Move into cells and use the biochemistry to make many copies of itself
This leads to the cell bursting and releasing all of the copies into the bloodstream
The damage and destruction of the cells makes the individual feel ill
Bacteria
Small
Multiply very quickly through dividing by a process called binary fission
They produce toxins that can damage cells
Protists
Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
Fungi
Can be single celled or have a body made of hyphae (thread-like structures)
They can produce spores which can be spread to other organisms
Ways pathogens are spread
Direct contact
By water
By air
Direct contact
Touching contaminated surfaces, kissing, contact with bodily fluids, direct skin to skin, microorganisms from faeces, infected plant material left in field
By water
Drinking or coming into contact with dirty water
By air
Pathogens can be carried in the air and then breathed in (a common example is the droplet infection, which is when sneezing, coughing or talking expels pathogens in droplets which can be breathed in)
Ways to reduce the damage of disease
Improving hygiene
Reducing contact with infected individuals
Removing vectors
Vaccination
Improving hygiene
Hand washing, using disinfectants, isolating raw meat, using tissues and handkerchiefs when sneezing
Removing vectors
Using pesticides or insecticides and removing their habitat
Vaccination
Injecting a small amount of a harmless pathogen into an individual's body, they can become immune to it so it will not infect them. This means they cannot pass it on.
Herd immunity
When a large proportion of the population is vaccinated, the spread of the pathogen is reduced as there are less people to catch the disease from
Viruses are particularly dangerous as they can enter all types of cells, and scientists are yet to develop medicines to cure them
Measles
Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection) and blindness
How it is spread: Droplet infection
How it is being prevented: Vaccinations for young children to reduce transmission
HIV
Symptoms: Initially flu-like symptoms, then the virus attacks the immune system and leads to AIDS (a state in which the body is susceptible to many different diseases)
How it is spread: By sexual contact or exchange of bodily fluids such as blood
How it is being prevented: Using condoms, not sharing needles, screening blood when it is used in transfusions, mothers with HIV bottle-feeding their children instead of breastfeeding, use of antiretroviral drugs (stop the virus replicating in the body)
Tobacco mosaic virus
Symptoms: Discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield
How it is spread: Contact between diseased plants and healthy plants, insects act as vectors
How it is being prevented: Good field hygiene and pest control, growing TMV-resistant strains
Salmonella food poisoning
Symptoms: Fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they secrete)
How it is spread: These bacteria can be found in raw meat and eggs, unhygienic conditions
How it is being prevented: Poultry are vaccinated against Salmonella, keeping raw meat away from cooked food, avoid washing it, wash hands and surfaces when handling it, cook food thoroughly
Gonorrhoea
Symptoms: Thick yellow or green discharge from the vagina or penis, pain when urinating
How it is spread: It is a sexually transmitted disease spread through unprotected sexual contact
How it is being prevented: By using contraception such as condoms and antibiotics (used to be treated with penicillin but many resistant strains are developing)
Rose black spot
Symptoms: Purple or black spots on leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early
How it is spread: The spores of the fungus are spread in water (rain) of by wind
How it is being prevented: By using fungicides or stripping the plant of affected leaves (have to be burnt)
Malaria
Symptoms: Fevers and shaking (when the protists burst out of blood cells)
How it is spread: The vector is the female Anopheles mosquito, in which the protists reproduce sexually. When the mosquito punctures the skin to feed on blood, the protists enter the human bloodstream via their saliva.
How it is being prevented: Using insecticide coated insect nets while sleeping, removing stagnant water to prevent the vectors from breeding, travellers taking antimalarial drugs to kill parasites that enter the blood
Non-specific defence system
The skin
The nose
The trachea and bronchi
The stomach
The skin
Acts as a physical barrier
It produces antimicrobial secretions to kill pathogens
Good microorganisms known as skin flora compete with the bad microorganisms for space and nutrients
The nose
Has hairs and mucus (sticky substance) which prevent particles from entering your lungs
The trachea and bronchi
Secrete mucus in order to trap pathogens
Cilia (hair-like structures on cells) beat to waft mucus upwards so it can be swallowed
The stomach
Produces hydrochloric acid that kills any pathogens in your mucus, or food and drink
Ways the specific immune system protects you
Phagocytosis (engulfing and consuming pathogens)
Producing antibodies
Producing antitoxins
Phagocytosis
This destroys them, meaning they can no longer make you feel ill
Producing antibodies
Each pathogen has an antigen on their surface, which is a structure which a specific complementary antibody can bind to. Once antibodies begin to bind to the pathogen, the pathogens start to clump together, resulting in it being easier for white blood cells to find them.
If you become infected again with the same pathogen, the specific complementary antibodies will be produced at a faster rate. The individual will not feel the symptoms of the illness. They are said to be immune.
Producing antitoxins
They neutralise the toxins released by the pathogen by binding to them
Vaccination
The vaccine contains a dead or inactivated form of the pathogen
This stimulates white blood cells to produce antibodies complementary to the antigens on the pathogen
Antibiotics
Medicines that kill bacterial pathogens inside the body, without damaging body cells
They cannot kill viruses as they use body cells to reproduce, meaning any drugs that target them would affect body tissue too
They can be taken as a pill, syrup or directly into the bloodstream
Different antibiotics are effective against different types of bacteria, so receiving the correct one is important
Their use has decreased the number of deaths from bacterial diseases
An example is Penicillin
Painkillers
Only treat the symptoms of the disease, rather than the cause
The great concern is that bacteria are becoming resistant to antibiotics
Antibiotic resistance
Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics
When these bacteria are exposed to antibiotics, only the non-resistant one die
The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases
This means that antibiotics that were previously effective no longer work
Ways to prevent antibiotic resistance
Stop overusing antibiotics
Finishing courses of antibiotics to kill all of the bacteria
Many drugs were initially discovered in natural sources
Epidemics (lots of cases in an area) can be prevented through herd immunity