B3

• Pathogens are microorganisms that enter the body and cause disease.
• The types of pathogens are bacteria, viruses, protists or fungi.
• Bacteria are very small living cells. They can make you feel ill by producing toxins that damage your cells and tissues.
• Viruses are not cells. They reproduce rapidly inside your body. They live inside your cells and replicate themselves using the cells' machinery to produce many copies of themselves. The cell usually bursts, releasing all the new viruses. This cell damage is what makes you feel ill.
• Protists are single-celled eukaryotes. Some protists are parasites. Parasites live on or inside other organisms and can cause them damage. They are often transferred to the organism by a vector, which doesn't get the disease itself.
• Fungi come in different shapes. Some are single-celled, others have a body which is made up of hyphae. These hyphae can grow and penetrate human skin and the surface of plants, causing diseases. They can produce spores, which can be spread to other plants and animals.
• Pathogens can be spread in different ways:

  • Water

  - Some pathogens can be picked up by drinking or

  bathing in dirty water.

  • Air

  - Pathogens can be carried in the air, and then

  breathed in. Some airborne pathogens are carried in

  the air in droplets that are produced when you cough

  or sneeze.

  • Direct contact

  - Some pathogens can be picked up by touching

  contaminated surfaces, including the skin.
• Rose Black Spot (fungal disease)

  • Causes black or purple spots to develop on the leaves
  • Prevents photosynthesis from happening
  • Spreads through the environment in water or wind
  • It can be treated by using fungicides
• Measles, HIV and TMW are viral diseases.
• Malaria is a disease caused by a protist.
• almonella (bacterial disease)

  • Salmonella is a type of bacteria that causes food poisoning
  • Infected people can suffer from fever, stomach cramps, vomiting and diarrhoea
  • Symptoms are caused by the toxins that bacteria produce
  • You can get salmonella food poisoning by eating food that's been contaminated with salmonella bacteria
• Tobacco Mosaic Virus (viral disease)

  • Affects many species of plants
  • Causes a mosaic pattern on the leaves
  • May cause them to become discoloured
  • Prevents photosynthesis from happening
• HIV (viral disease)

  • Spread by sexual contact or bodily fluids
  • Can also be spread when people share needles
  • Initially causes flu-like symptoms
  • Can be controlled with antiretroviral drugs
  • Virus attacks the immune cells
  • If the body's immune system is badly damaged, it can't cope and the HIV may develop into AIDS
• Measles (viral disease)

  • Spread by droplets from an infected person's sneeze or cough
  • Develops a rash and fever
  • Can be very serious or even fatal
  • Most people are vaccinated against it when they are young
• Gonorrhoea (bacterial disease)

  • It is a sexually transmitted disease (STD)
  • STDs are passed on by sexual contact
  • Gonorrhoea is caused by bacteria
  • It is usually treated with an antibiotic called penicillin, but this has become thicker to treat as bacteria has become resistant to it
  • To prevent the spread of gonorrhoea, people can be treated with antibiotics and should use barrier methods of contraception
• The spread of disease can be reduced or prevented by:

  • Being hygienic - using simple hygiene measures
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• The defence system in the body:

  • Skin acts as a barrier to pathogens. It also secretes antimicrobial substances which kill pathogens
  • Hairs and mucus in your nose trap particles that could contain pathogens
  • The trachea and bronchi secrete mucus to trap pathogens. They are also lined with cilia
  • The stomach produces hydrochloric acid, which kills pathogens that make it far away from the mouth
• The immune system attacks pathogens by:

  1. Consuming them - white blood cells engulf foreign cells and digest them, this is called phagocytosis
  2. Producing antibodies - when white blood cells come across a foreign antigen, they produce antibodies which are carried around the body to find bacteria or viruses.
  3. Producing antitoxins - these counteract the toxins produced by the invading bacteria
• Vaccination

  • Vaccinations involve injecting small amounts of dead or inactive pathogens. These carry antigens, which cause your body to produce antibodies to attack them - even though the pathogen is harmless.
  • After this, if live pathogens of the same type appear, the white blood cels can rapidly mass-produce antibodies to kill off the pathogen.
• Pros and Cons of vaccination:

  • Pros

  - Vaccines have helped control lots of communicable

  diseases that were once common in the UK.

  - Big outbreaks of disease can be prevented if a large

  percentage of the population is vaccinated.

  • Cons

  - Vaccines don't always work

  - You can sometimes have a bad reaction to a vaccine
• Painkillers are drugs that relieve pain, however, they don't actually tackle the cause of the disease or kill pathogens. They just help to reduce the symptoms.
• Antibiotics actually kill the bacteria causing the problem without killing your own body cells. Different antibiotics kill different types of bacteria, so it's important to be given the right ones. They can't destroy viruses.
• Bacteria can mutate - sometimes this leads to the bacteria becoming resistant to an antibiotic.
• Plants produce a variety of chemicals that can defend themselves against pathogens. Some of these chemicals can be used as drugs to treat human diseases or relieve symptoms.
• The three main stages of drug testing:

  1. In preclinical testing, drugs are tested on human cells and tissues in the lab.
  2. The next step in preclinical testing is to test the drug on live animals.
  3. If the drug passes the tests on animals then it's tested on human volunteers in a clinical trial.
• Monoclonal antibodies are identical antibodies.
• Plants need mineral ions from the soil. If there aren't enough, plants suffer deficiency symptoms.

  Nitrates are needed to make proteins and therefore for growth. A lack of nitrates causes stunded growth.

  Magnesium ions are needed for making chlorophyll, which is needed for photosynthesis. Plants without enough magnesium suffer from chlorosis and have yellow leaves.
• Plants can be infected by viral, bacterial and fungal pathogens.