infection and response Flashcards
what is the definition of health?
the state of physical and mental well-being.
what are pathogens?
microorganisms that cause infectious disease. these may be viruses, bacteria, protists, or fungi. they may infect plants or animals, and can be spread by direct contact, by water, or by air.
- 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.
describe Tobacco Mosaic VIRUS (TMV):
- widespread communicable plant infection; infects many species, e.g. tomatoes, tobacco.
- causes the 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.
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.
- 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.
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.
- 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 altogether, 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.
- causes 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.
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.
- 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.
- 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.
- symptoms include: pain while urinating, thick yellow/green discharge.
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, spread by a pathogen (an example of a protist).
- infected individuals experience repeated bouts of fever, and it can be fatal.
what is the lifecycle of malaria? PROTIST
- an infected person is bitten by a mosquito, and the malaria pathogen passes into the insect.
- 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 non-specific defence systems?
a system that prevents a pathogen from entering the human body.
how does the skin protect against pathogens?
- forms a protective 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.
- 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.
how do the trachea and bronchi protect against pathogens?
- the trachea and bronchi 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, which kills pathogens 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 are the three functions of white blood cells?
- ingest and destroy pathogens (phagocytosis)
> cell detects chemicals released from
the pathogen and moves towards it.
> it ingests the pathogen, and uses
enzymes to destroy it. - making antibodies (produced by lymphocytes, a type of white blood cell)
- lymphocytes produce antibodies against anything that it detects as foreign, and these are called antigens.
> protein molecules produced by white
blood cells
> sticks to the pathogen, causing them to stick together so they can’t move around the body, and makes it easier for them to be engulfed through phagocytosis.
- 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. - producing anti-toxins.
- certain types of bacteria produce toxins, which can invade and destroy cells, making the individual feel ill.
> anti-toxins stick to toxin molecules and
prevent them from damaging cells by neutralising them.
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.
- 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.
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 of an illness, but don’t help cure the problem, as the pathogens doing the damage will still be there.
- antibiotics will actually cure the illness, as they can directly kill bacteria, or prevent the growth of any new bacteria. specific bacteria should be treated by specific antibiotics.
> however, this will only work if the
illness is caused by a bacteria, as
antibiotics only work to kill bacteria, not
viruses, for example.
> as viruses are so different to bacteria,
the antibiotics can’t do anything to them.
> even if antibiotics could cure viruses,
they wouldn’t be able to find them, as
viruses hide within our bodies’ cells. this
makes it almost impossible to destroy
them without destroying the cell as well.
> each antibiotic can only kill certain
types of bacteria, so doctors sometimes
have to do a test first to know which
antibiotic to prescribe.
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).
describe some extractions of traditional drugs from plants and microorganisms:
- the heart drug digitalis originates from foxgloves.
- the painkiller aspirin originates from willow.
- penicillin was discovered by Alexander Fleming from the penicillium mould.
- 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 main stages of drugs testing?
PRECLINICAL:
1. the substance is tested on human cells and tissues, which are grown in a lab.
> through this, we can cheaply test tons
of different substances.
> it doesn’t tell us much about how the
substance will affect an entire organism.
- 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.
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.
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.
how are monoclonal antibodies produced?
- injecting a mouse with an antigens means that its lymphocytes will produce antibodies against that antigen.
- we can then collect these lymphocytes, however, these won’t divide by mitosis.
- 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 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 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 are some uses of monoclonal antibodies?
- used in pregnancy testing.
> these antibodies are used to detect a
specific hormone (HCG), which is
produced by the placenta of a developing
foetus, and only found in the urine of
pregnant women.
> monoclonal antibodies are attached to
the end of the test strip, and if she’s
pregnant, the antibodies will bind to the
HCG, triggering a visible change in colour
or pattern.
> pregnancy tests are cheap and easy to
use. the woman urinates on the test strip,
and looks for a reaction.
> the test is highly accurate if used
correctly. - 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 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.
how can we diagnose plant diseases?
by recognising these symptoms:
- discolouration
- spots on leaves
- stunted growth
- decay/rot
- growths
- malformed stems/leaves
how can we identify plant diseases?
- use a garden manual/website.
- take the infected plant to a lab to identify the pathogen.
- use testing kits containing monoclonal antibodies.
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?
- 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?
- plants release antibacterial chemicals, which kill bacteria and protect the plant.
- can also release poisons to prevent herbivores from grazing on the plant.
what are plants’ mechanical responses against attack?
- 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.
