CIE

Question 1

Describe how the malarial parasite is transmitted.

Answer 1

female Anopheles mosquito ; either takes blood meal / AW, from infected person or parasites enter mosquito in blood meal from infected person ;

takes blood meal / AW, from uninfected person ; parasite / pathogen / plasmodia, transferred in mosquito’s, saliva / anticoagulant ; ref. to transfusion malaria / congenital or mother-foetus malaria / needle sharing / needle stick injury for max 1

Question 2

Explain how using such a vaccine may give long-term immunity to malaria.

Answer 2

protein is) antigen ;

following vaccination (clonal) selection for, appropriate / corresponding / specific, B cell ; clonal expansion / divide (by mitosis) (to form B cell clone) ; memory cells ;

on infection by parasite (B cells / plasma cells) secrete antibody ; A immunoglobulin / Ig secondary response (qualified) / higher levels of antibody / rapid production of antibody ; ref. to antigen-antibody specificity ; antibody attaches to, surface protein / antigen, on parasite ; prevents attachment to red blood cell ; A prevents entry into red blood cell

Question 3

Researchers have been trying to develop a successful vaccine against malaria for about 20 years. Explain why it has proved so difficult to develop such a vaccine.

Answer 3

genetic complexity of Plasmodium ; A ref to Plasmodium, being eukaryotic / having many genes many antigens ; many stages in life cycle (within human) ; antigens change / antigenic variation, in different stages ; Plasmodium / parasite, lives within cells ; A antigenic concealment A only briefly free in the blood stream antibodies cannot work against stages within cells

Question 4

explain why it is difficult to assign some organisms to trophic levels.

Answer 4

some animals feed at different (trophic) levels / animals do not obtain all their food from one (trophic) level ; A correct reference to at least two consumer levels animals may feed on different (trophic) levels at different, times / seasons ; some food chains, do not start from primary producers / start from decomposing matter ;

named examples from food web ;

Question 5

State two factors that are likely to influence the efficiency of energy transfer by herbivorous copepods.

Answer 5

proportion of, phytoplankton / copepods, that is digested / some remains undigested ; phytoplankton have cell walls ; proportion that is absorbed after digestion ; loss in, egestion / faeces ; in terms of energy loss in, excretion ; loss or energy loss in, respiration / heat (by copepods) ; availability energy losses in movement / AW ; AVP ; e.g. denser phytoplankton means less energy loss in feeding

Question 6

Describe how M. tuberculosis is transmitted from an infected person to an uninfected person

Answer 6

(infected person) coughs / sneezes / spits / releases sputum / breathes out / exhales ; A releases mucus R talks aerosol / droplets / moist air, inhaled / breathed in (by uninfected person) ;

Question 7

Suggest why fatality ratios for TB are higher in some of the countries than in others.

Answer 7

poor / dense / overcrowded, housing / accommodation ; low protein diets linked to lowered immunity ; not, diagnosed / treated, early enough ; DOTS / described, not used ; lack of vaccination / vaccinations ineffective ; antibacterial drugs / antibiotics / AW, not available / too expensive ; medical services not available, qualified e.g. in rural areas / AW ; idea of TB, linked to HIV/AIDS / opportunistic disease ; MDR – TB / XDR – TB / not completing the course of antibiotic treatment increases resistance ; no effective antibiotics to use ; no facilities for isolating people ; lack of, testing / treatment of, cattle / milk ; A unpasteurised milk difficulty in obtaining reliable data / AW ;

Question 8

ecosystem

Answer 8

all the organisms and the physical factors that influence them in an area, such as a forest

Question 9

habitat

Answer 9

a place where an organism lives

Question 10

community

Answer 10

all the organisms / plants and animals / populations / AW, in the ecosystem / forest / place / area / habitat ;

Question 11

niche

Answer 11

role of organism in an ecosystem

Question 12

population

Answer 12

all the organisms of the same species in an ecosystem at the same time

Question 13

suggest why there are few predators, such as jaguars and harpy eagles, in the forest ecosystem even though there are many producers, such as trees.

Answer 13

predators are, secondary consumers / tertiary consumers / top carnivores ; (population, size / number of) predators limited by numbers of prey / sloths / AW ; energy loss, between trophic levels / along food chain / inefficient energy transfer ; detail e.g. only 10% transfer / respiration / heat / movement / excretion / inedible parts / egestion / to decomposers; (prey numbers small so) competition for, food / prey ; predators hunted by humans ; habitats / areas, of predators destroyed ;

Question 14

reasons for decreased mortality rates

Answer 14

decreasing mortality rate because earlier diagnosis (so fewer die) ; improved, health care / treatment (extends life) ;

Question 15

Explain how it is possible to reduce the number of deaths during a cholera epidemic in countries such as those in West Africa.

Answer 15

provide, boiled water / bottled water / sterile water ; A valid description of method to, remove / kill, bacteria provide, oral / intravenous, rehydration therapy / ORT ; A ORS (contains) glucose and, salts / electrolytes ; absorption of salts helps to absorb glucose ; (absorption of salts) increases water uptake, by osmosis / AW ; deaths usually caused by (rapid) dehydration ; idea of rapid provision (of, ORT / medical supplies / personnel) ; provide antibiotics (for severe cases) ; safe sewage disposal, qualified ; R sewage treatment plants

Question 16

Explain why cholera is unlikely to be transmitted in developed countries.

Answer 16

transmission cycle is broken ; sewage treatment plants / mains drainage ; human faeces do not come into contact with drinking water supply ; water treatment plants ; A drinking water is, chlorinated / treated, to kill bacteria ; drinking water is piped to homes ;

Question 17

Define the term term commnicable disease

Answer 17

caused by pathogen, transmissible / communicable / contagious / transferable / passed from
one person to another ;

Question 18

Explain why malaria is found in mostly sub Saharan africa, but TB is found everywhere.

Answer 18

Anopheles / mosquito / vector, survives / breeds / lives, within the tropics / in hot and
humid areas ; ora
2 Plasmodium / pathogen / parasite, needs to reproduce within the mosquito (at
temperatures above 20°C) ;
3 eradicated in some countries outside the tropics ;
4 ref. to LEDCs and, poor / non-existent, mosquito control programmes ;
5 mosquitoes resistant to, DDT / insecticides / pesticides ;
6 Plasmodium resistant to, drugs / chloroquine / other named drug ;
7 TB is transmitted, by, droplets / coughing / sneezing ; A in the air
8 no vector / no mosquito / no requirement for hot or humid conditions ;
9 ref. to, HIV infection / lower immunity / immunocompromised ;

Question 19

Explain how vaccination provides immunity as an important part of programmes to control and eradicate infectious diseases

Answer 19

active immunity ;
2 vaccine contains, antigen(s) / pathogen / microorganism / named type ;
3 (primary) immune response ;
4 B lymphocytes / B cells / plasma cells, synthesise / produce / secrete / release,
antibodies ;
5 ref. to T helper cells (enhancing humoral response) ;
6 clonal selection / described ;
7 specific, (T / B) lymphocytes / antibodies ; A ‘particular’ / AW
8 memory cells, remain (in circulation) / give long-term immunity / give immunological
memory / AW ;
9 fast(er) second(ary) response ;
10 ref. to boosters / AW ;
11 immunised person cannot spread disease to others ;
12 herd immunity / unimmunised people are safe(r) ;
13 surveillance of population for signs of disease / when there is an outbreak ;
14 ref. to ring immunity / AW ;

Question 20

Suggest the advantages gained by legumes of having Rhizobium living in their roots

Answer 20

provide source of, fixed nitrogen
/ usable nitrogen / organic nitrogen / amino acids / ammonia
/ ammonium ions / AW ; R nitrate
ref. to protein production in legume ;
legume can, colonise / grow in, nitrogen / nitrate, deficient or poor soils ;
A not dependent on nitrate in soil
compete successfully with non-leguminous plants ;

Question 21

Suggest two reasons for the differences shown in estimated life expectancy without HIV/AIDS between the different African countries.

Answer 21

more educated population ; in context of healt
2 better/greater access to, health care/AW ;
3 higher level of preventive medicine ; e.g. immunisation programmes
4 better diet ; A ref. to less malnourished
A ref. to access to food supplies
5 greater access to, therapeutic medicines/drugs ; A antibiotics
6 better/less overcrowded, housing/living conditions ;
7 better, sanitation/sewage treatment ;
8 greater access to uncontaminated drinking water ;
R clean water unqualified
9 fewer, fatal diseases/AW ;
10 ref. to effects of, civil war/war ;
11 ref. to natural disaster

Question 22

List two factors in the prevention and control of HIV/AIDS that would help to improve average life expectancy in the African countries

Answer 22

anti HIV drug therapy/AW ;
2 ref. to treatment of AIDS-related diseases ;
3 ref. to education to prevent, transmission/spread ;
4 use/provide free, condoms/femidoms ; A dental dams
5 avoid promiscuity ; A one sexual partner
6 HIV mothers avoid breast feeding ;
7 heat treat/screen, blood (for transfusion) ;
8 needle-exchange schemes/AW ; A ref. to sterile syringes
9 use of sterile equipment, qualified e.g. in surgery/tattooing/piercing ;
10 testing for HIV status/contact tracing ;
11 ref. to vaccine development ;

Question 23

Outline the events that occur in a newly-infected person, which lead to the production of antibodies to HIV.

Answer 23

primary/immune, response ;
2 ref. specificity; in correct context
3 (HIV/virus) antigens ;
4 antigen presentation/antigen presenting cell/APC/described ;
5 clonal selection/described ; e.g. recognition of/binding to, antigen by, B-lymphocyte
6 sensitisation/activation/described ; e.g. cell growth or cellular changes
7 clonal proliferation/formation of clone/mitosis/cell division/AW ;
8 B-lymphocytes/B-cells/plasma cells, synthesise/produce/secrete/release, antibody ;
9 T(helper)-lymphocyte response described ; e.g. cytokine production

Question 24

Suggest how a change in the gene can lead to the different enzymes being made

Answer 24

altered, (mRNA) codon(s)/triplet(s) ; A named type of mutation
changed/AW, amino acid(s) ;
ref. to effects of stop codon ; e.g. shortened polypeptide chain
different, primary structure/described ;
A ref. to differences in, transcription/translation
ref. to different properties of, R group/side chain (of normal v replaced amino acid) ;
altered tertiary structure/AW ; A different R group interactions
A change/loss of, active site
idea of globular to fibrous change/hydrophilic R groups no longer to outside ;

Question 25

what a producers

Answer 25

photosynthetic/autotrophic/fix carbon/ have chlorophyll at the start of the food web/at the first trophic level/the source of energy to rest of food web

Question 26

Describe one method of controlling the spread of malaria by targeting its vector and explain its effect

Answer 26

any named biological control method e.g B. thuringiensis ; kills mosquito larvae ; use of insecticides ; kills (adult) mosquitoes ; elimination of standing water ; removes, mosquito breeding sites/egg-laying areas ; use of oil on water ; prevents maturation of/kills, mosquito larvae ;

Question 27

Suggest how HIV infection may have led to an increase in malarial infections in sub Saharan africa

Answer 27

HIV, infects/AW, T (helper)–lymphocytes/T-cells ; qualified ref. to immune system ; (HIV and) malaria may be contracted via blood transfusion ; ref. to reduced number of workers so malaria prevention not carried out

Question 28

Explain what is meant by the term nitrogen fixation

Answer 28

conversion of/AW, nitrogen (gas)/N2 ; in context of atmospheric nitrogen (to) ammonium (ions/compounds)/NH4 + /amino acids ; further detail ; e.g. nitrogenase (enzyme)/ref. conversion from unreactive (nitrogen) to reactive (compound)/reduction of nitrogen/ATP required/anaerobic conditions required for enzyme function

Question 29

Explain the importance of this process in making nitrogen from animals available for uptake by plants

Answer 29

) supplies, ammonia/ammonium ions, for, nitrifying bacteria/nitrification ; ammonia/ammonium ions, converted/oxidised/AW ; to nitrite ; to nitrate ; Nitrosomonas /Nitrobacter ; in correct context ref. nitrate useable form for plants ;

Question 30

State the trophic levels to which each of the organisms named in the passage belong and outline the energy losses that occur in the food chain.

Answer 30

energy losses in respiration ; heat loss, qualified ; e.g. heat loss, from digestion / movement / metabolism heat loss in respiration = 1 mark indigestible parts ; A named, e.g. cellulose inedible parts ; excretion ; A named excretory products egestion ; I waste death, not eaten

Question 31

State one factor, other than drug therapy, that contributed to the steady decrease in the number of new cases of tuberculosis

Answer 31

ref. (BCG) vaccine / vaccination programme ; improvements in housing conditions / less overcrowding (housing) / better ventilated homes ; R better standards of living unqualified earlier detection / mass, chest X-ray / screening ; i.e. in preventing spread improvements in diet (leading to better immune system) / AW ; improved awareness of, transmission / AW ; R better education unqualified contact tracing / explained ; ref. testing / treating, cattle / milk ;

Question 32

Outline three reasons why, in many developed countries, the number of new cases of tuberculosis is now increasing

Answer 32

development of antibiotic resistance (by organism) ; A drug resistance R immunity ref. impact of HIV infection ; higher rate of immigration from countries with high incidence / AW ; increase in tourism to countries with high incidence ; reduced surveillance leading to undetected cases (and hence spread) ; (detected cases, MDR) unwillingness / AW, to maintain drug regimen / AW ; ref. to vaccination programmes no longer taking place ; ref. to poor / overcrowded, housing (in cities) / AW ; must be in context of developed countries

Question 33

Streptomycin was the first antibiotic to be discovered that was effective against the pathogen that causes tuberculosis. Streptomycin causes the death of the pathogen by binding to ribosomes and inhibiting protein synthesis. (i) Suggest two ways in which streptomycin acts at ribosomes to inhibit protein synthesis Streptomycin does not harm mammalian cells. Suggest an explanation for this.

Answer 33

binding of tRNA prevented ; (so) no anticodon-codon binding ; peptide bond formation prevented ; mRNA attachment prevented ; inhibition of enzymes involved in translation ; ribosome movement along mRNA, hindered / prevented ; inhibits association of large and small subunits / AW also cell surface membrane impermeable ; degraded, before entry into / within, the cell ; broken down by enzymes ; eukaryotic / 80S (22nm) / larger / different, ribosomes / ribosome structure

Question 34

why is In agriculture, canglucose + nitrate -> water + carbon dioxide + nitrogen be undesirable

Answer 34

nitrate required for, amino acid / protein / nucleic acid, production in plants ; A other relevant named N-containing biochemicals nitrogen (gas) not useable form for (most) plants ; removal of nitrate slows / AW, growth of plants ; A reduces crop yield A plants need nitrates for growth decreases fertility of soil / fertilisers need to be added to soil ;

Question 35

For Examiner’s Use 6 In anaerobic soil, bacteria, such as Pseudomonas stutzeri, can use nitrate ions (NO3–) as a source of oxygen for their respiration. The word equation below summarises the process Suggest how bacteria, such as Pseudomonas stutzeri, can be used in the process of purifying water for drinking

Answer 35

(ii) P. stutzeri / bacteria, can be (added to the water and) used to, remove nitrate / carry out denitrification ; detail ; e.g. use of filter bed ref. to leave for sufficient time to remove nitrates nitrogen escapes to air

Question 36

In recent years there has been an increase in flooding of agricultural land worldwide. Explain why crop yields are often significantly reduced even after the flood water has drained away.

Answer 36

1 air / oxygen, will not get into soil ; 2 lack of oxygen reduces uptake of ions by plants / AW ; 3 ref. saprobiotic bacteria and fungi / nitrifying bacteria / (some) nitrogen fixing bacteria, are aerobic ; 4 ref. reduced populations (of bacteria in mp 2) ; 5 example of effect on nitrogen cycle ;; 6 e.g. slower rate / AW, of decomposition / decay nitrogen fixation cannot occur (as rapidly) nitrification cannot occur / nitrate will not be produced / less nitrate produced (more) denitrification will occur 7 crops / plants, will use up remaining nitrate ; 8 ref. leaching of, nitrates / other nutrients, for growth or (only) low levels of nitrates / other nutrients, for growth remain in soil ; A ref. leaching reducing soil fertility 9 AVP ; e.g. named example of another nutrient, with role will take time to, recover nitrate levels / resume nitrogen fixation ; fertilisers (previously) applied washed away ;

Question 37

Antibiotic resistance is a serious worldwide problem. Suggest how antibiotics can be used effectively to avoid the development of widespread resistance in bacteria.

Answer 37

do not prescribe for viral diseases ; 2 only use when necessary / do not overprescribe ; 3 only available on prescription / not available ‘over the counter’ ; 4 people must, complete the course / take as instructed ; R take a long course 5 test to find out which is most appropriate antibiotic to use ; A use most, appropriate / effective, antibiotics A use narrow-spectrum antibiotics 6 details of sensitivity test ; 7 rotate / AW, antibiotics / use in combination ; R use many antibiotics 8 do not use same antibiotics for humans and animals ;

Question 38

The amoeboid cells of D. discoideum feed on protein-rich material and break it down to form ammonium ions (NH4 +). The cell membranes of D. discoideum have transporter proteins that are responsible for the excretion of ammonium ions. Describe what happens to the ammonium ions excreted by D. discoideum into the soil.

Answer 38

1 nitrification / nitrifying / oxidation ; 2 ammonium ions to nitrite ions ; 3 nitrite ions to nitrate ions ; A one mark for ammonium to nitrate 4 one named microorganism in correct context Nitrosomonas / Nitrobacter ; R Rhizobium 5 ammonium / nitrate / AW, absorbed by plants / leached / AW ;

Question 39

The amoeboid cells of D. discoideum feed on protein-rich material and break it down to form ammonium ions (NH4 +). The cell membranes of D. discoideum have transporter proteins that are responsible for the excretion of ammonium ions. Suggest why a transporter protein is required for the removal of ammonium ions from D. discoideum.

Answer 39

ammonium ions are (positively) charged ; A hydrophilic / polar / water-soluble 2 cannot pass through, phospholipid bilayer / membrane ; either 3 active transport ; 4 moved against concentration gradient ; or 3 facilitated diffusion ; 4 moves down its concentration gradient ;

Question 40

Explain how the virus that causes measles is transmitted

Answer 40

(infected) person, sneezes / coughs / talks / breathes out, (airborne) droplets / aerosol/ moist air ; inhaled/ inspire/ breathed in, by uninfected, person ;

Question 41

Explain the functions of variable region

Answer 41

binds / attaches / combines, to antigen ; | ref. to specificity ;

Question 42

Explain the functions of disulphide bond

Answer 42

holds, polypeptides /heavy chains / long chains, together ; | maintains, tertiary / quaternary / 3D, structure/ shape ;

Question 43

Explain the functions of constant region

Answer 43

binds to, receptors / cell (surface) membrane, on, phagocytes / macrophages ; antigen, marking/ tagging, for, phagocytosis / macrophage action ; AW

Question 44

Antibiotics are prescribed to people who have HIV/AIDS for the treatment of secondary infections, but not to treat the HIV infection. Explain why this is so.

Answer 44

antibiotics are not effective against HIV or viruses / antibiotics are effective against, (named) bacteria/ bacterial disease ; A fungi/ protoctists / protists / malaria R antibiotics prevent infection 2 idea that viruses have no, sites / targets, where antibiotics can work ; 3 viruses have no, cell walls /ribosomes / cell membranes ; A have different enzymes 4 viruses are within cells, idea that antibiotics cannot reach them ; 5 people with HIV are more susceptible to bacterial infections /reference to immune suppression/weak immune system ;

Question 45

Describe how V. cholerae is transmitted from an infected person to an uninfected person

Answer 45

one mark for infected person with contaminated faeces, e.g. faeces / sewage, contaminates (drinking)water/ cooking utensils / vegetable plots / crops / food ; A diarrhoea for faeces R (human) waste unqualified A ref. to houseflies landing on contaminated faeces one mark for uninfected person eating contaminated food/using contaminated utensils / drinking contaminated water ; A bacteria enters water in context of drinking R infected food or water I handling contaminated food A faecal-oral route for two marks

Question 46

Explain the importance of nitrogen-fixing organisms, such as in ecosystems

Answer 46

provides ammonium (ions)/ ammonia/nitrogen(ous) compounds /fixed nitrogen/ organic nitrogen ; A organic compounds R nitrate / nitrite R nitrate/ nitrite, and ammonia A formulae NH3 /NH4 + if only a formula is used then it must be completely correct accept the following in context of plants / animals for synthesis of amino acids / nucleotides ; synthesis of protein/ nucleic acids /DNA/RNA ; proteins required for, growth/ enzymes / tissue repair/AW ; nucleic acids for storage of genetic information/AW ; idea of offsets loss of, (fixed) nitrogen/ nitrate ions ; reduces effect of (fixed) nitrogen as a limiting factor (for growth) ;

Question 47

Explain what is meant by the term non-self antigen.

Answer 47

non-self foreign/AW ; A ref. to epitope(s) I pathogen /organism antigen macromolecule/(glyco)protein/ carbohydrate/ polysaccharide/ oligosaccharide ; stimulates /AW, an immune response/production of antibodies ; A results in formation of antigen-antibody complexes A other described events in an immune response

Question 48

Outline how B-lymphocytes recognise non-self antigens.

Answer 48

antibody / immunoglobulin/ IgG, on cell surface/on cell membrane ; (act as) receptors ; ref. to antigen-binding/AW ; (shape) specific / complementary, to antigen ;

Question 49

Outline how plasma cells produce antibody molecules.

Answer 49

DNA/ gene transcribed/ mRNA using DNA as template/AW ; A transcription unqualified idea of mRNA associating with ribosome(s) ; ref. to tRNA with specific amino acid (carried to ribosome) ; pairing/AW of codons on mRNA with anticodons on tRNA ; formation of peptide bonds (between adjacent amino acids) ; antibody /protein/ polypeptide(s), enters RER/ moves to Golgi body ; ref. to forming, secondary / tertiary structure ; antibody /protein/ polypeptide(s), modified/processed/glycosylated/ formation of quaternary structure/ formation of disulphide bond(s) in Golgi (body / apparatus / complex) ; I ref. to packaging

Question 50

Describe how antibody molecules are released from the plasma cell.

Answer 50

vesicles move to cell/ surface/plasma, membrane (via cytoskeleton) ; R secreting vesicles unqualified vesicles fuse with cell (surface) membrane/exocytosis ; R active transport movement of vesicle/ exocytosis requires energy or ATP/ is active ;

Question 51

Explain the role of meomory cells

Answer 51

) memory cells ; A form immunological memory I ‘gives immunity’ remain/ stay in circulation/ blood/lymphatic system ; R ‘last a long time/ long lived’ unqualified for secondary response ; fast(er) response when exposed again to same pathogen/ same antigen ; A fast(er) clonal selection/ fast(er) clonal expansion A divide quickly /rapidly A long(er) lasting response to form plasma cells (and more memory cells) ; more antibodies produced/higher concentration of antibodies ; R if in context of memory cells to prevent person feeling ill/ to prevent symptoms ;

Question 52

Acute lymphoblastic leukaemia (ALL) is a cancer of B-lymphocytes. It is very rare in adults, but more common in children. A study in 2009 found that exposure to tobacco smoke in the home may put children at risk of developing ALL. Suggest how smoking by adults in the home may put their children at risk of cancers, such as ALL

Answer 52

breathing in/ inhale smoke/ ‘second hand’ smoke/ sidestream smoke ; A passive smoking I exposed to smoke 2 (tobacco smoke contains) carcinogen(s) ; 3 causes mutation/ described ; e.g. change to/alters / damages, DNA R if in wrong type of cell 4 leads to uncontrolled cell division/ mitosis / growth ; 5 forming a tumour/ mass of cells ; 6 correct ref. to (proto-)oncogenes /tumour suppressor genes ; e.g. formation of oncogenes / mutation of tumour suppressor genes / ‘switching off’ tumour suppressing genes mutation of correct named gene = 2 marks e.g. mutation of tumour suppressor gene

Question 53

Explain the role of nitrogen fixation in the nitrogen cycle.

Answer 53

1 either converts, (inorganic) nitrogen/ dinitrogen/N2, into organic nitrogen/ ammonia/NH3 / ammonium/NH4 + ; R if nitrate given or lightning converts, nitrogen/ ammonia/NH3 / ammonium/NH4 + , into, nitrite/ nitrate (ions) ; 2 reduces nitrogen/ breaks triple bond ; 3 makes (fixed) nitrogen available to, legumes / other organisms / community / AW ; A ref. to amino acids / proteins not to be awarded if it follows nitrification 4 increase soil fertility ; 5 balances the loss of fixed nitrogen in, denitrification/ ocean deposits ; [

Question 54

Farmers in some parts of the world grow legume crops together with cereal crops in the same field. This is known as intercropping. Explain how intercropping results in an increase in the yield of the cereals when the legumes die.

Answer 54

idea of decay /decomposition ; e.g. breakdown by, (saprophytic) bacteria/ fungi 2 legumes eaten by, detritivores ; A named detritivores 3 decomposers produce proteases ; 4 to, hydrolyse/ convert/ change/AW, protein to amino acids ; 5 amino acids are deaminated ; 6 (amino acids) to, ammonia/NH3 / ammonium (ions)/NH4 + ; 7 nitrifying bacteria/Nitrosomonas, convert ammonia to nitrite (ions); 8 nitrifying bacteria/Nitrobacter, convert nitrite to nitrate (ions) ; if mp7 or mp8 not awarded allow one mark for the following as mp9 9 (named) nitrifying bacteria convert, ammonia/ ammonium, to nitrate (ions) ; mp10 only to be awarded following nitrification 10 nitrate (ions) used for making, amino acids / proteins (hence increase in growth of cereals) ;

Question 55

explain how the response to a second infection by this bacterial pathogen differs from the first.

Answer 55

faster ; in context of whole secondary response 2 memory cells; in context of production during the first response 3 idea that there are many more cells specific for this pathogen ; 4 (so) increases chances of encountering pathogens more quickly /AW ; 5 fast(er) production of, B lymphocytes / plasma cells / antibodies /helper (T) cells / cytotoxic T cells / cytokines ; 6 greater concentration of antibodies (in, blood/ lymph) or greater numbers of, B/ plasma, cells ; A more, antibodies / plasma cells /B cells 7 pathogen, removed/ killed, faster ; 8 person does not become ill/ no symptoms ; A pathogen does not, spread through the body / infect cells /AW

Question 56

Suggest how each of the following reduces the effectiveness of an immune response. (i) The number of T-lymphocytes is reduced in a person with HIV/AIDS.

Answer 56

little/ no/ slower/weak, immune response ; stated function of T-lymphocytes, does not occur/ occurs slowly ; e.g. release of cytokines / stimulating macrophages / stimulating B cells / killing infected cells high susceptibility to infectious diseases ;

Question 57

Suggest how each of the following reduces the effectiveness of an immune response Some pathogens are covered in cell surface membranes from their host

Answer 57

pathogen not recognised, as non-self/ foreign ; | pathogen is recognised as self ; A non-foreign

Question 58

Suggest how each of the following reduces the effectiveness of an immune response B-lymphocytes do not mature properly and do not recognise any antigens

Answer 58

no, antibodies /plasma cells / memory (B) cells, produced ; no humoral response ; no antigen presentation by B cells ;

Question 59

name of TB pathogen type of organism

Answer 59

Mycobacterium tuberculosis bacterium via, (airborne) droplets / aerosol(s) (infection) ;

Question 60

``` name of malaria pathogen type of organism mode of transmission ```

Answer 60

Plasmodium ; protoctist (feeding or biting by) Anopheles / mosquito ;

Question 61

what are the different modes of transmission of HIV

Answer 61

sexual intercourse/ passed via semen/ passed via vaginal fluids /AW ; blood transmission ; A described, e.g. blood transfusion sharing (contaminated), needles / syringes accept transmitted in body fluids for one mark if above two points not gained mother to, foetus / baby, transmission ; A described, e.g. across placenta/ during birth/ breastfeeding

Question 62

Explain why antibiotics do not affect viruses.

Answer 62

b) antibiotics (only) used against bacteria (and some fungi) ; idea that antibiotics act at a cell structure not possessed by virus ; e.g. viruses, do not have, a cell wall/ a cell surface membrane/ribosomes suggestion that viruses are, inside host cells / not within reach ; antibiotics act only on, living/ growing, cells (viruses do not grow) ; antibiotics do not act on, protein coat/ capsid/ capsomeres / viral envelope ;

Question 63

suggest the role of viral polymerase

Answer 63

replication of RNA/ to make copies of genes /AW ; transcription/ production of mRNA ; detail ; e.g. to make viral proteins ;

Question 64

outline how monnoclonal antibodies are made

Answer 64

immunise/ inject/AW, mice / small mammals, with /antigen ; immune response occurs / leave for a number of weeks ; A description harvest/ collect/AW, splenocytes /B-lymphocytes /B-cells / plasma cells ; fuse with, myeloma cells / cancer cells ; A tumour form hybridoma cells ; select for (hybridoma) cells secreting antibody against, /antigen ;

Question 65

An activated B-lymphocyte divides repeatedly by mitosis to produce many identical plasma cells. (i) Explain why it is important that many identical plasma cells are produced.

Answer 65

part of the immune response ; A primary / secondary, response many plasma cells 2 to produce high, concentration / level / AW, of, antibody / immunoglobulin ; 3 (high concentration antibody so) more effective against pathogens / AW ; identical plasma cells 4 specific / particular / AW, to an, antigen / epitope ; in context of antibodies or plasma cells 5 antibody (molecules) produced are all the same ; A ora, qualified 6 only the gene coding for particular antibody, switched on / transcribed / expressed ;

Question 66

Explain why tuberculosis (TB) is known as an infectious disease.

Answer 66

caused by, a pathogen ; 2 transmissible / communicable ; A passed from, person / animal, to person ignore contagious in context of tuberculosis 3 (pathogen is) a bacterium / Mycobacterium (tuberculosis / bovis) / M. tuberculosis / M. bovis ; 4 mode of transmission detail ; one from aerosol / droplet, infection / transmission in droplets, from (infected) person, exhaling / AW / coughing / sneezing / talking in droplets, / inhaled / AW, by (uninfected) person person, drinks (unpasteurized) milk / eats meat, from infected cattle A contaminated, milk / meat

Question 67

Outline the role of antibiotics in the treatment of infectious diseases, such as TB

Answer 67

kill bacteria / bactericidal ; A cause bacteria to, lyse / burst A destroy 2 (or) bacteriostatic / prevents bacterial growth / prevents bacterial replication; A ref. to preventing protein synthesis / inhibiting metabolic reactions 3 ref. to preventing spread (of bacteria) within body ; A prevents reservoir for re-infection 4 do not affect, human cells / human tissue / not toxic (to humans) ; 5 prevents death / consequences may be fatal if no antibiotic treatment / AW ; A ref. to, alleviating symptoms / faster recovery A restores good health / person feels well again / person cured 6 ref. to role in preventing, transmission / spread, of disease ; do not confuse with mp 3 ref. to (antibiotic) treatment of TB ; e.g. one of isoniazid, rifampicin (rifampin), pyrazinamide, ethambutol, streptomycin one of 6–12 months (latent), longer for active disease, two years or more for drug-resistant forms need combination treatment if active disease ref. to, MDR-TB / multidrug- resistant TB or XDR-TB / extensively drug-resistant TB 8 part of DOTS regimen / described ; (directly observed therapy short-course / direct observation treatment short course) [max 4]

Question 68

) Suggest what epidemiological evidence would lead to the conclusion that tobacco smoking is a risk factor for TB.

Answer 68

statistical, correlation / link / association, between smoking and TB ; AW A another valid suggestion in addition to mps 2-6 suggesting link 2 where TB, cases / death rates, are high tobacco smoking is also high ; 3 in areas where there is, no overcrowding / AW, smokers have higher number of TB cases ; 4 (ref. projects) death rates from TB reduced where patients stop smoking ; 5 higher cases TB in work places where smoking occurs ; 6 higher cases of TB in children living with parents who smoke

Question 69

Suggest and explain how the effects of smoking can increase the risk of becoming infected with TB

Answer 69

.1 lack of / paralysed / AW, cilia, so mucus, not wafted away / accumulates ; R dead cilia 2 pathogen / bacteria / Mycobacterium, remains in lungs / accumulates ; 3 ref. to increased opportunity / AW, for bacteria to, enter cells / infect ; 4 nutrients provided by excess mucus encourage growth ; AW 5 smoking weakens the immune system ; 6 detail ; e.g. fewer / less active / AW, phagocytes / macrophages

Question 70

List two treatments used by medical practitioners to treat coronary heart disease.

Answer 70

``` coronary bypass (surgery) / coronary artery bypass (graft) ; A bypass, surgery / graft / operation R heart bypass heart transplant ; angioplasty ; stent (insertion / AW) ; ```

Question 71

Define the term gene mutation.

Answer 71

change / alteration / AW, in sequence / order / arrangement, of, bases /nucleotides (of DNA / gene) ; change to give a new allele ; one additional detail ; (may result in) altered, changed / non-functioning / no, polypeptide / protein ref. to changed genetic code / different codons different sequence of amino acids / different primary structure named type of mutation example e.g. HbS

Question 72

Explain why existing vaccines may no longer be effective when the surface antigens of a disease-causing organism change.

Answer 72

ref. specificity ; in context of the immune response qualified ; e.g. existing , (B / T) lymphocytes / B-cells / T-cells, no longer activated / no recognition ora R if T lymphocytes produce antibodies existing plasma cells do not produce new antibody ora existing memory cells no longer activated / AW ora different / new, immune response required ora

Question 73

State precisely the type of immunity gained by a person who has been vaccinated.

Answer 73

artificial active

Question 74

Outline two reasons why measles is still common in many parts of the world, even though the vaccine is available.

Answer 74

ref. malnourishment / poor diet, vaccine ineffective / poor immune response / insufficient protein for antibody production ; 2 some (healthy) people do not respond to vaccines ; 3 one-dose not always effective / problems administering boosters ; AW 4 ref. percentage cover / herd immunity, insufficient ; A description A idea of people in rural areas have less / no, access to vaccine A people avoid vaccine, worry about side-effects / other reason 5 ref. cost to authorities ; e.g. of, administering vaccination programme 6 people in some areas cannot afford to buy vaccine 7 vaccine may not be thermostable ; AW 8 high density of population / overcrowding, increases chance of spread ;

Question 75

three ways food web turns to organic matter in the soil

Answer 75

excretion egestion ; death idea of shed body parts ; e.g. leaf fall/ shed petals / fruit drop/ moulting

Question 76

People with sickle cell anaemia have a form of haemoglobin that is unable to bind to oxygen efficiently. The cause of the condition is a mutation in the gene coding for the β-globin polypeptide of haemoglobin. Outline how this mutation can lead to an altered amino acid sequence of the β-globin polypeptide

Answer 76

nucleotide/ base, sequence of, DNA/ gene, changed/AW ; A new allele (formed) 2 base substitution (mutation)/(DNA) thymine replaced by adenine/(DNA is) CTC to CAC/CTT to CAT (template codon) ; this cannot be used for mp 1 as well 3 altered/ changed, mRNA codon ; (allow codons) A idea of different mRNA R altered genetic code 4 (mRNA codon is) GAG to GUG/GAA to GUA ; 5 glutamic acid, substituted/replaced/AW, by valine ; A glutamate A glu and val 6 tRNA/ anticodon, with different amino acid (to ribosome) ; A tRNA with different anticodon 7 AVP ; e.g.amino acid substitution at position 6 valine, hydrophobic /AW (R-group) glutamic acid, polar/AW (R-group)

Question 77

Discuss the factors that should be considered when making recommendations concerning the prevention of sexual transmission of HIV. and solutions

Answer 77

(geographical) availability of condoms so condoms should be available (in all relevant locations) ; where available, insufficient stock of condoms condoms should be stocked in sufficient quantities ; condoms (available but) unaffordable free/affordable, condoms (should be provided) ; A condoms should be provided; low level/ no, advertising campaigns for condom use ref. advertising campaigns for, condom use/ safe sex /protective sex ; poor condom storage (idea of deterioration) safe storage of condom supplies (to avoid deterioration) ; lack of education in, use of condoms / how HIV is spread/other relevant R low level of awareness of HIV/ lack of education about HIV ref. education ; e.g. should use condoms / proper use of condoms A (should practice) safe sex / protective sex ; low level of (interest in) condom use or, religious / cultural, objections A few people use condoms ref. changing perception of people to encourage use (of condoms) ; identifiable, high risk / named high risk, groups e.g. sex workers, (male) homosexuals, multiple partners, IV drug abusers (in context of sexual activity) idea of targeting, high risk / named high risk, groups ; e.g. sex workers, homosexual males, multiple partners, IV drug abusers IV drug abusers (in context of sexual activity) low rate of male circumcision encourage circumcision procedure/ train health personnel ; poor treatment of sexually transmitted infections treatment of sexually transmitted infections (as risk of contracting HIV increases) ; no/ poor/AW, antiretroviral therapy ref. antiretroviral therapy reducing risk of sexual transmission ;

Question 78

role of t hlper cells

Answer 78

``` release/AW, cytokine/ lymphokine/ interleukin ; stimulate/AW, humoral/B-lymphocyte/ B-cell, response ; humoral/B-lymphocyte/B-cell, response not stimulated ; (stimulate B-cell response so) antibodies produced ; A secreted/released R if antibodies from T-cells stimulate/AW, A (result in) angry macrophages A make macrophages more active (in phagocytosis) remain in circulation for second encounter with antigen ; AW ```

Question 79

Suggest how whooping cough is transmitted

Answer 79

1 aerosol/ droplet, infection ; only need to have one of ‘infected’/ ‘uninfected’ to gain mps 2 and 3 2 infected/AW, person, coughs / breathes / spits / talks / sneezes ; 3 uninfected/AW, person, inhales / inspires / breathes in, droplets ; 2/ 3 allow one mark if mps 2 and 3 given with no reference to, infected/ uninfected 4 organism/ pathogen/bacteria/B. pertussis, in, airborne droplets / droplets in air ; A without ‘airborne’ or ‘in air’ if mp 2 gained

Question 80

Suggest how phagocytes can recognise the difference between healthy body cells and cancerous tumour cells.

Answer 80

healthy body cells, (recognised as) self/ have self-antigens ; A non-foreign 2 cancer(ous)/ tumour, cells, (recognised as) non-self/ have non-self antigens ; A foreign 3 idea that changes occur to structure of cell surface membrane of, cancer(ous)/ tumour, cells ; 4 phagocytes have receptors for, non-self/ foreign, antigens or phagocytes have receptors for antibody complexed to non-self/ foreign antigens ;

Question 81

Only a small proportion of the light energy striking the leaves of producers becomes converted to chemical energy. The proportion that is converted is known as the photosynthetic efficiency (PE). (i) Outline the possible reasons why a large proportion of light energy striking the leaves of plants is not converted into chemical energy.

Answer 81

energy losses from 1 reflection (from leaf surface) ; 2 idea that some light, passes through (leaf)/ misses chloroplasts / strikes non-photosynthetic tissue ; A suggestion that cell walls may not allow all of light through 3 heating plant ; I lost as heat to surroundings A converted to heat 4 evaporation ; A transpiration 5 not all light (reaching chlorophyll) is, the right wavelength (for photosynthesis)/AW/ absorbed by chlorophyll ; A idea that only a proportion of light energy is useable A absorbed and, lost as phosphorescence/ lost as luminescence/re-emitted 6 ref. to photosynthetic process inefficient ; A loss of heat energy during photosynthesis 7,8 AVP ;; e.g. ref. to photorespiration ref. to factors that limit photosynthesis

Question 82

Only a small proportion of the light energy striking the leaves of producers becomes converted to chemical energy. The proportion that is converted is known as the photosynthetic efficiency (PE). Suggest the advantages of growing crops with high PE for food production or for biofuel.

Answer 82

increased production of / more, biomass / plant matter / named (e.g. carbohydrate / cellulose / starch / oils) ; R more plants I more crop I food 2 (so) more energy / more energy stores ; A more chemical energy produced A higher energy A suggestion that high PE crop may be more energy dense 3 more crop / greater yield, per unit, area / volume / time ; A each year 4 idea of (comparatively) less space required (for growing) ; 5 ref. to supplying increasing demand for, food / fuel ; 6 more, profit (for farmers) / economic / AW ; I cheaper 7 AVP ; e.g. efficient use of carbon dioxide

Question 83

``` Name two organic compounds containing nitrogen that are made by plants and state one function of each in plant growth. ```

Answer 83

mino acids production of proteins (for cell growth); A provide energy / for respiration proteins cell division/ mitosis / increase in cell number/ increase in, biomass or yield/(cell) membranes ; A reproduction A cell cycle A (tissue) repair A provide energy / for respiration enzymes synthesis of, macromolecules or organic molecules / anabolic reactions / for photosynthesis / for respiration ; [max 2] A named molecules e.g. carbohydrates / amino acids / proteins / lipids / nucleic acids (organic / nitrogenous) bases component/ synthesis of, nucleotides component of, DNA/RNA/ nucleic acids ; nucleotides component/ synthesis of, DNA/RNA ; DNA ref. genes /genetic material/ coded information/ genetic information, (for protein synthesis) ; RNA ref. transcription/ translation/ protein synthesis ; (some) phospholipids (for cell) membranes ; R lipids ATP synthesis / anabolic reactions /active transport/ translocation/ described ; A provide energy for reactions chlorophyll photosynthesis / light (dependent) stage ; NADP (in) photosynthesis / light (dependent) stage ; NAD (involved in) respiration ; FAD (involved in) respiration ; auxin growth hormone/ cell elongation/ cell division ; cytokinin growth hormone/root growth ;

Question 84

Planning the prevention and control of a disease using a vaccination programme means that financial costs must be considered. State two examples of these costs.

Answer 84

1 preparing/ manufacturing/ purchasing, vaccine ; A cost to provide vaccine free to developing countries 2 disposables / equipment to administer (vaccine) ; e.g. syringes / needles /(protective) gloves 3 storage ; e.g. space, security 4 refrigeration/ maintaining cold chain ; 5 transport (of, vaccine/ health care workers) ; 6 wages / training, of staff involved ; e.g. wages for, health care workers administering vaccine/ staff involved in training health care workers 7 record keeping/ contact tracing ; 8 advertising/ informing/ marketing/education ; 9 research/ development ; 10 setting up vaccination/ immunisation, camps (for remote/ epidemic, areas) ; I building, hospitals / clinics

Question 85

Explain what is meant by a gene.

Answer 85

treat as neutral unit of inheritance sequenceof, nucleotides /bases ; section/ length/ part, of DNA (molecule) ; codes for a polypeptide ; A protein for polypeptide A enzyme A information to produce a polypeptide A codes / information, for sequence of amino acids / primary structure (of a, polypeptide/ protein) R genetic code for a polypeptide

Question 86

Outline how a gene mutation can lead to the formation of an altered polypeptide where one amino acid is replaced by a different amino acid.

Answer 86

(in DNA/ gene) altered, sequence/AW, of, nucleotides / bases ; I DNA sequence 2 base substitution or base/ nucleotide, replaces another, base/ nucleotide; A example must be in context of, DNA/ gene 3 (mRNA synthesised) during transcription ; 4 (mutation leads to) altered/AW, mRNA/ messenger RNA ; 5 (only) one (mRNA) codon changed/ a different codon ; A one DNA, triplet/ codon, changed I ref. to codons changed 6 tRNA, with / has, a different anticodon ; 7 (tRNA) brings, a different/ a changed/ the incorrect, amino acid, during translation/ to the ribosome ; 8 codon-anticodon, binding/ complementary /AW ; A matches R amino acid with anticodon

Question 87

Explain how natural disasters can sometimes result in transmission of communicabl diseases to more individuals.

Answer 87

general ref. to problems associated with increased numbers of people and lack of infrastructure ; examples ;; e.g. problem providing, safe / uncontaminated, drinking water ; faeces / sewage, mixing with drinking water ; A no / poor, sanitation unable to practise good hygiene ; A example e.g. hands not washed after defaecation infected people sharing latrines with uninfected / AW ; lack of, medical care / treatment, leading to larger pool of infected people (at any one time) lack of, health services / drugs / antibiotics / ORT / skilled personnel unable to supply sufficient vaccines lack of food / poor diet, so vaccines less effective credit relevant examples linked to a particular type of disaster

Question 88

Explain why the Plasmodium parasites were killed using radioactivity and not by using high temperatures.

Answer 88

ref. vaccines contain antigens ; 2 antigens are (mostly), proteins / glycoproteins ; 3 antigens, denatured by heat / not denatured by radioactivity ; A proteins denatured in context of antigenic proteins R parasite is denatured 4 detail e.g. loss of tertiary structure / bonds break ; 5 shape to be maintained for specificity of immune response / AW ; 6 AVP ; e.g. ref. to production of memory cells (for immunity)

Question 89

explain why the researchers decided to use the form of the | parasite which is injected by mosquitoes and not the form which leaves the liver.

Answer 89

1 first form of, pathogen / parasite, free / exposed, in plasma ; A not inside cells 2 second form of, pathogen / parasite, concealed / hidden, in liver / red blood cells ; for either mp 2 or 3 3 ref. to degree of exposure to antibodies / lymphocytes idea that 4 fewest number of parasites to destroy / earlier defence always more effective ; 5 vaccination against form leaving liver would, not protect against liver invasion / still cause liver damage ; 6 AVP ; e.g. suggestion that first form of parasite is easier to harvest

Question 90

Outline the events that occur following injection of the parasites, which lead to the production of antibodies

Answer 90

1 primary (immune) response / artificial active response ; 2 antigen presentation / described ; 3 clonal selection / described ; e.g. A specificity to malarial antigen 4 clonal proliferation / B-lymphocyte division by mitosis / AW ; A B cell 5 detail of changes occurring from B-lymphocyte to plasma cell ; 6 B-lymphocytes / B cells / plasma cells, produce antibody ; 7 correct ref to role of Th cells in context ;

Question 91

commmunity

Answer 91

all populations of all species within a specified area / AW, at a particular time ;

Question 92

describe the features of producers.

Answer 92

photosynthetic / carry out, photosynthesis / carbon fixation ; A autotrophic 2 conversion of light energy to chemical energy ; 3 equation ; 4 have light-absorbing pigments ; A chlorophyll 5 ref. to independence or dependence of other organisms ; in context of energy 6 ref. to input of energy to ecosystem ; 7 base of the food chain(s) / first trophic level / AW ; A consumed by, herbivores / primary consumers

Question 93

In the wild, only about 10% of the energy taken in by the catfish in their food is used to increase biomass. Suggest why this percentage is lower in the wild than in the pond

Answer 93

more confined space so less movement ; move more so greater energy loss (through respiration / as heat ) ; more predators so use more energy escaping from them ;

Question 94

Dead animal and plant material can also contribute to the pool of inorganic nitrogen in soil. Describe how this happens.

Answer 94

decomposition/decay ; A reference to decomposers saprotrophs / bacteria/ fungi ; A detritivores digest/ breakdown/ hydrolyse, organic nitrogen/ protein/ amino acids / urea ; protease/urease ; deamination ; production of ammonium (ions)/ ammonification ; nitrification/ammonium (ions) to nitrate (ions) ;

Question 95

Nitrogen and phosphate are both cycled more rapidly in ecosystems where there are high rates of growth within trophic levels and high rates of energy flow between trophic levels. With reference to the use of both nitrogen and phosphate in organisms, explain this statement.

Answer 95

growth linked to, increase in cell size/ cell number ; 2 growth linked to, increase in biomass /reproduction ; 3 increases energy available as food for next trophic level ; 4 nitrogen is in, amino acids / proteins, for growth ; 5 ATP (containing phosphate) required for, transcription/protein synthesis / enzyme synthesis / anabolic reactions /growth ; 6 idea that, growth of cells / cell division, requires membrane synthesis ; 7 nitrogen in membrane proteins / phosphate in membrane phospholipids ; 8 (cell division and), DNA, synthesis /replication ; 9 idea that more biomass (per unit time) returned to soil ; 10 AVP ; e.g. ref. to phosphate taken up by plants and passed into food chain

Question 96

Define the terms: | (i) vaccination

Answer 96

1 (method to) stimulate/AW, an immune response ; A gives immunological memory 2 giving/AW, antigens ; 3 (method to provide long-term) artificial active immunity ; 4 one relevant detail ; e.g. no ability to cause disease ref. to, harmless /AW, form of pathogen used (protection through) production of (specific) memory cells (contains, pathogen/antigen) in an injection or an oral dose A (to provide long-term) artificial active immunity if not already credited in mp 3

Question 97

communicabe disease.

Answer 97

(disease) caused by, a pathogen/ microorganism ; A two of bacteria, virus, fungus, protoctist one relevant detail e.g. transmissable/ communicable/ passed from one organism to another/AW ; A spread to others if qualified affecting the normal function of the body / causing ill health ;

Question 98

Suggest why TB is more likely to be fatal in people who have HIV/AIDS than in those who do not have HIV/AIDS.

Answer 98

(HIV/AIDS leads to) weak immune system/reduced immunity (to disease) ; detail ; e.g. reduced action of phagocytes Th lymphocytes low in number B-lymphocyte response low (so TB) pathogens, can multiply faster/ are not destroyed before they cause disease ; idea that important, organs / systems, may already be suffering from consequences of HIV/AIDS (so more likely to stop functioning) ; ref. to, inactive/dormant/ latent, TB more likely to become active ;

Question 99

Suggest advantages of Rhizobium living in root nodules of leguminous plants.

Answer 99

idea that Rhizobium will receive, photosynthates /assimilates (from plant) ; gains, carbohydrate/ amino acids ; for energy / growth/replication ; receives oxygen ; idea of (nodules provide) correct living conditions /ideal habitat/ anaerobic conditions (for nitrogenase)/AW ; A ref. to protection, qualified mutualistic relationship ; A described

Question 100

Explain the role of Rhizobium in the growth of leguminous plants.

Answer 100

involed in nitrogen fixing and the production of, ammonium/NH4 + / ammonia/NH3 ; (fixed/ useable) nitrogen transferred to plant ; used for amino acid production (in plants) ; ref. to other uses relevant to growth ; e.g. in DNA replication/transcription increased/used in, protein synthesis ; A named protein (for) production of new, cells / tissues ;

Question 101

Some transcription factors may prevent transcription. | Suggest two ways in which they may do this.

Answer 101

may prevent breaking of hydrogen bonds between, base pairs / bases /nucleotides, (and access of RNA polymerase) ; attachment of, RNA polymerase (to DNA) ; progress / functioning, of RNA polymerase (along gene) ; synthesis / elongation of (pre) mRNA ; AVP ; e.g. interfere with action of helicase

Question 102

Suggest why plasma cells contain a large quantity of rough endoplasmic reticulum.

Answer 102

(endoplasmic reticulum/RER) has ribosomes ; (ribosomes /RER) site of protein synthesis ; antibodies are proteins ; RER for, modification/transport/ transport vesicle formation ;

Question 103

(e) State two reasons why the vaccination programme was successful in eradicating smallpox

Answer 103

two relevant e.g. 1 vaccine, thermostable/ freeze-dried ; A idea of longer shelf-life/ no wastage 2 virus did not mutate ; A pathogen/ strain 3 same vaccine could be used everywhere ; 4 cheap to produce (in large quantities) ; 5 ease of production ; 6 used a live virus / vaccine gave a strong immune response ; 7 no need for boosters ; 8 ease of administration ; e.g. ref. to enthusiastic volunteers needles could be, sterilised/re-used 9 high percentage cover/AW ; 10 ref. to ring vaccination/ described ; 11 global effort/AW

Question 104

Explain how a single dose of vaccine can provide immunity for up to 10 years when the plasma cells are short-lived.

Answer 104

memory cells produced (along with plasma cells) ; to max 2 idea of greater number of (specific immune system) cells ; (memory cells are) long(er) lived/remain in circulation ; memory T and B cells ; ref. to/ detail of, faster secondary response (to give immunity) ;

Question 105

Describe how nitrogen in nitrate can be returned to the atmosphere in the form of nitrogen gas.

Answer 105

by bacteria ; denitrification/reduction; ref. anaerobic conditions ; A ref. to waterlogging

Question 106

) ecosystem

Answer 106

``` idea of (unit made up of ) biotic and abiotic, components ; AW further detail ; interacting/ functioning together ; A idea of self-sustaining unit ```

Question 107

Explain what is meant by the term non-self antigens.

Answer 107

non-self foreign / AW ; A not from the person’s own body triggers / AW, an immune response/production of antibodies ; A other events in immune response described antigen protein/ glycoprotein ; A polysaccharide ref.to, binding of specific antibody /formation of antigen-antibody complex ;

Question 108

During the first few years after the introduction of streptomycin treatment, an increasing number of M. tuberculosis bacteria developed resistance to streptomycin. Outline how this happened.

Answer 108

incomplete treatment/ dose not finished ; 2 not all bacteria killed/ some bacteria survive ; R TB for bacteria 3 mutation ; R mutation to give immunity 4 further detail of mutation ; 5 selection of resistant bacteria/resistant bacteria selected for ; 6 resistant bacteria reproduce/ vertical resistance ; 7 death of, susceptible/ non-resistant, bacteria ; 8 AVP ; e.g. horizontal resistance/described

Question 109

describe the modes of action of the two cells in defence against infectious diseases. phagocyte

Answer 109

phagocyte move to sites of infection ; ingest / engulf / pseudopodia enveloping / phagocytosis of / endocytosis of, bacteria / microbes / pathogens / AW ; R antigens, virus (form) phagocytic / endocytotic, vacuoles ; A vesicles, phagosomes ref to lysosomes ; enzymes / named (hydrolytic) enzymes ; digest / hydrolyse, (bacteria / AW) ; antigen presentation / description ;

Question 110

describe the modes of action of the two cells in defence against infectious diseases. plasma cell

Answer 110

produce / secrete / release / synthesise , antibodies ; A make into, plasma / tissue fluid / lymph ; A blood antibodies are proteins ; ref to, RER / ribosomes ; specificity qualified e.g. of, antibodies / lymphocyte / plasma cell or description e.g. each type of plasma cell produces one type of antibody ; Golgi (body) packages antibodies / ref to formation of (Golgi) vesicles ;

Question 111

Explain why the antibiotics used to treat TB are taken in combination over a long period of time.

Answer 111

(bacteria likely to be) resistant to (at least) one antibiotic (so useless) ; less likely to be resistant to all / chance that bacteria will develop resistance to all antibiotics used is very small ; ref to mutation / change to DNA ; (bacteria are) inside cells where protected from antibiotics ; (mycobacteria) divide / grow, slowly ; ensures all bacteria killed / reduces below critical level ; otherwise, bacteria remain / reservoir of infection ; (so) prevents development of antibiotic resistance ;

Question 112

Describe the roles of T-lymphocytes in a primary immune response

Answer 112

helper cells secrete / release / produce, cytokines / lymphokines / hormones ; to stimulate B cells to, divide / develop into plasma cells ; (which) produce antibodies ; stimulate macrophages to carry out phagocytosis ; cytotoxic / killer T cells seek out / find / bind to, (foreign) antigens, on host cells / pathogens ; destroy, virally infected host cells / intracellular parasites / viruses ; attach to surface of cells / ‘punch holes’ into cells / disrupt cell surface (plasma) membrane; (release) toxic substances / hydrogen peroxide (into cells) / interferons ;

Question 113

Describe three functions of cell surface membranes,

Answer 113

control of entry and exit of substances ; barrier to, polar molecules / water soluble molecules ; adhesion ; idea of retaining, large molecules / cell contents; allow substances across, passively / by diffusion ; ref to channel proteins ; A pore allow transport protein once move substances through carrier proteins ; active transport ; ref to facilitated diffusion ; endocytosis / exocytosis / phagocytosis / pinocytosis ; recognise, hormones / neurotransmitters / chemical signals ; sites of chemical reactions / sites for enzymes ; the recognition of antigens

Question 114

Explain why malaria is restricted to the tropics

Answer 114

transmitted by, Anopheles / mosquito / (insect) vector ; P. falciparum / parasite, needs, warm / hot, temperatures / >20oC, to complete its life cycle (in the mosquito) ; requirement for areas of still water (ref. mosquito life cycle); eradicated in areas outside tropics (e.g. North America)

Question 115

Describe how antibodies provide protection against pathogens

Answer 115

secreted / synthesised / produced / released, by, plasma cells / B lymphocytes / B cells ; 2 combines / AW, with, antigens / pathogens / toxins / viruses / bacteria / microbes ; A ‘bonds with’ / ‘sticks to’ / ‘attaches to’ R ‘disease’ 3 ref to, specificity / described ; in context of antibody / B cells / antigen 4 variable region is antigen binding region ; R ‘receptors on antibodies’ 5 neutralises toxins / antitoxin(s) ; 6 lysis of pathogens / described / lysin(s) ; R breaks down 7 prevents viruses entering cells ; 8 clumps / agglutinates / aggregates / AW, bacteria ; R ‘coagulation’ 9 opsonisation / opsonins ; A enable recognition 10 coats / AW, bacteria to facilitate phagocytosis ; only in context 8 or 9 11 receptors on phagocytes for constant regions (of antibodies)

Question 116

Discuss the problems in attempting to control the spread of HIV/AIDS

Answer 116

1 no (effective) vaccine ; 2 HIV has a high mutation rate ; 3 antigens change / different antigens / different strains ; 4 no cure ; 5 drugs, are expensive / not widely available / not effective / AW ; 6 vertical transmission / mother to child ; problems with: 7 symptomless carriers (spreading the virus) ; 8 testing people for HIV status ; 9 providing, condoms / femidoms ; 10 promiscuity ; 11 educating about risks / AW ; 12 reuse of needles ; 13 tracing contacts (of infected people) ; 14 testing / screening, blood donations ; 15 treating, blood / blood products, to, destroy / inactive / ‘kill’, HIV ; 16 ref to cultural issues ; accept relevant examples 17 ref to poverty ; 18 AVP ; e.g. war / civil disturbance, out of date drugs, ref to transport links ignore resistance of HIV

Question 117

Explain why the energy efficiency between secondary and tertiary consumers is greater than that between producers and primary consumers

Answer 117

1 some parts inedible ; 2 indigestible / cannot digest cellulose or lignin ; 3 more material goes to decomposers (rather than consumers) ; 4 plant material is less energy rich / animal flesh is more energy rich ; 5 manipulated data in support ; e.g. ×2 to decomposers from producers 0.8% (energy available to primary consumers divided by the energy available to plants)

Question 118

Describe the roles of decomposers in recycling nitrogen

Answer 118

protein → ammonia / ammonium ions = 1 mark 1 convert protein → amino acids ; 2 deamination ; 3 urea / amino acids → ammonia / ammonium ions ; A ammonification 4 make, ammonia / ammonium ions, available to nitrifying bacteria ; A role of nitrifying bacteria / correctly named

Question 119

Very little of the energy consumed by grazing animals is available to carnivores. State two reasons why this is so

Answer 119

loss (of energy-containing food in producers or in grazers) in indigestible parts / not being absorbed / faeces / egestion ;; one mark for producer, one mark for grazer excretion (in, grazers / herbivores / primary consumers) ; respiration (in, grazers / herbivores / primary consumers) ; loss of energy in movement / AW (in, grazers / herbivores / primary consumers) ; AVP ; e.g. heat energy

Question 120

State why lung cancer is categorised as a non-infectious disease

Answer 120

not transmissible from one person to another / AW ; | not caused by a pathogen ; R bacterium / virus / fungus / AW / ‘worm’

Question 121

Explain the roles of the cells in an immune response

Answer 121

foreign / AW, antigens are non-self ; non-self / foreign antigens, induce immune response ; AW ora macrophage / APC (A) phagocytosis / described ; cuts up / AW, bacterium / pathogen ; presents antigens / becomes antigen presenting cell / antigens on cell surface ; B/T, cells (B and C) antigen recognition by lymphocytes ; (with) complementary / specific, receptors / immunoglobulins (B) / antibodies (B) ; divide by mitosis ; A clonal expansion ref. formation of memory cells (for secondary response); Th cells (C) secrete cytokines to stimulate B cells ; cytokines stimulate macrophages ; Tc/k cells (C) ref. destroy pathogen / AW ; produce perforin / AW ; B cells (B) B cells become plasma cells ; (plasma cells) secrete antibodies ; AVP ; e.g. macrophages, non-specific / faster response ref. specificity of, lymphocytes / B and T cells antibody variable region is the antigen binding site

Question 122

Describe how mitosis is involved in an immune response

Answer 122

occurs in both primary and secondary (immune) responses ; selected / specific / AW ; lymphocytes / B -cells / T-cells / divide (by mitosis) ; clonal expansion / described in terms of producing, clone / many cells ; A idea that different types of immune cell can result reference mitosis in memory cells (for rapid) secondary response ;

Question 123

how macrophages function to protect the lungs from becoming infected

Answer 123

1 recognise, non-self / foreign, antigens, (on pathogen) ; 2 receptors (on macrophage) bind antigens (on pathogen) ; 3 (or), pathogen / AW, adheres / ‘sticks’, to (cell surface) membrane ; 4 infolding of (macrophage cell surface) membrane around / engulf / phagocytosis of, pathogen ; R engulf antigen 5 vacuole / vesicle / phagosome, forms ; 6 ref. to lysosomes ; 7 hydrolytic / digestive / named, enzymes ; e.g. lysozyme / protease / nuclease A pathogen broken down by enzymes 8 hydrolysis of named compound(s) ; 9 ref. to destroying / killing, pathogen ; 10 ref. to antigen presentation ; accept idea even though does not occur in alveoli

Question 124

what is meant by keystone species

Answer 124

changing numbers of keystone species has (large) effect on the rest of the ecosystem ;

Question 125

autotroph

Answer 125

carries out photosynthesis/photosynthetic ; A acts as a producer synthesises (complex) organic compounds from inorganic, compounds ; uses light energy ;

Question 126

heterotroph

Answer 126

obtains energy from, complex/organic, compounds ; A insects/animals ref. digestion/absorption soluble products ; AW acts as a consumer/feeds on other organisms ;

Question 127

Suggest how a change in the amino acid sequence of the enzyme results in antibiotic resistance.

Answer 127

change in, tertiary / quaternary, structure (of enzyme) ; A change in polypeptide, folding / coiling ; (enzyme) binding site for antibiotic, lost / changes shape ; R active site unless clear that substrate binding and catalytic site remains unchanged antibiotic / nalidixic acid, cannot bind (so enzyme remains active) ; allow ecf for active site

Question 128

Discuss the consequences of multiple resistance for health authorities

Answer 128

risk of, further spread / wider epidemic, (from people still infected) ; AW 2 reduces chance of succesful treatment / higher death rates ; 3 increased, treatment / hospitalisation times ; A takes longer to treat A more complex treatment 4 increased costs of treatment / strain on health budget / AW ; 5 risk of, further resistance / resistance to all antibiotics ; 6 fewer antibiotics left that are effective ; A risk that no antibiotics will be left to successfully treat 7 need to find, new antibiotics / alternative treatment ; A difficulty in finding new treatments / AW 8 (so) cost of research ; allow cost once 9 AVP ; e.g. strain on, resources / health personnel, to treat other diseases need to identify type of resistance so that effective treatment is given education, qualified [4]

Question 129

Suggest how the binding of monoclonal antibody to the diseased cells causes their destruction by cells of the person’s immune system.

Answer 129

four from 1 ref. to monoclonal antibody, is recognised as, non-self / foreign ; or diseased cell (now) recognised as non-self / foreign ; 2 stimulates an immune response ; max three suggestions from 3 recognition and binding by / activation of / AW, T-lymphocytes / B-lymphocytes / AW ; A clonal selection A T- / B-, cell 4 ref. to specificity so healthy cells not destroyed ; 5 clonal expansion / mitosis ; 6 plasma cells (formed that) secrete antibody ; A B-lymphocyte 7 consequence ; e.g. antibody binds monoclonal antibody to lead to cell destruction 8 T-helper lymphocyte secretes cytokine, to activate macrophages / B-lymphocyte response / T-killer response ; AW e.g. stimulates humoral response 9 T-killer / T-cytotoxic, releases, perforin to, punch holes in (cell) membrane / cause death of cell ; AW 10 detail of involvement of phagocytes / macrophages ; e.g. receptor recognition of (monoclonal) antibody engulf the diseased cells with monoclonal antibody attached / AW A diseased cell (with monoclonal antibody) destroyed by phagocytosis [4]

Question 130

Explain the term auto-immune disease.

Answer 130

one of failure to distinguish self and non-self (antigens) ; A foreign for non-self immune response / antibodies produced, against self antigens ; in context of lack of good health R does no harm [1]

Question 131

Apart from a cost benefi t, suggest one advantage of using immobilised phosphatase to produce dephosphorylated DNA.

Answer 131

enzyme / phosphatase, can be reused ; enzyme / phosphatase, easily recovered ; enzyme / phosphatase, doesn’t contaminate, DNA / product ; less purifi cation of product / DNA, required ; A less downstream processing required enzyme / phosphatase, longer shelf life / AW ; enzyme / phosphatase, more stable to, temperature / pH

Question 132

State one way of immobilising an enzyme

Answer 132

in (sodium) alginate (beads) / encapsulation ; A other named methods, e.g. entrapment / trapped in pores of silica gel adsorption onto, clay / glass / resin (within) polymer / partially permeable membrane, microspheres covalent bonding to support, material / collagen

Question 133

B-lymphocyte activation can occur as a result of direct contact with a specifi c antigen on the invading pathogen. State two other ways for the B-lymphocyte to become exposed to the antigen.

Answer 133

antigen-presenting cell ; A description e.g. macrophage that has phagocytosed pathogen and has antigens on surface vaccine containing antigen ;

Question 134

Suggest why antibodies need to be globular proteins

Answer 134

soluble in, blood / plasma / tissue fl uid / lymph ; tertiary / quaternary, structure allows formation of, variable site ; AW idea of easier to transport (than fi brous proteins)

Question 135

With reference to antibody structure, explain what is meant by quaternary protein structure.

Answer 135

more than one, polypeptide ; (antibodies have) two heavy and two light, polypeptides / chains ;

Question 136

Name the type of cell used to produce monoclonal antibody.

Answer 136

hybridoma (cell)

Question 137

) Phagocytic cells contain many lysosomes. | Describe the function of lysosomes in destroying ingested bacterial cells.

Answer 137

lysosomes fuse with, vacuole / vesicle / phagosome ; A form secondary lysosomes lysosomes contain, enzymes / named digestive enzyme ; (catalyse) hydrolysis / digestion ; A breakdown (digests / breaks down) protein / murein (or peptidoglycan) / carbohydrate / lipid / phospholipid / nucleic acid / DNA / RNA ; named bond ; e.g. peptide, glycosidic, ester, phosphodiester [4 max]

Question 138

community

Answer 138

all populations / all organisms / all plants + animals (+ microorganisms) ; R all the species in same, place / ecosystem / area / (common) habitat, (at same time) ;

Question 139

Explain the significance of the following statements in the control of malaria. (i) The female Anopheles mosquito has been more closely studied with regard to malaria than the male Anopheles mosquito

Answer 139

(only) female feeds on blood / male does not feed on blood ; female requires blood (protein) for (development of) eggs ; (only) female carries, pathogen / disease-causing organism / Plasmodium / parasite ; A (only) female transmits the disease (only) female is vector ; ora ignore female carries, the disease / malaria

Question 140

Explain the significance of the following statements in the control of malaria.The infective stages of the malarial organism are present in anti-coagulant produced by the mosquito.

Answer 140

anti-coagulant (in saliva) is passed when mosquito, sucks blood / feeds / bites / takes a blood meal ; anti-coagulant prevents blood clotting when mosquito, sucks blood / feeds / bites / takes a blood meal ;

Question 141

Explain the significance of the following statements in the control of malaria After circulating in the blood for a short time, the pathogen enters liver cells of the newly infected person and then enters red blood cells.

Answer 141

in marking accept Plasmodium / pathogen / causative organism / malarial organism where parasite is given below short time (in blood plasma) for exposure to cells of the immune system / AW ; next stage(s) of life cycle inside cells ; A sporozoites into merozoites in liver / merozoites into schizonts in red blood cells parasite gains, food / energy, from cells ; parasite, reproduces / multiplies, inside (liver / red blood) cells ; damage to / bursting of / lysis of / impaired function of, cells ; (antimalarial) drugs cannot penetrate (liver / red blood) cells ; parasite, concealed / ‘hides’, from host immune system ; A antigen concealment ; no symptoms, until parasite leaves cells / while parasite is in cells ; idea that people incubating disease are symptomless ; A symptomless carriers idea that treatment unlikely to prevent spread from infected person ; AVP ; examples different stages provide problems with drug / vaccine development AVP ; mode of action of potential drugs – block attachment sites on cells parasite in blood cells allows testing by taking blood samples further development of any idea given above

Question 142

Discuss the factors that determine the distribution of malaria worldwide

Answer 142

(mainly in) tropics / between the tropics or any two named, areas and/or countries, affected ; e.g. areas (sub-Saharan) Africa, Central America, South America, South Asia, Central Asia, Middle East, Caribbean e.g. countries India, Sri Lanka, China, Vietnam, Cambodia, Brazil, Kenya 1 (areas where) both parasite, and, vector / mosquito / Anopheles, are present ; 2 Anopheles / mosquito / vector, survives / breeds / lives, in, hot and humid areas / moist tropical areas ; ora A standing / stagnant, water 3 parasite, needs to reproduce within the mosquito (at temperatures above 20°C) ; 4 eradicated in some countries / any e.g. (USA, Italy) ; 5 ref to LEDCs and, poor / non-existent, control programmes ; A poor health facilities / poor drug supplies / AW 6 mosquitoes resistant to, DDT / insecticides / pesticides ; 7 parasite resistant to, chloroquine / drugs ; 8 link between human population density and Anopheles ; e.g. human activity provides (lots of) breeding sites for Anopheles 9 occurs where named high risk group(s) exist ; e.g. refugees, HIV-positive pregnant women (more likely to pass HIV to unborn children), (young) children 10 (outside tropics) disease spread by, travellers / tourists / migrants / refugees ; 11 AVP ; most cases / over 90% cases, in (sub-Saharan) Africa not, at high altitude / in deserts different species of Plasmodium differ in geographical distribution / AW misdiagnosis (so not reported) changing pattern linked to, global warming / changes in land use / deforestation / irrigation / other relevant named R references to sickle cell

Question 143

x Suggest an explanation for the fact that a different mixture of enzymes is required to remove the walls of plant cells compared to the walls of fungal cells.

Answer 143

idea that plant cell walls and fungal cell walls have different components fungal cell walls made of, glucans / chitins / fungal cellulose / different components to plant cell walls ; A peptidoglycan / murein A plant cell walls contain cellulose, but fungi do not idea of specificity in context of question enzymes are specific ; A specificity explained e.g. both substrates not complementary / shape of active site specific to one substrate

Question 144

Explain why the person is unlikely to become ill if they are infected by the same pathogen some months later.

Answer 144

active (artificial) immunity ; 2 memory cells / immunological memory ; 3 idea that many specific, B-cells / T-cells / lymphocytes, in the body ; A large(r) clones of specific, B- / T-cells or lymphocytes actual invasion by the pathogen 4 fast secondary (immune) response ; 5 fast increase in antibodies / immediate production of antibodies ; ignore incorrect type of cell secreting antibodies 6 high(er) concentration of antibodies are produced ; A more antibodies produced 7 pathogen destroyed before person becomes ill / AW ; R antigen A pathogen do not, increase in number / infect cells / AW

Question 145

Some parents decide that their children should not take part in a vaccination schedule. Suggest how a country-wide vaccination schedule can give protection against infection to unvaccinated children.

Answer 145

(if) most / sufficient / many / AW, people / children, immunised / vaccinated ; A herd immunity reduces the pool of infected, people / children, in the, community / population ; A fewer people can catch disease and be source of infection A protects those unvaccinated as, disease / illness, does not spread A less chance of transmission A pathogen cannot develop in immunised people A reduced exposure to pathogen

Question 146

Describe and explain the benefits to humans of the presence of nitrogen-fixing bacteria, such as A. vinelandii, in agricultural land.

Answer 146

increase / maintain, nitrogen content of soil ; A add, ammonium / nitrates, to soil 2 increase / maintain, soil fertility ; 3 uptake / absorption, of, ammonium ions / nitrates /fixed nitrogen (by plants) ; 4 (plants use) for, amino acid / protein, production ; 5 increased, growth / yield, of (crop) plants ; 6 ref. feeding, livestock / human populations ; 7 reduced need for fertilisers ; 8 example of environmental benefit of reduced fertilisers ; 9 cost saving from reduced use of fertilisers ; 10 qualified ref. to, Rhizobium / legumes ;

Question 147

The humpback whale is a carnivore, feeding on krill and herring. The herring feed on krill.In terms of energy transfer, explain how the humpback whale is able to reach such a large size.

Answer 147

plenty of food available / AW; A feeding on more than one trophic level 2 further detail; e.g. phytoplankton efficient at converting light energy phytoplankton blooms little / no competition ref. efficient feeding mechanism 3 short food chains / fewer links of the food chain; 4 less energy lost overall; A idea in terms of percent lost at each level 5 few, indigestible / inedible parts;

Question 148

The thickness of blubber in humpback whales decreases during the non-feeding season and increases during the feeding season. Suggest explanations for this observation.

Answer 148

fat / blubber = triglyceride; 2 fat / blubber / triglyceride, used as energy, store / reserve; decreases 3 less fat in cells; ora A fewer fat-filled cells / less adipose tissue 4 mobilised / respired / converted to fatty acids (A glucose), to release energy (during non-feeding season); 5 energy (from fat mobilisation) used, qualified; e.g. for movement increases 6 food eaten / during feeding season, conversion to, fat / AW (for storage); 7 ref. thermal insulation; A idea of prevents heat loss R keeps it warm

Question 149

After infection, the ingested typhoid bacteria are engulfed by phagocytes. (i) Explain why the phagocytes act only against the bacteria and not against human cells.

Answer 149

1 bacterial (surface) antigens / epitopes, act as, non-self / foreign antigens; 2 human cells have self antigens; 3 (antigens are), proteins / polysaccharides; 4 (non-self antigen) will trigger phagocytosis / phagocytes have receptor (only) for, bacterial / non-self, antigens / proteins; ora for self antigens 5 ref. to non-self and self antigens containing different sequences of amino acids / self antigens are products of body’s genotype / AW; 6 idea that phagocytes bind to antibodies complexed with (non-self) antigens (and human cells will not have bound antibody);

Question 150

Unlike other bacteria, the typhoid bacteria are able to survive and multiply within the phagocytes. Suggest an explanation for this observation

Answer 150

cmechanism to prevent, phagosome formation / lysosome fusion with phagocytic vacuole able to withstand attack by (hydrolytic) enzymes contain enzyme inhibitors able to degrade (hydrolytic) enzymes protective capsule

Question 151

With reference to coronary heart bypass surgery, discuss the difficulties in achieving a balance between prevention and cure.

Answer 151

cure for, coronary artery disease / atherosclerosis in artery; A arteriosclerosis so less risk of, myocardial infarction / heart attack / AW; prevention of coronary artery disease to avoid bypass surgery one example; e.g. no smoking increase exercise low, (saturated) fat / cholesterol, diet reduce alcohol consumption reduce salt intake statins avoid, excessive / AW, sugar avoid obesity ref. to difficulties in getting people to change lifestyle to prevent; disadvantage of, surgical procedure / cure; accept ora prevention e.g. invasive / painful costly medical lost time / money, by absence from work risk of complications / graft rejection / infection risk / graft becoming diseased / collapsing AVP; e.g. idea that as cure is available, more difficult to encourage prevention

Question 152

State the main difference in the composition of the plant cell wall compared to the bacterial cell wall.

Answer 152

plant cell cellulose ; treat as neutral ref. to microfibrils / fibres bacterial cell murein / peptidoglycan ; A peptoglycan / polysaccharide and amino acid

Question 153

) Suggest why the sloth and its fur can be described as a small ecosystem.

Answer 153

has biotic and abiotic components / biological and physical components ; A living and non-living components 2 described by use of examples from text ; e.g. water and organisms A fur as an abiotic factor 3 ref. energy flow / nutrient cycling ; A described e.g. food web, algae as producers, fungi as decomposers A food chains look for at least one link 4 ref. interactions / functional entity ; AW e.g. self-contained / self-sustaining / inter-relationships

Question 154

there are differences in the number of cholera cases reported between the high economic status country and the low economic status countries. Suggest three reasons to explain these differences.

Answer 154

look for comparative statements A points if both sides are compared even without ref. to high or low economic country if not comparative, A if stated as low (or high if ora) economic status country max 1 if no points stated as low or high but all points themed as low or high points below are for low economic status countries – ora for high poor sanitation ; water no/ poor water treatment or ref. to unable/ do not know to boil water ; no bottled water or have to drink contaminated/ unsafe/ unclean water ; sewage inadequate/ poor treatment of sewage or sewage contamination of crops ; medical no/ poor access to (oral) rehydration therapy ; vaccines not available/ effective (because poor diet) ; I vaccination programmes in Canada antibiotics / drugs / medication not available ; other greater number of refugee camps / squats ; less able to cope after natural disasters ; less education about disease prevention/ transmission ; poor hygiene/ described ; e.g. not washing hands after defecating

Question 155

Suggest two reasons why some vaccination programmes may fail to prevent epidemics.

Answer 155

1 required percentage cover not reached/ high percentage cover required/ not enough people vaccinated ; 2 some do not respond successfully to vaccine ; 3 poor diet/ lack of vitamin A ; 4 poor storage of non-thermostable vaccine ; 5 vaccine not cost-free to population ; 6 inaccessible vaccination stations for some of the population ; 7 ref.to difficulty in giving boosters ; 8 ref.to reluctance to have children vaccinated ; 9 lack of advertising/ campaigns /education to encourage vaccination ; 10 different strain (to the one used in vaccine)/ antigens changing; R ref.to resistance

Question 156

Outline the response produced by B-lymphocytes on exposure to Morbillivirus in an individual who already has immunity to measles.

Answer 156

ref. to secondary (immune) response ; 2 memory (B), lymphocytes / cells ; 3 recognition of/ binding to antigens ; A clonal selection A proteins /glycoproteins (on Morbillivirus) 4 clonal expansion/ described ; 5 plasma cells secrete antibodies ; 6 idea of faster production/ higher levels of antibody ; 7 ref. to T (helper)-lymphocytes, release cytokines / stimulate humoral response; [max

Question 157

Suggest and explain the advantages of using glucose isomerase from T. thermophilus to produce high fructose corn syrup, rather than using glucose isomerase that has an optimum temperature of 37 °C.

Answer 157

1 maximum / peak of, activity, at lower pH for free enzyme ora or free enzyme lower optimum pH ora or free enzyme pH 7.4 / 7.5/ 7.6 v immobilised pH 8.5 ; 2 free enzyme has higher/AW activity, at pH, 6 / 6.5/ 7/ 7.5 ; A up to pH 8 ora for immobilised (lower up to pH 8) * or free enzyme has higher activity over greater range of pH** (between pH 6–9) ; 3 data to support mp 2 ; *any one pH and comparative activity ** needs two pHs and comparative activities A manipulated data 4 free enzyme has lower activity, pH 8 to pH 9 ; A after pH 8.0 ora for immobilised (higher after pH 8) 5 data to support mp 4 ; any one pH and comparative activity /manipulated data increase to max activity 6 free enzyme has (slightly) steeper increase in activity as pH increases to pH 7 ; ora 7 data to support mp 6 ;

Question 158

Explain how the action of lysozyme will lead to the destruction of the bacterial cell.

Answer 158

breakdown /weaken / digests /AW, cell wall ; A destroyed / damaged I breaks cross-links / cross-links cannot form (water enters so) lysis occurs / bursts /AW ;

Question 159

Suggest possible explanations for the decrease in the number of people newly infected with HIV.

Answer 159

stated precaution(s) to reduce risk of infection by 1 using, condoms / femidoms ; A safe(r) sex / use protection during sexual intercourse 2 abstinence / monogamy / less promiscuity ; 3 not sharing needles / using sterile needles / needle exhange ; A syringes 4 not breast feeding ; 5 (heat) treated blood (products) / testing potential blood donors or donated blood ; 6 ref to contact tracing ; 7 increased awareness of, precautions / risks / transmission ; 8 increased use of (antiviral) drugs reduces transmission ; 9 some strains are less infective than others ; 10 less reporting of new cases ; 11 AVP ; e.g. fewer HIV+ babies born (to HIV+ mothers) improved, screening / detection, qualified

Question 160

the relationship between | new HIV infections and deaths due to HIV/AIDS. is a postive linear correlation. explain why

Answer 160

idea that estimates are subject to large uncertainty / AW ; idea that needed for any use of the data for planning health services / AW ; AVP ; e.g. explanation of mp 1 rather than general statement, such as symptomless carriers many new cases not diagnosed many new cases not reported remote areas

Question 161

the interaction of all living organisms with each other and their non-living environment in a self-contained location

Answer 161

ecosystem

Question 162

Explain how nitrogen from compounds in the dead leaves is made available to the growing plants.

Answer 162

1 protein / amino acids, (in leaf litter) ; 2 ref to, decomposition / decay / decomposers / saprobiotic bacteria or fungi ; 3 deamination ; 4 amino acid converted to, ammonia / ammonium ; 5 ammonia / ammonium, converted / oxidised , to nitrite (ions) / NO2 ; 6 nitrite (ions) / NO2 , converted to, nitrate (ions) / NO3 ; 7 by, nitrification / nitrifying bacteria / named example ; e.g. Nitrosomonas / Nitrobacter 8 nitrate (ions) / NO3 , taken up / absorbed, by mangrove / plant (roots) ; 9 AVP ; e.g. ammonia / ammonium, taken up

Question 163

Explain the importance of taking a complete course of antibiotics.

Answer 163

1 (to ensure) all bacteria are, killed / removed / eliminated / destroyed / AW ; R virus / bacteria and virus ignore antigen or pathogen or disease ‘all’ may be implied e.g. award if gain mp 2,3,4 2 (so) no reservoir of infection remains / AW / ora ; 3 (disease) cannot be transmitted / cannot infect others / AW e.g. spread / ora ; 4 no recurrence / disease does not return ; in context of same person 5 to reduce chance of / AW, (antibiotic / drug) resistance developing ; R idea that human becomes resistant to antibiotics 6 ref. to mutation in context of resistance ;

Question 164

State why penicillin, which is an enzyme inhibitor, can be taken by humans.

Answer 164

ideas that (humans) do not have the enzyme for cell wall synthesis ; A penicillin only inhibits bacterial enzymes penicillin will not inhibit any human enzyme ; (human cells) do not have cell walls ;

Question 165

Suggest the effect which penicillin will have on bacterial cells.

Answer 165

cell wall synthesis will stop / slow / be inhibited ; A inhibit, murein / peptidoglycan, synthesis ref. to uptake of water by osmosis ; cell cannot withstand osmotic stress / cell cannot withstand turgor pressure / lysis / bursting / AW ; A cell wall weakened bacteria die / are killed / destroyed ; stops bacteria dividing / reproducing / ‘replicating’ ; AVP ; e.g. detail of action of penicillin (e.g. prevents cross-links forming), (penicillin) only works on growing cells

Question 166

Explain why only a small percentage of the energy present at each trophic level is available to the organisms at the next level.

Answer 166

c) energy loss at each level because of 1 inedible parts / not all of the organism can be eaten ; 2 indigestible parts / not all is digested / egestion / faeces ; 3&4 energy / heat, losses from ;; respiration R energy used for respiration movement A energy used for movement excretion digestion ignore energy not utilised by plants by e.g. reflection from leaves, etc.

Question 167

Outline what happens to the nitrogen-containing compounds in the organisms at the top of the food web.

Answer 167

1 decomposers / saprotrophs / bacteria / fungi / scavengers / detritivores ; 2 digest / breakdown / hydrolyse, protein / urea ; 3 idea of assimilation in / growth of, decomposers / AW ; 4 deamination ; 5 production of ammonium (ions) / ammonification ; A ammonia / NH3 6 nitrification described or denitrification described ; A formulae for ammonium ions, nitrite ions and nitrate ions but must be correct including signs A nitrification described in terms of ammonium (ions) to nitrate (ions) ignore nitrogen fixation as used correctly (N2 to fixed N) ignore uptake of nitrate ions or ammonium ions by plants do not credit nitrification if any confusion with nitrogen fixation

Question 168

When a pathogen enters the body, a primary immune response occurs. This response includes the production of antibodies. Describe the stages in the immune response that lead to antibody being produced against a specific antigen.

Answer 168

antigen recognised as / AW, non-self / foreign ; accept once for macrophage, B-lymphocyte or T-lymphocyte A non-self / foreign, antigen leads to immune response 2 idea of phagocytosis leading to antigen presentation ; 3 antigen (on pathogen or APC) binding to, receptor / membrane, of B-cell(s) / B-lymphocyte(s) ; A clonal selection of B-lymphocytes occurs 4 (helper) T-cell / T-lymphocyte, activate B-cells ; I killer T-cells A release cytokines to stimulate B-cells 5 B-cells / B-lymphocytes, divide by mitosis ; A replicates / proliferates by mitosis A clonal expansion of B-cells 6 plasma cells, formed / AW ; 7 plasma cells / B-cells / B-lymphocytes, produce / secrete / AW, antibody / immunoglobulin / Ig ;

Question 169

Bacteria in root nodules of leguminous plants carry out nitrogen fixation. Describe how nitrogen that is available to these bacteria can eventually become part of animal protein.

Answer 169

nitrogen, converted / reduced / fixed, to, ammonium / ammonia (in root nodules) ; A correct equation ( ) () () 2 e6N 8H 2 NH4 2/ NH3 − + + ++ → R if nitrogen fixation is said to happen in the soil I nitrogen fixation is carried out by leguminous plant 2 (catalysed by) nitrogenase ; accept if part of equation 3 ATP, hydrolysed / AW ; accept if part of equation 4 ref. to anaerobic conditions ; 5 ammonia (converted) to amino acids to protein (in plants) ; 6 plant protein, digested / hydrolysed / broken down, by animals (into amino acids and absorbed) ; 7 amino acids used to synthesise (animal) protein ;

Question 170

(iv) Suggest why there are few drugs that have any effect on viruses

Answer 170

two from 1 idea that there are few targets for drugs ; A e.g. virus has no, cell wall / cell membrane /ribosomes 2 no / few, enzymes ; 3 antibiotics only work on, growing / living, cells ; A viruses have no, metabolism / growth 4 viruses are inside (host) cells / not within reach of antibiotics ; R if antibodies 5 antibiotics do not work on, protein coat / capsid/ viral envelope ; I capsule

Question 171

The search for new antibiotics is important because there are many strains of bacteria that are resistant to antibiotics. Suggest two ways to reduce the spread of antibiotic resistance.

Answer 171

) two from do not use for viral infections ; do not use as preventative medicine ; antibiotics should only be used (for treatment) when necessary ; carry out antibiotic sensitivity test ; ensure, correct /effective, antibiotic, prescribed/used ; AW ensure people take the correct dose ; ensure people complete the course of their antibiotic ; A ensure people follow the instructions ensure people do not use, left-over/other people’s, antibiotics ; only supply on prescription / not over the counter/AW ; only use, wide / broad, spectrum antibiotic when pathogen not known ; A ora use narrow spectrum antibiotic when pathogen is known use more than one antibiotic (at the same time) ; A mixture of antibiotics /antibiotics in combination monitor antibiotics to check that they are effective ; report cases of antibiotic resistance ; reporting patterns of antibiotic resistance (temporal and geographical) ; rotate antibiotics so not used all the time ; keep some antibiotics to use as a last resort ; do not use the same antibiotics for animals as for humans ; reduce use of antibiotics in, food production /(livestock) agriculture ; use other antimicrobial drugs ; develop new, types of antibiotics /drugs, to kill bacteria ; ensure /improve, knowledge of, healthcare professionals /public ; A ref. to education about awareness of antibiotic resistance ref. to breaking transmission cycle/ described example of a method ; e.g. vaccines /good hygiene in hospitals break transmission cycle of resistant bacteria/ described example ; e.g. quarantine

Question 172

) Explain why countries that have established vaccination programmes still have cases

Answer 172

1 measles introduced by people who caught the disease when abroad ; A any e.g. tourists / visitors /travellers /returning tourists / migrants /displaced people 2 idea that herd immunity, needs to be >90%/ is not 100% ; A herd immunity not achieved 3 some people in these countries have not been vaccinated ; A too young to receive vaccine /refusal of vaccination /live in remote places /war zones /AW ; 4 some people do not respond to the vaccine ; A people have weak immune system / malnutrition 5 some people do not receive booster(s) ; 6 (reconstituted) vaccine is not thermostable /difficult to maintain the cold chain ;