Question
Explain the role of cells in the defence against infectious disease.[7]
▶️Answer/Explanation
Ans
a.cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes
OR
mucous membranes produce mucus to trap pathogens
OR
stomach cells produce hydrochloric acid which kills microbes;
b.platelets start the clotting process preventing access of pathogens;
c.(two types of) white blood cells fight infections in the body;
d.phagocytes ingest pathogens (by endocytosis/phagocytosis);
e.gives non-specific immunity to diseases / ingest any type of pathogen;
f.production of antibodies by lymphocytes/B cells;
g.in response to particular pathogens/antigens;
h.gives specific immunity;
i.lymphocyte/B cell makes only one type of antibody;
j.plasma cells produce large quantity of (one type of) antibody;
k.some lymphocytes act/remain as memory cells;
l.can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered;
m.results in faster defence against second exposure to specific antigen/pathogen/disease;
Question
a. Using the Punnett grid, explain how two parents can have children with any of the different ABO blood groups.
[3]
b. Distinguish between the structure of arteries and the structure of veins. [3]
c. Explain how cuts in the skin are sealed by blood clotting. [2]
▶️Answer/Explanation
Markscheme
a. correct gametes of one parent as IA AND i in header line/column
AND
correct gametes of other parent as IB AND i in header column/line
b. correct corresponding genotypes in inner squares as IAIB, IAi, IBi, ii
c. corresponding phenotypes of children identified as AB, A, B and O
d. ratio of phenotypes is 1:1:1:1 OWTTE
Allow ECF.
a. arteries have thicker (muscular) walls/layer/tunica (media)
OR
veins have thinner (muscular) walls/layer/tunica (media)
b. arteries have no valves
OR
veins have valves
c. arteries have thicker elastic layer
OR
veins have thinner elastic layer
d. arteries have a smaller lumen/bore
OR
veins have a larger lumen/bore
Accept answers presented in a table.
a. clotting factors released from platelets
b. clotting process involves a cascade/series of reactions
c. produces thrombin
d. causes rapid conversion of fibrinogen into fibrin
e. fibrin makes a mesh to seal the wound OWTTE
Question
The diagram shows the human heart.
a.i. On the diagram, label the aorta. [1]
a.ii. On the diagram, label the right atrium. [1]
b. Explain how valves control the flow of blood through the heart.[2]
c. Outline the causes and consequences of blood clot formation in coronary arteries.[2]
d. Outline the role of lymphocytes in defence against disease.[2]
▶️Answer/Explanation
Markscheme
both labelled clearly as in diagram ✔
both labelled clearly as in diagram ✔
a. valves open and close in response to changes in blood pressure/heart contraction/pumping ✔
b. valve prevents backflow/maintains direction of blood flow ✔
c. valves allow heart chambers to fill/to empty ✔
a. coronary heart disease/CHD/coronary artery disease/CAD occurs when there is reduction of oxygen to the heart muscle ✔
b. high ratio of LDL to HDL/fatty diet leads to plaque formation in arteries ✔
c. plaque breaks off causing damage that activates blood clot formation ✔
d. clots «in the bloodstream» may block a coronary artery/coronary thrombosis reducing blood flow/oxygen
OR
clots can cause heart attack/muscle death ✔
e. sickle cell anemia «crisis» produces blood clots «that can cause coronary/arterial blockage» ✔
a. produce antibodies ✔
b. memory cells confer immunity ✔
c. specific immunity results from production of antibodies specific to a particular antigen ✔
d. recognize pathogens ✔
e. destroy foreign cells/cancer cells ✔
Question
a. Outline how cuts in the skin are sealed to prevent blood loss.[4]
b. Outline how two parents could have a child with any of the four ABO blood groups.[4]
c. Explain how ventilation and lung structure contribute to passive gas exchange.[7]
▶️Answer/Explanation
Markscheme
a. platelets respond to/detect skin/blood vessel damage ✔
b. platelets release clotting factors ✔
c. clotting factors trigger a chain/cascade of reactions ✔
d. «leading to» formation of thrombin ✔
e. thrombin causes fibrinogen conversion into fibrin ✔
f. blood clot seals the wound due to fibrin network of fibres ✔
Accept answers presented as a flow chart.
a. «first set of» gametes/parental genotype IA, i ✔
b. «other set of» gametes/parental genotype IB, i ✔
c. «genotypes of offspring are respectively» IAIB, IBi, IAi, ii ✔ All four correct required.
d. «phenotypes of offspring are respectively» AB, B, A, O ✔ All four correct required linked to genotypes
Award marks only for the first grid if more than one drawn;
e.g. of Punnett grid
Answers can be given in a Punnett grid or in prose.
Accept the four possible blood groups of the offspring anywhere in the answer.
a. air carried through trachea AND bronchi/bronchioles AND alveoli ✔ All three required in correct order.
b. alveoli increase the surface area/thin walled for gas exchange ✔
c. gas exchange carried out through type I pneumocytes ✔
d. type II pneumocytes secrete surfactant to reduce surface tension ✔
e. moist surface/surfactant allows gases to diffuse in solution ✔
f. ventilation/moving blood maintains concentration gradients of oxygen and carbon dioxide ✔
g. between air in alveoli and blood in «adjacent» capillaries
OR
oxygen diffuses from alveoli to capillaries and carbon dioxide from capillaries to alveoli ✔ OWTTE
h. external intercostal muscles/diaphragm contract during inspiration ✔
i. lowering air pressure «in lungs»/increasing thorax volume ✔
j. relaxation of external intercostal muscles/diaphragm enable «passive» expiration ✔
k. internal intercostal «and abdominal muscles» contract «to force» expiration ✔
l. expiration due to increasing air pressure «in lungs»/decreasing thorax volume ✔
Accept correctly annotated diagram.