Biology paper 1 topic 3&4

• Types of Pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Pathogens


  Microorganisms that enter the body and cause disease
• Bacteria


  • They are small cells (about 1/100th the size of your body cells)
  • They can reproduce rapidly inside your body
  • They can produce toxins (poisons) that damage your cells
• Viruses


  • They are not cells, they are tiny (about 1/100th the size of a bacterium)
  • They can reproduce rapidly inside your body
  • They live inside your cells and replicate using the cells' machinery
• Protists


  • They are single-celled eukaryotes
  • Some are parasites that live on or inside other organisms and can cause them damage
  • They are often transferred to the organism by a vector (an insect that carries the protist)
• Fungi


  • Some are single-celled, others have a body made up of hyphae (thread-like structures)
  • The hyphae can grow and penetrate human skin and the surface of plants, causing diseases
  • The hyphae can produce spores, which can be spread to other plants and animals
• Ways pathogens can be spread

  • Water
  • Air
  • Direct contact
• Cholera is a bacterial infection that's spread by drinking water contaminated with the diarrhoea of other sufferers
• The influenza virus that causes flu is spread through the air in droplets produced when you cough or sneeze
• Athlete's foot is a fungus which makes skin itch and flake off, it's most commonly spread by touching the same things as an infected person, e.g. shower floors and towels
• Viral diseases to know about

  • Measles
  • HIV
  • Tobacco mosaic virus
• Measles


  • It is spread by droplets from an infected person's sneeze or cough
  • People with measles develop a red skin rash and show signs of fever (high temperature)
  • Measles can be very serious or even fatal if there are complications like pneumonia or brain infection
• HIV


  • It is spread by sexual contact or by exchanging body fluids such as blood
  • It initially causes flu-like symptoms for a few weeks, then the person doesn't experience symptoms for several years
  • The virus attacks the immune cells
  • If the immune system is badly damaged, the virus is known as late stage HIV infection or AIDS
• Tobacco mosaic virus (TMV)


  • It affects many species of plants like tomatoes
  • It causes a mosaic pattern on the leaves of the plants - parts become discoloured
  • The discolouration means the plant can't carry out photosynthesis as well, so the virus affects growth
• Fungal disease to know about

  • Rose black spot
• Rose black spot


  • It causes purple or black spots to develop on the rose plant leaves
  • The leaves can then turn yellow and drop off
  • This means less photosynthesis can happen, so the plant doesn't grow very well
  • It spreads through the environment in water or by the wind
  • Gardeners can treat it using fungicides and by stripping the plant of affected leaves
• Disease caused by a protist


  • Malaria
• Malaria


  • Part of the malarial protist's life cycle takes place inside the mosquito
  • Mosquitoes pick up the malarial protist when they feed on an infected animal, and then infect other animals when they feed on them
  • Malaria causes repeating episodes of fever and can be fatal
  • The spread of malaria can be reduced by stopping the mosquitoes from breeding and protecting people from mosquito bites
• Bacterial diseases to know about

  • Salmonella
  • Gonorrhoea
• Salmonella


  • It causes food poisoning with symptoms like fever, stomach cramps, vomiting and diarrhoea
  • People get it by eating food contaminated with Salmonella bacteria, e.g. undercooked chicken
  • In the UK, most poultry is given a vaccination against Salmonella to control the spread
• Gonorrhoea


  • It is a sexually transmitted disease (STD) passed on by sexual contact
  • Symptoms include pain when urinating and a thick yellow/green discharge
  • It was originally treated with penicillin but strains have become resistant, so other antibiotics are now used
  • To prevent spread, infected people are treated with antibiotics and barrier contraception is used
• Ways to reduce or prevent the spread of disease

  • Being hygienic
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• Hygiene measures


  • Washing hands thoroughly before preparing food or after sneezing can stop you infecting others
• Destroying vectors


  • Killing insects that spread disease or destroying their habitat to prevent breeding
• Isolating infected individuals


  • Prevents them from passing the disease on to others
• Vaccination


  • Vaccinating people and animals against communicable diseases means they can't develop the infection and pass it on
• The human body has features that stop many pathogens getting inside in the first place, like the skin acting as a barrier and secreting antimicrobial substances
• The body also has an immune system that can attack pathogens that do get inside, using white blood cells to consume them, produce antibodies, and produce antitoxins
• Vaccination


  • Involves injecting small amounts of dead or inactive pathogens to stimulate the body to produce antibodies
  • If the live pathogen then tries to attack, the antibodies can rapidly kill it off
• Pros of vaccination


  • Vaccines have helped control many communicable diseases
  • Vaccination of a large percentage of the population can prevent epidemics
• Cons of vaccination


  • Vaccines don't always work and provide immunity
  • There can sometimes be bad reactions to vaccines, though these are very rare
• Painkillers


  Drugs that relieve pain but don't tackle the underlying cause or kill pathogens
• Antibiotics


  Drugs that kill or prevent the growth of bacteria causing an infection, without killing the body's own cells
• Antibiotics don't destroy viruses, as viruses reproduce using the body's own cells which makes them difficult to target without also killing the body's cells
• Antibiotic resistance


  • Bacteria can mutate to become resistant to antibiotics
  • This allows resistant strains to survive and reproduce, increasing the population of resistant bacteria
  • To slow resistance, doctors avoid over-prescribing antibiotics and patients must finish the full course
• Many drugs were originally discovered by studying chemicals from plants used in traditional cures, such as aspirin from willow and digitalis from foxgloves
• Some drugs were also extracted from microorganisms, like the antibiotic penicillin discovered from mould by Alexander Fleming
• It's important for doctors to avoid over-prescribing antibiotics to prevent the spread of resistant strains
• Doctors will only prescribe antibiotics for something more serious, not for a sore throat
• It's important to finish the whole course of antibiotics and not stop once you feel better