biology b3+b4

• Pathogens


  Microorganisms that enter the body and cause communicable (infectious) disease
• Pathogens


  • Can infect plants and animals
• Bacteria


  Small cells that can reproduce very quickly in the body
• Bacteria


  Produce toxins that make you feel ill, damaging your cells and tissues
• Viruses

  Much smaller than bacteria; they can also reproduce quickly in the body
• Viruses


  Live inside your cell where they replicate, then burst out of the cell, releasing new viruses
• Protists


  Eukaryotes (multicellular); some are parasites which live on or inside other organisms, often carried by a vector
• Fungi


  Sometimes single celled, others have hyphae that grow and penetrate human skin and the surface of plants
• Pathogens can be spread in many ways, for example:

  Water - by drinking dirty water, e.g. cholera.

  Air - carried by air and breathed in, e.g. influenza.

  Direct contact - touching contaminated surfaces including the skin, e.g. athlete's foot.
• Measles


  Spread by droplets of liquid from sneezes and coughs, symptoms include a red rash on the skin and a fever, can be serious or even fatal, can lead to pneumonia, most people are vaccinated against when very young
• HIV


  Spread by sexual contact or exchanging body fluids, can be controlled by antiviral drugs which stop the viruses replicating, attacks the cells in the immune system, if the immune system is badly damaged the body cannot cope with other infections, this is the late stage and is called AIDS
• Tobacco mosaic virus


  Affects plants, parts of the leaves become discoloured, this means plants cannot carry out photosynthesis, this will affect the plants growth
• Fungal

  Rose black spot shows as black spots on the leaves of the plant, this means less photosynthesis occurs. As a result, the plant does not grow as well. It is spread by the wind or the water. They can be treated by using fungicides and taking the leaves off the infected plant.
• Protists

  Malaria is caused by a protist, mosquitoes are the vectors.

  They become infected when they feed on an infected animal. The protist is inserted into the blood vessel.

  Malaria can cause fever, it can also be fatal.
• Bacterial Diseases

  Salmonella bacteria causes food poisoning. Symptoms include fever, stomach cramps, vomiting and diarrhea. The symptoms are caused by the toxins produced by the bacteria. Food contaminated with salmonella can give you food poisoning. Most poultry in the UK will have had a vaccination against salmonella.
• Bacterial Disease

  Gonorrhoea is a sexually transmitted bacterial disease, passed on by sexual contact. Symptoms include pain when urinating and thick yellow/green discharge from the vagina or penis. To prevent the spread, people should be treated with antibiotics and use a condom.
• How to prevent the spread:

  Being hygienic - washing hands thoroughly.

  Destroying vectors -

  killing vectors by using insecticides or destroying their habitat.

  Isolation -

  isolating an infected person will prevent the spread.

  Vaccination -

  people cannot develop the infection and then pass it on.
• The skin acts as a barrier to pathogens.
• Hairs and mucus in your nose trap particles.
• The trachea and bronchi secrete mucus to trap pathogens. They also have cilia which move backwards and forwards to transport the mucus towards the throat. This traps any pathogens and the mucus is usually swallowed.
• The stomach contains hydrochloric acid to kill any pathogens that enter the body via the mouth.
• White blood cells:

  •Phagocytosis is when white blood cells engulf pathogens and then digest them.

  •They produce antitoxins to neutralise the toxins.

  •They also produce antibodies. Pathogens have antigens on their surface, antibodies produced by the white blood cells lock on to the antigen on the outside of the pathogen. White blood cells can then destroy the pathogens. Antibodies are specific to one antigen and will only work on that pathogen.
• Vaccinations have been developed to protect us from future infections. A vaccination involves an injection of a dead or weakened version of the pathogen. They carry antigens which cause your body to produce antibodies which will attack the pathogen. If you are infected again, the white blood cells can produce antibodies quickly.
• Pros of vaccination

  •Helps to control communicable

  diseases that used to be very

  common.

  •Epidemics can be prevented.

  Cons of vaccination

  •They don't always work.

  •Some people can have a bad reaction to a vaccine - however, that is very rare.
• Fighting Disease - Drugs

  Painkillers relive the pain and symptoms, but do not tackle

  the cause.

  Antibiotics kill the bacteria causing the problem, but do not work on viruses. Viruses are very difficult to kill because they live inside the body cells.
• three main stages in drug testing:

  Pre-clinical testing:

  1. Drugs are tested on human cells and tissues.
  2. Testing carried out on living animals.

  Clinical testing:

  3. Tested on healthy human volunteers in clinical trials. Starts with a very low dose, then tested on people with the illness to find the optimum dose.
• Placebo is a substance that is like the drug, but does not do anything.
• Placebo effect is when the patient thinks the treatment will work even though their treatment isn't doing anything.
• Blind trial is when the patient does not know whether they are getting the drug or the placebo.
• Double-blind trial is when both the doctor and the patient do not know whether they are getting the drug.
• Chemicals produced by plants to defend themselves can be used to treat human diseases or help with symptoms.

  Aspirin->willow tree

  Digitalis->foxglove

  Penicillin->mould-penicillium
• Photosynthesis


  A chemical reaction which takes place in plants, converting carbon dioxide and water into glucose and oxygen, using light energy absorbed by chlorophyll
• Photosynthesis


  Carbon dioxide + water -> glucose + oxygen
• Photosynthesis


  • An endothermic reaction
  • Takes place inside chloroplasts in plant cells
• Photosynthesis reaction: 6CO2 + 6H2O -> C6H12O6 + 6O2
• Glucose from photosynthesis


  Used for respiration, stored as starch/fat/oils, used to produce cellulose or amino acids for protein synthesis
• Limiting factors


  Things that stop photosynthesis from occurring at a faster rate (temperature, light intensity, carbon dioxide level)
• Increasing temperature


  Increases rate of reaction up to 45°C, then enzymes become denatured
• Increasing light intensity


  Increases rate of reaction due to more energy
• Increasing carbon dioxide concentration

  Increases rate of reaction due to more reactants available