BIO UNIT 2

Question 1

Name two processes that take place in the nucleus of a diatom.

Answer 1

DNA replication // production of
mRNA

Question 2

Describe how a decrease in biodiversity within an ocean habitat could
be determined.

Answer 2

count number of (different) species (in the ocean habitat) / determine
species richness (1)
* count number of individuals in each species / determine species
{evenness / abundance} (1)
* calculate index of diversity (1)
* calculate heterozygosity index / assess genetic diversity (1)
* compare to previous {value / year} to see if there is a decrease (1)

Question 3

endemic.

Answer 3

{the (Edelweiss) plant / the species} is only found in {one area / one
geographical location

Question 4

magnification

Answer 4

• how many times bigger an object appears in an image than in real life

Question 5

Describe the roles of the tube nucleus and the generative nucleus.

Answer 5

controls the growth of the pollen tube (1)
* controls the production of {digestive / hydrolytic} enzymes (1)
* (which allows) the (male) {nucleus / nuclei / gamete(s)} to
{enter / reach} {ovule / ovary / micropyle / egg cell / polar nuclei /
female gamete} (1)
Generative nucleus:
* (divides to) form two {male / haploid} nuclei (1)* one nucleus {fertilizes / fuses with} the egg cell nucleus / one
nucleus {fertilizes / fuses with} the polar nuclei (1)

Question 6

A
(b) Describe how the nucleus of a sperm cell enters an egg cell.

Answer 6

• {sperm cell / acrosome} releases {enzymes / acrosin / protease} (1)
• (therefore) the {enzymes / acrosin} digest the zona pellucida (1)
• (resulting in) the sperm cell membrane fusing with {egg cell / oocyte}
  membrane (allowing the nucleus to enter the egg cell) (

Question 7

Describe the role of the rough endoplasmic reticulum and the Golgi apparatus
in the production of these enzymes.

Answer 7

translation occurs on the {rough endoplasmic reticulum / rER /
ribosomes} (1)
* formation of {2° / 3° / 3D / correct named bonds} structure in
rER (1)
* {polypeptide / protein} is packaged into vesicles by rER /
{vesicles fuse with / protein transported to} Golgi (1)
* modification occurs in Golgi (apparatus)

Question 8

Suggest how these enzymes will prevent more than one sperm nucleus
entering the egg cell.

Answer 8

the cortical granules fuse with cell membrane and release
{enzymes / proteases} (1)
* (which result in) {hardening / thickening} of the zona pellucida (1)
* {acrosome enzymes / acrosin} can no longer {digest / penetrate}
the zona pellucida (1)

Question 9

Give two reasons how education could help conserve the
Grandidier’s baobab.

Answer 9

Madagascan people will (be taught to) not cut down the Baobab
trees (1)
* Madagascan people will (be taught to) promote the planting of
{seeds / saplings} to increase the population (

Question 10

calcium pectatte

Answer 10

make the cell wall more stable

Question 11

Describe what happens to DNA during interphase

Answer 11

(at start of interphase) DNA unwrap from histones / {DNA /
chromosomes} {uncoil / uncondensed} (1)
* DNA {is replicated / synthesis / is checked for errors} (1)
* DNA undergoes transcription (

Question 12

) Explain how DNA methylation can alter the expression of some genes

Answer 12

{methyl / -CH3} groups are added to {gene / cytosine / CpG} (1)
* genes become {switched off / deactivated / silenced} (

Question 13

Explain why epigenetic changes to genes, such as DNA methylation, are
passed on by mitosis.

Answer 13

the DNA methylation is copied when the DNA is replicated /
{methylated DNA is / epigenetic changes are} replicated (1)
* (therefore) daughter cells will contain the same DNA methylation
after cell division /

Question 14

Describe one piece of information that would need to be collected in order to
determine if the scientist was correct.
IF THE ANIMAL IS OLDER

Answer 14

correct example of molecular evidence (1)
* to see if the sequences from Akhal-Teke and Turkoman
breeds are {the same /

Question 15

organ.

Answer 15

roup of) tissues which work together to perform {a function /
functions}

Question 16

Explain how the structure of starch enables the potato tubers to have a high
energy content.

Answer 16

polymer of glucose (1)
* compact molecule so lots of {glucose / starch / energy} can
be stored (

Question 17

Explain two anatomical adaptations of these penguins that enable them to
survive in this environment.

Answer 17

{streamlined shape / webbed feet / wings} enable the penguin
to swim (1)
* {long / sharp / big / pointed} beak to {catch / eat} prey (1)
* small SA: vol to reduce heat loss in cold water (1)
* {layer of lipid / blubber / feathers} for {insulation /
thermoregulation} (1)

Question 18

uggest one way that these penguins can be shown to belong to
different species.

Answer 18

• when penguins from different islands breed together they
  produce {infertile / sterile} offspring (1)
• differences in {genotype / phenotype}

Question 19

Explain how different species of gentoo penguin could have formed.

Answer 19

the different islands are located a long distance away from each
other / the different penguin populations would not meet to
breed / no gene flow between populations (1)
* {genetic variation / mutations / different alleles} in penguin
population(s) (1)
* different selection pressure on each island (1)
* {beneficial / advantageous} allele(s) may {give selective
advantage in different areas / mean those individuals are more
likely to survive} (1)
* penguins with {beneficial / advantageous} {allele(s) /
characteristics} pass these alleles onto their offspring (until the
populations become genetically dissimilar to each other) (1)
* the {populations / penguins} on different islands are unable to
reproduce to form fertile offspring (

Question 20

locus

Answer 20

{location / position} of a {gene / allele} on a chromosome

Question 21

Explain how these alleles can produce fruit flies with different coloured eyes.

Answer 21

different alleles {have a different DNA base sequence / code for
different mRNA} (1)
* which may result in a different {polypeptide / protein /
pigment} being produced (1)
* flies may inherit two different alleles / (different allele
combinations) may result in {further / intermediate}
{phenotypes / eye colours} (in addition to colours in tabl

Question 22

Explain how histone modification can affect gene expression.

Answer 22

methylation is addition of a {methyl / CH3} histone methylation results in DNA being
more tightly wrapped around histone methylation results in the gene being {switched off /
silenced / not expressed / not transcribed} (1)
* acetylation results in the gene being {switched on /
expressed / activated / transcribed} (1)
* (because) {RNA polymerase / transcription factors} can’t
{bind / access} (if gene is switched off) / converse (1)

Question 23

Explain how a captive breeding programme could maintain the genetic
diversity of Malayan tapir populations

Answer 23

nalyse {individual’s alleles / gene pool} / identify individuals with
different alleles (1)
* use a stud book (1)
* breed {individuals / tapirs} {with different alleles / from different
populations} (1)
* (therefore) preventing loss of alleles (from gene pool) (1

Question 23

Explain why the body cells of the mother and baby have genetic similarities
and difference

Answer 23

• (the body cells of) baby will have {26 / half the} chromosomes
  that are {similar / identical} to those in the mothers (cells) (1)
• the other {26 / half of} chromosomes in the baby body cells will
  be (genetically) different as they came from the {sperm cell /
  father} (1)
• (there may be genetic differences in the gamete chromosomes
  inherited from the mother) due to {mutation / crossing over

Question 24

Describe the role of the rough endoplasmic reticulum in the formation of extracellular enzymes.

Answer 24

ranslation occurs at rER ribosomes / {polypeptide (chain) / chain of amino acids} enters rER (1) * formation of {α-helix / β-pleated sheet / secondary structure / tertiary structure / 3D shape / globular structure} (1) * (causing) formation of {hydrogen bonds / covalent bonds / ionic bonds / disulphide bridges} * {polypeptide / protein / enzyme} packaged into (transport) vesicle to go to Golgi apparatus (1)

Question 25

seed banks

Answer 25

collection of seeds from multiple plants of species D (to ensure different alleles) (1) * {washing / disinfecting / sterilising} seeds to remove (decomposing) microbes (1) * x-ray seeds to check {viability / presence of embryo} (1) * {freeze the seeds / dry the seeds / store in very low temperatures} to {prevent germination / maintain viability / prevent growth of microbes / reduce enzyme activity / keep them dormant} (1) * {germination / growth / pollination} of genetically different plants to collect new seeds (1

Question 26

Describe how two structures in this tissue enable it to carry out its function. (PHLOEM

Answer 26

* {(continuous) tube / hollow tube / sieve plate} allows {flow of solution / movement of sucrose / translocation} (1) * contain plasmodesmata allow {entry /exit} of {sucrose / water / molecules} (1) * companion cells to {move sucrose into sieve tube (elements) provide ATP for active transport} (1) * (cellulose) cell wall to withstand pressure (1

Question 27

sustainable.

Answer 27

will not run out / more plants can be grown / renewable / available to future generations (1) * biodegradable / can be broken down by {decomposers / bacteria / fungi} (more rapidly) (1) * carbon neutral (

Question 28

Explain why an embryo cell and an endosperm cell contain different quantities of DNA.

Answer 28

the female gamete(s) and the male nuclei are haploid (1) * female gamete nucleus was fertilised by {one / a} male {nucleus / gamete} (to form the embryo cell) (1) * embryo (cell) is {2n / diploid} (1) * (whereas two) polar nuclei were fertilised by {one / a} male {nucleus / gamete} (to form the endosperm cell) (1) * an endosperm (cell) is {3n / triploid} (

Question 29

Describe a drug trial method that a scientist could use to determine if this extract is: * safe to use in humans * more effective than t

Answer 29

drug containing L. candidum) extract tested on human (skin) {cells / tissues} (1) * appropriate {dosage / concentrations} (of drug containing L. candidum extract) identified / identification of {side effects / toxicity} (1) * (phase 1 / preliminary) tests on (people / volunteers) who {are healthy / do not have skin burns} (1) * (phase 2) - drug tested on {small / 100 to 500} groups of (patients / people) who have (skin) burns (1) * (phase 3) - drug tested on {large groups of / 1000 to 3000} (patients / people) who have (skin) burns (1) * double blind test involves one group receiving extract and the other receiving current (skin burn / hospital) treatment

Question 30

y species richness

Answer 30

number of (different) species in a {community / this part of the lake / specific area / habitat / ecosystem

Question 31

why stain

Answer 31

so chromosomes become visible

Question 32

Explain how isolation caused the formation of six fox populations with different characteristics.

Answer 32

each population of island fox cannot mate with individuals on another island (1) * (as each island has) different {(environmental) conditions / habitats / selection pressures} (1) * individual with advantageous allele will (survive and) {reproduce/pass onto offspring} (1) * (resulting in) populations being genetically different (to each other) / offspring on one island would be genetically different to offspring on a different island / accumulation of different genetic material results in new subspecies (

Question 33

Explain how conservation could achieve these goals.

Answer 33

establish protected areas / increase food source (1) * reduce the population of {golden eagles / dogs / racoons} (1) * (reduce deaths from disease by) {treating diseased foxes (with medication) / vaccination} (1) * use of captive breeding programme (to increase population size) / reintroduce (captive bred) foxes (1) * {analysis of genotype of foxes used in captive breeding programme / use of stud books} to ensure genetic diversity of fox population is maintained (1

Question 34

linkage

Answer 34

(loci of) {the genes / flower colour and pollen grain size (genes)} being on same {chromosome

Question 35

Give three differences between a cell wall with secondary thickening and a cell wall without secondary thickening.

Answer 35

cell wall with secondary thickening {is thicker / has more layers} (1) * cell wall with secondary thickening contains lignin (1) * cell wall with {secondary thickening / lignin} is {stronger / more supported / less flexible / has pits} (1) * cell wall with {secondary thickening / lignin} is {waterproof / impermeable to water} (1)

Question 36

Explain how secondary thickening contributes to the physical properties of sclerenchyma fibres

Answer 36

econdary thickening involves addition of) lignin (1) * which results in (increased) strength (1) IMP

Question 37

Describe the function of pits in the xylem vessel.

Answer 37

allows {movement of named substances / communication} (1) * between (adjoining) cells water ,inorganic minerals

Question 38

Explain how these three structures contribute to the function of pepins.

Answer 38

because circular DNA) contains {genes / alleles/ bases/ genetic information} which will be {copied onto mRNA / transcribed / codes for a protein / codes for a sequence of amino acids} (1) * (because) ribosomes will translate mRNA base sequence into an amino acid sequence (1) partially permeable / {compartmentalise / encloses} the {DNA / ribosomes} from the cytoplasm

Question 39

Explain how a lack of magnesium ions could result in yellow leaves and reduced growth.

Answer 39

* magnesium (ions) are needed for the formation of {chlorophyll / chloroplasts} (1) * (yellow leaves are due to) {fewer / no} {chlorophyll (molecules) / chloroplasts / green pigments} (1) * (reduced growth is due to) {reduced / no} {production of glucose / carbohydrate / photosynthesis} (1) need clear statement

Question 40

niche.

Answer 40

role of an organism in its {environment / habitat / ecosystem} (1)

Question 41

Explain how these skeletal muscle cells can contain the same genes as the morula cells but be different in structure and function.

Answer 41

differential gene expression occurred (1) * only genes needed for skeletal muscle cell formation are {active / switched on} (1) * due to {epigenetic modification / histone modification / DNA methylation} (1) * only {active / switched on/ skeletal muscle} genes are transcribed (into mRNA) (1) * translation (of mRNA) occurs (at the ribosome) (1) * (resulting in) formation of proteins needed in {skeletal muscle cells / mitochondria / muscle contraction} (1)

Question 42

one role of starch molecules

Answer 42

store of {glucose / energy}

Question 43

starch

Answer 43

carbon neutral and its renewable

Question 44

Explain how the phenotypes of an individual can show genetic linkage in the inheritance of two genes

Answer 44

* (loci of the genes) are {on same chromosome / close together} (1) * * (therefore the different versions of the) two genes have a higher chance of being {inherited together

Question 45

Explain how different proteins can be synthesised from this mRNA that has had introns removed.

Answer 45

some exons can be {cut out / removed} (1) * (exons cut / exons joined) by enzymes (1) * exons can be joined together in different orders (1) * translation occurs (at ribosome) (1) * (therefore) different {amino acid sequences / primary structure / polypeptide chains} are produced (1

Question 46

GOLGI

Answer 46

modifies and packages into secretory vescicles

Question 47

use of nitrogen

Answer 47

nucleic acids amino acids

Question 48

Describe the structure of a blastocyst.

Answer 48

{outer / single} cell layer / trophoblast (1) * inner cell mass / embryoblast / contains pluripotent cells (on the inside) (1) * hollow / fluid filled / (fluid filled) cavity / blas

Question 49

Histone modification and DNA methylation are processes that occur when totipotent stem cells develop into pluripotent stem cells. Explain how these two processes alter the activation of genes in the cells.

Answer 49

(DNA methylation is the) addition of {methyl / CH3} group(s) (1) * to cytosine (1) * (histone modification is the) {methylation / phosphorylation/ acetylation} of {histones / lysine} (1) * (resulting in) compacting chromatin / DNA wrapped more tightly around histones (1) * (resulting in) inhibition of {transcription factor / RNA polymerase} binding (1) * (therefore) preventing {transcription / gene expression} (1)

Question 50

Compare and contrast the structure and function of lysosomes and acrosomes.

Answer 50

Similarities * both contain (digestive / hydrolytic) enzymes (1) * both {have single membrane / membrane bound (organelles)} (1) Differences (max 2) * a lysosome is spherical whereas an acrosome is {curved / not} (1) * a lysosome is involved with intracellular digestion whereas an acrosome is involved with extracellular digestion (1) * a lysosome (enzyme) is involved in breaking down {cell components / microbe cells / virus} whereas an acrosome (enzyme) is involved in digesting the {outer layers of an egg cell / zona pellucida} (

Question 51

) Give two differences in the arrangement of the DNA in a cell at the beginning of interphase and at the end of prophase I.

Answer 51

(at the beginning of) interphase the DNA is {in the nucleus / surrounded by nuclear membrane / surrounded by nuclear envelope} whereas it is not at the end of prophase (I) (1) * DNA is uncoiled at the beginning of interphase whereas it is condensed at the end of prophase (I) (1) * DNA has not been replicated at the beginning of interphase whereas it has been replicated at the end of prophase (I) (1)

Question 52

tissue.

Answer 52

group of (similar) cells working together to perform a (specific) function (

Question 53

xplain how these subspecies of snow leopard could form.

Answer 53

consideration of fragmentation of snow leopard range / separation of different populations / geographical isolation / populations in {central / northern/western / different areas in Asia} * consideration of how the fragmentation developed * consideration of different {environment / conditions} in each of the different locations (northern/eastern/southern) * idea of (different) selection pressures / (new) selection pressure occurs * idea of genetic variation in population / some individuals have different alleles / mutations have occurred / mutations resulted in different alleles * idea that different {mutations / alleles / adaptations} will be advantageous in different habitats * natural selection occurs / survival of the fittest * individuals with advantageous {allele / mutation} will have an increased chance of {surviving / reproducing} * passing on {advantageous allele / mutation} to offspring / increasing frequency of (advantageous) allele in gene pool * example of an advantageous {allele / phenotype} linked to the {habitat / location} * consideration of differences {in gene pool / phenotypes / anatomical, behavioural and physical adaptations} developing in different snow leopard populations * idea that inbreeding could occur / consideration of founder effect consideration of (little) reproductive isolation / different populations having different (mating) behaviour or breeding times * sub-species can still breed together to form fertile offspring

Question 54

Give a reason as to why these different populations are described as subspecies and not different species of snow leopard

Answer 54

individuals (from different sub-species) can (still) breed together to produce fertile offspring (1

Question 55

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

Answer 55

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

Question 56

Compare and contrast the structures of phloem sieve tubes and xylem vessels. (4)

Answer 56

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

Question 57

species richness.

Answer 57

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

Question 58

Explain why increased methylation of this gene could cause the growth of a tumour.

Answer 58

{methyl groups / CH3} are added to {DNA / the gene/ cytosine} (1) * (resulting in RB) gene being {switched off / silenced} (1) * (methylation) prevents the binding of {RNA polymerase / transcription factors} (1) * (therefore) translation (of mRNA) does not occur (1) * (therefore the) {RB / tumour suppressor} protein isn't produced (1) * and {the cell cycle / mitosis} continues (forming a tumour) / {reduced / no} inhibition of tumour growth

Question 59

role of phloem.

Answer 59

{transport/ translocation} of {sucrose / amino acids} (1)  from {source /site of production / leaves} to {sink / site of use / site of storage} (1)

Question 60

Explain how a mutation could cause the development of teeth in a chicken embryo.

Answer 60

(because) mutation resulted in these genes {becoming switched on / being expressed / not being switched off / remaining switched on} (1) * {transcription of / (active) mRNA made from} (active tooth production) genes (1) * (therefore) translation (of mRNA) occurs / proteins formed (for teeth development) (1) * (proteins cause) structural change to (beak) cells changes them into teeth cells (1)

Question 61

Describe how post-transcriptional changes of pre-mRNA can produce active mRNA

Answer 61

all introns {cut out / removed} (1) * some exons {cut out / removed} (1) * by {spliceosomes / enzymes} (1) * exons are joined together to form active mRNA (1)