Biology 3

Pathogens (viruses, bacteria, protists & fungi)  cause infectious diseases

-infect plants & animals

-spread by direct contact, air or water

Bacteria & viruses reproduce quickly inside body

-produce toxins= damage tissues (made humans ill)

Viruses live & reproduce inside cell= cell damage

Measles = viral disease (can be fatal)

-fever & red skin rashes

-spread by inhalation of droplets (through sneezing & coughing)

-young are vaccinated

HIV = flu like illness & attacks body's immune cells

-late stage immune system is damaged (can't deal with infection/ cancer)

-spread through sexual contact, body fluids or blood through shared needles

Tobacco Mosaic virus(TMV)= plant pathogen affecting many plant species (tomatoes)

-give mosaic pattern of discolouration on leaves

-affects growth through lack of photosynthesis

Salmonella= sprad though bacteria ingested in food or food prepared in unhygienic conditions

-poultry vaccinated against Salmonella (control spread)

-causes fever, abdominal cramps, vomitting & diarrhoea (caused by bacteria & toxins)

Gonorrhoea= sexually transmitted disease (spread through sexual contact)

-thick yellow or green discharge from reproductive organs or pain urinating

-caused by bacterium & treated with antibiotic penicillin (only until resistant strains appear)

-spread controlled by antibiotics & barrier methods

Rose Black spot= fungal disease (purple or black spots appear on leaves turn yellow & drop early)

-affects growth (photosynthesis reduced)

-spread through environment (water/wind)

-treated with fungicides / removing & destroying affected leaves

Malaria= caused by protists (pathogen)

-has life cycle (include mosquito)

-caused recurrent episodes of fevers & can be fatal

-controlled by preventing vectors (mosquitos) breeding & using nets (prevents biting)

The human body protects against pathogens with (non -specific defence systems):

-skin

-nose

-trachea & bronchi

-stomach

Immune system defends body against disease by trying to destroy pathogens 

White blood cells help defend by:

-phagocytosis

-antibody production

-antitoxin production

Vaccination prevent illness & reduce the spread of pathogens to the population

Vaccination:

-small quantity of dead/ inactive pathogen into body

-white blood cells stimulated to produce antibodies

-if same pathogen re-enters body WBC responds quickly to prevent infection

Antibiotic (penicillin) help cure bacterial disease by killing infective bacteria in body

-use specific antibiotic for specific bacteria

-reduce deaths

-strains resistant to antibiotics= concern

-cannot kill viral pathogens

Painkillers & other medicines treat symptom (do not kill pathogens)

Difficult to develop drugs without damaging body tissues

Traditional drugs extracted from plants & microorganisms:

-heart digitalis orginates from foxgloves

-aspirin originates from willow

-Penicillin (discovered by Fleming) from Penicillium mould

New drugs synthesised by chemist (but chemical extracted from plant)

New drugs tested & trialed before use (tested for toxicity, efficiency & dose)

Preclinical test done in laboratory on cells, tissue & live animals

Clinical trials on volunteers & patients

-low doeses given at start

-clinical trials go further to fine optimum dose (only if drug is safe

-double blind tests (patients given placebo)

Monclonal antibodies created from single clone of cells

-antibodies specific to one binding site of protein antigen (able to target specific chemical or cells in body)

Steps:

-stimulate mouse lymphocytes (produce specific antibody)

-lymphocytes combined with tumour cells= hybridoma

-hybridoma cell divide to make antibody

-hybridoma cells cloned to make same antibody

-large amount of antibody collected & purified

Diagnosis (pregnancy tests)

Used to measure levels of hormones/chemicals in blood or detect pathogens

Locate specific molecules in cell/ tissue by binding to them (with dye)

Treat diseases

-cancer by binding to radioactive substance, drug or chemical to stop growth/ divide of cells

-deliver substance to cancer cells without harming other cells

Plant diseases are detected by stunted growth, malformed leaves, spots on leaves, discolouration, area of decay, presence of pests & growths

Can be identfied by

-manuals or websites

-testing infected plant in lab

-testing kits with monoclonal antibodies

Plant infected by viral, bacterial or fungal pathogens including insects

Knowledge on plant disease is limited 

damage= ion deficiencies

-nitrate deficiency= stunted growth

-magnesium deficiency= chlorosis

Physical defence against microorganisms:

-cell walls

-tough waxy cuticle on leaves

-Layers of dead cells around stems which fall off

Chemical defence:

-Antibacterial chemicals

-Posions to deter herbivores

Mechanical adaptations

-Thorns & hairs

-Leave which drop/ curl when touched

-Mimicry to trick animals