Infection and Response

• Pathogens are microorganisms that cause infectious disease.
• A communicable disease can be spread from person to person and is spread by a pathogen.
• Viruses live and reproduce inside cells, causing cell damage. A virus invades a cell and then reproduces inside the cell. This can then cause the cell to burst open and die.
• Pathogens 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.
• How can you reduce the spread of pathogens?

  • Washing hands before eating meals
  • Vaccination
  • Isolating if you show any symptoms
  • Cleaning work surfaces
  • Sterilising water to kill bacteria
• What is measles?

  Measles is a viral disease showing symptoms of fever and a red skin rash. Measles is a serious illness that can be fatal if complications arise. For this reason most young children are vaccinated against measles. The measles virus is spread by inhalation of droplets from sneezes and coughs. Measles cannot be killed with antibiotics because it is a virus.
• What is HIV?

  HIV initially causes a flu-like illness. Unless successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells. Late stage HIV infection, or AIDS, occurs when the body's immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.
• What is tobacco mosaic virus?

  Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis as there is less chlorophyll.
• What is salmonella?

  Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions. In the UK, poultry are vaccinated against salmonella to control the spread. Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.
• What is gonorrhoea?

  Gonorrhoea is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating. It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. Gonorrhoea is spread by sexual contact. The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.
• Explain the malaria life-cycle?

  1. A person is bitten by the vector, a mosquito, and the malaria pathogen passes into the mosquito.
  2. Mosquito enters cell and feeds on blood. Bursts cell and enters another.
  3. Less oxygenated blood flows through body.
• How can you reduce the spread of malaria?

  • Use mosquito nets to avoid being bitten
  • Remove stagnant water to prevent mosquitoes from breeding
  • Take antimalarial drugs
• How does the skin act as defence system?

  • Acts as protective barrier
  • Produces sebum to kill bacteria (antimicrobial secretions)
  • Skin produces scabs if there is open wound
• How does the nose act as a defence system?

  • Has hair and mucus which prevents particles from entering the lungs
• How do the trachea and bronchi act as a defence system?

  • Have tiny hair called cilia, waft mucus upwards so it can be swallowed
  • Secrete mucus to trap pathogens
• How does the stomach act as a defence system?

  Hydrochloric acid which kills pathogens
• How is phagocytosis used to help white blood cells defend against pathogens?

  White blood cells engulf pathogens. The white blood cell secretes enzymes which digest the pathogens so they can no longer make you feel sick.
• How does producing antibodies help white blood cells defend against pathogens?

  The lymphocytes release antibodies which is complmenterary to the antigen on the surface of the pathogen. Once antibodies bind to the pathogen, the pathogens clump together making it easier for phagocytosis to take place.
• If a person becomes infected with the same pathogen, the complementary antibodies will be produced at a faster rate. This is because memory cells are produced so the immune response to later exposure takes place faster. The individual is now immune.
• How does producing antitoxins help white blood cells defend against pathogens?

  White blood cells produce chemicals called antitoxins which neutralise the toxins released by the pathogens by binding to them which prevents them from damaging cells, making the person feel less sick.
• What is rose black spot?

  Rose black spot is a fungal disease where purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced. It is spread in the environment by water or wind. Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.
• Rose black spot causes the rate of photosynthesis to go down which reduces the rate of growth.
• A vaccine is introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies.
• If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.
• If enough people are vaccinated against a pathogen, it will also protect the unvaccinated people. This is herd immunity.
• How can the use of antibiotics lead to antibiotic resistance?

  If antibiotics are over used, bacteria begins to evolve so it is not killed by antibiotics. Mutations can occur during reproduction which means certain bacteria cannot be killed by antibiotics. The resistant bacteria then survive and reproduce so the population of resistant bacteria increases. This means antibiotics that were previously effective no longer work.
• Antibiotics cannot kill viruses because viruses live inside cells and reproduce, any drugs that target viruses would affect body tissue as well.
• Preclinical testing is done in a laboratory using cells, tissues and live animals. This isn't carried out on humans as the appropriate toxicity has not been found yet.
• Clinical tested is done on healthy patients and volunteers.
• Explain the stages of clinical testing.

  1. Very low doses of the drug are given to make sure there are no harmful side effects.
  2. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug.
  3. Patients are then given a placebo so the effect of the drug can be checked.
• What is a placebo?

  A placebo is a drug that appears to look like a prescribed drug but has no active drug in it.
• What is the importance of a double blind-trial?

  This stops bias so that doctors do not pay closer attention to the volunteers that are receiving the drug.
• If a person is re-exposed to an illness, antibodies are produced quickly in larger quantities to kill the pathogen.
• How do plants defend themselves against harmful microorganisms?

  • Cell wall: difficult to penetrate
  • Dead cells: fall off and take off any pathogens
  • Production of antibacterial chemicals: to kill bacteria
• Explain why prescribing an antibiotic will not cure HIV

  HIV is a virus. Antibiotics only kill bacteria.
• Explain why plants with TMV have stunted growth.

  Less photosynthesis takes place because of a lack of chlorophyll, this means less glucose is made so less energy is released for growth. Glucose is also needed to produce amino acids which help with growth.
• How do plant stings act as a defence mechanism?

  Stops herbivores and other animals from eating them so less of the plant is removed/damaged.
• How could a gardener identify which pathogens are affecting their plants?

  1. Compare them using other photos
  2. Send them to a lab
• Describe how the immune system defends the body against disease.

  Phagocytes: Engulf cells

  Produces antibodies: Attach to cells and kill them, clump them together so phagocytes can engulf more cells

  Produce antitoxins: Neutralise bacterial toxins so there is less tissue damage so you feel less ill.
• Why are results studied by other scientists?

  For peer review and to avoid bias and make sure conclusions are correct.