QUESTION 1.
(a) Topic: 1.2 (Cell as the basic units of living organisms)
(a) Topic: 1.2 (Cell as the basic units of living organisms)
Fig. 1.1 is a diagram showing part of a cell surface membrane of an animal cell.
(a) (i) State the approximate thickness of the membrane as shown by the line G–H.
(ii) Complete Table 1.1 to show:
• the names and functions of the components of the cell surface membrane
• the letters of the labels in Fig. 1.1 that identify each component.
(b) Fig. 1.2 is a drawing of a transmission electron micrograph (TEM) of a cell from the palisade
mesophyll of a leaf.
The drawing does not show all of the organelles visible in a transmission electron micrograph.
(i) Complete Fig. 1.2 by drawing and labelling:
• a mitochondrion
• rough endoplasmic reticulum
• smooth endoplasmic reticulum.
Your drawings should show the detail that can be seen in a transmission electron
micrograph. [3]
(ii) Identify the organelle labelled X and state one function of this organelle.
name …………………………………………………………………………………………………………………
function ………………………………………………………………………………………………………………
▶️Answer/Explanation
Ans:-
(a)(i) 7 nm ; A a suitable range A within the range 5 to 10 nm unit must be shown
(ii) one mark per row – name and letter must agree in row 3 – glycolipid and glycoprotein
If no rows are correct or one row is correct, mark by column to give max 2 if one or two columns are correct
(b)(i) each organelle must be drawn in the cytoplasm and labelled for a mark
max 2 if organelles are drawn correctly but not labelled or are not labelled correctly
labels must clearly identify the organelles R any 3D drawings
mitochondrion with two membranes and at least one crista ;
rough endoplasmic reticulum with at least one cisterna (two lines close together) and ribosomes attached on the outside ;
R if any ribosomes completely inside the organelle
smooth endoplasmic reticulum with at least one tube with no ribosomes ;
A RER and SER as labels
A if RER or SER attached to nuclear envelope
(ii) Golgi body / dictyosome ; A Golgi, apparatus / complex plus any one from:
modifies / processes, protein(s) / polypeptide(s) / lipid(s) ; A any suitable type of modification or a description
e.g. glycosylation / addition of sugars forming tertiary or quaternary structures
packaging of proteins into (Golgi) vesicles ; I transports
AVP ; e.g. forming lysosomes / cell wall enzymes assembled
QUESTION 2.
(a) Topic: 8.1 (The circulatory system)
(b) Topic: 8.1 (The circulatory system)
(c) Topic: 8.1 (The circulatory system)
(a) Water is the main component of blood. Explain how the properties of water make it suitable as the main component of blood.
(b) Fig. 2.1 is a diagram of the circulation in a mammal.
(i) Complete Fig. 2.1 by naming P and Q. Write your answers on Fig. 2.1.
(ii) Describe the functions of P and Q.
(iii) Explain why the mammalian circulation is described as a closed, double circulation.
(c) Fig. 2.2 is a transmission electron micrograph of a cross‐section of an arteriole. Blood flows
from muscular arteries through arterioles into capillary networks.
The lining of the arteriole is folded because the arteriole has constricted. This constriction
causes the blood pressure to decrease from 12.7kPa in the muscular artery to 2.7kPa at the
end of the arteriole.
(i) Explain why it is important that the pressure of blood decreases as it passes through arterioles.
(ii) Compare the structure of a muscular artery with the structure of the arteriole shown in Fig. 2.2.
▶️Answer/Explanation
Ans:-
2(a) any three from:
1 water is a, good / universal / AW, solvent ;
A dissolves many substances / description of solvent action
A solvent for / dissolves, (named) ions and (named) polar molecules
2 transport of one named substance for a correct reason ;
e.g. urea for excretion
3 high specific heat capacity ; A a full description
e.g. the amount of heat that must be added to, one unit of mass of the substance / 1 gram or 1 cm3 of water, to
increase the temperature by, one unit / 1 °C
4 so temperature of blood remains (fairly) constant / heat is dispersed throughout the body ; must be linked to mp
I temperature of water is constant
AVP ; e.g. water is (di)polar
(b)(i) P – aorta
A dorsal aorta
Q – vena cava ; I superior and inferior
(ii) 1 aorta / P, transports / delivers / AW, oxygenated blood to the, organs / body / respiring tissues / systemic circulation
or
aorta / P, transports / AW, blood at high pressure to, organs / body / respiring tissues / systemic circulation ;
2 vena cava / Q, transports / returns / AW, deoxygenated blood to the, right atrium / heart (from systemic circulation)
or
vena cava / Q, transports / AW, blood at low pressure to the, right atrium / heart ;
A vena cava / Q, collects blood from, veins / systemic circulation
alternative
3 aorta / P, transports oxygenated blood and, vena cava / Q, transports deoxygenated blood ;
4 blood in aorta to, organs / body / respiring tissues / systemic circulation, and blood in vena cava to, right atrium / heart ;
(iii) closed blood is contained within vessels ;
A at least three from heart, arteries / arterioles, veins / venules, capillaries
double
blood flows twice through the heart in, one / each, (complete), circuit/circulation (of the body) ;
A pulmonary circulation and systemic circulation A described
(c)(i) any two from:
(blood at high pressure) will, burst / damage, capillaries ;
A cannot withstand high pressure
capillaries have thin walls / capillary walls are composed of one (thin) layer of (endothelial) cells ;
A capillary walls are one cell thick
R capillaries have cell walls
idea that at low pressure blood flows slowly to allow, exchange / diffusion, of substances (in capillaries) ;
A efficient exchange (of substances)
AVP ; e.g. idea that pressure will be low at venous end of capillaries so that tissue fluid is reabsorbed
(ii) any three from:
I functions
similarities
1 (both have) endothelium / tunica intima ; A tunica interna
2 both have) tunica media / smooth muscle ;
differences
muscular artery – accept ora for arteriole
3 smaller lumen to wall thickness / ratio of wall thickness to lumen width is smaller ;
A thicker wall ; I artery is ‘bigger / thicker / wider’, unqualified
4 wider lumen ;
5 more smooth muscle (layers) / thick (layer) v thin (layer), smooth muscle ;
A thicker tunica media
6 more / presence of, elastic, fibres / tissue ;
A no elastic lamina
7 more / presence of, collagen (fibres) ;
8 AVP ; e.g. ref. to blood vessels in wall of artery (vasa vasorum)
e.g. no vesicles in endothelium
e.g. artery has, tunica externa / adventitia
A tunica externa not (clearly) visible in arteriole
QUESTION 3.
(a) Topic: 10.1 (Infectious diseases)
(b) Topic: 10.1 (Infectious diseases)
(a) A class of students was studying the features of some human pathogens. One of the students
constructed a flow chart to identify four different human pathogens. The student used
information about the structure and mode of transmission of each of these pathogens.
Fig. 3.1 shows the partially completed flow chart.
Complete the flow chart in Fig. 3.1 by identifying:
• the modes of transmission
• the scientific names of the pathogens
• the name of one of the diseases.
(b) HIV has a nucleic acid core of RNA. The virus also contains the enzyme reverse transcriptase.
After HIV enters T lymphocytes, reverse transcriptase catalyses the formation of DNA using
activated DNA nucleotides with the viral RNA as a template.
Some drugs, such as tenofovir, have been developed to inhibit the action of reverse transcriptase.
The structure of tenofovir is similar to the structure of deoxyribose adenosine monophosphate, as shown in Fig. 3.2.
After tenofovir is absorbed into cells it is phosphorylated twice and can be used by reverse transcriptase in the synthesis of DNA.
When a tenofovir molecule is added to the DNA strand being synthesised, the process stops.
Suggest the mechanism of action of tenofovir to prevent the synthesis of DNA by reverse
transcriptase. Use the information in Fig. 3.2 in your answer.
Pre‐exposure prophylaxis (PrEP) is the use of therapeutic drugs to prevent the replication of
HIV in the body following infection. The drugs are taken by people who are at risk of becoming
infected. Tenofovir is one of these therapeutic drugs.
In 2016, the United Nations (UN) set a global target of 3 million PrEP users by 2020.
Table 3.1 shows the number of people across the world who received a therapeutic drug for
PrEP in each of the years between 2012 and 2019.
(i) Calculate the percentage of people who received PrEP in 2019 as a percentage of the target set by the UN in 2016.
Give your answer to the nearest whole number.
(ii) PrEP does not prevent transmission of HIV. State and explain how health authorities can reduce the transmission of HIV.
▶️Answer/Explanation
Ans:-
3(a) (insect) vector / Anopheles / (a) mosquito ;
Plasmodium, falciparum / ovale / malariae / vivax ; A knowlesi
Vibrio cholerae and cholera ;
A other pathogens and associated diseases that are transmitted in the same way
Mycobacterium, tuberculosis / bovis ;
airborne droplets / droplet infection / aerosol (infection) ;
I air droplets
I water droplets from, coughing / sneezing
A alternative transmission only if Mycobacterium bovis stated
e.g. (eating) contaminated meat (from infected cattle)
(drinking) contaminated milk
(drinking) unpasteurised milk from contaminated, cows / cattle
(b) any two from:
tenofovir competes with, (activated / phosphorylated) adenine nucleotide / deoxyribose adenosine triphosphate / dATP, for
active site / to prevent nucleotides being added to elongating chain ;
A (tenofovir acts as a) competitive inhibitor (of reverse transcriptase)
tenofovir forms a phosphodiester bond to elongating DNA strand, but stops further reactions / AW ;
tenofovir has, no 3 ́ -OH so next nucleotide cannot form a phosphodiester bond / no (deoxy)ribose so cannot form
phosphodiester bond ;A pentose R sugar unqualified
(c)(i) 20 (%) ; R answers with decimal places
(ii) there must be at least one statement or at least one explanation to gain max 4, otherwise mark to max 3
any four from:
1. supply, condoms / femidoms / dental dams / item(s) for protection during sex ;
2. barrier to transmission during sexual intercourse ;
3. ref. to, needle exchange schemes / other suitable support for intravenous drug (ab)users ; I clean needles
4. decreases risk of sharing contaminated equipment / AW ;
5. use, new needles / new syringes / sterilised equipment / AW, for medical procedures ; I clean needles
6. decreases risk of transmission from contaminated blood ;
7. provide testing for HIV, in high risk groups / to individuals at high risk ;
8. for early diagnosis so newly infected people so can start drug treatment immediately ;
8. test pregnant women for HIV / provide powdered milk to women who are HIV positive ;
9. prevent women who are HIV positive passing HIV in breast milk ;
10. prevent people who are HIV positive being blood donors / screen donated blood / heat-treat donated blood ;
11. prevent people receiving blood infected with HIV, during blood transfusions / operations ;
12. carry out contact tracing ;
13. locate people who, are undiagnosed / may be HIV positive / should be offered test ;
14. supply (named) drug(s) to people, living with HIV / who are HIV positive / pregnant women with HIV ;
15. prevents HIV, spreading throughout the body / infecting more T-lymphocytes ; A to reduce viral load
16. provide, education / information, about, HIV treatments / HIV transmission ;
17. to raise awareness of ways to reduce infection / AW ; A use of barrier methods during sex / safer sex
18.AVP ; e.g. law to make it illegal to knowingly transmit the virus
QUESTION 4.
(a) Topic: 9.1 (The gas exchange system)
(b) Topic: 9.1 (The gas exchange system)
(c) Topic: 9.1 (The gas exchange system)
Fig. 4.1 is a scanning electron micrograph showing the tissue that lines the bronchi in the gas
exchange system.
Fig. 4.2 is a transmission electron micrograph of a horizontal section made at the position indicated
by the two arrows in Fig. 4.1.
(a) (i) Name the cells labelled A and B in Fig. 4.1.
A ……………………………………………………………………………………………………………………….
B ……………………………………………………………………………………………………………………….
(ii) Describe how the tissue shown in Fig. 4.1 is adapted to its function in the gas exchange system.
(b) (i) The structures labelled X in Fig. 4.1 have a characteristic internal appearance, as seen in Fig. 4.2.
Describe the internal appearance of the structures labelled X.
(ii) Explain how Fig. 4.2 shows that each of the structures labelled X are intracellular.
(c) Stem cells are found in the lining of the bronchi.
Describe the function of centrioles and explain how they are involved in the cell cycle of a stem cell.
▶️Answer/Explanation
Ans:-
(i) A ciliated epithelial (cell) ; R ciliated epithelium B– goblet (cell) ;
(ii) 1 goblet cells / B, secrete / produce / release, mucus / mucin ;
2 mucus, covers / AW, the (ciliated) epithelium to trap (named) particles ;
or
idea that mucus prevents (named) pathogens reaching, epithelial cells / alveoli / gas exchange surface ; I lungs
A acts as a barrier to (named) pathogens
3 cilia / ciliated epithelial cells, move mucus (and trapped material), upwards / towards mouth / towards throat
or
pharynx / away from alveoli / away from gas exchange surface / away from lungs / out of the airways ;
I ‘out of the lungs’ / ‘to be swallowed’ unqualified / out of the respiratory system / out of the gas exchange system
(b)(i) 9+2, pattern / arrangement / structure ; composed of microtubules ;
AVP ; e.g. ref. to dynein ‘arms’ / AW outer 9 are, pairs of microtubules / doublets, and central two are single
(ii) idea that each cilium / structure X, is surrounded by cell (surface) membrane (so contents are inside the, cell / cytoplasm) ;
(c) must have either mp1 or mp2 or both to gain max 4, otherwise max 3
1 (centrioles) make / organise, microtubules ; A microtubular organising centre / MTOC
2 to form, the spindle / spindle fibres ;
3 (during each cell cycle) each centriole, replicates / duplicates / forms two centrioles ;
4 during, S phase / G2 phase ; A before mitosis mp4 is linked to mp3
5 centriole pairs / centrioles, move to the (opposite) poles (of cell during prophase of mitosis) ; R if incorrect phase R ‘poles of nucleus’
6 centrioles, lengthen / shorten, the spindle fibres / microtubules ; I ‘contract’
QUESTION 5.
(a) Topic: 7.1 (Structure of transport tissues)
(a) Topic: 7.2 (Transport mechanisms)
The pressure of water vapour inside and outside leaves can be measured. The difference between
these pressures is known as the leaf vapour pressure deficit (LVPD).
LVPD is one of the factors that influences the rate of transpiration.
Scientists measured the effect of changing the LVPD on the rate of transpiration in several species
of flowering plant that live in a variety of different habitats. Two of these species were:
• Nerium oleander, a species that is adapted to grow in hot, dry conditions
• Helianthus annuus, a species that is not adapted for survival in hot, dry conditions.
Fig. 5.1 shows the effect of increasing the LVPD on the transpiration rates of the two species.
All other factors were kept constant. key
————Helianthus annuus
_______Nerium oleander
(a) Compare the results of the two species shown in Fig. 5.1.
(b) Fig. 5.2 shows part of a plant of N. oleander.
Fig. 5.3 shows a cross‐section of part of an oleander leaf.
Fig. 5.4 is a drawing of a high-power view of region N on Fig. 5.3.
State and explain two adaptations shown by the leaves of N. oleander that are visible in Fig. 5.3 and Fig. 5.4.
one adaptation visible in Fig. 5.3 explanation
one adaptation visible in Fig. 5.4 explanation
▶️Answer/Explanation
Ans:-
(a) both units must be used at least once any three from:
1 no transpiration when LVPD is 0 kPa ;
2 (both) increase in transpiration rate until 2.5 kPa ;
3H. annuus rate remains constant between 2.5 and 3.0 kPa, N. oleander rate decreases slightly ;
4 H. annuus has higher rate of transpiration (at all LVPDs) ; ora for N. oleander
5 H. annuus has a higher rate of increase (between 0 and 2.5 kPa) ; A steeper gradient
6 any comparative data quote from Fig. 5.1 ;
must include figures and units from both axes and data must come from both species
(b) if a correct adaptation does not match the figure, allow ecf for the explanation Fig. 5.3
any four from:
1 three layers of thick-walled cells at, upper / lower, surface ;
A two layers of cells under epidermis / epidermis and (two layers of) hypodermis
2 reduces, diffusion of water vapour to atmosphere / cuticular transpiration ;
A increases the distance for water vapour to diffuse
3 no stomata on upper surface / stomata only on lower surface ;
4 stomata not exposed to direct sunlight / AW ;
5 (stomata in) pits / depressions / cavities / chambers / crypts / infoldings / grooves / AW (on lower side of leaf) ;
6 creates humid atmosphere in, pit / AW or reduces the, diffusion / water potential, gradient (for water vapour) ;
A vapour pressure gradient A minimises effect of, external air currents / windFig. 5.3 or Fig. 5.4
7 thick walled epidermis ;
8 reduces diffusion of water vapour through lower epidermis ;
9 thick (waxy) cuticle (on epidermis / surface) ;
10 reduces diffusion of water vapour through cuticle / reduces cuticular transpiration ; A (waxy) cuticle is waterproof
11 (epidermal) hairs / trichomes (around stomata / fill pits) ;
12 reduces air movement / traps still air / creates humid atmosphere / traps water vapour or reduces the, diffusion / water potential, gradient for water vapour ;
QUESTION 6.
(a) Topic: 11.2 (Antibodies and vaccination)
(b) Topic: 11.2 (Antibodies and vaccination)
Antibodies are produced by plasma cells.
Fig. 6.1 shows antigens bound to antigen‐binding sites of an antibody molecule.
(a) (i) Explain how the structure of an antigen‐binding site makes it specific to a particular antigen, as shown in Fig. 6.1.
(ii) State the function of the hinge region of the antibody shown in Fig. 6.1.
(iii) Antibodies can bind to membrane receptors on cells of the immune system, such as macrophages.
Suggest an advantage of antibodies binding to receptors on macrophages.
(b) It is estimated that the immune system of each person can make enough antibodies to bind to
over 1012 different antigens.
When plasma cells make antibody molecules they combine the polypeptides produced by the
expression of genes for heavy chains and the genes for light chains.
Research has shown that producing this very large number of antibodies is only possible by
modifying the primary transcripts of the genes that code for heavy chains and the genes that code for light chains.
Suggest how this modification of the primary transcripts occurs in plasma cells.
▶️Answer/Explanation
Ans:-
(i) any two from:
1 (antigen-binding site / variable region) has a shape that is complementary to antigen ; A tertiary / quaternary, structure
2 (antigen-binding site / variable region has) specific, sequence(s) of amino acids / primary structure(s) ;
3 idea that different amino acids have different, R-groups / side chains, so give different, tertiary structures / shapes (for
binding to antigens) ;AVP ; e.g. correct ref. to epitope(s)
(ii) idea that allows flexibility for binding (to antigens) ; A at different angles for flexibility / allows variable region(s) to move
(iii) any one from:
idea that easier for macrophage to engulf, antibodies that have bound antigens / antibody-antigen complexes ;
facilitates / AW, destruction of pathogens ‘marked’ by antibodies ; A ref. to opsonisation
I stimulates phagocytosis of the pathogen, unqualified
(b) any two from:
1 removal of introns (from primary transcript) ;
2 (after removal of introns) exons, are joined together, in different, sequences / combination(s) ; A alternative splicing
3 not all the exons are used (in making the polypeptides) ; I capping and polyA tails