried out on humans?

Because the drug could be extremely toxic.

Clinical testing

Clinical testing is carried out on humans.

• First stage of clinical testing- Very low doses of the drug are given to healthy volunteers- This is to check the drug is safe in humans.

• If the drug is found to be safe then the clinical testing continues to find the optimal dose.

What is the optimal dose?

The best dose to treat the disease with the fewest side-effects

What is a placebo?

A tablet or an injection with no active drug in it.

Why do some patient get better when they’re given a placebo?

Because they think they’re being treated so they believe they’re going to get better.

Double-blind trial

• The test group receives the active drug.

• The placebo/control group receive a dummy drug which looks exactly like the active drug but it has no active ingredient.

• In a double blind trial, neither the patients nor the doctors know which people are receiving the active drug and which are receiving the placebo.

• This is to stop bias in case the doctors pay closer attention to people receiving the active drug.

What are antibodies produced by?

• White blood cells called lymphocytes.

• Lymphocytes produce antibodies against anything that the body detects as foreign (these foreign objects are called antigens)

What can scientists do with lymphocytes?

• Trigger them to produce antibodies- this can be very useful.

• For example, antibodies are used in pregnancy testing kits and certain cancer treatments.

What’s the problem with collected lymphocytes?

• They will not divide by mitosis.

• So, we fuse our lymphocytes with a tumour cell because tumour cells are very good at dividing by mitosis.

• The cells produced from this fusion is called a hybridoma?

What can hybridoma cells do?

• Produce antibodies and divide by mitosis.

• The antibodies produced from a single hybridoma clone are all identical.

• These are called monoclonal antibodies.

What are monoclonal antibodies?

• Antibodies produced from a single hybridoma clone

Describe stages of creating monoclonal antibodies from lymphocytes (mouse)

1. Inject mouse with an antigen, then lymphocytes will produce antibodies against the antigen.

2. Then collect the lymphocytes from the mouse.

3. The lymphocytes will not divide by mitosis so it’s fused with a tumour cell, producing a hybridoma cell.

4. Then select a single hybridoma cell producing the desired antibody and allow it to divide by mitosis to form a clone of identical hybridoma cells which are called monoclonal antibodies.

5. A large amount of the monoclonal antibody can then be collected and purified.

Key facts about monoclonal antibodies

• They’re produced from a single clone of hybridoma cells, meaning that that they are specific to one binding site on one protein antigen.

• The benefit of this is that monoclonal antibodies can target a specific chemical or specific cells in the body, meaning that it has a large number of uses.

• We can produce any monoclonal antibodies that we want.

Monoclonal antibodies in pregnancy testing

• Monoclonal antibodies are used to detect a specific hormone.

• This hormone is produced by the placenta of the developing foetus.

• Pregnancy kits based on monoclonal antibodies are cheap and easy to use- the woman simply urinates on a test strip and looks for a reaction.

• It’s also highly accurate if it’s used correctly.

Monoclonal antibodies to measure levels of hormones in blood

• Monoclonal antibodies can be used to measure the levels of hormones in blood.

• For example if someone’s tired all the time, they may not have a sufficient amount of certain hormones.

• So a blood sample is is taken and sent off for analysis- the test for these hormones uses monoclonal antibodies.

Uses of monoclonal antibodies: to detect pathogens in the blood

• Monoclonal antibodies can be used to detect pathogens in the blood e.g. viruses.

• Advantage of using monoclonal antibodies in these cases is that they are completely specific to what we’re looking for.

Use of monoclonal antibodies in cell or tissue

• Monoclonal antibodies can be used to locate or identify specific molecules in a cell or tissue.

Monoclonal antibodies: treating diseases

• Cancer cells undergo uncontrolled mitosis and they spread around the body.

• Scientists make antibodies specific to cancer cells.

• Then a radioactive substance or toxic drug can be attached to the antibody.

• When the antibody is injected into the blood, it attaches to the cancer cells and now the radioactive substance or toxic drug stops the cancer cells from growing and dividing.

• Advantage is that the antibody delivers the substance specifically to the cancer cells without harming other cells in the body.

• Disadvantage is that there could be very-harmful side effects.

Plant diseases

• TMV

• RBS

• Plants being attacked by insects such as aphids.

How do aphids cause plant disease?

• They extract nutrients such as sugars from the plant, stunting it’s growth.

How to detect plant disease?

• Stunted growth

• Spots on leaves

• Areas of decay/rot

• Growths

• Malformed stems or leaves

• Discolouration

• The presence of pests

How to identify signs of plant disease?

• Using a garden manual or website

• Take the infected plant to a lab to identify the pathogen

• Use testing kits containing monoclonal antibodies.

Is plant ion deficiency diseases caused by pathogens?

No

Plant ion deficiency diseases

• A lack of nitrate ion causes stunted growth as nitrate is needed for protein synthesis therefore growth.

• A lack of the magnesium ion causes the condition chlorosis, because magnesium is required to make chlorophyll.

  • In chlorosis, leaves leave their colour

Plant defence systems: Physical responses

• Cellulose cell walls- it’s difficult for microorganisms to penetrate.

• Tough waxy cuticle- makes it difficult for microorganisms to penetrate which protects the plant from attack.

• Layers of dead cells around the stem (bark on trees) acts as a barrier to entry by microorganisms

  • As bark ages, it eventually falls off and is replaced with fresh bark underneath.

Plant defence systems: Chemical responses

• Plants release antibacterial chemicals which kill bacteria and prevent them attacking the plant.

• Plants can release poisons to deter herbivores from grazing on the plant.

Plants defence system: mechanical response

• Sharp thorns directly protect a plant from being eaten by a herbivore.

• Other plants have hairs which irritate the mouth of herbivores, making the plant difficult to eat.

• Some plants droop or curl when they’re touched which can scare herbivores.

• Some harmless plants resemble harmful ones which protects the plant as herbivores are less likely to eat it as they can easily mistake it for a harmful plant.