Immune System
Level 2 (Recall & Understanding)
Time limit: 30 minutes
Total marks: 40
Instructions: Answer all questions. Marks are shown in brackets.
Q1. Define the following terms: (a) antigen, (b) antibody, (c) immunological memory. [3]
Q2. Distinguish between innate immunity and adaptive immunity by giving three points of difference. [3]
Q3. The skin and mucous membranes form the body's first line of defence. (a) Name two physical barriers to pathogen entry. [2] (b) Name two chemical barriers and state the role of each. [3]
Q4. Describe the inflammatory response. In your answer, name the chemical released by mast cells, and list three visible signs of inflammation. [5]
Q5. Describe the process of phagocytosis carried out by macrophages and neutrophils, in the correct sequence of steps. [4]
Q6. Distinguish between B cells and T cells with respect to: (a) site of maturation, (b) main function, (c) the type of immunity each is associated with. [3]
Q7. (a) Draw and label a simple diagram of an antibody (immunoglobulin) molecule, showing the heavy chains, light chains, antigen-binding sites, and variable/constant regions. [4] (b) State two functions of antibodies. [2]
Q8. Explain the role of MHC molecules in antigen presentation. Distinguish between MHC class I and MHC class II with respect to which cells display them and which T cells recognise them. [4]
Q9. Compare active immunity and passive immunity using the table headings: source of antibodies, speed of onset, and duration of protection. [4]
Q10. (a) Define a vaccine. [1] (b) Explain what is meant by herd immunity and state one reason it protects individuals who are not vaccinated. [2] (c) State one difference between an allergy and an autoimmune disorder. [2]
END OF PAPER
Answer keyMark scheme & solutions
Q1. [3] (1 mark each)
- (a) Antigen — a foreign molecule (often a protein/glycoprotein on a pathogen surface) that is recognised by the immune system and triggers an immune response. (1)
- (b) Antibody — a Y-shaped protein (immunoglobulin) produced by plasma (B) cells that binds specifically to an antigen. (1)
- (c) Immunological memory — the ability of the adaptive immune system to respond faster and more strongly upon re-exposure to a previously encountered antigen, due to memory cells. (1)
Q2. [3] (1 mark per valid difference)
| Innate | Adaptive |
|---|---|
| Non-specific | Specific to antigen |
| Rapid (present from birth) | Slower on first exposure |
| No memory | Has immunological memory |
| Barriers, phagocytes, inflammation | B cells, T cells, antibodies |
| Any three contrasts = 3 marks. |
Q3. [5]
- (a) Physical barriers (any 2): intact skin/keratinised epidermis; mucous membranes/mucus; cilia; hairs. (1 each, max 2)
- (b) Chemical barriers (any 2 with role): lysozyme in tears/saliva — kills bacteria by digesting cell walls; stomach acid (HCl, low pH) — kills ingested microbes; sebum/sweat (low pH, fatty acids) — inhibits microbial growth. (1 for barrier + role, ×… actually 1.5 each ≈ 3 total; award 3 for two correct barrier+role pairs.)
Q4. [5]
- Tissue damage/infection → mast cells release histamine (1)
- Histamine causes vasodilation of local blood vessels → increased blood flow (1)
- Increased capillary permeability → plasma and phagocytes leak into tissue (1)
- Phagocytes (neutrophils, macrophages) attracted to site (chemotaxis) (1)
- Three signs: redness, heat, swelling (also pain) (1)
Q5. [4] (1 mark each, sequence)
- Chemotaxis / recognition — phagocyte attracted to and binds the pathogen (aided by opsonins). (1)
- Engulfment — cell membrane extends around pathogen, enclosing it in a phagosome (vesicle). (1)
- Fusion — phagosome fuses with a lysosome forming a phagolysosome. (1)
- Digestion — lysosomal enzymes (e.g. lysozyme) destroy the pathogen; debris is expelled/antigen presented. (1)
Q6. [3] (1 mark each)
- (a) B cells mature in bone marrow; T cells mature in the thymus. (1)
- (b) B cells produce antibodies; T cells kill infected cells / help & coordinate the response. (1)
- (c) B cells → humoral immunity; T cells → cell-mediated immunity. (1)
Q7. [6]
- (a) Diagram: Y-shaped molecule showing two heavy chains + two light chains joined by disulfide bonds; two antigen-binding sites at the tips; variable regions (at tips) and constant regions (stem/Fc). (4 — 1 per correctly shown/labelled feature)
- (b) Functions (any 2): neutralisation of toxins/pathogens; agglutination (clumping); opsonisation (marking for phagocytosis); complement activation. (1 each, max 2)
Q8. [4]
- MHC molecules are cell-surface proteins that display (present) antigen fragments to T cells. (1)
- MHC class I — on all nucleated cells; presents intracellular (e.g. viral) antigens; recognised by cytotoxic T cells (CD8). (1.5)
- MHC class II — on antigen-presenting cells (macrophages, dendritic cells, B cells); presents extracellular antigens; recognised by helper T cells (CD4). (1.5)
Q9. [4] (table, ~1.3 marks per row; full = 4)
| Active immunity | Passive immunity | |
|---|---|---|
| Source of antibodies | Made by own body | Received ready-made |
| Speed of onset | Slow (days–weeks) | Immediate |
| Duration | Long-lasting (memory cells) | Short-lived (no memory) |
| (Award 4 for all three rows correct.) |
Q10. [5]
- (a) A vaccine is a preparation of weakened/inactivated pathogen or its antigens given to stimulate active immunity without causing disease. (1)
- (b) Herd immunity — when a large proportion of a population is immune, transmission of the pathogen is greatly reduced. (1) Unvaccinated individuals are protected because there are too few susceptible hosts for the pathogen to spread. (1)
- (c) Allergy = immune overreaction to a harmless foreign antigen (allergen); autoimmune disorder = immune system attacks the body's own (self) tissues. (2)
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{"claim": "Paper total marks equal 40", "code": "marks=[3,3,5,5,4,3,6,4,4,5]; result = (sum(marks)==40)"},
{"claim": "There are 10 questions on the paper", "code": "marks=[3,3,5,5,4,3,6,4,4,5]; result = (len(marks)==10)"},
{"claim": "Q7 splits into 4 (diagram) + 2 (functions) = 6", "code": "result = (4+2==6)"}
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