a level biology qurestions

Question 1

describe the role of proteins in the production of polypeptides - dont include transcription

Answer 1

Mrna binds to ribosomes
two codon binding sites
fromation of peptide bond between amino acids

Question 2

suggest how glycogen acts as a source of energy

Answer 2

hydolysed to glucose which is used in respiration

Question 3

suggest and explain two ways the surfsce membrsne of cell linngs the uterus may be adpated to a;llow rapid transport of nutrients

Answer 3

large sa:vol
lots of protein channels for facillitated diffusion

Question 4

Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some
of these cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton
(hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3
does this.

Answer 4

-co trasnport
-uses atp
- changes shape of the protein when sodium ion and proton bind

Question 5

describe how bacteria divide

Answer 5

1. Binary fission;
2. Replication of (circular) DNA;
3. Division of cytoplasm to produce 2 daughter
   cells;
4. Each with single copy of (circular) DNA;

Question 6

Suggest one advantage to a bacterium of secreting an extracellular protease in its
natural environment.
Explain your answer.

Answer 6

1. To digest protein;
2. (So) they can absorb amino acids for
   growth/reproduction/protein synthesis/synthesis
   of named cell component;

Question 7

describe how phagocytosis of a virus leads to presentation of its antigen

Answer 7

1. Phagosome/vesicle fuses with lysosome;
2. (Virus) destroyed by lysozymes/hydrolytic
   enzymes;
3. Peptides/antigen (from virus) are displayed on
   the cell membrane;

Question 8

An environmental scientist investigated a possible relationship between air
pollution and the size of seeds produced by one species of tree.
He was provided with a very large number of seeds collected from a population of
trees in the centre of a city and also a very large number of seeds collected from a
population of trees in the countryside.
Describe how he should collect and process data from these seeds to investigate
whether there is a difference in seed size between these two populations of trees

Answer 8

1. Use random sample of seeds (from each
   population);
2. Use (large enough) sample to be representative
   of whole population;
3. Indication of what size was measured eg mass;
4. Calculate a mean and standard deviation (for
   each population);
5. Use the (Student’s) t-test;
6. Analyse whether there is a significant difference
   between (the means of) the two populations;

Question 9

suggest and explain why the combined actions of endopeptidases and exopeptidase are more efficient than exo on their own

Answer 9

endopeptidases hydrolyse internal peptide bond
more ends

Question 10

why the addition of respiratory inhibitors stop the absorption of amino acids

Answer 10

no atp produced
na ions. not moved
no diffusion gradient for na

Question 11

reasons why ph would remain constant in hyrodlyses of triglyceride

Answer 11

enzymes denatured and. no more fatty acids produced

Question 12

name the part of a pancreatic cell that produces the inactive form of trypsin

Answer 12

ribosome

Question 13

state the advantage of producing trypsin in an active form inside cells in the pancreas

Answer 13

does n to digest protein inside cell
sp pancreatic tissue damaged

Question 14

messenger RNA is used during translation is to from polypeptides
describe how Myrna is produced in the nucleus of the cell

Answer 14

Helicase
breaks hydrogen bonds
only one dna strand acts as template
rna nucleotide attracted to exposed
according to base pairing rule
rna polymerase join nucleriudes together
pre Mrna qsplikced to remove introns

Question 15

the concentration of glucose in the blood rises after eating a meal containing carbohydrates

Answer 15

-starch digested to maltose
-maltose digested to glucose
-digestion of sucrose =single step

Question 16

healthy people have amylase in their blood. This does not cause any harmful effects in the body explain why

Answer 16

amylase is specific so no starch in humannbloof

Question 17

pancreatitis can lead to the release of prote3in digesting enzymes into the blood this is harmful t the body
suggest one reason why

Answer 17

could digest own body/proteins
eg.membrane protein

Question 18

describe how these phagocytosis white blood cells destroy bacteria

Answer 18

Phagocyte attracted to bacteria by chemicals

engulf bacteria
bacteria in vacuole
lysosome fuses with
bacteria hydrolysed/digested

Question 19

the epithelial cells that line Ithe small intestine are adapted for the absorption of glucose. Explain how

Answer 19

microbial provide a large
many mitochondria produce atp
Carrier protein for active transport
channel/carrier for facillitated
co transport of sodium ions
membrane bound enzymes digests disaccharides

Question 20

describe the role of enzymes of the digestive system in the complete breakdown of starch

Answer 20

amylase
starch to maltose
maltase
maltose to glucose
hydrolysis of glycosisdc bond

Question 21

describe the processes involved in the absorption of the products of starch digestion

Answer 21

glucose moves in with sodium via channel/carrier protein
sodium removed by active transport
into blood
maintaining low conc of sodium
glucose moves into blood by facilitated diffusion

Question 22

duggrdt hoe the chylomicrons leave the epithelial cells

give a reason for your answer

Answer 22

exocysiris
too large to leave via other method

Question 23

if a sample of blood is mixed with dissolved lipids and no cells seen then why

Answer 23

phopsholipid bilayer is dissolved

Question 24

in each cardiac cycle the arterial pressure has a maximum value explain the link between the maximum value and the events of the cardiac cycle

Answer 24

corresponds to ventricles contracting

Question 25

the water potential of the plasma at the venue end of the capillary is more negative than the water potential at the arteriole end

Answer 25

plasma proteins are too large

Question 26

what causes the absence of heamoglobin in tissue fluid

Answer 26

haemgoblib. in rbc

Question 27

haemoglobin is a protein with a quaternary structure what does this mean

Answer 27

several polypeptide chains

Question 28

explain how oxygen in a red blood cells is made available for respiration in active tissue

Answer 28

low ph
dissociation of haemoglobin

Question 29

the hydrostatic pressure of blood at the arteriole end of the capillary helps to form tissue fluid explain how

Answer 29

hydrostatic pressure higher than osmotic effect
forces out small molecules

Question 29

describe how the increase in pressure of the blood in the artery results from the events in the cardiac cycle

Answer 29

caused by blood leaving the heart as a result of ventricles contracting

Question 30

the elastic fibres in the wall of the artery to help smooth blood flow what happens to these fibres as the pressure of the blood in the artery changes

Answer 30

-stretch as pressure increases
-recoil

Question 31

give one way in which the structure of the wall of Ana artery is sismila to the structure of the wall pf the capillary

Answer 31

both have endothelium cells

Question 32

why data represented as %

Answer 32

easier to compare if sample size is effectifekt the same

Question 33

what is partial pressure meant

Answer 33

measure of conc of gas

Question 34

explain the advantage of the difference in dissociation curve during exercise (lower than rest)

Answer 34

haemoglobin has a lower affinity for oxygen
more o2 for respiration

Question 35

give two ways in which total oxygen supplied to muscles during excserise is increased

Answer 35

inc depth
inc stoke volume

Question 36

after several mo nth of training an athlete has had the sane cardiac output has a lower resting heart rate than before explain why

Answer 36

inc in volume/size of ventricles

Question 37

explain how the structure of the arteries reduces fluctuations in pressure

Answer 37

Islamic which allows it to recoil

Question 38

explain how the structure of the capillaries is related to function

Answer 38

one cell thick so short diffusion distance

Question 39

describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary

Answer 39

-hp forces water out
-hp higher than wp
proteins remain in blood
-wp higher than hp
-water returns by osmosis
-water moves out at arteriole

Question 40

which chamber of the heart produces the increase in pressure recorded in the aorta

Answer 40

left ventricle

Question 41

explain how aerobic respiration in cells leads to a change in the ph of blood plasma

Answer 41

co2 produced and h+ ions released

Question 42

what os the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma ph decreases

Answer 42

high rate response low ph
more o2 released

Question 43

explain how efficient gas exchange is ensures by the dissociation curve for the foetus being to the left of the dissociation curve for the women

Answer 43

fetal haemoglobin has a greater affinity for oxygen
loads oxygen from mothers blood

Question 44

a women tajes moderate excerisse explain what causes her heart rate to increase while she excserises

Answer 44

rate of respiration increases
carbon dioxide conc inc
chemoreceptors in aporta
impulses to medulla
inc frequency of impulses
along sympathetic pathway to sinoatrial node

Question 45

describe the route taken when electrical impulses are transmitted from the sinoatrial node to the muscles of the ventricles in a healthy heart

Answer 45

through cardiac muscle;
to atrioventricular node;
along bundle of His / Purkyne fibres;

Question 46

explain why there is a net loss of water from. capillary at the arterial end

Answer 46

at arterial end) hydrostatic pressure / blood pressure;
greater than pressure of water potential gradient / greater than osmotic uptake;

Question 47

the total volume of fluid that passes from the capillaries to the surrounding tissue fluid is normally greater than the volume that is reabsorbs into them
describe what happens to the extra fluid

Answer 47

removed by lymphatic system / lymph; returned to blood;

Question 48

tissue fluid accumulates in the tissues of people who do not eat enough protein explain why

Answer 48

less protein in blood;
water potential gradient is lower (less –ve / higher ).

Question 49

explain the advantage of the curve for metal haemoglobin being fiddferent from the curve of adult haemoglobin

Answer 49

fetal haemoglobin has higher affinity for oxygen / takes up oxygen (becomes saturated) at lower partial pressure;
at partial pressures when adult haemoglobin dissociates fetal haemoglobin takes up oxygen;

Question 50

how does the elastic tissue help to smooth out the flow of blood in the blood vessels

Answer 50

stretches / expands to accommodate increase in blood
volume / when ventricle contracts / increase in blood pressure; recoils when blood volume decreases / when ventricle
relaxes / blood pressure decreases;

Question 51

the maximum pressure in the left atrium is lower than the maximum pressure in the left ventricle
what causes this difference in maximum pressure

Answer 51

less muscle / thin(ner) wall in left atrium;

Question 52

explain how a change in ph from 7.4 to 7.2 affects the supply pf xugen by haemoglobin to the tissue

Answer 52

more oxygen unloaded / given up / affinity decreased / reduced saturation; oxyhaemoglobin dissociates at higher oxygen concentration / partial pressure / more oxygen unloaded at the same ppO ;

Question 53

in the light dependent reaction of photosynthesis , the carbon in co2 becomes carbon in tp explain how

Answer 53

.
1)Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. To produce two molecules of glycerate 3-phosphate / GP;
3. Reduced to triose phosphate / TP;
4. Requires reduced NADP;
5. Energy from ATP;

Question 54

the scientists monitored the number of hours of sunshine per month. Explain why they monitored the number of hours of sunshine

Answer 54

So that they could eliminate this factor from affecting the yield

Question 55

the temp ,fertiliser number of pests were controlled during investigation . name one other factor which should have been controlled during the investigation. explain why variation in this factor would affect yield.

Answer 55

variety of tomato
yield will vary with different varieties

Question 56

additional information is required for tomato growth to decide whether it is economically profitable to addd extra co2 to produce very early tomato

Answer 56

1)costs of co2 supply
2)price of tomatoes

Question 57

in the light dependent reaction of photosynthesis light enemy generates atp

Answer 57

1)light excites electrons
2)redox reaction series
3)etc
4)energy released
5)atp generated from ads and phosphate

Question 58

describe the light independent reactions of photosynthesis and explain how they show the continued synthesis of hexose sugars

Answer 58

-co2 =RUBP
-2GP-TP
-energy/atp
-ewduced nap
-tp forms hexose
-all rubs reformed

Question 59

explain why the increase in the dry mass of a plant over 12 months is less than the mass of hexose produced over the same period

Answer 59

-some hexose used in resp
-co2 produced
-some parts of the plant are eaten

Question 60

changing the co2 had a greater effect on the rate of transpiration when the plants were wasters than when they were kept in dry conditions. explain why

Answer 60

dry conditions-stomata partially closed
due to turgor in guard cells

Question 61

in the presence of oxygen respiration yields more atp per molecule of glucose than it does in the absence of oxygen explain why

Answer 61

-oxygen as terminal hydrogen
-atp formed in glycolysis
-aerobic respiration

Question 62

describe how light energy absorbed by chlorophyll molecule is used to synthesis atp

Answer 62

-excitation of electrons leave chlorophyll atp prodcued
-etc
-loss of energy by electrons
-adp and pi

Question 63

role of chlorophyll in photolysis

Answer 63

-absorbs light
-loses electrons

Question 64

how the energy pf light is converted into chemical energy in the light dependant reactions

Answer 64

-electeons raised ti higher energy levels
-etc
-act produced

Question 65

exlain why between 300-360 secs the conc of radioactive rubs increased

Answer 65

-no co2 to combine with
-rubp- gp-tp

Question 66

atp function in light independent reactions

Answer 66

provides energy for gp-tp

Question 67

reduced nadp function in light independent reactions

Answer 67

provides h/electrins from gp-tp

Question 68

explain why the concentration of oxygen and amount of add fell during the investigation

Answer 68

-adp and phosphate forms atp
-oxygen used to form water

Question 69

describe how reduced nadp is reduced in the light dependent reactions of photosynthesis

Answer 69

-electrons from chlorophyll

Question 70

explain why there is twice the amount of glyxerate 3 phosphate as ribulose biphopshate when the co2 conc is high

Answer 70

more co2 binding to rubp to produce 2 gp

Question 71

explain the rise in the amount of rubp after the co2 conc is reduced

Answer 71

less used to combine to co2

Question 72

explain how lack of light caused the amount of radioactively labelled glycerine 3 phosphate to rise

Answer 72

-atp and reduced nap fromed
-gp is not being used to form rubp

Question 73

where does light independent take ;lace

Answer 73

stroma

Question 74

explain why the tubes were placed the same distance from the lamp

Answer 74

same amount of heat

Question 75

explain how enhancing the co2 conc helps inc yield

Answer 75

rate of photosynthesis increased;
normal atmospheric concentration a limiting factor / more / faster production of biomass or sugars / more products of photosynthesis transported to fruits;

Question 76

maintaining a high temp in. a glasshouse in winter when the light intensity is low may reduced the yield explain how

Answer 76

increases rate of respiration; rate of photosynthesis too low to replace respiratory loss

Question 77

two products of light dependent stage

Answer 77

nadph
atp

Question 78

the products od the light dependent reaction are used in light independent of photosynthesis what are these products used for

Answer 78

to make sugars 9
44

Question 79

Explain what is meant by the tertiary structure of a protein

Answer 79

Way in which the whole protein / polypeptide is folded / shape adopted by whole protein molecule / further folding of 2° structure;

Question 80

Explain how heating an enzyme leads to it being denatured.

Answer 80

More (kinetic) energy;
Bonds / specified bonds (holding tertiary structure) break;

Question 81

Describe how the sequence of amino acids in part of the protein from Job’s enable this protein to act as an enzyme inhibitor.

Answer 81

1)
2. This is tertiary structure;
3. Has similar shape to substrate;
4. Fits / competes for active site;
5. Fits at site other than active site;
6. Distorting active site;
7. Therefore substrate will not fit (active site)

Question 82

Haemoglobin is a protein with a quaternary structure. What is meant by a quaternary structure?

Answer 82

aggregation of several polypeptide chanins / tertiary structures

Question 83

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

Answer 83

Low pH / (more)H
Oxygen diffuses from r.b.c. to tissues;

(increased) dissociation of haemoglobin;

Question 84

Haemoglobin is broken down in the liver. One product of this breakdown is amino acids. Give one use in the body of these amino acids

Answer 84

Deaminated for use in respiration / used in protein synthesis / suitable

Question 85

(b) How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?

Answer 85

body temp 37 degrees optimum for enzymes
excesss can denature
fewer e-s complex
fewer complexes
cannot bind
reaction slowed

Question 86

4
Lactose is a disaccharide found in milk. In the small intestine, it is digested into glucose and galactose by the enzyme lactase. Molecules of lactase are located in the plasma membranes of cells lining the small intestine.
(a) What evidence in the paragraph suggests that galactose is a monosaccharide

Answer 86

digestion of a disaccharide into monosaccharides

Question 87

Name one other digestive enzyme that is located in the plasma membranes of cells lining the small intestine

Answer 87

dipeptidase

Question 88

Give an advantage of lactase and other digestive enzymes being located in the plasma membranes of cells lining the small intestine, rather than being secreted into the lumen of the small intestine.

Answer 88

more effective absorption of products by the enzymes

Question 89

(c) The absorption of galactose from the small intestine is reduced if the absorbing cells are treated with a respiratory inhibitor, such as cyanide. Suggest an explanation for this.

Answer 89

no atp formed
active transport into cell

Question 90

explain why the rate of the reaction decreases as the reactions

Answer 90

substrate decreases so fewer complexes

Question 91

Explain how inhibitors affect the rate of enzyme-controlled reactions.

Answer 91

-inhibitors in general - prevent entry ,binding of substrate to active
-fewer e-s complexes formed
-competitive -
-non competitive -binds to alloestric site and change shape of active sire

Question 92

name two polymer present in mammals and fish that contain nitrogen

Answer 92

proteins
haemoglobin

Question 93

describe how urea is removed from the blood

Answer 93

-hydorstatic pressure
-ultrafiltrartion at Bowmans capsule
-through basement membrane
-enabled by small size of urea molecule

Question 94

Explain how urea is concentrated in the filtrate.

Answer 94

-reabroption of water
-by osmosis
-active transport of ions

Question 95

by what processes does used urea enter the fluid in the abdominal cavity from the blood

Answer 95

by (simple) diffusion;

Question 96

why dialysis fluid changed every five hours

Answer 96

to maintain concentration gradients

Question 97

how to ensure specimens collected at random

Answer 97

-random coordinates and grid area

Question 98

how non competitive inhibitor would decrease the rate of the reaction catalysed by the enzyme

Answer 98

binds to allosteric binding site
changes shape
can no longer bind

Question 99

how amino acids are closely held together to form active site

Answer 99

amino acid chains folds
disulphide bridges holding structure together

Question 100

The higher the altitude, the lower the mean temperature. Explain how the lower temperature at high altitude reduces the growth of plants.

Answer 100

-lower enzyme activity
-decrease in rate of photo and less carb produced
-lowerr resp
-less nutrient uptake

Question 101

Which two substances are formed when two amino acid molecules join together

Answer 101

dipeptide and water

Question 102

Explain how a change in the primary structure of a globular protein may result in a different three-dimensional structure.

Answer 102

sequence of amino acids change
tertiary structure changes
bonds formed in different places

Question 103

explain why there is no further decrease in there conc of potassium ion in the solution with the inhibitor after 60 minutes

Answer 103

absorption viz diffusion no longer occurs
because no conc gradient

Question 104

The substance malonate is an inhibitor of respiration. It has a structure very similar to the substrate of an enzyme that catalyses one of the reactions of respiration. Explain how malonate inhibits respiration

Answer 104

binds to complimentary acirvcw sure
prevent substrate from forming enzyme substrate complex

Question 105

(c) Explain how
(i) raising the temperature to 35 °C affects carbohydrase activity;

Answer 105

inc kr
inc collisooms
fast rate of es complexes being formed
inc take of break down of starch

Question 106

decreasing the pH affects carbohydrase activity

Answer 106

changes shape of the active site
disrupts the bonds
fewer es formed
inc h+ ions
decreases break down of starch

Question 107

describe how you would carry out an investigation to find the optimum temperature for the acritivty of urease

Answer 107

method to maintain tens- water bath
-time taken touters indictor blue

Question 108

describe how t lympjpcytes recognise and respond to the influent Virus

Answer 108

receptor recognise shape
clone
destroy virus

Question 109

1e) Explain how a change in a sequence of DNA bases could result in a non-functional enzyme.

Answer 109

Change in (sequence of) amino acids / primary structure;
Change in hydrogen / ionic / disulfide bonds leads to change in tertiary structure / active site (of enzyme

Question 110

2(d) The scientists found that, in a second species of bacterium, 29% of the bases were guanine.
Explain the difference in the percentage of guanine bases in the two species of bacterium.

Answer 110

Different genes;
Different (DNA) base sequences

Question 111

3(b) A piece of mRNA is 660 nucleotides long but the DNA coding strand from which it was transcribed is 870 nucleotides long.

Explain this difference in the number of nucleotides.

What is the maximum number of amino acids in the protein translated from this piece of mRNA? Explain your answer.
Number of amino acids and
Explanation

Answer 111

220; allow 218 or 219-allow 2
Three bases / nucleotides code for one amino acid;

Question 112

3bii two differences between the structure of mana and trna

Answer 112

mRNA has no base-pairing, tRNA has base-pairing / mRNA linear,
tRNA cloverleaf shape; mRNA has no binding site for amino acids,
tRNA has; mRNA different for each gene / many kinds, only few / 20 / 64 kinds of tRNA; accept mRNA longer / larger / more nucleotides than tRNA

Question 113

4b A particular gene is 562 base-pairs long. However, the resulting mRNA is only 441 nucleotides long. Explain this difference

Answer 113

idea that DNA contains introns / mRNA is only exons / mRNA is “edited’;

Question 114

4c tetracycline binds to bacterial ribosomes. This is shown in the diagram.
Protein synthesis in bacteria is similar to that in eukaryotic cells. Explain how tetracycline stops protein synthesis.

Answer 114

binds to / blocks codon / triplet on mRNA so anticodon / tRNA will not fit in / base-pair;
amino acids not delivered / joined;

Question 115

5a)Explain why there are clear zones around some of the discs containing antibiotic.

Answer 115

antibiotic has diffused / spread / moved into agar; killed / inhibited bacteria;

Question 116

5c) tacycline prevents bacterial growth by preventing protein synthesis. Give two other ways in which antibiotics can prevent bacterial growth.

Answer 116

disrupts cell wall / prevents cell wall synthesis; stops DNA replication;

Question 117

6(ii) At what stage in the cell cycle would these errors in copying DNA bases occur?

Answer 117

S-phase / interphase;

Question 118

6e)Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is synthesised.

Answer 118

1) mana leaves nucleus through nuclear pore
2) to ribosome
3)trena molecule bring amino acids to ribosomes
4)specific trna molecule for specific amino acid
5)anticodon of trna corresponds to complimwntayr codon on MRNA
6)peptide bond from and collects another amino acida
8)ribosomes move along mrna

Question 119

7a)sequence of pertain synthesis

Answer 119

cbefad

Question 119

ii )in which part of the cell does the two strands of dna molecules separate

Answer 119

nucleus

Question 120

8a)what is the role of rna polymerase in transcription

Answer 120

join / attach nucleotide

Question 121

ii) name the organelle involved in translation

Answer 121

ribosome

Question 122

9a give two factors other than cost that should be considers when selecting an antibiotic to treat and bacterial disease

Answer 122

side effects / allergic reactions / low toxicity to cells;
interaction with other drugs / effective in conditions of use / reasonably stable; should only act on the problem bacteria / narrow spectrum;
how much resistance the bacteria have built up;

Question 123

b tetracycline- prevents tRNA binding
Chloramphenicol- prevents peptide bonds forming
explain how each of these antibiotics slows down the rate pf growth of bacteria

Answer 123

tetracycline
prevents tRNA binding to ribosomes / amino acid / mRNA
amino acids not available / brought / picked up;
chloramphenicol
prevents amino acids being joined / prevents primary structure forming;
no enzymes / no structural proteins formed

Question 124

10a. describe the role of trna in the process of translation

Answer 124

(b) anticodon complementary to codon / reads message on mRNA; specific amino acid;
carried / transferred (to ribosome);
correct sequence of amino acids along polypeptide;

Question 125

11a- name one mutagenic agent

Answer 125

high energy radiation

Question 126

11bi describe how a deletion mutation alters the structure of a gene

Answer 126

removal of one or more bases / nucleotide;
frameshift / (from point of mutation) base sequence change;

Question 127

11bii for example describe and explain how the altered gene could result in flax plants with white coloured flowers

Answer 127

sequence of bases in mRNA would change;
(sequence of) amino acids different / different primary structure; (active site / enzyme 1) changed tertiary shape / changed active sites;
white pigment does not bind;
lilac pigment not produced / white pigment remains unchanged / enzyme 1 does not function;

Question 128

12) Chlamydomonas lives in fresh-water ponds. It uses its flagella to swim towards light of moderate intesnitryt but away from v eat bright light
using infdirmaton. in the diagram explain the advnagteg of this behaviour

Answer 128

chloroplast, so cell photosynthesises and moves to optimum / best light intensity for photosynthesis;
avoids damage due to bright light;

Question 129

(b)
A Chlamydomonas cell has two flagella. These flagella contain a single sort of protein. A flagellum consists of a bundle of 242 filaments. Each filament consists of 7500 protein molecules. Each protein molecule contains 900 amino acid units.
(i) What would be the minimum number of nucleotides in the coding region of the mRNA used to synthesise this protein?

Answer 129

2700

Question 130

13C Give two factors which might increase the frequency at which a mutation in DNA occurs.

Answer 130

high energy radiation / X rays / ultraviolet light / gamma rays; high energy particles / alpha particles / beta particles;
named chemical mutagens e.g. benzene / caffeine / pesticide / mustard gas / tobacco tar / free radicals;
(two named examples of any of the above = 2 marks)
length of time of exposure (to a mutagen); dosage (of mutagen);

Question 131

13 Lysozyme is an enzyme consisting of a single polypeptide chain of 129 amino acids.
(a) What is the minimum number of nucleotide bases needed to code for this enzyme?

Answer 131

387

Question 132

14 B Describe how the information on mRNA is translated into CFTR at the ribosome.

Answer 132

codon on mRNA;
specific / complementary base pairing with; anti-codon on tRNA;
specific tRNA for each amino acid;
protein formed by condensation reactions / peptide bonds formed;

Question 133

15 BI Describe the role of macrophages in stimulating B lymphocytes.

Answer 133

antigen in membrane presented to lymphocytes / produce cytokinins;

Question 134

16 )Mitochondria contain the genes needed for the synthesis of the enzymes involved in the electron transport chain. One of these enzymes is cytochrome oxidase. If a mutation occurs during replication of the mitochondrial genes, functional cytochrome oxidase may not be produced.
S Explain why mutation of a mitochondrial gene might result in no functional cytochrome oxidase being produced.

Answer 134

16
change in base / nucleotide (in DNA);
change in base sequence of mRNA / change in codons / idea of frameshift following deletion or addition / incorrect tRNA / anticodon; incorrect amino acids / different primary structure / fomation of new stop codon;
different tertiary structure / different 3D structure / different polypeptide / shortened polypeptide;
different shape of active site / no active site presen

Question 135

18) Starting with mRNA, describe how the process of translation leads to the production of a polypeptide.

Answer 135

mRNA attaches to ribosome;
codon on mRNA;
binds to an anti-codon on tRNA;
each tRNA brings a specific amino acid;
sequence of codons / bases on mRNA determines order of amino acids; formation of peptide bonds / amino acids joined by condensation reactions;

Question 136

21 (b)
Explain how a gene codes for a protein

Answer 136

Base sequence (on DNA/in gene);
Determines sequence of amino acids;
By determining base sequence on (messenger) RNA; Code is a triplet code/three base code for an amino acid;

Question 137

21 a two different res tween the structure of dna and rna

Answer 137

Large molecule
Smaller
Double stranded
Single stranded
Contains Thymine (T)
Contains Uracil (U)
Contains deoxyribose
Contains ribose

Question 138

20b describe the part played by rna in protein synthesis

Answer 138

Carries coded information about the sequence of amino acids; Copied from DNA/gene;
Code is in sequence of bases / triplet / three bases / a codon codes for one amino acid;
Moves out of nucleus/goes into cytoplasm; To ribosomes

Question 139

(a) Explain why it was important that the piece of the epidermis that the student removed was thin.

Answer 139

single layer of cells so light can pass through

Question 140

1b Suggest how the student could have used his slide to find the number of stomata per cm

Answer 140

Method of determining area of field of view / area seen using microscope;
Count number of stomata in field of view;
Repeats and calculation of mean;

Question 141

1c The stomata on the leaves of pine trees are found in pits below the leaf surface. Explain how this helps to reduce water loss.

Answer 141

Water vapour accumulates / increased humidity / reduced air movement (around stomata);
Water potential / diffusion gradient reduced;

Question 142

2a What is a tissue?

Answer 142

Group of) similar / identical cells / cells with a common origin

Question 143

2bi Starch was present in the cells of this tissue. Describe how the student could find out where in the cells the starch was present.

Answer 143

Add iodine / stain specific for starch to the slide / cells / tissue / add iodine / stain specific for starch and examine under microscope;
Blue-black / blue / black / purple;

Question 144

2b ii The student cut a thin section of the tissue. Explain why it was important that the section was thin.

Answer 144

Need a single layer of cells / only a few cells thick / not too many layers / detail obscured by cells underneath;
Light must be able to pass through;

Question 145

2c The cell walls of potato cells contain cellulose. Cellulose and starch are both carbohydrates. Describe two ways in which molecules of cellulose are similar to molecules of starch.

Answer 145

Both are polymers / made of monomers;
Joined by condensation / molecules can be broken down by hydrolysis;
Both have 1-4 links;
Contain C(arbon), H(ydrogen) and O(xygen) / both made up of glucose;
Both insoluble;
Both contain glycosidic bonds;

Question 146

3a the scientists put the same number of skin tumour cells in each dish at the start of this investigation. Explain why it was important to put the same number of cells in each dish.

Answer 146

To ensure the colour is the same at the start;

Question 147

3c An article in a newspaper claimed that these data show that bromelain can be used to treat cancer.
Give three reasons why we should be careful about accepting this claim.

Answer 147

Use of mouse cells (rather than human);
(Carried out) in vitro / not in living organisms;
Only tested on one type of cancer;

Question 148

3d The rate of cell division is important in investigations into cancer. Suggest why.

Answer 148

The faster the rate of division the faster the cancer would grow;
By measuring rate of cell division you could see how effective the treatment was;

Question 149

3e cientists have investigated the effects of bromelain on cancer growth in humans. Suggest why they gave bromelain in addition to, rather than instead of, the usual treatment.

Answer 149

Not ethical to replace conventional treatment;
As life of patient is at risk (if bromelain not effective);

Question 150

5aiExplain why
(i) the leaves were homogenised,

Answer 150

break open cells / release cell contents;

Question 151

4
Scientists use optical microscopes and transmission electron microscopes (TEMs) to investigate cell structure. Explain the advantages and the limitations of using a TEM to investigate cell structure.

Answer 151

Advantages:
1 Small objects can be seen;
2 TEM has high resolution as wavelength of electrons shorter;
Accept better
Limitations:
3 Cannot look at living cells as cells must be in a vacuum / must cut section / thin specimen;
4 Preparation may create artefact
5 Does not produce colour image;

Question 152

why buffer solution used

Answer 152

keep pH the same / controls pH;

Question 153

6a Organelle found in plant cells. Contains
inner membranes arranged in stacks. Organelle B
Name organelle B.

Answer 153

Chloroplast;

Question 154

6c ii The ground liver was centrifuged at low speed. The pellet that formed at the bottom of the centrifuge tube was thrown away and the supernatant centrifuged again at higher speed. Explain why it was necessary to first centrifuge the ground liver at low speed in order to obtain a suspension of organelle D

Answer 154

To remove organelle C / nuclei; Which are larger / more dense;

Question 155

7e (e) Skin cells may be studied with a transmission electron microscope or an optical microscope. Explain the advantages and limitations of using a transmission electron microscope to study cells

Answer 155

Advantages:
1 Small objects can be seen;
2 TEM has high resolution as wavelength of electrons shorter;
Accept better
Limitations:
3 Cannot look at living cells as cells must be in a vacuum;
4 must cut section / thin specimen;
5 Preparation may create artefact
6 Does not produce colour image;

Question 156

9a Labelled antibodies and an electron microscope can be used to produce images locating proteins on the surface of organelles, but cannot be used to observe cross bridge cycling in muscle cells. Explain why.

Answer 156

1. e.m. gives high resolution due to short wavelength of electrons;
2. antibodies attach specifically to target proteins;
3. gold particles are electron dense;
4. electrons must pass through a vacuum so material must be dead / fixed for e.m.; 5. cross-bridge cycling requires living cells / metabolism / named aspect-e.g. ATP synthesis;

Question 157

9b Describe the role of calcium ions and ATP in muscle contraction.

Answer 157

1. Ca removes blocking molecules / uncovers binding site on actin;
   2+
2. correct references to Ca binding to troponin / moving tropomyosin;
3. allows myosin heads to attach to actin filaments;
4. allows sliding of the actin and myosin filaments;
5. binding of ATP causes myosin (head) to detach (from actin); 6. (hydrolysis of) ATP releases energy;
6. which changes the configuration / cocking of the myosin head;

Question 158

10c Starting with some lettuce leaves, describe how you would obtain a sample of undamaged chloroplasts. Use your knowledge of cell fractionation and ultracentrifugation to answer this question.

Answer 158

1. Chop up (accept any reference to crude breaking up); 2. Cold;
2. Buffer solution;
3. Isotonic / same water potential;
4. Filter and centrifuge filtrate;
5. Centrifuge supernatant;
6. At higher speed;
7. Chloroplasts in (second) pellet;

Question 159

13 a Suggest two variables, other than genotype, which need to be controlled to ensure similar root growth in different plants. In each case give the reason for your answer.

Answer 159

ll plants of the same age, so same time for cell divisions / differentiation; all plants given the same watering, so same amount of water for
cell expansion;

Question 160

12c Describe how a sample consisting only of chloroplasts could be obtained from homogenised plant tissu

Answer 160

use of differential centrifugation / or description;
first / low-spin pellet discarded / spin at low speed to remove cell
wall material / cell debris;
supernatant re-spun at higher speed / until pellet with chloroplasts is found; method of identifying chloroplasts e.g. microscopy;

Question 161

13b Suggest how the proportion of dividing cells in a thin section could be determined.

Answer 161

count cells using microscope;
count number of cells in cell division / where chromosomes visible; and then the total number of cells in field of view;

Question 162

13 c Explain the change in the proportion of dividing cells with increasing distance from the root tip.

Answer 162

only cells at tip have ability to divide / cells further back don’t divide; cells further back differentiating / named example of
(accept reference to loss of totipotent cells)
differentiated tissue / too old / reduction in plant hormone;
cell wall too thick / vacuole too large to allow division;

Question 163

16ii Explain why an electron microscope shows more detail of cell structure than a light microscope.

Answer 163

electron microscope has a greater resolving power / objects closer
together can be distinguished;
electron (beams) have a shorter wavelength

Question 164

16c The length of mitochondria can vary from 1.5 μm to 10 μm but their width never exceeds 1μm. Explain the advantage of the width of mitochondria being no more than 1μm.

Answer 164

diffusion pathway / short pathway to the centre / large SA:V ratio

Question 165

17ci Give the evidence to show that DMD is caused by a recessive allele.

Answer 165

8 has DMD but 3 and 4 do not / 12 has DMD but 6 and 7 do not / neither parent has the condition but their child has

Question 166

17di the number of copies of gene fragments F and G shows that person Explain how.

Answer 166

No gene fragment G;

Question 167

18bi The organelles labelled X all have very similar shapes in this cell. Explain why they appear to have different shapes in this drawing.

Answer 167

Sections cut at) different angles/in different planes;

Question 168

18(ii) Large numbers of organelles X and Z are found in mucus-secreting cells. Explain why.

Answer 168

Z modifies/packages/transports/secretes mucus/ Z adds sugars to proteins; X provides ATP/energy (for this);

Question 169

1a describe how ATP is resynthesised in cells.

Answer 169

1. From ADP and phosphate;
2. By ATP synthase;
3. During respiration/photosynthesis;

Question 170

1b
(b) Give two ways in which the hydrolysis of ATP is used in cells.

Answer 170

. To provide energy for other reactions/named process;

2. To add phosphate to other substances and make them more reactive/change their shape;

Question 171

2a (a) Phospholipids are one of the storage molecules found in cherry seeds.
Name the type of reaction used to break down phospholipids to release phosphat

Answer 171

Hydrolysis (reaction);

Question 172

2b The scientists concluded that an increase in phosphate in the embryo was linked to growth of the embryo.

Suggest two reasons why an increase in phosphate can be linked to growth of embryo

Answer 172

phosphate required to make rna
phosphate required to make dna
phosphate to make atp/adp
phosphate to make membrane
phosphate required for phosphorylation

Question 173

2d The chilling requirement of seeds of certain plant species is considered to be an adaptation for survival in countries with seasonal changes in environmental conditions.
Suggest how this adaptation may enable these plant species to survive and respond to seasonal changes.

Answer 173

(d) 1.
Seeds/embryo remain dormant/inactive in winter/cold

2. Seeds/plants develop in spring/summer

Question 174

3a (a) Describe the roles of calcium ions and ATP in the contraction of a myofibril.

Answer 174

.1)calcium ions diffuse into mcirofibmilism for ends reticulum
2. (Calcium ions) cause movement of tropomyosin (on actin);
3. (This movement causes) exposure of the binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each myosin head causes myosin heads
Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
to detach (from actin sites).

Question 175

3b ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.

Answer 175

1)releases relatively small amount of energy / little energy lost as heat;

2. Releases energy instantaneously

3)phosphorylkatess other compounds making them more reactive
4)can be rapidly resynthesised
5)is not lost from cells

Question 176

4a (a) ATP is useful in many biological processes. Explain why.

Answer 176

Releases energy in small / manageable amounts;

Broken down) in a one step / single bond broken immediate energy compound / makes energy available rapidly;

3. Phosphorylates / adds phosphate makes (phosphorylated substances) more reactive / lowers activation energy;

Reformed / made again;

Question 177

4c Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP during respiration. Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis.

Answer 177

In the dark no ATP production in photosynthesis;

2. Some tissues unable to photosynthesise / produce ATP;
3. ATP cannot be moved from cell to cell / stored;
4. Plant uses more ATP than produced in photosynthesis;
5. ATP for active transport / synthesis (of named substance);

Question 178

5b (b)
Write a simple equation to show how ATP is synthesised from ADP.

Answer 178

ADP+Pi→ATP;

Question 179

5c Give two ways in which the properties of ATP make it a suitable source of energy in biological processes.

Answer 179

1.
Energy released in small / suitable amounts;

Soluble;

Involves a single / simple reaction;

Question 180

5d Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP.

Answer 180

ATP cannot be stored / is an immediate source of energy;
ATP only releases a small amount of energy at a time

Question 181

6a (a)
Describe the part played by the inner membrane of a mitochondrion in producing ATP.

Answer 181

electrons transferred down etc
provides energy to take protons
protons pass back through membrane
energy used to combine adp and phosphate

Question 182

6b A scientist investigated ATP production in a preparation of isolated mitochondria. He suspended the mitochondria in an isotonic solution and added a suitable respiratory substrate together with ADP and phosphate. He bubbled oxygen through the preparation.
(i)
(ii)
Why was the solution in which the mitochondria were suspended isotonic?

Answer 182

Prevent damage to mitochondria caused by water / osmosis / differences in water potential

Question 183

bii Explain why the scientist did not use glucose as the respiratory substrate.

Answer 183

Glucose is used / broken down during glycolysis in cytoplasm / not in mitochondria;

Question 184

7ai n anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose?

Answer 184

2 molecule

Question 185

7 ii Give two advantages of ATP as an energy-storage molecule within a cell

Answer 185

(ii)
Cannot pass out of cell;
Quickly / easily broken down (hydrolysed) / broken
down in a on-step reaction / immediate source of energy; Stores / releases small amounts of energy;

Question 186

describe how NAD is regenerated in anaerobic respiration in yeast cells.

Answer 186

Formed when reduced NAD used to reduce / donate H ions to pyruvate / convert pyruvate to ethanol;

Question 187

8a (a)
Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae.

Answer 187

more cristae / larger surface area) for electron transport chain /
more enzymes for ATP production / oxidative phosphorylation; muscle cells use more ATP (than skin cells)(not just more respiration);

Question 188

8b Substance X enters the mitochondrion from the cytoplasm. Each molecule has three carbon atoms name substance x

Answer 188

pyruvate

Question 189

9ii When glucose is respired what happens to the energy which is not incorporated into ATP?

Answer 189

released as heat

Question 190

9bi When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration.

Answer 190

lgucose only partly broken down

Question 191

9bii At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this.

Answer 191

(ii) lactate / lactic acid has built up / been produced; oxygen used to break down lactate / convert it back to pyruvate / glucose / glycogen

Question 192

10a Name the substance that muscles use as their immediate energy source

Answer 192

atp

Question 193

11 The movement of the woodlice in low relative humidity is an advantage to their survival. Explain how.

Answer 193

Low humidity results in more woodlice moving;
So increased movement increased chance of leaving dry / unfavourable environment so reduce water loss / reduce evaporation;

Question 194

Explain why the following steps were necessary in finding the water content of straw:

heating the straw until it reaches constant mass

not heating the straw above 90°C

Answer 194

both are polymers / polysaccharides / built up from many sugar units / both contain glycosidic bonds / contain (C)arbon, (H)ydrogen and (O)xygen;

Question 195

covering of lignin protects cellulose from enzyme attack (line 14). Use your knowledge of the way in which enzymes work to explain why cellulose-digesting enzymes do not digest lignin.

Answer 195

hemicellulose shorter / smaller than cellulose / fewer carbons; hemicellulose from pentose / five-carbon sugars and cellulose from hexose / glucose / six-carbon sugars;

Question 196

student investigated the stages of mitosis in a garlic root. The root tip was placed on a microscope slide with a stain. A cover slip was placed on top and the root tip was firmly squashed.
(a) Explain why
a root tip was used;
a stain was used;
the root tip was firmly squashed.

Answer 196

where mitosis / division / growing occurs

to distinguish chromosomes / chromosomes not visible without stain;

(iii) to let light through / thin layer;

Question 196

12e Describe the structure of a cellulose molecule and explain how cellulose is function in cells.

Answer 196

1. made from β-glucose;
2. joined by condensation / removing molecule of water / glycosidic bond; 3. 1 : 4 link specified or described;
3. “flipping over” of alternate molecules;
4. hydrogen bonds linking chains / long straight chains;
5. cellulose makes cell walls strong / cellulose fibres are strong; 7. can resist turgor pressure / osmotic pressure / pulling forces; 8. bond difficult to break;
6. resists digestion / action of microorganisms / enzymes;

Question 197

2a (iii)
Cell C is in interphase. Give two processes which occur during interphase that enable cell division to occur.

Answer 197

Increase in volume of cell / volume of cytoplasm / increase in mass / cell bigger; increase in number of organelles;
synthesis of protein / named protein;
DNA replication / increase / chromosomes copied;
ATP synthesis / respiration;

Question 198

Division of the nucleus by meiosis produces haploid cells from a diploid cell. Nuclei produced by mitosis have the same number of chromosomes as the parent nucleus.
4 (a)
What is the biological importance of reducing the chromosome number when the cell divides by meiosis?

Answer 198

Later fertilisation / cell fusion; (NOT just ‘sexual reproduction’)
Restoring diploid / original number / not doubling chromo

Question 199

4b mitosis and emisosis differences

Answer 199

Homologous) chromosomes associate in pairs
(Homologues) independent / do not pair (IGNORE ref. separation
Crossing-over / chiasmata formation
No crossing-over;
Two / (nuclear stages) divisions / → 4 offspring cells
One / (nuclear stage) division / → 2 offspring cells;
Genetically different (product)
Genetically identical (product);

Question 200

5a give one process which occurs in the nucleus of a cell during interphase which is necessary before cell division can take place

Answer 200

replication / duplication / doubling of chromosomes / replication of DNA / transcription of DNA;

Question 201

5c
Explain one advantage of cells lining the human gut dividing very frequently.

Answer 201

to replace cells;

Question 202

6 (ii) Describe two ways in which both types of tumour ma

Answer 202

may damage organ concerned;
may cause blockages / obstructions;
may damage / exert pressure on other organs;

Question 203

bi Explain the link between sunbathing and skin cancer.

Answer 203

ecause sun’s radiation contains ultra violet radiation; this causes mutation of genes which control division;

Question 204

bii Suggest why fair-skinned people are at a greater risk of skin cancer than dark-skinned people when sunbathing.

Answer 204

because fair skin has little melanin which protects against u.v. radiation

Question 205

iii Suggest why people with a family history of cancer are at a greater risk of cancer than those with no family history of cancer.

Answer 205

because cancer has genetic component / may have inherited (onco)gene / gene which gives predisposition to / causes cancer;

Question 206

7
(a) Explain why the new embryos produced are a clone.

Answer 206

produced by mitosis; genetically identical;

Question 207

(b) If embryos with more than eight cells are split up, the separated cells fail to develop into new embryos. Suggest why.

Answer 207

cells lost ability to control development / no longer totipotent / cells have differentiated / become specialised;

Question 208

8a cell cycle events

Answer 208

(D) B E A C;

Question 209

8b phase in whcug dna rep occurs

Answer 209

metaphase

Question 210

10a
Describe and explain how the structure of DNA results in accurate replication.

Answer 210

2 base pairing / hydrogen bonds holds strands together
3 hydrogen bonds weak / easily broken, allow strands to separate;
4 bases (sequence) (exposed so) act as template / can be copied;
5 A with T, C with G / complementary copy;
6 DNA one parent and one new strand;
(b)
(c)
1) two strands therefore semi-conservative replication (possible);

Question 211

9c (c)
Most plants produce seeds after fertilisation in sexual reproduction. However,
dandelions produce small, windblown seeds without fertilisation taking place. Suggest two advantages to the dandelion of being able to reproduce from these seeds, as well as from pieces of root.

Answer 211

dispersal / prevent overcrowding / competition / colonise ; increased number of (proven) offspring; (not quicker)

Question 212

(b) Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.

Answer 212

chromosomes shorten / thicken / supercoiling;
chromosomes (each) two identical chromatids / strands / copies
(due to replication);
chromosomes / chromatids move to equator / middle of the spindle / cell; attach to individual spindle fibres;
spindle fibres contract / centromeres divide / repel;
(sister) chromatids / chromosomes (separate)
move to opposite poles / ends of the spindle;
each pole / end receives all genetic information /
identical copies of each chromosome;
nuclear envelope forms around each group of chromosomes / chromatids / at each pole;

Question 213

A cancerous tumour is formed by uncontrolled mitotic division. This results
cells with an inadequate blood supply. Drugs are being developed which only kill cells in a low oxygen environment. Suggest how these drugs could be useful in the treatment of cance

Answer 213

ancer cells killed, normal body cells survive;
cancer cells low oxygen (as blood supply cannot satisfy demand);

Question 214

13a what is clone

Answer 214

genetically identical cells / individuals;

Question 214

12b Explain why meiosis is important in sexual reproduction, apart from producing gametes that are genetically different.

Answer 214

produces haploid cells / chromosome number halved;
fertilisation maintains the diploid / chromosome number (in next generation);

Question 215

13b (b) Name the type of cell division occurring in a developing embryo.

Answer 215

mitosis

Question 216

13c he embryo cells used are from an early stage of development. Explain why

Answer 216

no differentiation at this stage / same genes being expressed;

Question 217

13 e Give two differences between the nuclei removed from the embryo cells and the nuclei discarded from the unfertilised egg cells.

Answer 217

embryo cell diploid, egg cell haploid;
contain different alleles / forms of the colour gene

Question 218

14a Research scientists can increase the nutritional value of potatoes by genetically engineering potato plants. A gene which results in increased protein production has been removed from cells of an amaranth plant and inserted into cells of a potato plant.
(a) Describe how a gene could be removed from cells of an amaranth plant and inserted into cells of a potato plant.

Answer 218

cut out gene using an) endonuclease / restriction enzyme; reference to specificity / recognition site;
sticky ends;
use the same enzyme to cut;
plasmid / virus / potato DNA;
fixed by ligase;
method of introducing vector e.g. micropipette / virus injects DNA / remove plant cell wall

Question 219

13f nly 30% of the cloned cells successfully developed into embryos. Suggest a reason for this low success rate.

Answer 219

damage to nucleus / cells during transfer

Question 220

14b Whole potato plants can be produced from genetically identical potato cells grown in a tissue culture. Use your knowledge of genes to suggest how different cells, such as leaf and root cells, can develop from genetically identical cells.

Answer 220

different genes are expressed; producing different enzymes / proteins

Question 221

15b (b)
Describe two events during interphase which prepare a cell for mitosis.

Answer 221

DNA replication;
synthesis or proteins / build-up of energy stores / growth / increase in cytoplasm;
replication of organelles / named example;

Question 222

16 a (a) Describe what is meant by a malignant tumour.

Answer 222

mass of undifferentiated / unspecialised / totipotent cells; uncontrolled cell division;
metastasis / (cells break off and) form new tumours / spread to other parts of body;

Question 223

1a (a)
Gas exchange in fish takes place in gills. Explain how two features of gills gas exchange.

Answer 223

(a)
Filaments / lamellae provide large surface area;
Thin / flattened epithelium / one / two cell layers so short diffusion pathway (between water and blood);
Countercurrent / blood flow maintains concentration / diffusion gradient;

Question 224

1bii (
The scale for plotting body mass is a logarithmic scale. Explain why a logarithmic scale was used to plot body mass

Answer 224

Large / wide range of values (so can fit on graph);;

Question 225

1biii The zoologist measured oxygen uptake per gram of body mass. Explain why he measured oxygen uptake per gram of body mass.

Answer 225

Enables comparison;
As animals differ in size / mass;

Question 226

(ii) Apart from reduced elasticity, explain how changes to the lung tissue efficiency of gas exchang

Answer 226

Allow description of process of engulfing
Alveoli / lungs will not inflate / deflate fully / reduced lung capacity;
Breathing out particularly affected / no longer passive;
Alveolar walls thicken;
Longer diffusion pathway;
Scarred / fibrous tissue;
Reduces surface area (for gaseous exchange);

Question 227

(c) (i)
Doctors did not make the link between exposure to asbestos and an increased risk of developing lung cancer for many years. Use information in the passage to explain why.

Answer 227

Cancer develops 20 – 30 years after exposure (to asbestos);

Question 228

(ii) Give one factor, other than asbestos, which increases the risk of developing lung cancer.

Answer 228

Smoking / air pollution / specified industrial source;

Question 229

3 (a)
A fish uses its gills to absorb oxygen from water. Explain how the gills of a for efficient gas exchange.

Answer 229

large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient;;

3. Water and blood flow in opposite directions / countercurrent;
4. (Point 4) maintains concentration gradient (along gill) / equilibrium not reached / as water always next to blood with lower concentration of oxygen;
5. Circulation replaces blood saturated with oxygen;
6. Ventilation replaces water (as oxygen removed);

Question 230

Mackerel live in the surface waters of the sea. Toadfish live on the seabed in deep water.
(b) The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why.

Answer 230

Mixing of air and water (at surface);
Air has higher concentration of oxygen than water;
Diffusion into water;
Plants / seaweeds near surface / in light;
Produce oxygen by photosynthesis;

Question 231

(5c)
Explain how movement of the liver causes air to enter a crocodile’s lungs.

Answer 231

liver moves back;
increases volume of lungs;
pressure lower (in lungs than outside);

Question 232

(d) Describe the difference in the composition of gases in inhaled and exhaled
air. Explain how
these differences are caused.

Answer 232

1 inhaled air contains more oxygen than exhaled air;
2 inhaled air contains less carbon dioxide than exhaled air;
3 inhaled air contains less water (vapour);
4 relative amount / percentage of nitrogen also changes;
5 respiration results in lower blood oxygen / higher blood carbon dioxide;
6 oxygen enters blood / carbon dioxide leaves blood in alveoli;
7 by diffusion;
8 water vapour diffuses from moist surface;

Question 233

6b sorgum has few stomata per mm2 of lear surface area
explain how this is an adaption to the conditions in which is grows

Answer 233

grows in arid / dry conditions;
less surface area;
(rate of) transpiration / water loss would be reduced;

Question 233

8 ci. Use information from the graph to sketch a curve on the axes below to show how the volume of air in the lungs changes during inspiration.
The intercostal muscles are between the ribs. In normal breathing, describe the part played by the intercostal muscles
(i) during inspiration;

Answer 233

ontract;
ribs move upwards / out;
increasing volume / decreasing pressure in chest

Question 234

8c ii he intercostal muscles are between the ribs. In normal breathing, describe the part played by the intercostal muscles
(ii) during expiration.

Answer 234

(ii) intercostal muscles relax;

Question 235

9b Explain what causes the oxygen concentration in the tracheae to fall when close

Answer 235

oxygen is used in) respiration therefore diffuses (from tracheae) to tissues; oxygen unable to enter organism;

Question 236

(c) The insect lives in dry conditions. Suggest an advantage of the pattern of spiracle movements shown in the diagram.

Answer 236

spiracles not open all the time; therefore there is less water loss (by diffusion through spiracles);

Question 237

10 In the lungs, the alveoli are the site of gas exchange.
(a) A large number of small alveoli is more efficient in gas exchange than a smaller number of larger alveoli. Explain why.

Answer 237

Small alveoli with) large surface area; For diffusion;

Question 238

10 c just before a person starts to exhale, the composition of the air in an alveolus differs from the composition of the air in the trachea.
(i) Give two ways in which the composition would differ.

Answer 238

Less oxygen / more carbon dioxide / more water vapour;

Question 239

di
Through which vessel does blood leave the heart to go to the lungs?

Answer 239

Pulmonary artery

Question 240

dii ggest why blood returning to the heart from the lungs contains some carbon dioxide.

Answer 240

Concentrations reach equilibrium / become equal; Diffusion occurs when there is a concentration gradien

Question 241

13 Describe the part played by the diaphragm in causing air to enter the lungs during breathing

Answer 241

diaphragm (muscle) contracts; Flattens / Increases volume of chest; Reduced pressure allows air to enter;

Question 241

10b (b) Describe how an increase in lung volume leads to air entering the lungs.

Answer 241

Produces lower pressure (and air moves in down pressure gradient);

Question 242

14 b Cell A is a eukaryotic cell. Give two features that may be found in a prokaryotic cell which are not found in cell A.

Answer 242

ell wall;
Capsule;
Flagellum;
Mesosomes;
Plasmid;
Genetic material / DNA / nucleoid; Ribosomes;

Question 243

17a
Describe the features of fish gills that give them a large surface area.

Answer 243

(gills have) lamellae on filaments; lots of both;

Question 244

20ai
(i) Explain how the structure of the gill makes oxygen uptake efficient.

Answer 244

(a)
(i)
one feature;
then linked Explanation;
(many) filaments / lamellae / secondary lamellae; so large surface area;
large number of capillaries; (NOT “good blood supply”) maintains a diffusion gradient / removes oxygen;
thin epithelium / lamellae wall; short diffusion pathway;

Question 244

19 I (i)
Explain how the cuticle reduces water loss.

Answer 244

waxy so) impermeable to water / waterproof / stops water passing through;

Question 245

20 aii ater containing dissolved oxygen flows over the gill in the opposite direction to the blood flow inside. Explain why this arrangement is important for efficient oxygen uptake.

Answer 245

maintains diffusion / concentration gradient / equilibrium not reached;
diffusion occurs across whole length (of lamellae / gill);

Question 246

20b
There is a one-way flow of water over the gills of a fish whereas there is a two-way flow of air in the lungs of a mammal. Suggest one advantage to a fish of this one-way flow of water over its gills.

Answer 246

ess energy needed / continuous flow of water or O ;

Question 247

21a (a)
Describe how air is taken to lungs

Answer 247

contraction of (diaphragm) muscles flattens diaphragm; contraction of intercostal muscles raises ribcage; increase in volume decreases pressure;

Question 248

22a Describe and explain how fish maintain a flow of water over their gills.

Answer 248

. mouth opens, operculum / opercular valve shuts;
2. floor of mouth lowered;
3. water enters due to decreased pressure / increased volume; 4. mouth closes, operculum / opercular valve opens;
5. floor raised results in increased pressure / decreased volume; 6. high / increased pressure forces / pushes water over gills;

Question 249

(b)
Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood.

Answer 249

1. alveoli provide a large surface area;
2. walls of alveoli thin to provide a short diffusion pathway; 3. walls of capillary thin / close to alveoli provides
   a short diffusion pathway;
3. walls (of capillaries / alveoli) have flattened cells;
4. cell membrane permeable to gases;
5. many blood capillaries provide a large surface area;
6. intercostal / chest muscles / diaphragm muscles / to ventilate lungs /
   maintain a diffusion / concentration gradient;
7. wide trachea / branching of bronchi / bronchioles for efficient
   flow of air;
8. cartilage rings keep airways open;

Question 250

23a When first hatched, the young of some species of fish are less than 2 mm
Explain how these young fish get enough oxygen to their cells without having gills.

Answer 250

exchange / diffusion across body surface / skin; short diffusion pathway / distance / large SA:V ratio

Question 251

24a Explain how the ventilation mechanism of a fish and the structure of its gills result in the efficient uptake of oxygen from water.

Answer 251

laments / lamellae ;
large SA;
gill plates or secondary lamellae;
large number of capillaries;
to remove oxygen / to maintain a gradient;
thin epithelium;
short diffusion pathway;
pressure changes;
to bring in more water / to maintain gradient;
countercurrent flow (or description);
exchange / diffusion along whole length / concentration gradient maintained / equilibrium not achieved / blood always meets water with higher oxyge

Question 252

24c A rise in the temperature of water decreases the amount of oxygen dissolved in the water. As the water temperature rises, the rate of ventilation in a fish also rises. Explain the advantage of this.

Answer 252

to provide same amount of oxygen;
need to have more water flowing over gills;
OR
metabolic rate / respiration increases (with increase in temperature); so more oxygen required;

Question 253

25a Describe two differences between active transport and facilitated diffusion.

Answer 253

Active transport against / facilitated down with concentration gradient;

Active transport uses ATP/energy, /facilitated doesn’t

Question 254

25b Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.

Answer 254

(b) Lipid/fatty acid part of membrane is non-polar/hydrophobic;
Accept lipid/fatty acid bilayer
Oxygen and carbon dioxide small/ non-polar (molecules);
Oxygen/carbon dioxide can diffuse through/dissolve in/ get between molecules in this layer;
Down a concentration gradient;

Question 255

(c) Explain why ventilation of the lungs increases the efficiency of gas exchange.

Answer 255

(c) Brings more oxygen/removes carbon dioxide;
Maintains diffusion/concentration gradients;
Between alveoli and blood/capillaries;

Question 256

26ai Hydrogen peroxide reacts with two amino acids in alpha-1-antitrypsin. Explain how this reduces activity of the protein.

Answer 256

Changes shape of antitrypsin;
Reference to hydrogen/ionic/disulfide bonds;
No longer attaches to/interacts/ reacts with trypsin;

Question 257

1d the arrows in Figure 2 show the directions in which each new DNA strand is being produced.
(d) Use Figure 1, Figure 2 and your knowledge of enzyme action to explain why the arrows point in opposite directions.

Answer 257

(Figure 1 shows) DNA has antiparallel strands / described;

3. Enzymes have active sites with specific shape;
4. Only substrates with complementary shape / only the 3’ end can bind with
   active site of enzyme / active site of DNA polymerase.

Question 258

4bi (i) Humans and grasshoppers have very similar percentages of each base in their DNA but they are very different organisms.Use your knowledge of DNA structure and function to explain how this ispossible

Answer 258

have different genes
so bases in diff sequence
so diff amino acid sequence codes for diff polypeptides

Question 259

ii The DNA of the virus is different from that of other organisms. Use the table above and your knowledge of DNA to suggest what this difference is. Explain your answer.

Answer 259

1. Circular / non-linear (DNA);
   Accept converse for eukaryotic DNA
   Ignore: references to nucleus, binary fission, strands and plasmids
2. Not (associated) with proteins / histones;
   Accept does not form chromosomes / chromatin
3. No introns / no non-coding DNA

Question 260

5a 5
(a) The events that take place during interphase and mitosis lead to the production of two genetically identical cells. Explain how.

Answer 260

DNA replicated;
Involving) specific / accurate / complementary base-pairin
(Ref to) two identical / sister chromatids;
Each chromatid / moves / is separated to (opposite) poles / ends of cell.
2 max

Question 261

b(i) The student cut thin sections of tissue to view with an optical microscope. Explain why it was important that the sections were thin.

Answer 261

To allow (more) light through;
A single / few layer(s) of cells to be viewed.

Question 262

6a (a) Explain how the structure of DNA is related to its functions.

Answer 262

Sugar-phosphate (backbone) / double stranded / helix so provides strength / stabil
2. Long / large molecule so can store lots of information;
Helix / coiled so compact;
Base sequence allows information to be stored / base sequence codes for amino acids / protein;

5. Double stranded so replication can occur semi-conservatively / strands can act as templates / complementary base pairing / A-T and G-C so accurate replication / identical copies can be made;
6. (Weak) hydrogen bonds for replication / unzipping / strand separation / many hydrogen bonds so stable / strong;

Question 263

7a) DNA helicase is important in DNA replication. Explain why

Answer 263

Separates / unwinds / unzips strands / helix / breaks H-bonds;
So) nucleotides can attach / are attracted / strands can act as template

Question 264

11ii Describe what happens during this stage that results in the production genetically identical cells.

Answer 264

Chromosome / centromere splits / chromatids / ‘chromosomes’ separate / pulled apart;
To (opposite) sides / poles / centrioles (of cell);

Question 265

8 cii Explain how the doctor could have recognised which cells were in interphase when looking at the tissue samp

Answer 265

No visible chromosomes / chromatids / visible nucleus;

Question 266

(11 a) In prophase of mitosis, the chromosomes become visible. Describe what happens in
metaphase anapahse

Answer 266

spindle formed / chromosome / centromere / chromatids attaches to spindle;
Chromosomes / chromatids line up / move to middle / equator (of cell);

Question 267

11bi Cells lining the human intestine complete the cell cycle in a short time. Explain the advantage of these cells completing the cell cycle in a short time.

Answer 267

Form / replace cells quickly / rapidly / divide / multiply / replicate rapidly

Question 268

(13 c) (i)
Hydrogen bonds are important in cellulose molecules. Explain why.

Answer 268

Holds chains / cellulose molecules together / forms cross links between chains / cellulose molecules / forms microfibrils, providing strength / rigidity (to cellulose / cell wall);

Hydrogen bonds strong in large numbers;x

Question 268

ii A starch molecule has a spiral shape. Explain why this shape is important to its function in cells

Answer 268

(ii) Compact / occupies small space / tightly packed;

Question 269

15 e
(e) Explain how a change in a sequence of DNA bases could result in a non-functional enzyme.

Answer 269

Change in hydrogen / ionic / disulfide bonds leads to change in tertiary structure / active site (of enzyme);
Substrate cannot bind / no enzyme-substrate complexes form;

Change in (sequence of) amino acids / primary structure;

Question 270

18ai (i)
(ii)
Explain what is meant by a polymer.

Answer 270

olecule) made up of many identical / similar molecules / monomers / subunits;

Question 270

20 e ii Restriction enzymes that can cut the DNA of chromosomes 2 and 3 produce pieces that are too small for analysis. Explain why these restriction enzymes produce small DNA fragments.

Answer 270

Recognition sites contain only AT pairs; Which would occur very frequently;

Question 271

ii Give one example of a biologically important polymer other than starch or protein.

Answer 271

Cellulose

Question 272

21a
Explain why the replication of DNA is described as semi-conservative.

Answer 272

each strand copied / acts as a template;
(daughter) DNA one new strand and one original / parent strand;

Question 273

22a
Describe and explain how the structure of DNA results in accurate replication.

Answer 273

1 two strands therefore semi conservative rep
2 base pairing / hydrogen bonds holds strands together
3 hydrogen bonds weak / easily broken, allow strands to separate;
4 bases (sequence) (exposed so) act as template / can be copied;
5 A with T, C with G / complementary copy;
6 DNA one parent and one new strand;

Question 273

22b Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.

Answer 273

(b) 1 chromsosomes shorten
2 chromosomes (each) two identical chromatids / strands / copies
(due to replication);
3 chromosomes / chromatids move to equator / middle of the spindle / cell;
4 attach to individual spindle fibres;
5 spindle fibres contract / centromeres divide / repel;
6 (sister) chromatids / chromosomes (separate)
move to opposite poles / ends of the spindle;
7 each pole / end receives all genetic information /
identical copies of each chromosome;
8 nuclear envelope forms around each group of chromosomes /
chromatids / at each pole;

Question 274

22c A cancerous tumour is formed by uncontrolled mitotic division. This results
cells with an inadequate blood supply. Drugs are being developed which only kill cells in a low oxygen environment. Suggest how these drugs could be useful in the treatment of cancer.

Answer 274

(c)
cancer cells killed, normal body cells survive;
cancer cells low oxygen (as blood supply cannot satisfy demand

Question 275

23b(b)
Give two ways in which the structure of a molecule of tRNA differs from the structure of a molecule of mRNA.

Answer 275

tRNA ‘clover leaf’ shape; (allow reference to loop / folded structure) tRNA standard length;
tRNA has an amino acid binding site;
tRNA has anticodon available / three exposed bases;
tRNA has hydrogen bonds (between base pairs);

Question 276

24a Explain what is meant by an allel

Answer 276

diff from of a gene

Question 277

b Explain how DNA replicates.

Answer 277

ydrogen bonds broken;
semi-conservative replication / both strands used (as templates);
nucleotides line up complementary / specific base pairing / A and T / C and G; DNA polymerase

Question 278

c Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another

Answer 278

deletion causes frame shift / alters base sequence (from point of mutation); changes many amino acids / sequence of amino acids (from this point); substitution alters one codon

Question 279

25 ci he sequence of bases on one strand of DNA is important for protein is its role?

Answer 279

determines (sequence of) amino acids / specific protein produced / mRNA formation;

Question 280

25cii How are the two strands of the DNA molecule held together

Answer 280

hydrogen bonds

Question 281

iii Give one advantage of DNA molecules having two strand

Answer 281

stability

Question 282

28b Describe the part played by RNA in protein synthesis.

Answer 282

Carries coded information about the sequence of amino acids; Copied from DNA/gene;
Code is in sequence of bases / triplet / three bases / a codon codes for one amino acid;
Moves out of nucleus/goes into cytoplasm; To ribosomes;

Question 283

29 b (b)
Describe how, after the parent DNA strands separated, the second strand of DNA in region Y was formed.

Answer 283

semi-conservative replication; Complementary pairing;
Hydrogen bonding (of bases/nucleotides); Condensation/described of nucleotides; DNA polymerase involved;

Question 284

dna vs rna

Answer 284

Smaller
Double stranded
Single stranded
Contains Thymine (T)
Contains Uracil (U)
Contains deoxyribose
Contains ribose

Question 285

explain how a gene codes for a protein

Answer 285

Base sequence (on DNA/in gene);
Determines sequence of amino acids;
By determining base sequence on (messenger) RNA; Code is a triplet code/three base code for an amino acid;

Question 286

30 c what are homologous chromosomes

Answer 286

Pairs of chromosomes/two chromosomes;
With genes for same features / with same genes; At same loci / in same sequence;

Question 287

1a what is a phylogenic group

Answer 287

(Grouped according to) evolutionary links/history/relationships / common ancestry;

Question 287

1b what is a species

Answer 287

ble to reproduce;
to produce fertile offspring

Question 287

2c one source of prehsistoriic dna

Answer 287

bone/skin/preserved remains

Question 287

2e Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity.

Answer 287

2. Population might have started with small number of individuals / by one pregnant female
   interbreeding

Question 288

what is meant by genetic diversity

Answer 288

number of different alleles of each genes

Question 289

4a Give three ways in which courtship behaviour increases the probability of successful mating

Answer 289

2. Stimulates / synchronises mating / production / release of gametes;
3. Recognition / attraction of mate / opposite sex;
4. Indication of (sexual) maturity / fertility / receptivity / readiness to mate;

Question 290

4(b) The scientists wanted to know if the recorded natural song was less effective than the natural song in stimulating courtship behaviour.

suggest how the scientists could determine if the recorded natural song was less effective than the natural song

Answer 290

Use a (real) male (with intact wings / no wing removed);
Determine (percentage) response

Question 291

5c this classification system consists of a hierarchy as there are small groups within larger groups.
Give one other feature of a hierarchy that is shown in the diagram.

Answer 291

no overlap

Question 292

6ai what isn meant by a hierarchy

Answer 292

groups within groups
no overlap between groups

Question 293

bi explain the role of independent segregation in meiosis

Answer 293

(To provide) genetic variation;
Allows) different combinations of maternal and paternal chromosomes

Question 294

6ii A zedonk is the offspring produced from breeding a mountain zebra with a donkey.
* The body cells of a mountain zebra contain 32 chromosomes.
* The body cells of a donkey contain 62 chromosomes.
Use this information to suggest why zedonks are usually infertile.

Answer 294

Zedonk has) 47 / odd / uneven number of chromosomes;
Chromosomes cannot pair / are not homologous / chromosome number cannot be halved / meiosis cannot occur / sex cells / haploid cells are not produced;

Question 295

7ii The forest was cleared to make more land available for agriculture.
After the forest was cleared the species diversity of insects in the area Explain why.

Answer 295

decrease in variety if plants
fewer habitats
decrease in variety of food

Question 296

9 The Amazonian forest today contains a very high diversity of bird species.
* Over the last 2 000 000 years, long periods of dry climate caused this forest to separate into a number of smaller forests.
* Different plant communities developed in each of these smaller forests.
* Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.
(a) Use the information provided to explain how a very high diversity of bird species has developed in the Amazonian forest.

Answer 296

no interbreeding
mutation
different selection pressures
adapted organisms survive and breed
change in allele frequency

Question 297

9b Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this.

Answer 297

Similar / same environmental / abiotic / biotic factors / similar / same selection pressures / no isolation / gene flow can occur (within a species);

Question 298

(10c) The biologists analysed the amino acid sequences of the blood protein samples from these hummingbirds.
Explain how these sequences could provide evidence as to whether the crimson topaz and the fiery topaz are different species.

Answer 298

Different species would have different amino acid sequences;

Amino acid sequence is the result of DNA / alleles / base sequence;

Question 299

(14a)
An order is a taxonomic group. All seals belong to the same order. Name one other taxonomic group to which all seals belong.

Answer 299

kingdom /phylum/class

Question 299

what is meant by genetic diversity 14c

Answer 299

difference in dna /base sequence/alleles/ genes

Question 300

15d In another investigation, the same female guinea pig was twice mated with another male which had long, brown hair. Of the 14 offspring, 10 had short, black hair and 4 had long, black hair. The investigators expected equal numbers of offspring with these two phenotypes. They used a χ2 test to determine whether the observed results fitted the expected 1:1 ratio.
Give a suitable null hypothesis for the investigation.

Answer 300

There is no (significant) difference between observed and expected results / any difference is due to chance;

Question 301

19 ci Despite differences in form, leopards, tigers and lions are classified as different species of the same genus. Cheetahs, although similar in form to leopards, are classified in a different genus.
(i)
(ii)
Describe one way by which different species may be distinguished.

Answer 301

do not interbreed to rpdoducde fertile pfffsping

Question 302

ii Suggest two other sources of evidence which scientists may have used to classify cheetahs and leopards in different genera.

Answer 302

(ii) fossil record;
evolutionary history / phylogeny;
biochemical differences e.g. DNA / proteins / cytochromes; homologous features / named feature;

Question 303

(20 b) Differences in cyanide production may affect the total number of clover plants growing in different areas. Describe how you would use quadrats in an investigation to determine whether or not there is a difference in the number of clover plants in two large areas of equal size.

Answer 303

large (and equal) number of quadrats in each area;
(reject several)
random sampling method, described;
(accept described ‘systematic’ method)
percentage cover / point hits per quadrat / count plants; mean / average value for each area;

Question 304

l ake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
21 (a) Describe one way in which scientists could find out whether cichlids from two different populations belong to the same species.

Answer 304

breed together if fertile offspring then same species

Question 305

21b During the last 700 000 years there have been long periods when the water level was much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of the cichlids may have occurred following the formation of separate, smaller lakes.

Answer 305

isolation of two populations;
variation already present due to mutations;
different environmental conditions / selection pressures leading to selection of different features and hence different alleles;
different frequency of alleles;
separate gene pools / no interbreeding;

Question 306

21c
Many species of cichlids are similar in size and, apart from their colour, in appearance. Suggest how the variety of colour patterns displayed by these cichlids may help to maintain the fish as separate species.

Answer 306

selection of mate dependent on colour pattern; prevents interbreeding / keeps gene pools separate;

Question 307

22a
Explain the principles which biologists use to classify organisms into groups.

Answer 307

large groups are divided into smaller groups;
(not just ‘hierarchical’ )
members of a group have features in common based on anatomy / fossils / embryology / DNA / specific aspect of cell biology
/ homologous structures;
reflects evolutionary history;

Question 308

cWhat does the phylogenetic tree show about the evolutionary relationship between fungi and insects?

Answer 308

(insects and fungi) have common ancestor;
they diverged a long time ago / before others referred to in phylogenetic tree;

Question 309

23bi
(b) Suggest how the courtship sequences provide evidence to support the claim that the two species are
(i) closely related;
ii speerate species

Answer 309

similar sequence / actions / sign stimuli;

Question 310

23c During courtship, vibration of the wings creates a sound. The sound is different in the two species of fruitfly. Explain how this prevents mating between members of different species.

Answer 310

(acts as) sign stimulus;
responds only to species-specific sound;

Question 311

1(d) The scientists placed traps to collect the dung beetles at sites chosen at random.
Explain the importance of the sites being chosen at random.

Answer 311

no bias

Question 312

1e
(e) On the intensive farms, the farmers had removed hedges to increase land for grazing. This resulted in a decrease in the diversity of birds on these farms.
Explain why the removal of hedges caused a decrease in the diversity of bird

Answer 312

-Removes species/types of plant/insect;
-Fewer food sources;
-Fewer habitats/niches;

Question 313

2a species diversity

Answer 313

Number of species in a community;

Question 314

2(b) Give two pieces of information needed to calculate an index of diversity for a community.

Answer 314

Number of (organisms of) each species;
Total number of organisms (of all species)

Question 315

2c A scientist investigated the effect sewage entering a river had on the distribution of organisms living in the river. Where sewage entered the river, he found a high density of organisms but a low index of diversity.
Suggest how sewage entering the river could explain the scientist’s findings.

Answer 315

Described effect of sewage
Prevents some/many species colonising/ reproducing/remaining
Sewage is food source for (individuals of) some/a few/species;
(So) increase only in their numbers;

Question 316

(d) A second scientist repeated the investigation of the first scientist at the same place. The second scientist obtained a high index of diversity.

Explain how the second set of results affects the ability of the scientists to make any conclusions about the effect of sewage on the index of diversity

Answer 316

Results are not repeatable / are not representative

Can’t make any conclusions;

Question 317

dii
Suggest the additional steps that should be taken by the scientists before they are able to make any conclusions about the effect of sewage entering this river.

Answer 317

Do repeats to find a pattern/distribution/mean (of index of diversity);

Question 318

4a
Species richness and an index of diversity can be used to measure biodiversity within a community.
(a) What is the difference between these two measures of biodiversity?

Answer 318

Species richness measures only number of (different) species / does not measure number of individuals.

Question 319

4b (b) The traps in the canopy were set at 16–27 m above ground level. Suggest why there was such great variation in the height of the traps.

Answer 319

trees vary in height

Question 320

5a
Ecologists investigated the size of an insect population on a small island. They used a mark-release-recapture method. To mark the insects they used a fluorescent powder. This powder glows bright red when exposed to ultraviolet (UV) light.
(a) The ecologists captured insects from a number of sites on the island. Suggest how they decided where to take their samples.

Answer 320

draw grid over map of area
select squares/coordinates at random

Question 321

5b Give two assumptions made when using the mark-release-recapture method.

Answer 321

no emigration
no losses to predation
marking does not affect survival
birth rate and date rate equal
all belong to one population

Question 322

5e he ecologists expected to obtain the same result from their calculations of the number of insects on this island on each day during the period 1–5 days after release. In fact, their estimated number increased after day 1.
During the same period, the number of insects they caught decreased.
The method used by the ecologists might have caused these changes.
Use the information provided to suggest one way in which the method used by the ecologists might have caused the increase in their estimates of the size of the insect population.

Answer 322

Scientists removed large numbers of insects (which were not returned) from same area
affecting ratio of marked to unmarked

Question 323

6ii the ecologists also determined the index of diversity of lizards in an oil palm plantation next to the woodland area. They found fewer species of plant in the oil palm plantation. Lizards feed on plants and insects.
Explain why fewer species of plant would lead to fewer species of lizard in the oil palm plantation.

Answer 323

1. (So) few(er) habitats / niches
2. (So) lower diversity of insects / fewer insect species / fewer insect types;
3. (So) fewer food sources / less variety of food

Question 324

7a What two measurements are needed to calculate an index of diversity?

Answer 324

Number of (individuals of) each species;

Total number of individuals / number of species;

Question 325

7b I Some fields acted as controls. They were sprayed with a solution that did not contain
the herbicide. Explain the purpose of these control fields.

Answer 325

(Shows) results are due to the herbicide / are not due to another factor / (to) compare the effect of using and not using the herbicide / shows the effect of adding the herbicide;

Question 326

8ai
(a) Name the process that resulted in the development of woodland from farmland.

Answer 326

succession

Question 327

8b Explain the increase in the diversity of birds as the woodland develope

Answer 327

Greater variety / diversity of plants / insects / more plant / insect species;
More food sources / more varieties of food;
Greater variety / more habitats / niches;

Question 328

8c (i)
Give two factors which could be limiting the rate of photosynthesis in the sun plant between points A and B on the figure.

Answer 328

temp co2

Question 329

8cii Explain why CO uptake is a measure of net productivity. 2

Answer 329

Shows (gross) photosynthesis / productivity minus respiration / more carbon dioxide used in photosynthesis than produced in respiration;

Question 330

9a what is a species

Answer 330

Group of similar organisms / organisms with similar features / organisms with same genes / chromosomes;

Reproduce / produce offspring;

That are fertile;

Question 331

9f After the forest was cleared the species diversity of insects in the area Explain why

Answer 331

Decrease in variety of plants / fewer plant species;

fewer habitats
decrease in variety of food

Question 332

11a (a) There are ethical and economic arguments for maintaining biodiversity.

Suggest one ethical argument for maintaining biodiversity.

Answer 332

(We should maintain biodiversity to)
Prevent extinction / loss of populations / reduction in populations / loss of habitats / save organisms for future generations (idea of);

Question 333

Suggest one economic argument for maintaining biodiversity.

Answer 333

1. medical / pharmaceutical uses;
2. commercial products / example given;
3. tourism;
4. agriculture;
5. saving local forest communities;

Question 334

11d The ecologists noted that the species of birds surviving on the coldest islands had a larger body size than those surviving on warmer islands.
Explain how a larger body size is an adaptation to a colder climate

Answer 334

(Larger birds have) a low(er) SA:VOL;

(So) less heat loss / more heat retained;

Question 335

12a The scientists collected insects at sites chosen at random. Explain the importance of the sites being chosen at random.

Answer 335

removes biases

Question 336

12d Farmers were offered grants by the government to plant hedges around their fields. Explain the effect planting hedges could have on the index of diversity for animals.

Answer 336

Greater variety of plants
nother habitat / more habitats / places to live / niches / another food source / more food types;

Question 337

13a A student investigated the diversity of plants at several sites on a golf course. At each site she took a large number of random samples

Answer 337

produces a more reliable mean

Question 338

ii
Explain the importance of taking samples at random.

Answer 338

removes biases

Question 339

13c he golf course was produced.
The golf course had
* some areas of
* some areas of
* some areas of
surrounded by undeveloped grassland from which it had been
very short grass which was cut frequently
longer grass which was cut less frequently
long grass and shrubs which were never cut.
The index of diversity for the insects on the golf course was higher than that for the surrounding undeveloped grassland.
Explain the effect of developing this golf course on the index of diversity of insects.

Answer 339

increase in variety of plants
more habitats
greater variety of food sources

Question 340

14a Costa Rica is a Central American country. It has a high level of species diversity.
(a) There are over 12 000 species of plants in Costa Rica. Explain how this has high species diversity of animals.

Answer 340

More habitats / niches;

Greater variety / different foods;

Question 341

14b (b)
The number of species present is one way to measure biodiversity. Explain why an index of diversity may be a more useful measure of biodiversity.

Answer 341

Also measures number of individuals in a species / different proportions of species;
Some species may be present in low / high numbers

Question 342

14ci Crops grown in Costa Rica are sprayed with pesticides. Pesticides are substances that kill pests. Scientists think that pollution of water by pesticides has reduced the number of species of frog

Answer 342

Large surface area to volume (ratio) / permeable / thin (outer layer); Correct reference to diffusion

Question 343

15a (a)
What information is required to calculate an index of diversity for a particular community?

Answer 343

Number of a / each (species);

Question 344

b (b) Farmers clear tropical forest and grow crops instead. Explain how this causes the diversity of insects in the area to decrease.

Answer 344

Lower diversity of plants / few species of plants / less variety of plants / few plant layers;
Few sources / types of food / feeding sites; / few habitats / niches;
Fewer (species of) herbivore so few (species of) carnivores;

Question 345

(d) A farmer who wanted to increase the diversity of birds on his land read about this investigation.
He concluded that clearing the plants from one bank would not decrease diversity as much as clearing the plants from both banks. Evaluate this conclusion.

Answer 345

Total number of birds along ditch B / ditch with one side cleared greater than along ditch A / ditch with both sides cleared;

But only gives data for all birds / does not give data for species / data not about diversity;

single ditch / single occasion / not repeated / no control;

Question 346

18a Deforestation reduces the diversity index of an area cleared in this way. Explain why.

Answer 346

deforestation removes many habitats / niches fewer species / fewer types of organisms;

Question 347

(b) Because the forest soil is often nutrient-poor, nitrogen-containing fertilisers may be applied to ensure good crop yields. Use your knowledge of the nitrogen cycle to explain the
potential benefit of applying a fertiliser containing ammonium nitrate rather containing potassium nitrat

Answer 347

1. nitrate ions in fertiliser available / absorbed immediately;
2. ammonium converted to nitrate by nitrifying bacteria
3. fertiliser would provide only the initial release of nitrate / potassium nitrate;

Question 348

19 (a) Describe how you would have collected the samples in order to ensure they were representative of the habitats being investigated and could be compared with each other.

Answer 348

Samples collected at random;
Method for choosing random sites – random
coordinates / position from tables / calculator / other suitable means

Question 349

19c meant by the term ecological niche?

Answer 349

n organism’s role / in the ecosystem / community;

Question 350

20aii (ii) Give one advantage of calculating the index of diversity rather than just recording the number of species present.

Answer 350

Takes account of number of individuals / abundance / population size

Question 351

23a (a) Explain how different proportions of cyanogenic plants may have evolved in populations in different parts of Europe

Answer 351

colder / below 0°C (January) areas, cyanogenic plants die in this cold / acyanogenic survive;
non-cyanogenic allele / gene passed on more often / its frequency increases; warmer (January) areas cyanogenic plants at advantage,
because of less herbivore selection pressure / feeding;
so cyanogenic survive more often to pass on cyanogenic allele / gene

Question 352

23b ifferences in cyanide production may affect the total number of clover plants growing in different areas. Describe how you would use quadrats in an investigation to determine whether or not there is a difference in the number of clover plants in two large areas of equal size.

Answer 352

large (and equal) number of quadrats in each area;
(reject several)
random sampling method, described;
(accept described ‘systematic’ method)
percentage cover / point hits per quadrat / count plants; mean / average value for each area;
statistics test to see if differences significant.

Question 353

24c Apart from providing a habitat for predators of crop pests, give two biological benefits of replanting hedgerow

Answer 353

increases biodiversity;
source of food for animals;
habitat / nest for animals;
reduce need for insecticides / attracts insects away from crop; windbreaks / prevent erosion / run-off / leaching;
migratory corridors;

Question 354

1a They measured the maximum diameter of each shrimp’s eye. They also measured the length of its antenna. From these measurements they calculated the mean values for each site. Figure 2 shows their results

Explain why they measured the maximum diameter

Answer 354

(So results) can be compared / so measurement is the same each time / because eye is not perfectly round / uniform;

Question 355

bii The data in Figure 2 are mean values. Explain how standard deviations of these cmean values would help you to interpret the data in Figure 2

Answer 355

More standard deviations overlap, the less likely it is that differences are real / significant / the more likely they are caused by chance;

standard deviation gives a measure of spread

Question 356

f The biologists who studied these shrimps wanted to know if the shrimps living in the cave were the same species as those living in the open. They used breeding experiments to investigate this.
(i) Describe how the biologists should carry out these breeding experiments.

Answer 356

1.
Cross shrimps from two sites / watch courtship;
2. Breed young together / observe mating;
3. Allow 1 mark for any method of improving quality of results e.g. carry out reciprocal crosses / large number of crosses / isolate beforehand;

Question 357

(ii) The results of breeding experiments would help the biologists to decide whether the shrimps were the same species. Explain how.

Answer 357

If same species the shrimps would breed, producing fertile young / courtship species specific

Question 358

2a The number of patients infected with the bacterium MRSA has increased in some hospitals. Scientists have suggested ways to reduce the transmission of MRSA in hospitals. Suggest two ways to reduce the transmission of MRSA in hospitals.

Answer 358

solation / quarantine / ‘kept separate’;
Screening / testing (of patients / doctors etc);
Sterilisation of wards / equipment / method to improve hygiene;

Question 359

2b The minimum inhibitory concentration (MIC) is the lowest concentration of a substance that prevents the growth of a microorganism.
When antibiotics are prescribed for treating patients, higher doses than the MIC are recommended. Suggest two reasons why.

Answer 359

May be broken down / metabolised / excreted quickly;
To kill the microorganisms / bacteria;
Reference to antibiotic resistance;

Question 360

d The effectiveness of these drugs was tested in double-blind trials using human volunteers. In a double-blind trial neither the volunteers nor the scientists know which treatment a particular volunteer is receiving.
(i) Suggest two ways in which a double-blind trial improves reliability.

Answer 360

Prevents bias;
Vested interest (of scientists);
Prevents ‘placebo’ / positive / negative / psychological effects / ‘demand characteristics’ (in volunteers);

Question 361

(ii) Suggest two factors the scientists should have considered when selecting adult volunteers for this trial

Answer 361

Age;
Ethnicity;
Lifestyle;
Body mass;
Health;

Question 362

3bi Pernicious anaemia is another type of anaemia. One method of identifying pernicious anaemia is to measure the diameter of the red blood cells in a sample of blood that has been diluted with an isotonic salt solution. Explain why an isotonic salt solution is used to dilute the blood sample.

Answer 362

Has same water potential;
No (net) water movement / osmosis;
Cells will not swell / burst / change size;

Question 363

3iii
Haemoglobin has a quaternary structure. Explain what is meant by a structure.

Answer 363

(iii)
More than one polypeptide chain;

Question 364

4b (b) Describe briefly how you would use a statistical test to find whether there is a significant correlation between mean March temperature and the date when chaffinches laid their first egg.

Answer 364

Construct null nypothesis;
Use Spearman rank (and calculate test statistic);
Look up in table (to find critical value of P = 0.05 / 5 %); Use figure (in table) to accept or reject null hypothesis

Question 365

c In chaffinches, the date of laying the first egg is determined by a number of factors. These include day length and temperature. What is the advantage to the bird of egglaying being determined by
(i) daylength
temp

Answer 365

(Particular daylength) always occurs at same time of year / valid example; Birds do not start laying eggs when period of warm weather occurs early in year;
Synchronises breeding behaviour;
Sufficient foraging time for food collection for young;

Question 366

(d) Scientists found that there was a correlation between mean annual temperature and the date when chaffinches laid the first egg. Can you conclude that higher temperatures cause earlier laying of the first egg?
Explain your answer.

Answer 366

A correlation does not indicate a causal relationship; As may be due to another factor / named factor;

Question 366

(5a) Give two ways in which courtship behaviour increases the probability of successful mating.

Answer 366

Recognition of same species;
Stimulates release of gametes;
Recognition of mate / opposite gender;
Indication of sexual maturity / fertility;

Question 367

Give one way in which reproduction in seahorses increases the probability of
(i)fertilisation
(ii)survival of young seahorses

Answer 367

Internal fertilisation / fertilisation occurs in pouch / limited area;
Protection from predators

Question 368

5f Scientists studied two species of North American seahorse. They thought that these two species are closely related. Describe how comparisons of biological molecules in these two species could be used to find out if they are closely related.

Answer 368

Compare) DNA;
(a)
Sequence of bases / nucleotides;
Compare same / named protein;
Sequence of amino acids / primary structure;

Question 369

7a Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP

Answer 369

Excitation of chlorophyll molecule / electrons / energy of (pairs of) electrons raised to higher energy level;
Electron(s) emitted from chlorophyll molecule;
Electron(s) to electron transport chain;
Loss of energy by electron(s) along electron transport chain;
Energy lost by electron(s) is used to synthesise ATP;
From ADP + P

Question 370

8a (a)
Some antibiotics bind with specific receptors in the plasma membranes of bacteria. The structure of these receptors is determined genetically. Bacteria can become resistant to an antibiotic because a gene mutation results in an altered receptor.
Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation conferring resistance in just one bacterium.

Answer 370

1. frequent use of antibiotic creates selection pressure / antibiotic kills bacteria;
2. bacteria with mutation / resistance have (selective) advantage over others / described; 3. (survive to) reproduce more than other types pass on advantageous allele / mutated allele in greater numbers;
3. frequency of (advantageous) allele increases in subsequent generations;
4. frequency of resistant types increases in subsequent generations;

Question 371

9a Give two possible causes of this variation that result from meiosis during gamete formation.

Answer 371

Continuous variation – range of values / not discrete categories / many categories / no gaps;

Question 372

9b
(b) When comparing variation in size between two groups of organisms, it is often considered more useful to compare standard deviations rather than ranges. Explain why.

Answer 372

Rangeinfluencedbysingle‘outlier’( acceptanomaly)/
converse for S.D.;
S.D. shows dispersion / spread about mean / range only shows highest and lowest values / extremes

Question 373

10a Explain what is meant by stabilising selection and describe the circumstances under which it takes place.

Answer 373

Occurs in an unchanging environment;
Range / S.D is reduced
Increasing proportion of populations becomes well adapted to environment;

Question 374

11(i) At the start of the investigation, the agar was sterilised. Explain why.

Answer 374

to ensure that no unwanted bacteria will be present;

Question 375

14b Explain how data from studies of identical twins and non-identical twins could provide further evidence about the genetic control of intelligence.

Answer 375

(b) identical twins have same genotype / converse for non-identical; compare identical and non-identical twins / identical twins who have been separated / non-identical twins in same environment; if genetic - similarity between identical twins / converse;
large sample required / use a statistical test

Question 376

15a
(a) Explain why the plants produced form a clone.

Answer 376

mitosis
genetically identical

Question 377

b (b) Suggest one reason why the plants in a clone may not be identical in appearance.

Answer 377

environmental conditions / named environmental factor / mutation;

Question 378

(c) Most plants produce seeds after fertilisation in sexual reproduction. However,
dandelions produce small, windblown seeds without fertilisation taking place. Suggest two advantages to the dandelion of being able to reproduce from these seeds, as well as from pieces of root.

Answer 378

dispersal / prevent overcrowding / competition / colonise
increased number of (proven) offspring; (not quicker)

Question 379

19 xplain how crossing over can contribute to genetic variation.

Answer 379

sections of chromatids exchanged; sections have different alleles;
new combinations of (linked) alleles;

Question 380

(c) Mud higher up the shore receives fresh water draining from the land. Ragworms are able to survive in this mud because they can tolerate the absorption of water into their tissues. Explain what causes a ragworm to absorb water when higher up the shore.

Answer 380

body has lower water potential;

water diffuses along a water potential gradient / by osmosis;

Question 381

20b(b) Explain how competition might have played a part in the evolution of the long curved beak of the curlew.

Answer 381

ariation in beak length in curlews / one species;
longer / more curved beaked curlews outcompete / at advantage / suggested advantage e.g. larger / curled beaks access more food; reproduction;
genes passed on (to offspring

Question 382

21a Describe how you would collect a random sample of each population.

Answer 382

generation of random co-ordinates; use of 10 or more quadrats;
collection of all dog whelks in quadrat;

Question 383

1b G. lamblia can attach itself with its sucker. Explain how this is an adaptation to living in the intestines

Answer 383

Enables organism to remain in area (of food source) / prevent its removal;

Question 384

di Explain why the antibodies used in this test must be monoclonal antibodies.

Answer 384

ll have same shape / only binds to Giardia / one type of / specific antigen;

Question 385

ii Explain why the Giardia antigen binds to the antibody in step 2.

Answer 385

Has complementary (shape) / due to (specific) tertiary structure / variable region

Question 386

2bii Apart from reduced elasticity, explain how changes to the lung tissue efficiency of gas exchange.
reduce the

Answer 386

Alveoli / lungs will not inflate / deflate fully / reduced lung capacity;
Breathing out particularly affected / no longer passive;

Question 387

3aPhagocytes and lysosomes are involved in destroying microorganisms. Describe how.

Answer 387

Phagocytes engulf pathogens / microorganisms;
Enclosed in a vacuole / vesicle / phagosome;
Lysosomes have enzymes;
That digest / hydrolyse molecules / proteins / lipids / microorganism;

Question 388

5a Describe how B-lymphocytes respond when they are stimulated by antigens.

Answer 388

divide by mitosis / form clones; produce plasma cells;
(plasma cells) make antibodies; (plasma cells) produce memory cells;

Question 389

6a What is an antigen?

Answer 389

olecule / part of molecule / protein / glycoprotein / named molecule; that stimulates an immune response / eq;

Question 390

7a What is vaccination?

Answer 390

Injection of antigens
Antigen from) attenuated microorganism / non-virulent microorganisms / dead
microorganisms / isolated from microorganism;
Stimulates the formation of memory cells;

Question 391

10a What is an antibody?

Answer 391

protein / immunoglobulin; specific to antigen;
idea of ‘fit’ / complementary

Question 392

ii (ii) Describe how antibodies are produced in the body following a viral infection.

Answer 392

1. virus contains antigen;
2. virus engulfed by phagocyte / macrophage; 3. presents antigen to B-cell;
3. memory cells / B-cell becomes activated; 5. (divides to) form clones;
4. by mitosis;
5. plasma cells produce antibodies;
6. antibodies specific to antigen;
7. correct reference to T-cells / cytokines;

Question 393

iii Suggest why it is advisable for people to be vaccinated against influenza every year.

Answer 393

Different strain / type of virus each year / virus mutates;
With different antigens;
Influenza antibodies / memory cells (rapidly) destroyed / need replacing

Question 394

11a Give two reasons why it would be important to use sterile techniques during this investigatio

Answer 394

To prevent contamination of apparatus with other microorganisms / bacteria; To prevent personal contact with bacteria;
To prevent release of bacteria into air;

Question 395

c An influenza virus consists of a protein coat surrounding nucleic acid. The influenza vaccine consists only of the protein coat of the virus. Explain how the influenza vaccine produces immunity in the body.

Answer 395

(Protein coat) carries antigens which stimulates B-cells / production of antibodies; Production of memory cells;

Question 396

13 ii (ii) What is a monoclonal antibody?

Answer 396

reference to hybrid cell from tumour / cancer and B-lymphocyte / hybridoma;
antibodies all the same / from one type of plasma cell; specific to / complementary to / fits only one antigen;

Question 397

bi
Explain why this test detects prostate cancer, but not any other disease.

Answer 397

antibodies specific / only binds to PSA;
PSA only associated with prostate cancer / not with other diseases;

Question 398

15ei Use your knowledge of enzymes to explain why restriction enzymes only cut DNA at specific restriction sites.

Answer 398

Different lengths of DNA have different base sequences / cut at specific sequence;
Results in different shape / different shape of active site;
Therefore (specific sequence) will only fit active site of enzyme;

Question 399

ii Restriction enzymes that can cut the DNA of chromosomes 2 and 3 produce pieces that are too small for analysis. Explain why these restriction enzymes produce small DNA fragments.

Answer 399

Recognition sites contain only AT pairs; Which would occur very frequently;

Question 400

16a Give two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease

Answer 400

side effects / allergic reactions / low toxicity to cells;
interaction with other drugs / effective in conditions of use / reasonably stable; should only act on the problem bacteria / narrow spectrum;
how much resistance the bacteria have built up;

Question 401

17a An antigen in a vaccine leads to the production of antibodies. Describe the part played by B lymphocytes in this process.

Answer 401

1 macrophages present antigens to B lymphocytes;
2 antigen binds to / is complementary to receptors on lymphocyte;
3 binds to a specific lymphocyte;
4 lymphocytes become competent / sensitised;
5 (B) lymphocytes reproduce by mitosis / (B) lymphocytes cloned;
6 plasma cells secrete antibodies;

Question 402

17b Hepatitis B vaccine contains a viral antigen produced by genetically modified bacteria. Describe how the isolated gene that codes for a protein in the virus’s coat could be transferred to the bacterial cells.

Answer 402

1 restriction enzymes
2 to cut plasmid / to form sticky ends in plasmid;
3 (use) ligase(to join) gene to plasmid;
4 culture bacteria with (in medium containing) plasmids
5 to allow uptake of plasmids / transformation;
6 use of cold shock / chemical treatment (to enhance uptake) / heat

Question 403

18a Salmonella typhimurium causes food poisoning in humans but not in other
Explain why these bacteria attach to human cells but not to the cells of other mammals.

Answer 403

bacteria have ligands / antigens / proteins / glycoproteins / polysaccharides (on membrane / wall);

complementary to receptors / fits / binds / attaches to specific recepto

Question 404

Salmonella bacteria release toxins that cause the body temperature to rise. Although a small increase in body temperature can be beneficial, a large increase can cause serious harm.
Explain how a large increase in a person’s body temperature can cause harm.

Answer 404

enzymes denatured / tertiary / secondary structure altered / altered active sites / breaks hydrogen bonds;
prevents named chemical reactions / metabolic pathways;

Question 405

Some species of bacteria, which live in soil and decompose organic material, release exotoxins. Suggest how the release of exotoxins benefits the bacteria.

Answer 405

(c)
inhibits / kills other bacteria / fungi / decomposers / reduces competition;

Question 406

(d) Washing hands with anti-bacterial soap reduces the risk of transmission of the bacteria that cause food poisoning. Tea tree oil is a plant extract used in soaps. It is claimed to have anti-bacterial properties. Outline a method for investigating this claim.

Answer 406

(d)
1 prepare a bacterial lawn / culture / sample;
(accept mix bacteria with agar / medium)
2 with oil and one with control / water / range of concentrations; 3 appropriate method of standardising how sample applied,
e.g. discs / wells;
4 appropriate measure of effectiveness / size / diameter of clear zone; 5 the larger the zone the greater the effectiveness;
6 use of aseptic technique;

Question 407

20c (c)
New drugs have recently become available for treating influenza. One type is a neuraminidase inhibitor. Explain how this type of drug would act as a treatment for influenza.

Answer 407

alter shape of active site of neuraminidase / block active site; virus unable to leave host cells;

Question 408

21a Changes to the protein coat of the influenza virus cause antigenic variability. Explain how antigenic variability has caused some people to become infected more than once with influenza viruses.

Answer 408

memory B / T cells do not recognise (new antigens); antibodies previously produced are not effective
as shape not complementary to new antigen;

Question 409

Describe the role of macrophages in stimulating B lymphocytes.

Answer 409

antigen in membrane presented to lymphocytes / produce cytokinins;

Question 410

23bi child was given the MMR vaccine and was given a second dose of the vaccine as a booster later.
(i) It took more than a week for antibodies to appear in the child’s blood after the first vaccination. Explain why.

Answer 410

(Takes time for) antigen to be recognised;
(Takes time for) T cells to be activated;

B-cell activation/clonal selection/expansion; Plasma cells to make (specific) antibodies;

Question 411

23bii The concentration of antibodies increased immediately after the second vaccination. Explain why.

Answer 411

Memory cells (present);
Respond immediately / can produce antibodies immediately;

Question 412

24a (a)
Describe how HIV is replicated after it has entered a human cell.

Answer 412

Reverse transcriptase;

Enzyme uses (HIV) RNA to make DNA (copy);
DNA joined to (host) cell’s DNA/chromosome;
DNA used to make HIV RNA (copies)
And HIV capsid proteins/enzymes;
Made at (host) ribosomes;
Assembly of new virus particles;
Budding off from membrane (of host cell);

Question 413

The destruction of T-cells by HIV leads to the death of an infected person. Explain how.

Answer 413

Not enough/no T-cells to activate B-cells/lead to antibody production/ activate immune system;

Person unable to fight /more prone to (opportunistic) infections/cancer;

Question 414

27b escribe how new viruses are produced after HIV has infected a T cell.

Answer 414

DNA copy made (of viral RNA);
Inserted into host DNA / chromosomes;
(Uses viral DNA to) make viral proteins/particles; Makes viral RNA;
(Host) cell makes new viruses;
“Budding off” / wrapped in cell membrane;

Question 415

28b Describe how humans produce antibodies against a pathogen such as Salmonella.
(c) (i)
HIV infects some human cells, such as T-cells, but not others. Suggest why.
.

Answer 415

Salmonella pathogen has specific antigen on surface; Salmonella pathogen engulfed by macrophage;
T-cells activate B-cells;
B-cell with complementary/specific receptor antibody activated/ clonal selection;
B-cells divide/form clone/clonal expansion;
Plasma cells make antibodies;
Specific to antigen/bind to salmonella bacterial antigen;

Question 416

(c) (i)
HIV infects some human cells, such as T-cells, but not others. Suggest why.

Answer 416

HIV binds to specific receptor;
Only present on certain cells / T-cells;

Question 417

Antibiotics are not used to treat viral infections, such as HIV. Explain why.

Answer 417

Antibiotics stop metabolism, viruses don’t have metabolism; Viruses hide in cells, antibiotics can’t reach;

Question 418

30 hese scientists injected laboratory mice with cotinine. Describe how this injection stimulates mice to produce antibodies against cotinine.

Answer 418

Cotinine is an antigen;
Antigen/cotinine binds to (specific) T-cell/activates T-cell; T-cell activates B-cells;
Specific B cell becomes activated;
(Specific) B cell divides/ clonal expansion;
Forms (clone of) plasma cells;
(Plasma) cell produces antibodies;

Question 419

(b) Explain why the number of HIV particles in the blood
(i) rises during the first few months after infection

Answer 419

Antibodies are proteins with tertiary structure/specific shape/binding sites; Antibodies specific shape for cotinine;

Question 420

how to figure out if a cell is going through mitosis in a diagram

Answer 420

Individual chromosomes are visible because they have condesned

each chromosomes is made up of two chromatids because dna has replicated

the chromosomes are not arranges in homologous pairs which they would be if it was mitosis

Question 421

When preparing the cells for observation the scientist placed them in a solution that
had a slightly higher (less negative) water potential than the cytoplasm. This did not
cause the cells to burst but moved the chromosomes further apart in order to reduce
the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart.

Answer 421

water moves into the cell by osmosis
cell gets bigger

Question 422

The dark stain used on the chromosomes binds more to some areas of the
chromosomes than others, giving the chromosomes a striped appearance.
Suggest one way the structure of the chromosome could differ along its length to
result in the stain binding more in some areas.

Answer 422

difference in base sequence

Question 423

Describe the method the student would have used to obtain the results in Figure 3.
Start after all of the cubes of potato have been cut. Also consider variables he should
have controlled

Answer 423

method to ensure all cut surfaces of the 8 cu es are exposed to sucrose solution

controlling temp
drying cubes before measuring
measure mass of cubes at stated time intervals

Question 424

Suggest and explain two ways in which the scientists could have improved the
method used for data collection in this bee collection investigation.

Answer 424

collect at more times of the year so more points on graph

counted number of individuals in each species so that they could calc index of diversity

collected from more sites

Question 425

Formation of an enzyme-substrate complex increases the rate of reaction.
Explain how

Answer 425

reduces activation energy
due to bending bonds

Question 426

The genetic code is described as degenerate.
What is meant by this? Use an example from Table 1 to illustrate your answer.

Answer 426

more than one codon codes for a single amino acids

Question 427

A change from Glu to Lys at amino acid 300 had no effect on the rate of reaction
catalysed by the enzyme. The same change at amino acid 279 significantly reduced
the rate of reaction catalysed by the enzyme.
Use all the information and your knowledge of protein structure to suggest reasons for
the differences between the effects of these two changes

Answer 427

both negatively charged to positively charged change in amino acid

change in amino acid 300 does not change the shape of active site

Question 428

The scientists tested their null hypothesis using the chi-squared statistical test.
After 1 cycle their calculated chi-squared value was 350
The critical value at P=0.05 is 3.841
What does this result suggest about the difference between the observed and
expected results and what can the scientists therefore conclude

Answer 428

there us a less than 0.5% probability that the difference between observed and expected occurred by chance

calculated value is greater than criticall value so the null hypothesis ca be rejected

can be concluded that the promotion of plants that produce 2n gametes does change from one breeding cycle to the next

Question 429

Explain how the treatment with antivenom works and why it is essential to use passive
immunity, rather than active immunity

Answer 429

antibodies bind to the toxin and causes its destruction

active immunity would be too slow

Question 430

A mixture of venoms from several snakes of the same species is used.
Suggest why.

Answer 430

may be different form of antigen
different antibodies

Question 431

During vaccination, each animal is initially injected with a small volume of venom.
Two weeks later, it is injected with a larger volume of venom.
Use your knowledge of the humoral immune response to explain this vaccination
programme

Answer 431

b cells specific to the venom reproduce by mitosis

b cells produce plasma cells and memory cells

second dose produce antibodies in secondary immune response in higher conc and quickly

Question 432

Describe the gross structure of the human gas exchange system and how we breathe
in and out

Question 433

Mucus produced by epithelial cells in the human gas exchange system contains
triglycerides and phospholipids.
Compare and contrast the structure and properties of triglycerides and phospholipids

Question 434

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with
the sugar, lactose, attached.
Describe how lactose is formed and where in the cell it would be attached to a
polypeptide to form a glycoprotein