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Lung Disease - Tuberculosis (TB) Key points.
Tuberculosis is caused by the pathogenic bacteria: Mycobacterium tuberculosis.
TB infection: Step 1 - Step 6.
TB common symptoms.
How does TB affect Ventilation Rate?
TB is a common, secondary infectious disease.
Viruses are the smallest and simplest of the microorganisms,
they are acellular - which means "they are not made of cells!"
Since viruses are acellular and cannot reproduce (in fact, viruses don't actually fulfil any of the seven characteristics of life on their own)... viruses are classified as NON-LIVING.
So, viruses are non-living (consider them more like complex chemical packages than simple living organisms), and think about their definition: -
"Viruses are obligate parasites which are only able reproduce (replicate) inside host cells"
What does the term obligate mean?
Well the term obligate means that "something is obliged to - i.e. it has to, it just has no option" in this case a virus 'has to' reside inside a living host cell so that it can "highjack" the host cell in order to replicate.
Therefore viruses are known as intracellular parasites.
...and what is a parasite?
Parasites are organisms that "live" inside or on other species and cause harm to the host species.
Well as we now know, viruses are not alive, but they do require a host cell to replicate - and when they do replicate, they cause damage to the host, Hence viruses are [intracellular] parasites.
So, Viruses Differ from eukaryotic and prokaryotic cells in 3 main ways, what are they?
A Level Biology - The Basic Structure of a Virus
Viruses (Virions) are tiny! On average they range in size from about 10nm to 400nm so it stands to reason that viruses cannot be seen with a light microscope. Thus, viruses were first observed in the 1930s using more powerful electron microscopy.
Viruses are defined as “obligate intracellular parasites” which exist either extracellularly or intracellularly.
Extracellular, i.e. outside of a host cell viruses are “inactive” or “dormant” because they do not have the necessary cellular machinery (e.g. DNA or RNA, Enzymes, Ribosomes, Golgi, ER etc.) which would allow them to replicate, or multiply (outside of the host).
Intracellular. Viruses are known to infect all cells, from all classifications of life. There are viruses that infect prokaryotes (bacteria), the so called bacteriophages, but mostly viruses infect eukaryotic organisms, such as plants, algae, fungi, protists and of course, viruses that infect animals.
A complete virus particle is known as a virion.
The terms virus and virion are often used synonymously. However, for clarity just be aware that a “virion” is the “dormant” yet, complete form of a virus which is transmitted between host cells.
Whilst a “virus” is the “active infectious agent". Once inside a host cell, the virus dismantles into its separate parts, and can now be reproduced (replicated) by using the host cells “machinery” (DNA or RNA, Ribosomes, Enzymes, etc).
There is always an exception!
There is always an exception! Biology is the study of life, all the fascinating forms of life, interactions, cycles and biochemistry that make life possible… Biology is vast, complicated and multidisciplinary - to say the least. And, there are always exceptions. Viruses for example are so tiny they cannot be seen without an electron microscope… that is unless the virus is the comparatively massive mimi virus! Mimi viruses are from the family of mimiviridae (commonly called the giant viruses) and these large viruses (average size 400nm) infect amoebas. Now 400nm is massive if you’re a virus, so 600nm would be considered gigantic! So when Megavirus chilensis was first discovered in 2010 it became the new big boy in town measuring in at (on average) 600nm and some measuring 750nm! large enough to be observed with a light microscope!
In 2013 another new ‘giant’ virus was discovered - the pandoravirus. This giant virus is not only impressive because of its size (500nm) but also its genome. Described as “evolutionary innovators” these giant viruses have muddied the waters of what was once the clear distinction between the viral world and that of the cellular world, due to their genomes being as complex as some simple eukaryotic cells.
To throw another spanner in the works, there are also the Acidionus Two-Tailed Viruses (from the family Bicaudaviridae. These hyperthermophilic archaeal viruses have shown extracellular activity - that is to say they have shown to be “active” outside of their host cells. Now, the Acidionus Two-Tailed Viruses still require the host cell to replicate, but following host cell lysis, two “protein tails” composed of 800 amino acids begin to project out and continue to assemble from each end of the virion until they reach a length at least equal to that of the capsid. But what is more perplexing is that the protein tails are only produced if the virions are exposed to high temperatures (hence the viruses being classified as hyperthermophilic). The natural environment of the Acidionus Two-Tailed Viruses are acidic hot springs with a pH of around 1.5, and temperatures of 85 - 93°C.
ALL viruses (virions) contain: -
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Nucleic acid. The nucleic acid in a virus can be either DNA or RNA (never both) and may be single or double-stranded. Viruses are classified according to the type of nucleic acid they contain,(e.g. HIV is an RNA virus whilst the Epstein–Barr virus is a DNA virus).
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A capsid (protein coat called made of subunits called capsomeres). If the capsid proteins are closely bound to the nucleic acid, then the combination is called a nucleocapsid. Capsids are composed of many repeating subunits and typically have simple geometrical shapes, i.e. helix viruses such as the tobacco mosaic virus or icosahedral viruses (An icosahedron is a regular polyhedron with 20 equilateral triangular faces). Examples of icosahedral viruses are adenovirus, poliovirus and rhinovirus.
Many viruses have simple structures containing nothing more than a capsid and nucleic acid, but many viruses have slightly more complex structures with additional features such as: -
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A lipid envelope. Viral envelopes derive from the plasma (cell membrane) or nuclear membranes of host cells.
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Proteins which attach the capsid to the envelope (called matrix proteins).
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Glycoproteins which allow the virus to attach to host cells.
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Enzymes, (e.g. Reverse transcriptase) which are required to replicate the viral nucleic acid or incorporate it into a host cell.
Tobacco mosaic virus (TMV) has a very simple structure: just a coil of RNA surrounded by a helical capsid.
Adenovirus contains single stranded DNA surrounded by an icosahedral capsid.
Bacteriophages: e.g. T2 virus have complex structures that combine icosahedral and helical capsids.
The human influenza A virus is enveloped virus. It contains 8 single- stranded RNA segments
combined with capsomeres to form helical nucleocapsids surrounded by a sphere of matrix proteins attached to a lipid envelope.
The human immunodeficiency virus (HIV) is an enveloped retrovirus. It comprises 2 copies of single-stranded RNA together with some enzymes, surrounded by an icosahedral capsid, which is in turn surrounded by a sphere of matrix proteins attached to a lipid envelope.
Viruses can only reproduce (or Replicate!) inside host cells.
The general strategy of viral replication is broadly speaking "the same" in the sense that a virus uses the host cell enzymes to replicate and translate viral RNA or DNA. which consequently use host cell machinery (Ribosomes, ER, Golgi etc.) to making more virus particles. upon completion, newly synthesised viruses then either burst out of the cell (the lytic cycle) or for viruses such as influenza and HIV which have lipid envelopes, their strategy is to 'bud' out of the host cell acquiring their lipid envelope!
There are two methods of viral replication: -
Lysis (The lytic cycle) and The "budding" cycle.
Lysis (the lytic cycle) results in the death of an infected host cell. A common example of a human virus which replicates this way is variola major (the virus that causes smallpox).
Alternatively, viruses such as influenza A, which have a “ lipid envelope” are typically released from the host cell by “budding” (budding is exocytosis). It is through the budding process that results in the acquisition of the viral lipid envelope upon on release of the virus from the host cell.
As outlined above, the two commonly assessed viral diseases in a-level biology are Influenza and HIV/AIDS which both replicate via ‘budding’ since both these viruses possess a lipid envelope. However, remember HIV is a retrovirus so exhibits a slightly different mechanisms of replication when compared to influenza.
Firstly we'll learn the lytic cycle (for an unspecified viral infection). (The second method "the budding cycle will be covered in HIV replication)
A-Level Biology: - Infectious Viral Diseases
Infectious diseases caused by viruses:
The Diseases often examined are HIV/AIDS and Influenza which you need to know more about and are considered below.
HIV and AIDS
Human immunodeficiency Virus (HIV), a retrovirus (i.e. one that contains single-stranded RNA and the enzyme reverse transcriptase).
How is HIV/AIDS transmitted?
Through infected semen or vaginal secretions during sexual activity, or through infected blood in transfusions or contaminated needles. Infected mothers can also pass the virus on to their children through the placenta or milk. Before 1985 many hospital patients, especially haemophiliacs, became infected through blood transfusions, but since 1985 all blood donations in the UK are tested for HIV. Many drug addicts have been infected through sharing needles. By far the most important method of transmission of HIV world-wide is unprotected sexual intercourse. HIV cannot survive in air and therefore cannot be transmitted by skin contact or kissing.
HIV in the blood attaches to cells that carry the "CD4" antigen, including the T lymphocyte and macrophage white blood cells. After entering these cells it becomes a provirus in the nuclear DNA, remaining dormant but being replicated for a long latency period of 8-10 years. Eventually the virus particles are re-assembled and emerge into the blood, rupturing and killing the T cells in the process. The lack of T cells leaves the immune system severely compromised.
What are the signs and symptoms of HIV/AIDS?
Like other retroviruses, HIV has a long latency of 8-10 years, during which time there are no symptoms, but the individual is infectious. After this period the person starts to shows mild symptoms of the AID-related complex (ARC), such as tiredness, fever, weight loss and diarrhoea. This is followed by the more serious symptoms of full-blown AIDS. Since the immune system no longer functions the patient has no defence against a variety of opportunistic infections. The most common of these are Kaposi's sarcoma (a skin cancer), TB and pneumonia, which is usually fatal.
Can HIV/ADIS be Treated?
There is as yet no cure or vaccination for AIDS, though drugs like AZT can delay its onset for many years. Vaccinations are difficult because the HIV genome is highly variable (probably because reverse transcriptase make many base copying errors). Prevention of AIDS has concentrated on "safe sex" education (using condoms and reducing promiscuity), not sharing needles, and screening blood transfusions.
Defence Against Infectious Disease:
We are surrounded by microbes in the air, on the ground and all other surfaces, and in our food and water. The only reason we are still alive is because humans (and all other animals) have a very powerful defence mechanism – The Immune System.
Can you describe the course of HIV infection?
In your A Level Biology it is essential that you know the structure of the HIV Virus and that HIV infects T-cells. You MUST be able to interpret a graph detailing the course of HIV/AIDS infection.
Influenza (caused by Human Influenza virus (type A, B or C).
How is influenza transmitted?
Influenza Transmission is through airborne droplet infection from the coughs and sneezes of infected individuals. Infected people are infectious from a day before symptoms show themselves until a week afterwards. The virus invades the epithelial cells lining the upper respiratory tract (nose, mouth, throat, trachea and bronchi) and reproduces inside them, killing many cells in the process. These dead cells increase the amount and thickness of mucus produced during an infection, which irritates the throat, causing coughing.
What are the signs and symptoms of influenza?
The onset is sudden after an incubation period of 1-4 days, and the symptoms include fever, shivering, headache, muscular pain, coughing of excess mucus and a loss of appetite. Recovery normally takes about 4 days, unless there are secondary infections, which can be fatal if untreated. The influenza pandemic of 1918 killed 22 million people world-wide, making it the greatest killer disease ever.
How can Influenza be treated?
Treatment is by bed rest with plenty of fluids and analgesic drugs like asprin or paracetamol. Since this is a viral infection, antibiotics are useless.
Can influenza be prevented?
Vaccination is difficult because of genetic changes in the influenza virus, but vaccinations based on a variety of antigens are now used to protect at-risk groups (infants and elderly). Prevention would require the quarantine (isolation) of influenza flu victims.
Links to (practical microbiology) Can Virus be Cultured in a Lab?
Yes, But Because viruses are parasites, they cannot be cultured in the lab like other microbes. Instead they must be grown inside their specific living host cells. In the past this meant infecting whole animals or plants, but with improvements in tissue culture techniques almost any host cell can now be grown in the lab and infected with a virus. Bacteriophages are perhaps the most-studied of all viruses, simply because their hosts, bacteria, are so easy to grow in the lab.
A Level Biology - The Lytic Cycle.
The Steps Involved in Viral Replication.
What are the 5 steps of the Lytic Cycle?
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Viral attachment
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Viral nucleic acid (either DNA or RNA) is released into the host cell
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Viral nucleic acid is replicated (using host cell ‘machinery’).
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New viruses “self assemble”
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Newly formed viruses burst (remember lysis means to burst) out from the host cell.
A Level Biology - The Steps Involved in Viral Replication (the 'budding cycle') using HIV as the example.
HIV Replication.
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The virus attaches to the host cell membrane, and the viral and cell membranes fuse. This releases the nucleocapsid into the cytoplasm.
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The viral enzyme reverse transcriptase is used to synthesise double-stranded DNA from the single stranded viral RNA. The DNA enters the nucleus and is incorporated into the host's genome, where it is called a provirus.
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The provirus remains dormant for years. It is replicated every time the host cell divides.
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At some trigger signal the provirus DNA is transcribed to RNA and viral proteins are synthesised.
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The RNA and proteins are assembled into new virus particles (without lipid envelopes). The glycoproteins migrate to the cell membrane.
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The virus particles are released by exocytosis (budding), acquiring the lipid envelope from the cell membrane. (This does eventually kill the host cells).
A Level Biology - The Steps Involved in Viral Replication (the 'budding' cycle) of influenza.
Influenza replication.
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The virus attaches to the host cell membrane, which stimulates endocytosis.
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The viral envelope fuses with the vesicle membrane, releasing the nucleocapsid into the cytoplasm.
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Viral RNA enters the nucleus, where it is replicated to form mRNA, using the viral RNA polymerase enzyme.
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mRNA is now used to synthesise more viral RNA and capsid proteins.
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The RNA and proteins are assembled into new virus particles (without envelopes). The glycoproteins migrate to the cell membrane.
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The virus particles are released by exocytosis (budding), acquiring the lipid envelope from the cell membrane. (This does eventually kill the host cells).
Even though the viral replication cycle is essentially the same for influenza and HIV (i.e both 'bud' out from the host cell acquiring their lipid envelopes, you should know both and be able to compare and contrast them (remember the key difference is due to HIV being a retrovirus!)
Cells of the Immune System
In this section you’ll learn about the human immune system, more specifically immunology and the defence against infectious disease.
We are surrounded by microorganisms!
Microbes are in the air, in the soil, on the ground and all other surfaces, in our food and our water, in fact microbes are a vital part of our environments playing key ecological roles but not all microorganisms are beneficial... some are pathogenic and we humans (and all other prokaryotic and eukaryotic organisms) are constantly being bombarded with potentially infectious and deadly microorganisms!
So, the question is: Why are we able to combat them and survive?
The reason we are still alive is because humans (and all other animals) have a very elegant and powerful defence mechanism known as – The Immune System. In this section you'll learn about how the immune system responds to and fights infections diseases!
The Immune System
The parts of the immune system are spread all over the body. They include: -
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The lymph and blood vessels. These transport pathogens and leukocytes all over the body.
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The lymph nodes. These contain millions of phagocyte and lymphocyte cells, which identify and remove pathogens from lymph.
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The spleen. This also contains millions of phagocyte and lymphocyte cells, which identify and remove pathogens from blood.
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The thymus. This is where blood stem cells are differentiated into T-lymphocytes.
So, What are antigens?
An antigen is a large molecule (e.g. protein, glycoprotein, lipoprotein or polysaccharide) on the outer surface of a cell.
All living cells have these antigens as part of their cell membrane or cell wall.
Can you give examples of several antigens?
Remember the basic structure of a virus? Well, the capsid proteins of viruses and even individual protein (capsid) molecules can be classed as antigens.
What is the purpose of an antigen?
An antigens purpose is for cell communication. For example, cells from different individuals have different antigens. In contrast, all the cells from the same individual have the same antigens. Antigens are genetically controlled, which means close relatives have more similar antigens than unrelated individuals do.
A good example of antigens is the ABO blood grouping system.
Blood groups are an example of antigens on red blood cells (but remember, all cells have them!).
A Level Biology - The Immune System: Antibody Structure and Function
What are Lymphocytes?
There are two kinds of lymphocyte – B-lymphocytes (or just B-cells) and T-lymphocytes (or just T-cells).
B-cells are called that because they mature from stem cells in the Bone marrow.
T-cells are called that because they mature from stem cells in the Thymus.
B-cells make antibodies.
An antibody (also called an immunoglobulin) is a protein molecule that can bind specifically to an antigen.
Antibodies all have a similar structure composed of 4 polypeptide chains (2 heavy chains and 2 light chains) joined together by strong disulphide bonds to form a Y-shaped structure. The stem of the Y is called the constant region because in all immunoglobulins it has the same amino acid sequence, and therefore same structure.
The ends of the arms of the Y are called the variable regions of the molecule because different immunoglobulin molecules have different amino acid structure and therefore different structures.
These variable regions are where the antigens bind to form a highly specific antigen-antibody complex, much like an enzyme-substrate-complex.
Each B-cell has around 100000 membrane-bound antibody molecules on its surface and can also secrete soluble antibodies into its surroundings. Every human has around 100000000 different types of B cell, each making antibodies with slightly different variable regions. Between them, these antibodies can therefore bind specifically to 100000000 different antigens, so there will be an antibody to match almost every conceivable antigen that might enter the body.
T-cells have receptor molecules on their surfaces which are very similar, but not identical, to antibodies.
These receptors also bind specifically to antigens to form antigen-receptor complexes.
Each T-cell has around 100000 receptor proteins, and again there are about 100000000 different types of T-cell, each with slightly different receptor molecules, so they can also specifically bind to any conceivable antigen.
T-cells do not secrete soluble proteins.
The B and T cells are exposed to so many "self" antigens on every normal cell they come across, that they quickly "learn" to recognise them very early in life. From then on self antigens are ignored, but any non-self antigens are recognised and stimulate an immune response…
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Complement System. This comprises more than 20 different proteins, which kill microbes by making pores in their cell membranes and can also inhibit viral reproduction inside cells. They are also involved in activating other parts of the immune system.
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Inflammation. This is a localised response to an injury or infection. The granulocyte cells and the affected cells release chemicals, including histamines and prostaglandins, which stimulate: vasodilation to increase the flow of blood to the area (so the area turns red); capillary leakage so that phagocytes and granulocytes can enter the local tissue fluid (so the area swells); sensory neurone impulses (so the area is tender or painful); blood clotting to seal a wound (so a scab is formed). The dead pathogens and phagocytes, together with excess tissue fluid, are release as pus. The chemicals also help to stimulate the specific immune response (see below).
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Fever. This is caused by pyrogen chemicals, which include some of the inflammation chemicals as well as bacterial endotoxins. These stimulate the hypothalamus of the brain to increase the body's temperature from 37°C up to 39°C. This helps the immune system and inhibits growth of some pathogenic bacteria.
The Third Line of Defence – The Specific Immune System.
1. Antigen Presentation
Infection is started when cells with non-self antigens enter the blood of tissue fluid. The antigens can be from a variety of sources:
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a virus capsid protein or envelope protein.
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on the surface of a bacterial cell.a toxin released from a bacterium.
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on a macrophage that has ingested a pathogen.
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on the surface of cells of a transplanted organ.
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on a cancerous cell
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on a cell infected with a virus so that it has viral proteins on its surface
Macrophages are the most important antigen-presenting cells because they are the most numerous. They constantly inspect the surface of every cell they come into contact with in the blood, spleen, lymph nodes, tissue fluid and alveolar spaces. If the antigens are not recognised as self antigens, then the macrophage ingests the antigen and its cell by phagocytosis. Some of the antigens pass to the surface of the macrophage, which thus becomes an antigen-presenting cell. This amplifies the number of antigens. The macrophage also secretes cytokine chemicals (also called lymphokines or interleukins) to stimulate the lymphocytes.
2. Clonal Selection
At birth we have less than 100 copies of each type of B or T lymphocyte. Whenever a particular antigen enters the body it comes into contact with all the various cells in the blood and lymph, including the lymphocytes. Sooner or later the antigen will encounter a lymphocyte with a matching receptor molecule, to which it can bind tightly. As soon as a match is found, the binding of the antigen to the receptor stimulates the lymphocyte to divide repeatedly by mitosis, making an army of about 1000000 identical cloned B and T lymphocyte cells. This is called clonal selection, because only the selected cell is cloned. This army of clones can now destroy the infecting microbe…
3. T-Cells and Cell-Mediated Immunity
The T-lymphocytes differentiate into cells with different functions.
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Cytotoxic T-cells (or killer T-cells) bind to antigens on infecting cells and kill the cells by releasing perforin proteins. These insert into the cell membrane of the other cell, where they make a pore, which allows water to diffuse in so that the cell bursts.
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Helper T-cells bind to antigens on infecting cells and secrete chemicals called cytokines. These stimulate all the other white blood cells (phagocytes, granulocytes and B lymphocytes) and speed up the immune response. The AIDS virus HIV destroys these helper T-cells, and the immune system doesn't work nearly as well without them.
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Memory T-cells remain the blood for many decades after the infection. This means that the same antigen will be identified much more quickly in a subsequent infection, when the memory T-cells will quickly divide to form cytotoxic T-cells and helper T-cells.
4. B-Cells and Antibody-Mediated Immunity (or humoral immunity)
The B-lymphocytes also differentiate into cells with different functions.
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Plasma cells secrete free soluble antibodies. These antibodies are carried around the blood, lymph and tissue fluid binding to any antigens they come into contact with and forming antibody-antigen complexes. A single B-cell can divide to form 1000000 plasma cells, each of which can release 100 antibodies each second for 4 days. So during the immune response to an infection there is an enormous number of antibodies in the body and it is highly likely that every antigen will be targeted by one. The antibodies help to kill cells in various ways. By binding to antigens on viruses and bacteria they prevent the viruses or bacteria attaching to cells and so infecting them. Similarly, when antibodies bind to free toxin proteins, they change the shape of the active region so that these proteins can no longer take part in the reactions that caused disease. Because each antibody molecule has two antigen-binding sites (one on each arm of the Y), antibodies can stick antigens together into large clumps. This process, called agglutination, immobilises viruses and cells, and precipitates soluble toxins so that they can easily be destroyed by phagocytes or killer T-cells. Large antigen-antibody complexes also stimulate the various activities of the nonspecific immune response, such as phagocytosis, complement production and inflammation.
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Memory B cells continue to secrete antibodies in small quantities for many decades, and can multiply rapidly to produce an instant supply of plasma cells if the same pathogen invades again.
The immune Response.
Three Lines of Defence: Humans have three lines of defence against invading pathogens: -
1. Physical Barriers – the skin and associated chemicals stop microbes entering the body.
2. The non-specific immune system – phagocytes quickly destroy microbes that pass the first line of defence
3. The specific immune system – lymphocytes kill any microbes that pass the second line of defence, and remain on guard for future attacks.
The First Line of Defence – Physical Barriers
The body has many mechanism to try to stop microbes entering the body, particularly the bloodstream.
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The skin is a tough, impenetrable barrier (which is why we use it to make leather shoes). The outer layer, the epidermis, is 20-30 cells thick (about as thick as a sheet of paper) and its cells are toughened by the protein keratin. The next layer, the dermis, is 20-40 times thicker and provides the main structure for the skin as well as all the receptor cells, blood vessels and hairs. Cells are constantly being lost from the surface of the skin (to form dust) and are replaced by new cells from further down.
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Sweat and tears, secreted by glands in the skin, contain lysozyme enzymes, which destroy (lyse) bacteria growing on the surface of the skin by digesting their peptidoglycan cell walls.
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The digestive tract is a potential entry route for pathogens, but it is protected by concentrated acid in the stomach, which denatures microbial enzymes and cell surface proteins, as well as protease enzymes. Saliva also contains lysozymes.
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The respiratory tract is another potential entry route, but it is protected by sticky mucus secreted by glands in the bronchi and bronchioles, which traps microbes and other particles in inhaled air before they can reach the delicate alveoli. Mucus contains lysozymes, and cilia constantly sweep the mucus upwards to the throat, where it is swallowed so that the microbes are killed by the stomach acid.
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The human body is home to billions of bacterial cells called variously the natural microbiota, the normal flora, the commensal flora (because they have a non-harmful or commensal relationship with their host) or even the "friendly bacteria". There are more bacteria cells in a human than there are human cells. These commensal bacteria colonise the skin, mouth, lower digestive tract, respiratory tract and vagina, and they help prevent infection by out-competing pathogenic microbes for food and space.
The Second Line of Defence – The Nonspecific Immune System
The second line of defence is the non-specific immune system, a host of quick, non-specific methods of killing microbes that have passed the first line of defence and entered the body. Some of the main methods are: -
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Phagocytosis. Phagocytes are large, irregularly-shaped leukocyte cells that remove bacteria, viruses, cellular debris and dust particles. The phagocytes are constantly changing shape, and they flow over microbes, surrounding and ingesting them through the process of phagocytosis to form a phagosome. The phagosome then fuses with lysosomes - small vesicle containing lysozymes, which are released into the phagosome, killing and digesting the microbe. Different phagocyte cells work in different locations: neutrophils circulate in the blood, while macrophages are found in lymph, tissue fluid, lungs and other spaces, where they kill microbes before they enter the blood.
A Level Biology The ELISA test
The cells of the immune system.
The cells of the immune system are the white blood cells (or leukocytes).
Leukocytes are derived from stem cells, which are produced in huge numbers in the bone marrow (the soft centre of large bones). These stem cells differentiate to form dozens of different kinds of leukocytes, which fall into four categories: -
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Phagocytes - for phagocytosis. e.g. Macrophages, Neutrophils & Monocytes.
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Granulocytes - for inflammation. e.g. Mast cells, Eosinophils & Basophils.
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T Lymphocytes - for cell-mediated immunity. e.g. Helper T-cells, Killer T-cells & Memory T-cells.
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B Lymphocytes - for antibody-mediated immunity. e.g. B-cells Plasma B-cells Memory B-cells.
Phagocytes and granulocytes are a part of the Non-Specific Immune System whilst T-Cells and B-Cells (T and B lymphocytes) are a part of the Specific Immune System.
Phagocytes and granulocytes form part of the non-specific immune system.
Whilst Phagocytes and granulocytes are very effective and 'kill' pathogens quickly and indiscriminately these cells of the non-specific immune system don't "Learn from Experience". Thus, host defense by means of phagocytes and granulocytes does not lead to immunity to a particular disease.
B-Cells and T- cells (the B and T Lymphocytes) form part of the specific immune system.
B-Cells and T-Cells form part of the specific immune system, which is a much more complex and sophisticated series of events that not only 'kill' invading pathogens, but also remember the pathogen's features! Thus, host defense via T-Cells and B-Cells leads to immunological memory. Therefore, upon reinfection by the same pathogen the immune system "remembers particular features" and can quickly respond.
The key difference of the specific immune system is that it is capable of recognising 'foreign
cells' as distinct from its own cells. This notion of self and non-self recognition is achieved by making use of specific proteins knows as antigens.
All animals have a non-specific immune system, However, only vertebrates have a specific immune system, which leads 'scientists' to believe that the specific immune response is a evolutionary adaptation conferring a survival advantage!
Primary and Secondary Immune Responses
The first time a new antigen is encountered there are only a few lymphocyte cells of each kind (<100) for the antigen to encounter, so it can take several days for clonal selection to take place and the clone army to be assembled. Furthermore the clone army tends to be fairly small. This slow and weak response to a first infection is called the primary immune response. It is during this period that the symptoms of the disease are shown, partly due to toxins and cell death due to the pathogen, and partly due to the immune response itself (e.g. fever, inflammation).
After a primary response memory cells (both T and B lymphocytes) remain in the blood. This means that after a subsequent infection by the same antigen the clonal selection stage can be bypassed and the specific immune response is much faster and much greater (i.e. more clone B and T lymphocytes and antibodies are produced). This is called the secondary immune response, and is so fast that the pathogen is destroyed before it reproduces enough to cause disease. In other words the individual is immune to that disease. Note that the non-specific immune response is the same in all infections.
This immunity works well for many diseases, such as chicken pox, measles or mumps. We think of these as childhood diseases because it is common to catch them once as children and never catch them again.
However it appears that you can keep on catching some diseases, such as the common cold and the flu.
Why does the secondary immune response not work with these diseases?
Because these microbes have constantly-changing antigens. This is referred to as antigenic variability, and it is caused by mistakes in DNA or RNA replication (mutations) due to poor polymerase enzymes.
The result is that each infection causes a new primary response, with all the trappings of the accompanying disease. With some diseases the pathogen is so active and the toxins so effective that the first infection causes a disease that is fatal (e.g. cholera, smallpox, diphtheria, AIDS).
Immunisation
We have been able to make use of the immune system's memory to artificially make people immune to certain diseases even without ever having caught them. The trick is to inject with an antigen that will promote the primary immune response, but has been modified so that it is novirulent (or non pathogenic), i.e. will not cause the disease. The immune system is thus fooled into making memory cells so that if the person is ever infected to the real virulent pathogen, the more powerful secondary immune response is triggered and the pathogen is killed before it can cause the disease. This technique is called vaccination and is commonly used to provide artificial immunity to a number of potentially-fatal diseases. In the UK children are commonly vaccinated against diphtheria, tetanus, whooping cough, polio, measles, mumps, rubella and TB.
There are several different ways of making vaccines. In each case the aim is to make an antigen that
is good enough to bind to antibodies and so stimulate an immune response, but defective in some
way so that it will not cause a disease. Five different kinds of vaccine are used:
1. Live non-virulent strains. The microbe is sub-cultured for many generations in the laboratory, each time selecting the least virulent and slowest growing cells to start the next generation. This is an example of selective breeding, and it results in microbial cells that still contain the same antigens as their pathogenic relatives, but are deficient in some aspect of their pathogenicity. They may be slow-growing, unable to make toxins, unable to attach, etc. One vaccine made this way is for rubella.
2. Killed virulent organisms. The pathogens are first grown in culture to create a large number of cells, then killed using chemicals (such as formaldehyde) or radiation so as not to denature the antigen. This is the oldest technique, but there is a danger that any cells surviving the treatment are still pathogenic. Vaccines made this way include whooping cough and influenza.
3. Isolated antigens from a pathogen. The pathogens are first grown in culture to create a large number of cells, then the cells are disrupted and the antigen proteins are chemically isolated from the cell membranes. One vaccine made this way is for influenza.
4. Genetically engineered antigens. If the gene for the antigen has been identified it can be inserted into another microbe (bacterium or yeast) using genetic engineering techniques. The new transgenic microbe is then grown in culture, where it will make and secrete the antigen into its surroundings, from where it can easily be isolated. This is the newest method and also the safest, but it only works for antigens that are pure proteins, not glycoproteins. One vaccine made this way is for hepatitis B.
5. Modified toxins (Toxoids). Bacterial toxins can be purified and chemically modified so that they are no longer toxic, but still function as antigens in promoting an immune responses. One vaccine made this way is for diphtheria. The choice of vaccine depends on several factors including safety, cost, ease of delivery (injection, oral) and side effects.
Passive Immunity
Injecting antigens to promote an immune response is called active immunity, but it is also possible to inject antibodies against certain pathogens into the blood. This is called passive immunity and is used when someone has already been infected (or is likely to become infected) with a pathogen. The antibodies in it assist the body's normal immune response and help it deal with serious diseases. Antibodies are either prepared from the blood serum of an infected human (or rarely animal), called an antiserum, or are made by genetic engineering. Passive immunisation is not very common, but can be used for rabies, tetanus, measles and hepatitis B, and is being tried to combat AIDS.
Passive immunity also occurs naturally when a mother passes antibodies to her child. Antibodies can pass across the placenta to the foetus and are also found in colostrum, the milk produced in the first few days after birth. Since the baby's digestive system does not function at this stage, the immunoglobulin proteins can be absorbed intact. This passive immunity helps the new-born baby survive in a world full of pathogens, and is one reason why breastfeeding is so important
The different kinds of active and passive immunity are summarised in the table below...
Download and complete the Table summarising active and passive immunity.
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★ AQA Specification Reference: - 3.2.1.2 Structure of prokaryotic cells and of viruses. Viruses are acellular and non-living. The structure of virus particles to include genetic material, capsid and attachment protein. Being non-living, viruses do not undergo cell division. Following injection of their nucleic acid, the infected host cell replicates the virus particles.
★ CIE Specification Reference: - 1 Cell structure: Outline the key features of viruses as non-cellular structures (limited to protein coat and DNA/RNA).
★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - N/A
★ Edexcel (Biology B) Specification Reference: - Topic 2: Cells, Viruses and Reproduction of Living Things. 2.2 Viruses: Understand that the classification of viruses is based on structure and nucleic acid. Know that viruses are not living cells. Know the lytic cycle of a virus and latency.
★ OCR (Biology A) Specification Reference:
★ OCR (Biology B) Specification Reference:
★ WJEC Specification Reference: - Core Concepts 2. Cell structure and organisation: Learners should be able to demonstrate and apply their knowledge and understanding of: The structure of viruses. The relationship between the pathogenicity of viruses and their mode of
reproduction.
★ AQA Specification Reference: - 3.2.4 Cell recognition and the immune system. Structure of the human immunodeficiency virus (HIV) and its replication in helper T cells.
★ CIE Specification Reference: - 10 Infectious disease: b) state the name and type of causative organism (pathogen) of each of the following diseases: cholera, malaria, tuberculosis (TB), HIV/AIDS, smallpox and measles (detailed knowledge of structure is not required. c) explain how cholera, measles, malaria, TB and HIV/AIDS are transmitted d) discuss the biological, social and economic factors that need to be considered in the prevention and control of cholera, measles, malaria, TB and HIV/AIDS (a detailed study of the life cycle of the malarial parasite is not required). 11 Immunity: Not HIV Specific - useful for: c) describe and explain the significance of the increase in white blood cell count in humans with infectious diseases.
★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics: 6.6 Understand how Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV) infect human cells, causing a sequence of symptoms that may result in death.
★ Topic 6: Microbiology and Pathogens: 6.6 Understand how Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV) infect human cells, causing a sequence of symptoms that may result in death. Also - Not HIV Specific but useful for: 6.7 Response to infection.
★ OCR (Biology A) Specification Reference: - 4.1.1 Communicable diseases, disease prevention and the immune system: Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the different types of pathogen that can cause communicable diseases in plants and animals. To include, viruses – HIV/AIDS (human).
★ OCR (Biology B) Specification Reference: - 3.2.1 Pathogenic microorganisms: Learners should be able to demonstrate and apply their knowledge and understanding of: how pathogens (including bacteria, viruses and fungi) cause communicable disease. The causes, means of transmission, symptoms and the principal treatment of tuberculosis (TB) and HIV/AIDS. To include an outline of the general mechanisms of pathogenicity by bacteria (toxin production), viruses (taking over cell metabolism) and fungi (enzyme secretion). the structure of the Human Immunodeficiency Virus (HIV). To include the use of diagrams showing the location of enzymes and the nature of the genetic material.
★ WJEC Specification Reference: - Immunology and Disease: but useful for:
1. Disease: - Learners should be able to demonstrate and apply their knowledge and understanding of: The structure of viruses. Learners should be able to demonstrate and apply their knowledge and understanding of: (d) the relationship between the pathogenicity of viruses and their mode of reproduction.
★ AQA Specification Reference: - 3.2.4 Cell recognition and the immune system. Structure of the human immunodeficiency virus (HIV) and its replication in helper T cells.
★ CIE Specification Reference: - 10 Infectious disease: b) state the name and type of causative organism (pathogen) of each of the following diseases: cholera, malaria, tuberculosis (TB), HIV/AIDS, smallpox and measles (detailed knowledge of structure is not required. c) explain how cholera, measles, malaria, TB and HIV/AIDS are transmitted d) discuss the biological, social and economic factors that need to be considered in the prevention and control of cholera, measles, malaria, TB and HIV/AIDS (a detailed study of the life cycle of the malarial parasite is not required). 11 Immunity: Not HIV Specific - useful for: c) describe and explain the significance of the increase in white blood cell count in humans with infectious diseases.
★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics: 6.6 Understand how Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV) infect human cells, causing a sequence of symptoms that may result in death.
★ Edexcel (Biology B) Specification Reference: - Topic 6: Microbiology and Pathogens: Response to infection.
★ OCR (Biology A) Specification Reference: - 4.1.1 Communicable diseases, disease prevention and the immune system: Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the different types of pathogen that can cause communicable diseases in plants and animals. To include, viruses – HIV/AIDS (human).
★ OCR (Biology B) Specification Reference: - 3.2.1 Pathogenic microorganisms: Learners should be able to demonstrate and apply their knowledge and understanding of: how pathogens (including bacteria, viruses and fungi) cause communicable disease. The causes, means of transmission, symptoms and the principal treatment of tuberculosis (TB) and HIV/AIDS. To include an outline of the general mechanisms of pathogenicity by bacteria (toxin production), viruses (taking over cell metabolism) and fungi (enzyme secretion). the structure of the Human Immunodeficiency Virus (HIV). To include the use of diagrams showing the location of enzymes and the nature of the genetic material.
★ AQA Specification Reference: - 3.2.1.2 Structure of prokaryotic cells and of viruses. Prokaryotic cells are much smaller than eukaryotic cells. They also differ from eukaryotic cells in having: cytoplasm that lacks membrane-bound organelles, smaller ribosomes, no nucleus; instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins, a cell wall that contains murein, a glycoprotein. In addition, many prokaryotic cells have: one or more plasmids, a capsule surrounding the cell, one or more flagella. All cells arise from other cells. Binary fission in prokaryotic cells involves: Replication of the circular DNA and of plasmids. Division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.
★ CIE Specification Reference: - 1. Cell structure. Outline key structural features of typical prokaryotic cells as seen in a typical bacterium (including: unicellular, 1–5μm diameter, peptidoglycan cell walls, lack of membrane-bound organelles, naked circular DNA, 70S ribosomes)
★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 3: Voice of the Genome. 3.4 Know the ultrastructure of prokaryotic cells, including cell wall, capsule, plasmid, flagellum, pili, ribosomes, mesosomes and circular DNA.
★ Edexcel (Biology B) Specification Reference: - Topic 2: Cells, Viruses and Reproduction of Living Things. 2.1 Eukaryotic and prokaryotic cell structure and function. iii) Know the ultrastructure of prokaryotic cells and the structure of organelles, including: nucleoid, plasmids, 70S ribosomes and cell wall. Topic 6: Microbiology and Pathogens as basic introduction to bacterial cell division, before moving on to the different phases of a bacterial growth curve.
★ OCR (Biology A) Specification Reference: - 2.1 Foundations in biology. 2.1.1 Cell structure. The similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells.
★ OCR (Biology B) Specification Reference: - Module 2: Cells, chemicals for life, transport and gas exchange. 2.1.1 Cells and microscopy: h (i) the ultrastructure of prokaryotic cell, as revealed by an electron microscope. to include: Circular DNA, plasmids, mesosome, pili and flagella in prokaryotic
★ WJEC Specification Reference: - Core Concepts. 2. Cell structure and organisation, (b) the structure of prokaryotic cells. Basic understanding of how bacterial cells divide, applied to growth conditions. covered in section 4. Microbiology.
★ AQA A Level Biology Specification Reference: - 3.2.4 Cell recognition and the immune system. Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify: - Pathogens; cells from other organisms of the same species; abnormal body cells; toxins. Definition of antigen. The role of helper T cells.
The use of antibodies in the ELISA test.
★ CIE A Level Biology Specification Reference: - 11 Immunity: An understanding of the immune system shows how cells and molecules function together to protect the body against infectious diseases and how the body is protected from further infection by the same pathogen. Phagocytosis is a more immediate non-specific part of the immune system, while the actions of lymphocytes provide effective defence against specific pathogens. Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts. Describe the modes of action of B-lymphocytes and T-lymphocytes. Relate the molecular structure of antibodies to their functions. Explain the meaning of the term immune response, making reference to the terms antigen, self and non-self.
★ Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics. 6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme action, interferon, and phagocytosis. 6.8 Understand the roles of antigens and antibodies in the body’s immune response. 6.9 Understand the differences between the roles of B cells (B memory and B effector cells) and T cells (T helper, T killer and T memory cells) in the body’s immune response.
★ Edexcel A Level Biology (Biology B) Specification Reference: - Topic 6: Microbiology and Pathogens. 6.2 Bacteria as pathogens i Understand that bacteria can be agents of infection, invading and destroying host tissues and producing toxins. 6.7 Response to infection: ii Understand the development of the humoral immune response, including the role of: Antigen presenting T cells, T helper cells and cytokines. Antibodies. iii Understand the development of the cell-mediated immune response including the role of: Antigen presenting cells T helper cells and T killer cells.
★ OCR A Level Biology (Biology A) Specification Reference: - 4.1 Communicable diseases, disease prevention and the immune system.
★ OCR A Level Biology (Biology B) Specification Reference: - 3.2 Pathogens, immunity and disease control, 3.2.2 The immune system. T helper cells, T killer cells. Non-specific immune responses to include phagocytosis and inflammation. Definition: Antigen.
★ WJEC A Level Biology Specification Reference: - Immunology and Disease: Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the meaning of the following terms: pathogenic, infectious, carrier, disease reservoir, endemic, epidemic, pandemic, vaccine, antibiotic, antigen, antibody, resistance, vector, toxin, antigenic types.
★ AQA Specification Reference: - Cell recognition and the immune system. Phagocytosis of pathogens. The subsequent destruction of ingested pathogens by lysozymes. The formation of an antigen-antibody complex, leading to the destruction of the antigen, limited to agglutination and phagocytosis of bacterial cells.
★ CIE Specification Reference: - The immune system: Phagocytosis is a more immediate non-specific part of the immune system, while the actions of lymphocytes provide effective defence against specific pathogens. state that phagocytes (macrophages and neutrophils) have their origin in bone marrow and describe their mode of action.
★ Edexcel (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics: 6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme action, interferon, and phagocytosis.
★ Edexcel (Biology B) Specification Reference: - Topic 6: Microbiology and Pathogens: Response to infection. Understand that bacteria can be agents of infection, invading and destroying host tissues and producing toxins. ii Understand that pathogenic effects can be produced by exotoxins (Staphylococcus spp.), endotoxins (Salmonella spp.) and invasion of host tissue (Mycobacterium tuberculosis). 6.7 Response to infection - Understand the development of the cell-mediated immune response. Understand the role of T and B memory cells in the secondary immune response.
★ OCR (Biology A) Specification Reference: - 4.1 Communicable diseases, disease prevention and the immune system. Different types of pathogen e.g. bacteria – tuberculosis (TB), Viruses – HIV/AIDS (human). The structure and mode of action of phagocytes.
★ OCR (Biology B) Specification Reference: - 3.2.2 The immune system. the mode of action of phagocytes - non-specific immune responses to include phagocytosis and inflammation. To include the roles of cytokines, opsonins, phagosomes and lysosomes.
★ WJEC Specification Reference: - Core Concepts 3. Cell membranes and transport - Cell membranes are essential in the control of the movement of substances into and out of the cell. They also play a vital role in cell recognition. (c) the following transport mechanisms: diffusion and factors affecting the rate of diffusion; osmosis and water potential; pinocytosis; facilitated diffusion; phagocytosis; secretion (exocytosis); active transport and the influence of cyanide.
★ AQA A Level Biology Specification Reference: - 3.2.4 Cell recognition and the immune system. Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify: - The role of B cells.
★ CIE A Level Biology Specification Reference: - 11 Immunity: An understanding of the immune system shows how cells and molecules function together to protect the body against infectious diseases and how the body is protected from further infection by the same pathogen. Phagocytosis is a more immediate non-specific part of the immune system, while the actions of lymphocytes provide effective defence against specific pathogens. Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts. Describe the modes of action of B-lymphocytes and T-lymphocytes. Relate the molecular structure of antibodies to their functions. Explain the meaning of the term immune response, making reference to the terms antigen, self and non-self.
★ Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics. 6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme action, interferon, and phagocytosis. 6.8 Understand the roles of antigens and antibodies in the body’s immune response. 6.9 Understand the differences between the roles of B cells (B memory and B effector cells) and T cells (T helper, T killer and T memory cells) in the body’s immune response.
★ Edexcel A Level Biology (Biology B) Specification Reference: - Topic 6: Microbiology and Pathogens. 6.2 Bacteria as pathogens i Understand that bacteria can be agents of infection, invading and destroying host tissues and producing toxins. 6.7 Response to infection: ii Understand the development of the humoral immune response, including the role of: Antigen presenting T cells, T helper cells and cytokines. Antibodies. iii Understand the development of the cell-mediated immune response including the role of: Antigen presenting cells T helper cells and T killer cells.
★ OCR A Level Biology (Biology A) Specification Reference: - 4.1 Communicable diseases, disease prevention and the immune system. Different roles and modes of action of B and T lymphocytes in the specific immune response. The primary and secondary immune responses - To include T memory cells and B memory cells. To include the significance of cell signalling (reference to interleukins), clonal selection and clonal expansion, plasma cells, T helper cells, T killer cells and T regulator cells.
★ OCR A Level Biology (Biology B) Specification Reference: - 3.2 Pathogens, immunity and disease control, 3.2.2 The immune system. B cells.
★ WJEC A Level Biology Specification Reference: - Immunology and Disease - the role of T lymphocytes and B lymphocytes in cell-mediated and humoral immune responses
★ AQA A Level Biology Specification Reference: - 3.2.4 Cell recognition and the immune system. Definition of antibody. Antibody structure. The formation of an antigen-antibody complex, leading to the destruction of the antigen, limited to agglutination and phagocytosis of bacterial cells.
★ CIE A Level Biology Specification Reference: - 11 Immunity: An understanding of the immune system shows how cells and molecules function together to protect the body against infectious diseases and how the body is protected from further infection by the same pathogen. Relate the molecular structure of antibodies to their functions.
★ Edexcel A Level Biology (Biology A – Salters-Nuffield) Specification Reference: - Topic 6: Immunity, Infection and Forensics. 6.7 Understand the non-specific responses of the body to infection, including inflammation, lysozyme action, interferon, and phagocytosis. 6.8 Understand the roles of antigens and antibodies in the body’s immune response. 6.9 Understand the differences between the roles of B cells (B memory and B effector cells) and T cells (T helper, T killer and T memory cells) in the body’s immune response.
★ Edexcel A Level Biology (Biology B) Specification Reference: - Topic 6: Microbiology and Pathogens. 6.2 Bacteria as pathogens i Understand that bacteria can be agents of infection, invading and destroying host tissues and producing toxins. 6.7 Response to infection: ii Understand the development of the humoral immune response, including the role of: Antigen presenting T cells, T helper cells and cytokines. Antibodies. iii Understand the development of the cell-mediated immune response including the role of: Antigen presenting cells T helper cells and T killer cells.
★ OCR A Level Biology (Biology A) Specification Reference: - 4.1 Communicable diseases, disease prevention and the immune system. The structure and general functions of antibodies - To include the general protein structure of an antibody molecule. An outline of the action of opsonins, agglutinins and anti-toxins.
★ OCR A Level Biology (Biology B) Specification Reference: - 3.2 Pathogens, immunity and disease control, 3.2.2 The immune system. The structure and general function(s) of antibodies. To include descriptions of antibody structure from diagrams AND an outline of the action of opsonins and agglutinins.
★ WJEC A Level Biology Specification Reference: - Immunology and Disease. Learners should be able to demonstrate and apply their knowledge and understanding of: Antibody.
★ AQA 3. Students should be able to: interpret information relating to the effects of lung disease on gas exchange and/or ventilation. (TB, Asthma, Fibrosis and Emphysema).
★ CIE 10.1 Infectious diseases. b) state the name and type of causative organism (pathogen) of each of tuberculosis (TB). c) explain how, TB is transmitted.
★ Edexcel (Biology A – Salters-Nuffield) 6.6 Understand how Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV) infect human cells, causing a sequence of symptoms that may result in death.
★ Edexcel (Biology B) 6.2 Bacteria as pathogens: ii Understand that pathogenic effects can be produced by invasion of host tissue (Mycobacterium tuberculosis).
★ OCR (Biology A) 4.1.1 Communicable diseases, disease prevention and the immune system. (a) bacteria – tuberculosis (TB). (b) the means of transmission (TB).
★ OCR (Biology B) 3.2 Pathogens, immunity and disease control: 3.2.1 Pathogenic microorganisms. (a) how pathogens, e.g. bacteria - cause communicable disease. (b) the causes, means of transmission, symptoms and the principal treatment of tuberculosis (TB) To include droplet infection, details of primary and secondary TB and also opportunistic infections (HIV, AIDS).
★ WJEC Specification Reference: - IMMUNOLOGY AND DISEASE - (c) the following diseases in terms of: the types of organisms; source of infection; tissue affected; mode of transmission; prevention; control methods and treatment, - tuberculosis.