infection and response

Pathogens - microorganisms that enter the body and cause disease

• cause communicable diseases
• both plants and animals can be infected by pathogens

For example - bacteria, viruses, protists, fungi

Bacteria - very small cells, which reproduces rapidly inside the body

• make you feel ill 
• produces toxins that damage cells and tissues

For example - salmonella bacteria can cause food poisoning

Viruses - are not cells and are very tiny, they reproduce very quickly

• live inside cells and replicate themselves 
• cell will then burst, releasing all new viruses
• cell damage is what makes you feel ill

For example -  HIV infects and destroys that helps defends body against disease. HIV sufferers are more likely to get ill from infection by other pathogens

Protists - are all eukaryotes and most of them are single-celled

Parasites - live on or inside other organisms and can cause them damage, transferred to the organism by a vector

Vector - carries parasites without getting the disease itself

For example - malaria caused by a protist that lives inside a mosquito

Fungi - some are single-celled, others are made up of hyphae

Hyphae - thread-like structures that grow and penetrates human skin and plant surfaces causing diseases. Produces spores which spread to other plants and animals

For example - black spot fungus that infects rose plants

Water

• picked up by drinking and bathing in dirty water
• cholera is a bacterial infection spread by drinking water contaminated with diarrhoea

 Air

• carried through the air and then breathed in
• influenza virus causes flu 

Direct contact

• picked up by touching contaminated surfaces including skin
• athlete's foot spread by touching same things as infected person

Measles - a viral disease

• spread through droplets from an infected person's sneeze or cough

Symptoms

• develop a red skin rash
• fever

Risks

• lead to pnuemonia
• encephalitis (brain infection)

Prevention

• vaccination

HIV - a virus spread by sexual contact or by exchanging bodily fluids

Symptoms

• flu in first few weeks
• no symptoms for a few years

Risks

• attacks immune system
• body can't cope with other infections or cancers

Prevention

• controlled with antiretroviral drugs

TMV -  a virus that affects many species of plants

Symptoms

• mosaic patterns on leaves
• discoloured leaves

Risks

• can't carry out photosynthesis
• affects growth of plant

Rose black spot - a fungus that spreads through the environment in water or by wind

Symptoms

• purple or black spots
• yellow leaves
• leaves drop off

Risks

• less photosynthesis can happen
• plant doesn't grow well

Prevention

• fungicides
• destroying plant of affected leaves

Malaria - caused by a protist

Causes

• mosquitos feed on other animals
• infects it by inserting protists into blood vessels

Symptoms

• repeating episodes of fever

Prevention

• spraying exposed skin with insect repellant
• sleeping under a mosquito net

Salmonella - a type of bacteria that is caught by eating food that has been contaminated by that bacteria

Symptoms

• fever
• stomach cramps
• vomiting
• diarrhoea

Prevention

• UK poultry gets vaccinated

Gonorrhoea - a sexually transmitted disease that is passed on by having unprotected sex

Symptoms

• pain when they urinate
• thick yellow/green discharge from vagina or penis

Prevention

• use contraception
• treated with antibiotics

Being hygienic

• washing hands

Destroying vectors

• using insecticides
• destroying their habitat so they can't breed

Isolating infected individuals

• medical staff wearing protective clothing

Vaccination

• getting the different meningitis vaccines

Body's defenses 

• skin - acts as a barrier to pathogens, secretes antimicrobial substances that kill pathogens
• hairs and mucus - trap particles containing pathogens
• trachea and bronchi - secrete mucus to trap pathogens
• cilia - waft mucus to the back of the throat where it can be swallowed
• hydrochloric acid in the stomach - kills pathogens that make it far from the mouth

• white blood cells engulf foreign cells and digest them (phagocytosis)
• produces antibodies that counteract toxins
• white blood cells produce proteins (antibodies)
• antibodies produce rapidly and are carried around the body
• antibodies kill pathogens
• person is now naturally immune to that pathogen

Vaccination - small amounts of dead or inactive pathogens

• carry antigens causing white blood cells to produce antibodies to attack them
• white blood cells rapidly mass-produce antibodies to kill off the pathogens
• when vaccinated, the person is immune to that pathogen and won't get ill       

For example - the MMR vaccine is given to children, it contains weakened versions of measles, mumps, and rubella all in one vaccine                           

Pros

• helped control lots of infectious diseases 
• big outbreaks of disease (epidemics) can be prevented

Cons

• vaccines don't always work
• don't give you immunity
• sometimes you can have a bad reaction

Painkillers - drugs that relieve pain

• don't tackle the cause of disease
• help reduce symptoms

For example - lots of 'cold remedies' don't cure colds - they have no effect on the cold virus itself

Antibodies - drugs that kill the bacteria that is causing the problem

• don't kill your own body cells
• don't destroy viruses
• reduces the number of deaths from communicable diseases

• bacteria can mutate
• mutations cause bacteria to be resistant to an antibiotic
• only non-resistant strains of bacteria will be killed
• individual resistant bacteria will survive and reproduce
• natural selection

Slowing the development down

• important for doctors to avoid over-prescribing antibiotics
• important to finish the whole course of antibiotics

Aspirin

• used as a painkiller and to lower fever
• developed from a chemical found in willow

Digitalis

• used to treat heart conditions
• developed from a chemical found in foxgloves

Penicillin

• discovered by Alexander Fleming
• developed from mould on a Petri dish producing a substance that killed bacteria

Main 3 stages

1. preclinical testing on human cells and tissues

2. preclinical testing on live animals

3. clinical testing on human volunteers

Cells and tissues

• tested on in a lab
• can't test drugs that affect the whole body on cells and tissues

For example - testing a drug for blood pressure must be done on a whole animal because it has an intact circulatory system

Live animals

• to test whether the drug works and produces the effect (efficacy)
• to find out how harmful it is (toxicity)
• to find out the concentration that should be given (dosage)
• the safest way to make sure a drug isn't dangerous before given it to humans

• if the drug passes the test on animals then tested on human volunteers

1) drug is tested on healthy volunteers

2) low dosage of the drug is given then gradually increased

3) drugs can now be tested on people suffering from the illness

4) now the optimum dose is found

Placebo - a substance that is like the drug being tested but it doesn't do anything

Placebo effect - when the patient expects the treatment to work and so feels better even though the treatment doesn't do anything

• patients get put into 2 groups
• group 1 was given the new drug
• group 2 was given a placebo

Blind trials - the patient doesn't know whether they're getting the drug or placebo

Double-blind trials - neither the patient nor the doctor know until all the results have been gathered

Thalidomide - a sleeping pill

• developed in the 1950s
• relieves morning sickness
• not drug tested
• started causing abnormal limb development
• drug was banned
• now they have restarted testing it
• it is now used in the treatment of leprosy and other diseases

Lymphocytes - type of white blood cells

Hybridoma cells - cloned to get lots of identical cells

• antibodies produced by B-lymphocytes
• monoclonal antibodies produced from clones of lymphocytes
• all antibodies are identical
• tumor cells don't produce antibodies but divide lots
• antibodies are collected and purified
• only bind to target specific molecules

Test stick

• has antibodies to the hormone with blue beads attached

If pregnant

• urine moves up the stick, carrying the hormone and beads
• beads and hormones bind to antibodies on the test
• stick turns blue

If not pregnant

• urine moves up a stick, only carrying the blue beads

Control window

• shows if the test has worked properly or not
• control window should match the stick

Cancer cells - have antigens on their cell membranes that aren't found on normal body cells (tumour markers)

Anti-cancer drug

• attaches to these monoclonal antibodies
• could be a radioactive substance, toxic drug or a chemical
• stops cancer cells from growing and dividing
• antibodies giving to the patient through a drip
• these antibodies only bind to tumour markers
• the drug kills cancer cells
• doesn't kill normal body cells near the tumour

Monoclonal antibodies

• used to bind to hormones and other chemicals
• used to measure blood levels
• used to test blood samples in labs for certain pathogens

For example - ELISA test used to detect banned drugs in athletes' urine

For example - pathogen strains that cause gonorrhoea can be identified using monoclonal antibodies

Monoclonal antibodies

• used to locate specific molecules on a cell or in a tissue

In research

1. monoclonal antibodies made that will bind to specific molecules

2. antibodies are bound to a fluorescent dye

3. if monoclonal antibodies are present they can be detected by the dye

Advantages

• cancer treatment
• lower side effects than for standard chemotherapy/radiotherapy

Disadvantages

• cause fever, vomiting, and low blood pressure 
• not as widely used as treatments as scientists thought they would

Deficiency diseases

• nitrates needed to make proteins and therefore growth 
  • lack of nitrates causes stunted growth

• magnesium needed to make chlorophyll for photosynthesis
  • lack of magnesium suffer from chlorosis and yellow leaves

Pathogen diseases

• infected by viral, bacterial, and fungal

• plants can also be infested and damaged by insects
• easy to spot

For example - aphids are an insect that can cause huge damage to plants

Common signs of disease

• stunted growth
• spots on leaves
• patches of decay
• abnormal growths
• malformed stems or leaves
• discoloration

For example - a fungal disease called brown rot affects fruit on plum trees, causing plums to go brown and rot

For example - crown gall is a bacterial disease that causes growths on plants

Examples

• looking up signs in a gardening manual or on a website
• taking the infected plant to a lab, where scientists identify the pathogen
• using test kits to identify pathogens using monoclonal antibodies

Physical defences

• waxy cuticle - providing to stop pathogens entering
• cell walls made from cellulose - stop pathogens entering after passing through the cuticle
• layers of dead cells - barrier to stop pathogens entering

Chemical defences

• antibacterial chemicals - which kill bacteria 
• poison - which can deter herbivores 

Mechanical defences

• thorns and hairs - stop animals from touching or eating them 
• drooped or curled leaves - knocks insects off  
• plants mimic other organisms - tricks other plants to not eat them