4.1.1 Communicable Diseases, Disease Prevention and the Immune System

Riya Patel
Flashcards by Riya Patel, updated more than 1 year ago
Riya Patel
Created by Riya Patel over 2 years ago


OCR A A Level Biology

Resource summary

Question Answer
Define 'pathogen' A disease-causing microorganism
What are the organisms pathogens live in called? Hosts
Name four types of pathogens Bacteria Protoctista Fungi Virus
Define 'communicable' Able to be transmitted from one sufferer to another (infectious, contagious)
Name two bacterial communicable diseases in animals (Give the name of each of their pathogens) Bacterial meningitis (Streptococcus pneumoniae) Tuberculosis (Mycobacterium tuberculosis and M. bovis)
Name a bacterial communicable disease in plants (Give the name of its pathogen) Ring rot (Clavibacter michiganensis)
Name two communicable diseases in animals caused by viruses (Give the name of each of their pathogens) HIV/AIDS (Human immunodeficiency virus) Influenza (from family Orthomyxoviridae)
Name a communicable disease in plants caused by a virus (Give the name of its pathogen) Tobacco mosaic virus (Tobacco mosaic virus)
Name a communicable disease caused by protoctista in animals (Give the name of its pathogen) Malaria (Plasmodium falciparum, P. vivax, P. ovale, P. malaria)
Name a communicable disease in plants caused by protoctista (Give the name of its pathogen) Potato/tomato late blight (Phytopthora infestans)
Name two fungal communicable diseases in animals (Give the name of each of their pathogens) Ring worm (cattle) (Trichophyton verrucosum) Athlete's foot (Trichophyton rubrum)
Name a fungal communicable disease in plants (Give the name of its pathogen) Black sigatoka (Mycosphaerella fijiensis)
What are the characteristics of tuberculosis? A disease affecting many parts of the body, killing the cells and tissue with the lungs often being the most affected
What are the characteristics of bacterial meningitis? It is an infection of the meninges (membranes that surround the brain and spinal cord) where the membranes become swollen and may cause damage to the brain and nerves.What are the characteristics of
What are the characteristics of ring rot? Causes a ring of decay in the vascular of a potato tuber or tomato and is often accompanied by leaf wilting
What are the characteristics of HIV/AIDS? Attacks the cells of the immune system and compromises the immune response
What are the characteristics of influenza? Attacks the respiratory system and causes muscle pains and headaches
What are the characteristics of the tobacco mosaic virus? Causes mottling (marking with spots), leaf curling, necrosis and discolouration of leaves
What are the characteristics of black sigatoka in bananas? Causes leaf spots on the banana plants which reduces yield
What are the characteristics of late blight in tomatoes and potatoes? Rapidly spreading watery rot of leaves In potatoes a white fungal growth may affect stems and tubers and in tomatoes mature fruit will decay rapidly.
What are the characteristics of ringworm in cattle? Growth of fungus in skin with spore cases erupting through the skin to cause rashes
What are the characteristics of athlete's foot? Fungal growth under the skin of the feet, particularly between the toes
What are the characteristics of malaria? The parasite in the blood causes headaches and fever and may progress to coma and death if left untreated.
What are some methods of prevention/treatment against tuberculosis? Vaccines before infection Better housing Improved health facilities and nutrition Antibiotics
What are some methods of prevention/treatment against bacterial meningitis? Maintain healthy habits (do not smoke, rest well, etc.) Prophylaxis (antibiotics to prevent others getting sick) Vaccinations Pregnant women should get tested for group B Streptococcus
What are some methods of prevention/treatment against HIV/AIDS? No cure but effective treatments enable most to live long and healthy lives Avoid sharing needles Use of condoms HIV prevention medication Screening for HIV in pregnancy
What are some methods of prevention/treatment against influenza? Stay away from those infected or stay at home if sick Wash hands thoroughly Clean and disinfect frequently touched surfaces
What are some methods of prevention/treatment against malaria? Avoid mosquito bites (insect repellent, mosquito nets, covering arms and legs) Complete course of antimalarial tablets if travelling to a high risk area Seek medical advice if symptoms develop
What are some methods of prevention/treatment against ring worm? Keep areas dry and free of moisture Reduce density of animals
What are some methods of prevention /treatment against athlete's foot? Antifungal cream/powder Wash feet with soap and water daily Change socks daily/wear cotton socks Avoid being barefoot in public showers
What are some methods of prevention /treatment against ring rot? Only certified seed from reliable sources (all in EU derived from material tested for all quarantined diseases) Implement good hygiene practises (regular equipment cleaning and disinfection) Do not dump waste on agricultural land (can harbour disease)
What are some methods of prevention /treatment against the tobacco mosaic virus? Remove infected plants Wash hands in between plants Crop rotation to prevent spread Grow TMV resistant plants Disinfect any equipment
What are some methods of prevention /treatment against late blight? Scouting (inspect growing crops regularly) Avoid dense vegetation for good drainage and air movement to reduce moisture Crop rotation Application of fungicides
What are some methods of prevention /treatment against black sigatoka? Removal and destruction of diseased leaves Good drainage and spacing to reduce humidity Host-plant resistance (genetic) Use of suitable pesticides
Define 'direct transmission' Passing a pathogen from host to new host, with no intermediary
Name four methods of direct transmission Direct physical contact (touching infected people or contaminated surfaces) Faecal-oral transmission (eating/drinking contaminated food/drink) Droplet infection (inhalation of contaminated water droplets) Transmission of spores (carried by air, reside on surfaces or in soil)(e.g. anthrax, tetanus)
How can direct physical contact transmission be prevented? Hygiene (wash hands regularly) Keep surfaces clean Use condoms Clean and disinfect cuts and abrasions Sterilise surgical instruments
How can faecal-oral transmission be prevented? Treatment of waste water and drinking water Thoroughly wash fresh food with treated water Careful preparation and thorough cooking of all food
How can transmission by droplets be prevented? Catch it- bin it- kill it Cover mouth when coughing or sneezing (use a tissue and ensure correct disposal)
How can transmission by spores be prevented? Use of a mask Washing skin after contact with soil
Give some examples of social factors that may affect transmission of pathogens Overcrowding (many living in one house) Poor ventilation Poor health (e.g. HIV/AIDS sufferers more susceptible to other diseases) Poor diet Homelessness Living or working with people who have migrated from areas where a disease is more common
Define 'indirect transmission' Passing a pathogen from host to new host, via a vector
Describe the life cycle of Plasmodium in the transmission of malaria
Describe some methods of direct transmission of pathogens in plants Many pathogens are present in the soil so infect the plant after being absorbed through the roots (especially if damaged from replanting, burrowing animals and movement from storms) Many fungi produce spores for sexual or asexual reproduction and these can be carried by wind (airborne) When leaves with pathogens in them shed, they pathogen can grow and infect other plants through the soil - the pathogen may enter the fruit and seeds which means offspring may be infected
Describe how plant pathogens can be indirectly transmitted It often occurs as a result of insect attack. Spores or bacteria attach to a burrowing insect (e.g. beetle) which attacks an infected plant and when it attacks another, the pathogen is transmitted to the uninfected plant. The beetle acts as a vector.
How does climate affect disease? Many protoctists, bacteria and fungi can grow and reproduce more rapidly in warm and moist conditions so tend to be more common in warmer climates. In cooler climates, they may be damaged or killed so animals and plants living in warmer climates are more likely to become infected.
What are passive defences with relation to plant pathogens? They are defences present before infection with the role to prevent entry and spread of the pathogen (include physical barriers and chemicals)
Name some of the physical defences of plants (7) Cellulose cell wall Lignin thickening of cell walls Waxy cuticles Bark Stomatal closure Callose Tylose
Describe the defence of the cellulose cell wall Acts as a physical barrier and most contain a variety of chemical defences that can be activated when a pathogen is detected
Describe lignin thickening of cell walls Lignin is a phenolic compound that is waterproof and almost completely indigestible
How do waxy cuticles act as defences for plants? They prevent water collecting on the cell surfaces and since pathogens collect in water and need water to survive, the absence of water is a passive defence.
Why is bark a passive defence? Most contains a variety of chemical defences that work against pathogenic organisms
How does stomatal closure work against pathogens? Stomata act as possible points of entry for pathogens so when pathogenic organisms are detected, guard cells (which control stomatal aperture) close the stomata in that part of the plant
How does callose act as a passive defence? It is a large polysaccharide that is deposited in the sieve tubes at the end of the growing season. It blocks the flow in the sieve tube which can prevent the pathogen spreading around the plant.
What is a tylose? A balloon-like swelling or projection that fills the xylem vessel
How does tylose formation prevent pathogen entry and spreading? When a tylose is fully formed, it plugs the vessel so it can no longer carry water. Blocking the xylem vessels prevents spread of pathogens through the heartwood and the tylose contains a concentration of chemicals such as terpenes that are toxic to pathogens.
Give some examples (4) of chemical defences in plants Terpenoids Phenols Alkaloids Hydrolytic enzymes
Despite some chemicals being present before infection, why are many not produced until the plant detects an infection? The production of chemicals require a lot of energy
What are terpenoids? A range of essential oils with antibacterial and antifungal properties and may also create a scent (e.g. menthols and menthones from mint plants)
Describe the action of phenols They have antibiotic and antifungal properties. Tannins (in bark) inhibit insect attack as the compounds bind to salivary proteins and digestive enzymes to deactivate them. If insects ingest high amounts of tannins, they will not grow and will eventually die which helps prevent transmission of pathogens.
What are alkaloids and what do they do? Nitrogen-containing compounds (e.g. caffeine, nicotine, cocaine, morphine) that give a bitter taste to inhibit herbivores feeding. This prevents damage which allows pathogens to enter. They also inhibit or activate enzymes in metabolic reactions.
What are hydrolytic enzymes? Give some examples They are found in the spaces between cells and include chitinases (break down chitin in fungal cell walls), glucanases (hydrolyse glycosidic bonds in glucans) and lysozomes (capable of degrading bacterial cell walls).
What are defensins (defensive proteins)? Small cysteine-rich proteins that have broad anti-microbial activity. They act upon molecules in the plasma membrane of pathogens and help inhibit the action of ion transport channels.
How are active defences activated in plants? When pathogens attack, specific chemicals (e.g. specific proteins and glycolipids) in their cell walls can be detected by the plant cells. In response, plants fortify the already present defences (both physical and chemical).
Describe some examples of active defences in plants Cell walls thickened and strengthened with additional cellulose Deposition of callose between plant cell wall and cell membrane near invading pathogen - strengthens cell wall and blocks plasmodesmata Oxidative bursts that produce highly reactive oxygen molecules capable of damaging pathogen cells Increased production of chemicals Necrosis - deliberate cell suicide where a few cells are sacrificed to save the rest of the plant (kills cells surrounding pathogen to limit its access to water and nutrients) Canker - sunken necrotic lesion in the woody tissue such as the main stem or branch (causes death of the cambium tissue in the bark)
Define 'primary defences' Those that prevent pathogens entering the body
Why are primary defences non-specific? They will prevent the entry of any pathogen
Name some of the primary defences against disease in animals Skin Blood clotting and skin repair Mucous membranes Expulsive reflexes Inflammation
What is the outer layer of the skin called and what is the name of most of the cells that it consists of? Epidermis (Made of layers of cells, most of which are keratinocytes)
How does the skin act as a primary defence? The cells of the epidermis are produced by mitosis at the base of the epidermis. They then migrate out to the surface and as they do this, they dry out and the cytoplasm is replace by keratin (protein) - keratinisation. Keratinisation takes about 30 days so by the time the cells reach the surface, they are no longer alive and the keratinised layer of dead cells acts as an effective barrier to pathogens.
What is the purpose of blood clotting? To prevent excess blood loss and to make a temporary seal to prevent infection while the skin repairs
Describe the process of blood clotting and skin repair It involves calcium ions and at least 12 clotting factors. Many of the clotting factors are released from platelets and from the damaged tissue and they activate an enzyme cascade. After the clot has formed, it begins to dry and form a scab. As the scab dries, it shrinks which draws the sides of the cut together to make a temporary seal, under which the skin is repaired. Once the new skin is completed, the scab is released.
Why are mucous membranes needed? Certain substances (oxygen, nutrients in food) need to enter the blood. To allow them to do this, the exchange surfaces are thinner and less well protected from pathogens. As the air and food we take in may harbour microorganisms the airways, lungs and digestive system are at risk of infection.
Explain how mucous membranes act as a primary defence against disease The epithelial layer contains goblet cells which secrete mucus. Mucus lines the passages and traps any pathogens that may be in the air. Ciliated cells in the epithelium are tiny, hair-like organelles that move in a coordinated fashion to waft the layer of mucus along. They move it up to the top of the trachea where it enters the oesophagus. It is swallowed and passes down the digestive system where most pathogens are killed by the acidity in the stomach.
How do expulsive reflexes act as primary defences? Areas prone to attack are sensitive. They respond to irritation that may be caused by the presence of microorganisms or the toxins they release. The reflexes include coughing, sneezing and vomiting. Coughing and sneezing are sudden expulsions of air that will carry with them the microorganisms that cause the irritation.
Describe the process of inflammation Microorganisms present in the tissue are detected by mast cells. They release histamine (cell signalling substance). Histamine causes vasodilation and makes the capillary walls more permeable to white blood cells and some proteins. Blood plasma and phagocytic white blood cells leave the blood and enter the tissue fluid which leads to increased production of tissue fluid which causes oedema. Excess fluid is drained into the lymphatic system where lymphocytes are stored which can lead to pathogens coming into contact with lymphocytes which initiates specific immune responses.
What are antigens? Proteins or glycoproteins belonging to the plasma membrane that are chemical markers on the outer membrane of pathogens and are specific to the organism. They allow the pathogen to be recognised as foreign if it invades the body.
What are opsonins? Proteins that bind to the antigen on a pathogen and then allow phagocytes to bind Type of antibody but some are not very specific so can attach to a variety of pathogenic cells
What is the purpose of opsonins? They enhance the ability of phagocytic cells to bind and engulf the pathogen
What type of defence is phagocytosis? Secondary non-specific defence
Define 'phagocytosis' The engulfment and digestion of pathogens by specialised cells in the blood and tissue fluid
Define 'neutrophil' A type of white blood cell that engulfs foreign matter and traps it in a large vacuole (phagosome), which fuses with lysosomes to digest the foreign matter
How are neutrophil cells recognised? By their multi-lobed nucleus
Where are neutrophils made? Bond marrow
Explain how neutrophils act as secondary defence They are released in large numbers as a result of infection and contain a large number of lysosomes.
What are macrophages? Larger cells manufactured in the bone marrow that do not fully digest pathogens
In what form do macrophages travel in the blood before settling in body tissues? Travel as monocytes
What do macrophages do? When macrophages engulf a pathogen, they do not fully digest it. The antigen from the surface of the pathogen is saved and moved to a special protein complex on the surface of the cell. The cell becomes an antigen-presenting cell which exposes the antigen on its surface so other immune system cells can recognise it. The protein complex ensures the antigen-presenting cell is not mistaken for a foreign cell and attacked by other phagocytes.
Define 'antigen-presenting cell' A cell that isolates the antigen from a pathogen and places it on the plasma membrane so that it can be recognised by other cells in the immune system
What are some of the specialisations of phagocytes? Receptors on the plasma membrane that bind to the opsonin or a specific antigen Lobed nucleus to allow cells to squeeze through narrow gaps Well-developed cytoskeleton to help cell to change shape to engulf a pathogen and move lysosomes and vacuoles around Many lysosomes containing lysin Many mitochondria to release energy from glucose Many ribosomes to synthesise the enzymes involved
What two types of cells are involved in the specific immune response? B lymphocytes (B cells) T lymphocytes (T cells) They are white blood cells with a large nucleus and specialised receptors on their plasma membranes.
What does the immune response produce? Antibodies
What are antibodies and what do they do? Specific proteins released by plasma cells that can attach to pathogenic antigens. They are the cells that actually neutralise the foreign antigens.
What does immune response provide? Long-term memory through the release of memory cells, which circulate in the body for a number of years
Name the four types of cell that T lymphocytes develop or differentiate into T helper cells (Tₕ) T killer cells (Tₖ) T memory cells (Tₘ) T regulator cells (Tᵣ)
What do T helper cells do? Release cytokines (chemical messengers) that stimulate the B cells to develop and stimulate phagocytosis
What do T killer cells do? Attack and kill host-body cells that display the foreign antigen by injecting hydrogen peroxide or enzymes (Destroy our own body cells that are infected)
What is the role of T memory cells? Provide long term-immunity
What is the role of T regulator cells? They shut down the immune response after the pathogen has been successfully removed and also help prevent autoimmunity.
Name the two types of cell B lymphocytes develop into Plasma cells B memory cells (Bₘ)
What is the purpose of plasma cells? They circulate in the blood, manufacturing and releasing the antibodies
What do B memory cells do? Remain in the body for a number of years and act as the immunological memory
What is the name of the mechanism that helps coordinate the action of the cells in specific immune response? Cell signalling
How is the communication between cells achieved? Through the release of hormone-like chemicals called cytokines
Why is it important that the cells communicate effectively in specific immune response? There are numerous cell types involved so it is important they communicate with one another to coordinate their actions and carry out response correctly and efficiently.
Outline the communication using cytokines using the example of macrophages Macrophages release monokines. Some monokines attract neutrophils by chemotaxis (movement of cells towards a certain chemical). Others stimulate B cells to differentiate and release antibodies.
Outline the communication using cytokines by T cells T cells and macrophages release interleukins, which can stimulate the clonal expansion and differentiation of B and T cells.
Define 'interleukins' Signalling molecules that are used to communicate between different white blood cells
Define 'clonal expansion' An increase in the number of cells by mitotic cell division (proliferation)
What are autoimmune diseases? Diseases which occur when the immune system attacks a part of the body. They arise when antibodies start to attack our own antigens- possible because antigens that are not normally exposed become exposed to attack.
Give two examples of autoimmune diseases Arthritis - painful inflammation of a joint that starts with antibodies attacking the membranes around the joint Lupus - causes swelling and pain of any part of the body
Specific defence pathways diagram
What shape are antibody molecules? Y-shaped
How many regions are there in antibody molecules and what are their names? 2 distinct regions Variable region Constant region
How many polypetide chains make up an antibody molecule? 4 polypeptide chains
In antibody molecules, what holds the polypeptides together? Disulfide bridges
What is the role of the hinge region in antibody molecules? Allows flexibility so molecules can grip more than one antigen
What is the variable region? The top region of an antibody molecule that has a specific shape specific to the shape of the antigen
What is the constant region? The region which is the same in all antibodies that may have a site for easy binding of phagocytic cells
Draw an antibody molecule
Name the three main groups of antibodies Opsonins Agglutinins Anti-toxins
Describe the process of opsonisation
What are agglutinins? Antibodies that cause pathogens to stick together
How do agglutinins work? Because each antibody molecule has two identical binding sites it is able to crosslink pathogens by binding to two of them. When many antibodies do this, they clump together (agglutinate) pathogens.
What are the benefits of agglutination? The agglutinated pathogens are physically impeded from carrying out some functions (e.g. entering host cells). They are readily engulfed by phagocytes
How do anti-toxins work? Some antibodies bind to molecules that are released by pathogenic cells but these molecules may be toxic so the action of anti-toxins renders them harmless.
Define 'primary immune response' The initial response caused by a first infection
Define 'secondary immune response' A more rapid and vigorous response caused by a second or subsequent infection by the same pathogen
What happens in primary immune response? When an infecting agent is first detected, the immune system starts to produce antibodies but it takes a few days before the number of antibodies in the blood rises to a level that can combat the infection. Once the pathogens are dealt with, the number of antibodies rapidly drops.
What happens in secondary immune response? There will be B and T memory cells circulating in the blood. If a pathogen enters the body again, they recognise the specific antigens and the production of antibodies starts sooner and is much more rapid. This response is usually quick enough to prevent any symptoms being detected by the host.
Describe the graph showing primary and secondary immune response
Define 'active immunity' Where the immune system is activated and manufactures its own antibodies
Define 'passive immunity' Immunity achieved when antibodies are passed to the individual through breast feeding or injection
Define 'natural immunity' Immunity achieved through normal life processes
Define 'artificial immunity' Immunity that is achieved as a result of medical intervention
Give an example of each type of immunity
Define 'vaccination' A way of stimulating an immune response so that immunity is achieved
How do vaccinations work? Deliberate exposure to antigenic material that has been rendered harmless The immune system treats the antigenic material as a real disease so the immune system is activated and antibodies and memory cells are manufactured.
Give some of the forms the antigenic material in vaccines can take Whole, live microorganisms that are have very similar (but harmless) antigens to the organism that causes a real disease Harmless or weakened (attenuated) version of the pathogenic organism Dead pathogen Preparation of the antigens from a pathogen Toxoid - harmless version of a toxin
What is a herd vaccination? Using a vaccine to provide immunity to all or almost all of the population at risk. Once enough people are immune, the disease can no longer spread and 'herd immunity' is achieved.
Give an example of when herd vaccination is used in the UK In the UK, there is a vaccination programme to immunise young children against the following diseases: diphtheria, tetanus, whooping cough, polio, meningitis, measles, mumps and rubella.
What is ring vaccination and when might it be used? It is used when a new case of a disease is reported and involves vaccinating all the people in the immediate vicinity of the new case. Used in many parts of the world to control the spread of livestock disease
Define 'epidemic' A rapid spread of disease through a high proportion of the population
What is a pandemic? Worldwide epidemic
Give three reasons why new drugs are needed New diseases are emerging There are still many diseases for which there are no effective treatments Some antibiotic treatments are becoming less effective
Define 'antibiotic' A chemical which prevents the growth of microorganisms and can be antibacterial or antifungal
How was the antibiotic penicillin discovered? Accidental discovery
How do traditional remedies aid drug development? Many drugs have been used for centuries because people have noted that certain plants or extracts have a beneficial effect. The World Health Organisation says 80% of the world's population relies on traditional medicines.
Describe how observation of wildlife has provided information about plants with medicinal properties Monkeys, bears and other animals rub citrus oils on their coats as insecticides and antiseptics Birds line their nests with medicinal leaves to protect chicks from blood-sucking mites
What is personalised medicine? Sequencing technology and molecular modelling make screening of genomes of plants or microorganisms possible to identify potential medicinal compounds from the DNA sequences. Once the technology is fully developed, it may be possible to sequences the genes from individuals with a particular condition and develop specific drugs for it.
What is synthetic biology? The development of new molecules that mimic biological systems is one form. Another way that it is used is to design and construct new devices and systems that may be useful in research, healthcare or manufacturing.
What are the benefits of using antibiotics? Before they were used, many people died as a result of wounds or surgery when they became infected. Use of antibiotics became widespread during WW2 to prevent infection of wounds.
What are the risks of using antibiotics? Over-use and misuse of antibiotics have enabled microorganisms to develop resistance. Many of the current antibiotics have limited effectiveness. Examples of bacteria that have become infamous for their multiple resistance to a range of antibiotics include Clostridium difficile (C. diff) and methicillin-resistant Staphylococcus aureus (MRSA).
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