Infection and Response - topic 3 (paper 1)

• Pathogens, which include viruses, bacteria, protists and fungi, are microorganisms that cause infectious disease.
• Pathogens can infect plants or animals, spreading through either direct contact, by water or by air.
• Viruses are very small, move into cells and use the biochemistry of it to make many copies of itself, leading to the cell bursting and releasing all of the copies into the bloodstream.
• Bacteria are small, multiply very quickly through dividing by a process called binary fission, and produce toxins that can damage cells.
• Protists are some that are parasitic, meaning they use humans and animals as their hosts, causing damage.
• Fungi can either be single celled or have a body made of hyphae (thread-like structures), can produce spores which can be spread to other organisms.
• Communicable (Infectious) Diseases are caused by pathogens, which include viruses, bacteria, protists and fungi, and can infect plants or animals, spreading through either direct contact, by water or by air.
• Chemical defences are used to deter predators or kill bacteria, with poisons coming from foxgloves, tobacco plants, deadly nightshades, and yew, which deter herbivores.
• Mimicry is used in some plants to trick animals, with some drooping to look like unhealthy plants so that animals avoid them.
• Plants can have patterns that appear to look like butterfly eggs, so butterflies do not lay their eggs here in order to avoid competition.
• Species from the 'ice plant family' have a stone and pebble-like appearance in order to avoid predation.
• Mechanical defences include thorns and hairs that make it difficult and painful for animals to eat them, but do not defend against insects.
• Some leaves can droop or curl when touched, allowing them to move away and move insects off their leaves.
• Antibacterial compounds kill bacteria, such as mint plant and witch hazel.
• Viruses are particularly dangerous as they can enter all types of cells, and scientists are yet to develop medicines to cure them.
• Measles symptoms include fever and red skin rash, which can lead to other problems such as pneumonia, encephalitis and blindness.
• HIV symptoms initially include flu-like symptoms, then the virus attacks the immune system and leads to AIDS, a state in which the body is susceptible to many different diseases.
• HIV is spread by sexual contact or exchange of bodily fluids such as blood.
• The advantages of using monoclonal antibodies are that they only bind to specific cells, meaning healthy cells are not affected, but it is difficult to attach monoclonal antibodies to drugs.
• An example of using antibodies is screening donated blood for HIV infections.
• If the molecules are in the sample, the antibodies bind to it, and the dye can be observed.
• Monoclonal antibodies can be engineered to treat many different conditions, but they are expensive to develop.
• Plants can also be affected by viral, bacterial and fungal pathogens, and the common signs of plant diseases are: stunted growth, spots on leaves, areas of decay, abnormal growths, malformed stems or leaves, and discolouration.
• In research to find or identify certain molecules on a cell or tissue, the same method as above is applied, and scientists look for a build up of the fluorescence.
• In the treatment of disease, such as cancer, cancer cells have antigens on their cell membranes known as tumour markers, which can be targeted.
• Plants have a number of physical, chemical and mechanical adaptations to prevent the invasion of microorganisms, including a tough waxy cuticle that stops entry into leaves, cellulose cell walls that form a physical barrier into the cells, and layers of dead cells around stems which stop pathogens entering.
• There are three main ways to treat cancers using monoclonal antibodies: producing monoclonal antibodies that bind to the tumour markers in order to stimulate the immune system to attack the cell, using monoclonal antibodies to bind to receptor sites on the cell surface membrane of the cancer cells, and using monoclonal antibodies to transport toxic drugs, chemicals or radioactive substances as they can only bind to cancer cells.
• The spread of HIV can be reduced by using condoms, not sharing needles, screening blood when it is used in transfusions, and mothers with HIV bottle-feeding their children instead of breastfeeding.
• Tobacco mosaic virus, a plant pathogen affecting many species of plants including tomatoes, causes symptoms such as discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield.
• Tobacco mosaic virus is spread through contact between diseased plants and healthy plants, with insects acting as vectors.
• Producing antitoxins involves neutralising the toxins released by the pathogen by binding.
• Epidemics can be prevented through herd immunity.
• Bacteria are becoming resistant to antibiotics due to mutations during reproduction, meaning certain bacteria no longer respond to antibiotics.
• Bad reactions, such as fevers, can occur in response to vaccines, although very rare.
• The vaccine contains a dead or inactivated form of the pathogen, stimulating white blood cells to produce antibodies complementary to the antigens on the pathogen.
• Vaccinations replicate the first infection so that when the person is exposed to the real disease they do not feel any symptoms, just like in a secondary infection.
• Discovery and development of drugs involves testing for toxicity, efficacy, and dose, using preclinical testing and clinical trials.
• Antibiotics can be taken as a pill, syrup or directly into the bloodstream.
• Vaccinations are not always effective in providing immunity.
• Vaccinations work by immunising a large proportion of the population, reducing the spread of the pathogen and creating herd immunity.