infection and response Flashcards
What are pathogens?
- microorganisms that cause infectious disease
What are the type of pathogens?
- viruses
- bacteria
- protists
- fungi
How can pathogens be spread?
- direct contact
- by water
- by air
How are pathogens spread through direct contact?
- touching contaminated surfaces
e.g. kissing, contact with bodily fluids, direct skin to skin, microorganisms
from faeces, infected plant material left in field
How are pathogens spread in water?
- drinking or coming into contact with dirty water
e.g. cholera
How are pathogens spread in the air?
- pathogens can be carried in the air and then breathed in
- droplet infection - sneezing, coughing or talking expels pathogens in droplets which can be breathed in
How do viruses cause cell damage?
- move into the cells and use the biochemistry of it to make copies of itself
- leads to cell bursting and releasing copies into the bloodstream
How do viruses make us feel ill?
- damage and destruction of cells when it bursts make individual feel ill
How does bacteria make us feel ill?
- they produce toxins that can damage cells
What are protists?
- eukaryotic pathogens which are sometimes parasitic - use humans and animals as their hosts
- often transferred between organisms by vectors
What are fungi?
- can be single-celled or have a body made up of hyphae
- grow and penetrate human skin and the surface of plants, causing diseases
- hyphae can produce spores that can be spread to organisms
- spores can travel through the wind and infect organisms
What are vectors?
- animals that carry a disease but do not get the disease themselves
How do bacteria and viruses spread?
- they reproduce rapidly inside the body - binary fission
- they divide every 20 minutes under ideal conditions
What is the difference between bacteria and viruses?
- viruses themselves cannot reproduce - only once they enter a host cell
- bacteria can reproduce by themselves
How can we reduce the spread of pathogens?
- Improving hygiene - hand washing, using disinfectants, isolating raw meat, using
tissues and handkerchiefs when sneezing - Reducing contact with infected individuals
- Removing vectors - using pesticides or insecticides and removing their habitat
- vaccination- by injecting a small amount of a harmless pathogen into an individual’s
body, become immune, will not infect them, cannot pass it on. - Use condoms to prevent transmission of STIs
- Provide clean drinking water rather than containing cholera
What is a communicable disease?
- a disease that can be spread from person to person
- are infectious and are spread via pathogens
What pathogen causes measles?
- virus
What are the symptoms of measles?
- fever and red skin rash
How can measles be fatal?
- can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection), and blindness
How are measles spread?
- droplets in the air
- when an infected person coughs or sneezes are inhaled by another person
How can measles be prevented?
- vaccinations for young children to reduce transmission
What pathogen causes HIV?
- virus
What are the symptoms of HIV?
- initially flu-like symptoms
- disappears after one or two weeks
What happens if HIV isn’t successfully controlled?
- virus attacks the patient’s immune cells
- over time, immune system becomes severely damaged
- immune system becomes so badly damaged, that it is unable to fight off other infections
- patients can now easily contract infections like tuberculosis and cancer
How is HIV spread?
- through sexual contact or exchange of bodily fluids
What is late-stage HIV called?
- AIDS - a state in which the body is susceptible to many different diseases
- at this point, the disease is fatal
How can HIV be prevented/treated?
- using condoms, not sharing needles, screening blood when used in transfusions
- use of antiretroviral drugs (stops the virus from replicating)
How do antiretroviral drugs work in HIV?
- prevent the virus from multiplying inside the patient
- virus does not damage the patient’s immune system any further
- patients who take these drugs do not go on to develop AIDS, can lead a normal life expectancy
Why aren’t antiretroviral drugs a cure for HIV/AIDS?
- must be taken for the rest of the patient’s life
- otherwise the viruses will start reproducing again and damage the immune system
What pathogen causes TMV?
- virus
What is TMV?
- a widespread plant pathogen affecting many species of plants including tomatoes
What are the symptom of TMV?
- discolouration of the leaves -gives a distinctive ‘mosaic’ pattern
- stunted growth
Why is TMV bad for a plant?
- discolouration means less chlorophyll - rate of photosynthesis reduces
- negative effect on the growth of the plant - less glucose is produced, therefore less amino acids and proteins can be produced
How is TMV spread?
- contact between diseased and healthy plants
- insects act as vectors
How can TMV be prevented?
- good field hygiene and pest control
- growing TMV-resistant strains
What pathogen causes salmonella?
- bacteria
- they live in the gut of different animals
What are the symptoms are salmonella?
- fever, stomach cramps, vomiting, diarrhoea
- caused by the toxins they secrete
How is salmonella spread?
- spread by bacteria ingested in food
- by food prepared in unhygienic conditions
How can salmonella be prevented?
- poultry are vaccinated against salmonella
- keeping raw meat away from cooked food
- wash hands and surfaces when handling
- cook food thoroughly
What pathogen causes gonorrhoea?
- bacteria
What are the symptoms of gonorrhoea?
- thick yellow or green discharge from the vagina or penis
- pain when urinating
How is gonorrhoea spread?
- via unprotected sexual contact
How is can gonorrhoea be prevented/treated?
- using contracpetion
- antibiotics - used to be easily treated with penicillin but bacteria developing antibiotic-resistant strains
What pathogen causes rose black spot?
- fungi
What are the symptoms of rose black spot?
- purple or black spots develop on the leaves of a plant
- often turn yellow and drop early
Why is rose black spot bad for a plant?
- rate of photosynthesis is reduced due to a lack of chlorophyll in the yellow areas of the leaves
- reduces the rate of growth of the plant , less glucose, less amino acids and proteins, less growth
How is rose black spot spread?
- spores of the fungus are spread in water or by wind
How can rose black spot be prevented/treated?
- using fungicides
- removing and destroying the affected leaves to prevent the fungus spreading to the other parts of the plant
- have to be burnt
What pathogen causes malaria?
- protists
- enters the RBC and damages them
What are the symptoms of malaria?
- repeating episodes of fevers, shaking (when protists burst out of the cell)
How is malaria spread?
- vector is the female mosquito - protists reproduce sexually
- when mosquito punctures skin, protists enter the human bloodstream via their saliva
- infected person bitten by another mosquito
- blood of the person containing malarial pathogen passes into the mosquito
- infected mosquito bites a different person and passes the malaria protist to them
How can malaria be prevented?
- preventing vectors from breeding - draining areas of still water
- spraying insecticides - kills the mosquitos
- mosquito nets - avoid being bitten (these nets may be covered in insecticides)
- antimalarial drugs - kills parasites that enter the blood
What are the non-specific human defence systems?
- prevents pathogens from entering the body
- skin, nose, trachea and bronchi, stomach
How does the skin protect the human body against pathogens?
- acts as a protective physical barrier -has a layer of dead cells, difficult for pathogens to penetrate
- secretes antibacterial substances - kill pathogens on its surface
- skin flora (good microorganisms) compete with bad for space and nutrients
- forms scabs when it is damaged
How does the nose protect the human body against pathogens?
- lined with nose hair and mucus - traps and prevents pathogens from entering the respiratory system
How do the trachea and bronchi protect the human body against pathogens?
- lined with cilia (hair-like structures) - wafts pathogen-containing mucus upwards where it can be swallowed and killed by stomach acid
- lined with mucus - traps pathogens
How does the stomach protect the human body against pathogens?
- contains hydrochloric acid - kills pathogens and microorganisms found in food
- prevents them from entering the blood via the digestive system
What happens if a pathogen enters the body?
- the immune system tries to destroy it and any toxins they produce
- protects us in case the same type of pathogen invades us in the future
What happens if the non-specific defence systems are unable to prevent and kill the pathogen and it gets into the blood?
- we rely on white blood cells to defend our body from infection
What are the 3 ways can white blood cells defend our bodies against pathogens?
- phagocytosis
- antibody production
- antitoxin production
How does phagocytosis defends our body against pathogens?
- WBC called phagocytes detect the foreign antigen and engulf, ingest and destroy pathogens using enzymes
How does antibody production defends our body against pathogens?
- each pathogen has an antigen on their surface which a specific complementary antibody can bind to
- once antibodies bind, pathogens start to clump together - easier for WBC to find and destroy them
- if you become infected again with the same pathogen, the complementary antibody will produce at a faster rate - symptoms not felt
How does antitoxin production defends our body against pathogens?
- neutralise the toxins produced by bacteria
- binds to the toxins and prevents them from damaging cells to prevent us feeling ill
How do vaccinations work?
- contain small quantities of a dead or inactive form of a pathogen- dead so it will not infect the patient
- foreign antigen stimulates the WBC to produce antibodies against the dead or inactive pathogen – antibodies will be specific in shape to the antigen binding site of the pathogen
- lymphocytes become memory cells and divide by mitosis and remain in the body for years
- when re-exposed to the real pathogen, the memory WBC produce the correct antibody very quickly - destroys the pathogen quickly, preventing the person being infected
Why is it important that a very large number of people are vaccinated against pathogens?
- introduces herd immunity - most people are vaccinated, so they protect the unvaccinated people from being infected
- this is because there is no one who can pass the pathogen onto the unvaccinated person
What are the pros of using vaccinations in the prevention of disease?
- vaccines eradicated many infectious diseases that were once common and deadly e.g. smallpox and polio
- epidemics are prevented through herd immunity - reduces death and costs of diseases
What are the cons of using vaccinations in the prevention of disease?
- don’t always work - not effective in providing immunity
- side effects - some people may react badly to particular vaccines
e.g. swelling or fevers (however rare)
How do antibiotics treat disease?
- are medicines that help to cure bacterial disease
- can be taken as a pill, syrup or directly into the bloodstream
- kills infective bacteria inside the body without damaging body cells
- different antibiotics are effective against different types of bacteria - receiving the correct one is important
- cannot destroy viruses
e.g. penicillin
What only treats the symptom of the disease?
- painkillers are drugs that relieve pain - reduces symptoms
- do not kill the pathogen
e.g. aspirin
What are the problems with antibiotics?
- bacteria are becoming resistant to antibiotics
- mutations can occur during reproduction - results in certain bacteria no longer
being killed by antibiotics - when these bacteria are exposed to antibiotics, only the non-resistant one die
- resistant bacteria survive and reproduce - population of resistant bacteria increases
- antibiotics that were previously effective no longer work
- resistant strain could cause a serious infection that can’t be treated by antibiotics
e.g. MRSA causes serious wound infections, resistant to meticillin
How can we prevent the development of resistant strains in antibiotics?
- stop overusing antibiotics - unnecessarily exposes bacteria to the antibiotics
- finishing courses of antibiotics to kill all of the bacteria
Why is it difficult to kill viruses?
- difficult to develop drugs that kill viruses without also damaging the body’s tissues
How are plants used as drugs?
- plants produce a variety of chemicals to defend themselves against pests and pathogens
- these chemicals can be used as drugs to treat human diseases or relieve symptoms
Name drugs traditionally extracted from plants
- Aspirin is used as a painkiller - originates from willow
- Digitalis is used to treat heart conditions - originates from foxglove
How was penicillin discovered?
- Alexander Fleming was growing bacteria on plates
- he found mould (Penicillium mould) on his culture plates with clear rings
around the mould - indicated there was no longer any bacteria there - found that the mould was producing a substance called penicillin, which
killed bacteria
How are most new drugs made?
- are synthesised by chemists in the pharmaceutical industry
- however, the starting point may still be a chemical extracted from a plant
What are the cautions for new medical drugs?
- new medical drugs have to be tested and trialled before being used
- to check that they are safe and effective
What are new drugs extensively tested for?
- toxicity - how harmful it is
- efficacy - whether the drug works and produces the effect you’re looking for
- dose - the concentration that should be given, and how often it should be given
What is preclinical testing?
- uses cells, tissues and live animals
- to test efficacy, find out about its toxicity, and find the best dosage
- some people think it’s cruel, however is the safest way
What is clinical testing?
- using volunteers and patients
How do clinical trials take place?
- first, it’s tested on healthy volunteers with a low dose to ensure there are no harmful side effect
- if safe, further clinical trials are carried out to find the optimum dose for the drug
- to test how well it works, patients are split into two groups
- one group receives the drug and one receives a placebo - so the effect of the new drug can be observed
- can be single-blind or double-blind
- before results are published, they are peer reviewed to check for repeatability - prevents false claims
What is the placebo effect?
- when the patient expects the treatment to work and so feels better, even though the treatment isn’t doing anything
How can a placebo be given?
- as a sugar pill
What are double blind trials?
- neither the patient or doctor knows
whether they are receiving the drug - removes any biases the doctor may
have when they are recording the results
What are monoclonal antibodies?
- are identical antibodies, that have been produced from the same immune cell
- ability to bind to only one protein antigen - means they can be used to target chemicals and cells in the body
- have many different medical uses
e.g. pregnancy testing.
How are antibodies produced?
- by a type of WBC called a B-lymphocyte
What do lymphocytes produce?
- antibodies that are used against anything that the body detects as foreign (has a foreign antigen)
What is an antigen?
- a protein on the surface of all cells, specific to each cell
- WBC can detect when a foreign antigen of a pathogen is present
How do you produce monoclonal antibodies?
1) mice are injected with desired antigen to simulate lymphocytes to produce antibodies specific to the antigen
2) lymphocytes are collected from the mice - produces antibodies but do not divide
3) combined with tumour cells - do not produce antibodies but divide rapidly
4) a hybridoma is formed - produces antibodies and divides rapidly through mitosis
5) hybridoma is left to produce clones of itself and produce lots of antibodies
6) antibodies are collected and purified
What is present in a pregnant woman’s urine?
- a hormone called human chorionic gonadotrophin (hCG)
How are monoclonal antibodies used in pregnancy tests?
- there are two sections of the stick.
- the first section has mobile antibodies complementary to the hCG hormone - also attached to blue beads.
- the second section has stationary antibodies complementary to the
hCG hormone - stuck down to the stick.
1) the individual urinates on the first section - if hCG is present it binds to the mobile antibodies attached to blue beads to form hCG/antibody complexes.
2) are carried in the flow of liquid and moves up the stick to the second section.
3) the stationary antibodies then bind to the HCG/antibody complexes - as they are bound to a blue bead, it results in a blue in
4) this indicates that you are pregnant
5) if not, urine still moves up, but there is nothing to stick the blue beads onto the test strip - doesn’t go blue
What are found in cancer cells?
- have antigens on their cell membranes that aren’t found on normal body cells
- known as tumour markers
How are monoclonal antibodies used to treat diseases?
- producing monoclonal antibodies that bind to the tumour markers, - stimulates the immune system to attack the cell
- binds to receptor sites on the cell surface membrane of the cancer cells - growth-stimulating molecules cannot bind, stopping the cell from dividing.
- used to transport toxic drugs, chemicals or radioactive substances as they can only bind to cancer cells - doesn’t kill normal body cells
How are monoclonal antibodies used in laboratories?
- can be used to measure and monitor levels of hormones or chemicals in the blood.
1) monoclonal antibodies are modified - will bind to the molecule you are looking for.
2) the antibodies are also bound to a fluorescent dye.
3) if the molecules are in the sample then the antibodies bind to it, and the
dye can be observed.
e.g. screening donated blood for HIV infections.
How are monoclonal antibodies used in research?
- to find or identify certain molecules on a cell or tissue
- the same method as laboratories is used - scientists look for a build up of the fluorescence
What are the disadvantages of monoclonal antibodies?
- in certain trials have been found to produce very harmful side-effects - fever. vomiting, low blood pressure
- aren’t as widely used as everyone hoped for when first developed
- expensive to develop
- hard to attach monoclonal antibodies to drugs
What are the advantages of monoclonal antibodies?
- only bind to specific cells - healthy cells are not affected
- able to produce mouse-human hybrid cells to reduce the chance of triggering an immune response
- can be engineered to treat many different conditions
What can plants be attacked by?
- pathogens
e.g. TMV and rose black spot - insects
e.g. aphids - extract nutrients like sugars from the plant by piercing phloem with their mouthpiece - lack of glucose = less amino acids can be produced = less proteins produced = stunted growth
What makes up amino acids?
*glucose and nitrate ions
How can plant diseases can be detected?
- stunted growth - nitrate deficiency
- spots on leaves - black spot fungus on roses
- areas of decay (rot) - black spot fungus on roses, blights on potatoes
- abnormal growths e.g. crown galls - bacterial infection
- malformed stems or leaves - aphid infestation
- discolouration - magnesium deficiency, TMV
- the presence of pests
How can plant diseases can be identified?
- reference to a gardening manual or website
- taking infected plants to a laboratory to identify the pathogen
- using testing kits that contain monoclonal antibodies
What can plants be infected by, and what can plants be damaged by?
- infected by a range of viral, bacterial and fungal pathogens, as well as by insects
- damaged by a range of ion deficiencies
How can plants be damaged by nitrate deficiency?
- nitrate ions are needed to make amino acids - makes proteins by converting sugars made in photosynthesis
- a lack of nitrate ions means less proteins are synthesised
- leads to stunted growth in plants
How are plants damaged by magnesium deficiency?
- magnesium ions are needed to make chlorophyll,
- magnesium ion deficiency leads to chlorosis
- leaves of the plant become yellow
Why is the understanding of ion deficiencies important?
- it allows horticulturists (people that cultivate plants) to provide optimum conditions for plants
What are the 3 different types of plant defences?
- physical
- chemical
- mechanical
Name the physical plant defence responses
- strong cellulose cell walls - act as a physical barrier against microorganisms
- thick, tough waxy cuticle on leaves - stops entry into leaves and their cells from becoming infected by bacteria and fungi
- layers of dead cells around stems - form a physical barrier against microorganisms and fall off with the pathogens
e.g. bark
Name the chemical plant defence responses
- produce antibacterial chemicals - kills bacteria
e.g. mint plant, witch hazel - produce poisons - deters herbivores
e.g. foxglove, deadly nightshade
Name the mechanical plant defence adaptations
- thorns and hairs - make it difficult and painful to eat, avoid being eaten, doesn’t defend against insects
- leaves which droop or curl when touched - prevent themselves from being eaten, knock insects off and move away from things
- mimicry to trick animals
- some plants droop to look unhealthy
- plants can have patterns that look like butterfly eggs - butterflies do not lay eggs
e.g. passion flower - stone pebble like appearance - avoide predation
e.g. ice plant famliy
