biology unit 3: infection and responce

spread by

direct contact

water or air

vectors (organisms that carry the pathogen without getting infected)

reduce by:

hygiene measures such as washing hands and sneezing into a handkerchief.

destroying or preventing vectors e.g mosquito nets.

isolation of infected individuals

vaccination.

virus.

e.g measles - fever and red skin rash. spread through coughing and breathing in droplets from these. fatal if complications.

e.g 2 HIV --> AIDS - sexual contact or exchange oif bodily fluids. - flu like illness - if untreated -> enter lkynth nodes and attack immune cells - antiviral drugs

bacteria

damage cells directly or produce toxins that damage the tissues.

reproduce rapidly in cells and cause them to burst.

salmonella - food poisioning - food that isnt coioked properly or not prepared in hygenic conditions. - toxins cause fever adominal pain, vomiting and dirrhoea.

gonorrhoea - std - thick yellow or green discharge from vagina or penis when urinating. - used to be treated with penicillin but some are now resistant. - use barrier contraception such as condom.

protists.

single celled organisms that are eukaryotic.

malaria - travels by vector (mosquito) bites - seveere fever - fatal - killing mosquitos or using nets.

fungal

rose black spot - spores carried from plant to plant by water or wind - purple or black spots on leaves turn yellow and drop early - stunt the growth as photosynthesis reduced - fungicides and removing and destroying infected leaves to treat.

body defenses against pathogens,

enzymes in tears destory microorganisms,
the nose traps particles that contain pathogens
sheet of mucus traps particles and bacteria - cila create a wave motion which sweeps mucus along.
glands produce hydrochloric acid which kills bacteria in food.
skin. sebaceous gland produced sebum which kills bacteria and fungi.

white blood cells.

phagocytosis - microorganisms invade the body , wbc finds microorganism and engulfs it, wbc injects the microorganism, destroyed and digested.

antibody - attach to antigen molecules on pathogen, antigens are markers on the surface of the microorganism. wbcs become sensitised to antigens and produce antibodies. antibodies then lock onto antigens. causes microorganisms to clump together so that other wbcs can digest them

vaccination

small quantities of dead or weakened form of pathogen injected.

antibiotics.

only kill bacteria. Due to overuse superbugs are resistant. e.g MRSA.

to reduce this: dont take antibiotics unless really needed, for non serious infections, for viral infections, complete antibiotic corse to kill all bacteria.

required practical

  1. inoculate petri dish with a culture of bacteria,
  2. soak small disks of filter paper in different antibiotics,
  3. using forceps, plate antibiotic discs ion surface of agar plate
  4. incubate the sealed dish upside down at 25 degrees for several days.

independent variable - type of antibiotic. dependant variable - area around each disk that is clear of bacteria
control variables - conc of antibiotic, Lengh of time the discs are soaked.

digitalis - heart drug from foxgloves.
aspirin - painkiller from willow tree
penicillin from mould.

trials.

new drugs tested before human trials to see if it is non toxic.

then tested on pateints to find if it works and to find optimum dose.

double blind trials - some patients given a placebo and other real drug. nor doctor or pateint knows which is which.

monoclonal antibodies

produced from a single cell that is tumerous to divide many times to clone itself. antibodies only bind to one antigen so can target a specific antigen. mouse cell + tumour cell = hybridoma.

used in: pregnancy tests.- bind to hormone HCG found i9n urine in pregnancy.
levels of chemicals and hormones in blood to detect pathogens
some disease treatment - cancer to deliver a radioactive substance, toxic drug or chemical that stops cells dividing.
Many side effects so not widely used.

identifying plant disease.

stunted growth, spots of leaves, areas of decay, growths, malformed stems or leaves, discolouration, presence of pests.
identify the disease - gardening manual or website, infected plants to laboratory to identify pathogen - testing kits which contain monoclonal antibodies.

examples of plant diseases.

tobacco mosaic virus - infects tobacco plans + others including tomatos - mosaic pattern of discolouration. reduced chlorophyll and stunted growth

plant defenses.

aphids - greenfly or black fly. feed from phloem. taking sugars away from plant.

deficiency diseases. stunted growth = nitrate deficiency. needed for protein synthesis.
chlorosis = magnesium deficiency. magnesium ions for chlorophyll.

cellulose cell walls, tough and waxy cuticle on leaves. layers of dead cells around stems which fall off and take pathogens with them.

some chemical defenses - antibacterial chemicals - mint and witch hazel. poisons deter herbivores - tobacco, foxgloves and nightshade.

mechanical adaptations - thorns and hairs to deter animals from eating or touching them, leaves that droop or curl when touched.
mimicry. trick animals. e.g white dead nettle doesn't sting but looks like stinging nettle.