Infection and response

• Pathogens

  microorganisms that enter the body and cause communicable diseases which are easily spread
• Bacteria

  • very small living cells which can rapidly reproduce inside your body
  • they make you feel ill by producing toxins that damage your cells and tissues
• Fungi

  • some are single celled others have a body made up of hypae (thread-like structures)
  • these hyphae can grow and penetrate human skin and the surface of plants causing dieases
  • the hyphae can produce spores which can be spread to other plants and animals
• Different ways pathogens are spread

  • Water- some can be picked up by drinking or bathing in dirty water, e.g. cholera
  • Air- can be carried in the air and then breathed in, some airborne pathogens are carried in the air in droplets produced when you cough or sneeze
  • Direct contact- can be picked up by touching contaminated surfaces, including the skin
• Measles

  • viral disease that is spread by droplets from an infected persons cough or sneeze
  • when infected you develop a red skin rash and a fever
  • can sometimes lead to pneumonia or inflammation of the brain
  • most people are vaccinated against measles when they are young
• Hiv

  • a virus that is spread by sexual contact or exchanging bodily fluids (eg sharing needles)
  • initially causes flu like symtpoms for a few weeks
  • usually the person doesnt then experience symptoms for several years, during this time hiv can be controlled with antiviral drugs
  • the virus attacks the immune cells
  • if the bodys immune system is badly damaged it cant cope with other infections or cancers
• TMV

  • a virus that affects many species of plants
  • causes a mosaic pattern on the leaves and parts of the leaves become discoloured
  • this discolouration means the plant cant carry out photosynthesis as well so the virus affects growth
• Rose Black Spot

  • fungus that causes purple or black spots to appear on the leaves of rose plants
  • the leaves then turn yellow and drop off
  • less photosythensis can happen so it doesnt grow very well
  • spreads via water or the wind
  • can be treated with fungacides and by removing infected leaves
• Salmonella

  • type of bateria that causes food poisoning
  • symptoms include fever, stomach cramps, vomiting and diarrhoea
  • these symptoms are caused by toxins that the bacteria produce
  • can get it by eating food that has been contaminated by the bacteria
• Gonorrhoea

  • STD
  • passed on by sexual contact
  • caused by bacteria
  • will cause pain during urination and a thick yellow discharge from the vagina or penis
  • originally treated with an antibiotic (penicillin) but strains of the bacteria have now become resistant to it
  • to prevent spread people should use barrier methods of contraception
• Preventing the spread of Disease

  • being hygenic- e.g. washing hands
  • destroying vectors - by removing the organisms that spread the disease you can prevent it from being passed on
  • isolating infected individuals
  • Vaccination
• The bodys defences

  • skin acts as a barrier to pathogens
  • hairs and mucus in the nose trap particles that can contain pathogens
  • trachea and brochi secrete mucus to trap pathogens
  • they are also lined with cillia, hair like structures that waft the mucus back up the throat so it can be swallowed
  • stomach produces hydrochloric acid which kills pathogens that make it far from the mouth
• White blood cells engulf and destroy invading pathogens
• Antibodies bind to specific antigens on pathogen surfaces and mark them for destruction by white blood cells
• Phagocytes engulf and digest pathogens using lysosomes
• The three ways white blood cells can attack pathogens:

  • consuming them
  • producing antibodies
  • producing antitoxins
• Consuming

  • white blood cells can engulf foreign cells and digest them (this is called phagosytosis)
• Producing antibodies

  • every pathogen has unique antigens on its surface
  • when some types of white blood cell come across a foreign antigen they start to produce protiens called antibodies
  • these lock onto the antigens so they can be discovered by other white blood cells
  • antibodies are then rapidly reproduced and carried all around the body to find all similar bacteria/ viruses
  • if you are infected with the same pathogen again the white blood cells will produce antibodies to kill it - you are now naturally immune
• antibodies are specific to that type of antigen
• Producing antitoxins

  they counteract toxins produced by invading bacteria
• Vaccination

  • involve injecting small amounts of dead or inactive pathogens
  • these carry antigens which your body produces antibodies to attack
  • if live pathogens appear after this the white blood cells can rapidly mass-produce to kill off the pathogens
• Pros of vaccination

  • they have helped control lots of communicable diseases
  • big outbreaks of diseases can be prevented if a large percentage of the population is vaccinated - this is called herd immunity
• Cons of vaccination:

  • dont always give you immunity
  • can have a bad reaction (e.g swelling or sometimes more serious things such as fevers and seizures) but this is very rare
• Different types of drugs:

  • painkillers - do not tackle the cause if the disease or kill pathogens but they help to reduce symptoms
  • Antibiotics - kill or prevent the growth of the bacteria without killing your own body cells, they are specific to types of bacteria so you need to be treated with the correct one
  • antibiotics cannot destroy viruses- viruses reproduce using your bodys cells so it is difficult to develop drugs that kill the virus and not your body cells
• Bacteria becoming resistant

  • bacteria can mutate and sometimes this can cause them to become resistant to an antibiotic
  • if you have an infection some of the bacteria may be resistant to antibiotics, the individual resistant bacteria will syrvive and reproduce and the population of the resistant strain increases
  • to slow down the development of resistant strains doctors cannot over-pescribe antibiotics
  • it is also important to finish the whole course of antibiotics
• Drugs from plants

  • Aspirin is a painkiller used to reduce fever- it comes from chemicals in willow
  • digitalis is used to treat heart conditions and it comes from chemicals in foxglove
• Drugs from microorganisms

  • Alexander flemming found that mould on the petri dish he left unattended was producing a substabce that killed that bacteria around it - this substance was called penicillin
• Today plants are made on a large scale in the pharamcetuial industry however the process might still start with a chemical extracted from a plant
• Monoclonal antibodies treating disease

  • different cells n the body have different antigens on the cell surface so you can make monoclonal antibodies that bind to specific cells in the body
  • cancer cells have different antigens to those found on normal body cells - these are called cancer markers
• Monoclonal antibodies other uses

  • bind to hormones and other chemicals in blood to measure their levels
  • test blood samples in labs for certain pathogens
  • locate specific molecules in a cell or in a tissue:

  1. first, monoclonal antibodies are made that will bind to the specific molecules you are looking for
  2. the antibodies are the bound to a flurorescent dye
  3. if the molecules are present in the sample the monoclomal antibodies will bind to them and they can be detected using the dye
• Cons to monoclonal antibodies

  • cause more side effects than originally expected
  • not as widley used as first thought for this reason
• Mineral ions and plants

  • plants need mineral ions from soil or they suffer defficiency symptoms
  • nitrates are needed to make protiens and therefore for growth - a lack of nitrates stunts growth
  • magnesium ions are needed to make chorophyll (needed for photosynthesis) so a lack of it will cause chlorosis and yellow leaves
• Physical plant defences

  • most stems and leaves have a waxy cuticle- provides a barrier for pathogens
  • plant cells are surrounded by cells walls which form a physical barrier against pathogens that make it past the waxy cuticle
  • layers of dead cells around their stems (e.g. outer part of bark) which again act as a barrier
• Chemical plant defences

  • some can produce antibacterial chemicals which kill bacteria
  • others can produce poisins which can deter herbivores
• Mechanical plant defences

  • some have thorns and hairs which stop animals touching and eating them
  • other have leaves that droop or curl when something touches them, prevents insects eating them by knocking them off
  • some plants can mimic other organisms which tricks other organisms into not eating them
• what are antibodies produced by?

  B-lymphocytes (a type of white blood cell)
• monoclonal antibodies are produced by lots of clones of a single white blood cell, this means all the anitgens are identical and will only target one specific protien antigen
• monoclonal antibodies from mice:

  • mouse is injected with chosen antigen
  • B-lymphocytes taken from the mouse
  • fast dividing tumor cells (from a lab) are then fused with the B-lymphocytes
  • this makes a hybridoma cell
  • this cell divides quickly to produce lots of clones that produce the monoclonal antibodies