4.3 Infection and response

Completed flashcard set

Define communicable diseases

Communicable diseases are diseases that can be spread from one organism to another

• They are spread by pathogens

What are pathogens?

Pathogens are microorganisms that cause infectious/ communicable disease

Name the types of pathogen and describe what they do

• Viruses

  • Viruses live and reproduce rapidly inside of cells, causing cell damage; they live inside of cells and replicate themselves rapidly to produce many copies of themselves. The cell will usually burst, releasing all of the new viruses; this cell damage is what makes you feel ill

• Bacteria

  • Bacteria are very small cells that may reproduce rapidly and produce poisons (toxins) that damage tissues and make us feel ill

• Protists

  • Protists are eukaryotic (and usually single-celled). Some protists are parasites that are often transferred to the organism by a vector (who doesn’t get the disease themself) and live on or inside other organisms and can cause them damage

• Fungi

  • Fungal cells are eukaryotes

Describe the ways in which pathogens can be spread

• By water

  • Eg. through drinking or bathing in dirty water

• By air

  • Eg. can be carried in the air by droplets produced from coughing or sneezing and inhaled

• By direct contact

  • Eg. by touch, by sexual intercourse

Name the three viral diseases

• Measles

• HIV (human immunodefficiency virus)

• TMV (tobacco mosaic virus)

Describe the symptoms of measles (and its complications), how it is spread, and how it is prevented

Measles is a viral disease.

• Fever

• Red skin rash

It is a serious illness that can be fatal if complications arise (eg. can lead to pneumonia or inflammation of the brain)

It is spread by inhalation of droplets from sneezes and coughs.

Many young children are vaccinated against measles when they are young

Describe the symptoms of HIV (and its complications), how it is spread and how it is prevented

HIV is a viral disease.

• Initially causes a flu-like illness

Unless successfully controlled by antiretroviral drugs, the virus attacks the body’s immune cells.

HIV can progress into AIDS which occurs when the body’s immune system becomes so damaged that it can no longer deal with other infections or cancers.

It is spread by unprotected sexual contact or exchange of bodily fluids (eg. blood when people share needles when taking drugs)

In the early stages, can be controlled by antiretroviral drugs which prevent the virus from replicating in the body.

Extra precautions should be taken to avoid infections from other diseases because the immune system is weak.

What do antiretroviral drugs do?

Prevent viruses from replicating in the body

Describe the symptoms of TMV, how it is spread and how it is prevented

TMV is a virus that affects many species of plants (including tomatoes, tobacco plants).

• It infects chloroplasts, causing a distinctive ‘mosaic pattern of discolouration on leaves’

This limits the plant’s ability to photosynthesise, which can affect the plant’s growth and leads to a reduction in crop yield

It is spread by plants touching one another.

Infected plants need to be removed and burned immediately and hands and equipment should be washed in between handling infected plants.

Name the two bacterial diseases

• Salmonella

• Gonorrhoea

Describe the symptoms of salmonella, how it is spread and how it is prevented

Salmonella is a type of bacteria that causes food poisoning

• Fever

• Stomach cramps

• Vomiting

• Diarrhoea

These symptoms are caused by bacteria and the toxins they secrete.

Salmonella is spread by bacteria ingested in food, or on food prepared in unhygienic conditions.

In the UK poultry are vaccinated against salmonella to control the spread.

Prepare food in hygienic conditions.

Describe the symptoms of gonorrhoea, how it is spread and how it is prevented

Gonorrhoea is a sexually transmitted bacterial disease

• Thick yellow or green discharge from the vagina or penis

• Pain when urinating

It is passed by sexual contact.

Was originally treated by antibiotic penicillin, however many strains of the bacteria have become resistant to it.
Spread can be controlled by treatment with antibiotics or the use of barrier method of contraception such as a condom.

Name the fungal disease

• Rose black spot

Describe the symptoms of rose black spot, how it is spread and how it is prevented

Rose black spot is a fungal disease

• Purple or black spots on leaves

• Eventually leaves turn yellow and drop off early

This reduces a plant’s capability for photosynthesis, so it affects growth

It spreads through the environment through spores in water or by wind. Spores can also be spread by direct transmission.

Can be treated using fungicide and by removing and destroying the infected leaves so that the fungus cannot spread to other plants.

Name the disease caused by a protist

• Malaria

What is a vector?

An organism that spreads infection by carrying and transmitting pathogens to other living things without causing the disease itself

Describe the symptoms of malaria, how it is spread and how it is prevented

The pathogens that cause malaria are protists

• Recurrent episodes of fever

• Diarrhoea

• Vomiting

• Headaches

Can be fatal

Part of the malarial protist’s life cycle takes place inside the mosquito; the mosquitoes are vectors (organisms that spread infection by carrying and transmitting pathogens to other organisms without causing the disease themselves); they pick up the malarial vector when they feed on an infected animal. Every time the mosquito feeds on another animal, it infects it by inserting the protist into the animal’s blood vessels.

Controlled by preventing mosquitoes from breeding (eg. by killing them using insecticides)

Using mosquito nets to avoid being bitten

Describe the two types of human defence systems

• Non specific: the defence fights against pathogens regardless of what type of pathogen it is or what type of disease it causes

• Specific: each antibody is specific to a particular pathogen

What is the purpose of the non-specific human defence system

To prevent pathogens from entering the body

Describe the non-specific human defence systems against pathogens

• Skin

  • Forms a barrier to pathogens that is difficult for pathogens to penetrate to enter the body

  • Secretes antimicrobial substances which kill pathogens

• Nose, trachea, bronchi

  • Hair and mucus in nose trap particles that could contain pathogens to prevent them from entering the respiratory system

  • Goblet cells in trachea and bronchi secrete mucus to trap pathogens to prevent them from entering the respiratory system

  • Lined with cilia (thin, hair-like structures) which sweep them back to throat where it can be swallowed into the stomach

• Stomach

  • Produces hydrochloric acid that kills pathogens

What is the purpose of the immune system?

• To destroy pathogens

• To neutralise toxins produced by pathogens

• Protect us in case the same pathogen enters the body again in the future

What are white blood cells? What is their purpose?

White blood cells are cells produced in bone marrow that defend the body against infection and diseased cause by pathogens

They do this through:

• phagocytosis

• antibody production

• antitoxin production

Describe the process of phagocytosis

Phagocytes are a type of white blood cell

• The white blood cell detects chemicals released by the pathogen and moves towards it

• The phagocyte binds to the pathogen

• The phagocyte engulfs and breaks down (digests) the pathogen, using enzymes to destroy it

Describe the process and purpose of antibody production

Antibodies are protein molecules produced by white blood cells

• Every pathogen has unique molecules (antigens) on its surface

• When B-lymphocytes come across a foreign antigen, they begin to produce antibodies

  • They may bind to the invading cells, causing the pathogens to clump together, so that they can be found and destroyed by other white blood cells like phagocytes more easily

  • They may cause lysis (pathogens to burst), killing them

  • Can bind to pathogens and destroy them

• The antibodies produced are specific to that type of antigen, so they will not bind to any other cells

• Antibodies are produced rapidly and carried around the body to find all similar bacteria or viruses

• Once a specific type of antibody has been produced by the immune system, it can rapidly produced again to kill the pathogen if the body is re-infected by the same pathogen

• This means that the person is now naturally immune to the pathogen and will not get ill

Describe the process and purpose of antitoxin production

• Antitoxins are a chemical that can be produced by white blood cells

• Antitoxins bind to toxin molecules and neutralise them, preventing them from damaging cells

Describe the process and purpose of vaccination

• Vaccination involves introducing small quantities of dead or inactive forms of a pathogen

• To stimulate the white blood cells (B-lymphocytes) to produce antibodies specific to that pathogen’s antigens

• If the same pathogen re-enters the body, the white blood cells respond quickly to produce the correct antibodies, preventing infection (as once a specific type of antibody has been produced, it can be rapidly produced again)

• This means that the individual has developed immunity against the pathogen

Give a way that the spread of pathogens can be reduced

• Mass vaccination can contribute to herd immunity

• By immunising a large proportion of the population, it reduces the spread of pathogens as the pathogen is unable to spread from person to person as immune individuals cannot catch the infection

Give the purpose of painkillers

Painkillers are drugs that treat the symptoms of the disease (eg. relieve pain), but do not kill the pathogens

Describe how bacterial disease can be cured

Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside of the body

• Specific bacteria should be treated with specific antibiotics

• Antibiotics cannot cure viral diseases

Explain the process of antibiotic resistance

• Bacteria can evolve rapidly because they reproduce at a fast rate

• Mutations in the DNA of bacteria can cause some bacteria to be resistant to antibiotics, producing new strains

• The resistant strains will not be killed when an individual takes antibiotics

• They survive and reproduce, passing on their antibiotic-resistant alleles to the next generation, so the population of the resistant strain increases

• As the non-resistant bacteria are killed, there is little competition (eg. for nutrients and space), so the population of resistant bacteria continues to increase

Why is it difficult to develop drugs that kill viruses?

As viruses reproduce inside of body cells, so it is difficult to develop drugs that destroy just the virus without harming the body’s cells

State the causes of antibiotic resistance

• Overuse of antibiotics in medicine and farming (as they add selection pressure which increases the rate of natural selection)

• Incompletion of antibiotics course

Where did drugs traditionally come from?

• Plants

• Microorganisms

Give the examples of drugs and the plants + microorganisms that they originated from

• The heart drug digitalis originates from foxgloves

• The painkiller aspirin originates from willow

• Penicillin was discovered by Alexander Fleming from 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

What are drugs tested for?

• Dosage

  • Testing to discover the optimum quantity required to treat the disease

• Toxicity

  • Testing to see if they are toxic and have harmful side effects

• Efficacy

  • Testing how effective the drug is against the disease

Describe the process of discovery and development of potential new medicines

There are three main stages in drug testing:

• Pre-clinical testing (done in a laboratory)

  • Drugs are tested using computer modelling

  • Drugs are then tested using human cells and tissues in a lab

  • Drugs are tested on live animals (to test efficacy, toxicity and dosage)

• Clinical testing

  • Phase 1

    • Drugs are tested on a small number of healthy volunteers to check that there are no harmful side effects when the body is working normally

    • At the start of the trial a very low dose of the drug is given and this is gradually increased (toxicity)

  • Phase 2

    • Drugs are tested on people suffering from the illness to test the efficacy and optimum dosage

  • Phase 3

    • Double blind trials: patients with the disease are randomly split into two different groups; one is given the new drug and the other is given a placebo (an inactive substance made to resemble a drug for researches to use as a control).

    • As the trials are double blind, neither the patient or doctors knows who has been given the drug or the placebo until the results are gathered; this is to reduce the placebo effect in patients and so doctors monitoring patients and analysing results aren’t subconsciously influenced by their knowledge

    • This is to compare the efficacy and toxicity of the new drug to other current drugs

What are monoclonal antibodies?

• Monoclonal antibodies are identical copies of a single type of antibody that is specific to one binding site on one protein antigen

  • This makes them able to target specific chemicals or specific cells in the body

• Monoclonal antibodies are produced from a single clone of cells (so that all of the antibodies made are identical and highly specific — needs clones as one cell can only produce a small amount of antibody)

They are produced from many clones of a single B-lymphocyte; therefore all of the antibodies are identical and are specific to the binding site of one protein antigen

Therefore, this means that they are able to target a specific chemical or specific cells in the body

Describe how monoclonal antibodies are produced

• Monoclonal antibodies are produced from many clones of a single white blood cell

• They are produced by injecting a mouse with a specific antigen to stimulate the mouse’s lymphocytes to make a particular antibody

• The lymphocytes are combined with a particular kind of tumour cell to make a hybridoma cell

• Find a hybridoma cell that produces antibodies that are specific to the pathogen antigen

• The hybridoma cell can both divide rapidly (due to the tumour cell) and produce specific antibodies (due to the lymphocyte)

• Scientists clone the single hybridoma cells (allowing them to divide)

• to produce many identical cells that all produce the same antibody

• A large amount of the antibody produced by the cloned hybridomas can be collected and purified

True or false: only pathogens have antigens on their surface

False. Virtually all cells have antigens on their surface that antibodies can bind to (allowing monoclonal antibodies to bind to specific target cells, hormones, chemicals etc.)

State and explain the uses of monoclonal antibodies

• For diagnosis such as in pregnancy tests

• In laboratories to measure the levels of hormones and other chemicals in blood

• To detect pathogens in blood

• In research to locate or identify specific molecules in a cell or tissue by binding them with a fluorescent dye

Firstly monoclonal antibodies are made that will bind to the specific molecules that you are looking for. The antibodies are then bound to a fluorescent dye.

If the molecules are present in the sample you’re analysing, the monoclonal antibodies will attach to them, and they can be detected using the dye.

• To treat some diseases

For cancer, the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells from growing and dividing. The monoclonal antibody can deliver the substance to the target cancer cells without harming other cells in the body.

Describe how pregnancy tests work

Pregnancy tests work using monoclonal antibodies

• A hormone is found only in the urine of women that are pregnant

• The bit of the stick that is urinated on has some antibodies that are specific to the hormone with blue beads attatched

• The test strip has some more antibodies that are specific to the hormone stuck onto it (so they cannot move)

• If you are pregnant and you urinate on the stick; the hormone in the urine binds to the antibodies on the blue beads

• The urine moves up the stick, carrying the hormone and the beads

• The hormone binds to the stuck antibodies on the test strip, so it is unable to move; as the hormones are also binded to the antibodies on the blue beads, the blue beads get stuck on the test strip and are also unable to move

• So the blue beads get stuck on the test strip, turning it blue

If you are not pregnant, the urine still moves up the stick carrying the blue beads, however there is nothing to stick the blue beads to the test strip, so it doesn’t go blue.

Give the advantages and disadvantages of monoclonal antibodies

Advantages: they can target specific cells (useful for cancer treatment)

Disadvantages: they create much more side effects than expected

State the ways that plant diseases can be detected by

• Stunted growth

• Spots on leaves

• Areas of decay (rot)

• Growths

• Malformed stems or leaves

• Discolouration

• The presence of pests

State the ways that you can identify plant diseases

• Reference to a gardening manual or website

• Taking infected plants to a laboratory where scientists can identify the pathogen

• Using testing kits that identify the pathogen using monoclonal antibodies

State the specific plant diseases

• Viral disease: tobacco mosaic virus

• Fungal disease: rose black spot

• Insects that can cause disease: aphids

Describe how plants can be damaged by a range of ion deficiency conditions

Plants need mineral ions from soil; if plants do not receive enough, they suffer deficiency symptoms

• Nitrates

  • Nitrates are needed for protein synthesis and are therefore needed for growth

  • Symptoms: stunted growth

• Magnesium

  • Magnesium ions are needed to make chlorophyll, which is needed to absorb light energy for photosynthesis

  • Symptoms: chlorosis (yellow leaves)

What is the difference between a plant’s physical defences and mechanical adaptations?

Physical: resist invasion by microorganisms and pathogens, protecting against infection

Mechanical: prevents physical consumption or damage

Describe plant’s physical defences

Physical defences are used to resist invasion of microorganisms and pathogens, protecting against infection

• Cellulose cell walls

• Tough waxy cuticle on leaves

• More regular shedding of layers of dead cells around stems (bark on trees) which fall off

These are all physical barriers that prevent pathogens from entering

Describe plant’s chemical defences

• Production of antibacterial chemicals (kill bacteria)

• Poisons to deter herbivores

Describe plant’s mechanical adaptations

• Thorns and hairs to deter animals

• Leaves which droop or curl when touched (to move away from things, knock insects off of them)

• Mimicry (appearing to be other harmful organisms) to trick animals into not eating them

Describe how insects can cause plant disease

Aphids!

• Feed on the sap of plants, depriving the plant of nutrients it needs to grow

• Reduced growth rate

• Leaves to discolour and curl

May also act as vectors, transferring pathogens

What are memory cells?

• After an infection with a specific pathogen, some of the specific antibody-producing lymphocytes remain in the bloodstream

• Known as memory cells

• So that if pathogen reinfects

• The immune response is much more rapid

• As the existing memory cells are able to divide rapidly,

• producing clones of the specific lymphocyte that can produce the specific antibodies to destroy the pathogen before its numbers can rise

• causing damage to cells and tissues

• preventing the individual from experiencing symptoms

Are lymphocytes specific to pathogens?

Yes each lymphocyte is specific to one type of antigen

• Once it binds to the specific antigen, it rapidly divides by mitosis to increase numbers of lymphocytes that produce that specific antibody

Give reasons why placebos and double-blind trials are used to trial drugs

Placebo:

• Take into account psychological effect

• To provide a comparison

Double blind trial:

• Doctors/nurses treating differently, avoiding biased results

Double blind: avoiding bias

Why is cancer treatment difficult? (Monoclonal antibodies are useful for solving this issue)

• Cancer (uncontrollable cell division) can occur in any type of cell or tissue

• So are difficult to target

Why are monoclonal antibodies so useful for cancer treatment?

• Monoclonal antibodies are antibodies produced from a single clone of identical hybridoma cells

• They are specific to the binding site of one specific protein antigen

• Monoclonal antibodies can be produced to be specific to any antigen

• Antibody can be created to be specific to target antigen on cancer cells/ tumour

• Radioactive substance/ chemical can be attached to antibody

• When monoclonal antibodies bind to the cancer cells, so will the chemical, which will stop the cancer cells from dividing

A scientist noticed that in one area the gorse plants had yellow leaves and had stunted growth.

One reason for yellow leaves and stunted growth is a deficiency of nitrate ions in the soil.

Explain four other possible reasons for the yellow leaves and stunted growth.

Do not refer to nitrate ions in your answer.

• Lack of magnesium ions

  • Magnesium is responsible for producing chlorophyll; not enough chlorophyll for sufficient photosynthesis

• Infection by pathogen

  • Leaves become discoloured so less photosynthesis

• Infected by aphids

  • Aphids pierce plant tissues and remove sugars from phloem

• Lack of available light

  • So chlorophyll breaks down

Not enough glucose to make proteins for growth

Or to release energy for growth