Edexcel International GCSE (9-1) Biology Student Book by Philip Bradfield Steve Potter (z-lib.org)

ANSWERS 343

7 II- a Reduced growth / photosynthesis (1), affecting the 7 II> a Flow diagram should have boxes showing the stages
appearance of the crop so not harvested / unfit for in order: (1) the two strands of the DNA separate;
sale(1) (2) each strand acts as a template for the formation
of a new strand; (3) DNA polymerase assembles
I 70 nucleotides alongside the two strands; (4) Two DNA
molecules formed.
'l§'l 60
b I Caused by an addition, duplication or deletion of
1:- a base, resulting in all triplets of bases after the
e£1 50 mutation being different and so different amino
"'C acids are coded for.
40
.Q ii Caused by a change in one base in a triplet, by
substitution or inversion, so that it codes for a
i-~ d ifferent amino acid. Triplets after the mutation are
0 30 not altered; so subsequent amino acids will not be
c affected.
~ 20
-""~ 8 II- a Five.
Iii
10 b AUG GAG CCA GUA GGG
I!! c ATG GAG CCA GTA GGG
d The mRNA base sequence is converted into the amino
o
o 10 20 30 40 50 acid sequence of a protein during a process called
translation. The mRNA sequence consists of a triplet
day code. Each triplet of bases is called a codon. Reading
of the mRNA base sequence begins at a start codon
Axes correct way round, labelled (1), all points and ends at a stop codon. Molecules of tRNA carrying
correctly plotted on both curves (2), key to each an amino acid bind to the mRNA at an organelle called
curve (1), points joined by straight lines (1) the ribosome.

II Sprayed: 12 (1), unsprayed 40 (1). CHAPTER 17

Ill The Control shows whether there is any infection 1 11> D
without the fungicide (1). It is needed to be able to
see how much effect the fungicide is having on the 5 11> a Both types of division start with each chromosome
infection, i.e. as a comparison (1). copying itself / DNA replicating / DNA copying itself/
chromatids forming.
iv By day 30, the infection in the unsprayed (Control)
plants was approximately the same as in Year 1 (1 ). Plus any two of:
However the infection in the sprayed plants had Mitosis produces two daughter cells, meiosis
increased (1 ). This was probably because the plants produces four daughter cells.
had developed resistance to the fungicide (1). Daughter cells from mitosis are genetically identical
to each other and the parent cell; daughter cells
UNIT 5 ANSWERS from meiosis are genetically different from each
other and the parent cell.
CHAPTER 16 Mitosis produces daughter cells with the same
number of chromosomes as the parent cell / diploid
1 11- C to diploid; meiosis halves the chromosome number
/ diploid to haploid.
5 II- a A= base / thymine; B = base I cytosine; C =
deoxyribose / sugar; D = phosphate; E = nucleotide. b Mitosis, they are formed by division of body cells to
produce more body cells.
b Franklin used X-ray diffraction on DNA to find out
about its structure. Watson & Crick used Franklin's c Because the number of chromosomes per cell is
data and other information to build a model of the reduced by half.
structure of DNA.
6 II> a They have been formed by mitosis, so are genetically
c A always pairs with T, and C always pairs with G. identical.

6 11> a A gene is a length of DNA that codes for a protein. b Meiosis is used to form pollen and egg cells, so
fertilisation results in seeds that are genetically
ii Alleles are different forms of a gene. different from each other.

b A chromosome is a structure in the nucleus of a cell 7 II- a Control.
composed of DNA (and proteins). b Plants from cuttings would be genetically identical,
which is better in order to compare the effect s of the
c I Both have 23 pairs of chromosomes in each cell. treatment with nitrogen-fixing bacteria. Seeds would
be genetically different, so their growth might depend
ii Woman's skin cells contain XX sex chromosomes, on their genes, rather than the treatment.
man's contain XY.

344 ANSWERS

c The nitrogen-fixing bacteria provide nitrates needed 7 I> a Gametes of parents = R and r
for growth. This is an environmental effect on growth, Genotypes of F1 = Ar
rather than a genetic one. Therefore the environment Genotypes of F1 parents = Ar and Ar
plays a big part in t he growth of these plants. Gametes of F1 parents R, R and r, r
Genotypes of F2 =
8 1> a Meiosis, because sperm are gametes that are haploid
Rr
/ contain half the number of chromosomes of body
cells. R~
b Mitosis, because body cells are dividing to produce
more body cells with the normal chromosome number. b A, B and C are red, D is yellow.

c Mitosis, because body cells are d ividing to produce 8 I> a Individual 8 has cystic fibrosis, but neither of his
more body cells with the normal chromosome number. parents does, so they must be heterozygous and the
allele must be recessive. If the allele was dominant,
d Meiosis, because pollen grains are gametes that are he would have to have inherited at least one dominant
haploid / contain half the number of chromosomes of allele from one parent, so that parent would have
the plant's body cells. cystic fibrosis too.

e Mitosis, because the zygote must divide to produce b 3 and 4 must be heterozygous for the gene, as they do
more body cells with the normal chromosome not have the disease, but their son does. 11 must be
number. homozygous for the gene, since she has the disease.

9 1> a Genetic - eye colour is inherited and not affected by c I Probability that the next child is male is 1 in 2,
or0.5:
the environment.
Xy
b Genetic - it depends on inheriting XX or XY
chromosomes. X~
X~
c Environmental - the pH of soil is a feature of the
plant's environment. Ii Let A = the normal allele of the gene and a = cystic
fibrosis gene.
d Both - genes determine whether a plant falls into the
tall or dwarf categories, but environmental factors Individual 11 's genotype = aa. Individual 1O's
affect how well each plant grows. genotype could be AA or Aa.

e Both - genes affect the risk level, but environmental So there are two possible outcomes:
factors such as diet, smoking, etc. also have an
effect. AA x aa

1O I> a Chromosomes align themselves along the equator of AA
the cell, attached to the spindle fibres.
a~
b Spindle fibres shorten and pull chromatids towards a~
opposite poles of the cell.

c Chromosomes reach the opposite poles of the cell.
Nucleus starts to re-form.

CHAPTER 18 Aa x aa
A
1 ... D 2 ... A 3 I> D 41> C a

5 I> a All tall. a~
b Alltall. a~
c Alltall.
d 3 tall : 1 short. Depending on whether 10 is AA or Aa, there could
e 1 tall : 1 short (or 2 :2). be no chance, or a 1 in 2 chance (0.5 probability)
All short. of their next child having cystic fibrosis. It could
also be argued that if the genotype of 1O is
6 1> a I Homozygous. unknown, the probability of the child having cystic
fibrosis is 1 in 4, or 0.25.
II Dominant gene hides the expression of the
recessive gene when heterozygous; recessive 91> a They must both be heterozygous. Let S = allele for
gene expressed only in homozygous form. short hair and s = allele for long hair.

b B and b; ii all Bb. ss

c I Heterozygous. :~

II B b There is a 1 in 4 chance of producing a longhaired
guinea pig (ss).
B~
b~

Phenotypes = 3 black : 1 red.

ANSWERS 345

b Breed the shorthaired guinea pig with a homozygous b It would decrease as it would not give an advantage;
longhaired guinea pig (ss). If it is heterozygous (Ss), rats that don't have the gene will breed equally well.
both longhaired and shorthaired offspring will be (In fact rats with the warfarin gene have a selective
produced (in a 1:1 ratio): disadvantage when warfarin is not being used,
althou gh students will not know this.)
:ms s
8 I> a They have a heavy beak, which is adapted to crush
If it is homozygous (SS), all offspring will have short hair: seeds.

ss b They have a long, narrow beak, which can be used to
~ probe under the bark of trees for insects.
~
c Ancestors showed slight variations in their beaks.
1 O I> a A gene is a length of DNA, coding for the production Where the variation enabled a bird to catch insects,
of a protein. Alleles are different forms of a gene. The or eat leaves and other food better than birds with
phenotype is the appearance of an organism, or the other types of beak, the birds survived better and
features that are produced by a gene. (The way that a reproduced (survival of the fittest), passing on their
gene is 'expressed'.) genes for the adaptation. Eventually groups of birds
became so different from members of other groups
b Let allele for red coat = R and allele for white coat =W that they couldn't interbreed, and formed new species.

(note t hat different letters are used, since this is a case 9 I> a As a result of (random) mutations.
of codominance). b Selection pressure: a factor in the environment that
affects the fitness of an organism. In this case the
I RR presence of toxic metals means that the non-tolerant
plants will be killed and not reproduce to pass on their
:~ genes.

ii R R Selective advantage: varieties that survive in the
presence of a selecti on pressure are said to have a
~R selective advantage. In this example the plants that
are tolerant lo toxic metals have a selective advantage
ww when compared with the non-tolerant plants.

iii R w Natural selection: the overall process that, when
metals are present, results in fewer non-tolerant plants
~R and an increase in the number of tolerant plants. If it
continues, natural selection results in evolution.
w WW
c When t here are no toxic metals, the metal-tolerant
c Ratios in (b) are: plants must have some sort of selective disadvantage
over the non-tolerant ones. For example, they may
I all roan; need to use metabolic energy (ATP) to protect their
cells against metals or get rid of metal ions. If there are
II 1 red: 1 roan; no metal ions in the soil, this is a waste of resources.

iii 1 red : 2 roan : 1 white.

CHAPTER 20

CHAPTER 19 1 I> D 21> C 3 I> B 4 I> A

1 I> D 2 I> B 31> A 4 I> D 5 1> a Both involve selection of which animals or plants

5 I> a It means that the organisms that are best adapted survive to breed.
to th eir environment are more likely to survive and
reproduce. b In selective breeding the farmer/ breeder does the

b Darwin and Wallace. selection. In natural select ion it is the survival of the

fittest in a habitat that leads to selection.

6 I> a An organism that causes disease. 6 I> a 1) Plants have resist ance to disease, so they are not
b Fungi and bacteria. killed by fungi, bacteria, etc.

c Random mutations produce some bacteria that are 2) Plants are better suited to climate, so can grow well
resistant to an antibiotic. If the antibiotic continues in a particular location.
to be used, the resistant bacteria will survive and the
non-resistant ones will be killed. The resistant bacteria 3) Plants have a better balance of nutrients; produce
have a selective advantage over the non-resistant more nutritious food, or have a high vitamin
bacteria; they quickly reproduce and cause disease. content etc.

(Or any other correct reason.}

7 I> a Rats with the resistant gene survived and reproduced, b Two from: quicker to produce large numbers of plants
so now many more rats carry the gene. Rats without because only a few cells needed; plants can be
the gene did not survive to reproduce. produced at any time of year since grown inside; large
numbers of plants can be stored easily until needed.

346 ANSWERS

c All have same genes since produced by mitosis from d One advantage from: quicker to produce large
cells of the same parent plant. numbers of plants because only a few cells needed;
plants can be produced at any time of year since
7 II> a Milk yield, and feed to milk conversion rate. grown inside; large numbers of plants can be stored
b Choose a cow with the best characteristics and give easily until needed. Disadvantage: all plants have
hormone I FSH injections to cause multiple ovulations. same genes, so susceptible to same diseases/ could
all be affected at same t ime (2).
Collect ova and use IVF to fertilise with sperm
collected from a bull with the best characteristics. 3 11> a Both 1 and 2 are t asters (1). If the gene was recessive,
Separate cells of embryos that develop and produce all their children would also be tasters, but 4 is a
large numbers of embryos. Screen for sex (males) and non-taster (1 mark for explanation or correct genetic
implant into surrogate mother cows. diagram).

8 11> a Hybrid G was produced by selective breeding. b Individual 3 is Tl (1), because if TI, she couldn't supply
Individual plants from pure lines of A and B were a 'I' allele to have daughters who are non-tasters (1).
selected (for size of cobs) and crossed to produce Individual 7 is II (1), because this is the only genotype
hybrid E. Similarly, individual plants from pure lines of that produces a taster (1).
C and D were selected and crossed to produce hybrid
F. Plants from hybrids E and F were then selected c Individual 5 could be either TI or Tl (1), since her
for their cob size, and crossed to produce hybrid G. husband 6 is a non-taster (II), and so she could donate
(Crossing would be done by transfer of pollen from a 'T' allele from either genotype to produce a son who
anthers to stigmas of plants.) is Tt (1 mark for explanation or correct genetic diagram).

b Cob G is larger, it has more seeds and the cobs are d Individual 3 must have the genotype Tl (1). Individual
more uniform size/shape. 4 must be It (1). So the c ross produces a 1:1 ratio of
tasters to non-tasters / probability is 0.5 that a child is
c Any sensible suggestion, e.g. breed from each under a taster (1 ). (1 mark for correct genetic diagram):
identical environmental conditions, or sequence the
genes to show differences. Tt

9 II> The essay should include: tE1E
• examples of traditional selective breeding of crop
plants or domestic animals 4 11> a D, C , B, E, F, A (all correct ; 2 marks, 1 mark if one or
• advantages of this type of artificial selection, e.g. to more wrong).
crop yield, characteristics of animals
• cloning of plants and its advantages b Mitosis (1), because there are only two cells produced
• cloning animals and its uses / only one division / no reduction division / no pairing
• causes for concern with cloned organisms (e.g. cloned of homologous chromosomes (1).
plants all genetically identical, so susceptible to same
pathogens; cloned animals like 'Dolly' may have C 46
genetic defects; ethical issues).
d Anytwoof:
END OF UNIT 5 QUESTIONS mitosis produces two daughter cells, meiosis
produces four daughter cells
1 11> a Toxic copper ions (1), only copper-tolerant plants will daughter cells from mitosis are genetically identical
grow and reproduce/ non-tolerant plants w ill die (1). to each other and the parent cell; daughter cells
from meiosis are genetically different from each
b Predat ion by lions (1), only those wildebeest that are other and the parent cell
fast runners (or equivalent) will survive and reproduce/ mitosis produces daughter cells with the same
slow animals will be killed and not reproduce (1). number of chromosomes as the parent cell / diploid
to diploid; meiosis halves the chromosome number
c Presence of pesticide (1), only th ose pests resistant to / diploid to haploid.
the pesticide will grow and reproduce/ non-resistant
pests will die (1). 5 11> a From the nucleus of a mammary gland cell of sheep A
(1).
2 11> a Tips of stems and side shoots removed (explants) (1);
exp/ants trimmed to 0.5-1 mm (1); put exp/ants onto agar b Nucleus of an egg is haploid / has half set of
containing nutrients and hormones (1); when exp/ants chromosomes; nucleus of an embryo is diploid / has
have grown transfer to compost in greenhouse (1). full set of chromosomes (1).

b All have same genes since produced by mitosis from c SheepA.
cells of the same parent plant.
d It does not involve fertilisation of an egg by a sperm (1);
c I Kinetin causes growth of shoots (1 ); auxin causes the embryo grows from a body cell nucleus (mammary
growth of callus and roots (1). gland cell nucleus) rather than from a zygote (1).

Ii Use 2 mg per dm3 of auxin to cause growth of e Cloning (genetically modified) animals to produce
callus (1), then reduce to 0.02 mg per dm3 and add human proteins (to treat diseases) (1). Cloning
1mg per dm3 of kinetin until shoots have grown (genetically modified) animals to supply organs for
(1). Then use 2 mg per dm3 of auxin and 0.02 mg transplants (1 ).
per dm3 of kinetin to grow roots (1).

ANSWERS 347

6 11> (One mark for each correct underlined term) CHAPTER 22

A gene is a section of a molecule known as DNA/ 1 11> B 211> C 311> D 411> A
deoxyribonucleic acid. The molecule is found within the
nucleus of a cell, within thread-like structures called 5 II> a 1 ; restriction endonuclease / restriction enzyme;
~somes. The strands of the molecule form a 2; (DNA) ligase.
double helix joined by paired bases. The base adenine
is always paired wit h its complementary base thymine, b It is a vector, used to transfer the gene into the
and the base cytosine is paired with guanine. During the bacterium.
process of transcription, the order of bases in one strand
of the molecule is used to form messenger RNA/ mRNA c They are cultured in fermenters.
which carries the code for making proteins out to the
cytoplasm. d It is identical to human insulin and gives better control
of blood glucose levels.
7 11> 50 base pairs (1)
6 II> The account should discuss how far xenotransplantation
• 30 (G) bases (1) /numbers ofC and G must be the has been developed and what advantages have been
same) suggested for it. It should look at what the biological
problems might be, and the ethical objections. It should
• 20 (T) bases (1) /C+G ; 60, rest; 40. T must be half be a balanced account.
the 40)
7 II> a Use Agrobacterium to insert plasmids containing the
• 20 (A) bases (1) (numbers of T and A must be the required gene into plant cells or use a gene gun -
same) firing a pellet of gold coated with DNA containing the
required gene.
• 100 deoxyribose sugar groups (1) (the same as the
number of bases) b The p lants are grown by m icropropagation.

c Egg cell.

UNIT 6 ANSWERS 8 II> Essay should describe a range of genetically engineered
products, such as:

CHAPTER 21 products from bacteria: human insulin, enzymes,
human growth hormone, etc

1 11> A 211> B 311> C 411> D • genetically modified plants, such as 'golden rice' and
crops resistant to herbicide
5 11> a Using (hot) steam under high pressure.
• genetically modified animals, e.g. sheep used to
b The air is needed to supply oxygen for aerobic produce human proteins, xenotransplantation.
respiration of t he microorganisms. It is filtered to
prevent contamination by unwanted microorganisms. The benefits of each example should be discussed.
The risks from genetic engineering should also be
c Microorganisms produce metabolic heat that could discussed, such as:
overheat the culture. The water jacket contains • 'escape' of genes from crop plants into natural plant
circulating cold water to cool the contents of the
fermenter and maintain a constant temperature. populations

d Nutrients. • transfer of 'hidden' pathogens in xenotransplanted
organs.
e Growth would be reduced. The paddles mix the
contents, so that the Penicillium cells are exposed to END OF UNIT 6 QUESTIONS
more nutrients, achieving a faster rate of growth.
1 II> a Restriction endonuclease / restriction enzyme (1).
6 11> a glucose -+ ethanol + carbon dioxide b An egg cell / egg (1), with its nucleus removed (1).
c An organism containing a gene / DNA / an allele from
b The fermentation air lock allows carbon dioxide to a different species (1 ).
escape from the jar but prevents air from entering. d Any three points for 3 marks:
• all sheep will be genetically identical / have same
c To raise the temperature of fermentation. Enzymes in genes / have same DNA
the yeast will work more quickly if they are near their
optimum temperature. • all sheep will produce Factor IX
• could be used to make more Factor IX
d High concentrations of ethanol kill the yeast cells. • faster reproduction of sheep
• only need to genetically modify the sheep once.
7 11> a To kill any natural bacteria in the milk. e Prevents blood loss (1 ); prevents entry of pathogens/
b It is the optimum temperature for growth and activity bacteria/ microorganisms (1 ).
of the yoghurt bacteria. Plasma and platelets (2).

c Pro1eins in the milk coagulate due to the fall in pH. 2 II> a It would not be possible to destroy these plants (1),
and the genes could jump to other species so that
d The drop in pH reduces the growth of the lactic acid they would also not be able to be destroyed (1).
bacteria.

e The low pH helps to prevent the growth of other
spoiling microorganisms.

348 ANSWERS

b The plants could spread to other areas and would 4 "" a An organism that has had genes transferred to it
increase in numbers, as they were resistant to pests (1) from another species (1).
(1 ). The genes could jump to other species and they
would also spread (1). II A small ring of DNA (1) in (the cytoplasm of) a
bacterium (1).
c The plants could spread to other areas and would
compete with other species and take over a habitat Ill A virus (1) that infects bacterial cells (1 ).
(1 ). The genes could jump to other species and they
would also compete with other species (1 ). b Four points from the following, for maximum of
4 marks: restriction endonucleases are enzymes
3 "" a To supply oxygen for aerobic respiration of the that cut DNA at specific points (1 ). They are used
to cut out genes from the DNA (1) by recognising
microorganisms (1). a certain base sequence (1). Different restriction
enzymes cut DNA at d ifferent places (1). Use of t he
b The temperature must be at the optimum for the same restriction enzyme on a plasmid allows the
enzymes in the microorganisms to work (1 ). If DNA to be inserted into the plasmid (1 ).
temperature is too low, reactions will be slow / if too
high enzymes will be denatured / microorganisms ii Ligases are enzymes that join cut ends of DNA (1)
killed (1). allowing genes to be put into plasmids (1).

c pH/ supply of nutrients (1). 5 "" a Yeast/ fungus (1 ).

d Disinfectants are difficult to wash out of the fermenter b In beer making, the yeast respires to produce ethanol
(1) and might kill the microorganism being grown (1) (1);
(steam just leaves harmless water.)
glucose -, ethanol + carbon dioxide (1 mark per side
e Two marks for any two from: human insulin works of equation).
better t han insulin from animal pancreases/ there
is no risk of transfer of pathogens using human c Barley contains starch (1), which is broken down to
insulin / using human insulin from microorganisms maltose (1), which is used by the yeast for respiration
is acceptable to people w ho object to using animal (1).
tissues.