infection and response

• pathogens can be spread through touch, water or air
• pathogens infect the plant or animal (host) and they rely on the host for the conditions and nutrients they need. once inside the host they can reproduce quickly. they can produce toxins and viruses that make you ill
• measles is a virus that is spread by droplets in the air and can cause fever, cough, red skin rash. most children are vaccinated as a child to prevent this
• HIV is a virus it is spread through bodily fluids e.g. sharing needles. it attacks the immune system and can be controlled by taking antiretroviral drugs.
• salmonella is a type of food poisoning caused by bacteria. it spreads through eating contaminated food and can cause fever, cramps, vomiting and diarrhoea
• gonorrhea is a STD caused by bacteria that is spread through sexual contact. can cause pain when urinating and is treated with penicillin. can be prevented through the use of condoms
• malaria is a protist that is spread through mosquitos. The mosquito is called a vector because it carries the protist that causes the disease. People with the disease suffer from repeated attacks of fever. it can be prevented removing standing water (where they breed)
• Tobacco mosaic virus (TMV) is a viral plant disease. It causes yellowing of leaves and stunted growth. it makes it harder for plants to photosynthesis and they grow more slowly
• Rose black spot is a fungal plant disease. it causes black or purple spots. The plant grows more slowly because it photosynthesises less. Infected plants can be treated with fungicides.

  Another treatment is to remove and destroy discoloured leaves.
• Skin, cilia and stomach acid are the first line of defence against pathogens.

  • The skin is a physical barrier, stopping pathogens from entering the body.
  • Cilia trap pathogens from the air when you breathe in. Then, when you blow your nose, the pathogens are removed.
  • The pathogens are then swallowed and destroyed by acid in the stomach. Stomach acid also kills pathogens found in food or drink.
• White blood cells are part of the body's immune system.

  White blood cells are found in the plasma in the blood.

  One type of white blood cell is called a phagocyte.

  Phagocytes destroy pathogens by engulfing (surrounding) them and digesting them
• Lymphocytes are another type of white blood cell.

  Lymphocytes produce antibodies (proteins) that bind to pathogens. This makes it easier for phagocytes to engulf a large amount at once.
• Vaccination introduces a small amount of dead or inactive (so harmless) pathogen into the body.

  This means that white blood cells can respond quickly to that pathogen in the future.
• In an unvaccinated community, any individual exposed to a pathogen can become ill.

  Each individual can then spread the pathogen to others. When more people are immunised, fewer people become ill and spread the disease.

  This is especially important to people who can't have immunisations, like young babies or people with illnesses.
• antibiotics are medicines that kill bacteria e.g. penecillin comes from penecillium mold.

  they can target a wide or small range of bacteria
• bacteria mutate quickly. This has led to new strains of bacteria that aren't killed by the antibiotics. These bacteria are known as resistant bacteria. Overusing antibiotics can lead to more bacteria becoming resistant to antibiotics.
• Antibiotics will not help a patient who's infected with a virus.

  Some viral infections are treated with antiviral drugs.

  Antiviral drugs slow down the growth of viral pathogens.
• Viruses live inside a host’s cells. This makes it hard to find drugs that target the virus without harming the host's cells
• Drugs were originally made from plants and microorganisms. e.g. digitals were extracted from foxglove
• Drugs need to be tested to see if they're effective. It's also important to check whether drugs are toxic (poisonous) and to identify any side effects. this is done in two stages:

  • The first stage is called preclinical testing.

  In preclinical testing, a drug is tested on cells, tissues or live animals in a laboratory.

  • The second stage is a clinical trial.

  
  

  In clinical trials, a drug is tested using human volunteers.
• Clinical trials use healthy volunteers and sick patients.

  The drug is first tested on healthy volunteers to make sure it's safe and check for side effects.

  Then the drug is given to sick patients.

  At the start of a clinical trial, the patients take low doses of a drug to check if it is safe.

  If it's safe, then more trials are held to find the best dosage.
• In a double blind trial, one group of patients gets the drug and another group gets a placebo.

  A placebo looks like the real drug but doesn't do anything.

  The patients and the researchers don't know which patients are in each group.

  The results show whether the drug is more effective than the placebo.