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5.1 Defence mechanisms AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1 Ans Two difference between non-sPecific and specific defence mechanism are:
| Non-specific defence response | Specific defence response |
| It is first line of defence mechanism | It is second line of defence mechanism. |
| It is not specific to type or foreign particles and pathogens | It is specific to pathogens and foreign particles. |
| In this type of response skin, mucous membranes, enzymes, natural microbial flora and complement proteins play important role. | In this type of response phagocytes, humoral and cell mediated immune responses are there. |
Q 2 Ans There is a time lag between infection and defence mechanism to bring infection under control. This is because the fact that there are so many different types of lymphocytes but few of each type. So, when one type of lymphocyte recognises the pathogen and its surface complementary proteins, it is stimulated to divide and build up its numbers to a level where it can be effective in destroying it. This division of lymphocytes to give rise same population of lymphocytes is known as clonal selection. This population then controls the infection. Q Ans It is inaccurate to say that body takes days to respond to the pathogen because body starts its mechanisms to prevent the growth of pathogen once it recognises the presence of pathogen in the body.
5.2 Phagocytosis AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1Ans (a)= phagocytosis; (b)= phagosome; (c)=lysozymes; (d) lysosomes Q 2 Ans Each time we blink our eyes, our eyelids wash tears over the surface of our eyes. Tears contain lysozymes, which will cleave peptidoglycan present in bacterial cell walls. Thus prevent infection in eyes.
5.3 T lymphocytes and cell-mediated immunity AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1 Ans Antigen is any part of an organism or substance that is recognised as non-self by the immune system and thus stimulates the immune response. Mostly antigens are proteins. It can be part of the cell surface membranes or cell walls of invading cells, such as microorganisms or abnormal body cell such as cancer cells. Q 2 Ans Two similarities between T cells and B cells:
- Both are types of White Blood cells or Lymphocytes. In case of adults both cells are produced from hematopoietic stem cells in the bone marrow.
- Both type of cells are involved in adaptive immunity.
Q Ans Differences between T cells and B cells:
| Property | B cells | T cells |
| Surface immunoglobulins | Present | Absent |
| Types of immunity | Humoral immunity | Cell-mediated immunity |
Bird flu Q 1Ans What is awesome about H5N1 and H1N1 (along with most other Influenza A viruses) is that they ignite something called a cytokine storm. The virus itself does not cause the suffocation, it is the body’s immune system that goes into overload that does this. The infection leads to accumulation of T-cells build up in lungs. This will block the airways thus causes suffocation. Q 2 Ans Birds carry the H5N1 virus and spread it very quickly because they can fly long distance in small amount of time.
5.4 B lymphocytes and humoral response AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1Ans After the first infection B cells are differentiated into plasma cells and memory cells. Memory cells will remain in body fluid and recognise the same pathogen if infects again once it enter the body. Rate of secretion of antibody and quantity of secreted antibody is increased as compared to primary immune response. This increased synthesis rate and quantity of antibodies ensure that a new infection is destroyed before it can cause any harm. Q 2 Ans Humoral immune response to a pathogen involves B cells which produces antibodies. It is secondary immune response and effective through blood fluid. Cell mediated immune response involves T cells but does not involve antibodies. In this immune response cells are involved. Q 3 Ans Three organelle find in large quantity in plasma cells are: Large number of mitochondria (provide energy for the production of antibodies), abundant endoplasmic reticulum (to make and transport the antibodies) and larger golgi apparatus (to sort .
5.5 Antibodies AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1 Ans Antibodies are made up of proteins. There is a diversity of antibodies because these are made up of proteins that occur in an almost infinite number of forms.
Q 2 Ans
Antibodies, also called immunoglobulins, Y-shaped molecules are proteins manufactured by the body that help fight against foreign substances called
antigens.
Antigens are any substance that stimulates the immune system to produce antibodies.
Antigens can be bacteria, viruses, or fungi that cause infection and disease. Following are some of the differences between Antigen and Antibody:
| S.N. | Antigen | Antibody |
| 1 | Generally proteins but can be lipids, carbohydrates or nucleic acids. | Antibodies are proteins. |
| 2 | Triggers the formation of antibodies. | Variable sites has the antigen binding domain. |
| 5 | Cause disease or allergic reactions. | Protects the body by immobilization or lysis of antigenic material. |
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Q 3 Ans Using drugs on terminally ill persons have both advantages as well as disadvantages. Advantages are as follows:
- Trying drugs on terminally ill patients removes the risk of healthy volunteer being harmed by the drygs.
- Terminally ill patients have less to lose due to the drug side effects if there will be any.
Beside advantages drugs trials limiting to terminally ill patients have disadvantages also.
- Sample size becomes small if we only take terminally ill patient.
- Response from a terminally ill person will be different to a patient who is in the early stages with the diseases so the results are unreliable.
Producing monoclonal antibodies Q 1 Ans Use of detergent results in holes formation in the cell plasma membrane. When the detergent is washed away the cell membrane re-synthesise thus both cells fuse with each other. Q 2 Ans After adding detergent the mixture is gently agitated to ensure the fusion of both cells. By the mixing of mixture, chances of the physical contact between both type of cells increases. Q 3 Ans Production of antibodies in large quantities has been an issue of concern because B cells are short lived and only divide inside a living organism. Thus by fusing the B cells with cancer tumour cells this problem is solved. Because the cancer cells divide continuously and can be grown in outside of the body by providing suitable conditions. Q 4 Ans B cell can fuse with B cell and tumour cell with other tumour cells. Q 5 Ans Monoclonal antibodies have to be modifying to make them human like cells before they can be inject. If not then immune system will recognise them as non-self and destroy them. Q 6Ans Drug trials directly on human is not ethical because the introduction of antibodies may cause a reaction in human that could be dangerous .The antigen could stimulate an over-response of the immune system.
5.6 Vaccination AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1 Ans Immunity is of two types: Passive and active immunity.
| Passive immunity | Active immunity |
| · It is produced by the introduction of antibodies into the individuals from an outside source. · In this type of immunity no direct contact between pathogen and its antigen is necessary to induce immunity. Immunity is acquired immediately. · Antibodies are not produced by the individuals by themselves. Thus no memory cells are formed and thus the immunity is for short term only. · Examples: anti-vemon given to the victim of snake bites and the fetal immunity which acquired by the fetus when antibodies pass across the placenta from the mother. | · This type of immunity involved the production of antibodies by the individual’s own immune system. · For developing this type of immunity direct contact with pathogen or its antigen is necessary. · In this case immunity takes time to develop and it is long lasting. · This type of immunity can be further divided into two types: - Natural active immunity: In this individual’s body produces their own antibodies in response to certain infection.
- Artificial active immunity: In this individuals develop immunity by the process of vaccination or immunisation. In this type of immunity immune response is induced without them suffering the symptoms of the disease.
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Q 2 Ans
- Mutation in pathogen causes change in its antigen. Thus the invented vaccine becomes ineffective against them because the new antigen is no longer identified by the immune system.
- Due to this failure in recognising the pathogen antigen, antibodies are not produced against them. This resulted in disease development.
- For example Influenza virus which changes its antigen frequently. This phenomenon is known as antigenic variability.
- Thus vaccination against influenza develops short-lived immunity and individuals may develop repeated bouts of influenza during their lifetime.
5.7 The human immunodeficiency virus (HIV) AQA AS Biology B5 Cell Recognition and Immune System Kerboodle Answer
Q 1 Ans A type of virus that uses RNA as its genetic material. After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV, the virus that causes AIDS, is a retrovirus. Q 2 Ans HIV is Human immunodeficiency virus whereas AIDS is acquired immunodeficiency syndrome. HIV virus causes AIDS. The below picture describes the differences between HIV and AIDS. Q 3 Ans People with impaired immune systems, such as those with AIDS are far less able to protect themselves from TB infections and so are more likely to contract and spread TB to others. Widespread use of condoms helps prevent HIV infection and so can reduce the number of people with impaired immune systems who are consequently more likely to contract TB. Banner 2
Practice questions:
Q 1 (a) Ans A pathogen is a tiny living organism, such as a bacterium or virus, which makes people sick. (b) Ans Phagocytosis is the process of engulfing of large particles such as bacteria in the vesicles formed from the cell-surface membrane. Types of cells that carry out phagocytosis are known as phagocytes. Summary of phagocytosis:
- Chemical products of pathogens or dead, damaged and abnormal cells attract phagocytes toward them.
- Phagocytes recognise the foreign particles by the receptors present on their membrane surface.
- Phagocytes engulf the pathogen to form a vesicle which is known as phagosome.
- In a phagocyte, lysosomes move toward the phagosome and fuse with them to form phagolysosome.
- Lysosomes have lysozymes within them. This lysozyme destroy the ingested foreign particle by hydrolysis of their cell walls.
- This process resulted in smaller and soluble products.
- These breakdown products of pathogens are absorbed into the cytoplasm of the phagocytes and discharged out of the cell.
(c) Ans Each antibody has a specific binding site that is complementary and specific to an antigen. It helps in forming
antigen-antibody complex. This reason is also known as variable region because of the diversity in binding sites. Each binding site has specific amino acid sequence that will result in specific 3D structure. This fits into the specific antigen. Q2 (aAns The antibody structure has more than one polypeptide chain. (b) Ans Antibody designed for stomach ulcer causing bacteria will only detect those bacteria only because:
- Antibody/variable region has specific amino acid sequence/primary structure; 2. The shape/tertiary structure of the binding site; 3. Complementary to/fits/binds with these antigens; 4. Forms complex between antigen and antibody;
Q 3 (a) (b) Ans Number of cases in 1 week =70; in 6
th week= 250. Total increase= 250-70= 180. Rate of increase of cases of Ebola = 180/70*100 = 2.57. (cAns Plotting the six months data on a log scale would show that increase is exponential. (d) Ans Ebola virus can remain in certain body fluids after a person has recovered from the infection. These fluids are semen, breast milk, ocular (eye) fluid, and spinal column fluid. Areas of the body that contain these fluids are known as immunologically privileged sites. These are sites of the body where viruses and pathogens, like Ebola virus, can remain undetected even after the immune system has cleared the virus from other sites of the body. Scientists are now studying how long the virus stays in these body fluids among Ebola survivors. During an Ebola outbreak, the virus can spread quickly within healthcare settings (such as clinics or hospitals). For viral infection antibiotics do not work. Q 4 Ans Epithelial cells have (1) Microvilli on their surface which facilitates absorption of foods. (2) There are more carrier proteins present on the surface of epithelial cells to ensure the transportation of absorbed food. (3) Number of mitochondria is large. Mitochondria provide energy required for the absorption of nutrients. (b) (i) Ans (i)
Antigens are any substance that stimulates the immune system to produce antibodies.
Antigens can be bacteria, viruses, or fungi that cause infection and disease. (ii) Ans Antigens are not able to pass through the cell-surface membranes of other epithelial cells because of the following reasons: (1) Antigens can be non-lipid soluble and large in size thus unable to cross the cell membrane. (2) There are no receptors present for the antigens on the cell-surface membrane. (c) Ans Microfold cells bind to antigens and process them thus lead to the activation of immune system. That s why using microfold cells use in vaccines will help in improving the immune system. (a) Ans The number of sexually active girls are very less at this age. So it is easy to achieve immunity against this virus at this age. (b) Ans Other HPV types have different antigens. So vaccine against type 16 and 18 will not work in other type of viruses. Because vaccine induces the production of memory cells and induces immune system against type 16 and 18 only. Immune response is specific. (c) Ans Amount of immune response and memory of an infection (in form of memory cells) is proportional to the amount of antigen. Thus more the antigen more will be memory cells produced and more amount of antibodies are produced. Thus the immune response will be quick. (d) Ans Vaccination programme is targeted for girls aged from 12 to 13 years. Thus it takes time to obtain the data that they are become immune to the virus because the girls at this age are not sexually active. Beside this, cancer takes time to develop. (e) Ans There are many types of HPV are known and the vaccine is against only for the type 16 and 18. Thus smear test will continue to be offered to women, even if they have been vaccinated to make sure that the women is not infected with any other type of HPV. Smear test is the way to monitor that the vaccine is working properly. (f) Ans The Department of Health has estimated that 80% of girls aged 12 to 13 need to be vaccinated to achieve herd immunity to HPV types 16 and 18.
| Health authority area | Number of girls aged 12-13 | Number of girls vaccinated | Percentage of girls vaccinated |
| A | 14053 | 11151 | 79.34% |
| B | 12789 | 10743 | 84.00% |
| C | 11892 | 8662 | 72.83% |
| D | 8054 | 6524 | 81.00% |
Based on these calculations it is clear that Area B would be most likely to show a reduction in the spread of HPV through the population. Banner 3
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