infection and response

Communicable Diseases

• pathogens are microorganisms which can cause infectious diseases - these can spread through direct contact, by water or by air and can infect people, animals and plants

Viruses

• very small

• they move into cells and use the biochemistry to make copies of itself

• this leads to cells bursting and releasing the copies of the virus into the bloodstream

• the damage and destruction of the cells makes the individual feel ill

Viral Diseases

• Measles

  • symptoms: fever, red skin rash, can lead to pneumonia and blindness

  • how it’s spread: droplet infection

  • prevention: MMR vaccines for young children

• HIV

  • symptoms: flu-like symptoms then virus attacks immune system leading to AIDS (body in a state where it is susceptible to many different diseases)

  • how it’s spread: sexual contact or exchanging bodily fluids

  • prevention: use condoms, not sharing needles, use of antiretroviral drugs (to prevent development of AIDS)

• Tobacco Mosaic Virus

  • symptoms: discolouration of the leaves so infected part cannot photosynthesise resulting in reduction of yield

  • how it’s spread: contact between diseased and healthy plants, insects as vectors

  • prevention: good field hygiene and pest control, growing TMV-resistant strains

Bacteria

• small

• they multiply very quickly through dividing by a process called binary fission

• produce toxins which can damage cells and make you feel ill

Bacterial Diseases

• Salmonella Food Poisoning

  • symptoms: fever, stomach cramps, vomiting, diarrhoea

  • how is it spread: found in raw meat and eggs, unhygienic conditions

  • prevention: poultry vaccinated, keep raw meat away from cooked food, wash hands and surfaces when cooking/handling raw meat, cook food thoroughly

• Gonorrhoea

  • symptoms: thick yellow or green discharge from the vagina / penis, pain when urinating

  • how it’s spread: unprotected sex

  • prevention: using contraception eg. condoms and antibiotics (some strains are antibiotic resistant)

Fungi

• they can either be single celled or have a body made of hyphae

• they can produce spores which spread to other organisms

• spread by direct contact, air, water

Fungal Diseases

• Rose Black Spot

  • symptoms: purple or black spots on leaves of rose plants reducing the area of the leaf available for photosynthesis, leaves turn yellow and drop early

  • how it’s spread: spores of the fungus are spread by rain or wind

  • prevention: using fungicides or stripping plant of affected leaves by burning them

Protists

• some are parasitic meaning they use humans and animals as their hosts

Protist Diseases

• Malaria

  • symptoms: fevers and shaking

  • how it’s spread: the vector is the mosquito in which the protists reproduces sexually - when mosquito punctures skin to feed on blood, protists enter human bloodstream via saliva

  • prevention: insecticide coated insect nets while sleeping, removing stagnant water to prevent vectors from breeding, travellers taking antimalarial drug to kill parasites which enter

Human Defence System

• non-specific defence system = works to prevent pathogens from entering the body

• Skin

  • physical barrier

  • produces antimicrobial secretions to kill pathogens

  • good microorganisms known as skin flora compete with bad microorganisms for space and nutrients

• Nose

  • has hairs and mucus which trap pathogens stopping them from entering lungs

• Trachea and Bronchi

  • secrete mucus to trap pathogens

  • lined with cilia waft mucus upwards so it can be swallowed

• Stomach

  • hydrochloric acid kills any pathogens in mucus or food and drink

Specific Immune System - WBC

• Phagocytosis

  • phagocytes = engulfs pathogen which destroys them so they can no longer make you feel ill

• Producing antibodies

  • lymphocytes = produce antibodies

  • each pathogen has an antigen on their surface which wbcs can detect

  • antigens have a structure which a specific complementary antibody can bind to

  • phagocytes can detect antibody bound pathogens to engulf them

  • antibodies which are not used are stored as memory cells

  • if you become infected again with the same pathogen, lymphocytes produce specific antibodies at a faster rate so the individual will not feel symptoms of the illness

• Producing antitoxins

  • lymphocytes = produce antitoxins which neutralise the toxins released by the pathogen by binding

Vaccination

• dead or inactivated form of the pathogen

• stimulates wbc to produce antibodies complementary to the antigens on the pathogen

Antibiotics and Painkillers

antibiotics = medicines that kill bacterial pathogens without damaging body cells

pain killers = medicines that treat symptoms of disease - not the cause

• Antibiotics

  • can be taken as pill, syrup or directly into bloodstream

  • different antibiotics for different bacteria so correct one must be taken

  • decreased number of deaths from bacterial diseases

    eg. penicillin

  • mutation can occur during reproduction resulting in antibiotic-resistant bacteria

  • antibiotic that used to be effective no longer work

• to prevent development of resistant strains:

  • don’t overuse antibiotics - unnecessary exposure of bacteria to antibiotics

  • finishing courses of antibiotics to kill all of the bacteria

Discovery and Development of Drugs

• many drugs were initially discovered in plants and microorganisms

• new drugs are mainly synthesised by chemists

• they need to be tested for toxicity, efficacy (how well they carry out their role), dose

• this is done through preclinical testing and clinical trials

• Plants

  • the chemical that plants use to kill pests and pathogens can be used to treat symptoms or human diseases

    • aspirin is used as a painkiller (from willow)

    • digitalis is used to treat heart problems (from foxgloves)

• Microorganisms

  • penicillin

    • Alexander Fleming was growing bacteria on plates

    • he found mould on his culture plates with clear rings around the moult indicating there was no longer any bacteria there

    • he found that the mould produced penicillin which killed bacteria

Any new drugs being developed need to be tested to ensure they are and effective

• preclinical testing = using cells, tissues and live animals

• clinical testing = using volunteers and patients

• first tested on healthy volunteers with a low dose to ensure no harmful side effects

• then drugs are tested on patients to find most effective dose

• placebo = appears to look like the drug but has no active ingredient so no effect

• single-blind trial = only the doctor knows whether the patient receives the drug or placebo

• double-blind trial = both doctor and patient don’t know whether patient receives drug or placebo; to eliminate biases

• results must be peer reviewed by other scientists to check for repeatability

Plant Disease

Signs of plant disease

• spots on leaves - rose black spot

• areas of decay - rose black spot / blights on potatoes

• abnormal growths - crown galls caused by bacterial infection

• discolouration - TMV / magnesium deficiency

Identify disease plant has by:

• using a gardening manual or website

• identifying pathogen by observing infected plant in lab

• test using monoclonal antibodies to identify the pathogen

Ion deficiencies

• nitrate deficiency

  • can stunt growth

  • nitrates in soil convert sugars made in photosynthesis into proteins

  • proteins are needed for growth

• magnesium deficiency

  • can cause chlorosis

  • magnesium is needed to make chlorophyll

  • green pigment which is vital for photosynthesis

  • if less is made parts of the leaves appear yellow which is known as chlorosis

Plant Defence

Physical - to prevent invasion by microorganisms

• tough waxy cuticles to stop entry into leaves

• cellulose walls form physical barrier into the cells

• plants have layers of dead cells around stems which stop pathogens entering

Chemical - to deter predators or kill bacteria

• poisons eg. foxgloves, tobacco plants deter herbivores which eat plants

• antibacterial compounds kill bacteria such as mint plant and witch hazel

Mechanical

• thorns and hairs make plants difficult and painful for animals to eat

• some leaves droop when touched allowing them to move insects off their leaves

• mimicry to trick animals:

  • some plants look unhealthy so animals avoid them

  • patterns which look like butterfly eggs so butterflies avoid laying eggs there to avoid competition

Monoclonal Antibodies

• identical antibodies produced from the same immune cell

  • their ability to bind to only one antigen can be used to target chemicals and cells in the body

How they’re produced

• scientists obtain mice lymphocytes which have been stimulated to produce a specific antibody

• they are combined with tumour cells to form a hybridoma cell

• the hybridoma can divide rapidly to produce clones of itself which all produce the same antibody

• the antibodies are collected and purified

Uses

Pregnancy Tests

• hCG is a hormone present in urine of pregnant women

• there are two sections of the stick

  • 1 - mobile antibodies complementary to hCG and are attached to blue beads

  • 2 - stationary antibodies complementary to hCG

• individual urinates on first section and if hCG is present, it binds to mobile antibodies with blue beads forming hCG/antibody complexes

• they are carried in flow of liquid to second section

• stationary antibodies bind to hCG/antibody complexes

• results in a blue line because of blue beads

• this indicates positive pregnancy test

Measuring and Monitoring in Labs

• monoclonal antibodies modified to bond to specific molecules for different hormones / chemicals in the blood

• antibodies bound to fluorescent dye

• dye can be observed if molecules are in the sample and antibodies bind to them

  eg. screening donated blood for HIV infections

Treatment of Cancer

• producing monoclonal antibodies which bind to tumour marker on cancer cells to stimulate immune system to attack the cell

• producing monoclonal antibodies which bind to receptor sites on the cell surface membrane so growth-stimulating molecules cannot bind and stops cell from dividing

• using monoclonal antibodies to transport toxic drugs, chemicals or radioactive substances as they can only bind to cancer cells