bio all 3

Question 1

Explain why the membrane is able to change its shape when cytoplasm flows
towards it.

Answer 1

the membrane is fluid (1)
* phospholipids (and proteins) can move (within the membrane)
(1)
* (presence of) cholesterol contributes to fluidity (1

Question 2

deletion

Answer 2

closer to the start greater the effect

Question 3

nzymes are specific to one substrate (1)

Question 4

Suggest how a person can be shown to have this disorder

Answer 4

genetic screening / named screening method / looking for a
mutation
* biochemical test / blood test / description of named molecule
whose level would be different
* family history / pedigree analysis

Question 5

Give one similarity, other than the presence of lignin, and one difference in
the structures of sclerenchyma fibres and xylem vessels.

Answer 5

both contain {cellulose / pits / dead cells / secondary
walls}
* both {are hollow / do not contain cytoplasm}
Difference (1)
* sclerenchyma contain end walls whereas xylem do not

Question 6

Root tips were then placed in acetic orcein in a
water bath at 55 °C and left for five minutesStep 4
A coverslip was placed over the root tips and
squashed gently
Step 5
The slide was then viewed first using low power and
then high power of a microscope

Answer 6

2, to {stain / dye / colour} the chromosomes
(1)
* 4, to spread / separate the cells out (1)
* 5, to locate and then magnify (the cells)

Question 7

Explain one safety precaution that must be taken when carrying out this procedure.

Answer 7

e.g. rinsing tips in water / wearing gloves /
goggles
because hydrochloric acid, acetic orcein is
corrosive / irritant

Question 8

State two factors, other than the antimicrobial effect, that could affect the area of
the zone of inhibition in this investigation.

Answer 8

• {solubility / concentration / volume} of
  extract / solvent used (1)
• size of molecules in the extract (1)
• rate of diffusion of extract into agar (1)

Question 9

SMOKING

Answer 9

because smoking {increases blood pressure / increases heart
rate / damages (endothelial) lining of arteries}

Question 10

factors not included

Answer 10

salt intake / fibre intake / alcohol intake / (body) mass / BMI /
obesity / hip waist ratio / level of exercise / stress levels / family
history / genetic factors / taking statins / diastolic blood
pressure

Question 11

Compare and contrast the structure of messenger RNA (mRNA) with the structure
of transfer RNA (tRNA).

Answer 11

 both contain {RNA (mono)nucleotides / ribose sugar / uracil
(and adenine, cytosine and guanine) / phosphodiester bonds}
(1)
 both are single stranded (1)
differences:
 mRNA is a straight chain and tRNA is {folded / clover-leaf
shaped} / mRNA does not have hydrogen bonds and tRNA
does (1)
 {size / length} of mRNA is variable and the {size / length} of
tRNA is constant (1)
 mRNA has codons and tRNA has {anticodons / amino acid
binding sites} (1)

Question 12

e term semi-conservative replication.

Answer 12

an increase in the number of (DNA) {molecules / double helices}
(1)
* each (new molecule) consists of one {parent / original / old}
strand and one new strand (1)

Question 13

Give two differences between an organ and a tissue.

Answer 13

organ has many functions whereas a tissue has {one / fewer} (1)
 organ has {many / several / group of} {cell types / tissues} whereas
a tissue has {one cell type / similar cells }

Question 14

Describe the methods that would be used to trial a drug containing
these compounds.

Answer 14

compound needs to be extracted from trees and used to make a drug
 compounds tested on Y. pestis in vitro
 tested on {animals / human cells}
 (phase 1 / preliminary) (small scale) tests on healthy {people / volunteers}
 review by independent {scientists / medics} to see if work can progress to stage 2
 (phase 2) - drug tested on {small / 100 to 500} groups of {patients / people} who have the {plague / disease}
 appropriate concentrations identified
 (phase 3) - drug tested on {larger groups of / 1000 to 3000} {patients / people} who have the plague
 placed randomly in two groups - one group receives {treatment / drug containing the chemical compounds} and the
other receives placebo
 double blind test
 analyse results with (appropriate) statistical test / test for significant difference

Question 15

Give two differences between genetic diversity and species richness.

Answer 15

 genetic diversity considers one species whereas species richness
considers {different / number of} species (genetic diversity considers {alleles / genotypes} whereas species
richness {is within a habitat / considers whole organisms / counts
number of species (in an area)}

Question 16

Seed banks

Answer 16

can store more seeds as they {take up less space / are smaller}
(1)
 seeds need less {maintenance / cost} (1)
 seeds can {survive longer than plants / be frozen }

Question 17

larger flagellum

Answer 17

more speed more chance of fertilization ,comp

Question 18

Describe how a totipotent stem cell becomes a pluripotent stem cell

Answer 18

differential gene expression (1)
 some genes have been (permanently) {inactivated / switched off}
(1)
 by epigenetic modification (1)
 {proteins / enzymes} {made / synthesised} (from active genes)
which permanently modify the cell

Question 19

Explain why the urease solution and the urea solution were kept in the water bath
at 40°C before and after being mixed.

Answer 19

for equilibration (1)
 because mixing the solutions at different temperatures would
make the temperature ≠ 40 °C
(1)
 (40 °C could be) optimum for urease
(1)
 (so if the mixture) {cooled down / warmed up} rate would
change during experiment
(1)
 ensures only pH is varied

Question 20

Describe how the events of the cardiac cycle change when the demand of
body cells for oxygen increases.

Answer 20

ardiac cycle is {shorter / faster /completed more
frequently} (1)
* ventricles contract more forcefully (during ventricular
systole)

Question 21

Explain why substrate concentration affects the rate of reaction.

Answer 21

as the concentration (of substrate) increases there are more
(substrate) molecules / particles (1)
* (therefore) a greater chance of {collisions with active site /
enzyme substrate complexes forming} increasing the rate of
reaction (1)
* {rate/graph} levels off when {all active sites are filled (at any one
time) / enzyme is saturated} (1

Question 22

Suggest why there is a difference in the solubility of sodium chloride and
glucose in water.

Answer 22

(glucose is a larger molecule than sodium chloride therefore)
glucose can be surrounded by more water molecules (1)
* glucose has {(many) hydroxyl groups / (more) polar groups} (1)
* (therefore) glucose forms (more) hydrogen bonds with water
molecules (1)
* strength of bonding (between particles) is lower in glucose
compared to sodium chloride (

Question 23

Explain why fatty acids are less soluble in blood than glucose and sodium chloride

Answer 23

• water is a polar solvent (1)
• fatty acids have {hydrophobic / non-polar} tails (1)
• {fatty acids / non-polar molecules} {do not form hydrogen
  bonds / do not dissolve in polar liquids / repel polar liquids}

Question 24

Suggest why CVD studies of this type are unreliable.

Answer 24

{difficult / impossible} to control all the {variables / risk
factors} (1)
* unreliable estimate of risk factors e.g. number of
cigarettes smoked (1

Question 25

) Explain how the structure of haemoglobin causes the oxygen dissociation curve of haemoglobin to be this sigmoidal (S) shape.

Answer 25

haemoglobin is composed of four sub-units (1) * binding of the first oxygen molecule is difficult (1) * binding of the other molecules becomes easier (1) * due to a conformational change (1) * as Hb becomes saturated less oxygen can bind (so the curve flattens out) (1)

Question 26

) Explain why the partial pressure of oxygen decreases as the blood flows through the arteries and into the veins.

Answer 26

arteries take blood to {tissues / cells}, veins take blood away from {tissues /cells} (1) * oxygen diffuses (out of the capillaries) into {the tissues /cells} (1) * because there is a lower {partial pressure / concentration} in tissues / cells (1) * carbon dioxide is {increasing in / entering} (the blood)

Question 27

Explain why the percentage saturation of haemoglobin in a person at high altitude is much lower than in a person at sea level

Answer 27

partial pressure of oxygen (in the atmosphere) at high altitudes is low / lower (than at sea level)} (1) * (therefore) the partial pressure of oxygen in the alveoli will be lower (1) * the concentration gradient between the alveoli and the blood will be smaller (1) * (therefore) the rate of diffusion of oxygen into the blood will be slower (1) * (therefore) the haemoglobin will not be able to bind to as much oxygen (1)

Question 28

cystic fibrosis

Answer 28

mmation (I points) * cilia cannot move mucus away (it is too thick) (credit this only once) * mucus (is very sticky and) traps bacteria * bacteria have ideal growth conditions (in mucus) * bacteria can cause (chest) infections * CF characterised by coughing {to remove mucus / as a result of infection} * {coughing / infection} damages {cells / tissues} (lining airways) * (leading to) inflammation of muscle (credit this only once)

Question 29

Describe the ethical issues relating to genetic screening.

Answer 29

screening may result in {an abortion /taking a human life} that is {unethical / against religious or cultural beliefs of some people} (1) * spare embryos from IVF are destroyed which is taking a human life (1) * individuals who are genetically linked may be {exposed to unwanted facts / disadvantaged} following testing (1) * screening may produce false results or {CVS / amniocentesis} increases risk of miscarriage (which results in death of foetus)

Question 30

) Explain how molecular evidence led to the reclassification of species and how the scientific community would have reviewed the evidence before it was accepted.

Answer 30

classification definitions historically based on similarities and differences in phenotype * some examples of phenotypes used for previous classification, e.g. beak shape, bird size, diet, habitat * previous classification had Ceyx madagascariensis as more closely related to other Ceyx kingfishers * more recent classification based on molecular evidence / molecular phylogeny * similarities and differences in mRNA / DNA / amino acid sequences identified * explanation of how they are compared * fewer differences means they are more closely related / have more recent common ancestor * reference to closer together on evolutionary tree * proposed classification had Ceyx madagascariensis as more closely related to Alcedo (leucogaster and / or cristata) * scientist proposing a reclassification * published in scientific journal * reference to peer review (of molecular evidence) * repetition of experiments by other scientists (to see if same data are collected) * extend the analysis e.g. look for similarities / differences in more genes * analysis of data to see if same conclusions can be reached / more research * statistical analysis

Question 31

Explain how xylem vessels are adapted for support and transport.

Answer 31

e.g. (cell) walls have secondary thickening / lignin in (cell) wall (1) e.g. (lignin in the cell wall) provides strength (1) ignore support e.g. hollow tubes with no {end walls / cytoplasm} (1) no obstruction to vertical movement / enables formation of continuous water column (1) e.g. narrow (1) to aid capillary action (1

Question 32

Explain why beta cells can produce insulin but other cells in the pancreas do not.

Answer 32

cell specialisation (1) * because gene (for insulin production) switched off in (other pancreas cells) due to {epigenetic modification / DNA methylation / histone modification} (1) * because gene (for insulin production) {active / switched on / expressed} in these (beta) cells (1) * therefore transcription of (active insulin) gene / (active) mRNA produced (1) * translation of (active) mRNA leads to synthesis of insulin protein (1)

Question 33

Explain the possible causes of this decrease.

Answer 33

deforestation (of mangroves) causing habitat loss (1) * reduction in food due to {deforestation (of mangroves) / competition with other species / overfishing} (1) * {pollution / change in salinity} of river making it unsuitable habitat (for the crocodile) (1) * {disease / hunting} (causing death of crocodiles)

Question 34

) Describe a valid method that could be used to compare the breaking force of these fibres

Answer 34

* how fibre fixed (1) * how force applied (1) * one variable which should remain constant stated (1) * replicate (the experiment/measurements) (1) * (and) calculate the mean/SD (1)

Question 35

Devise a method to determine the cross-sectional area of a fibre, using the following equipment

Answer 35

a (transverse) section/layer/slice of the fibre is cut (1) * ensure section is flat (1) * graticule calibrated (with stage micrometer) (1) * diameter measured/found * and converted to measurement with calibration data (1) * area calculated using πr2 (

Question 36

Explain why there is a delay of 0.01 seconds between atrial systole and ventricular systole.

Answer 36

because the atrioventricular valves have to close (before the ventricles contract) (1) * to prevent backflow of blood into the atria (1)

Question 37

gene code

Answer 37

bases ,degenarate and non overlaping code

Question 38

role of prothrombin

Answer 38

to be present in the blood (all the time) (1) and any TWO of the following: * needed to make thrombin (when blood needs to clot) (1) * which is an {enzyme / catalyst} (1) * so that fibrinogen can be converted into fibrin (1)

Question 39

Explain the conditions needed for the growth of bacteria.

Answer 39

water for {hydrolysis reactions / form cytoplasm / solvent / hydration} (1) * (some bacteria require) oxygen for (aerobic) respiration (1) * (suitable/optimum) temperature for {enzymecontrolled / metabolic} reactions to occur (at suitable rate) (1) * (suitable/optimum) pH for {enzyme-controlled / metabolic} reactions to occur (at suitable rate) (1) * named organic molecule and an explanation of why that organic molecule is needed (

Question 40

Describe the structure of sucrose.

Answer 40

glucose and fructose (1)  joined by glycosidic bond (1)

Question 41

Compare and contrast the structure of the aorta with the structure of the pulmonary artery.

Answer 41

both have walls containing {muscle cells / elastic fibres / an endothelial cell lining / an (outer) collagen layer} (1) * both have a valve (at the point they leave the heart) (1) Differences: * aorta has a {lumen with a wider diameter / thicker wall / more elastic tissue / more muscle tissue / more collagen} (1) * aorta has branches to more organs (1)

Question 42

Explain how the structure of glycogen relates to its role as an energy storage molecule

Answer 42

{polymer of glucose / polysaccharide} therefore has a high energy content (1) * {large molecule / polymer / polysaccharide} therefore {insoluble / has no osmotic effect} (1) * branched structure therefore {broken down / energy released / hydrolysis is} faster (1) * compact therefore has a high energy density (

Question 43

Explain the location of cholesterol in cell membranes

Answer 43

holesterol is a non-polar molecule (1) * fatty acid tails are non-polar (1) * cholesterol will be located within the {fatty acid tails / non-polar part} of membrane (1) * OH group will be located near the phosphate heads (1

Question 44

) Explain how the three-dimensional structure of lactase affects the mechanism of action of this enzyme.

Answer 44

lactase is soluble because of its {globular shape / external polar R groups} (1) * (and therefore) lactase collides with lactose (1) * active site of lactase is complementary to the lactose (1) * Formation of enzyme-substrate complex lowers the activation energy

Question 45

Describe the role of zoos in the conservation of endangered Sehuencas water frogs

Answer 45

captive breeding / breeding in zoos or in natural habitat * use of stud books (without ref to maintaining genetic diversity) * {conservation of / increase} frog habitat in Bolivia * guidance to local government / raising awareness of need for protected area e.g. national park * conservation in zoos / recreating similar habitat in zoos / protection from predators (in zoos) / food provision * eradication / treatment of {fungal / other} disease * protection from predators (in-situ) * reintroduction of frogs from captive breeding programme * suggested details of method of reintroduction * education of local population in {Bolivia / country where zoo is located}

Question 46

Describe how an unsaturated triglyceride is synthesised.

Answer 46

(one) glycerol and three fatty acids (1) * joined by {condensation reaction / ester bond} (1) * by enzymes (1) AND * (at least) one fatty acid is {unsaturated / has a CC double bond}

Question 47

Describe what will happen to these chromosomes when they enter the interphase stage of the cell cycle.

Answer 47

uncoiling (of chromosome) (1) * used in protein synthesis / DNA replication (in S phase) (

Question 48

Suggest why the number and size of the Golgi apparatus change during the cell cycle

Answer 48

mitosis / two cells formed from one cell (1) * therefore {number / size} of Golgi (in each cell) has to increase (in interphase / G1) (1) * to provide enough cell {contents / organelles} for two (daughter) cells (after mitosis has occurred) (1) * because increased {protein synthesis / protein modification / gene expression} will occur (in interphase) (1) * because named protein(s) are required (by the cell)

Question 49

Describe how seeds are treated and then stored in a seed bank

Answer 49

the water content is reduced (1) * the seeds are x-rayed (1) * the seeds are kept at {low temperature / dry}

Question 50

bonds in mrna

Answer 50

description that includes three of the following points:  phosphodiester bonds between (adjacent) {ribose and phosphate / (mono)nucleotides} (in each strand) (1)  covalent bonds attaching base to a {ribose (sugar) / sugar} (1)  {hydrogen / H} bonds between (complementary) bases (holding two strands together) (1)  {hydrogen / H} bonds holding double helix together

Question 51

Explain how a critical value table could be used to accept or reject a null hypothesis for this experiment.

Answer 51

{calculate / use} the number of degrees of freedom  use (a probability) value of (up to or equal to) 5%/0.05 (1)  compare (calculated) {value / result} to (critical) value (1)  if the (calculated) {value / result} is greater than (critical) value then null hypothesis is rejected

Question 52

Explain how using a colorimeter allows valid measurements of light transmitted through the betalain solutions.

Answer 52

because the same {light source / filter / size cuvette} used for all measurements (1)  because zeroing / calibrating (1)  because objective measurement (1)  because no light lost / gained

Question 53

Describe how the structure of capillaries relates to their function

Answer 53

e.g. single layer of cells / pores / small diameter ACCEPT thin cells / walls e.g. (single layer) gas exchange / diffusion of gases (in the lungs) (pores) plasma forced out / W

Question 54

glucose and glycogen

Answer 54

αlpha glucose (1) * contain C, H and O (only) (1) Differences : * glucose is a monosaccharide and glycogen is a polysaccharide (1) * glycogen has (1-4 / 1-6) glycosidic bonds but glucose does not (1)

Question 55

vacuole

Answer 55

provides support (1) * {stores/dissolves} named substance(s) (1)

Question 56

Describe how a Rhesus antigen would be produced from its polypeptide chain and transported to the cell surface membrane

Answer 56

polypeptide chain enters the rER (1) * {secondary/ tertiary} structure formed (1) * polypeptide is packaged into vesicles (by rER) / {(rER) vesicles fuse with / protein enters} Golgi (1) * carbohydrate added (to protein in Golgi) (1) * (glyco)protein is packaged into vesicles (by Golgi) and transported to cell surface membrane (

Question 57

Explain what happens at step D for the cell to become a specialised sperm cell.

Answer 57

(because) differential gene expression occurs (1) * (due to) epigenetic modification / DNA methylation / histone modification (1) * {transcription of / (active) mRNA made from} active genes (1) * (therefore) translation occurs to form a {polypeptide / protein} (1) * (proteins cause) {structural/functional} change to cells to change them into (specialised) sperm cell (1)

Question 58

ynthesis of organelles (1) * increase in cell size / growth of cell (1) * {synthesis / replication} of DNA (

Answer 58

cell cycle

Question 59

accuracy

Answer 59

* grow several plants in each solution (1) * calculation of (means and) SDs (1) * check for overlap (of means plus and minus SD) for each difference (1) * carry out a statistical test (

Question 60

Describe the structure of a nucleotide pair.

Answer 60

contain {deoxyribose / pentose / 5 carbon sugar}, phosphate and bases (1) * (mononucleotides / bases) held together by hydrogen bonds (1) * between {complementary bases / named example}

Question 61

Explain how the arrangement of cellulose molecules and secondary thickening in xylem vessels contributes to the physical properties of the cell wall.

Answer 61

cellulose molecules can be organised into microfibrils. (1) * (due to layers of) {cellulose / microfibrils} arranged in {different directions / a mesh} (1) * {hydrogen bonds in cellulose molecules / hydrogen bonds in microfibrils / layers (of microfibrils) / lignin / secondary thickening / pectate} add {strength / support / stability} (1) * {(cellulose) microfibrils / mesh} held together by {pectin / pectate} (1) * lignin makes {outside of xylem vessels / cell wall} impermeable (to water) (1) * the structure of lignin described (1

Question 62

Compare and contrast the structures of pre‑mRNA and active mRNA.

Answer 62

both are single-stranded (1) * both contain the bases A,U,C,G / both contain a base, phosphate group and ribose (sugar) / both contain phosphodiester bonds (1) * an exon on pre-mRNA contains same base sequence as the matching exon on active mRNA (1) Differences * pre-mRNA contains both introns and exons whereas active RNA only contains exons (1) * active mRNA may have {fewer / different order of} exons (than premRNA) (1)

Question 63

Describe the roles of phase I and phase II.

Answer 63

to test for side-effects (1) * to determine {safe / minimum /effective/ suitable} {dosage / concentration} (1) * to determine if it is more effective than {existing treatments / placebo} (1

Question 64

species richness

Answer 64

(species richness) is the number of (different) species in a habitat

Question 65

xplain how the change in frequency of this allele could be determined.

Answer 65

DNA analysis to identify different alleles (1) * use of Hardy-Weinberg equation / p2 +2pq+q2 (1) * (in order to) compare (recessive) allele frequency in previous generation(s) with current generation (1)

Question 66

phloem and xylem

Answer 66

Similarities: * both (fibres) contain cellulose (in the cell wall) (1) * both have tubular structures (1) * both do not contain a nucleus (1) Differences (max 3): * phloem (sieve tubes) have {sieve plates / (perforated) end walls} whereas xylem (vessels) have no {end walls / sieve plates} (1) * phloem (sieve tubes) {contain cytoplasm / are not hollow} whereas xylem (vessels) {do not contain cytoplasm / are hollow} (1) * phloem (sieve tubes) contain no {lignin / secondary thickening} whereas xylem contain {lignin / secondary thickening} (1) * phloem have plasmodesmata whereas xylem have pits (1

Question 67

root tip experiment

Answer 67

cut root tip * (root tips) placed in (warm) acid (1) * (root tips) then placed in named stain (1) * (root tip placed on a microscope slide and) {macerated / teased / described} / squashed (1) * use of high power (on a microscope) (1) * correct ref to safety issue (1)

Question 68

State one difference and one similarity between the nuclear envelope and the cell membran

Answer 68

 nuclear envelope double membrane, cell membrane single OR  {nuclear pore present in nuclear envelope, not in cell membrane / cell membrane has channels} (1) Similarity:  both membranes are phospholipid (bilayer)

Question 69

Explain how seed banks would prepare, store and assess viability of these seeds.

Answer 69

seeds would be (prepared by being) dried (1)  seeds would be treated with an antimicrobial (1)  seeds would be stored in suitable conditions (1)  samples of seeds would be {germinated / x-rayed / scanned} (to check viability) (1)  replacement seeds would be collected from (these plants)

Question 70

ii) Explain how scientists could breed new high-yielding varieties of eggplants which are resistant to R. solanacearum bacteria.

Answer 70

 set up a {breeding programme / stud book} (1)  {cross / breed} variety A with variety D (1)  (because) D has {lowest wilt percentage / lowest disease index / best resistance} and variety A has the highest yield / A and D will produce offspring with resistance and high yield (1)  infect grown offspring with the bacterium / check to see if offspring are resistant (1)  repeat using offspring with required characteristics (to get a new high-yielding and resistant variety)