OCR A Level Biology Past Paper PDF

Head to www.savemyexams.com for more awesome resources OCR A Level Biology Your notes 4.1 Communicable Diseases, Disease Prevention & the Immune System Contents 4.1.1 Common Pathogens & Communicable Diseases 4.1....

Head to www.savemyexams.com for more awesome resources OCR A Level Biology Your notes 4.1 Communicable Diseases, Disease Prevention & the Immune System Contents 4.1.1 Common Pathogens & Communicable Diseases 4.1.2 Transmission of Communicable Pathogens 4.1.3 Plant Defences Against Pathogens 4.1.4 Non-specific Immune Responses 4.1.5 Phagocytes 4.1.6 Blood Cells 4.1.7 The T Lymphocyte Response 4.1.8 The B Lymphocyte Response 4.1.9 Primary & Secondary Immune Responses 4.1.10 Antibodies 4.1.11 Opsonins, Agglutinins & Anti-toxins 4.1.12 Types of Immunity 4.1.13 Autoimmune Diseases 4.1.14 Principles of Vaccination 4.1.15 Sources of Medicine 4.1.16 Antibiotics Page 1 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.1 Common Pathogens & Communicable Diseases Your notes Common Pathogens & Communicable Diseases A disease is an illness or disorder of the body or mind that leads to poor health Each disease is associated with a set of signs and symptoms Communicable/infectious diseases are caused by pathogens and are transmissible (can be spread between individuals within a population) Both plants and animals can be affected by pathogens Infectious & non-infectious diseases table Definition Examples Disease caused by a pathogen that passes from infected individuals to uninfected Cholera, HIV/AIDS, malaria, Infectious disease individuals tuberculosis Also known as communicable disease Lung cancer, cardiovascular Non-infectious Long-term diseases that are not caused by disease, depression, cystic disease pathogens, fibrosis, vitamin deficiencies Many microorganisms are pathogens including: Bacteria Viruses Fungi Protoctists To control disease, it is very important to know what pathogen is causing it Bacteria Bacteria are a diverse range of prokaryotic organisms Some bacteria are non-pathogenic (they do not cause any disease or damage) while others are pathogenic Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces M. tuberculosis causes tuberculosis (TB) in humans The bacteria infect the lungs, causing a chronic cough and bloody mucus It is a disease often associated with poor hygiene and sanitation M. bovine in cows can also transmit to humans to cause TB Ring rot diseases in potato plants are caused by bacterial pathogens The bacteria infect the vascular tissue and prevent the transport of water, causing the plant to wilt and die Page 2 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The infection spreads into the potato tubers where the vascular tissue is arranged in a ring, producing the characteristic black ring of rot Your notes Viruses Viruses do not have a cellular structure This means they can't respire, produce ATP, replicate genetic material or synthesise protein They infect host cells and hijack their machinery to replicate their own genetic material and proteins The first virus ever discovered was the Tobacco Mosaic Virus (TMV) TMV infects several plant species It causes a distinct yellowing of the leaves which produces a mosaic pattern Three different influenza viruses infect humans to cause the flu Influenza A, influenza B and influenza C infect the cells that line the airways They cause a high temperature, body aches and fatigue Influenza A is the virus that causes the most cases of flu globally It has a capsid that surrounds 8 single-stranded molecules of RNA The human immunodeficiency virus (HIV) infects specific cells of the immune system It is an enveloped retrovirus The viral enzyme reverse transcriptase produces single-stranded DNA from its viral RNA DNA polymerase synthesises double-stranded DNA from this single-stranded DNA The double-stranded DNA is inserted into the host DNA and can remain inactive for many years Once activated the DNA provirus is used to synthesise new viruses Protoctista Protists are unicellular eukaryotes Plasmodium falciparum is a protist that causes severe forms of malaria in humans The parasite is spread by mosquitoes Infected individuals experience fever, chills and fatigue P. infestans causes the infamous potato blight The pathogen is unusual as it has some fungal characteristics It is transmitted via spores The first signs of potato blight are small, dark brown marks on the leaves which quickly increase in size and number The protist destroys potato and tomato crops leaving them completely inedible Fungi Fungi have a similar structure to plants Their eukaryotic cells have cell walls and large central vacuoles However, instead of being made of separate cells, their bodies consist of filaments known as hyphae These hyphae form a network and spread throughout a host/soil Fungal diseases are much more common in plants than animals Athletes foot is a fungal disease that exist on the surface of the skin Fungal diseases in plants tend to be much more serious and can threaten entire crops Page 3 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Black Sigatoka is a fungal disease in bananas It spreads through the leaves of the plant, reducing its ability to photosynthesise The lack of photosynthesis causes parts of the leaf to die; producing black streaks Your notes Eventually, the whole leaf dies Common pathogens and related communicable diseases in humans table Pathogen type Disease Method of transmission Bacterium Tuberculosis Airborne droplets HIV/AIDS Body fluids Virus Influenza Airborne droplets Protoctist Malaria Female mosquitoes Skin-to-skin contact with an infected Fungus Athlete's foot individual Contact with an item of clothing Common pathogens and related communicable diseases in plants table Pathogen type Disease Plant host Method of transmission An infected tuber can lead to the growth of infected new Bacterium Ring rot Potato, tomato plants Contaminated soil, water and equipment Leaf-to-leaf contact between plants Virus Tobacco mosaic Tobacco Humans touching different plants Spores are carried by wind Protoctist Late blight Potato, tomato from plant to plant Leaf-to-leaf contact Fungus Black sigakota Bananas Spread of spores by humans or within infected plant matter Page 4 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes These notes contain details of the binomial names of pathogens in order to provide a broad coverage of information about the diseases, however you are not required to memorise the binomial names for your exams. Page 5 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.2 Transmission of Communicable Pathogens Your notes Transmission of Communicable Pathogens Disease transmission In order for a population of pathogens to survive, they must be able to successfully transfer from host to host If pathogens are unable to find new hosts then they will go extinct Disease transmission is defined as the transfer of pathogens from an infected host to an uninfected host Transmission can be very risky for pathogens During the infective stages, pathogens produce a large number of individuals to increase the likelihood that some will find a new host and survive Transmission through contact between individuals Some pathogens are transferred through physical contact between individuals If the leaves of plants infected with Tobacco Mosaic Virus (TMV) touch the leaves of another uninfected plant, particles of the virus are transmitted Sometimes individuals being within close proximity to each other is sufficient for transmission The influenza viruses are spread in the air via tiny droplets of water. An infected individual breathes out droplets containing the virus and they are breathed in by an uninfected individual Spores can also be involved in the transmission of pathogens Spores are very small reproductive structures that are released into the environment. They are dispersed via wind or water Once they reach a food source (host) they begin growing Depending on the organism, spores can be produced via mitosis or meiosis so they can be haploid or diploid P. infestans which causes potato blight produces specialised spores called sporangia. These structures are adapted for wind dispersal Transmission of HIV/AIDS Human Immunodeficiency Virus is a retrovirus The HIV virus is not transmitted by a vector (unlike in malaria) The virus is unable to survive outside of the human body HIV is spread by intimate human contact and can only be transmitted by direct exchange of body fluids This means HIV can be transmitted in the following ways: sexual intercourse Page 6 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources blood donation sharing of needles used by intravenous drug users from mother to child across the placenta Your notes mixing of blood between mother and child during birth from mother to child through breast milk Transmission of tuberculosis (TB) When infected people with the active form of the disease cough or sneeze, the Mycobacterium tuberculosis bacteria enter the air in tiny droplets of liquid TB is transmitted when uninfected people then inhale these droplets TB, therefore, spreads more quickly among people living in overcrowded conditions The form of TB caused by Mycobacterium bovis occurs in cattle but is spread to humans through contaminated meat and unpasteurised milk Very few people in developed countries now acquire TB in this way, although meat and milk can still be a source of infection in some developing countries Transmission via a vector Vectors are involved in the transmission of pathogens A vector is any organism that transfers a pathogen from an infected individual to an uninfected individual The vector themselves usually aren't harmed by the pathogen A lot of disease vectors tend to be insects Insects are ideal vectors as they reproduce in large numbers which increases the likelihood of pathogen transmission Transmission of malaria Malaria is caused by one of four species of the protoctist Plasmodium These protoctists are transmitted to humans by an insect vector: Female Anopheles mosquitoes feed on human blood to obtain the protein they need to develop their eggs If the person they bite is infected with Plasmodium, the mosquito will take up some of the pathogen with the blood meal When feeding on the next human, Plasmodium pass from the mosquito to the new human’s blood Malaria may also be transmitted during blood transfusion and when unsterile needles are re-used Plasmodium can also pass from mother to child across the placenta Page 7 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The life cycle of Plasmodium falciparum Factors that affect disease transmission The transmission of disease ultimately depends on: The presence of the pathogens If the pathogen is not present in the population then it cannot spread The presence of susceptible individuals A high number of immune or resistant individuals in a population will reduce the likelihood of transmission Animals and plants can be resistant to some diseases Individuals who are resistant have mechanisms that prevent the infection or spread of pathogens within their body. They are not susceptible to disease. These mechanisms are coded for by their genes Individuals who are heterozygous for the sickle cell allele have resistance to malaria Some humans are even resistant to HIV Page 8 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Resistance is different to immunity When resistant individuals are exposed to the pathogen for the first time they do not develop the disease and suffer no symptoms Your notes An immune individual has been previously infected with the pathogen, suffered symptoms of the disease and recovered. They are highly unlikely to develop symptoms of the disease when exposed to the pathogen again The proportion of resistant or immune individuals in a population influences the potential for transmission (as they are not susceptible to disease) The higher the proportion, the lower the probability of transmission Different types of disease transmission are affected by different factors Human pathogens are affected by specific factors dictated by human behaviour and population size Factors affecting transmission Pathogens that spread through direct contact or by droplet infection need potential hosts to be within close proximity to each other Places or areas with high population densities are more likely to have high infection rates E.g. cities and schools Tuberculosis (TB) transmission is very high in places where many people have to sleep in confined quarters E.g. poor housing and homeless shelters Farmers who use monocultures to maximise yield and profit can experience large disease outbreaks Farmers grow a large number of crop plants in a small area As the crops grow the leaves of different plants touch each other, making the transmission of pathogens such as tobacco mosaic virus (TMV) very easy The transmission of a pathogen through vectors can be affected by the biology of the vectors involved Common disease vectors include mosquitoes and aphids The population of vectors (usually insects) is influenced by weather and climate Factors affecting the distribution of malaria Malaria is caused by one of four species of the protoctist Plasmodium but these protoctists are transmitted to humans by an insect vector (female Anopheles mosquitoes) The Anopheles mosquitoes favour habitats that have high rainfall, high temperatures and high humidity This means malaria can occur where these mosquitoes are present and, as a result, is found throughout the tropics and sub-tropics (about 80% of cases are in Africa) The Anopheles mosquitoes found in Africa also have longer lifespans and prefer biting humans than animals Page 9 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources In the 1950s, the World Health Organisation (WHO) coordinated a worldwide eradication programme. Whilst malaria was eradicated from some countries, the programme was mainly unsuccessful because: Your notes Plasmodium became resistant to the drugs being used to try and control it Anopheles mosquitoes became resistant to DDT and other insecticides being used against them There is evidence that there are an increasing number of malaria epidemics due to climatic and environmental changes that favour the spread of the Anopheles mosquitoes A social factor that has caused the number of cases of malaria in Africa, in particular, to increase in recent years is the increased migration of people due to war (when migration happens due to war the parasite can be transferred from areas that have the infection to new regions, and, if the Anopheles mosquito is breeding in the new region, then the mosquito vector will transfer the disease from one human to the next) Factors affecting the transmission of human diseases The degree or level of poverty in an area often correlates with the transmission of human diseases in that area Water-borne disease like typhoid, cholera and polio spread when human faecal matter enters and contaminates drinking water Those below the poverty line usually live in areas with crowded housing with no sewage systems, sanitation facilities or water treatment facilities. In addition, many people in these areas have limited access to hygiene products In the last 200 years, humans have spread across the globe, bringing their diseases and pathogens with them The level of human movement and migration that currently exists means that populations are more connected than ever In the past, the ocean and bodies of water would have acted as natural geographic barriers to prevent the spread of pathogens The first flu pandemic in 1918 took one year to spread around the globe. The flu pandemic in 2009 only took 3 months to reach West Africa from North America An individual can become infected in one country (where the disease exists) and get a flight to another country thousands of miles away. They may not show any symptoms until they have already arrived in the new country The historical danger of human migration is well known When colonisers arrived in the Americas they brought many European diseases with them, such as smallpox The Native Americans had no immunity or resistance as they had never been exposed to these pathogens before (they were a fully susceptible population) The invasive pathogens rapidly spread through the population causing a large number of deaths The behaviour or cultural practices of humans can also affect the transmission rate of diseases For example, in parts of Africa, it is a religious and cultural tradition to touch and kiss the dead. This was a major problem during Ebola outbreaks there and scientists had to work with the public to try Page 10 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources and inform them that this tradition was increasing the spread of the virus Your notes Examiner Tip The different terms used to describe disease transmission can be confusing, especially the ones that sound the same like endemic, epidemic and pandemic. Don't worry the definitions are below. Endemic - a disease that is always present in a population (even if very low numbers) Epidemic - there is a large increase in the number of cases in a population (an outbreak) Pandemic - an epidemic occurs on a large scale and crosses international boundaries Page 11 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.3 Plant Defences Against Pathogens Your notes Plant Defences Against Pathogens Just like animals, plants have defence mechanisms to protect themselves against infection and disease The different mechanisms are classified into two categories: passive and active Passive defence mechanisms are always present Some of these mechanisms are physical barriers that prevent pathogens from entering Some are chemicals that reduce or prevent the growth of pathogens Active defence mechanisms in plants are activated when pathogens invade Hypersensitivity deprives pathogens of resources The formation of physical barriers by callose plays a major role in limiting the spread of pathogens Cell signalling plays an important role in coordinating the active defence mechanisms Passive defence mechanisms Physical barriers make it harder for pathogens to gain entry into plants Examples of physical barriers: Waxy cuticle The only way that viruses and bacteria can penetrate the waxy cuticle of a leaf is if there is a wound on the leaf surface or stem. Wounds are commonly caused by grazing herbivores Cellulose cell wall Closed stomata Bark Casparian strip Some fungi species can invade a plant all the way to the endodermis but they are unable to push past the Casparian strip Chemical defences prevent pathogens from growing on the surface of the plant by creating acidic conditions Examples of chemical defences: Toxic compounds E.g. Catechol Sticky resin found in the bark This traps the pathogens so they can't spread Compounds that encourage the growth of competing microorganisms Microorganisms such as yeast found on the leaf surface are completely harmless to plants. They are strong competitors against harmful pathogens Page 12 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Enzyme inhibitors E.g. Tannins Your notes Receptor molecules They detect the presence of pathogens and trigger other defence mechanisms Active defence mechanisms Unlike animal cells, plant cells have cell walls. This means that substances can not freely move around the entire plant as the immune cells do in some animals, making cell signalling vital for plant defence The active defence mechanisms of a plant are activated once a pathogen has invaded Hypersensitivity is the rapid death of tissue surrounding the infection site Although quite an extreme response, it is very effective as it deprives the pathogens of host tissue, nutrients and energy Plants also create physical barriers to reduce the spread of a pathogen Reinforced cell walls are formed when fungi and bacteria invade The invasion of pathogens stimulates the release of compounds callose and lignin These molecules are deposited between the cell surface membrane and the cell wall Callose is a polysaccharide that forms a matrix shape. Antimicrobial compounds that kill pathogens (hydrogen peroxide and phenols) can be deposited in this shape Narrowing of the plasmodesmata Callose helps to reduce the size of the channels that connect neighbouring plant cells Ingrowths into the xylem vessels (tyloses) The cytoplasm of nearby cells grows into the xylem to create a wall made of callose Blockage of the phloem The sieve pores are filled with callose which prevents phloem sap from being transported The importance of cell signalling in plant defence Pathogens possess cellulase enzymes that digest the cellulose in plant cell walls The molecules produced from this breakdown of cellulose act as signals to cell surface receptors By stimulating these receptors they cause the release of defence chemicals called phytoalexins Phytoalexins have several modes of action Disrupting pathogen metabolism Delaying pathogen reproduction Disrupting bacterial cell surface membranes Stimulating the release of chitinases (enzymes that break down the chitin cell walls in fungi) Salicylic acid is another important signalling molecule involved in plant defence It migrates through the plant to uninfected areas. Once there it activates defence mechanisms that protect the plant against pathogens for a period of time This long-term protection is called systemic acquired resistance Page 13 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Ethylene is a signalling compound that allows plants to communicate Plants under attack from pathogens secrete ethylene onto their leaves. The ethylene vaporises, stimulating other leaves on the same plant to react (as well as other plants) Your notes Page 14 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.4 Non-specific Immune Responses Your notes Non-specific Immune Responses Vertebrate animals have developed complex mechanisms to defend themselves against the invasion of pathogens The different methods of defence can be divided into four categories: Physical: body tissues act as barriers, preventing the entry of pathogens E.g. skin, mucous membrane of the alimentary canal Cellular: cells detect and signal the presence of pathogens. Protective substances are secreted and the pathogens are ingested and digested Chemical: secreted substances generate an inhospitable environment for the growth of pathogens. These substances can trap pathogens, cause them to burst, or prevent them from entering cells and reproducing Commensal organisms: the harmless bacteria and fungi present on and in the body compete with pathogens for nutrients First line of defence A human has three lines of defence The first line of defence prevents the entry of pathogens and is comprised of the following: Skin Mucous membranes Expulsive reflexes Chemical secretions Skin Skin posses an outer layer of dry, dead, hardened cells filled with keratin Keratin is a tough fibrous protein This layer of cells acts as a physical barrier to pathogens There are secretions of sebum that contain fatty acids which have antimicrobial properties Evaporation of sweat from the skin leaves behind a salt residue The lack of moisture, low pH and high salinity creates an inhospitable environment for the growth of microorganisms Mucous membranes Mucous membranes line the gut, airways and reproductive system The mucous membrane consists of epithelial cells and mucus-secreting cells like goblet cells Page 15 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Mucus contains lots of glycoproteins with long carbohydrate chains. These chains are what make mucus sticky Viruses, bacteria, pollen and dust float about in the air that we breathe in Your notes Mucus in the airways (trachea, bronchi and bronchioles) can trap these particles The particles are then moved towards the back of the throat by cilia Cilia are small hair-like structures on the surface of cells. Some ciliated epithelial cells have motile cilia that beat and move in a wave-like manner to move mucus along the airway Expulsive reflexes When a pathogen irritates the lining of an airway it can trigger an expulsive reflex; a cough or sneeze Both a cough and sneeze result in a sudden expulsion of air. This expelled air contains secretions from the respiratory tract along with the foreign particles that have entered Chemical secretions Lysozymes are antimicrobial enzymes that breakdown the cell wall of bacteria These special enzymes are found in body fluids such as blood, tears, sweat, and breast milk Hydrochloric acid is produced by the cells that line the stomach The acid creates a low pH inside the stomach which helps to kill any bacteria that has been ingested alongside food The cells of the gut secrete mucus to prevent being damaged by hydrochloric acid Commensal microorganisms On average roughly 1kg of a human's weight is made up of the bacteria on or inside their body Candida albicans and E. coli are examples of bacteria commonly found on and in humans These microorganisms grow on the skin, in the mouth and intestines however they do not cause disease Their growth is limited by the defence mechanisms Hosting these microorganisms can have a major benefit for humans They compete with pathogenic microorganisms and prevent them from invading host tissue Antibiotics often kill friendly gut bacteria which can allow for opportunistic pathogens to grow Second line of defence When a pathogen manages to evade the first line of defence then the second line of defence will respond The second line of defence involves phagocytic cells and antimicrobial proteins responding to the invading pathogens Second-line responses include: Blood clotting Page 16 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Inflammation Wound repair Phagocytosis Your notes Blood clotting When the body is wounded it responds rapidly A break in the mucous membranes or skin membranes causes the release of molecules that trigger a chemical cascade which results in blood clotting Platelets release substances that undergo a series of chemical reactions The end product is that fibrin is formed, which forms a network, trapping platelets and forming a clot Blood clotting prevents excess blood loss, the entry of pathogens and provides a barrier (scab) for wound healing to occur Page 17 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The blood clotting cascade Examiner Tip You don't need to know all of the steps involved in the blood-clotting cascade for your exam! They key information to remember is that platelets trigger a chemical reaction cascade that results in the formation of fibrin, which forms a scab. Inflammation The surrounding area of a wound can sometimes become swollen, warm and painful to touch; this is described as inflammation Inflammation is a local response to infection and tissue damage. It occurs via chemical signalling molecules which cause the migration of phagocytes into the tissue and increased blood flow Body cells called mast cells respond to tissue damage by secreting the cell signalling molecule, histamine Histamine stimulates the following responses: Vasodilation increases blood flow through capillaries "Leaky" capillaries allow fluid to enter the tissues and creating swelling A portion of the plasma proteins leave the blood Phagocytes leave the blood and enter the tissue to engulf foreign particles Cells release cytokines that trigger an immune response in the infected area Cytokines are cell-signalling compounds that stimulate inflammation and an immune response They are small proteins molecules Interleukins are a group of cytokines Interleukin 1 (IL-1) and interleukin 6 (IL-6) promote inflammation Page 18 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources IL-1 targets the brain, causing drowsiness and fever Wound repair Your notes A scab is formed as a result of blood clotting Underneath this scab, there are stem cells that divide by mitosis to heal the wound Wound healing occurs in a number of overlapping stages: New blood vessels form Collagen is produced Granulation tissue forms to fill the wound Stem cells move over the new tissue and divide to produce epithelial cells Contractile cells cause wound contraction Unwanted cells die Page 19 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The process of wound repair involving the formation of granulation tissue Your notes All of the above are examples of non-specific immune responses Non-specific defences are present in humans from birth. The rapid response is the same for every pathogen; they do not distinguish between pathogens They are not always effective Page 20 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.5 Phagocytes Your notes Phagocytes: Structure & Mode of Action Phagocytes are white blood cells that are produced continuously in the bone marrow They are stored in the bone marrow before being distributed around the body in the blood They are responsible for removing dead cells and invasive microorganisms They carry out what is known as a non-specific immune response There are three main types of phagocyte, each with a specific mode of action. The three types are: Neutrophils Macrophages Dendritic cells As they are all phagocytes, they carry out phagocytosis (the process of recognising and engulfing a pathogen) but the process is slightly different for each type of phagocyte Neutrophils Neutrophils are short-lived cells that often leave the blood by squeezing through capillary walls to ‘patrol’ the body tissues During an infection they are released in large numbers from their stores They have a lobed nucleus which can be used to identify them in blood smears Mode of action: Chemicals released by pathogens, as well as chemicals released by the body cells under attack (e.g. histamine), attract neutrophils to the site where the pathogens are located This response to chemical stimuli is known as chemotaxis Neutrophils move towards pathogens, which may have antibodies attached to their surface antigens Neutrophils have receptor proteins on their surfaces that recognise antibody molecules and attach to them Once attached to a pathogen the cell surface membrane of a neutrophil extends out and around the pathogen, engulfing it and trapping the pathogen within a phagocytic vacuole This part of the process is known as endocytosis The neutrophil then secretes digestive enzymes into the vacuole The enzymes are released from lysosomes which fuse with the phagocytic vacuole These digestive enzymes destroy the pathogen After killing and digesting the pathogens, the neutrophils die Pus is a sign of dead neutrophils Page 21 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 22 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Neutrophils carry out phagocytosis, after which they digest the pathogen Macrophages Macrophages are larger than neutrophils and are long-lived cells After being produced in the bone marrow, macrophages travel in the blood as monocytes, which then develop into macrophages once they leave the blood After leaving the blood macrophages settle in the lungs, liver, spleen, kidney and lymph nodes Mode of action: Macrophages play an important role in initiating the specific immune response They carry out phagocytosis in a similar way to neutrophils but they do not destroy pathogens completely; instead they cut the pathogens up so that they can display the antigens of the pathogens on their surface Antigens are displayed as part of a structure called a major histocompatibility complex (MHC) The cell is now called an antigen-presenting cell and can be recognised by lymphocytes, another type of white blood cell Dendritic cells Dendritic cells are large phagocytic cells with lengthy extensions These extensions give them a large surface area to interact with pathogens and lymphocytes These cells can be found throughout the body Once they have ingested foreign material they transport it to the lymph nodes The role of antigen-presenting cells T-lymphocytes produce an immune response when they are exposed to a specific antigen T cells will only bind to an antigen if it is present on the surface of an antigen-presenting cell These cells present the antigens from toxins, foreign cells and ingested pathogens Page 23 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources They help to recruit other cells of the immune system to produce a specific immune response An antigen-presenting cell is one of the host's cells It might be a macrophage or a body cell that has been invaded by a pathogen and is displaying the Your notes antigen on its cell surface membrane Once the surface receptor of the T cell binds to the specific complementary antigen it becomes sensitised and starts dividing to produce a clone of cells Examiner Tip The vacuole formed around a bacterium once it has been engulfed by a phagocyte is called a phagosome. A lysosome fuses with the membrane of the phagosome (to form a phagolysosome) and releases lysozymes (digestive enzymes) to digest the pathogen. Page 24 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.6 Blood Cells Your notes Drawing Cells From Blood Smears To record the observations seen under the microscope (or from photomicrographs taken) a labelled biological drawing is often made Biological drawings are line pictures which show specific features that have been observed when the specimen was viewed There are a number of rules/conventions that are followed when making a biological drawing The conventions are: The drawing must have a title The magnification under which the observations shown by the drawing are made must be recorded A sharp HB pencil should be used (and a good eraser!) Drawings should be on plain white paper Lines should be clear, single lines (no thick shading) No shading The drawing should take up as much of the space on the page as possible Well-defined structures should be drawn The drawing should be made with proper proportions Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled Label lines should be kept to one side of the drawing (in parallel to the top of the page) and drawn with a ruler Drawings of cells are typically made when visualizing cells at a higher magnification power, whereas plan drawings are typically made of tissues viewed under lower magnifications (individual cells are never drawn in a plan diagram) Blood smears A blood smear is when a small amount of blood is spread on a glass microscope slide, stained and covered with a coverslip The different blood cells can then be examined using a microscope Red blood cells have no nuclei and a distinct biconcave shape White blood cells have irregular shapes Neutrophils have distinctive lobed nuclei They make up roughly 70% of all white blood cells Lymphocytes have very large nuclei that nearly occupy the entire cell Page 25 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The different blood cells present in a blood smear The lobed nucleus of a neutrophil Page 26 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes An example of blood cells drawn from the field of view of a microscope observing a blood smear Examiner Tip When producing a biological drawing, it is vital that you only ever draw what you see and not what you think you see.To accurately reflect the size and proportions of structures you see under the microscope, you should get used to using the eyepiece graticule.You should be able to describe and interpret photomicrographs, electron micrographs and drawings of typical animal cells. Page 27 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.7 The T Lymphocyte Response Your notes Specific Immune Response: T Lymphocytes Lymphocytes and antibodies provide the third line of defence against pathogens Unlike the first and second lines of defence, the third line is specific Specific immune responses are slower but more effective than non-specific immune responses Lymphocytes are A type of white blood cell Smaller than phagocytes Have a large nucleus that fills most of the cell Produced in the bone marrow before birth Travel around the body in the blood There are two types of lymphocytes (with different modes of action) T-lymphocytes (T cells) Lymphocytes that mature in the thymus gland B-lymphocytes (B cells) Lymphocytes that mature in the bone marrow Maturation of T-lymphocytes Immature T-lymphocytes originate in the bone marrow They move to the thymus gland in the chest, which is where they mature During the process of maturation T lymphocytes (T cells) gain specific cell surface receptors called T cell receptors (TCRs) These receptors have a similar structure to antibodies and are each complementary to a different antigen A small number of T cells have the same TCRs, these genetically identical cells are called clones T cells within each clone differentiate into different types of T cell: T helper cells and T killer cells There is a very large number of different T cells with different TCRs This variation allows the T cells to recognise a wide range of foreign antigens Foreign antigens can be found on the surface of microorganisms, their cell products and toxins The matured T cells remain inactive until they encounter their specific antigen Page 28 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Mature T lymphocytes have many different types of surface receptor, each of which is complementary to a different antigen T lymphocytes in the immune response In order to play their role in the immune response T cells need to be activated and increase in number; this process is described below Page 29 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Antigen presentation Macrophages engulf pathogens and present the pathogen antigens on their own cell surface membrane Your notes They become antigen-presenting cells (APCs) Clonal selection T cells with T cell receptors that are complementary to the specific pathogenic antigen bind to the APC They are the clones that have been selected for replication Binding to the complementary antigens causes the T cell to be activated Clonal expansion Activated T cells divide by mitosis to produce clones There are now many T cells in the blood, all of which have specific roles T helper cells These cells release chemical signalling molecules known as interleukins (a type of cytokines) Interleukins causes phagocyte activity to increase Interleukins is needed to activate B cells T killer cells T killer cells patrol the body in search of antigen-presenting body cells T killer cells attach to the foreign antigens on the cell surface membranes of infected cells and secrete toxic substances that kill the infected body cells, along with the pathogen inside Perforins secreted by T killer cells punch a hole in the cell surface membrane of infected cells, allowing toxins to enter T memory cells Memory cells remain in the blood, meaning that if the same antigen is encountered again the process of clonal selection will occur much more quickly Page 30 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Activated T cells divide by mitosis to produce clones. Cloned T helper cells produce chemicals that activate B cells while cloned T killer cells destroy infected body cells. Page 31 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.8 The B Lymphocyte Response Your notes Specific Immune Response: B Lymphocytes Maturation of B-lymphocytes B-lymphocytes (B cells) remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen During the process of maturation B cells gain specific cell surface receptors called B cell receptors (BCRs) The receptors on the cell surface of B cells are antibodies and are sometimes referred to as antibody receptors Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen A small number of B cells have the same BCRs, these genetically identical cells are called a clone Page 32 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Mature B cells have many different types of antibody receptor on their cell surface membranes B cells in the immune response In order to play their role in the immune response B cells need to be activated and increase in number; this occurs as follows: Page 33 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Clonal selection and activation B cells with complementary antibody receptors bind to antigens on antigen presenting cells; this is clonal selection Your notes These antigen presenting cells can be phagocytes, infected cells, or the pathogens themselves This binding, together with interleukins released by T helper cells activates the B cells Clonal expansion Activated B cells divide by mitosis to produce clones This results in large numbers of identical B-lymphocytes being produced over a few weeks Some of these B-lymphocytes differentiate into plasma cells Plasma cells secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut The other B-lymphocytes become memory cells that remain circulating in the blood for a long time Page 34 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Activated B cells differentiate into plasma cells and memory cells Page 35 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.9 Primary & Secondary Immune Responses Your notes Primary & Secondary Immune Responses During clonal expansion T and B cells form memory cells Memory cells form the basis of immunological memory – the cells can last for many years and often a lifetime There are two types of immune response: Primary immune response (responding to a newly encountered antigen) Secondary immune response (responding to a previously encountered antigen) The primary immune response The primary immune response has a considerate time delay It takes considerable energy and time for: The clonal selection and expansion of specific T cells and B cells The synthesis of antibodies Antibodies do not begin to appear in the blood until roughly 10 to 17 days after the foreign antigen first entered the body This time delay is why we often experience symptoms of a disease when we are first exposed to a pathogen Some of the B cells differentiate during clonal expansion to become plasma cells and memory cells Plasma cells are short-lived A portion of the selected T cells also differentiate into memory cells Memory cells remain circulating in the blood for a long time and allow for a rapid secondary immune response B memory cells and the secondary immune response If the same foreign antigen is found in the body a second time, the B memory cells recognise the antigen B memory cells divide very quickly and differentiate into plasma cells (to produce antibodies) and more memory cells This response is very quick, meaning that the infection can be destroyed and removed before the pathogen population increases too much and symptoms of the disease develop This response to a previously encountered pathogen is, relative to the primary immune response, extremely fast The response is quicker because there are more memory cells present to be selected than there were cells within the original clone (that existed prior to the first infection) Page 36 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources More memory cells can be selected and so more antibodies are produced within a short time period Your notes Page 37 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes During a secondary immune response, B memory cells that remained in the blood divide very quickly into plasma cells (to produce antibodies) and more memory cells Page 38 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The concentration of antibodies during the primary and secondary immune responses T memory cells and the secondary immune response T-lymphocytes also play a part in the secondary immune response They differentiate into memory cells, producing two main types: Memory helper T cells Memory killer T cells Just like the memory cells formed from B-lymphocytes, these memory T cells remain in the body for a long time and provide long-term immunity If the same antigen is found in the body a second time, these memory T cells become active very quickly Examiner Tip Immunological memory (made possible by memory cells) is the reason why catching certain diseases twice is so unlikely. For example, there is only one strain of the virus that causes measles, and each time someone is re-infected with this virus, there is a very fast secondary immune response so they do not get ill.However, some infections such as the common cold and influenza are caused by viruses that are constantly developing into new strains. As each strain has different antigens, the primary immune response (during which we often become ill) must be carried out each time before immunity can be achieved. Page 39 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.10 Antibodies Your notes Antibodies: Structure & Functions Structure Antibodies are globular glycoproteins called immunoglobulins Antibodies have a quaternary structure (which is represented as Y-shaped), with two ‘heavy’ (long) polypeptide chains bonded by disulfide bonds to two ‘light’ (short) polypeptide chains Each polypeptide chain has a constant region and variable region The constant regions do not vary within a class (isotype) of antibodies but do vary between the classes. The constant region determines the mechanism used to destroy the antigens There are 5 classes of mammalian antibodies each with different roles The amino acid sequence in the variable regions of the antibodies (the tips of the "Y") are different for each antibody. The variable region is where the antibody attaches to the antigen to form an antigen- antibody complex At the end of the variable region is a site called the antigen-binding site. Each antigen-binding site is generally composed of 110 to 130 amino acids and includes both the ends of the light and heavy chains The antigen-binding sites vary greatly giving the antibody its specificity for binding to antigens. The sites are specific to the epitope (the part of the antigen that binds to the antibody) A pathogen or virus may therefore present multiple antigens meaning different antibodies need to be produced The ‘hinge’ region (where the disulfide bonds join the heavy chains) gives flexibility to the antibody molecule which allows the antigen-binding site to be placed at different angles when binding to antigens This region is not present in all classes of antibodies Page 40 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A model of the generalised structure of an antibody molecule Function Antibodies are produced by B-lymphocytes Antibodies bind to specific antigens that trigger the specific immune response. Every antigen has one antibody Antigens include pathogens and their toxins, pollen, blood cell surface molecules and the surface proteins found on transplanted tissues The function of antibodies is to destroy pathogens within the body either directly, or by recruiting other immune cells Antibodies can act as anti-toxins, opsonins and agglutinins Page 41 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes You must know that each antibody will have a different variable region with an antigen-binding site that matches one antigen or toxin produced by a pathogen. The antigen-binding site (and therefore the antibody) is specific to one antigen. Page 42 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.11 Opsonins, Agglutinins & Anti-toxins Your notes Opsonins, Agglutinins & Anti-toxins The way in which antibodies function can vary Antibodies can combine with viruses and toxins of pathogens (e.g. bacteria) to block them from entering or damaging cells Antibodies can act as anti-toxins by binding to toxins produced by pathogens (e.g. the bacteria that cause diphtheria and tetanus) which neutralises them making them harmless Antibodies can attach to bacteria making them readily identifiable to phagocytes, this is called opsonisation. Once identified, the phagocyte has receptor proteins for the heavy polypeptide chains of the antibodies, which enables phagocytosis to occur Antibodies can attach to the flagella of bacteria making them less active, which makes it easier for phagocytes to do phagocytosis Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together (agglutination). This reduces the chance that the pathogens will spread through the body and makes it possible for phagocytes to engulf a number of pathogens at one time Antibodies (together with other molecules) can create holes in the cell walls of pathogens causing them to burst (lysis) when water is absorbed by osmosis Page 43 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 44 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The functions of antibodies vary according to which type of antigen they act on Page 45 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.12 Types of Immunity Your notes Types of Immunity Active immunity Active immunity is acquired when an antigen enters the body triggering a specific immune response (antibodies are produced) Active immunity is naturally acquired through exposure to microbes or artificially acquired through vaccinations The body produces memory cells, along with plasma cells, in both types of active immunity giving the person long-term immunity In active immunity, during the primary response to a pathogen (natural) or to a vaccination (artificial), the antibody concentration in the blood takes one to two weeks to increase. If the body is invaded by the same pathogen again or by the pathogen that the person was vaccinated against then, during the secondary response, the antibody concentration in the blood takes a much shorter period of time to increase and is higher than after the vaccination or first infection Page 46 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The primary and secondary response to the same antigen Passive immunity Passive immunity is acquired without an immune response. Antibodies are not produced by the infected person As the person’s immune system has not been activated then there are no memory cells that can produce antibodies in a secondary response. If a person is reinfected they would need another infusion of antibodies Depending on the disease a person is infected with (eg. tetanus) they may not have time to actively acquire the immunity, that is, there is no time for active immunity. So passive immunity occurs either artificially or naturally Artificial passive immunity occurs when people are given an injection / transfusion of the antibodies. In the case of tetanus this is an antitoxin. The antibodies were collected from people whose immune Page 47 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources system had been triggered by a vaccination to produce tetanus antibodies Natural passive immunity occurs when: Foetuses receive antibodies across the placenta from their mothers Your notes Babies receive the initial breast milk from mothers (the colostrum) which delivers a certain isotype of antibody (IgA) Comparing Active & Passive Immunity Table Examiner Tip Active immunity is when the body produces the antibodies whereas in passive immunity the body is given the antibodies. Page 48 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.13 Autoimmune Diseases Your notes Autoimmune Diseases Roughly 5% of the British population suffer from an autoimmune disease An autoimmune disease occurs when the body attacks itself The immune system damages cells of the body as a result Antibodies, T cells (helper and cytotoxic) and B cells attack one or more self-antigens Glycoproteins and glycolipids form surface antigens that enable the immune system to determine whether the cell belongs to the body or if it is foreign The attack can be targeted towards a single organ or it can be directed towards the entire body Rheumatoid arthritis Rheumatoid arthritis is an autoimmune disease that solely affects the joints It is different from osteoarthritis in several ways It usually begins in the fingers and hands, spreading to the shoulders and elsewhere Symptoms include muscle spasms, inflamed tendons, lethargy and constant joint pain Causes of autoimmune diseases The causes of autoimmune diseases are still not fully understood There is a lot of research currently underway in this field Scientists have deduced that genetics is an influencing factor Susceptibility to an autoimmune disease was shown to be inherited Susceptibility is the likelihood of an individual developing the disease when exposed to the specific pathogen or stimulus However, research has also suggested that the environment is also important When individuals moved from areas of low autoimmune disease prevalence (like Japan) to areas of higher autoimmune disease prevalence (like the USA) they showed an increased chance of developing an autoimmune disease Page 49 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.14 Principles of Vaccination Your notes Principles of Vaccination The principles underpinning vaccinations were discovered by Edward Jenner in the 1700s when he developed the first smallpox vaccine A vaccine is a suspension of antigens that are intentionally put into the body to induce artificial active immunity. A specific immune response where antibodies are released by plasma cells There are two main types of vaccines: Live attenuated Inactivated Vaccines are administered either by injection or orally (by mouth) The vaccinations given by injection can be into a vein or muscle Vaccinations produce long-term immunity as they cause memory cells to be created. The immune system remembers the antigen when reencountered and produces antibodies to it, in what is a faster, stronger secondary response Vaccination programmes are offered to citizens by the government as a major component of health protection The young in the population are given vaccines to protect them from diseases that were once common and caused serious harm For example, in the UK babies are vaccinated against polio and measles A country may not have had any cases of a particular disease for several years however international travel means there is the possibility that a disease could be reintroduced at any time by travellers coming from other countries By having their citizens vaccinated against diseases governments can prevent serious epidemics from occurring Effectiveness of vaccines Very few drugs are effective against viruses which is why vaccines are critical in controlling the spread of viruses Vaccines can be: Highly effective with one vaccination giving a lifetime’s protection (although less effective ones will require booster / subsequent injections) Generally harmless as they do not cause the disease they protect against because the pathogen is killed by the primary immune response Unfortunately, there can be problems with vaccines due to: People having a poor response (eg. they are malnourished and cannot produce the antibodies – proteins or their immune system may be defective) Antigenic variation – the variation (due to major changes) in the antigens of pathogens causes the vaccines to not trigger an immune response or diseases caused by eukaryotes (eg. malaria) have too Page 50 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources many antigens on their cell surface membranes making it difficult to produce vaccines that would prompt the immune system quickly enough Viruses having the capacity to change their surface antigens (the targets of vaccines) by: Your notes Antigenic drift – over time there are small changes in the structure and shape of antigens (within the same strain of virus) Antigenic shift – there are major changes in antigens (within the same strain of virus) Antigenic concealment – the pathogen ‘hides’ from the immune system by: Living inside cells Coating their bodies in host proteins Parasitising immune cells such as macrophages and T cells (eg. HIV) Remaining in parts of the body that are difficult for vaccines to reach (eg. Vibrio cholerae – cholera, remains in the small intestine) Cross-breeding – different strains of the virus invade the same cell, producing new viruses with antigens from different strains (essentially the strains swap antigens with each other) The strains of influenza viruses that cause human influenza have been known to crossbreed with viruses that cause similar diseases in other animals This crossbreeding can produce new strains of the human influenza virus that cause pandemics (as no individuals have immunity against them) Every year the World Health Organisation (WHO) tries to provide information about strains that are likely to spread in order to aid government decisions and the development of flu vaccines Herd immunity and ring immunity Herd immunity arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population Those who are not immunised are protected and unlikely to contract it as the levels of the disease are so low It is very important as it allows for the individuals who are unable to be vaccinated (e.g. children and those with weak immune systems) to be protected from the disease The proportion of the population that needs to be vaccinated in order to achieve herd immunity is different for each disease Governments will often vaccinate as many people as possible If vaccination rates fall below the required level then herd immunity can break down There was an outbreak of Measles in Swansea in 2012 due to a lack of vaccine uptake Ring immunity is another way by which mass vaccination programmes can work People living or working near a vulnerable (or infected) person are vaccinated in order to prevent them from catching and transmitting the disease The vaccinated individuals do not spread the pathogen onto others so those vulnerable individuals "within the ring" are protected as the people they interact with will not have the disease The challenges of eradicating disease Page 51 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Eradicating disease presents a challenge On one hand some pathogens are simply complicated and present with disease processes that are not straightforward and so a successful vaccine has not been developed Your notes On the other hand, diseases that could be eradicated where a vaccine does exist, have not been eliminated because too few in the community have been vaccinated It has also been difficult to eradicate other infectious diseases due to: Unstable political situations in areas such as Africa, Latin America and parts of Asia, perhaps resulting in civil unrest or wars Lack of public health facilities (poor infrastructure, few trained personnel, limited financial resources) Types of vaccines Live attenuated vaccines contain whole pathogens (e.g. bacteria and viruses) that have been ‘weakened’ These weakened pathogens multiply slowly allowing for the body to recognise the antigens and trigger the primary immune response (plasma cells to produce antibodies) These vaccines tend to produce a stronger and longer-lasting immune response They can be unsuitable for people with weak immune systems as the pathogen may divide before sufficient antibodies can be produced An example of this type of vaccine is the MMR (Measles, Mumps and Rubella) Inactivated vaccines contain whole pathogens that have been killed (‘whole killed’) or small parts (‘subunit’) of the pathogens (eg. proteins or sugars or harmless forms of the toxins – toxoids) As inactivated vaccines do not contain living pathogens they cannot cause disease, even for those with weak immune systems However, these vaccines do not trigger a strong or long-lasting immune response like live attenuated vaccines. Repeated doses and/or booster doses are often required Some people may have allergic reactions or local reactions (eg. sore arm) to inactivated vaccines as adjuvants (eg. aluminium salts) may be conjugated (joined) to the subunit of the pathogen to strengthen and lengthen the immune response An example of a whole killed vaccine is the polio vaccine An example of a toxoid subunit vaccine (where inactivated versions of the toxins produced by pathogens are used) is Diphtheria Smallpox The eradication of Smallpox is a success story, but its success had specific reasons that cannot be universally replicated in the struggle to eliminate disease Smallpox is a highly contagious disease caused by a virus that exists in two forms: Variola minor and Variola major, the latter being the worst of the two, with a death rate of 12 to 30% Smallpox was transmitted by direct contact and caused red spots (which filled with pus) to cover the body. People who recovered were disfigured as a result of scabs that formed from these spots. It also affected the eyes resulting in permanent blindness for many who recovered Page 52 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The WHO began an eradication programme against smallpox in 1967, stating their intention to eradicate the virus within ten years. The WHO did not declare smallpox eradicated until 1980 The programme focused on: Your notes Vaccination – the aim was to vaccinate more than 80% of populations at risk and if a case of smallpox was reported ring vaccination would occur (where everyone in the household with the reported case, the surrounding 30 households, relatives and anyone else who had contact would get vaccinated) Surveillance Its success was attributed to: The virus was stable – it did not mutate therefore its surface antigens did not change, therefore the same vaccine could be used worldwide which made it cheap to produce the vaccine The vaccine was a ‘live attenuated’ one, being produced from a harmless strain of a similar virus The vaccine could be transported without becoming unviable, as it could be freeze-dried and kept at high temperatures for up to 6 months, thus it was suitable for the tropics The symptoms made it easy to identify infected people (surveillance was possible) Humans being the only reservoirs of infection and there were no carriers making it easier to break the transmission pathway The consistency of the effort, vaccination, surveillance and containment of all outbreaks on a global scale Examiner Tip Remember vaccines trigger the primary immune response (T helper cells trigger B plasma cells to secrete specific antibodies) which leads to the production of memory cells which will give a faster and greater (higher concentration of antibodies) during the secondary response.Remember for a disease to be eradicated by a vaccine it should not: Mutate Have a life cycle that includes other organisms Have symptoms that make it hard to diagnose or trace Page 53 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.15 Sources of Medicine Your notes Sources of Medicine Discovering new drugs The worrying increase of antibiotic-resistant bacteria strains means that scientists are always looking for new antibiotics A lot of time and money is required to successfully develop a drug. There are several trials that a drug must pass before being approved by a national regulatory authority There are several different ways in which new drugs are discovered and developed: The analysis of an organism's genome to find candidate genes that may code for potential drugs Identifying molecules that fit into drug targets e.g. receptors and hormones or neurotransmitters and synapses Modifying drugs that already exist (this is done by using computer programmes that model the molecular structures of drugs and target molecules) Identification of useful compounds produced by organisms (e.g. fungi, plants, animals and actinobacteria) Microorganisms and plants as a source of medicine A large majority of the drugs we currently use have been obtained by studying other organisms Bacteria and fungi have provided many antibiotics Quite recently compounds called rifamycins have been discovered in marine actinobacteria. These compounds kill bacteria by inhibiting bacterial transcription Plants have been a major source of drugs for hundreds of years Artemisinin is a drug found in Sweet wormwood and it treats malaria by killing the pathogen while it is in the red blood cells Quinidine is derived from the Quinine tree and it treats a fast heart rate by blocking channel proteins in cardiac muscle to reduce impulse conduction Many plants are used in traditional Chinese medicine, scientists are keen to catalogue and study these plants to see what drugs they can provide Continued access to these drugs and the discovery of new drugs is a strong argument for maintaining biodiversity at a global level Microorganism and plant species may go extinct before we have the chance to discover what drugs they can provide Personalised medicine Currently, a "one type fits all" attitude is applied when prescribing drugs to individuals with the same disease or condition Page 54 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Personalised medicine involves the development of more targeted and personalised drugs to treat a variety of human diseases as well as the development of synthetic tissues For example, the drug isoniazid is used to treat TB. Some individuals metabolize the drug slowly Your notes (making it effective at treating the disease) while others metabolize it much faster (making it an ineffective treatment) Information gathered from genome projects like the Human Genome Project (HGP) can be used to develop genomic medicine Genomic medicine uses information about an individuals genes to influence their clinical care Ideally, doctors could prescribe the most effective drugs for an individual based on their genome Between individuals, there are differences in DNA base sequences. These differences can affect the tertiary structure of the proteins which are targeted by drugs The information gained from genetic testing could be used to divide the population into subgroups according to how they are likely to respond to specific drugs. This would ensure that individuals receive the most effective drugs that cause the least side effects Serious progress has been made in personalised cancer medicine Herceptin is an antibody drug used to treat some breast cancers, it affects a specific cell surface receptor. A patient is only given the drug if they are found to have high numbers of this receptor Genetic screening is also a form of personalised medicine as it allows for individuals with a high chance of developing specific diseases to be identified and for preventative measures or precautions to be taken Page 55 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 4.1.16 Antibiotics Your notes Using Antibiotics When humans experience a pathogenic bacterial infection they are often prescribed antibiotics by a healthcare professional Antibiotics are chemical substances that inhibit or kill bacterial cells with little or no harm to human tissue Many antibiotics are derived from naturally occurring substances that are harmful to prokaryotic cells (structurally or physiologically) but usually do not affect eukaryotic cells The aim of antibiotic use is to aid the body’s immune system with fighting a bacterial infection Penicillin is a well-known example; it was the first antibiotic to be discovered in 1928 by Sir Alexander Fleming Antibiotics are either described as being bactericidal (they kill) or bacteriostatic (they inhibit growth processes), they target prokaryotic features but can affect both pathogenic and mutualistic bacteria living on or in the body Some antibiotics are derived from fungi while others are synthetic or semi-synthetic Broad-spectrum antibiotics act on a wide range of bacteria while narrow-spectrum antibiotics act on a very small number of bacteria Doctors often prescribe broad-spectrum antibiotics (e.g. Amoxicillin) unless a culture has been taken to prove the need for a narrow-spectrum antibiotic Common Antibiotics & their Mechanisms of Action Page 56 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources In all species, there exists genetic diversity within populations, and the same applies to disease- causing bacteria Individual bacterial cells may possess alleles that confer resistance to the effects of the antibiotic Your notes These alleles are generated through random mutation and are not caused by antibiotic use, but antibiotic use exerts selection pressures that can result in an increase in their frequency Bacteria have a single loop of DNA with only one copy of each gene so when a new allele arises it is immediately displayed in the phenotype When an antibiotic is present: Individuals with the allele for antibiotic resistance have a massive selective advantage so they are more likely to survive, reproduce and pass genome (including resistance alleles) Those without alleles are less likely to die and reproduce Over several generations, the entire population of bacteria may be antibiotic-resistant Antibiotic resistance is an important example of natural selection Some pathogenic bacteria have become resistant to penicillin as they have acquired genes that code for the production of the enzyme β-lactamase (also known as penicillinase), which breaks down penicillin Page 57 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Bacteria evolve rapidly as they reproduce quickly and acquire random mutations – some of which confer resistance Examples of Antibiotic Resistance Genes Page 58 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Consequences of antibiotic resistance Commonly prescribed antibiotics are becoming less effective for many reasons, the main being: Overuse of antibiotics and antibiotics being prescribed when not necessary Large scale use of antibiotics in farming to prevent disease when livestock are kept in close quarters, even when animals are not sick Patients failing to complete the full course of antibiotics prescribed by doctors These factors have led to a reduction in the effectiveness of antibiotics, and an increase in the incidence of antibiotic resistance Bacteria living where there is widespread use of many different antibiotics may have plasmids containing resistance genes for several different antibiotics, giving them multiple resistance and presenting a significant problem for doctors In addition, resistance may first appear in a non-pathogenic bacterium, but then be passed on to a pathogenic species by horizontal transmission There is a constant race to find new antibiotics as resistant strains are continuously evolving Reducing antibiotic resistance & its impact Ways to prevent the incidence of antibiotic resistance increasing include: Tighter controls in countries in which antibiotics are sold without a doctor’s prescription Doctors avoiding the overuse of antibiotics, prescribing them only when needed (patients must only be given antibiotics when absolutely essential) – doctors should test the bacteria first to make Page 59 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources sure that they prescribe the correct antibiotic Antibiotics not being used in non-serious infections that the immune system will ‘clear up’ (patients must not keep unused antibiotics for self-medication of such non-serious infections in Your notes the future) When prescribed a course of antibiotics, the patient finishing the entire course (even if they feel better after a few days) so that all the bacteria are killed, and none are left to mutate to become resistant strains Antibiotics not being used for viral infections (antibiotics have no effect on viruses anyway, and this just provides an unnecessary chance for bacteria to develop resistance) The use of ‘wide-spectrum’ antibiotics being reduced and instead those antibiotics that are highly specific to the infection (‘narrow-spectrum’ antibiotics) being used The type of antibiotics prescribed being changed so that the same antibiotic is not always prescribed for the same infections and diseases (this reduces the chance of a resistant strain developing) The use of antibiotics being reduced and more tightly controlled in industries such as agriculture – controls are now in place to limit their use in farming, where antibiotics are used to prevent, rather than cure, bacterial infections The spread of already-resistant strains can be limited by: Ensuring good hygiene practices such as handwashing and the use of hand sanitisers (this has reduced the rates of resistant strains of bacteria, such as MRSA, in hospitals) Isolating infected patients to prevent the spread of resistant strains, in particular in surgical wards where MRSA can infect surgical wounds Examiner Tip Bacteria pass on alleles for antibiotic resistance through reproduction (vertical gene transfer) but they can also do it in another way.Bacterium possess plasmids which are a small circular piece of DNA that is not the main chromosome. Alleles for antibiotic resistance are often found on these plasmids. Plasmids can be easily transferred from one bacterium to another, even between different species. This is an example of horizontal gene transfer.This means that alleles for antibiotic resistance can be passed one from species of bacteria to another species. Page 60 of 60 © 2015-2025 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers