B3- Infection and response Flashcards
What are the four types of pathogen?
Virus, protozoa, bacteria, fungus.
Which pathogen needs a host cell to reproduce and what does this make them?
Viruses. They are therefore not cells and are always pathogens.
Describe how a virus invades a cell.
- Virus enters cell.
- Substances in the cell break down the virus’ outer membrane.
- The virus’ nucleic acid is released.
- The acid enters the cell’s chemical manufacturing system.
- The virus overpowers the cell; the cell begins producing viruses.
- The viruses are released once there are too many for the cell to hold- the cell is killed.
What are pathogens?
Microorganisms which cause communicable disease.
From smallest to largest, what order do the types of pathogens come?
Viruses → bacteria → fungi → protozoa.
What is a eukaryote?
An organism which has cells with nuclei or a cell with a nucleus. Eukaryotes are complex and include all animals and plants.
Describe bacteria.
- They are very small prokaryotic cells, about 1/100th the size of a body cell
- They reproduce rapidly inside the body
- They make you feel ill by producing toxins that damage cells and tissues
- However, they aren’t always parasites
Describe viruses.
- Not cells
- About 1/100th the size of a bacterium
- Make you feel ill by reproducing rapidly inside cells
Describe protozoa.
- They’re all eukaryotes and some are single-celled
- Some are parasites
- Parasites live on or inside organisms and cause damage
- They are often transferred to the organism via a vector which doesn’t get the disease itself
Describe funghi.
- Not always parasites
- Some are single-celled
- Others have a body made of threadlike structures called hyphae
- Hyphae can grow and penetrate human skin and the surface of plants, causing diseases
- Hyphae produce spores which can be spread to other plants and animals
In what ways can pathogens be spread?
- Ingested substances (water, food)
- Air
- Direct contact
Name 3 viral diseases.
- Measles
- HIV
- Tobacco mosaic virus
How is measles spread?
By droplets of fluid from an infected person’s sneeze/cough.
What are the symptoms of measles?
- Fever and red skin rash
- Can be fatal if there are complications
- E.g. can lead to pneumonia or a brain infection called encephalitis
How can measles be treated?
- Most people are vaccinated against it when they’re young
- If not, the disease must run its course
How is HIV spread?
- Sexual contact
- Exchanging bodily fluids, such as blood- e.g. when sharing needles taking drugs
What are the symptoms of HIV?
- Initially, flu-like symptoms for a few weeks
- Usually, no other symptoms are experienced for several years
- During this time, HIV can be controlled by antiretroviral drugs which stop the virus replicating
- The virus weakens the immune system by attacking immune cells. If it’s badly damaged, the body can’t cope with other infections, or cancers
- At this stage, HIV is known as late stage HIV infection or AIDS
HIV cannot be cured; how can it be prevented?
- Barrier contraception
- Not sharing needles
Why can’t HIV be cured, by our immune system or by drugs?
- When HIV copies its genes, it mutates into many different strains. As a result, the virus overpowers the body’s immune defenses
- It is a virus so reproduces inside cells. This means that it’s hard to kill it without damaging many of our cells
How is TMV spread? What does it affect?
Via vectors. Affects many species of plants.
What are the symptoms of TMV?
- Causes a mosaic pattern on leaves- parts become discoloured
- Discolouration means that plants can’t carry out photosynthesis as well
- TMV therefore inhibits growth
TMV can’t be treated; how can it be prevented?
Field hygeine and pest control.
What kind of disease is rose black spot?
Fungal.
How is rose black spot spread?
Through water and wind.
What are the symptoms of rose black spot?
- Causes purple/black spots to develop on the leaves of rose plants
- The leaves can then turn yellow and drop off
- Therefore, less photosynthesis can happen, so growth is inhibited
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How can rose black spot be treated?
- Using fungicides
- Stripping the plant of its affected leaves, which should be destroyed so that the fungus can’t spread to other plants
What causes malaria?
A protist.
How is malaria spread?
- Part of the malarial protist’s life cycle takes place inside the mosquito
- The mosquitoes are vectors- they pick up the protist when feeding on an infected animal
- When a mosquito feeds on an infected animal, it infects it by inserting the protist into the animal’s blood vessels
What are the symptoms of malaria?
Causes repeating episodes of fever. It can be fatal.
How can the spread of malaria be reduced?
Stopping mosquitoes from breeding.
How can people be protected from getting malaria from mosquitoes?
- Using insecticides
- Using mosquito nets
Why is malaria so difficult to eradicate?
- It is spread by mosquitoes
- It is constantly evolving
- It has several stages to its life cycle; each stage requires different ways to eradicate
Name 2 bacterial diseases.
- Salmonella
- Gonorrhea
How is salmonella spread?
It is foodborne: eating food contaminated with salmonella bacteria.
What are the symptoms of salmonella?
Food poisoning caused by toxins the bacteria produces:
- fever
- stomach cramps
- vomiting
- diarrhoea
How can salmonella be prevented?
- Avoiding contamination
- Food hygeine
- Most poultry in the UK is vaccinated against salmonella to control the spread
How can salmonella be treated?
Consuming fluids or, in extreme cases, antibiotics.
How is gonorrhoea spread?
It is an STD so by sexual contact.
What are the symptoms of gonorrhea?
- Pain when urinating
- Thick yellow/green discharge from the vagina/penis
How is gonorrhoea treated?
- Originally with an antibiotic called penicillin, but strains of the bacteria have now become resistant to it
- Now can now be treated with other antibiotics
How should gonorrhea be prevented?
Barrier contraception, e.g. condoms
Give three terms for diseases that easily spread.
- Contagious
- Communicable
- Infectious
Give 4 ways the spread of disease can be reduced/prevented.
- Hygiene e.g. washing hands before cooking/after sneezing
- Destroying vectors e.g. using insecticides or destroying insects’ habitats so that they can’t breed
- Isolating infected individuals
- Vaccination
What 5 features does the body have which stop a lot of pathogens entering?
- Skin acts as a barrier and secretes antimicrobial substances which kill pathogens.
- Hairs and mucus in the nose trap particles that could contain pathogens.
- The trachea and bronchi secrete mucus to trap pathogens.
- Trachea and bronchi are lined with ciliated cells which waft the mucus up to the back of the throat, where it can be swallowed.
- Stomach produces hydrochloric acid which kills pathogens that have entered the digestive system.
In what 3 ways can the immune system attack pathogens?
- Phagocytosis
- Producing antibodies
- Producing antitoxins.
What is phagocytosis?
Phagocytes, a type of white blood cell, engulf foreign cells/pathogens and digest them with enzymes.
Explain how the immune system produces antobodies.
- Every type of pathogen has a unique molecule, called an antigen, on its surface
- When B-lymphocytes come across a foreign antigen, they start to produce specific antibodies (type of protein) which lock onto the invading cells
- They are then found and destroyed by other white blood cells
- Antibodies are then produced rapidly and carried around the body to find all similar pathogens
- If the person is infected with that pathogen again, B cells will rapidly produce specific antibodies- they are naturally immune to that pathogen
What are antitoxins specific to?
They counteract toxins produced by invading bacteria.
What is a benefit of using vaccinations as opposed to letting the immune system deal with infection?
When infected with a new pathogen, it takes a few days for the immune system to fully respond. By then, you can already be quite ill, so vaccinations are a pre-empt to this.
What do vaccinations involve?
- A small amount of dead/inactive pathogens are injected
- These carry antigens, which cause the immune system to produce specific antibodies, even though the vaccine is harmless
- If live pathogens of the same type enter the body after that, they are recognised
- White blood cells can then rapidly produce antibodies to kill them, so you don’t get ill
What does the MMR vaccine contain?
Weakened versions of the viruses that cause measles, mumps and rubella (German measles).
What are two pros of vaccinations?
- They have helped control lots of communicable diseases that were once common in the UK. For example, smallpox is eradicated and polio infections have fallen by 99%.
- Epidemics can be prevented if a large percentage of the population is vaccinated: even people who aren’t vaccinated are unlikely to catch the disease because there are fewer people to pass it on. This is called herd immunity.
What are two cons of vaccinations?
- They don’t always give you immunity.
- People (uncommonly) have bad reactions to a vaccine, e.g. swelling, fever or even seizures.
What do painkillers do?
They relieve pain and help to reduce symptoms of infection, but don’t deal with the cause of disease or kill pathogens.
Give an example of a painkiller.
Aspirin.
How to antibiotics work?
- They kill/prevent growth of invading bacteria without killing body cells
- Different antibiotics kill different types of bacteria
- Antibiotics have greatly reduced the number of deaths from communicable diseases caused by bacteria
Why can’t antibiotics be used to treat viruses?
Viruses reproduce inside body cells. This makes it difficult to develop drugs that just kill the virus and not cells as well.
How do bacteria become resistant to antibiotics?
- Bacteria can mutate, causing some to become resistant to an antibiotic
- When treating an infection, some of the bacteria might be resistant to the antibiotic you use
- This means that only the non-resistant strains will be killed
- The resistant bacteria will survive and reproduce, the population increasing (this is an example of natural selection)
- The resistant strain could cause a serious infection that can’t be treated by antibiotics
Give an example of an antibiotic resistant bacteria.
MRSA causes serious wound infections and is resistant to the powerful antibiotic meticillin.
What should be done to slow down the development of strains of resistant bacteria?
- Doctors should avoid over-prescribing antibiotics
- People should finish their whole course of antibiotics, rather than stopping once they feel better
Plants produce a variety of chemicals to protect themselves against pests and pathogens. A lot of our current medicines were discovered by studying plants used in traditional cures. Give two examples.
- Developed from a chemical found in willow, aspirin is used as a painkiller and to lower fever.
- Developed from a chemical found in foxgloves, digitalis is used to treat heart conditions.
Give an example of a drug extracted from microorganisms.
- Alexander Fleming was clearing out some petri dishes containing bacteria
- He noticed that one dish also had mould on it, and that the area around the mould was free of bacteria
- He found that the mould was producing a substance, called penicillin, which killed the bacteria
What is the name for the drug industry?
The pharmaceutical industry.
What are the 3 main stages of drug testing?
- Preclinical testing
- Testing on animals
- Clinical trials
What does preclinical testing involve?
Testing drugs on human cells and tissues in a lab.
When testing drugs on live animals, what 3 things are investigated?
- Efficacy (how effective it is)
- Toxicity (whether it’s harmful)
- Dosage (how much, how often)
What are the 2 stages of clinical trials?
- Testing on healthy human volunteers (to make sure it doesn’t have harmful side effects when the body’s working normally). Dosage is gradually increased.
- Testing on people suffering from the illness. Optimum dosage is found (most effective, with the fewest side effects).
What is a placebo?
An inert (inactive) dose of a substance, typically a tablet, that does not contain an active drug ingredient and has no effect.
What is the placebo effect?
When a patient expects a treatment to work, so feels better, regardless of whether it has had an effect.
What two types of trialling do clinical trials typically involve?
- Blind trials
- Double blind trials
What are blind trials?
Patients are study are divided into 2 groups, one which receive the drug and the other a placebo (but the individuals don’t know which they get).
The doctor can see the actual effect of the drug, allowing for the placebo effect.
What are double blind trials?
Patients in a study are divided into 2 groups, one which receive the drug and the other a placebo.
Neither the individuals nor the doctor know which the patients get until the results are gathered.
This is so that the doctors, when monitoring and analysing, aren’t subconsciously influenced by their knowledge.
The results of drug testing aren’t published until they’ve been through peer review. What is this and why is it used?
- Peer review is when other scientists check that the work has been carried out rigorously and that the results have been interpreted validly.
- This helps to prevent false claims.
What type of blood cell produces antibodies?
B-lymphocytes.
What are monoclonal antibodies?
Identical antibodies produced from clones of a hybridoma. These antibodies are used to target one specific protein antigen.
Describe how monoclonal antibodies are produced. (6 marks)
- A mouse is injected with the antigen that the antibodies have been chosen to target.
- The mouse produces B-lymphocytes specific to this antigen.
- These are collected from the mouse.
- Because B-lymphocytes can’t reproduce quickly, they are fused with tumour cells (which very much can).
- This forms hybridoma cells, which are cloned to form a ball of cells.
- The ones which successfully produce antibodies are selected.
- The antibodies of these hybridomas are collected and purified - these are monoclonal antibodies.
Give 3 uses of monoclonal antibodies.
- Pregnancy tests.
- Treating diseases.
- Laboratory research.
How are monoclonal antibodies used in pregnancy tests? (6 marks)
The part of the stick which is urinated on contains monoclonal antibodies specific to the hormone HCG, found in the urine of pregnant women. Blue dye is attached to the antibodies.
- If you’re pregnant: the hormone binds to the mobile antibodies in the part you wee on. The urine moves up the stick, carrying the hormone and the dye. The dye and hormone bind to the immobile antibodies in the test strip (part that turns blue if preggies), getting stuck there and turning it blue.
- If you’re not pregnant: as the urine moves up the stick, it still carries the antibodies attached to the blue dye with it. But there is no HCG to bind to them, so the blue dye doesn’t get stuck to the test strip and so it doesn’t go blue.
How are monoclonal antibodies used to treat cancer? (6 marks)
- Body cells have specific antigens on their surface; you can make monoclonal antibodies specific to these.
- Cancer cells have antigens on their membranes (tumour markers) that aren’t on normal body cells.
- You can make MAs that will bind to these markers.
- An anti-cancer drug (e.g. a radioactive substance, toxic drug, or chemical which prohibits growth) can be attached to these MAs.
- The MAs are given to a patient through a drip.
- They target and kill the cancer cells w/o killing any normal body cells near the tumour.
What is the advantage of using monoclonal antibodies to treat cancer, over other treatments?
Other treatments (chemotherapy and radiotherapy) affect normal body cells as well as the cancerous ones, whereas MAs target specific cells. So the side effects of an antibody-based drug are lower than that of these other treatments.
How are monoclonal antibodies used in laboratory research? Give 3 examples of their use.
Can be used to:
- Bind to chemicals in blood (e.g. hormones) to measure their levels.
- Test blood samples for certain pathogens.
- Locate specific molecules in a cell/tissue.
This is done by making MAs specific to the substance, then binding them to a fluorescent dye. The substance is detectable by the presence of this dye (because the MAs bind to the substance being tested for).
Why are monoclonal antibodies not as widely used as scientists had orignially hoped?
They cause more side effects (e.g. fever, vomiting, low blood pressure) than expected; initially, scientists had thought this wouldn’t be the case, as they target specific cells/molecules.
Give 2 examples of mineral ion deficiency symptoms in plants.
- Nitrate deficiency: nitrates are needed to make proteins for growth. A lack causes stunted growth.
- Magnesium ion deficiency: magnesium is needed for making chlorophyll for photosynthesis. Plants who lack it suffer from chlorosis and have yellow leaves.
Give 7 common signs of disease in plants.
- Stunted growth
- Abnormal growths, e.g. lumps
- Malformed stems/leaves
- Spots on leaves
- Discolouration
- Patches of decay
- Infestation of pests
Give 3 examples of physical disease defences that plants have to prevent entry of pathogens.
- Waxy cuticle on leaves and stems provides a barrier.
- Cell walls (made of cellulose) form another.
- Layers of dead cells around stems, e.g. bark on trees.
Give 2 examples of chemical defences that plants have.
- Some produce antibacterial chemicals, e.g. the mint plant and witch hazel.
- Others produce poisons which deter herbivores, e.g. tobacco plants, foxgloves and deadly nightshade.
Give 2 examples of mechanical defences that plants have.
- Some have thorns and hairs that stop animals touching/eating them.
- Others have leaves that droop/curl when something touches them, which knocks off insects and moves them away from things.
- Some can mimic other organisms; e.g. the passion flower’s leaves have bright yellow spots which look like butterfly eggs, preventing other butterflies from laying their eggs there.
