infection and response Flashcards
what is the definition of health?
the state of physical and mental well-being.
what are microorganisms?
tiny organisms including bacteria, viruses, protists/protoctists and fungi
what are pathogens?
microorganisms that cause infectious disease. these may be viruses, bacteria, protists, or fungi. they may infect plants or animals
what do bacteria and viruses do?
- bacteria and viruses may reproduce rapidly inside the body.
- bacteria may produce toxins that damage tissues and make us feel ill.
- viruses live and reproduce inside cells, causing cell damage.
how do pathogens spread from person to person?
- AIR, e.g. in tiny droplets we expel when we cough or sneeze. influenza, measles
- CONTAMINATED FOOD/WATER. cholera is bacterial and spread by drinking the contaminated water containing the diarrhoea of someone with the disease. salmonella is spread by eating contaminated food
- DIRECT CONTACT. athlete’s foot (fungal infection) is spread by walking barefoot on contaminates surfaces
what are the 4 ways we can stop the spread of pathogens?
- HYGIENE. washing hands, cleaning cooking items
- KILL THE VECTORS (organisms that transport the pathogen). spray insecticides
- VACCINATIONS. if people can’t catch the disease in the first place, they can’t pass it on to anyone
- ISOLATE/QUARANTINE (only if it’s really serious)
describe Tobacco Mosaic VIRUS (TMV):
- widespread communicable plant infection; infects certain plant species, e.g. tomatoes, tobacco.
- causes patches on leaves to discolour in a mosaic pattern; because of this, the rate of photosynthesis is reduced, and the growth of the plant is also reduced, as the plant can’t produce enough sugars
- affects plants, not animals
- primary mode of transmission is direct contact with infected plants
describe Rose Black Spot: FUNGUS
- caused by a fungus, which can be spread by water or wind (the fungus reproduces sexually to create spores, which can be carried in the wind).
- causes the leaves to develop purple or black spots. the leaves often then turn yellow and fall off.
- this causes the rate of photosynthesis to fall, reducing the rate of growth.
how can Rose Black Spot be treated? FUNGUS
- spray the plants with chemicals which kills fungi (fungicides).
- we can remove the infected leaves and destroy them.
what is a virus?
- not cells and not living, but still considered an organism
- 10,000 times smaller than animal cells.
- can’t reproduce by themselves.
- once inside another cell, they can use the cell’s organelles to clone themselves, and can eventually burst the cell.
- this means the new virus cells can find other cells to take over, and destroy them, too.
- this damages our bodies, and makes us feel ill.
list the three viral diseases:
- measles
- HIV (human immunodeficiency virus)
- TMV (tobacco mosaic virus)
describe the measles VIRUS:
- spread by droplets, when an infected person coughs or sneezes.
- results in a red rash across the body and a high fever, and general illness.
- can be serious (and even fatal), but is rare in the UK as nearly everyone is vaccinated against it as a child.
describe the HIV VIRUS:
- stands for ‘Human Immunodeficiency Virus’
- spread by sexual contact, or by exchanging bodily fluids (e.g. blood, when people share needles).
- causes an inadequate immune system, leaving the person more susceptible to catching other communicable diseases.
what happens when an individual ‘catches’ HIV? VIRUS
- at first, they might get flu-like symptoms for a few weeks (e.g. fever, aches, tiredness)
- at this point, can be cured using antiretroviral drugs (prevent the viruses replicating)
- they’ll then start to feel better, but if no drugs are used, inside their body, the viruses are doing even more damage to their immune system.
- at one point, their immune system will become so weak that they’ll start to catch unusual infections (and even cancers)
- at this point, the person has developed AIDS, which is classed as a disease in which the immune system can’t cope anymore.
how can AIDS be treated?
- the individual can take ‘antiretroviral drugs’, preventing the virus from replicating within our bodies.
what is a bacteria?
- single celled organism.
- roughly 100x smaller than our own cells.
- some cause disease.
- can reproduce by themselves, but often replicate rapidly inside our bodies due to the good food supply.
- produce toxins, which make us feel ill by damaging our cells and tissues.
list the two bacterial diseases:
- salmonella
- gonorrhea
what is the salmonella bacteria? BACTERIAL
- causes food poisoning.
- can catch from any food that’s been contaminated with the bacteria, from food prepared in unhygienic conditions, but is most often from chicken that caught the disease while it was alive, and then passed on when the food isn’t cooked properly and therefore hasn’t killed all the bacteria
- salmonella is relatively rare in the UK, as most chickens are vaccinated against it.
what are the symptoms and cures of salmonella? BACTERIAL
- symptoms include: a fever, stomach cramps, vomiting and diarrhoea, as it affects the intestines
- usually passes by itself within a week, and just ensure you stay well hydrated.
describe the bacterial disease gonorrhoea: BACTERIAL
- an example of a sexually transmitted disease (STD).
- passed on through sexual contact, e.g. unprotected sex
- symptoms include: pain while urinating, thick yellow/green discharge from vagina/penis
how can you prevent and treat gonorrhea? BACTERIAL
prevention:
- avoid unsafe sex.
- use barrier methods of contraception (e.g. condoms)
treatment:
- we used to use the common antibiotic ‘penicillin’, which would kill it.
- however now, lots of gonorrhoea strains have become resistant to penicillin.
- this means we have to use rarer and more expensive antibiotics.
describe the fungal disease Chalara Ash Dieback: FUNGAL
- fungal disease that affects ash trees.
- causes leaf loss, marks on the bark and dead shoots and branches.
- once a tree is infected, the disease usually kills it, either directly or indirectly (by weakening the tree so that its more susceptible to other diseases).
- spread by fungal spores travelling in the wind.
- infected trees are usually cut down and burnt.
describe the fungal disease Athlete’s foot: FUNGAL
- relatively common infection of the feet.
- itchy rash caused by a fungus growing and multiplying on the skin.
- usually appears between the toes, where it’s warm and dark and moist.
- not usually serious, but should be treated to stop it spreading to other parts of the body or to other people.
- usually treated with creams or sprays, containing fungicides which kills the fungi.
describe the protist disease Malaria: PROTIST
- communicable disease, caused by a parasitic protist, which needs a host to survive
- infected individuals experience repeated bouts of fever and headaches in recurrent episodes, and it can be fatal.
- transported between hosts by mosquitoes
what is the lifecycle of malaria? PROTIST
- an infected person/animal is bitten by a mosquito, and the malaria pathogen passes into the insect along with the blood
- the mosquito now bites a different person and passes the malaria pathogen into them.
- this mosquito is a vector, as it carries the pathogen from one person to another.
how can we prevent the spread of malaria? PROTIST
- prevent the vector (mosquito) from breeding.
> they breed in still water, so we can drain
these areas, or spray these areas with
insecticides. - prevent the mosquito from biting humans.
> sleep under a mosquito net, and spray
the net with insecticide.
what are fungi?
- eukaryotic organisms
- can be either unicellular/multicellular
- the multicellular fungi have long, thread-like structures called hyphae, which come out of the main body and spread through the soil. these hyphae occasionally spread over plants/penetrate human skin and can cause disease
- the hyphae can also produce spores, which spread easily and grow into new fungi
what are protists?
- eukaryotes
- either unicellular/multicellular, but most are unicellular
- some are parasites (live on/inside another organism), and survive at that other organism’s expense
- transported by vectors (other organisms, like insects, that transport the protist between different host organisms). the vectors don’t get the disease themselves
what are non-specific defence systems?
- physical and chemical barriers
a system that prevents a pathogen from entering the human body.
how does the skin protect against pathogens?
- forms a protective physical barrier layer covering the body.
- the outer layer consists of dead cells and is difficult for pathogens to penetrate.
- also produces an oily substance, sebum, which kills bacteria (antimicrobial substance)
- if the skin is damaged, that could allow pathogens to enter the body, and to stop this, the skin scabs over.
how do the nostrils protect against pathogens?
- these present openings where the pathogens can enter the body.
- the nose contains hair and mucus, which can trap pathogens before they enter the breathing system.
what else acts as a barrier to reduce the entry of pathogens?
the enzymes in tears
how do the trachea and bronchi and bronchioles protect against pathogens?
- the trachea and bronchi and bronchioles are covered with tiny hairs called cilia, which are covered in mucus and can trap pathogens.
- the cilia now waft the mucus upwards towards the throat, where it is swallowed into the stomach.
how does the stomach protect against pathogens?
the stomach contains hydrochloric acid (very strong acid, around pH 2), which kills nearly all pathogens due to its acidity before they can make their way down further into the digestive system.
what are the main functions of the immune system?
- destroys pathogens and any toxins they produce.
- protects us in case the same type of pathogen invades us again in the future.
what do white blood cells do when there aren’t any pathogens to destroy?
continually patrol the body, circulating our blood and tissues
what are the three functions of white blood cells?
- ingest and destroy pathogens, engulf (phagocytosis)
- making antibodies (produced by lymphocytes, a type of white blood cell)
- lymphocytes produce antibodies against antigens
> protein molecules produced by
white blood cells
> bind to the pathogen, causing
them to stick together so they can’t
move around the body, and act as
signals for white blood cells to come
and makes it easier for them to be
engulfed through phagocytosis - producing anti-toxins.
- certain types of bacteria produce toxins, which can invade and destroy cells, making the individual feel ill.
> anti-toxins bind to toxin molecules
and prevent them from damaging cells
by neutralising them.
what is the process of phagocytosis?
- the phagocyte tracks down the pathogen and binds to it
- the phagocyte’s membrane will surround the pathogen and engulf it
- enzymes inside the phagocyte break down the pathogen in order to destroy it
what are phagocytes?
a special type of white blood cell, that performs phagocytosis
what’s important about antibodies?
- antibodies are extremely specific. e.g. a person who has caught measles will develop antibodies against the measles virus, and will only protect against a measles pathogen.
- antibodies can remain in the blood for a long time, meaning we’re protected if we’re ever infected with the same pathogen again. if the pathogen re-enters the body in the future, the body will produce so many antibodies so quickly that it will destroy all of the pathogens before they can develop (we are now immune to the disease)
what are antigens?
substances the immune system detects as being foreign, such as the cell wall of a bacteria, or a virus protein
how does a vaccination work?
- involves introducing small quantities of dead or inactive forms of a pathogen into the body.
- as the pathogen is dead/inactive, it cannot lead to the disease in the patient, yet it still contains the same antigens as the pathogen, so the body treats it as if it’s a proper pathogen
- the white blood cells are now stimulated to produce antibodies against the dead/inactive pathogen.
- simultaneously, the white blood cell divides by mitosis to produce copies of itself, which can stay in the blood for decades.
- if the same pathogen enters the body, even years later, the white blood cells can produce the correct antibodies quickly, preventing infection.
do vaccines work for bacteria or viruses?
both
what are the pros and cons of vaccines?
pros:
- protection from diseases
- control of common diseases: polio, smallpox, measles, whooping cough
- prevent outbreaks (epidemics), which kill lots of people
cons:
- don’t always work, and don’t grant full immunity (we generally check afterwards to see if it’s been effective)
- some have bad reactions to the vaccine (swelling around injection site. can cause fevers/seizures). rare
what happens when your body’s immune system is exposed to a pathogen?
generally develops immunity to that pathogen and any diseases it causes. once you’re immune, you can’t catch the disease anymore
describe ‘herd immunity’:
- there are always some people who don’t get vaccinated.
- if enough people are vaccinated, this also protects unvaccinated people.
- the unvaccinated person can’t catch the disease, as no one around them can pass the pathogen on.
what is the difference between painkillers and antibiotics?
painkillers (e.g. paracetamol, aspirin) relieve the symptoms and pain of an illness, but don’t help cure the problem, as the pathogens doing the damage will still be there
describe antibiotics:
- directly kill bacteria, or at least prevent the growth of any new bacteria, therefore they help to treat the disease
- only work if what’s causing the disease is bacteria, not a virus
- each antibiotic can only kill certain types of bacteria, so doctors might have to do a test first to find out which type of bacteria you have, before they can prescribe an antibiotic
- some bacteria have also become resistant to antibiotics, meaning we can’t use those same antibiotics to treat bacteria anymore
what is medication?
a drug used to prevent, treat or relieve the symptoms of disease
why don’t antibiotics work on viruses?
- made specifically to interfere with bacteria, and as viruses are so different to bacteria, antibiotics can’t do anything to them
- the antibiotics wouldn’t be able to find the viruses, as they hide within our body’s cells, making it almost impossible to destroy them without destroying the cells too
how can we reduce antibiotic resistance?
- patients taking antibiotics for the full prescribed course
- doctors only prescribing antibiotics for serious bacterial infections
describe the process of drug development and what is being looked for:
- most drugs are taken from microorganisms and plants, and are either directly used as medicine or slightly modified, to serve for our purposes.
- test efficacy (how well it works).
- toxicity (how harmful it is, e.g. side effects).
- dosage (how much of the drug should be given. the more drug, the more effective, but the more side effects).
describe some extractions of traditional drugs from plants and microorganisms:
- the heart drug digitalis originates from foxgloves.
- the painkiller aspirin originates from the bark of willow trees.
- penicillin was discovered by Alexander Fleming from the penicillium mould (fungus).
- most new drugs now are synthesised by chemists in the pharmaceutical industry. however, the starting point may still be chemical extracted from a plant.
what are the first stage and second stages of drug testing?
PRECLINICAL:
1. the substance is tested on human cells and tissues, which are grown in a lab.
> through this, we can easily and
cheaply test tons of different
substances.
> it doesn’t tell us much about how the
substance will affect an entire
organism/organ.
- the substance is tested on live animals (e.g. in the UK, everything must be tested on two live animals, such as mice and rabbits).
> as humans are also mammals, their
response is similar to what ours would
be.
what is the third stage of drug testing?
CLINICAL:
3. give the substance to healthy volunteers, starting with a low dosage. slowly increase the dose, with doctors keeping a close eye on volunteers.
> through this, we can find out what the
maximum dosage should be before
humans begin to feel side-effects.
- we then give the drug to people suffering from the particular illness, and slowly increase the dose. we’re now looking for the optimum dosage (maximum efficacy, minimum toxicity)
- once drug testing is complete, the results are written up and are peer reviewed by other scientists to check that the tests were fair, preventing false results
why is it important that new medicinal drugs undergo testing before they are used?
- to make sure they’re safe to use
- to determine the optimum dose
- to make sure they’re an effective treatment
how can we ensure that the clinical process of drugs testing is fair, and avoid unconscious bias?
- clinical trials should be blind, and we should use a placebo (a substance that’s just like the real drug, but doesn’t do anything).
- give half the volunteers the real drug, and the other half the placebo, but we don’t tell them which they’re taking (blind trial).
- most trials are double blind, where neither the doctors nor the volunteers know which drugs have been taken by whom, until the end of the study.
this all avoids unconscious bias, for example, if the volunteers knew they were taking the drug, they may be more likely to report more side effects, and the doctors may pay closer attention to the real volunteers
how are monoclonal antibodies produced?
- injecting a mouse with antigens (that we want our monoclonal antibody to bind to) meaning that its lymphocytes will produce antibodies against that antigen.
- we can then collect these lymphocytes, however, these won’t divide by mitosis very quickly.
- we can fuse our lymphocytes with a tumour cell, which are very good at dividing by mitosis.
- this produces a hybridoma cell, which can produce antibodies and divide rapidly by mitosis.
- we select a single hybridoma cell producing the desired antibody, and allow it to divide by mitosis, to create multiple identical hybridoma cells.
- the antibodies produced from these clones are all identical, and these are named monoclonal antibodies, as they all come from the same hybridoma clone.
what are antibodies produced by?
b-lymphocytes or b-cells (white blood cells)
what are monoclonal antibodies?
- produced from a single clone of hybridoma cells.
- specific to one binding site on one protein antigen.
- this means that monoclonal antibodies can target a specific chemical or specific cells in the body - they have a large number of uses.
- not as widely used yet as everyone had hoped when they were first developed.
what can you attach to the bottom of a monoclonal antibody?
- drugs
- radioactive materials
- fluorescent proteins
what are some uses of monoclonal antibodies?
- used to detect pathogens in the blood, e.g. viruses. monoclonal antibodies are advantageous, as they’re completely specific to what we’re looking for. can also measure the hormone levels or other chemicals in the blood.
- used to locate/identify specific molecules in a cell/tissues. they can be attached to fluorescent dyes, and the antibodies will stick to the molecule and allow us to see their location.
how are monoclonal antibodies used in pregnancy tests?
- pregnant women produce a hormone called HCG, which is excreted in their urine
- the test strip can detect this HCG, so be weeing on the test strip, it can tell the woman if there’s HCG in her urine, and thus whether she’s pregnant or not
what is the setup of a pregnancy test?
- on the right side of the test strip are a bunch of monoclonal antibodies, specific to HCG (can bind to HCG hormone if they come into contact with it). they’re fixed to the test strip
- on the left of the test strip is the part where you wee, containing blue beads covered in the same monoclonal antibodies as on the right side. these beads are free to move
what are the two different outcomes for when urinating on a pregnancy test strip?
- weeing on it when not pregnant causes the urine to wash the un fixed beads along the strip, so they’ll flow right over the line of fixed antibodies, and nothing will happen. the test strip won’t turn blue
- if you wee on it and are pregnant, the HCG in the urine will bind to the monoclonal antibodies on the blue beads, so now, when they flow over the test strip, the HCG they’re carrying binds to the fixed antibodies too, and the beads are stuck in place. by trapping loads of these tiny blue beads, the entire strip appears blue, which indicates a positive test result
why may you have an additional line on a pregnancy test strip?
the second line acts as a control, to show the test is working
- you may then need 2 lines to show pregnancy
how can monoclonal antibodies be used to kill cancer cells?
- can treat diseases. cancer cells undergo uncontrolled mitosis and spreads around the body. scientists make antibodies specific to cancer cells, and we attach a radioactive substance or toxic drug to the antibody.
> when the antibody is injected into the
blood, it attaches to the cancer cells, and
the radioactive substance/toxic drugs stop
the cancer cells from dividing.
advantage: the antibody delivers the substance to specifically the cancer cells, without damaging other cells of the body.
disadvantage: have been found to produce harmful side-effects.
how do aphids attack plants?
they are insects that extract nutrients (e.g. sugars) from the plant, stunting its growth.
- insects are NOT pathogens, as they can’t directly cause a disease, but they can carry pathogens.
what diseases can plants get?
- diseases from microorganisms: fungi, viruses, bacteria
- diseases from larger organisms: insects
- deficiency diseases: not having enough of the essential minerals (nitrate/magnesium ions)
how can we diagnose plant diseases?
by recognising these symptoms:
- discolouration
- spots on leaves
- stunted growth
- decay/rot
- abnormal growths/lumps
- malformed stems/leaves
how can we identify plant diseases?
- use a garden manual/website, by matching the symptoms you can see to the lists in it
- take the infected plant to a lab/plant pathologist to identify the pathogen through more detailed testing
- use testing kits containing monoclonal antibodies.
what detailed testing can a plant pathologist carry out?
- take a tissue sample and observe it under a microscope
- look for unique antigens that come from particular pathogens, perhaps using monoclonal antibodies
- run DNA tests that look for pathogen DNA
describe the method of trial and error in diagnosing plant diseases:
- if the plant has yellow leaves, so you think it may have a magnesium deficiency, supplement it with magnesium, to see if it fixes it
- if you believe the plant has a fungal disease, spray it with antifungal chemicals, to see if it fixes it
what are examples of plant ion deficiencies?
- a lack of the nitrate ion causes stunted growth; nitrate is needed for protein synthesis, and therefore growth.
- a lack of the magnesium ion causes chlorosis (the leaves lose their green colouration), as magnesium is required to make chlorophyll.
what are plants’ physical responses against attack?
physically prevent the entry of pathogens
- all plant cells have a cellulose cell wall, making it difficult for microorganisms to penetrate.
- leaves are covered with a thin, oily layer called the waxy cuticle, which is difficult for microorganisms to penetrate.
- bark is a barrier to entry for microorganisms. as bark ages, it eventually falls off, and is replaced with new bark from underneath.
what are plants’ chemical responses against attack?
actual chemicals that the plant secretes
- plants release antimicrobial substances, which kill bacteria or fungi and protect the plant.
- can also release poisons to prevent/deter herbivores/insects from grazing on the plant.
what are plants’ mechanical responses against attack?
similar to physical defences, but have more of a function than just simply being a barrier - structures that reduce the chance of being attacked
- sharp thorns directly prevent a plant from being eaten by herbivores.
- other plants have hairs, which irritates the mouth of herbivores, making plants difficult to eat.
- some plants have leaves which droop/curl when touched. it’s thought that this might scare herbivores, as they’re not used to plants that move like this.
- mimicry can be used. the white dead nettle is very similar to a stinging nettle, to deter predators, but has no sting.
