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    Describe the role of micro-organisms in the decomposition of organic matter and the recycling of carbon.

    Explain how bacterial and viral infectious diseases have a sequence of symptoms that may result in death, including the diseases caused by Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV).

    Explain the roles of antigens and antibodies in the body’s immune response including the involvement of plasma cells, macrophages and antigen-presenting cells.

    Distinguish between the roles of B cells (including B memory and B effector cells) and T cells (T helper, T killer and T memory cells) in the body’s immune response.

    Good replies to this would be great thanks!
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    (Original post by Taylor Swift)

    Explain the roles of antigens and antibodies in the body’s immune response including the involvement of plasma cells, macrophages and antigen-presenting cells.
    - Antigens are mainly proteins on the surface of pathogens (they can also be the actual pathogen themselves)
    - They help cells in the immune system identify pathogens. Specific antibodies can recognise antigens of a specific pathogen.
    - When a pathogen enters the body, macrophages can engulf and digest them (non-specific response). The antigens which were in the pathogen are then presenting on major histocompatability complexes (MHCs).
    - The macrophage is now an antigen-presenting cell.
    - T helper cells (with receptor sites specific to the particular antigen) bind to the APC and are stimulated to form T memory cells and active T helper cells
    - Active T helper cells produce cytokines which then stimulate B cells to produce B memory and B effector cells
    - B effector cells differentiate into Plasma cells
    - Tthese plasma cells produce antibodies that identify the specific antigen originally engulfed by the macrophage.
    - Antibodies can then bind to the specific pathogens and work different ways (eg cause clumping, help phagocytes indentify pathogens, destruct cell membrane etc)

    Sorry this is really long.
    Hope it helps though
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    (Original post by Taylor Swift)
    Describe the role of micro-organisms in the decomposition of organic matter and the recycling of carbon.
    -After death, the immune system isn't active so bacteria can invade body.
    -Succession occurs on a corpse, with each decomposer making way for the next.
    -Microorganisms consume sugars in body.
    -Respiration converts sugars to energy and release CO2 (carbon recycling).
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    Hey guys, does any one have other ways to get exam styled questions(=answers) for unit 4?; ive done all the past papers (since ive the done the jan exam but only manged too get a C so ill probably remember the answers)
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    [QUOTE=Taylor Swift;42982995]
    Explain how bacterial and viral infectious diseases have a sequence of symptoms that may result in death, including the diseases caused by Mycobacterium tuberculosis (TB) and Human Immunodeficiency Virus (HIV).
    QUOTE]

    Tuberculosis:
    - The bacteria enter into the lungs but do not cause any symptoms to appear. However, white blood cells attack these bacteria leading to the formation of tubercles.
    - Some of the bacteria might survive by producing a waxy coat around them which can protect them from the enzymes released by the white blood cells.
    - These bacteria remain dormant in the lung until the immune system of the body weakens. At this point the bacteria start to reproduce rapidly causing active tuberculosis to occur.
    - They target the lung tissue reducing the surface area of the alveoli and they also target the white blood cells weakening the immune system even more.
    - This causes the host to experience wight loss, fever, night sweats, loss of appetite and the person starts to cough up bloody sputum.
    - This can lead to death in several ways, the person might die due to malnutrition, other opportunistic infections or due to suffering from breathlessness.
    AIDS:
    - The viral RNA would be converted into viral DNA by the enzyme reverse transcriptase
    - Viral DNA enters into the nucleus of the cell by the enzyme Integrase
    - It controls the cell's metabolism causing more viruses to be produced
    - These escape from the T helper cell causing the T helper cell to burst
    - The viruses infect other T helper cells
    - This causes the number of T helper cells to fall
    - initially no symptoms appear but when number of T-helper cells decreases to a certain level , minor symptoms and infections (such as night sweats, loss of appetite, loss of weight and thrush) start to appear.
    - when the number of T helper cells becomes too low the body suffers from more dangerous diseases such as Kaposi's cancer, tuberculosis and pneumonia which lead to death
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    (Original post by Volltorb)
    Hey guys, does any one have other ways to get exam styled questions(=answers) for unit 4?; ive done all the past papers (since ive the done the jan exam but only manged too get a C so ill probably remember the answers)
    Have you done the ones in the text book? (If you have the green one)
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    Can someone tell me the main differences between the cell mediated and the humoral response please?
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    (Original post by Satta101)
    Can someone tell me the main differences between the cell mediated and the humoral response please?
    Humoral response involves:
    T helper activation stage
    1- The macrophages take in the pathogen and forming an APC
    2- These machrophage APC activate T helper cells to divide
    B effector stage
    3- B cells also take in the pathogen to form an APC
    4- The B cells which present the antigens bind to the active T helper cells (which produce cytokines) stimulating the B cells to divide into plasma cells and memory cells
    5- The plasma cells produce antibodies
    Cell mediated response
    1- The HOST cells take in the pathogen to form an APC
    2- The T killer cells bind to the APC cells
    3- T helper cells produce cytokines causing the T killer cells to divide into active T killer cells and T killer memorycells
    4- The active T killer cells cause pores to form in the membrane of the infected cells causing them to burst.
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    (Original post by shumen9523)
    Cell mediated response involves:
    T helper activation stage
    1- The macrophages take in the pathogen and forming an APC
    2- These machrophage APC activate T helper cells to divide
    B effector stage
    3- B cells also take in the pathogen to form an APC
    4- The B cells which present the antigens bind to the active T helper cells (which produce cytokines) stimulating the B cells to divide into plasma cells and memory cells
    5- The plasma cells produce antibodies
    Humoral response
    1- The HOST cells take in the pathogen to form an APC
    2- The T killer cells bind to the APC cells
    3- T helper cells produce cytokines causing the T killer cells to divide into active T killer cells and T killer memorycells
    4- The active T killer cells cause pores to form in the membrane of the infected cells causing them to burst.
    Thanks but isnt it the other way round? The humoral response causes antibodies to released?
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    (Original post by Satta101)
    Thanks but isnt it the other way round? The humoral response causes antibodies to released?
    Oh that's right !!! Sorry I got them both mixed up while I was writing my post
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    (Original post by Volltorb)
    Hey guys, does any one have other ways to get exam styled questions(=answers) for unit 4?; ive done all the past papers (since ive the done the jan exam but only manged too get a C so ill probably remember the answers)
    I know how you feel and I'm having a similar problem myself.
    Check out this link: (it contains questions from the old past papers)
    http://www.mediafire.com/?s1ctvexdb9u57xb
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    How does a reduced number of T-helper cells (due to HIV infection) cause an increase in the number of T-killer cells??
    [Saw this in the MS for Jan 2010, Q6 (c)(iii)]
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    (Original post by shumen9523)
    I know how you feel and I'm having a similar problem myself.
    Check out this link: (it contains questions from the old past papers)
    http://www.mediafire.com/?s1ctvexdb9u57xb
    This is quite good, thanks!
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    Just keep practicing past papers. Even if you have done them all, recycle them do them all again and read over mark schemes. They are very particular about the language so my teacher is very strict with us and its paid off for me.

    I revise using the specification making notes/diagrams on the points. Then rank them 1-3, 3 being what I really don't understand and need more practice on. Then do a past paper then go back to notes reinforce, do another past paper etc right up to the exam.
    Managed to get 66/90 for June 2010 which is an A*. Practice pays off!!


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    Does anyone have additional notes for unit 4? i ran out of study material besides doing past papers and revising the snab book
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    Do we have to know the details for all the biomes? Or do we just have to relate them with succession and all that?
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    Anyone has compilation of.answers from the markings schemes, found it to be useful
    Posted from TSR Mobile
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    (Original post by shumen9523)
    I know how you feel and I'm having a similar problem myself.
    Check out this link: (it contains questions from the old past papers)
    http://www.mediafire.com/?s1ctvexdb9u57xb
    Thanks man
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    (Original post by Satta101)
    Have you done the ones in the text book? (If you have the green one)
    Oh yea!, thanks for the reminder
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    mark scheme for 2013 paper please ?
 
 
 
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