past paper notes

Question 1

explain the role of auxin in cell elongation? /8

Answer 1

1) auxin binds to receptor
2) in cell surface membrane
3) auxin increases proton pump activity
4) more protons enter cell wall
5) cell wall becomes acidic
6) expansins activated
7) expansins breaks bonds between microfibrils
8) K+ enters the cell
9) water potential of cell decreases
more water enter cell by osmosis
10) turgor pressure
11) ref to acid growth hypothesis

Question 2

Explain, using examples, how the environment may affect the phenotype of individual
organisms. /7

Answer 2

1) phenotype results from interaction of genotype and environment
2) environment may, limit / modify, expression of gene
3) continuous variation example ; e.g. size / mass / height
4) qualified ; e.g. because, food / nutrients / ions, missing or malnutrition occurs
5) environment may, trigger / switch on, gene ;
6) such as temperature and change in animal colour
7) or UV light and melanin production
8) environment effect usually greater on polygenes
9) environment may induce mutation (affecting phenotype) ;

Question 3

Outline how a gene mutation may occur. /4

Answer 3

1) random/ spontaneous
2) change in sequence of base
3) base substitution
4) causes frameshift

Question 4

State two reasons why people may have objections to the growth of insect-resistant GM
crops. /2

Answer 4

1) resistance may be transferred to wild plants
2) contamination of food marketed as organic
3) may kill, useful insects / pollinators
4) decrease in biodiversity
5) potential health risks of humans (eating GM crops)
6) insects may become resistant (to toxin)

Question 5

Describe the properties of mtDNA that make it suitable for the study of evolution. /3

Answer 5

1) mutations occur at constant rate

2) mutations occur at faster rate than, nuclear / chromosomal, DNA ;

3) not protected by histone proteins ;

4) no enzymes to repair DNA mutations ;

5) many copies of mtDNA per cell ;

6) no mixing of DNA at fertilisation (as only inherited from mother)
or
circular DNA, so no crossing over

Question 6

Explain how rice is adapted to grow with its roots submerged in water /5

Answer 6

1) arenchyma in roots and stem allows oxygen to diffuse to roots for aerobic respiration

2) high tolerance to ethanol

3) root cells produce ethanol dehydrogenase to break down ethanol in anaerobic respiration

4) some leaves trap air underwater due to ridges on leaves

Question 7

Name the two enzymes present on the dip stick and outline the reaction catalysed by each
enzyme. /2

Answer 7

1) enzyme: glucose oxidase
reaction: glucose reacts
with glucose oxidase to
form hydrogen peroxide
and gluconic acid
2) enzyme: peroxidase
reaction: hydrogen
peroxide reacts with
peroxidase and
chromogen to form
coloured solution

Question 8

Sea otters may spend up to five minutes under water while searching for food. During this
time, respiration in anaerobic conditions takes place.
When a sea otter first returns to the surface of the ocean, its breathing is faster and deeper
than normal.
Explain why its breathing is faster and deeper than normal. /3

Answer 8

1) as anaerobic respiration causes formation of lactate in muscles this causes oxygen debt

2) so more oxygen needed than normal

3) to break down lactate to pyruvate

4) and for rexoygenation of haemoglobin

Question 9

Describe the proteins that are involved in the contraction of a sarcomere. /4

Answer 9

myosin is a fibrous protein with a globular head

actin is a globular protein

troponin and tropomyosin. tropomyosin

actin has binding site for myosin head

Question 10

Outline the effects of mutant alleles on the phenotype in albinism and haemophilia. /7

Answer 10

albinism:
1) the TYR gene which
codes for the enzyme
tyrosinase is mutated.
it is caused by
recessive ellele.
2) results in absence of
melanin
3) causes skin burn, pale
skin and pink eyes and
blurry vision

haemophilia:
1) caused by recessive
allele
2) fatctor 8 is not
produced
3) sex linked as gene is
on X chromosome
4) this prevents blood
clotting
5) leads to excessive
bleeding

Question 11

Describe how random sampling can be used to assess the distribution and abundance of
plants in an area. /6

Answer 11

1) area marked out as grid

2) coordinates obtained using random coordinate generator

3) quadrats used

4) quadrats placed at random coordinates

5) the size of quadrats should be same

6) count number within quadrat using blaun blanquet

7) repeat sampling

Question 12

Suggest measures that could help to protect wild populations of grey wolves in
south-west Europe. /3

Answer 12

national parks

provide them with healthcare and food

can be used to raise awareness by educating others

ban hunting

Question 13

Explain how the results of this technique would be used to confirm that phycoerythrin is
present in red algae and not present in a plant with green leaves. /3

Answer 13

calculate Rf value

compare Rf values of both pigments

find pigment present on chromatogram from red algae and absent from green leaves

identify pigments using reference point

Question 14

Suggest why Venus fly trap plants need to capture insects. /1

Answer 14

poor mineral content in soil

Question 15

Dogs have an exceptionally good sense of smell. They can detect molecules in the air with a
concentration of one part per trillion (1012).
(a) Olfactory receptor cells are the sensory receptors in the nasal cavity that respond to chemicals
in the air. They function in a similar way to the chemoreceptor cells in the taste buds of the
tongue.
Describe how olfactory receptor cells in the nasal cavity of dogs respond to chemicals to
generate an action potential. /5

Answer 15

chemicals binds to receptor cells

Na+ ions diffuse into cells via microvilli

membrane depolarised

receptor potential generated

voltage gated Ca2+ channels open and Ca2+ diffuses into cell

vesicles containing neurotransmitters move and fuse with cell membrane

exocytosis of neurotransmitters

neurotransmitters binds to receptor

receptor cells acts as transducer

Question 16

Describe the methods used to conserve endangered plant species. /7

Answer 16

botanic gardens

   can be used for research

  controlled growing conditions such as temperature, light intensity and CO2 concentration

  plants controlled so can be reintroduced back into wild

  store seeds

  seeds regularly checked for viability

   maintains genetic diversity

  seeds can be germinated prior to introduction back into natural habitat

Question 17

Explain the term F1 generation. /2

Answer 17

first generation of offspring

it is cross between recessive homozygous chromosomes and dominant homozygous
chromosomes

offpsring will be heterozygous

Question 18

Suggest two reasons why phenotypic ratios in the F2 generation do not always match
the expected ratios /2

Answer 18

linkage

environmental effects

mutations

Question 19

Explain why improving milk yields in cattle by selective breeding can be more challenging
than improving yields of crops by selective breeding /3

Answer 19

takes longer time to mature

fewer offsprings per cross

ethical issues

cattle require more care

milk yield must be measured over period of time ;

difficulty in identifying suitable males for use in crosses

Question 20

Describe the role of abscisic acid in stomatal closure. /4

Answer 20

abscisic acid binds to receptors

proton pumps are inhibited

opens Ca2+ channels

Ca2+ acts as second messenger

K+ diffuses out of guard cell

water potential of cell increases

water leaves cell by osmosis

cell becomes flaccid

Question 21

Describe the role of aquaporins in osmoregulation./3

Answer 21

(aquaporins are) water channel (proteins) ;

(more) aquaporins increase (cell surface) membrane permeability (to water)

of collecting duct (cells)

allow water to, be reabsorbed / move into tissue fluid or blood ;

Question 22

Explain what is meant by continuous variation and how it can be caused. /3

Answer 22

continuous variation has range of values

phenotypes are quantitative

polygenic/ controlled by many genes

different genes have an additive effect

environmental factors contribute to variation

Question 23

Outline the steps required to prepare the genome of an individual so that the genome is ready
for analysis using a microarray chip. /3

Answer 23

extract DNA from cells

cut DNA into small fragments using restriction enzymes

denature to make single stranded DNA

tagged with fluorescent dye

Question 24

Explain the need for a reduction division during meiosis. /4

Answer 24

meiosis produces gametes

gametes fuse to form zygote

zygote will have maternal and paternal chromosomes

gametes are haploid so zygote is diploid

prevents doubling of chromosome number

Question 25

Describe the functions of the internal membranes of the chloroplast in photosynthesis /7

Answer 25

photosynthetic / named / primary / accessory, pigments to absorb light (energy) ;

photosystems / antenna complex and reaction centre / light harvesting structures ;

photoactivation / electrons excited / emission of electrons ;

electrons move along electron transport chain ;

(cyclic / non-cyclic) photophosphorylation / light-dependent stage ;

site of photolysis / location of oxygen-evolving complex ;

thylakoids stacked to form grana

gives large surface area ;

thylakoid space or lumen to, form proton gradient / have high concentration of protons ;

thylakoid membrane is (relatively) impermeable, to maintain the proton gradient

ATP synthase to make ATP;

chemiosmosis

Question 26

Suggest reasons why more fish species than mammal species are endangered. /4

Answer 26

fish:
overfishing ;

(on water / at sea) difficult to enforce protective, laws / regulations

trophy hunting ;

climate change qualified ; e.g. increased ocean temperatures /

predatory species moving into new areas now water is warmer

pollution qualified ; e.g. plastics in the sea / oil spills / eutrophication

there are more species of fish than there are species of mammals ;

mammals:
more conservation projects for mammals

laws in place, banning hunting / protecting mammals

Question 27

Describe the role of seed banks in the protection of endangered species. /7

Answer 27

seed banks collects seed

    long term storage

    storage to prevent germination

    seeds are kept frozen

    seeds are regularly checked for viability

    seeds re stocked regularly

   seeds maintain genetic diversity

   can be used to increase number in future

   maintains biodiversity

   for research

Question 28

Suggest why a microarray is suitable for identifying the function of the transcription factor. /3

Answer 28

transcription factors regulate expression of genes

microarray can detect expression of genes

by fluorescence between two samples

Question 29

State two benefits to farmers of insect resistance in crops. /2

Answer 29

increase yield

increase quality of yield

no pesticides need to be used

Question 30

State two reasons why people may have objections to the growth of insect-resistant GM
crops. /2

Answer 30

resistance may be transferred to wild plants

contamination of food marketed as organic

may kill, useful insects / pollinators

decrease in biodiversity

potential health risks of
humans (eating GM crops)

insects may become resistant (to toxin)

Question 31

Suggest measures that could help to protect wild populations of grey wolves in
south-west Europe. /3

Answer 31

national parks

provide them with healthcare and food

can be used to raise awareness by educating others

ban hunting

Question 32

Explain why it is important to the gene pool of Sumatran tigers to move tigers from one zoo to
another. /3

Answer 32

create genetic diversity among them

increases hytrozygosity

hybrid vigor

reduces inbreeding depression

reduces chances of harmful recessive alleles together

Question 33

The AAV vector used was unable to replicate itself within the target cells.
Suggest why the researchers chose a vector that could not replicate. /2

Answer 33

To prevent virus from spreading into the body

to limit side effects

Question 34

Suggest and explain three ways in which the tank environment may make the phenotype of
a captive fish different from a wild fish. /3

Answer 34

controlled conditions so phenotype less varied

more oxygen so larger

less space so smaller

Question 35

Explain why ATP is needed in the first part of glycolysis. /2

Answer 35

ATP needed for phosphorylation of glucose

this activates glucose

Question 36

Explain the social benefits of this example of gene editing. /3

Answer 36

increases yield

improves quality of food

more income for farmers

cheaper

spend less on pesticides

Question 37

State the role of the enzyme cascade. /1

Answer 37

amplifies signal for faster response

Question 38

Explain how very dry conditions cause CO2 concentration to become the main limiting
factor of photosynthesis in plants. /3

Answer 38

humidity causes stomata to close

due to water stress

ABA causes stomata to close to prevent water loss

Question 39

Explain why the lumen of the afferent blood vessel needs to be wider than the lumen of the
efferent blood vessel. /2

Answer 39

to force out filterate from glomeruli into bowman’s capsule

small substances like glucose get pushed out but large substances like proteins cant

some reabsorbed back into blood at efferent blood vessel

Question 40

Explain why the reaction that takes place at high temperatures in C3 plants reduces the
rate of photosynthesis. /2

Answer 40

oxygen combines with RuBP

so less oxygen will combine with RuBP

Question 41

Explain why bioinformatics was used to compare these gene sequences and suggest a
conclusion that could be made from the percentage similarity data obtained. /2

Answer 41

why:

fast and accurate

more percentage similarity means more recent accestor

Question 42

stroma has higher pH when H+ move out into thylakoid space

leads to increased H+ concentration in thylakoid space

then H+ diffuses back into stroma through ATP synthase

Question 43

Describe the procedure of embryo transfer in a mammal such as a camel. /4

Answer 43

make male and and females camel mate

and remove embryo from mated female

select healthy embryo

may freeze embryo for later use

implant embryo in different female uterus

which is surrogate mother

Question 44

Explain the relationship between the absorption spectrum of the main chloroplast pigments
in a species of plant and the action spectrum for photosynthesis for that species. /2

Answer 44

absorption spectrum shows absorption of wavelength of light by photosynthetic pigments

action spectrum shows the rate of photosynthesis

higher absorption gives higher photosynthesis

Question 45

Name three molecules, other than coenzymes, that are found in the mitochondrial matrix
and explain their role in aerobic respiration. /3

Answer 45

pyruvate for links reaction

oxaloacetate to make citrate

citrate to make reduced NAD

enzymes to catalyse link reaction and krebs cycle

oxygen to accept protons

water as a solvent

DNA to make respiratory enzymes

Question 46

Suggest and explain how Pi
is transported across the inner membrane of the
mitochondrion into the matrix. /2

Answer 46

Pi by facilitated diffusion

Pi and H+ move together

as H+ ions diffuse through ATP synthase

Question 47

Suggest the advantages of linking ATP transport to ADP transport across the inner
membrane of the mitochondrion. /2

Answer 47

constant supply of ADP

so ATP can be continued to be made

Question 47

Outline how vigorous, uniform varieties of maize were developed by selective breeding. /4

Answer 47

breed plants with desired characteristics

breed offspring for many generations

so plants get smaller this causes inbreeding depression

cross pollinate 2 inbred lines, this is hybridisation

gives hybrid vigour in offspring

F1 seeds have same genotype

Question 48

Describe and explain the action of ADH on the cells of the collecting duct when the water
potential of the blood decreases. /5

Answer 48

detected by osmoreceptors in hypothalamus

pituitary gland releases ADH

ADH binds to receptors on collecting duct

g protein activated which activates adenyl cyclase

adenyl cyclase synthesises cAMP

cAMP causes protein kinase to be activated

so vesicles containing aquaporins fuse with cell surface membrane of collecting duct and makes it permeable

so water from collecting duct moves into blood by osmosis

Question 49

Explain why calvin cycle is described as a cycle? /2

Answer 49

no start and end, point / molecules ;

all, molecules / intermediates, present all the time ;

ribulose bisphosphate / RuBP / 5C molecule, is regenerated

Question 50

Give reasons why low genetic variation may decrease the long-term survival of a species. /3

Answer 50

less able able, to, adapt 

little variation for selection to act on ;

few useful / beneficial, alleles ;

all / most, (could be) killed by same, disease / selection pressure ;

if due to small population size this decreases species survival chance

Question 51

Outline the similarities in structure between a neuromuscular junction and a cholinergic
synapse. /4

Answer 51

Na+ enters post synaptic membrane

both have presynaptic and post synaptic membrane

have receptors for ACh

acetylcholine is vesicles

many mitochondria

synaptic cleft

Question 52

Medicine is defined as the diagnosis, treatment and prevention of disease.
Outline the different ways in which genetic technology can be applied to medicine, with reference
to named diseases. /7

Answer 52

genetic engineering is treatment from GM bacteria

make insulin (drug for diabetes)

make factor VIII (drug for haemophilia) ;

make adenosine deaminase (drug for SCID) ;

genetic, screening / diagnosis / testing ;

(detect) BRCA1 / BRCA2 ;

(detect number of repeats / allele for) Huntington’s ;

(detect allele for) cystic fibrosis / CFTR ;

example of action if diagnosis positive ;

gene therapy ;

insert / add, normal allele into (named), cells / tissue (of person) ;

to treat, eye disease(s) / LCA / Leber’s congenital amaurosis ;

to treat SCID

Question 53

Coenzymes are important in aerobic respiration.
Outline the roles of named coenzymes in aerobic respiration. /5

Answer 53

NAD and FAD

coenzymes are dehydrogenase enzymes

coenzymes get reduced in glycolysis, links reaction and krebs cycle by accepting proton

and then release hydrogen at oxidative phosphorylation at end of cristae

coenzyme A:

binds to acetyl

acetyl + 2C fragment + oxaloacetate = citrate

joins links reaction and krebs cycle

Question 54

Describe two processes in the liver that are stimulated by glucagon. /2

Answer 54

glycogenolysis- it is the break down of glycose to glucose

gluconeogeneis- it is the amino acids/ lipids to glucose

Question 55

Explain how different types of gene mutation can affect the phenotype and outline the effects
of the mutant alleles that cause Huntington’s disease on the phenotype of a person. /9

Answer 55

base substitution

       does not have a significant effect on phenotype

       base, insertion / deletion leads to, frame shift / described 

       has significant effect on phenotype 

    change in, primary structure / amino acid sequence / polypeptide made 
   change in, tertiary structure 

      loss of function in protein 

     premature) stop codon 

   Huntinton’s disease 
      mutant allele is dominant 
      dominant, allele has more repeats of base triplet CAG (than normal) 
     heterozygote will have disease 
    
   brain cells die more rapidly 

    involuntary movements 

    onset in middle age 

    greater number of CAG repeats affects, earlier onset / severity of disease

Question 56

Tumours can form in the liver.
Explain how a liver tumour develops. /2

Answer 56

uncontrolled mitosis

abnormal mass of cells formed

no programmed cell death

mutation of oncogene

Question 57

Describe and explain one characteristic of mtDNA that makes it more useful than using
nuclear DNA to provide evidence of evolution. /2

Answer 57

1) large quantities in the cell - so easier to extract

2) small genome size- so easier to locate specific section of DNA to test

3) mtDNA is a single copy of DNA- so only mutation causes it to change

4) inherited maternally- all mtDNA sections are shared between all members of family

5) faster molecular clock - more accurate time estimate

Question 58

Explain why the production of memory cells prevents the gene therapy from working in
long-term chronic conditions such as cystic fibrosis. /3

Answer 58

repeat treatment causes rapid immune response

so target cells short lived

decrease in gene expression

Question 59

With reference to the three types of vectors that are commonly used, discuss the challenges
in choosing appropriate vectors for use in gene therapy.
Do not include problems associated with an immune response in your answer. /4

Answer 59

liposomes: low ability to add gene into target cells

naked DNA: has to be injected into cells

                low efficiency of cellular uptake

                rapidly broken down

viruses: small packaging capacity

         cause mutation in host DNA

Question 60

(i) A region that contains voltage-gated channel proteins.
(i) A region that contains ligand-gated channel proteins

Answer 60

(i) pre synaptic membrane
(ii) post synaptic membrane

Question 61

Outline the steps involved in the introduction of disease resistance to varieties of wheat. /5

Answer 61

select plant resistant to wheat

by exposing plants to disease to show resistance

breed selected plants with resistance

grow offsprings

select offspring with resistance and breed together

repeat for many generations