Communicable Diseases

Frage	Antworten
Describe the structure of a virus	Around 0.02-0.3µm in diameter. The basic structure is some genetic material surrounded by protein.
How do viruses reproduce?	A virus invades a living cell and inserts its genetic material. The DNA takes over the biochemistry of the host cell to make more viruses.
What are bacteriophages?	They are viruses that infect bacteria
What are protoctista?	A group of eukaryotic organisms. A small percentage of which act as pathogens, causing disease in both animals and plants.
What are fungi?	Eukaryotic (often multicellular) organisms. Many are saprophytes which feed on dead and decaying matter, but some are parasitic.
What are the two ways pathogens damage host organisms?	Damaging the host tissue directly or producing toxins which damage the host tissue.
What pathogen causes ring rot?	Bacterium called Clavibacter michiganensis
What is ring rot?	A bacterial disease of potatoes, tomatoes and aubergines. It damages leaves, tubers and fruit.
What is the tobacco mosaic virus?	A virus that infects tobacco plants and various other species. It damages leaves, flowers and fruit. Resistant crop strains are available but there is no cure.
What is potato blight?	It's caused by the protoctist oomycete phytophthora infestans. The hyphae penetrate host cells and destroy leaves, tubers and fruit. There is no cure but resistant strains, careful management and chemical treatments can reduce infection risk
What is black sigatoka?	A banana disease caused by the fungus Mycosphaerella fijiensis, which attacks and destroys leaves. The hyphae penetrate and digest the cells, turning leaves black. Fungicide treatment can control the spread of the disease but the is no cure.
What is tuberculosis?	A bacterial disease of humans, cows, pigs, badgers and deer which is caused by mycobacterium tuberculosis and M.bovis. It destroys lung tissue and suppresses the immune system. It is both curable, by antibiotics, and preventable, by improving living standards and vaccination.
What is bacterial meningitis?	A bacterial infection caused by streptococcus pneumonia or Neisseria meningitides. It infects the meninges of the brain (protective membranes on the surface of the brain), which can spread into the rest of the body and cause septicaemia (blood poisoning) and rapid death. Vaccines can protect against some forms of bacterial meningitis
What is HIV/AIDS?	It targets T helper cells in the immune system of the body and gradually destroys the immune system - causing affected people to be more likely to get other diseases.
How does the HIV virus destroy the immune system?	It contains the enzyme reverse transcriptase, which transcribes the virus' RNA to a single stranded DNA molecule, which interacts with the genetic material of the host cell.
How is HIV spread?	Through exchanging bodily fluids, such as unprotected sex, shared needles, contaminated blood products and from mother to child.
What is influenza?	A viral infection of the ciliated epithelial cells in the gaseous exchange system. The cells are killed, leading to risk of the airways getting a secondary infection.
What is the pathogen that causes malaria?	The protoctista Plasmodium
What is the vector that spreads malaria?	Female Anopheles mosquitoes
How is malaria controlled?	The vector mosquitoes can be killed by insecticides and by removing standing water where they breed. Mosquito nets, window and door screens and long sleeved clothing can prevent people getting bitten.
What is ring worm?	A fungal disease that affects cattle, dogs, cats and humans. Different fungi affect different species. It causes a grey-white crusty, infectious, circular areas of skin. Anti fungal creams are an effective cure.
What is athlete's foot?	A human fungal disease which is a form of ring worm that grows and digests warm, moist skin in between toes.
What are the three methods of direct transmission of a disease?	Direct contact, Inoculation (entering directly into the body through wounds or animal bites) and Ingestion.
What are the three methods of indirect transmission of a disease?	Fomites (inanimate objects such as socks or bedding), Droplet infection (through coughing or sneezing) and Vectors (which transmits a pathogen from one host to another).
How is the probability of catching a communicable disease increased?	Overcrowding, poor nutrition, a compromised immune system, poor disposal of waste, climate change (which can introduce new vectors or diseases), culture, socioeconomic factors (untrained nurses, education about diseases).
How can pathogens be spread between plants?	Direct contact, soil contamination
What can act as a vector?	Wind, water, animals, humans
What increases the likelihood of the transmission of diseases in plants?	Planting crops that are susceptible to disease, overcrowding, poor mineral nutrition (which reduces plant resistance), damp warm conditions (which allows pathogens and spores to survive and spread) and climate change (increased rainfall and wind, vectors spreading to new areas)
How does callose help defend a plant from pathogens?	1) It is synthesised and deposited between cell walls and cell membranes surrounding the infected cell. These callose papillae act as barriers, preventing the pathogens entering the plants around the site of infection. 2) It is deposited continuously after the initial infection. Lignin is added making the mechanical barrier stronger. 3) It blocks sieve plates in phloem to prevent the spread of pathogens. 4) It is deposited in the plasodesmata, which are gaps in cell walls. This prevents the infection from spreading.
List some examples of chemicals that are used by plants for defense.	Insect repellents, insecticides, antibacterial compounds, antifungal compounds, anti-oomycetes (fungus-like eukarya), toxins.
What are chitinases?	Enzymes that break down the chitin in fungal cell walls.
What are glucanases?	Enzymes that break down glucans in the cell walls of oomycetes
How does skin prevent the entry of pathogens?	It has a skin flora of healthy microorganisms that outcompete pathogens for space of the body surface. The skin also produces sebum, an oily substance that inhibits the growth of pathogens.
How do mucous membranes prevent the entry of pathogens?	They line body tracts and secrete mucus that traps microorganisms. The mucus contains lysozymes, which destroy bacterial and fungal cell walls. It also contains phagocytes, which engulf pathogens.
What are non-specific animal defences?	Those that defend against all pathogens in the same way.
What is found in tears, urine and stomach acid to prevent pathogens entering the body?	Lysozymes
What are expulsive reflexes?	Coughs, sneezes, vomiting or diarrhoea - expel infective pathogens from the body
What happens when you get a cut?	Pathogens enter the wound, so the blood clots to seal it. Platelets stick together and begin to secrete several substances. Thromboplastin is produced, which is an enzyme that triggers reactions that result in the formation of a blood clot. Serotonin is also produced, which makes the smooth muscle in blood vessels to contract so less blood travels to the affected area. The clot dries out which forms a barrier from pathogens entering. Epidermal cells below the scab grow, sealing the wound permanently. Damaged blood vessels regrow. Collagen fibres are deposited to give the tissue strength.
Describe the inflammatory response.	Mast cells are activated in damaged tissue and release chemicals called histamines and cytokines. Histamines make blood vessels dilate, causing localised heat and redness and preventing pathogens from reproducing. Histamines also make blood vessels more permeable so blood plasma leaks out, causing an increase in tissue fluid around the affected area and causing swelling. Cytokines are also produced, they attract white blood cells to the site, which get rid of pathogens by phagocytosis.
How do fevers protect the body from pathogens?	When a pathogen invades the body, cytokines stimulate the hypothalamus to increase the temperature of the body. Most pathogens work at body temperature, so the increase in temperature inhibits pathogen reproduction. The higher temperature also allows the specific immune system to work faster.
Describe the process of phagocytosis.	1) Pathogens produce chemicals that attract phagocytes 2) Phagocytes recognises the pathogen as non-self 3) The phagocyte engulfs the pathogen and encloses it in a vacuole called a phagosome 4) The phagosome fuses with a lysosome to form a phagolysosome 5) Enzymes in the lysosome digest and destroy the pathogen.
What happens after a macrophage engulfs a pathogen?	It digests the pathogen, it's antigens then combine with the major histocompatibility complex (MHC). The MHC moves the pathogen's anitigens to the cell surface membrane of the macrophage and the cell becomes an antigen-presenting cell (APC). These stimulate other cells involved in the specific immune system.
What are cytokines?	They act as cell signalling chemicals and are produced by phagocytes that have engulfed a pathogen. They inform other phagocytes that the body is under attack and stimulate them towards the site of infection. They also stimulate the hypothalamus, which increases body temperature, and stimulate the specific immune system.
What is the function of opsonins?	They bind to pathogens, which makes them more easily recognisable for phagocytes. This works as receptors on the phagocytes cell membrane bind to the opsonins and engulf them.
Describe the structure of an antibody	Y-shaped glycoproteins called immunoglobulins. Made of two identical long polypeptide chains called heavy chains and two shorter chains called the chains. The chains are held together by disulphide bridges. They have a variable region, which is different in shape for each antibody, this is where antigens bind to the antibody. The rest of the antibody is the constant region.
What forms when an antigen binds to an antibody?	Antigen-antibody complex
What happens when an antibody binds to an antigen?	The pathogen can no longer harm cells, as the antibody acts as an anti-toxin, binding to the toxin-producing area of the pathogen. The antibody also acts as an agglutinin, causing antibody-antigen complexes to clump together, preventing them from spreading around the body and making the easier to engulf by phagocytes.
Where do B lymphocytes mature?	Bone marrow
Where do T lymphocytes mature?	Thymus gland
What do t helper cells do?	They bind to the surface antigens on APCs, which causes them o produce interleukins (a type of cytokine). These stimulate the activity of B cells.
What do t killer cells do?	They destroy pathogens by releasing a chemical called perforin, which makes holes in the cell membrane making it freely permeable.
What do t memory cells do?	These remember an antigen, so when they come into contact with them again the divide rapidly to form t killer cell clones which kill the pathogen.
What do t regulator cells do?	They stop the immune response once a pathogen has been eliminated. They also make sure the body recognises self antigens preventing an autoimmune response.
What do plasma cells do?	They produce antibodies for a particular antigen. They only live for a few days, producing about 2000 antibodies a second.
What do b effector cells do?	They divide to form plasma cells
What do b memory cells do?	Provide the immunological memory - remember a specific antigen and carry out a rapid response when they encounter them again
What is cell mediated immunity?	When T lymphocytes respond to the cells of an organism that have been infected, mutated or recognised as foreign. This triggers an immune response.
Outline the stages of cell mediated immunity	1) Macrophages engulf a pathogen and become APCs 2) Receptors on some T helper cells bind to the antigens, which activates them causing them to produce interleukins. 3) More T cells divide by mitosis. They all carry the right antigen to bind to the invading pathogen. 3) The T cells go on to either develop into T memory cells, produce interleukins or develop into T killer cells.
What do interleukins do?	They stimulate phagocytosis and stimulate B cells to divide
What is humoral immunity?	It is when the body responds to antigens found outside cells and to APCs. This stimulates the production of antibodies.
How does a B-lymphocyte become an APC?	They have antibodies on their cell membrane, which bind to complementary antigens and engulf them. The pathogen is then processed and the cell becomes an APC.
Outline the stages of humoral immunity	Activated T helper cells bind to a B cell APC. This is clonal selection. The T helper cells produce interleukins which activate the B cell. The activated B cell divides by mitosis to form plasma cell clones and B memory cells - this is clonal selection. The plasma cells produce antibodies that agglutinate the pathogens. This is a primary immune response. The cloned B memory cells live for a long time after the infection to be ready for a secondary immune response which is a lot faster.
What is an autoimmune disease?	When the immune system recognises own cells as non self and begins to attack them
How does type 1 diabetes affect the body and what are the possible treatments?	The insulin secreting cells of the pancreas are affected. Treatments include insulin injections, pancreas transplants, immunosuppressant drugs.
How does rheumatoid arthritis affect the body and what are the possible treatments?	Cells in joints are affected. Treatments include anti-inflammatory drugs, steroids, immunosuppressants and pain relief.
How does lupus affect the body and what are the possible treatments?	Often affects skin and joints, can also attack any organ in the body. Treatments include anti-inflammatory drugs, steroids, immunosuppressants.
What is natural active immunity?	When your immune system is activated to produce new antibodies and memory cells to destroy the pathogen. This lasts for a long time.
What is natural passive immunity?	When antibodies are passed from mother to child through breast milk. This immunity lasts until the baby can produce its own antibodies.
What is artificial passive immunity?	When antibodies from another organism are extracted and injected into the body to provide temporary immunity.
What is artificial active immunity?	When the body is stimulated to make its own antibodies by injecting a dead, inactive, attenuated (weakened), genetically engineered or isolated antigen, which is attacked by the immune system. This provides long-term immunity.
What is an epidemic?	When a communicable disease spreads rapidly to a lot of people at a local or national level.
What is a pandemic?	When the same disease spreads rapidly across a number of countries and continents.
What is pharmacogenomics?	Using personal genetic information to choose drugs more suited to it.
What is selective toxicity?	The ability to interfere with the metabolism of a pathogen without affecting the cells of the host.
What do sulfonamides do?	They interfere with metabolic reactions in bacteria.
What do polymixines do?	They make holes in cell membranes altering its permeability in bacteria.
What do tetracyclines and streptomycin do to bacteria?	Inhibit protein synthesis
What do penicillin and cephalosporins do to bacteria?	Weaken the cell wall so the cell is more easily damaged by the immune system.

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